Abstract:
A level shift circuit whereby a voltage shift amount is large, operation speed is fast, and the power consumption is low. A p-type first transistor is connected between the power supply line and the first node, a p-type second transistor is connected between the power supply line and the second node, and an n-type third transistor is connected between the ground line and the first node, and an n-type fourth transistor is connected between the ground line and the second node. The gate of the first transistor is connected to the second node, and the gate of the second transistor is connected to the first node. An input signal is supplied to the gate of the third transistor and an inverted value of the input signal is supplied to the gate of the fourth transistor. Additionally, this level shift circuit has a plurality of control transistors. The control transistor switches the ratio of the inflow current and emission current of the first node or the second node according to the control signal. The operation speed increases if this ratio is set high, and the voltage shift amount increases if this ratio is set low.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    2. Field of the Invention  
           [0002]    The present invention relates to a level shift circuit used for a semiconductor integrated circuit for example, and more particularly to a technology to increase the speed of operation of the level shift circuit.  
           [0003]    2. Description of Related Art  
           [0004]    In some cases a plurality of types of circuits are installed on one electronic equipment or on one circuit board. In such a case, signals are transmitted/received between each circuit. In the case of digital signals, two types of values, that is, low level or high level, are transmitted/received. The value of low level is often zero volts. And the value of high level is for example 1.5 volts, 3 volts and 5 volts. In some cases circuits with different high level values coexist on one electronic equipment or on one circuit board. Given such cases, a circuit at the transmission side or a circuit at the reception side must convert the high level values. If the high levels are not converted, the circuit at the reception side may recognize a high level as a low level in error.  
           [0005]    A level shift circuit is a circuit for converting the high level voltage of digital signals. For example, signals where the high level is 1.5 volts and the low level is zero volts can be converted into signals where the high level is 3 volts and the low level is zero volts by the level shift circuit.  
           [0006]    The level shift circuit is required to have a sufficient voltage shift amount. For example, 1.5 input signals must be converted to 3 volts, 5 volts or a higher voltage.  
           [0007]    Recently the demand for high-speed operation of a circuit is strong. Therefore it is also demanded that the level shift circuit be designed so as to operate at high-speed.  
           [0008]    Also recently the demand for the low power consumption of circuits is strong. Therefore it is also demanded that the level shift circuit be configured so as to decrease power consumption.  
         SUMMARY OF THE INVENTION  
         [0009]    It is an object of the present invention to provide a level shift circuit which has a large voltage shift amount, fast operation speed, and low power consumption.  
           [0010]    To achieve this, a level shift circuit according to the present invention comprises: a first transistor circuit which connects a first node and a first power supply line when a second node is at a second power supply potential, and does not connect these when the second node is at the first power supply potential; a second transistor circuit which connects the second node and the first power supply line when the first node is at a second power supply potential, and does not connect these when the first node is at the first power supply potential; a third transistor circuit which connects the first node and the second power supply line when an input signal is at a first input potential, and does not connect these when the input signal is at a second input potential; a fourth transistor circuit which connects the second node and the second power supply line when the input signal is at the second input potential, and does not connect these when the input signal is at the first input potential; and a fifth transistor circuit which switches the ratio of the inflow current or the emission current of the first node or the second node according to the control signal when the second node or the first node is connected to both the first power supply line and the second power supply line.  
           [0011]    According to the present invention, the fifth transistor circuit is installed, so the ratio of the inflow current and the emission current of the first node or the second node can be switched according to the control signal. By this, the operation speed can be increased by setting this ratio to high, and the voltage shift amount can be increased by setting this ratio to low. Additionally, according to the present invention, the operation speed can be increased without making the current capabilities of the third transistor circuit and the fourth transistor circuit extremely high, so power consumption is low. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    Other objects and advantages of the present invention will now be described with reference to the accompanying drawings.  
         [0013]    [0013]FIG. 1A and FIG. 1B are circuit diagrams depicting the configuration of the level shift circuit according to the first embodiment;  
         [0014]    [0014]FIG. 2A and FIG. 2B are circuit diagrams depicting the configuration of the level shift circuit according to the second embodiment;  
         [0015]    [0015]FIG. 3A and FIG. 3B are circuit diagrams depicting the configuration of the level shift circuit according to the third embodiment;  
         [0016]    [0016]FIG. 4A and FIG. 4B are circuit diagrams depicting the configuration of the level shift circuit according to the fourth embodiment;  
         [0017]    [0017]FIG. 5A and FIG. 5B are circuit diagrams depicting the configuration of the level shift circuit according to the fifth embodiment;  
         [0018]    [0018]FIG. 6A and FIG. 6B are circuit diagrams depicting the configuration of the level shift circuit according to the sixth embodiment;  
         [0019]    [0019]FIG. 7A and FIG. 7B are circuit diagrams depicting the configuration of the level shift circuit according to the seventh embodiment;  
         [0020]    [0020]FIG. 8A and FIG. 8B are circuit diagrams depicting the configuration of the level shift circuit according to the eighth embodiment;  
         [0021]    [0021]FIG. 9A and FIG. 9B are circuit diagrams depicting the configuration of the level shift circuit according to the ninth embodiment;  
         [0022]    [0022]FIG. 10A and FIG. 10B are circuit diagrams depicting the configuration of the level shift circuit according to the tenth embodiment;  
         [0023]    [0023]FIG. 11A and FIG. 11B are circuit diagrams depicting the configuration of the level shift circuit according to the eleventh embodiment; and  
         [0024]    [0024]FIG. 12A and FIG. 12B are circuit diagrams depicting the configuration of the level shift circuit as reference examples. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    Embodiments of the present invention will now be described with reference to the accompanying drawings. The size, shape and positional relationships of each composing element in these drawings are general enough to aide in understanding the present invention, and the numerical conditions described below are only examples.  
         [0026]    Related Art  
         [0027]    [0027]FIG. 12A and FIG. 12B are diagrams depicting the level shift circuit to be the basis of the present invention. The circuits shown in FIG. 12A and FIG. 12B are not included in the level shift circuits in accordance with the present invention.  
         [0028]    In the level shift circuit in FIG. 12A, the power supply potential to be supplied to the sources of the pMOS transistors  1211  and  1212  is 3 volts. The high level of the input signal IN is 1.5 volts, and the low level of the input signal is zero volts. The high level potential of the inverter  1215  is 1.5 volts.  
         [0029]    In this level shift circuit, the output of the inverter  1215  is at high level when the input signal IN is at low level. Therefore the nMOS transistor  1213  is OFF, and the nMOS transistor  1214  is ON. Since the nMOS transistor  1214  is ON, the potential of the node N 2 , that is, the signal level of the output signal OUT, is at low level. As a result, the pMOS transistor  1211  is ON, therefore the potential of the node N 2  is at high level. This means that the pMOS transistor  1212  is OFF.  
         [0030]    Now the case when the input signal IN is changed to high level (1.5 volts) will be described. In this case, the output of the inverter  1215  becomes to be at low level. Therefore the nMOS transistor  1213  turns ON, and the nMOS transistor  1214  turns OFF. At this time, the potential of the node N 2  remains at zero volts. As a result, both the pMOS transistor  1211  and the nMOS transistor  1213  are in ON state. And when the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  1212 , the pMOS transistor  1212  turns ON, which raises the potential level of the node N 2 , that is, the signal level of the output signal OUT, raises to high level (3 volts). When the potential of the node N 2  becomes high level, the pMOS transistor  1211  turns OFF, therefore the potential of the node N 1  drops to low level.  
         [0031]    Now the case when the input signal IN returns to low level will be described. In this case, the output of the inverter  1215  becomes to be at high level. Therefore the nMOS transistor  1213  turns OFF, and the nMOS transistor  1214  turns ON. At this time, the potential of the node N 1  remains at low level. As a result, both the pMOS transistor  1212  and the nMOS transistor  1214  are in ON state. And when the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  1211 , the pMOS transistor  1211  turns ON. By this, the potential of the node N 1  becomes high level, therefore the pMOS transistor  1212  turns OFF. As a result, the potential of the node N 2 , that is, the signal level of the output signal OUT, drops to low level.  
         [0032]    In the level shift circuit in FIG. 12B, the power supply potential supplied to the sources of the pMOS transistors  1221  and  1222  is 3 volts. The high level of the input signal IN is 1.5 volts, and the low level is zero volts. The high level potential of the inverter  1227  is 1.5 volts.  
         [0033]    This level shift circuit has the pMOS transistors  1223  and  1224 . These pMOS transistors  1223  and  1224  strongly turn ON when the gate potential is zero volts, and weakly turn ON when the gate potential is 1.5 volts. Here “strongly turn (s) ON” refers to becoming the ON state where the current capability is high, and “weakly turn (s) ON” refers to becoming the ON state where the current capability is low.  
         [0034]    In this level shift circuit, the output of the inverter  1227  is at high level when the input signal IN is at low level. Therefore the nMOS transistor  1225  is OFF, and the nMOS transistor  1226  is ON. The pMOS transistor  1223  strongly turns ON, and the pMOS transistor  1224  weakly turns ON. Since the nMOS transistor  1226  is ON, the potential of the node N 2 , that is, the signal level of the output signal OUT, is at low level, so the pMOS transistor  1221  is ON. Therefore the potential of the node N 1  is at high level. This means that the pMOS transistor  1222  is OFF.  
         [0035]    Now the case when the input signal IN changes to high level (1.5 volts) will be described. In this case, the output of the inverter  1227  becomes to be at low level. Therefore the nMOS transistor  1225  turns ON, the nMOS transistor  1226  turns OFF, the pMOS transistor  1223  weakly turns ON, and the pMOS transistor  1224  strongly turns ON. And when the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  1222 , the pMOS transistor  1222  turns ON, which raises the potential of the node N 2 , that is, the signal level of the output signal OUT goes to high level (3 volts). Therefore the pMOS transistor  1221  turns OFF.  
         [0036]    Now the case when the input signal IN returns to low level will be described. In this case, the output of the inverter  1227  becomes to be at high level. Therefore the nMOS transistor  1225  turns OFF, the nMOS transistor  1226  turns ON, the pMOS transistor  1223  strongly turns ON, and the pMOS transistor  1224  weakly turns ON. When the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  1221 , the pMOS transistor  1221  turns ON. By this, the potential of the node N 1  becomes high level, therefore the pMOS transistor  1222  turns OFF. As a result, the potential of the node N 2 , that is, the signal level of the output signal OUT, drops to low level.  
         [0037]    However, when the voltage shift amount (difference between the high level potential of the input signal IN and the high level potential of the output voltage OUT) is attempted to increase, the level shift circuit in FIG. 12A and FIG. 12B drops the operation speed. The reason thereof is described below.  
         [0038]    As mentioned above, in the case of the level shift circuit in FIG. 12A, the potential of the node N 1  must be dropped to lower level than the ON/OFF threshold level of the pMOS transistor  1212  when the input signal IN changes from low level to high level, and both the pMOS transistor  1211  and the nMOS transistor  1213  turn ON. Therefore the current which is supplied from the power supply to the node N 1  via the pMOS transistor  1211  must be lower than the current which is emitted from the node N 1  to the ground via the nMOS transistor  1213 .  
         [0039]    Additionally, in the case of the level shift circuit in FIG. 12A, the potential of the node N 2  must be dropped to lower level than the ON/OFF threshold level of the pMOS transistor  1211  when the input signal IN changes from high level to low level, and both the pMOS transistor  1212  and the rMOS transistor  1214  turn ON. Therefore the current which is supplied from the power supply to the node N 2  via the pMOS transistor  1212  must be lower than the current which is emitted from the node N 2  to the ground via the nMOS transistor  1214 .  
         [0040]    As a consequence, the level shift circuit in FIG. 12A is designed such that the current capability of the pMOS transistors  1211  and  1212  become lower than the current capability of the nMOS transistors  1213  and  1214 . Here the current capability of the MOS transistor depends on the gate potential. The pMOS transistors  1211  and  1212  strongly turn ON when the gate potential is zero volts. On the other hand, the signal IN (e.g. 1.5 volts), not the power supply potential (e.g. 3 volts), is applied to the gates of the nMOS transistors  1213  and  1214 , so the nMOS transistors  1213  and  1214  do not strongly turn ON. Therefore, the pMOS transistors  1211  and  1212  must be designed such that the current capability becomes low enough even if the pMOS transistors strongly turns ON.  
         [0041]    When the current capability of the pMOS transistors  1211  and  1212  is too high, either the voltage between the gate and source of the pMOS transistors  1211  and  1212  must be decreased, or the voltage between the gate and source of the nMOS transistors  1213  and  1214  must be increased in order to operate the level shift circuit normally. For this, the power supply potential of the level shift circuit must be decreased, or the high level potential of the input signal IN must be increased. Therefore as the current capability of the pMOS transistors  1211  and  1212  increases, the potential difference which can be shifted in the level shift circuit is decreased.  
         [0042]    Whereas, when the potential of the node N 1  drops to lower level than the ON/OFF threshold level, the pMOS transistor  1212  must recharge the node N 2  to a high level. So if the current capability of the pMOS transistor  1212  is low, it takes more time to raise the potential of the node N 2  to a high level. In the same way, when the potential of the node N 2  drops to lower level than the ON/OFF threshold level, the pMOS transistor  1211  must recharge the node N 1  to a high level. So if the current capability of the pMOS transistor  1211  is low, it takes more time to raise the potential of the node N 1  to a high level.  
         [0043]    In this way, in the case of the level shift circuit in FIG. 12A, the voltage shift amount decreases if the current capability of the pMOS transistors  1211  and  1212  is increased, and the operation speed decreases if the current capability of the pMOS transistors  1211  and  1212  is decreased.  
         [0044]    Whereas in the case of the level shift circuit in FIG. 12B, such a shortcoming is minimized by disposing the pMOS transistors  1223  and  1224 . The pMOS transistors  1223  and  1224  weakly turn ON when the potential of the nodes N 1  and N 2  is decreased, and strongly turn ON when the nodes N 1  and N 2  are recharged. However, even with the level shift circuit in FIG. 12B, a sufficient voltage shift amount and operation speed cannot be obtained.  
         [0045]    A method of implementing a level shift circuit where the voltage shift amount is high and operation speed is high is achieved by increasing the current capability of the pMOS transistors  1211  and  1212 , and further increasing the current capability of the nMOS transistors  1213  and  1214 . If the current capability of these MOS transistors  1211 - 1214  is too high, however, the through current generated when both MOS transistors  1211  and  1213  turn ON or when both MOS transistors  1212  and  1214  turn ON becomes extremely high, so power consumption increases, which is another problem.  
         [0046]    According to each embodiment of the present invention, transistors to solve the above problems are added to the circuits in FIG. 12A and FIG. 12B.  
         [0047]    First Embodiment  
         [0048]    [0048]FIG. 1A is a circuit diagram depicting the configuration of key components of the level shift circuit according to the present embodiment. As shown in FIG. 1A, this level shift circuit is comprised of the pMOS transistors  111  and  112 , the nMOS transistors  113 ,  114 ,  115  and  116 , and the inverter  117 .  
         [0049]    In the pMOS transistor  111 , the source is connected to the power supply line (not illustrated), the drain is connected to the node N 1 , and the gate is connected to the node N 2 .  
         [0050]    In the pMOS transistor  112 , the source is connected to the power supply line, the drain is connected to the node N 2 , and the gate is connected to the node N 1 . Here, in order to recharge the node N 2  at high-speed, it is preferable that the current capability of the pMOS transistor  112  is sufficiently high.  
         [0051]    In the nMOS transistor  113 , the source is connected to the ground line (not illustrated), the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0052]    In the nMOS transistor  114 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  117 .  
         [0053]    In the nMOS transistor  115 , the source is connected to the ground line, and the control signal L-SPEED is input from the gate.  
         [0054]    In the nMOS transistor  116 , the source is connected to the drain of the nMOS transistor  115 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  117 .  
         [0055]    The inverter  117  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0056]    In the present embodiment, the potential to be supplied from the power supply line, that is, the power supply potential, is 3 volts. Therefore the high level potential of the output signal OUT, that is, the high level potential of the node N 2 , is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  117 , is 1.5 volts or 3 volts.  
         [0057]    Operation of the level shift circuit shown in FIG. 1A will now be described.  
         [0058]    Initially the operation of this level shift circuit when the high level potential of the input signal IN and the inverter  117  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the nMOS transistor  115  turns ON.  
         [0059]    In this level shift circuit, the output of the inverter  117  is maintained at high level (1.5 volts) when the input signal IN is at low level (zero volts). Therefore, the nMOS transistor  113  is OFF and the nMOS transistors  114  and  116  are ON. Since the nMOS transistors  114  and  116  are ON, the potential of the node N 2  (that is, the signal level of the output signal OUT) is maintained at low level. This means that the pMOS transistor  111  is ON, so the potential of the node N 1  is at high level. Therefore the pMOS transistor  112  is OFF.  
         [0060]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  117  to low level. Therefore, the nMOS transistor  113  turns ON, and the nMOS transistors  114  and  116  turn OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  111  is maintained at ON state. In other words, both the pMOS transistor  111  and the nMOS transistor  113  are in ON state. And when the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  112 , the pMOS transistor  112  turns ON, and the potential of the node N 2  raises to high level (3 volts). If the current capability of the pMOS transistor  112  is sufficiently high, this recharging can be executed at high-speed. When the potential of the node N 2  becomes high level, the pMOS transistor  111  turns OFF, so the potential of the node N 1  drops to low level.  
         [0061]    Then the input signal IN changes to low level, which changes the output of the inverter  117  to high level. Therefore the nMOS transistor  113  turns OFF, and the nMOS transistors  114  and  116  turn ON. At this time, the potential of the node N 1  is maintained at low level, therefore the pMOS transistor  112  is maintained in the ON state. This means that both the pMOS transistor  112  and the nMOS transistors  114  and  116  are in ON state. In this level shift circuit, the nMOS transistors  115  and  116  are disposed in parallel with the nMOS transistor  114 , so the capability of emitting the charges stored in the node N 2  to the ground line is very high. Therefore, even if a pMOS transistor  112  with high current capability is in use, the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  111 . As a result, the pMOS transistor  111  turns ON, and the potential of the node N 1  becomes high level. By this, the pMOS transistor  112  turns OFF, and the potential of the node N 2  drops to low level.  
         [0062]    When the control signal L-SPEED is set to high level in this way, the potential of the node N 2  can be dropped to lower level than the ON/OFF threshold level of the pMOS transistor  111 , even if a pMOS transistor  112  with high current capability is in use. Therefore, the level shift circuit can execute a rise operation of the output signal OUT at high-speed, and can operate normally even if the voltage shift amount is high. Power consumption, however, is high since the through current increases when the pMOS transistor  112  and the nMOS transistors  114  and  116  are ON.  
         [0063]    Now operation of the level shift circuit when the high level potential of the input signal IN and the inverter  117  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistor  115  turns OFF.  
         [0064]    When the input signal IN is at low level, the output of the inverter  117  is maintained at high level (3 volts). Therefore the nMOS transistor  113  is OFF, and the nMOS transistor  114  is ON. Since the nMOS transistor  114  is ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  111  is ON, so the potential of the node N 1  is at high level. Therefore the pMOS transistor  112  is OFF. Since the nMOS transistor  115  is OFF, the ON/OFF of the nMOS transistor  116  has no influence on the general operation of the level shift circuit.  
         [0065]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  117  to low level. Therefore the nMOS transistor  113  turns ON, and the nMOS transistor  114  turns OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  111  is maintained in ON state. In other words, the pMOS transistor  111  and the nMOS transistor  113  are both in ON state. And when the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  112 , the pMOS transistor  112  turns ON, and the potential of the node N 2  rises to high level. If the current capability of the pMOS transistor  112  is sufficiently high, this recharging can be executed at high-speed. When the potential of the node N 2  becomes high level, the pMOS transistor  111  turns OFF, so the potential of the node N 1  drops to low level.  
         [0066]    Then the input signal IN changes to low level, which changes the output of the inverter  117  to high level. Therefore the nMOS transistor  113  turns OFF, and the nMOS transistor  114  turns ON. At this time, the potential of the node N 1  is maintained at low level, so the pMOS transistor  112  is maintained in the ON state. This means that both the pMOS transistor  112  and the nMOS transistor  114  are in ON state. Since the nMOS transistor  115  is OFF here, the nMOS transistors  115  and  116  do not contribute to emitting the charges stored in the node N 2 . However, the gate potential of the nMOS transistor  114  is 3 volts, so the current capability of the nMOS transistor  114  is sufficiently high. Therefore the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  111 . As a result, the pMOS transistor  111  turns ON, and the potential of the node N 1  becomes high level. By this, the pMOS transistor  112  turns OFF, and the potential of the node N 2  drops to low level.  
         [0067]    When the level shift amount is low or zero in this way, the potential of the node N 2  can be dropped to lower level than the ON/OFF threshold level of the pMOS transistor  111 , even if the nMOS transistors  115  and  116  are not used. In other words, the level shift circuit can increase the speed of the rise operation of the output signal OUT even without using the nMOS transistors  115  and  116 , and can operate accurately. By turning OFF the nMOS transistor  115 , the through current can be decreased when both the pMOS transistor  112  and the nMOS transistor  114  are ON, therefore power consumption can be decreased.  
         [0068]    Now a variant form of the level shift circuit in accordance with the present embodiment will be described with reference to FIG. 1B.  
         [0069]    The level shift circuit in FIG. 1B is comprised of the pMOS transistors  121 - 124 , nMOS transistors  125 - 128 , and the inverter  129 .  
         [0070]    In the pMOS transistor  121 , the source is connected to the power supply line, and the gate is connected to the node N 2 .  
         [0071]    In the pMOS transistor  122 , the source is connected to the power supply line, and the gate is connected to the node N 1 . Here, it is preferable that the current capability of the pMOS transistor  122  is sufficiently high to recharge the node N 2  at high-speed.  
         [0072]    In the pMOS transistor  123 , the source is connected to the drain of the pMOS transistor  121 , the drain is connected to the node N 1 , and the input signal IN is input from the gate. This pMOS transistor  123  strongly turns ON when the gate potential is zero volts, weekly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0073]    In the pMOS transistor  124 , the source is connected to the drain of the pMOS transistor  122 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  129 . This pMOS transistor  124  strongly turns ON when the gate potential is zero volts, weekly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0074]    In the nMOS transistor  125 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0075]    In the nMOS transistor  126 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  129 .  
         [0076]    In the nMOS transistor  127 , the source is connected to the ground line, and the control signal L-SPEED is input from the gate.  
         [0077]    In the nMOS transistor  128 , the source is connected to the drain of the nMOS transistor  127 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  129 .  
         [0078]    The inverter  129  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0079]    In the level shift circuit in FIG. 1B as well, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  129  is 1.5 volts or 3 volts.  
         [0080]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  129  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the nMOS transistor  127  turns ON.  
         [0081]    When the input signal IN is at low level, the output of the inverter  129  is at high level (1.5 volts). Therefore the nMOS transistor  125  is OFF, and the nMOS transistors  126  and  128  are ON. The pMOS transistor  123  strongly turns ON, and the pMOS transistor  124  weakly turns ON. Since the nMOS transistors  126  and  128  are ON, the potential of the node N 2  is at low level, so the pMOS transistor  121  is ON. This means that the potential of the node N 1  is at high level, and the pMOS transistor  122  is OFF.  
         [0082]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  129  to low level. Therefore the nMOS transistor  125  turns ON, the nMOS transistors  126  and  128  turn OFF, the pMOS transistor  123  weakly turns ON, and the pMOS transistor  124  strongly turns ON. And when the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  122 , the pMOS transistor  122  turns ON, and by this, the potential of the node N 2  rises to high level.  
         [0083]    Then the input signal IN changes to low level, which changes the output of the inverter  129  to high level. Therefore the nMOS transistor  125  turns OFF, the nMOS transistors  126  and  128  turn ON, the pMOS transistor  123  strongly turns ON, and the pMOS transistor  124  weakly turns ON. By this, the pMOS transistors  122  and  124  and the nMOS transistors  126  and  128  are in ON state. In this level shift circuit, the nMOS transistors  127  and  128  are disposed in parallel with the nMOS transistor  126 , so the capability of emitting the charges stored in the node N 2  to the ground line is very high. Therefore, even if a pMOS transistor  122  with a high current capability is in use, the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  121 . By this, the pMOS transistor  121  turns ON, and the potential of the node N 1  becomes high level. As a result, the pMOS transistor  122  turns OFF, and the potential of the node N 2  drops to low level.  
         [0084]    When the control signal L-SPEED is set to high level in this way, the potential of the node N 2  can be dropped to lower level than the ON/OFF threshold level of the pMOS transistor  121 , even if a pMOS transistor  122  with high current capability is in use. Therefore the level shift circuit can execute the rise operation of the output signal OUT at high-speed, and can operate normally even if the voltage shift amount is high. Power consumption, however, is high since the through current increases when the pMOS transistors  122  and  124  and the nMOS transistors  126  and  128  are ON.  
         [0085]    Now the operation of the level shift circuit when the high level potential of the input signal IN and the inverter  129  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistor  127  turns OFF.  
         [0086]    When the input signal IN is at low level, the output of the inverter  129  is at high level (3 volts). Therefore the nMOS transistor  125  is OFF, and the nMOS transistor  126  is ON. The pMOS transistor  123  strongly turns ON, and the pMOS transistor  124  weakly turns ON. Since the nMOS transistor  126  is ON, the potential of the node N 2  is at low level, and the pMOS transistor  121  is ON. So the potential of the node N 1  is at high level, therefore the pMOS transistor  122  is OFF. Since the nMOS transistor  127  is OFF, the ON/OFF of the nMOS transistor  128  has no influence on the general operation of the level shift circuit.  
         [0087]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  129  to low level. Therefore the nMOS transistor  125  turns ON, the nMOS transistor  126  turns OFF, the pMOS transistor  123  turns OFF, and the pMOS transistor  124  strongly turns ON. As a result, the potential of the node N 1  becomes zero volts, and the pMOS transistor  122  turns ON. By this, the potential of the node N 2  rises to high level.  
         [0088]    Then the input signal IN changes to low level, which changes the output of the inverter  129  to high level. Therefore the nMOS transistor  125  turns OFF, the nMOS transistor  126  turns ON, the pMOS transistor  123  strongly turns ON, and the pMOS transistor  124  turns OFF. By this, the potential of the node N 2  becomes zero volts, and the pMOS transistor  121  turns ON. As a result, the potential of the node N 1  becomes high level, and the pMOS transistor  122  turns OFF.  
         [0089]    When the level shift amount is low or zero, the potential of the node N 2  can be decreased to lower level than the ON/OFF threshold level of the pMOS transistor  121  without using the nMOS transistors  127  and  128  in this way. In other words, the level shift circuit can execute the rise operation of the output signal OUT at high-speed, and can operate accurately without using the nMOS transistors  127  and  128 . The power consumption is also low since the through current does not flow through the nodes N 1  and N 2 .  
         [0090]    Second Embodiment  
         [0091]    [0091]FIG. 2A is a circuit diagram depicting the configuration of key components of the level shift circuit according to the present embodiment. As shown in FIG. 2A, this level shift circuit is comprised of the pMOS transistors  211  and  212 , the nMOS transistors  213 - 216 , and the inverter  217 .  
         [0092]    In the pMOS transistor  211 , the source is connected to the power supply line, the drain is connected to the node N 1 , and the gate is connected to the node N 2 .  
         [0093]    In the pMOS transistor  212 , the source is connected to the power supply line, the drain is connected to the node N 2 , and the gate is connected to the node N 1 . In order to recharge the node N 2  at high-speed, it is preferable that the current capability of the pMOS transistor  212  is sufficiently high.  
         [0094]    In the nMOS transistor  213 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0095]    In the nMOS transistor  214 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  217 .  
         [0096]    In the nMOS transistor  215 , the source is connected to the ground line, the drain is connected to the source of the nMOS transistor  214 , and the control signal L-SPEED is input from the gate.  
         [0097]    In the nMOS transistor  216 , the source is connected to the ground line, the drain is connected to the source of the nMOS transistor  214 , and the gate is connected to the output terminal of the inverter  217 .  
         [0098]    The inverter  217  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0099]    In the present embodiment as well, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the inverter  217  is 1.5 volts or 3 volts.  
         [0100]    Operation of the level shift circuit shown in FIG. 2A will now be described.  
         [0101]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  217  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the nMOS transistor  215  turns ON.  
         [0102]    In this level shift circuit, the output of the inverter  217  is maintained at high level (1.5 volts) when the input signal IN is at low level. Therefore the nMOS transistor  213  is OFF, and the nMOS transistors  214  and  216  are ON. Since the nMOS transistors  214 ,  215  and  216  are ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  211  is ON, so the potential of the node N 1  is high level. Therefore the pMOS transistor  212  is OFF.  
         [0103]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  217  to low level. Therefore the nMOS transistor  213  turns ON, and the nMOS transistors  214  and  216  turn OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  211  is maintained in ON state. In other words, both the pMOS transistor  211  and the nMOS transistor  213  are in ON state. Then the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  212 . By this, the pMOS transistor  212  turns ON, and the potential of the node N 2  rises to high level. If the current capability of the pMOS transistor  212  is sufficiently high, this recharging can be executed at high-speed. When the potential of the node N 2  becomes high level, the pMOS transistor  211  turns OFF, so the potential of the node N 1  drops down to low level.  
         [0104]    Then the input signal IN changes to low level, which changes the output of the inverter  217  to high level. Therefore the nMOS transistor  213  turns OFF, and the nMOS transistors  214  and  216  turn ON. At this time, the potential of the node N 1  is maintained at low level, therefore the pMOS transistor  212  is maintained in the ON state. This means that the pMOS transistor  212  and the nMOS transistors  214 ,  215  and  216  are in ON state. In this level shift circuit, the nMOS transistors  215  and  216  are disposed in parallel with the source of the nMOS transistor  214 , so the capability of emitting the charges stored in the node N 2  to the ground line is very high. Therefore even if a pMOS transistor  212  with high current capability is in use, the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  211 . As a result, the pMOS transistor  211  turns ON, and the potential of the node N 1  becomes high level. By this, the pMOS transistor  212  turns OFF, and the potential of the node N 2  drops to low level.  
         [0105]    When the control signal L-SPEED is set to high level in this way, the potential of the node N 2  can be dropped to lower level than the ON/OFF threshold level of the pMOS transistor  211 , even if a pMOS transistor  212  with high current capability is in use. Therefore the level shift circuit can execute the rise operation of the output signal OUT at high-speed, and can operate normally even if the voltage shift amount is high. Power consumption, however, is high since the through current increases when the pMOS transistor  212  and the nMOS transistors  214  and  216  are ON.  
         [0106]    Now the operation of the level shift circuit when the high level potential of the input signal IN and the inverter  217  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistor  215  turns OFF.  
         [0107]    When the input signal IN is at low level, the output of the inverter  217  is maintained at high level (3 volts). Therefore the nMOS transistor  213  is OFF, and the nMOS transistors  214  and  216  are ON. Since the nMOS transistors  214  and  216  are ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  211  is ON, so the potential of the node N 1  is at high level. Therefore the pMOS transistor  212  is OFF. Since the nMOS transistors  215  is OFF, this has no influence on the general operation of the level shift circuit.  
         [0108]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  217  to low level. Therefore the nMOS transistor  213  turns ON, and the nMOS transistor  214  turns OFF. At this time, the potential of the node N 2  is maintained at zero volts. Therefore the pMOS transistor  211  is maintained in the ON state. This means that the pMOS transistor  211  and the nMOS transistor  213  are both in ON state. Then the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  212 , and the pMOS transistor  212  turns ON. By this, the potential of the node N 2  rises to high level (3 volts). If the current capability of the pMOS transistor  212  is sufficiently high, this recharging can be executed at high-speed. When the potential of the node N 2  becomes high level, the pMOS transistor  211  turns OFF, so the potential of the node N 1  drops to low level.  
         [0109]    Then the input signal IN changes to low level, which changes the output of the inverter  217  to high level. Therefore the nMOS transistor  213  turns OFF, and the nMOS transistor  214  turns ON. At this time, the potential of the node N 1  is maintained at low level, therefore the pMOS transistor  212  is maintained in ON state. By this, both the pMOS transistor  212  and the nMOS transistor  214  become ON state. Here, in this level shift circuit, the nMOS transistor  215  does not contribute to emitting the charges stored in the node N 2 , because the control signal L=SPEED is set to low level. However, the gate potential is 3 volts, so the current capability of the nMOS transistors  214  and  216  are sufficiently high. Therefore the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  211 . As a result, the pMOS transistor  211  turns ON, and the potential of the node N 1  becomes high level. By this, the pMOS transistor  212  turns OFF, and the potential of the node N 2  drops to low level.  
         [0110]    When the level shift amount is low or zero in this way, the potential of the node N 2  can be dropped to lower level than the ON/OFF threshold level of the pMOS transistor  211 , even without using the nMOS transistor  215 . In other words, the level shift circuit can increase the speed of the rise operation of the output signal OUT and can operate correctly even without using the nMOS transistor  215 . By not using the nMOS transistor  215 , the through current can be decreased when both the pMOS transistor  212  and the nMOS transistor  214  are ON, therefore power consumption can be decreased.  
         [0111]    Now a variant form of the level shift current in accordance with the present embodiment will be described with reference to FIG. 2B.  
         [0112]    The level shift circuit in FIG. 2B is comprised of the pMOS transistors  221 - 224 , the nMOS transistors  225 - 228 , and the inverter  229 .  
         [0113]    In the pMOS transistor  221 , the source is connected to the power supply line, and the gate is connected to the node N 2 .  
         [0114]    In the pMOS transistor  222 , the source is connected to the power supply line, and the gate is connected to the node N 1 . In order to recharge the node N 2  at high-speed, it is preferable that the current capability of the pMOS transistor  222  is sufficiently high.  
         [0115]    In the pMOS transistor  223 , the source is connected to the drain of the pMOS transistor  221 , the drain is connected to the node N 1 , and the input signal IN is input from the gate. This pMOS transistor  223  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0116]    In the pMOS transistor  224 , the source is connected to the drain of the pMOS transistor  222 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  229 . This pMOS transistor  224  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0117]    In the nMOS transistor  225 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0118]    In the nMOS transistor  226 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  229 .  
         [0119]    In the nMOS transistor  227 , the source is connected to the ground line, the drain is connected to the source of the nMOS transistor  226 , and the control signal L-SPEED is input from the gate.  
         [0120]    In the nMOS transistor  228 , the source is connected to the ground line, the drain is connected to the source of the nMOS transistor  226 , and the gate is connected to the output terminal of the inverter  229 .  
         [0121]    The inverter  229  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0122]    In the level shift circuit in FIG. 2B as well, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  217  is 1.5 volts or 3 volts.  
         [0123]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  229  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the nMOS transistor  227  turns ON.  
         [0124]    When the input signal IN is at low level, the output of the inverter  229  is at high level (1.5 volts). Therefore the nMOS transistor  225  is OFF, and the nMOS transistors  226  and  228  are ON. The pMOS transistor  223  strongly turns ON, and the pMOS transistor  224  weakly turns ON. Since the nMOS transistors  226 ,  227  and  228  are ON, the potential of the node N 2  is at low level, so the pMOS transistor  221  is ON. This means that the potential of the node N 1  is at high level, and the pMOS transistor  222  is OFF.  
         [0125]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  229  to low level. Therefore the nMOS transistor  225  turns ON. The nMOS transistors  226  and  228  turn OFF, the pMOS transistor  223  weakly turns ON, and the pMOS transistor  224  strongly turns ON. Then the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  222 , and the pMOS transistor  222  turns ON. As a result, the potential of the node N 2  rises to high level.  
         [0126]    Then the input signal IN changes to low level, which changes the output of the inverter  229  to high level. Therefore the nMOS transistor  225  turns OFF, the nMOS transistors  226  and  228  turn ON, the pMOS transistor  223  strongly turns ON, and the pMOS transistor  224  weakly turns ON. By this, the pMOS transistors  222  and  224  and the nMOS transistors  226 ,  227  and  228  turn ON. In this level shift circuit, the nMOS transistors  227  and  228  are disposed in parallel with the source of the nMOS transistor  226 , so the capability of emitting the charges stored in the node N 2  to the ground line is very high. Therefore, even if a pMOS transistor  222  with a high current capability is in use, the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  221 . As a result, the pMOS transistor  221  turns ON, and the potential of the node N 1  becomes high level. By this, the pMOS transistor  222  turns OFF, and the potential of the node N 2  drops to low level.  
         [0127]    When the control signal L-SPEED is set to high level in this way, the potential of the node N 2  can be dropped to lower level than the ON/OFF threshold level of the pMOS transistor  221 , even if the pMOS transistor  222  with a high current capacity is in use. Therefore the level shift circuit can operate at high-speed, and can operate normally even if the voltage shift amount is high. Power consumption, however, is high, since the through current increases when the pMOS transistors  222  and  224  and the nMOS transistors  226 ,  227  and  228  are ON.  
         [0128]    Now operation of the level shift circuit with the high level potential of the input signal IN and the inverter  229  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistor  227  turns OFF.  
         [0129]    When the input signal IN is at low level, the output of the inverter  229  is at high level (3 volts). Therefore the nMOS transistor  225  is OFF, and the nMOS transistors  226  and  228  are ON. The pMOS transistor  223  strongly turns ON, and the pMOS transistor  224  weakly turns ON. Since the nMOS transistor  226  and  228  are ON, the potential of the node N 2  is at low level. Therefore the pMOS transistor  221  is ON, and the potential of the node N 1  is at high level. As a result, the pMOS transistor  222  is OFF. Since the nMOS transistor  227  is OFF, this has no influence on the general operation of the level shift circuit.  
         [0130]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  229  to low level. Therefore the nMOS transistor  225  turns ON, the nMOS transistors  226  and  228  turn OFF, the pMOS transistor  223  turns OFF, and the pMOS transistor  224  strongly turns ON. As a result, the potential of the node N 1  becomes zero volts, and the pMOS transistor  222  turns ON. By this, the potential of the node N 2  rises to high level.  
         [0131]    Then the input signal IN changes to low level, which changes the output of the inverter  229  to high level. Therefore the nMOS transistor  225  turns OFF, the nMOS transistors  226  and  228  turn ON, the pMOS transistor  223  strongly turns ON, and the pMOS transistor  224  turns OFF. By this, the potential of the node N 2  becomes zero volts. Therefore the pMOS transistor  221  turns ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistor  222  turns OFF.  
         [0132]    When the level shift amount is low or zero, the potential of the node N 2  can be decreased to zero volts without using the nMOS transistor  227  in this way. As a result, the level shift circuit can accurately operate at high-speed, and power consumption is also low.  
         [0133]    Third Embodiment  
         [0134]    [0134]FIG. 3A is a circuit diagram depicting the configuration of key components of the level shift circuit according to the present embodiment. As shown in FIG. 3A, this level shift circuit is comprised of the pMOS transistors  311  and  312 , the nMOS transistors  313 - 318 , and the inverter  319 .  
         [0135]    In the pMOS transistor  311 , the source is connected to the power supply line, the drain is connected to the node N 1 , and the gate is connected to the node N 2 . In order to recharge the node N 1  at high-speed, it is preferable that the current capability of the pMOS transistor  311  is sufficiently high.  
         [0136]    In the pMOS transistor  312 , the source is connected to the power supply line, the drain is connected to the node N 2 , and the gate is connected to the node N 1 . In order to recharge the node N 2  at high-speed, it is preferable that the current capability of the pMOS transistor  312  is sufficiently high.  
         [0137]    In the nMOS transistor  313 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0138]    In the nMOS transistor  314 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  319 .  
         [0139]    In the nMOS transistor  315 , the source is connected to the ground line, and the control signal L-SPEED is input from the gate.  
         [0140]    In the nMOS transistor  316 , the source is connected to the drain of the nMOS transistor  315 , the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0141]    In the nMOS transistor  317 , the source is connected to the ground line, and the control signal L-SPEED is input from the gate.  
         [0142]    In the nMOS transistor  318 , the source is connected to the drain of the nMOS transistor  317 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  319 .  
         [0143]    The inverter  319  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0144]    In the present embodiment as well, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  319  is 1.5 volts or 3 volts.  
         [0145]    Operation of the level shift circuit shown in FIG. 3A will now be described.  
         [0146]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  319  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the nMOS transistors  315  and  317  turn ON.  
         [0147]    In this level shift circuit, the output of the inverter  319  is maintained at high level (1.5 volts) when the input signal IN is at low level. Therefore the nMOS transistors  313  and  316  are OFF, and the nMOS transistors  314  and  318  are ON. Since the nMOS transistors  314  and  318  are ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  311  is ON, so the potential of the node N 1  is high level. Therefore the pMOS transistor  312  is OFF.  
         [0148]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  319  to low level. By this, the nMOS transistors  313  and  316  turn ON, and the nMOS transistors  314  and  318  turn OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  311  is maintained in ON state. In other words, the pMOS transistor  311  and the nMOS transistors  313  and  316  are in ON state. In this level shift circuit, the nMOS transistors  315  and  316  are disposed in parallel with the nMOS transistor  313 , so the capability of emitting the charges stored in the node N 1  to the ground line is very high. Therefore even if a pMOS transistor  311  with high current capability is in use, the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  312 . As a result, the pMOS transistor  312  turns ON, and the potential of the node N 2  rises to high level (3 volts). When the current capability of the pMOS transistor  312  is sufficiently high, this recharging can be executed at high-speed. When the potential of the node N 2  becomes high level, the pMOS transistor  311  turns OFF, and the potential of the node N 1  drops to low level.  
         [0149]    Then the input signal IN changes to low level, which changes the output of the inverter  319  to high level. Therefore the nMOS transistors  313  and  316  turn OFF, and the nMOS transistors  314  and  318  turn ON. At this time, the potential of the node N 1  is maintained at low level, therefore the pMOS transistor  312  is maintained in the ON state. This means that the pMOS transistor  312  and the nMOS transistors  314 ,  317  and  318  are in ON state. In this level shift circuit, the nMOS transistors  317  and  318  are disposed in parallel with the nMOS transistor  314 , so the capability of emitting the charges stored in the node N 2  to the ground line is very high. Therefore even if a pMOS transistor  312  with high current capability is in use, the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  311 . As a result, the pMOS transistor  311  turns ON, and the potential of the node N 1  becomes high level. If the current capability of the pMOS transistor  311  is sufficiently high, this recharging can be executed at high-speed. When the potential of the node N 1  becomes high level, the pMOS transistor  312  turns OFF. Therefore the potential of the node N 2  drops to low level.  
         [0150]    When the control signal L-SPEED is set to high level in this way, the level shift circuit operates normally even if the pMOS transistors  311  and  312  with high current capability are in use. In other words, the level shift circuit can execute the rise and fall operation of the output signal OUT at high-speed, and operate normally even if the voltage shift amount is high. Power consumption, however, is high since the through current increases when the transistors  311 ,  313 ,  316  are ON and transistors  312 ,  314 ,  318  are ON.  
         [0151]    Now operation of the level shift circuit when the high level potential of the input signal IN and the inverter  319  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistors  315  and  317  turn OFF.  
         [0152]    When the input signal IN is at low level, the output of the inverter  319  is maintained at high level (3 volts). Therefore the nMOS transistors  313  and  316  are OFF, and the nMOS transistors  314  and  318  are ON. Since the nMOS transistor  314  is ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  311  is ON, so the potential of the node N 1  is at high level. Therefore the pMOS transistor  312  is OFF. Since the nMOS transistor  317  is OFF, the ON/OFF state of the nMOS transistor  318  has no influence on the general operation of the level shift circuit.  
         [0153]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  319  to low level. Therefore the nMOS transistors  313  and  316  turn ON, and the nMOS transistors  314  and  318  turn OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  311  is maintained in the ON state. In other words, both the pMOS transistor  311  and the nMOS transistor  313  are both in ON state. In this level shift circuit, the nMOS transistors  315  and  316  do not contribute of emitting the charges stored in the node N 1 . However, the gate potential is 3 volts, so the current capability of the nMOS transistor  313  is sufficiently high. Therefore the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  312 , even if the current capability of the pMOS transistor  311  is high. By this, the pMOS transistor  312  turns ON, and the potential of the node N 2  rises to high level (3 volts). If the current capability of the pMOS transistor  312  is sufficiently high, this recharging can be executed at high-speed. When the potential of the node N 2  becomes high level, the pMOS transistor  311  turns OFF, so the potential of the node N 1  drops to low level.  
         [0154]    Then the input signal IN changes to low level, which changes the output of the inverter  319  to high level. Therefore the nMOS transistors  313  and  316  turn OFF, and the nMOS transistors  314  and  318  turn ON. At this time, the potential of the node N 1  is maintained at low level, therefore the pMOS transistor  312  is maintained in the ON state. By this, both the pMOS transistor  312  and the nMOS transistor  314  become ON state. In this level shift circuit, the nMOS transistors  317  and  318  do not contribute to emitting the charges stored in the node N 2 . However, the gate potential is 3 volts, so the current capability of the nMOS transistor  314  is sufficiently high. Therefore the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  311 , even if the current capability of the pMOS transistor  312  is high. By this, the pMOS transistor  311  turns ON. As a result, the potential of the node N 1  rises to high level, and the pMOS transistor  312  turns OFF. Therefore the potential of the node N 2  drops to low level.  
         [0155]    When the level shift amount is low or zero in this way, the level shift circuit can be accurately operated at high-speed even if the control signal L-SPEED is set to low level. Also the nMOS transistors  315  and  317  are OFF, so power consumption is low.  
         [0156]    Now a variant form of the level shift circuit in accordance with the present embodiment will be described with reference to FIG. 3B.  
         [0157]    The level shift circuit in FIG. 3B is comprised of the pMOS transistors  321 - 324 , the nMOS transistors  325 - 330 , and the inverter  331 .  
         [0158]    In the pMOS transistor  321 , the source is connected to the power supply line, and the gate is connected to the node N 2 . In order to recharge the node N 1  at high-speed, it is preferable that the current capability of the pMOS transistor  321  is sufficiently high.  
         [0159]    In the pMOS transistor  322 , the source is connected to the power supply line, and the gate is connected to the node N 1 . In order to recharge the node N 2  at high-speed, it is preferable that the current capability of the pMOS transistor  322  is sufficiently high.  
         [0160]    In the pMOS transistor  323 , the source is connected to the drain of the pMOS transistor  321 , the drain is connected to the node N 1 , and the input signal IN is input from the gate. This pMOS transistor  323  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0161]    In the pMOS transistor  324 , the source is connected to the drain of the pMOS transistor  322 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  331 . This pMOS transistor  324  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0162]    In the nMOS transistor  325 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0163]    In the nMOS transistor  326 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  331 .  
         [0164]    In the nMOS transistor  327 , the source is connected to the ground line, and the control signal L-SPEED is input from the gate.  
         [0165]    In the nMOS transistor  328 , the source is connected to the drain of the nMOS transistor  327 , the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0166]    In the nMOS transistor  329 , the source is connected to the ground line, and the control signal L-SPEED is input from the gate.  
         [0167]    In the nMOS transistor  330 , the source is connected to the drain of the nMOS transistor  329 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  331 .  
         [0168]    The inverter  331  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0169]    In the level shift circuit in FIG. 3B as well, the potential supplied from the power supply line is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  319  is 1.5 volts or 3 volts.  
         [0170]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  331  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the nMOS transistors  327  and  329  turn ON.  
         [0171]    When the input signal IN is at low level, the output of the inverter  331  is at high level (1.5 volts). Therefore the nMOS transistors  325  and  328  are OFF, and the nMOS transistors  326  and  330  are ON. The pMOS transistor  323  strongly turns ON, and the pMOS transistor  324  weakly turns ON. Since the nMOS transistors  326  and  330  are ON, the potential of the node N 2  is at low level, so the pMOS transistor  321  is ON, which means that the potential of the node N 1  is at high level. Therefore the pMOS transistor  322  is OFF.  
         [0172]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  331  to low level. Therefore the nMOS transistors  325  and  328  turn ON, the nMOS transistors  326  and  330  turn OFF, the pMOS transistor  323  weakly turns ON, and the pMOS transistor  324  strongly turns ON. In this level shift circuit, the nMOS transistors  327  and  328  are disposed in parallel with the nMOS transistor  325 , so the capability of emitting the charges stored in the node N 1  to the ground line is very high. Therefore even if the pMOS transistor  323  with high current capability is in use, the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  322 . As a result, the pMOS transistor  322  turns ON, and the potential of the node N 2  rises to high level (3 volts).  
         [0173]    Then the input signal IN changes to low level, which changes the output of the inverter  331  to high level. Therefore the nMOS transistor  325  turns OFF, the nMOS transistors  326  and  330  turn ON, the pMOS transistor  323  strongly turns ON, and the pMOS transistor  324  weakly turns ON. In this level shift circuit, the nMOS transistors  329  and  330  are disposed in parallel with the nMOS transistor  326 , so the capability of emitting the charges stored in the node N 2  to the ground line is very high. Therefore even if the pMOS transistor  322  with high current capability is in use, the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  321 . By this, the pMOS transistor  321  turns ON. Then the potential of the node N 1  becomes high level, and the pMOS transistor  322  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0174]    When the control signal L-SPEED is set to high level in this way, the level shift circuit operates normally even if the pMOS transistor  321  with high current capability is in use. Therefore the speed of the rise and fall operation of the output signal OUT can be increased. Power consumption, however, is high, since the through current increases when the control signal L-SPEED is set to high level.  
         [0175]    Now operation of the level shift circuit when the high level potential of the input signal IN and the inverter  319  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistor  327  turns OFF.  
         [0176]    When the input signal IN is at low level, the output of the inverter  331  is at high level (3 volts). Therefore the nMOS transistor  325  is OFF, and the nMOS transistor  326  is ON. The pMOS transistor  323  strongly turns ON and the pMOS transistor  324  is OFF. Since the nMOS transistor  326  is ON, the potential of the node N 2  is at low level, and the pMOS transistor  321  is ON, so the potential of the node N 1  is at high level. As a result, the pMOS transistor  322  is OFF. Since the nMOS transistors  327  and  329  are OFF, the ON/OFF of the nMOS transistors  328  and  330  has no influence on the general operation of the level shift circuit.  
         [0177]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  331  to low level. Therefore the nMOS transistor  325  turns ON, the nMOS transistor  326  turns OFF, the pMOS transistor  323  turns OFF, and the pMOS transistor  324  strongly turns ON. As a result, the potential of the node N 1  becomes zero volts, and the pMOS transistor  322  turns ON. By this, the potential of the node N 2  rises to high level (3 volts).  
         [0178]    Then the input signal IN changes to low level, which changes the output of the inverter  331  to high level. As a result, the nMOS transistor  325  turns OFF, the nMOS transistor  326  turns ON, the pMOS transistor  323  strongly turns ON, and the pMOS transistor  324  turns OFF. Therefore the potential of the node N 2  becomes low level. Then the pMOS transistor  321  turns ON. As a result the potential of the node N 1  becomes high level, and the pMOS transistor  322  turns OFF.  
         [0179]    When the level shift amount is low or zero in this way, the potential of the nodes N 1  and N 2  can be decreased to zero volts without using the nMOS transistors  327 - 330  by turning the pMOS transistors  323  and  324  OFF. As a result, the level shift circuit can accurately operate at high-speed, and power consumption is also low.  
         [0180]    Fourth Embodiment  
         [0181]    [0181]FIG. 4A is a circuit diagram depicting the configuration of key components of the level shift circuit according to the present embodiment. As shown in FIG. 4A, this level shift circuit is comprised of the pMOS transistors  411  and  412 , the nMOS transistors  413 - 418 , and the inverter  419 .  
         [0182]    In the pMOS transistor  411 , the source is connected to the power supply line, the drain is connected to the node N 1 , and the gate is connected to the node N 2 . In order to recharge the node N 1  at high-speed, it is preferable that the current capability of the pMOS transistor  411  is sufficiently high.  
         [0183]    In the pMOS transistor  412 , the source is connected to the power supply line, the drain is connected to the node N 2 , and the gate is connected to the node N 1 . In order to recharge the node N 2  at high-speed, it is preferable that the current capability of the pMOS transistor  412  is sufficiently high.  
         [0184]    In the nMOS transistor  413 , the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0185]    In the nMOS transistor  414 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  419 .  
         [0186]    In the nMOS transistor  415 , the source is connected to the ground line, the drain is connected to the source of the nMOS transistor  413 , and the control signal L-SPEED is input from the gate.  
         [0187]    In the nMOS transistor  416 , the source is connected to the ground line, the drain is connected to the source of the nMOS transistor  413 , and the input signal IN is input from the gate.  
         [0188]    In the nMOS transistor  417 , the source is connected to the ground line, the drain is connected to the source of the nMOS transistor  414 , and the control signal L-SPEED is input from the gate.  
         [0189]    In the nMOS transistor  418 , the source is connected to the ground line, the drain is connected to the source of the nMOS transistor  414 , and the gate is connected to the output terminal of the inverter  419 .  
         [0190]    The inverter  419  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0191]    In the present embodiment as well, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  419  is 1.5 volts or 3 volts.  
         [0192]    Operation of the level shift circuit shown in FIG. 4A will now be described.  
         [0193]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  419  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the nMOS transistors  415  and  417  turn ON.  
         [0194]    In this level shift circuit, the output of the inverter  419  is maintained at high level (1.5 volts) when the input signal IN is at low level. Therefore the nMOS transistors  413  and  416  are OFF, and the nMOS transistors  414  and  418  are ON. Since the nMOS transistors  414  and  418  are ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  411  is ON, so the potential of the node N 1  is at high level. Therefore the pMOS transistor  412  is OFF.  
         [0195]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  419  to low level. By this, the nMOS transistors  413  and  416  turn ON, and the nMOS transistors  414  and  418  turn OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  411  is maintained in the ON state. In other words, the pMOS transistor  411  and the nMOS transistors  413  and  416  are in ON state. In this level shift circuit, the nMOS transistors  415  and  416  are disposed in parallel with the nMOS transistor  413 , so the capability of emitting the charges stored in the node N 1  to the ground line is very high. Therefore even if a pMOS transistor  411  with high current capability is in use, the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  412 . As a result, the pMOS transistor  412  turns ON, and the potential of the node N 2  rises to high level (3 volts). When the current capability of the pMOS transistor  412  is sufficiently high, this recharging can be executed at high-speed. When the potential of the node N 2  becomes high level, the pMOS transistor  411  turns OFF, and the potential of the node N 1  drops to low level.  
         [0196]    Then the input signal IN changes to low level, which changes the output of the inverter  419  to high level. Therefore the nMOS transistors  413  and  416  turn OFF, and the nMOS transistors  414  and  418  turn ON. At this time, the potential of the node N 1  is maintained at low level, therefore the pMOS transistor  412  is maintained in the ON state. This means that the pMOS transistor  412  and the nMOS transistors  414 ,  417  and  418  are in ON state. In this level shift circuit, the nMOS transistors  417  and  418  are disposed in parallel with the nMOS transistor  414 , so the capability of emitting the charges stored in the node N 2  to the ground line is very high. Therefore even if a pMOS transistor  412  with high current capability is in use, the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  411 . By this, the pMOS transistor  411  turns ON. Then the potential of the node N 1  becomes high level, and the pMOS transistor  412  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0197]    When the control signal L-SPEED is set to high level in this way, the level shift circuit operates normally even if the pMOS transistors  411  and  412  with high current capability are in use. Therefore the level shift circuit can execute the rise operation it and fall operation at high-speed. Power consumption, however, is high since the through current increases.  
         [0198]    Now operation of the level shift circuit when the high level potential of the input signal IN and the inverter  419  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistors  415  and  417  turn OFF.  
         [0199]    When the input signal IN is at low level, the output of the inverter  419  is maintained at high level (3 volts). Therefore the nMOS transistors  413  and  416  are OFF, and the nMOS transistors  414  and  418  are ON. Since the nMOS transistors  414  and  418  are ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  411  is ON, so the potential of the node N 1  is at high level. Therefore the pMOS transistor  412  is OFF. Since the nMOS transistors  415  and  417  are OFF, this has no influence on the general operation of the level shift circuit.  
         [0200]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  419  to low level. Therefore the nMOS transistors  413  and  416  turn ON, and the nMOS transistors  414  and  418  turn OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  411  is maintained in the ON state. In other words, the pMOS transistor  411  and the nMOS transistors  413  and  416  are in the ON state. In this level shift circuit, the nMOS transistor  415  does not contribute to emitting the charges stored in the node N 1 . However, the gate potential is 3 volts, so the current capability of the nMOS transistors  413  and  416  is sufficiently high. Therefore the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  412 , even if the current capability of the pMOS transistor  411  is high. As a result, the pMOS transistor  412  turns ON, and the potential of the node N 2  rises to high level (3 volts). If the current capability of the pMOS transistor  412  is sufficiently high, this recharging can be executed at high-speed. When the potential of the node N 2  becomes high level, the pMOS transistor  411  turns OFF, so the potential of the node N 1  drops to low level.  
         [0201]    Then the input signal IN changes to low level, which changes the output of the inverter  419  to high level. Therefore the nMOS transistors  413  and  416  turn OFF, and the nMOS transistors  414  and  418  turn ON. At this time, the potential of the node N 1  is maintained at low level, therefore the pMOS transistor  412  is maintained in the ON state. By this, the pMOS transistor  412  and the nMOS transistors  414  and  418  are in ON state. In this level shift circuit, the nMOS transistor  417  does not contribute to emitting the charges stored in the node N 2 . However, the gate potential is 3 volts, so the current capability of the nMOS transistors  414  and  418  is sufficiently high. Therefore the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  411 , even if the current capability of the pMOS transistor  412  is high. By this, the pMOS transistor  411  turns ON. Then the potential of the node N 1  rises to high level. If the current capability of the pMOS transistor  412  is sufficiently high, this recharging can be executed at high-speed. When the potential of the node N 1  becomes high level, the pMOS transistor  412  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0202]    When the control signal L-SPEED is set to high level in this way, the level shift circuit operates normally, even if the pMOS transistors  411  and  412  with high current capability are in use. In other words, the level shift circuit can execute the rise operation and the fall operation of the output signal OUT at high-speed. Power consumption, however, is high since the through current increases.  
         [0203]    Now a variant form of the level shift circuit in accordance with the present invention will be described with reference to FIG. 4B.  
         [0204]    The level shift circuit in FIG. 4B is comprised of the pMOS transistors  421 - 424 , the nMOS transistors  425 - 430 , and the inverter  431 .  
         [0205]    In the pMOS transistor  421 , the source is connected to the power supply line, and the gate is connected to the node N 2 . In order to recharge the node N 1  at high-speed, it is preferable that the current capability of the pMOS transistor  421  is sufficiently high.  
         [0206]    In the pMOS transistor  422 , the source is connected to the power supply line, and the gate is connected to the node N 1 . In order to recharge the node N 2  at high-speed, it is preferable that the current capability of the pMOS transistor  422  is sufficiently high.  
         [0207]    In the pMOS transistor  423 , the source is connected to the ft drain of the pMOS transistor  421 , the drain is connected to the node N 1 , and the input signal IN is input from the gate. The pMOS transistor  423  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0208]    In the pMOS transistor  424 , the source is connected to the drain of the pMOS transistor  422 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  431 . The pMOS transistor  424  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0209]    In the nMOS transistor  425 , the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0210]    In the nMOS transistor  426 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  431 .  
         [0211]    In the nMOS transistor  427 , the source is connected to the ground line, the drain is connected to the source of the nMOS transistor  425 , and the control signal L-SPEED is input from the gate.  
         [0212]    In the nMOS transistor  428 , the source is connected to the ground line, the drain is connected to the source of the nMOS transistor  425 , and the input signal IN is input from the gate.  
         [0213]    In the nMOS transistor  429 , the source is connected to the ground line, the drain is connected to the source of the nMOS transistor  426 , and the control signal L-SPEED is input from the gate.  
         [0214]    In the pMOS transistor  430 , the source is connected to the ground line, the drain is connected to the source of the nMOS transistor  426 , and the gate is connected to the output terminal of the inverter  431 .  
         [0215]    The inverter  431  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0216]    In the level shift circuit in FIG. 4B as well, the potential supplied from the power supply line is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  431  is 1.5 volts or 3 volts.  
         [0217]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  431  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the nMOS transistors  427  and  429  turn ON.  
         [0218]    When the input signal IN is at low level, the output of the inverter  431  is at high level (1.5 volts). Therefore the nMOS transistors  425  and  428  are OFF, and the nMOS transistors  426  and  430  are ON. The pMOS transistor  423  strongly turns ON, and the pMOS transistor  424  weakly turns ON. Since the nMOS transistors  426  and  430  are ON, the potential of the node N 2  is at low level, and the pMOS transistor  421  is ON, so the potential of the node N 1  is at high level. As a result, the pMOS transistor  422  is OFF.  
         [0219]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  431  to low level. By this, the nMOS transistors  425  and  428  turn ON, the nMOS transistors  426  and  430  turn OFF, the pMOS transistor  423  weakly turns ON, and the pMOS transistor  424  strongly turns ON. In this level shift circuit, the nMOS transistors  427  and  428  are disposed in parallel with the source of the nMOS transistor  425 , so the capability of emitting the charges stored in the node N 1  to the ground line is very high. Therefore even if a pMOS transistor  423  with high current capability is in use, the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  412 . When the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  422 , the pMOS transistor  422  turns ON, and the potential of the node N 2  rises to high level (3 volts).  
         [0220]    Then the input signal IN changes to low level, which changes the output of the inverter  431  to high level. Therefore the nMOS transistor  425  and  428  turn OFF, the nMOS transistors  426  and  430  turn ON, the pMOS transistor  423  strongly turns ON, and the pMOS transistor  424  weakly turns ON. In this level shift circuit, the nMOS transistors  429  and  430  are connected in parallel with the source of the nMOS transistor  426 , so the capability of emitting the charges stored in the node N 2  to the ground line is very high. Therefore even if a pMOS transistor  422  with high current capability is in use, the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  421 . By this, the pMOS transistor  421  turns ON. Then the potential of the node N 1  becomes high level, and the pMOS transistor  422  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0221]    When the control signal L-SPEED is set to high level in this way, the level shift circuit operates normally, even if a pMOS transistor  421  and  422  with high current capability is in use. In other words, the level shift circuit in accordance with the present embodiment can use the pMOS transistors  421  and  422  with high current capability, and can increase the speed of the rise operation and the fall operation of the output signal OUT. Power consumption, however, is high, since the through current increases when the control signal L-SPEED is set to high level.  
         [0222]    Now operation of the level shift circuit when the high level potential of the input signal IN and the inverter  431  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistor  427  and  429  turn OFF.  
         [0223]    When the input signal IN is at low level, the output of the inverter  431  is at high level (3 volts). Therefore the nMOS transistors  425  and  428  are OFF, and the nMOS transistors  426  and  430  are ON. The pMOS transistor  423  strongly turns ON, and the pMOS transistor  424  turns OFF. Since the nMOS transistors  426  and  430  are ON, the potential of the node N 2  is at low level, and the pMOS transistor  421  is ON, so the potential of the node N 1  is at high level. As a result, the pMOS transistor  422  is OFF. Since the nMOS transistors  427  and  429  are OFF, this has no influence on the general operation of the level shift circuit.  
         [0224]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  431  to low level. Therefore the nMOS transistors  425  and  428  turn ON, the nMOS transistors  426  and  430  turn OFF, the pMOS transistor  423  turns OFF, and the pMOS transistor  424  strongly turns ON. By this, the potential of the node N 1  becomes zero volts, and the pMOS transistor  422  turns ON. As a result, the potential of the node N 2  rises to high level (3 volts).  
         [0225]    Then the input signal IN changes to low level, which changes the output of the inverter  431  to high level. Therefore the nMOS transistors  425  and  428  turn OFF, the nMOS transistors  426  and  430  turn ON, the pMOS transistor  423  strongly turns ON, and the pMOS transistor  424  turns OFF. Therefore the potential of the node N 2  becomes low level. Then the pMOS transistor  421  turns ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistor  422  turns OFF.  
         [0226]    When the level shift amount is low or zero in this way, the pMOS transistors  423  and  424  can be turned OFF, and the potential of the nodes N 1  and N 2  can be decreased to zero volts without using the nMOS transistors  427 - 430 . As a result, the level shift circuit can accurately operate at high-speed, and power consumption is also low.  
         [0227]    Fifth Embodiment  
         [0228]    [0228]FIG. 5A is a circuit diagram depicting the configuration of key components of the level shift circuit according to the present embodiment. As shown in FIG. 5A, this level shift circuit is comprised of the pMOS transistors  511 - 514 , the nMOS transistors  515  and  516 , and the inverter  517 .  
         [0229]    In the pMOS transistor  511 , the source is connected to the power supply line, the drain is connected to the node N 1 , and the gate is connected to the node N 2 .  
         [0230]    In the pMOS transistor  512 , the source is connected to the power supply line, the drain is connected to the node N 2 , and the gate is connected to the node N 1 .  
         [0231]    In the pMOS transistor  513 , the source is connected to the power supply line, and the control signal L-SPEED is input from the gate.  
         [0232]    In the pMOS transistor  514 , the source is connected to the drain of the pMOS transistor  513 , the drain is connected to the node N 2 , and the gate is connected to the node N 1 .  
         [0233]    In the nMOS transistor  515 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0234]    In the nMOS transistor  516 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  517 .  
         [0235]    The inverter  517  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0236]    In the present embodiment, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  517  is 1.5 volts or 3 volts.  
         [0237]    Operation of the level shift circuit shown in FIG. 5A will now be described.  
         [0238]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  517  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the pMOS transistor  513  turns OFF.  
         [0239]    When the input signal IN is at low level, the output of the inverter  517  is maintained at high level (1.5 volts). Therefore the nMOS transistor  515  is OFF, and the nMOS transistor  516  is ON. Since the nMOS transistor  516  is ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  511  is ON, so the potential of the node N 1  is at high level. Therefore the pMOS transistor  512  is OFF. Since the nMOS transistor  513  is OFF, the ON/OFF of the nMOS transistor  514  has no influence on the general operation of the level shift circuit.  
         [0240]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  517  to low level. Therefore the nMOS transistor  515  turns ON, and the nMOS transistor  516  turns OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  511  is maintained in the ON state. Then the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  512 , and the pMOS transistor  512  turns ON. By this, the potential of the node N 2  rises to high level (3 volts). As a result, the pMOS transistor  511  turns OFF, and the potential of the node N 1  drops to low level.  
         [0241]    Then the input signal IN changes to low level, which changes the output of the inverter  517  to high level. Therefore the nMOS transistor  515  turns OFF, and the nMOS transistor  516  turns ON. At this time, the potential of the node N 1  is maintained at low level, and the pMOS transistor  512  is maintained in the ON state. By this, both the pMOS transistor  512  and the nMOS transistor  514  become ON state. Then the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  511 , and the pMOS transistor  511  turns ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistor  512  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0242]    According to the present embodiment, when the control signal L-SPEED is set to high level in this way, the speed of the rise operation of the output signal OUT is not increased since the pMOS transistors  513  and  514  are not in use. However, the level shift circuit can be operated normally even if the level shift amount is high, and power consumption is low since the through current is low.  
         [0243]    Now operation of the level shift circuit when the high level potential of the input signal IN and the inverter  517  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistor  513  turns ON.  
         [0244]    In this level shift circuit, the output of the inverter  517  is maintained at high level (3 volts) when the input signal IN is at low level. Therefore the nMOS transistor  515  is OFF, and the nMOS transistor  516  is ON. Since the nMOS transistor  516  is ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  511  is ON, so the potential of the node N 1  is at high level. Therefore the pMOS transistors  512  and  514  are OFF.  
         [0245]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  517  to low level. Therefore the nMOS transistor  515  turns ON, and the nMOS transistor  516  turns OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  511  is maintained in the ON state. In other words, both the pMOS transistor  511  and the nMOS transistor  515  are ON. Then the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  512 . By this, the pMOS transistors  512  and  514  turn ON, and the potential of the node N 2  rises to high level (3 volts). According to the present embodiment, the node N 2  is recharged by the two pMOS transistors  512  and  514 , so the potential of the node N 2  rises at high-speed. When the potential of the node N 2  becomes high level, the pMOS transistor  511  turns OFF, and the potential of the node N 1  drops to low level.  
         [0246]    Then the input signal IN changes to low level, which changes the output of the inverter  517  to high level. Therefore the nMOS transistor  515  turns OFF, and the nMOS transistor  516  turns ON. At this time, the potential of the node N 1  is maintained at low level, therefore the pMOS transistors  512  and  514  are maintained in the ON state. By this, the pMOS transistors  512  and  514 , and the nMOS transistor  516  are in ON state. Since the gate potential here is 3 volts, the current capability of the nMOS transistor  516  is sufficiently high. Therefore the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  511 . By this, the pMOS transistor  511  turns ON. Then the potential of the node N 1  becomes high level, and the pMOS transistors  512  and  514  turn OFF. As a result, the potential of the node N 2  drops to low level.  
         [0247]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the recharging capability to the node N 2  can be increased, therefore the speed of the rise operation of the output signal OUT can be increased.  
         [0248]    Now a variant form of the level shift circuit in accordance with the present invention will be described with reference to FIG. 5B.  
         [0249]    The level shift circuit in FIG. 5B is comprised of the pMOS transistors  521 - 526 , the nMOS transistors  527  and  528 , and the inverter  529 .  
         [0250]    In the pMOS transistor  521 , the source is connected to the power supply line, and the gate is connected to the node N 2 .  
         [0251]    In the pMOS transistor  522 , the source is connected to the power supply line, and the gate is connected to the node N 1 .  
         [0252]    In the pMOS transistor  523 , the source is connected to the drain of the pMOS transistor  521 , the drain is connected to the node N 1 , and the input signal IN is input from the gate. This pMOS transistor  523  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0253]    In the pMOS transistor  524 , the source is connected to the drain of the pMOS transistor  522 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  529 . The pMOS transistor  524  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0254]    In the pMOS transistor  525 , the source is connected to the power supply line, and the control signal L-SPEED is input from the gate.  
         [0255]    In the pMOS transistor  526 , the source is connected to the drain of the pMOS transistor  525 , the drain is connected to the source of the pMOS transistor  524 , and the gate is connected to the node N 1 .  
         [0256]    In the nMOS transistor  527 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0257]    In the nMOS transistor  528 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  529 .  
         [0258]    The inverter  529  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0259]    In the level shift circuit in FIG. 5B as well, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the inverter  529  is 1.5 volts or 3 volts.  
         [0260]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  529  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the nMOS transistor  525  turns OFF.  
         [0261]    When the input signal IN is at low level, the output of the inverter  529  is at high level (1.5 volts). Therefore the nMOS transistor  527  is OFF, and the nMOS transistor  528  is ON. The pMOS transistor  523  strongly turns ON, and the pMOS transistor  524  weakly turns ON. Since the nMOS transistor  528  is ON, the potential of the node N 2  is at low level, and the pMOS transistor  521  is ON, so the potential of the node N 1  is at high level. Therefore the pMOS transistor  522  is OFF.  
         [0262]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  529  to low level. By this, the nMOS transistor  527  turns ON, the nMOS transistor  528  turns OFF, the pMOS transistor  523  weakly turns ON, and the pMOS transistor  524  strongly turns ON. When the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  522 , the pMOS transistor  522  turns ON. Therefore the potential of the node N 2  rises to high level (3 volts). Since the pMOS transistor  525  is OFF, the ON/OFF of the pMOS transistor  526  has no influence on the general operation of the level shift circuit.  
         [0263]    Then the input signal IN changes to low level, which changes the output of the inverter  529  to high level. Therefore the nMOS transistor  527  turns OFF, the nMOS transistor  528  turns ON, the pMOS transistor  523  strongly turns ON, and the pMOS transistor  524  weakly turns ON. By this, the pMOS transistors  522  and  524 , and the nMOS transistor  528  turn ON. And the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  521 . By this, the pMOS transistor  521  turns ON. Then the potential of the node N 1  becomes high level, and the pMOS transistor  522  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0264]    When the control signal L-SPEED is set to high level in this way, the speed of the rise operation of the output signal OUT is not increased since the pMOS transistors  525  and  526  are not in use. However, the level shift circuit can be operated normally even if the level shift amount is high, and power consumption is low since the through current is low.  
         [0265]    Now operation of the level shift circuit when the high level potential of the input signal IN and the inverter  529  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistor  525  turns ON.  
         [0266]    When the input signal IN is at low level, the output of the inverter  529  is at high level (3 volts). Therefore the nMOS transistor  527  is OFF, and the nMOS transistor  528  is ON. The pMOS transistor  523  strongly turns ON, and the pMOS transistor  524  is OFF. Since the nMOS transistor  528  is ON, the potential of the node N 2  is low level. Therefore the pMOS transistor  521  is ON, and the potential of the node N 1  is at high level. As a result, the pMOS transistors  522  and  526  are OFF.  
         [0267]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  529  to low level. Therefore the nMOS transistor  527  turns ON, the nMOS transistor  528  turns OFF, the pMOS transistor  523  turns OFF, and the pMOS transistor  524  strongly turns ON. By this, the potential of the node N 1  becomes zero volts, and the pMOS transistors  522  and  526  turn ON. Then the potential of the node N 2  rises to high level (3 volts). According to the present embodiment, the node N 2  is recharged by the two pMOS transistors  522  and  526 , so the potential of the node N 2  rises at high-speed. When the potential of the node N 2  becomes high level, the pMOS transistor  521  turns OFF.  
         [0268]    Then the input signal IN changes to low level, which changes the output of the inverter  529  to high level. Therefore the nMOS transistor  527  turns OFF, the nMOS transistor  528  turns ON, the pMOS transistor  523  strongly turns ON, and the pMOS transistor  524  turns OFF. By this, the potential of the node N 2  becomes zero volts. Then the pMOS transistor  521  turns ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistor  522  turns OFF.  
         [0269]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the recharging capability of the node N 2  can be increased, therefore the speed of the rise operation of the output signal OUT can be increased.  
         [0270]    Sixth Embodiment  
         [0271]    [0271]FIG. 6A is a circuit diagram depicting the configuration of key components of the level shift circuit according to the present embodiment. As shown in FIG. 6A, this level shift circuit is comprised of the pMOS transistors  611 - 614 , the nMOS transistors  615  and  616 , and the inverter  617 .  
         [0272]    In the pMOS transistor  611 , the source is connected to the power supply line, the drain is connected to the node N 1 , and the gate is connected to the node N 2 .  
         [0273]    In the pMOS transistor  612 , the drain is connected to the node N 2 , and the gate is connected to the node N 1 .  
         [0274]    In the pMOS transistor  613 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  612 , and the control signal L-SPEED is input from the gate.  
         [0275]    In the pMOS transistor  614 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  612 , and the gate is connected to the node N 1 .  
         [0276]    In the nMOS transistor  615 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0277]    In the nMOS transistor  616 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  617 .  
         [0278]    The inverter  617  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0279]    According to the present embodiment, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  617  is 1.5 volts or 3 volts.  
         [0280]    Operation of the level shift circuit shown in FIG. 6A will now be described.  
         [0281]    Is Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  617  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the pMOS transistor  613  turns OFF.  
         [0282]    When the input signal IN is at low level, the output of the inverter  617  is maintained at high level (1.5 volts). Therefore the nMOS transistor  615  is OFF, and the nMOS transistor  616  is ON. Since the nMOS transistor  616  is ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  611  is ON, and the potential of the node N 1  is at high level. Therefore the pMOS transistors  612  and  614  are OFF. Since the nMOS transistor  613  is OFF, this has no influence on the general operation of the level shift circuit.  
         [0283]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  617  to low level. Therefore the nMOS transistor  615  turns ON, and the nMOS transistor  616  turns OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  611  is maintained in the ON state. When the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  612 , the pMOS transistors  612  and  614  turn ON, and the potential of the node N 2  rises to high level (3 volts). By this, the pMOS transistor  611  turns OFF, and the potential of the node N 1  drops to low level.  
         [0284]    Then the input signal IN changes to low level, which changes the output of the inverter  617  to high level. Therefore the nMOS transistor  615  turns OFF, and the nMOS transistor  616  turns ON. At this time, the potential of the node N 1  is maintained at low level, and the pMOS transistors  612  and  614  are maintained in the ON state. By this, both the pMOS transistor  612  and the nMOS transistor  614  become ON state. When the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  611 , the pMOS transistor  611  turns ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistors  612  and  614  turn OFF. As a result, the potential of the node N 2  drops to low level.  
         [0285]    When the control signal L-SPEED is set to high level in this way, the speed of the rise operation of the output signal OUT is not increased since the pMOS transistor  613  is not in use. However, the level shift circuit can be operated normally even if the level shift amount is high, and power consumption is low since the through current is low.  
         [0286]    Now the operation of the level shift circuit when the high level potential of the input signal IN and the inverter  617  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the pMOS transistor  613  turns ON.  
         [0287]    In this level shift circuit, the output of the inverter  617  is maintained at high level (3 volts) when the input signal IN is at low level. Therefore the nMOS transistor  615  is OFF, and the nMOS transistor  616  is ON. Since the nMOS transistor  616  is ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  611  is ON, so the potential of the node N 1  is at high level. Therefore the pMOS transistors  612  and  614  are OFF.  
         [0288]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  617  to low level. Therefore the nMOS transistor  615  turns ON, and the nMOS transistor  616  turns OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  611  is maintained in ON state. In other words, both the pMOS transistor  611  and the nMOS transistor  615  are in the ON state. Then the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  612 . By this, the pMOS transistors  612  and  614  turn ON, and the potential of the node N 2  rises to high level (3 volts). According to the present embodiment, the potential of the node N 2 , that is, the output signal OUT, rises at high-speed since the current is supplied from two pMOS transistors  613  and  614  to the source of the pMOS transistor  612 . When the potential of the node N 2  becomes high level, the pMOS transistor  611  turns OFF, and the potential of the node N 1  drops to low level.  
         [0289]    Then the input signal IN changes to low level, which changes the output of the inverter  617  to high level. Therefore the nMOS transistor  615  turns OFF, and the nMOS transistor  616  turns ON. At this time, the potential of the node N 1  is maintained at low level, therefore the pMOS transistors  612  and  614  are maintained in the ON state. By this, the pMOS transistors  612 ,  613  and  614  and the nMOS transistor  616  turn ON. Since the gate potential is 3 volts, the current capability of the nMOS transistor  616  is sufficiently high. Therefore the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  611 . The pMOS transistor  611  is thereby turned ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistors  612  and  614  turn OFF. As a result, the potential of the node N 2  drops to low level.  
         [0290]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the recharging capability to the node N 2  can be increased. Therefore the speed of the rise operation of the output signal OUT can be increased.  
         [0291]    Now a variant form of the level shift circuit in accordance to the present invention will be described with reference to FIG. 6B.  
         [0292]    The level shift circuit in FIG. 6B is comprised of the pMOS transistors  621 - 626 , the nMOS transistors  627  and  628 , and the inverter  629 .  
         [0293]    In the pMOS transistor  621 , the source is connected to the power supply line, and the gate is connected to the node N 2 .  
         [0294]    In the pMOS transistor  622 , the gate is connected to the node N 1 .  
         [0295]    In the pMOS transistor  623 , the source is connected to the drain of the pMOS transistor  621 , the drain is connected to the node N 1 , and the input signal IN is input from the gate. The pMOS transistor  623  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0296]    In the pMOS transistor  624 , the source is connected to the drain of the pMOS transistor  622 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  629 . The pMOS transistor  624  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0297]    In the pMOS transistor  625 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  622 , and the control signal L-SPEED is input from the gate.  
         [0298]    In the pMOS transistor  626 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  622 , and the gate is connected to the node N 1 .  
         [0299]    In the nMOS transistor  627 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0300]    In the nMOS transistor  628 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  629 .  
         [0301]    The inverter  629  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0302]    In the level shift circuit in FIG. 6B as well, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the inverter  629  is 1.5 volts or 3 volts.  
         [0303]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  629  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the nMOS transistor  625  turns OFF.  
         [0304]    When the input signal IN is at low level, the output of the inverter  629  is at high level (1.5 volts). Therefore the nMOS transistor  627  is OFF, and the nMOS transistor  628  is ON. The pMOS transistor  623  strongly turns ON, and the pMOS transistor  624  weakly turns ON. Since the nMOS transistor  628  is ON, the potential of the node N 2  is at low level, and the pMOS transistor  621  is ON, so the potential of the node N 1  is at high level. Therefore the pMOS transistors  622  and  626  are OFF.  
         [0305]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  629  to low level. By this, the nMOS transistor  627  turns ON, the nMOS transistor  628  turns OFF, the pMOS transistor  623  weakly turns ON, and the pMOS transistor  624  strongly turns ON. When the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  622 , the pMOS transistors  622  and  626  turn ON. When the pMOS transistors  622  and  626  turn ON, the potential of the node N 2  rises to high level (3 volts). Since the pMOS transistor  625  is OFF, this has no influence on the general operation of the level shift circuit.  
         [0306]    Then the input signal IN changes to low level, which changes the output of the inverter  629  to high level. Therefore the nMOS transistor  627  turns OFF, the nMOS transistor  628  turns ON, the pMOS transistor  623  strongly turns ON, and the pMOS transistor  624  weakly turns ON. By this, the pMOS transistors  622 ,  624  and  626  and the nMOS transistor  628  turn ON. Then the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  621 . By this, the pMOS transistor  621  turns ON. As a result, the potential of the node N 1  becomes high level, and the pMOS transistor  622  turns OFF. Therefore the potential of the node N 2  drops to low level.  
         [0307]    When the control signal L-SPEED is set to high level in this way, the speed of the rise operation of the output signal OUT is not increased since the pMOS transistor  625  is not in use. However, the level shift circuit can operate normally even if the level shift amount is high, and power consumption is low since the through current is low.  
         [0308]    Now operation of the level shift circuit when the high level potential of the input signal IN and the inverter  627  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistor  625  turns ON.  
         [0309]    When the input signal IN is at low level, the output of the inverter  629  is at high level (3 volts). Therefore the nMOS transistor  627  is OFF, and the nMOS transistor  628  is ON. The pMOS transistor  623  strongly turns ON, and the pMOS transistor  624  is OFF. Since the nMOS transistor  628  is ON, the potential of the node N 2  is low level, the pMOS transistor  621  is ON. Therefore the potential of the node N 1  is at high level. As a result, the pMOS transistors  622  and  626  are OFF.  
         [0310]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  629  to low level. Therefore the nMOS transistor  627  turns ON, the nMOS transistor  628  turns OFF, the pMOS transistor  623  turns OFF, and the pMOS transistor  624  strongly turns ON. By this, the potential of the node N 1  becomes zero volts, and the pMOS transistors  622  and  626  turn ON. As a result, the potential of the node N 2  rises to high level (3 volts). According to the present embodiment, the potential of the node N 2  rises at high-speed since current is supplied to the source of the pMOS transistor  622  by the two pMOS transistors  625  and  626 . When the potential of the node N 2  becomes high level, the pMOS transistor  621  turns OFF.  
         [0311]    Then the input signal IN changes to low level, which changes the output of the inverter  629  to high level. Therefore the nMOS transistor  627  turns OFF, the nMOS transistor  628  turns ON, the pMOS transistor  623  strongly turns ON, and the pMOS transistor  624  turns OFF. By this, the potential of the node N 2  becomes zero volts. Then the pMOS transistor  621  turns ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistor  622  turns OFF.  
         [0312]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the recharging capability of the node N 2  can be increased, therefore the speed of the rise operation of the output signal OUT can be increased.  
         [0313]    Seventh Embodiment  
         [0314]    [0314]FIG. 7A is a current diagram depicting the configuration of key components of the level shift circuit according to the present embodiment. As shown in FIG. 7A, this level shift circuit is comprised of the pMOS transistors  711 - 716 , the nMOS transistors  717  and  718 , and the inverter  719 .  
         [0315]    In the pMOS transistor  711 , the source is connected to the power supply line, the drain is connected to the node N 1 , and the gate is connected to the node N 2 .  
         [0316]    In the pMOS transistor  712 , the source is connected to the power supply line, the drain is connected to the node N 2 , and the gate is connected to the node N 1 .  
         [0317]    In the pMOS transistor  713 , the source is connected to the power supply line, and the control signal L-SPEED is input from the gate.  
         [0318]    In the pMOS transistor  714 , the source is connected to the drain of the pMOS transistor  713 , the drain is connected to the node N 1 , and the gate is connected to the node N 2 .  
         [0319]    In the pMOS transistor  715 , the source is connected to the power supply line, and the control signal L-SPEED is input from the gate.  
         [0320]    In the pMOS transistor  716 , the source is connected to the drain of the pMOS transistor  715 , the drain is connected to the node N 2 , and the gate is connected to the node N 1 .  
         [0321]    In the nMOS transistor  717 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0322]    In the nMOS transistor  718 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  719 .  
         [0323]    The inverter  719  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0324]    According to the present invention, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  719  is 1.5 volts or 3 volts.  
         [0325]    Operation of the level shift circuit shown in FIG. 7A will now be described.  
         [0326]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  719  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the pMOS transistors  713  and  715  turn OFF.  
         [0327]    When the input signal IN is at low level, the output of the inverter  719  is maintained at high level (1.5 volts). Therefore the nMOS transistor  717  is OFF, and the nMOS transistor  718  is ON. Since the MOS transistor  718  is ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  711  is ON, and the potential of the node N 1  is at high level. Therefore the pMOS transistor  712  is OFF. Since the nMOS transistors  713  and  715  are OFF, the ON/OFF of the nMOS transistors  714  and  716  have no influence on the general operation of the level shift circuit.  
         [0328]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  719  to low level. Therefore the nMOS transistor  717  turns ON, and the nMOS transistor  718  turns OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  711  is maintained in the ON state. When the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  712 , the pMOS transistor  712  turns ON, and the potential of the node N 2  rises to high level (3 volts). By this, the pMOS transistor  711  turns OFF, and the potential of the node N 1  drops to low level.  
         [0329]    Then the input signal IN changes to low level, which changes the output of the inverter  719  to high level. Therefore the DMOS transistor  717  turns OFF, and the nMOS transistor  718  turns ON. At this time, the potential of the node N 1  is maintained at low level, and the pMOS transistor  712  is maintained in the ON state. By this, both the pMOS transistor  712  and the DMOS transistor  718  become ON state. When the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  711 , the pMOS transistor  711  turns ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistor  712  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0330]    When the control signal L-SPEED is set to high level in this way, the speed of the rise operation and the fall operation of the output signal OUT is not increased, since the pMOS transistor  713 - 716  are not in use. However, the level shift circuit can operate normally even if the level shift amount is high, and power consumption is low since the through current is low.  
         [0331]    Now operation of the level shift circuit when the high level potential of the input signal IN and the inverter  719  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistors  713  and  715  turn ON.  
         [0332]    In this level shift circuit, the output of the inverter  719  is maintained at high level (3 volts) when the input signal IN is at low level. Therefore the nMOS transistor  717  is OFF, and the nMOS transistor  718  is ON. Since the nMOS transistor  718  is ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistors  711  and  714  are ON, so the potential of the node N 1  is at high level. And this also means that the pMOS transistors  712  and  716  are OFF.  
         [0333]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  719  to low level. Therefore the nMOS transistor  717  turns ON, and the nMOS transistor  718  turns OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistors  711  and  714  are maintained in the ON state. In other words, the pMOS transistors  711  and  714  and the nMOS transistor  717  are in the ON state. Since the gate potential is 3 volts here, the current capability of the nMOS transistor  717  is sufficiently high. Because of this, the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  712 . By this, the pMOS transistors  712  and  716  turn ON, and the potential of the node N 2  rises to high level (3 volts). According to the present embodiment, the potential of the node N 2  rises at high-speed, since the node N 2  is recharged by the two pMOS transistors  712  and  716 . When the potential of the node N 2  becomes high level, the pMOS transistors  711  and  714  turn OFF. Therefore the potential of the node N 1  drops to low level.  
         [0334]    Then the input signal IN changes to low level, which changes the output of the inverter  719  to high level. Therefore the nMOS transistor  717  turns OFF, and the nMOS transistor  718  turns ON. At this time, the potential of the node N 1  is maintained at low level, and the pMOS transistors  712  and  716  are maintained in the ON state. By this, the pMOS transistors  712  and  716  and the nMOS transistor  718  turn ON. Since the gate potential is 3 volts here, the current capability of the nMOS transistor  718  is sufficiently high. Therefore the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  711 . Therefore the pMOS transistor  711  and  714  turns ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistors  712  and  716  turn OFF. As a result, the potential of the node N 2  drops to low level. According to the present embodiment, the potential of the node N 2 , which is the output signal OUT, falls at high-speed, since the node N 1  is recharged by the two pMOS transistors  711  and  714 .  
         [0335]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the recharging capability to the nodes N 1  and N 2  can be increased, therefore the speed of the rise operation and the fall operation of the output signal OUT can be increased.  
         [0336]    Now a variant form of the level shift circuit in accordance with the present invention will be described with reference to FIG. 7B.  
         [0337]    The level shift circuit in FIG. 7B is comprised of the pMOS transistors  721 - 728 , the nMOS transistors  729  and  730 , and the inverter  731 .  
         [0338]    In the pMOS transistor  721 , the source is connected to the power supply line, and the gate is connected to the node N 2 .  
         [0339]    In the pMOS transistor  722 , the source is connected to the power supply line, and the gate is connected to the node N 1 .  
         [0340]    In the pMOS transistor  723 , the source is connected to the drain of the pMOS transistor  721 , the drain is connected to the node N 1 , and the input signal IN is input from the gate. This pMOS transistor  723  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0341]    In the pMOS transistor  724 , the source is connected to the drain of the pMOS transistor  722 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  731 . This pMOS transistor  724  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0342]    In the pMOS transistor  725 , the source is connected to the power supply line, and the control signal L-SPEED is input from the gate.  
         [0343]    In the pMOS transistor  726 , the source is connected to the drain of the pMOS transistor  725 , the drain is connected to the source of the pMOS transistor  723 , and the gate is connected to the node N 2 .  
         [0344]    In the pMOS transistor  727 , the source is connected to the power supply line, and the control signal L-SPEED is input from the gate.  
         [0345]    In the pMOS transistor  728 , the source is connected to the drain of the pMOS transistor  727 , the drain is connected to the source of the pMOS transistor  724 , and the gate is connected to the node N 1 .  
         [0346]    In the nMOS transistor  729 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0347]    In the nMOS transistor  730 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  731 .  
         [0348]    The inverter  731  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0349]    In the level shift circuit in FIG. 7B as well, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the inverter  731  is 1.5 volts or 3 volts.  
         [0350]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  731  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the nMOS transistors  725  and  727  turn OFF.  
         [0351]    When the input signal IN is at low level, the output of the inverter  731  is at high level (1.5 volts). Therefore the nMOS transistor  729  is OFF, and the nMOS transistor  730  is ON. The pMOS transistor  723  strongly turns ON, and the pMOS transistor  724  weakly turns ON. Since the nMOS transistor  730  is ON, the potential of the node N 2  is at low level, and the pMOS transistor  721  is ON, so the potential of the node N 1  is at high level. Therefore the pMOS transistor  722  is OFF. Since the pMOS transistors  725  and  727  are OFF, the ON/OFF of the pMOS transistors  726  and  728  have no influence on the general operation of the level shift circuit.  
         [0352]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  731  to low level. By this, the nMOS transistor  729  turns ON, the nMOS transistor  730  turns OFF, the pMOS transistor  723  weakly turns ON, and the pMOS transistor  724  strongly turns ON. By this, the pMOS transistors  721  and  723 , and the nMOS transistor  729  turn ON. According to the present embodiment, the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  722  since the current capability of the pMOS transistor  721  is low. By this, the pMOS transistor  722  turns ON, therefore the potential of the node N 2  rises to high level (3 volts).  
         [0353]    Then the input signal IN changes to low level, which changes the output of the inverter  731  to high level. Therefore the nMOS transistor  729  turns OFF, the nMOS transistor  730  turns ON, the pMOS transistor  723  strongly turns ON, and the pMOS transistor  724  weakly turns ON. By this, the pMOS transistors  722  and  724 , and the nMOS transistor  730  turn ON. According to the present embodiment, the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  721 , since the current capability of the pMOS transistor  722  is low. By this, the pMOS transistor  721  turns ON. Therefore the potential of the node N 1  becomes high level, and the pMOS transistor  722  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0354]    When the control signal L-SPEED is set to high level in this way, the speed of the operation of the output signal OUT is not increased, since the pMOS transistor  726  and  728  are not in use. However, the level shift circuit can operate normally even if the level shift amount is high, and power consumption is low since the through current is low.  
         [0355]    Now operation of the level shift circuit when the high level potential of the input signal IN and the inverter  727  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistors  725  and  727  turn ON.  
         [0356]    When the input signal IN is at low level, the output of the inverter  731  is at high level (3 volts). Therefore the nMOS transistor  729  is OFF, and the nMOS transistor  730  is ON. Also the pMOS transistor  723  strongly turns ON and the pMOS transistor  724  is OFF. Since the nMOS transistor  730  is ON, the potential of the node N 2  is at low level, therefore the pMOS transistors  721  and  726  are ON. So the potential of the node N 1  is at high level, and as a result, the pMOS transistors  722  and  728  are OFF.  
         [0357]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  731  to low level. Therefore the nMOS transistor  729  turns ON, the nMOS transistor  730  turns OFF, the pMOS transistor  723  turns OFF, and the pMOS transistor  724  strongly turns ON. Since the potential of the node N 1  becomes zero volts, the pMOS transistors  722  and  728  turn ON. As a result, the potential of the node N 2  rises to high level (3 volts). According to the present embodiment, the potential of the node N 2 , that is, the output signal OUT, rises at high-speed, since the node N 2  is recharged by the two pMOS transistors  722  and  728 . When the potential of the node N 2  becomes high level, the pMOS transistors  721  and  726  turn OFF.  
         [0358]    Then the input signal IN changes to low level, which changes the output of the inverter  731  to high level. Therefore the nMOS transistor  729  turns OFF, the DMOS transistor  730  turns ON, the pMOS transistor  723  strongly turns ON, and the pMOS transistor  724  turns OFF. By this, the potential of the node N 2  becomes zero volts. Then the pMOS transistors  721  and  726  turn ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistors  722  and  728  turn OFF.  
         [0359]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the recharging capability to the nodes N 1  and N 2  can be increased, therefore the speed of the rise operation and the fall operation of the output signal OUT can be increased.  
         [0360]    Eighth Embodiment  
         [0361]    [0361]FIG. 8A is a circuit diagram depicting the configuration of key components of the level shift circuit according to the present embodiment. As shown in FIG. 8A, this level shift circuit is comprised of the pMOS transistors  811 - 816 , the nMOS transistor  817  and  818 , and the inverter  819 .  
         [0362]    In the pMOS transistor  811 , the drain is connected to the node N 1 , and the gate is connected to the node N 2 .  
         [0363]    In the pMOS transistor  812 , the drain is connected to the node N 2 , and the gate is connected to the node N 1 .  
         [0364]    In the pMOS transistor  813 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  811 , and the control signal L-SPEED is input from the gate.  
         [0365]    In the pMOS transistor  814 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  811 , and the gate is connected to the node N 2 .  
         [0366]    In the pMOS transistor  815 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  812 , and the control signal L-SPEED is input from the gate.  
         [0367]    In the pMOS transistor  816 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  812 , and the gate is connected to the node N 1 .  
         [0368]    In the nMOS transistor  817 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0369]    In the nMOS transistor  818 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  819 .  
         [0370]    The inverter  819  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0371]    According to the present embodiment, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  819  is 1.5 volts or 3 volts.  
         [0372]    Operation of the level shift circuit shown in FIG. 8A will now be described.  
         [0373]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  819  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the pMOS transistors  813  and  815  turn OFF.  
         [0374]    When the input signal IN is at low level, the output of the inverter  819  is maintained at high level (1.5 volts). Therefore the nMOS transistor  817  is OFF, and the nMOS transistor  818  is ON. Since the nMOS transistor  818  is ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistors  811  and  814  are ON, and the potential of the node N 1  is at high level. Therefore the pMOS transistors  812  and  816  are OFF. Since the pMOS transistors  813  and  815  are OFF, this has no influence on the general operation of the level shift circuit.  
         [0375]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  819  to low level. Therefore the DMOS transistor  817  turns ON, and the nMOS transistor  818  turns OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistors  811  and  814  are maintained in the ON state. According to the present embodiment, the current capability of the pMOS transistors  811  and  814  is sufficiently low, so the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistors  812  and  816 . By this, the pMOS transistors  812  and  816  turn ON, and the potential of the node N 2  rises to high level (3 volts). By this, the pMOS transistors  811  and  814  turn OFF, and the potential of the node N 1  drops to low level.  
         [0376]    Then the input signal IN changes to low level, which changes the output of the inverter  819  to high level. Therefore the nMOS transistor  817  turns OFF, and the nMOS transistor  818  turns ON. At this time, the potential of the node N 1  is maintained at low level, and the pMOS transistor  812  is maintained in the ON state. By this, the pMOS transistors  812  and  816 , and the nMOS transistor  818  turn ON. According to the present embodiment, the current capability of the pMOS transistors  812  and  816  is sufficiently low, so the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistors  811  and  814 . Therefore the pMOS transistors  811  and  814  turn ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistors  812  and  816  turn OFF. As a result, the potential of the node N 2  drops to low level.  
         [0377]    When the control signal L-SPEED is set to high level in this way, the speed of the rise operation of the output signal OUT is not increased since the pMOS transistor  813  is not in use, and the speed of the fall operation of the output signal OUT is not increased since the pMOS transistor  815  is not in use. However, the level shift circuit can operate normally even if the level shift amount is high, and power consumption is low since the through current is low.  
         [0378]    Now operation of this level shift circuit when the high level potential of the input signal IN and the inverter  819  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the pMOS transistors  813  and  815  turn ON.  
         [0379]    In this level shift circuit, the output of the inverter  819  is maintained at high level (3 volts) when the input signal IN is at low level. Therefore the nMOS transistor  817  is OFF, and the nMOS transistor  818  is ON. Since the nMOS transistor  818  is ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistors  811  and  814  are ON, so the potential of the node N 1  is at high level. As a result, the pMOS transistors  812  and  816  are OFF.  
         [0380]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  819  to low level. Therefore the nMOS transistor  817  turns ON, and the nMOS transistor  818  turns OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistors  811  and  814  are maintained in the ON state. In other words, the pMOS transistors  811  and  814 , and the nMOS transistor  817  are in the ON state. Since the gate potential is 3 volts here, the current capability of the nMOS transistor  817  is sufficiently high. Because of this, the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  812 . By this, the pMOS transistors  812  and  816  turn ON, and the potential of the node N 2  rises to high level (3 volts). According to the present embodiment, the potential of the node N 2  rises at high-speed since the current is supplied to the source of the pMOS transistor  812  by the two pMOS transistors  815  and  816 . When the potential of the node N 2  becomes high level, the pMOS transistors  811  and  814  turn OFF, therefore the potential of the node N 1  drops to low level.  
         [0381]    Then the input signal IN changes to low level, which changes the output of the inverter  819  to high level. Therefore the nMOS transistor  817  turns OFF, and the nMOS transistor  818  turns ON. At this time, the potential of the node N 1  is maintained at low level, and the pMOS transistors  812  and  816  are maintained in the ON state. By this, the pMOS transistors  812  and  816 , and the nMOS transistor  818  turn ON. Since the gate potential is 3 volts here, the current capability of the nMOS transistor  818  is sufficiently high. Therefore the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  811 . Therefore the pMOS transistors  811  and  814  turn ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistors  812  and  816  turn OFF. As a result, the potential of the node N 2  drops to low level. According to the present embodiment, the potential of the node N 2  drops at high-speed, since the node N 1  is recharged by the two pMOS transistors  811  and  814 .  
         [0382]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the recharging capability to the nodes N 1  and N 2  can be increased, therefore the speed of the rise operation and the fall operation of the output signal OUT can be increased.  
         [0383]    Now a variant form of the level shift circuit in accordance to the present invention will be described with reference to FIG. 8B.  
         [0384]    The level shift circuit in FIG. 8B is comprised of the pMOS transistors  821 - 828 , the nMOS transistors  829  and  830 , and the inverter  831 .  
         [0385]    In the pMOS transistor  821 , the gate is connected to the node N 2 .  
         [0386]    In the pMOS transistor  822 , the gate is connected to the node N 1 .  
         [0387]    In the pMOS transistor  823 , the source is connected to the drain of the pMOS transistor  821 , the drain is connected to the node N 1 , and the input signal IN is input from the gate. This pMOS transistor  823  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0388]    In the pMOS transistor  824 , the source is connected to the drain of the pMOS transistor  822 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  831 . This pMOS transistor  824  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0389]    In the pMOS transistor  825 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  821 , and the control signal L-SPEED is input from the gate.  
         [0390]    In the pMOS transistor  826 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  821 , and the gate is connected to the node N 2 .  
         [0391]    In the pMOS transistor  827 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  822 , and the control signal L-SPEED is input from the gate.  
         [0392]    In the pMOS transistor  828 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  822 , and the gate is connected to the node N 1 .  
         [0393]    In the nMOS transistor  829 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0394]    In the nMOS transistor  830 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  831 .  
         [0395]    The inverter  831  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0396]    In the level shift circuit in FIG. 8B as well, the power supply potential is 3 volts. Therefore the high level potential of the output signal OUT is 3 volts. The high level potential of the input signal IN and the high level potential of the inverter  831  is 1.5 volts or 3 volts.  
         [0397]    Initially operation of this level shift circuit when the high level potential of the input signal IN and the inverter  831  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the nMOS transistors  825  and  827  turn OFF.  
         [0398]    When the input signal IN is at low level, the output of the inverter  831  is at high level (1.5 volts). Therefore the nMOS transistor  829  is OFF, and the nMOS transistor  830  is ON. The pMOS transistor  823  strongly turns ON, and the pMOS transistor  824  weakly turns ON. Since the nMOS transistor  830  is ON, the potential of the node N 2  is at low level, and the pMOS transistors  821  and  826  are ON, so the potential of the node N 1  is at high level. Therefore the pMOS transistors  822  and  828  are OFF. Since the pMOS transistors  825  and  827  are OFF, this has no influence on the general operation of the level shift circuit.  
         [0399]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  831  to low level. By this, the nMOS transistor  829  turns ON, the nMOS transistor  830  turns OFF, the pMOS transistor  823  weakly turns ON, and the pMOS transistor  824  strongly turns ON. By this, the pMOS transistors  821 ,  823  and  826 , and the nMOS transistor  829  turn ON. Then the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistors  822  and  828 . By this, the pMOS transistors  822  and  828  turn ON, and the potential of the node N 2  rises to high level (3 volts).  
         [0400]    Then the input signal IN changes to low level, which changes the output of the inverter  831  to high level. Therefore the nMOS transistor  829  turns OFF, the nMOS transistor  830  turns ON, the pMOS transistor  823  strongly turns ON, and the pMOS transistor  824  weakly turns ON. By this, the pMOS transistors  822 ,  824  and  828 , and the nMOS transistor  830  turn ON. Then the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  821 . By this, the pMOS transistor  821  turns ON. Therefore the potential of the node N 1  becomes high level, and the pMOS transistor  822  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0401]    When the control signal L-SPEED is set to high level in this way, the speed of the output signal OUT is not increased, since the pMOS transistors  825  and  827  are not in use. However, the level shift circuit can operate normally even if the level shift amount is high, and power consumption is low since the through current is low.  
         [0402]    Now operation of the level shift circuit when the high level potential of the input signal IN and the inverter  827  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistors  825  and  827  turn ON.  
         [0403]    When the input signal IN is at low level, the output of the inverter  831  is at high level (3 volts). Therefore the nMOS transistor  829  is OFF, and the nMOS transistor  830  is ON. Also the pMOS transistor  823  strongly turns ON, and the pMOS transistor  824  is OFF. Since the nMOS transistor  830  is ON, the potential of the node N 2  is at low level, therefore the pMOS transistors  821  and  826  are ON, so the potential of the node N 1  is at high level. As a result, the pMOS transistors  822  and  828  are OFF.  
         [0404]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  831  to low level. Therefore the nMOS transistor  829  turns ON, the nMOS transistor  830  turns OFF, the pMOS transistor  823  turns OFF, and the pMOS transistor  824  strongly turns ON. Since the potential of the node N 1  becomes zero volts, the pMOS transistors  822  and  828  turn ON. As a result, the potential of the node N 2  rises to high level (3 volts). According to the present embodiment, the potential of the node N 2  rises at high-speed, since current is supplied to the pMOS transistor  822  from the two pMOS transistors  827  and  828 . When the potential of the node N 2  becomes high level, the pMOS transistors  821  and  826  turn OFF.  
         [0405]    Then the input signal IN changes to low level, which changes the output of the inverter  831  to high level. Therefore the nMOS transistor  829  turns OFF, the nMOS transistor  830  turns ON, the pMOS transistor  823  strongly turns ON, and the pMOS transistor  824  turns OFF. By this, the potential of the node N 2  becomes zero volts. Then the pMOS transistors  821  and  826  turn ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistors  822  and  828  turn OFF.  
         [0406]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the recharging capability of the nodes N 1  and N 2  can be increased, therefore the speed of the rise operation and the fall operation of the output signal OUT can be increased.  
         [0407]    Ninth Embodiment  
         [0408]    [0408]FIG. 9A is a circuit diagram depicting the configuration of key components of the level shift circuit in accordance with the present embodiment. As shown in FIG. 9A, this level shift circuit is comprised of the pMOS transistors  911 - 914 , the nMOS transistors  915  and  916 , and the inverter  917 .  
         [0409]    In the pMOS transistor  911 , the source is connected to the power supply line, the drain is connected to the node N 1 , and the gate is connected to the node N 2 .  
         [0410]    In the pMOS transistor  912 , the source is connected to the power supply line, the drain is connected to the node N 2 , and the gate is connected to the node N 1 .  
         [0411]    In the pMOS transistor  913 , the source is connected to the power supply line, and the control signal L-SPEED is input from the gate.  
         [0412]    In the pMOS transistor  914 , the source is connected to the drain of the pMOS transistor  913 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  917 .  
         [0413]    In the nMOS transistor  915 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0414]    In the nMOS transistor  916 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  917 .  
         [0415]    The inverter  917  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0416]    According to the present embodiment, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  917  is 1.5 volts or 3 volts.  
         [0417]    Operation of the level shift circuit shown in FIG. 9A will now be described.  
         [0418]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  917  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level (3 volts). By this the pMOS transistor  913  turns OFF.  
         [0419]    When the input signal IN is at low level, the output of the inverter  917  is maintained at high level (1.5 volts). Therefore the nMOS transistor  915  is OFF, and the nMOS transistor  916  is ON. Since the nMOS transistor  916  is ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  911  is ON, and the potential of the node N 1  is at high level. Therefore the pMOS transistor  912  is OFF. Since the nMOS transistor  913  is OFF, the ON/OFF of the nMOS transistor  914  has no influence on the general operation of the level shift circuit.  
         [0420]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  917  to low level. Therefore the nMOS transistor  915  turns ON, and the nMOS transistor  916  turns OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  911  is maintained in the ON state. When the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  912 , the pMOS transistor  912  turns ON, and the potential of the node N 2  rises to high level (3 volts). By this, the pMOS transistor  911  turns OFF, and the potential of the node N 1  drops to low level.  
         [0421]    Then the input signal IN changes to low level, which changes the output of the inverter  917  to high level. Therefore the nMOS transistor  915  turns OFF, and the nMOS transistor  916  turns ON. At this time, the potential of the node N 1  is maintained at low level, and the pMOS transistor  912  is maintained in the ON state. By this, both the pMOS transistor  912  and the nMOS transistor  916  turn ON. When the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  911 , the pMOS transistor  911  turns ON. By this, the potential of the node N 1  becomes high level, and the pMOS transistor  912  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0422]    When the control signal L-SPEED is set to high level in this way, the speed of the rise operation of the output signal OUT is not increased, since the pMOS transistors  913  and  914  are not in use. However, the level shift circuit can operate normally even if the level shift amount is high.  
         [0423]    Now operation of this level shift circuit when the high level potential of the input signal IN and the inverter  917  is 3 volts will be described. In this case the control signal L-SPEED is set to low level, so the nMOS transistor  913  turns ON.  
         [0424]    In this level shift circuit, the output of the inverter  917  is maintained at high level (3 volts) when the input signal IN is at low level. Therefore the nMOS transistor  915  is OFF, the nMOS transistor  916  is ON, and the pMOS transistor  914  is OFF. Since the nMOS transistor  916  is ON and the nMOS transistor  914  is OFF, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  911  is ON, so the potential of the node N 1  is at high level. By this the pMOS transistor  912  turns OFF.  
         [0425]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  917  to low level. Therefore the nMOS transistor  915  and the pMOS transistor  914  turn ON, and the nMOS transistor  916  turns OFF. Since the pMOS transistor  914  turns ON and the nMOS transistor  916  turns OFF, the potential of the node N 2  becomes high level. In other words, according to the present embodiment, the pMOS transistor  914  turns ON as soon as the nMOS transistor  916  turns OFF, so the node N 2  changes to high level at high-speed. Then the pMOS transistor  911  turns OFF, and the node N 1  becomes low level. By this, the pMOS transistor  912  turns ON.  
         [0426]    Then the input signal IN changes to low level, which changes the output of the inverter  917  to high level. Therefore the nMOS transistor  915  and the pMOS transistor  914  turn OFF, and the nMOS transistor  916  turns ON. By this, the potential of the node N 2  becomes low level. At this time, the pMOS transistor  912  is ON, but the current capability is sufficiently low, so the node N 2  drops lower level than the ON/OFF threshold level of the pMOS transistor  911 . By this, the pMOS transistor  911  turns ON. Therefore the potential of the node N 1  becomes high level, and the pMOS transistor  912  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0427]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the recharging capability of the node N 2  can be increased, therefore the speed of the rise operation of the output signal OUT can be increased.  
         [0428]    Now a variant form of the level shift circuit in accordance with the present embodiment will be described with reference to FIG. 9B.  
         [0429]    The level shift circuit in FIG. 9B is comprised of the pMOS transistors  921 - 925 , the nMOS transistors  926  and  927 , and the inverter  928 .  
         [0430]    In the pMOS transistor  921 , the source is connected to the power supply line, and the gate is connected to the node N 2 .  
         [0431]    In the pMOS transistor  922 , the source is connected to the power supply line, and the gate is connected to the node N 1 .  
         [0432]    In the pMOS transistor  923 , the source is connected to the drain of the pMOS transistor  921 , the drain is connected to the node N 1 , and the input signal IN is input from the gate. This pMOS transistor  923  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0433]    In the pMOS transistor  924 , the source is connected to the drain of the pMOS transistor  922 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  928 . This pMOS transistor  924  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0434]    In the pMOS transistor  925 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  924 , and the control signal L-SPEED is input from the gate.  
         [0435]    In the nMOS transistor  926 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0436]    In the nMOS transistor  927 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  928 .  
         [0437]    The inverter  928  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0438]    Just like the level shift circuit in FIG. 9A, another pMOS transistor may be disposed between the drain of the pMOS transistor  925  and the node N 2 , where the gate of this pMOS transistor is connected to the output terminal of the inverter  928 . In this case as well, the operation of the level shift circuit is almost the same as the case of the circuit in FIG. 9A (mentioned later). However, connecting the drain of the pMOS transistor  925  to the source of the pMOS transistor  924  requires less number of transistors of the level shift circuit, as shown in FIG. 9B.  
         [0439]    In the level shift circuit in FIG. 9B as well, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  928  is 1.5 volts or 3 volts.  
         [0440]    Initially operation of this level shift circuit when the high level potential of the input signal IN and the inverter  928  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the nMOS transistor  925  turns OFF.  
         [0441]    When the input signal IN is at low level, the output of the inverter  928  is at high level (1.5 volts). Therefore the nMOS transistor  926  is OFF, and the nMOS transistor  927  is ON. The pMOS transistor  923  strongly turns ON, and the pMOS transistor  924  weakly turns ON. Since the nMOS transistor  927  is ON, the potential of the node N 2  is at low level. By this, the pMOS transistor  921  turns ON, so the potential of the node N 1  is at high level. As a result, the pMOS transistor  922  is OFF.  
         [0442]    Then the input signal IN changes to the high level (1.5 volts), which changes the output of the inverter  928  to low level. By this, the nMOS transistor  926  turns ON, the nMOS transistor  927  turns OFF, the pMOS transistor  923  weakly turns ON, and the pMOS transistor  924  strongly turns ON. When the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  922 , the pMOS transistor  922  turns ON. As the pMOS transistor  922  turns ON, the potential of the node N 2  rises to high level (3 volts). Since the pMOS transistor  925  is OFF, this has no influence on the general operation of the level shift circuit.  
         [0443]    Then the input signal IN changes to low level, which changes the output of the inverter  928  to high level. Therefore the nMOS transistor  926  turns OFF, the nMOS transistor  927  turns ON, the pMOS transistor  923  strongly turns ON, and the pMOS transistor  924  weakly turns ON. By this, the pMOS transistors  922  and  924 , and the nMOS transistor  927  turn ON. Then the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  921 . By this, the pMOS transistor  921  turns ON. Therefore the potential of the node N 1  becomes high level, and the pMOS transistor  922  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0444]    When the control signal L-SPEED is set to high level in this way, the speed of the rise operation of the output signal OUT is not increased, since the pMOS transistor  925  is not in use. However, the level shift circuit can operate normally even if the level shift amount is high.  
         [0445]    Now operation of this level shift circuit when the high level potential of the input signal IN and the inverter  927  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistor  925  turns ON.  
         [0446]    When the input signal IN is at low level, the output of the inverter  928  becomes high level (3 volts). Therefore the nMOS transistor  926  is OFF, and the nMOS transistor  927  is ON. The pMOS transistor  923  strongly turns ON, and the pMOS transistor  924  turns OFF. Since the nMOS transistor  927  is ON, the potential of the node N 2  is at low level. By this, the pMOS transistor  921  turns ON, and the potential of the node N 1  is at high level. As a result, the pMOS transistor  922  is OFF.  
         [0447]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  928  to low level. Therefore the nMOS transistor  926  turns ON, the pMOS transistor  923  turns OFF, and the pMOS transistor  922  turns ON. Also the pMOS transistor  924  strongly turns ON. So current is supplied from the pMOS transistors  922  and  925  to the node N 2  via the pMOS transistor  924 . The output of the inverter  928  becomes low level, so the nMOS transistor  927  turns OFF. Therefore the potential of the node N 2  changes to high level at high-speed. As a result, the pMOS transistor  921  turns OFF.  
         [0448]    Then the input signal IN changes to low level, which changes the output of the inverter  928  to high level. Therefore the mMOS transistor  926  turns OFF, the nMOS transistor  927  turns ON, the pMOS transistor  923  strongly turns ON, and the pMOS transistor  924  turns OFF. By this, the potential of the node N 2  drops to low level. Then the pMOS transistor  921  turns ON, and the potential of the node N 1  becomes high level. As a result, the pMOS transistor  922  turns OFF.  
         [0449]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the recharging capability of the node N 2  can be increased, therefore the speed of the rise operation of the output signal OUT can be increased.  
         [0450]    Tenth Embodiment  
         [0451]    [0451]FIG. 10A is a circuit diagram depicting key components of the level shift circuit in accordance with the present embodiment. As shown in FIG. 10A, this level shift circuit is comprised of the pMOS transistors  1011 - 1016 , the nMOS transistors  1017  and  1018 , and the inverters  1019  and  1020 .  
         [0452]    In the pMOS transistor  1011 , the drain is connected to the node N 1 , and the gate is connected to the node N 2 .  
         [0453]    In the pMOS transistor  1012 , the drain is connected to the node N 2 , and the gate is connected to the node N 1 .  
         [0454]    In the pMOS transistor  1013 , the source is connected to the power supply line, and the control signal L-SPEED is input from the gate.  
         [0455]    In the pMOS transistor  1014 , the source is connected to the drain of the pMOS transistor  1013 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  1020 .  
         [0456]    In the pMOS transistor  1015 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  1011 , and the gate is connected to the output terminal of the inverter  1019 .  
         [0457]    In the pMOS transistor  1016 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  1012 , and the gate is connected to the output terminal of the inverter  1019 .  
         [0458]    In the nMOS transistor  1017 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0459]    In the nMOS transistor  1018 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  1020 .  
         [0460]    The inverter  1019  inputs the control signal L-SPEED from the input terminal, inverts this control signal L-SPEED, and outputs it.  
         [0461]    The inverter  1020  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0462]    According to the present embodiment, the power supply voltage is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  1020  is 1.5 volts or 3 volts.  
         [0463]    Operation of the level shift circuit shown in FIG. 10A will now be described.  
         [0464]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  1020  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level (3 volts). By this, the pMOS transistor  1013  turns OFF, and the pMOS transistors  1015  and  1016  turn ON.  
         [0465]    When the input signal IN is at low level, the output of the inverter  1020  is maintained at high level (1.5 volts). Therefore the nMOS transistor  1017  is OFF, and the nMOS transistor  1018  is ON. Since the nMOS transistor  1018  is ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  1011  is ON, and the potential of the node N 1  is at high level. Therefore the pMOS transistor  1012  is OFF. Since the nMOS transistor  1013  is OFF, the ON/OFF of the nMOS transistor  1014  has no influence on the general operation of the level shift circuit.  
         [0466]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  1020  to low level. Therefore the nMOS transistor  1017  turns ON, and the nMOS transistor  1018  turns OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  1011  is maintained in the ON state. Then the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  1012 . Therefore the pMOS transistor  1012  turns ON, and the potential of the node N 2  rises to high level (3 volts). By this, the pMOS transistor  1011  turns OFF, and the potential of the node N 1  drops to low level.  
         [0467]    Then the input signal IN changes to low level, which changes the output of the inverter  1020  to high level. Therefore the nMOS transistor  1017  turns OFF, and the nMOS transistor  1018  turns ON. At this time, the potential of the node N 1  is maintained at low level, and the pMOS transistor  1012  is maintained in the ON state. Then the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  1011 . By this, the pMOS transistor  1011  turns ON. Then the potential of the node N 1  becomes high level, and the pMOS transistor  1012  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0468]    When the control signal L-SPEED is set to high level in this way, the speed of the rise operation of the output signal OUT is not increased, since the pMOS transistors  1013  and  1014  are not in use. However, the level shift circuit can operate normally even if the level shift amount is high.  
         [0469]    Now operation of this level shift circuit when the high level potential of the input signal IN and the inverter  1020  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistor  1013  turns ON, and the pMOS transistors  1015  and  1016  turn OFF.  
         [0470]    In this level shift circuit, the output of the inverter  1020  is maintained at high level (3 volts) when the input signal IN is at low level. Therefore the nMOS transistor  1018  is ON, and the pMOS transistor  1014  is OFF. So the potential of the node N 2  is maintained at low level. Since the pMOS transistors  1015  and  1016  are OFF, the ON/OFF of the pMOS transistors  1011  and  1012 , and the nMOS transistor  1017  has no influence on the general operation of the level shift circuit.  
         [0471]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  1020  to low level. Since the pMOS transistor  1014  turns ON and the nMOS transistor  1018  turns OFF, the potential of the node N 2  becomes high level. In other words, according to the present embodiment, the pMOS transistor  1014  turns ON as soon as the nMOS transistor  1018  turns OFF, so the potential of the node N 2  changes to high level at high-speed.  
         [0472]    Then the input signal IN changes to low level, which changes the output of the inverter  1020  to high level. Therefore the pMOS transistor  1014  turns OFF, and the nMOS transistor  1018  turns ON. By this, the potential of the node N 2  becomes low level. In other words, according to the present embodiment, the nMOS transistor  1018  turns ON as soon as the pMOS transistor  1014  turns OFF, so the potential of the node N 2  changes to low level at high-speed.  
         [0473]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the speed of the rise operation and the fall operation of the node N 2  can be increased.  
         [0474]    Now a variant form of the level shift circuit in accordance with the present embodiment will be described with reference to FIG. 10B.  
         [0475]    The level shift circuit in FIG. 10B is comprised of the pMOS transistors  1021 - 1026 , the nMOS transistors  1027  and  1028 , and the inverters  1029  and  1030 .  
         [0476]    In the pMOS transistor  1021 , the gate is connected to the node N 2 .  
         [0477]    In the pMOS transistor  1022 , the source is connected to the power supply line, and the gate is connected to the node N 1 .  
         [0478]    In the pMOS transistor  1023 , the source is connected to the drain of the pMOS transistor  1021 , the drain is connected to the node N 1 , and the input signal IN is input from the gate. This pMOS transistor  1023  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0479]    In the pMOS transistor  1024 , the source is connected to the drain of pMOS transistor  1022 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  1030 . This pMOS transistor  1024  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0480]    In the pMOS transistor  1025 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  1024 , and the control signal L-SPEED is input from the gate.  
         [0481]    In the pMOS transistor  1026 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  1021 , and the gate is connected to the output terminal of the inverter  1029 .  
         [0482]    In the nMOS transistor  1027 , the source is connected to the ground line, the drain is connected to the node N 1 , and the input signal IN is input from the gate.  
         [0483]    In the nMOS transistor  1028 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  1030 .  
         [0484]    The inverter  1029  inputs the control signal L-SPEED from the input terminal, inverts this signal L-SPEED, and outputs it.  
         [0485]    The inverter  1030  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0486]    In the level shift circuit in FIG. 10B, another pMOS transistor may be disposed between the drain of the pMOS transistor  1025  and the node N 2 , where the gate of this pMOS transistor is connected to the output terminal of the inverter  1030 , just like the pMOS transistor  1014  of the level shift circuit in FIG. 10A. Additionally, another pMOS transistor may be disposed between the pMOS transistor  1021  and the power supply line, where the gate of this pMOS transistor is connected to the output terminal of the inverter  1029 , just like the pMOS transistor  1016 . Even if these transistors are added, operation of the level shift circuit is almost the same as operation of the circuit in FIG. 10A (described later). However, the level shift circuit shown in FIG. 10B requires less number of transistors than the circuit having these transistors.  
         [0487]    In the level shift circuit in FIG. 10B as well, the power supply potential is 3 volts. The high level potential of the output signal OUT is 3 volts. And the high level potential of the input signal IN and the high level potential of the output of the inverter  1030  is 1.5 volts or 3 volts.  
         [0488]    Initially operation of this level shift circuit when the high level potential of the input signal IN and the inverter  1030  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the pMOS transistor  1025  turns OFF, and the pMOS transistor  1026  turns ON.  
         [0489]    When the input signal IN is at low level, the output of the inverter  1030  is at high level (1.5 volts). Therefore the nMOS transistor  1027  is OFF, and the nMOS transistor  1028  is ON. The pMOS transistor  1023  strongly turns ON, and the pMOS transistor  1024  weakly turns ON. Since the nMOS transistor  1028  is ON, the potential of the node N 2  is at low level. By this, the pMOS transistor  1021  turns ON, so the potential of the node N 1  is at high level. As a result, the pMOS transistor  1022  is OFF.  
         [0490]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  1030  to low level. By this, the nMOS transistor  1027  turns ON, the nMOS transistor  1028  turns OFF, the pMOS transistor  1023  weakly turns ON, and the pMOS transistor  1024  strongly turns ON. When the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  1022 , the pMOS transistor  1022  turns ON. By this, the potential of the node N 2  rises to high level (3 volts). Since the pMOS transistor  1025  is OFF, this has no influence on the general operation of the level shift circuit.  
         [0491]    Then the input signal IN changes to low level, which changes the output of the inverter  1030  to high level. Therefore the nMOS transistor  1027  turns OFF, the nMOS transistor  1028  turns ON, the pMOS transistor  1023  strongly turns ON, and the pMOS transistor  1024  weakly turns ON. Then the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  1021 . By this, the pMOS transistor  1021  turns ON. Therefore the potential of the node N 1  becomes high level, and the pMOS transistor  1022  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0492]    When the control signal L-SPEED is set to high level in this way, the speed of the rise operation of the output signal OUT is not increased, since the pMOS transistor  1025  is not in use. However, the level shift circuit can operate normally even if the level shift amount is high.  
         [0493]    Now operation of this level shift circuit when the high level potential of the input signal IN and the inverter  1030  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the pMOS transistor  1025  turns ON, and the pMOS transistor  1026  turns OFF.  
         [0494]    When the input signal IN is at low level, the output of the inverter  1030  becomes high level (3 volts). Therefore the nMOS transistor  1028  is ON, and the pMOS transistor  1024  is OFF. This means that the potential of the node N 2  is at low level. Since the nMOS transistor  1027  is OFF and the pMOS transistor  1026  is OFF, the potential of the node N 1  is undefined. As a result, the ON/OFF of the pMOS transistor  1022  is also undefined.  
         [0495]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  1030  to low level. Therefore the nMOS transistor  1027  turns ON, the nMOS transistor  1028  turns OFF, the pMOS transistor  1024  strongly turns ON, and the pMOS transistor  1025  turns ON. Since the nMOS transistor  1028  turns OFF and the pMOS transistor  1025  turns ON, the potential of the node N 2  becomes high level. Also the nMOS transistor  1027  turns ON, so the node N 1  becomes low level. Therefore the pMOS transistor  1022  turns ON. According to the present embodiment, the pMOS transistor  1024  turns ON as soon as the nMOS transistor  1028  turns OFF, so the potential of the node N 2  changes to high level at high-speed.  
         [0496]    Then the input signal IN changes to low level, which changes the output of the inverter  1030  to high level. Therefore the nMOS transistor  1027  turns OFF, the nMOS transistor  1028  turns ON, the pMOS transistor  1024  turns OFF. Since the nMOS transistor  1028  turns ON and the pMOS transistor  1024  turns OFF, the potential of the node N 2  becomes low level. Also the node N 1  is maintained at low level even if the nMOS transistor  1027  turns OFF, because the pMOS transistor  1026  is in OFF state. So the pMOS transistor  1022  remains OFF. According to the embodiment, the pMOS transistor  1024  turns OFF as soon as the nMOS transistor  1028  turns ON, so the potential of the node N 2  changes to low level at high-speed.  
         [0497]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the speed of the rise operation and the fall operation of the output signal OUT can be increased.  
         [0498]    Eleventh Embodiment  
         [0499]    [0499]FIG. 11A is a circuit diagram depicting key components of the level shift circuit in accordance with the present embodiment. As shown in FIG. 11A, this level shift circuit is comprised of the pMOS transistors  1111 - 1115 , the nMOS transistors  1116  and  1117 , and the inverter  1119 .  
         [0500]    In the pMOS transistor  1111 , the source is connected to the power supply line, the drain is connected to the node N 1 , and the gate is connected to the node N 2 .  
         [0501]    In the pMOS transistor  1112 , the source is connected to the power supply line, the drain is connected to the node N 2 , and the gate is connected to the node N 1 .  
         [0502]    In the pMOS transistor  1113 , the source is connected to the power supply line, and the control signal L-SPEED is input from the gate.  
         [0503]    In the pMOS transistor  1114 , the source is connected to the drain of the pMOS transistor  1113 , and drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  1119 .  
         [0504]    In the pMOS transistor  1115 , the source is connected to the power supply line, the drain is connected to the node N 1 , and the control signal L-SPEED is input from the gate.  
         [0505]    In the nMOS transistor  1116 , the source is connected to the ground line, and the input signal IN is input from the gate.  
         [0506]    In the nMOS transistor  1117 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  1119 .  
         [0507]    In the nMOS transistor  1118 , the source is connected to the drain of the nMOS transistor  1116 , the drain is connected to the node N 1 , and the control signal L-SPEED is input from the gate.  
         [0508]    The inverter  1119  inputs the input signal IN from the input terminal, inverts this input signal IN, and outputs it.  
         [0509]    According to the present embodiment, the power supply voltage is 3 volts. Therefore the high level potential of the output signal OUT, that is, the high level potential of the node N 2 , is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  1119  is 1.5 volts or 3 volts.  
         [0510]    Operation of the level shift circuit shown in FIG. 11A will now be described.  
         [0511]    Initially operation of the level shift circuit when the high level potential of the input signal IN and the inverter  1119  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level (3 volts). By this, the pMOS transistors  1113  and  1115  turn OFF, and the nMOS transistor  1118  turns ON.  
         [0512]    When the input signal IN is at low level, the output of the inverter  1119  is maintained at high level (1.5 volts). Therefore the nMOS transistor  1116  is OFF, and the nMOS transistor  1117  is ON. Since the nMOS transistor  1117  is ON, the potential of the node N 2  is maintained at low level. This means that the pMOS transistor  1111  is ON, and the potential of the node N 1  is at high level. Therefore the pMOS transistor  1112  is OFF. Since the nMOS transistor  1113  is OFF, the ON/OFF of the nMOS transistor  1114  has no influence on the general operation of the level shift circuit.  
         [0513]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  1119  to low level. Therefore the nMOS transistor  1116  turns ON, and the nMOS transistor  1117  turns OFF. At this time, the potential of the node N 2  is maintained at zero volts. This means that the pMOS transistor  1111  is maintained in the ON state. Then the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  1112 . Therefore the pMOS transistor  1112  turns ON, and the potential of the node N 2  rises to high level (3 volts). By this, the pMOS transistor  1111  turns OFF, and the potential of the node N 1  drops to low level.  
         [0514]    Then the input signal IN changes to low level, which changes the output of the inverter  1119  to high level. Therefore the nMOS transistor  1116  turns OFF, and the nMOS transistor  1117  turns ON. At this time, the potential of the node N 1  is maintained at low level, and the pMOS transistor  1112  is maintained in the ON state. Then the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  1111 . By this, the pMOS transistor  1111  turns ON. Then the potential of the node N 1  becomes high level, and the pMOS transistor  1112  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0515]    When the control signal L-SPEED is set to high level in this way, the speed of the operation of the output signal OUT is not increased, since the pMOS transistors  1113 ,  1114  and  1115  are not in use. However, the level shift circuit can operate normally even if the level shift amount is high.  
         [0516]    Now operation of this level shift circuit when the high level potential of the input signal IN and the inverter  1119  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the nMOS transistors  1113  and  1115  turn ON, and the pMOS transistor  1118  turns OFF.  
         [0517]    In this level shift circuit, the output of the inverter  1119  is maintained at high level (3 volts) when the input signal IN is at low level. Therefore the nMOS transistor  1117  is ON, and the pMOS transistor  1114  is OFF. So the potential of the node N 2  is maintained at low level. Since the pMOS transistor  1118  is OFF, the ON/OFF of the nMOS transistor  1116  has no influence on the general operation of the level shift circuit. Also the pMOS transistor  1115  is fixed to the ON state, so the potential of the node N 1  is fixed to high level. As a result, the pMOS transistor  1112  is fixed to the OFF state.  
         [0518]    Then the input signal IN changes to high level (3 volts), which changes the output of the inverter  1119  to low level. Since the pMOS transistor  1114  turns ON and the nMOS transistor  1117  turns OFF, the potential of the node N 2  becomes high level. In other words, according to the present embodiment, the pMOS transistor  1114  turns ON as soon as the nMOS transistor  1117  turns OFF, so the potential of the node N 2  changes to high level at high-speed.  
         [0519]    Then the input signal IN changes to low level, which changes the output of the inverter  1119  to high level. Therefore the pMOS transistor  1114  turns OFF, and the nMOS transistor  1117  turns ON. By this, the potential of the node N 2  becomes low level. In other words, according to the present embodiment, the nMOS transistor  1117  turns ON as soon as the pMOS transistor  1114  turns OFF, so the potential of the node N 2  changes to low level at high-speed.  
         [0520]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the speed of the rise operation and the fall operation of the node N 2  can be increased.  
         [0521]    Now a variant form of the level shift circuit in accordance with the present embodiment will be described with reference to FIG. 11B.  
         [0522]    The level shift circuit in FIG. 11B is comprised of the pMOS transistors  1121 - 1126 , the nMOS transistors  1127 - 1129 , and the inverter  1130 .  
         [0523]    In the pMOS transistor  1121 , the source is connected to the power supply line, and the gate is connected to the node N 2 .  
         [0524]    In the pMOS transistor  1122 , the source is connected to the power supply line, and the gate is connected to the node N 1 .  
         [0525]    In the pMOS transistor  1123 , the source is connected to the drain of the pMOS transistor  1121 , the drain is connected to the node N 1 , and the input signal IN is input from the gate. The pMOS transistor  1123  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0526]    In the pMOS transistor  1124 , the source is connected to the drain of the pMOS transistor  1122 , the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  1130 . This pMOS transistor  1124  strongly turns ON when the gate potential is zero volts, weakly turns ON when the gate potential is 1.5 volts, and turns OFF when the gate potential is 3 volts.  
         [0527]    In the pMOS transistor  1125 , the source is connected to the power supply line, the drain is connected to the source of the pMOS transistor  1124 , and the control signal L-SPEED is input from the gate.  
         [0528]    In the pMOS transistor  1126 , the source is connected to the power supply line, the drain is connected to the node N 1 , and the control signal L-SPEED is input from the gate.  
         [0529]    In the nMOS transistor  1127 , the source is connected to the ground line, and the input signal IN is input from the gate.  
         [0530]    In the nMOS transistor  1128 , the source is connected to the ground line, the drain is connected to the node N 2 , and the gate is connected to the output terminal of the inverter  1130 .  
         [0531]    In the nMOS transistor  1129 , the source is connected to the drain of the nMOS transistor  1127 , the drain is connected to the node N 1 , and the control signal L-SPEED is input from the gate.  
         [0532]    The inverter  1130  inputs the input signal IN from the input terminal, inverts this signal IN, and outputs it.  
         [0533]    In the level shift circuit in FIG. 11B, another pMOS transistor may be disposed between the drain of the pMOS transistor  1125  and the node N 2 , where the gate of this pMOS transistor is connected to the output terminal of the inverter  1130 , just like the level shift circuit in FIG. 11A. Even if such a transistor is added, the operation of the level shift circuit is almost the same as the operation of the circuit in FIG. 11A (described later). However, the level shift circuit shown in FIG. 11B requires less number of transistors than the circuit having these transistors.  
         [0534]    In the level shift circuit in FIG. 11B as well, the power supply potential is 3 volts. The high level potential of the input signal IN and the high level potential of the output of the inverter  1130  is 1.5 volts or 3 volts.  
         [0535]    Initially operation of this level shift circuit when the high level potential of the input signal IN and the inverter  1130  is 1.5 volts will be described. In this case, the control signal L-SPEED is set to high level. By this, the pMOS transistors  1125  and  1126  turn OFF, and the nMOS transistor  1129  turns ON.  
         [0536]    When the input signal IN is at low level, the output of the inverter  1130  is at high level (1.5 volts). Therefore the nMOS transistor  1127  is OFF, and the nMOS transistor  1128  is ON. The pMOS transistor  1123  strongly turns ON, and the pMOS transistor  1124  weakly turns ON. Since the nMOS transistor  1128  is ON, the potential of the node N 2  is at low level. By this, the pMOS transistor  1121  turns ON, so the potential of the node N 1  is at high level. As a result, the pMOS transistor  1122  is OFF.  
         [0537]    Then the input signal IN changes to high level (1.5 volts), which changes the output of the inverter  1130  to low level. By this, the nMOS transistor  1127  turns ON, the nMOS transistor  1128  turns OFF, the pMOS transistor  1123  weakly turns ON, and the pMOS transistor  1124  strongly turns ON. When the potential of the node N 1  drops to lower level than the ON/OFF threshold level of the pMOS transistor  1122 , the pMOS transistor  1122  turns ON. By this, the potential of the node N 2  rises to high level (3 volts).  
         [0538]    Then the input signal IN changes to low level, which changes the output of the inverter  1130  to high level. Therefore the nMOS transistor  1127  turns OFF, the nMOS transistor  1128  turns ON, the pMOS transistor  1123  strongly turns ON, and the pMOS transistor  1124  weakly turns ON. Then the potential of the node N 2  drops to lower level than the ON/OFF threshold level of the pMOS transistor  1121 . By this, the pMOS transistor  1121  turns ON. Therefore the potential of the node N 1  becomes high level, and the pMOS transistor  1122  turns OFF. As a result, the potential of the node N 2  drops to low level.  
         [0539]    When the control signal L-SPEED is set to high level in this way, the speed of the rise operation of the output signal OUT is not increased, since the pMOS transistor  1125  is not in use. However, the level shift circuit can operate normally even if the level shift amount is high.  
         [0540]    Now operation of this level shift circuit when the high level potential of the input signal IN and the inverter  1127  is 3 volts will be described. In this case, the control signal L-SPEED is set to low level, so the pMOS transistors  1125  and  1126  turn ON, and the pMOS transistor  1129  turns OFF.  
         [0541]    When the input signal IN is at low level, the output of the inverter  1130  becomes high level (3 volts). Therefore the nMOS transistor  1128  is ON, and the pMOS transistor  1124  is OFF. This means that the potential of the node N 2  is at low level. Since the nMOS transistor  1129  is OFF, the ON/OFF of the nMOS transistor  1127  has no influence on the general operation of the level shift circuit. Also the pMOS transistor  1126  is fixed to the ON state, so the potential of the node N 1  is fixed to high level, and the pMOS transistor  1122  is fixed to the OFF state. As a result, the ON/OFF of the pMOS transistors  1121  and  1123  have no influence on the general operation of the level shift circuit.  
         [0542]    Then the input signal IN changes to high level, which changes the output of the inverter  1130  to low level. Therefore the nMOS transistor  1128  turns OFF, and the pMOS transistor  1124  strongly turns ON. By this, the potential of the node N 2  becomes high level. According to the present embodiment, the pMOS transistor  1124  turns ON as soon as the nMOS transistor  1128  turns OFF, so the potential of the node N 2  changes to high level at high-speed.  
         [0543]    Then the input signal IN changes to low level, which changes the output of the inverter  1130  to high level. Therefore the nMOS transistor  1128  turns ON, and the pMOS transistor  1124  turns OFF. By this, the potential of the node N 2  becomes low level. According to the present invention, the pMOS transistor  1124  turns OFF as soon as the nMOS transistor  1128  turns ON, so the potential of the node N 2  changes to low level at high-speed.  
         [0544]    When the control signal L-SPEED is set to low level in this way, the level shift amount cannot be increased very much, but the speed of the rise operation and the fall operation of the output signal OUT can be increased.  
         [0545]    As described above, according to the present invention, the ratio between the inflow current and the emission current of the first node or the second node can be switched by the control signal. As a result, operation speed can be increased by setting this ratio high, and the voltage shift amount can be increased by setting this ratio low.