Patent Abstract:
A semiconductor integrated circuit is disclosed, which comprises a pre-charge type dynamic circuit, a static circuit which realizes the same logic as the dynamic circuit, a selection circuit which is connected to an input section of each of the dynamic circuit and the static circuit, a control circuit which controls the selection circuit to select either the dynamic circuit or the static circuit at the time of testing a semiconductor chip.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-297568, filed Oct. 10, 2002, the entire contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a semiconductor integrated circuit (LSI), particularly to a circuit technology to suppress electric power consumption, which is applied to, for example, a high-speed micro processor, logic in memory LSI, or the like.  
           [0004]    2. Description of the Related Art  
           [0005]    A semiconductor integrated circuit is basically divided into a dynamic circuit and a static circuit. In general, the dynamic circuit operates at high speed. However, in a case where channel-leaks increase due to variations in manufacturing process of LSIs, there is a problem in that the dynamic circuit malfunctions or the operation is unstable.  
           [0006]    [0006]FIG. 10 shows an OR-circuit of four inputs as an example of the dynamic circuit.  
           [0007]    In this circuit, a keeper circuit KP is connected to a dynamic node A of a domino circuit of four inputs.  
           [0008]    In a pre-charging period, the dynamic node A is pre-charged to “1” level (“H” level). In an evaluation period after the pre-charge period, if all inputs are at “0” and the dynamic node A is at “1” level, then the dynamic circuit operates properly. However, the dynamic circuit may malfunction because the electric potential of the dynamic node A may decrease due to a channel leak current. To prevent the malfunction, the keeper circuit KP operates so as to prevent the electric potential from decreasing.  
           [0009]    In the four inputs OR-circuit, if the size of the transistors (MOSFETs) of the keeper circuit KP is too large, the domino circuit operates slowly. On the contrary, if the size of the transistors of the keeper circuit KP is too small, a problem arises in that the domino circuit may malfunction due to a channel leak.  
           [0010]    Incidentally, as a countermeasure against the instability of dynamic circuit operation due to processes variation, known is a technology to stabilize the operation by providing a sense amplifier circuit in double scheme. (For example, Fujisawa et al, “A Dual-Phase-Controlled Dynamic Latched Amplifier for High-Speed and Low-Power DRAMs, IEEE JSSCC Vol. 36, No. 7, July 2001 pp1120-1126).  
           [0011]    [0011]FIG. 11 shows a circuit in which a sense amplifier circuit is provided in double scheme in a DRAM disclosed in the bulletin as cited above.  
           [0012]    In the circuit shown in FIG. 11, two sense amplifiers, i.e., a first sense amplifier (1st-phase DDL amp.)  91  and a second sense amplifier (2nd- phase DDL amp.)  92 , are provided and operated at the different timing.  
           [0013]    In this case, a sense enable signal EN 1  for controlling the first sense amplifier  91  is transmitted faster than a sense enable signal EN 2  for controlling the second sense amplifier  92 . Then, an output signal OUT 1  of the first sense amplifier  91  is outputted faster than an output signal OUT 2  of the second sense amplifier  92  which starts an operation in accordance with the sense enable signal EN 2 . The output signal OUT 2  of the second sense amplifier  92  and the output signal OUT 1  of the first sense amplifier  91  are compared to each other by an error correcting selector  93 . When an error is detected in data, it is corrected.  
           [0014]    That is, when a threshold voltage of the transistors is decreased due to process variation, the output of the sense amplifier circuit is corrected by the output signal OUT 2 .  
           [0015]    On the other hand, the static circuit operates stably against the process variation in manufacturing. However, the operation speed of the static circuit is lower than dynamic circuits. If a multi-input circuit is realized so as to increase the operation speed of the static circuit, a large number of MOSFETs are connected in a cascade scheme. In such a circuit, the threshold voltage of the MOSFETs increases because an electric potential across a source and substrate of the MOSFETs is applied in the reverse direction. However, the electric potential difference across the source and drain of the MOSFETs becomes small.  
           [0016]    For this reason, the multi-input circuit of the static circuit is often configured in a manner that small input circuits are connected in a multistage way. For example, as shown in FIG. 12, a four input circuit is often realized by combining two two-input input stage circuits  101  and a two-input output stage circuit  102 .  
           [0017]    Meanwhile, as we can see on a microprocessor etc., an LSI that operates at very high-speed, in which the operation frequency becomes several GHz, has been manufactured in these days. However, in proportion to the high-speed operation frequency, the electric power consumption increases, which is a serious problem.  
           [0018]    As one of the countermeasures, there has been developed a technology to reduce the electric power consumption by using clock control method. In this technology, for a process that does not need the high-speed operation so much, the frequency of the clock signal is set low to suppress the electric power consumption.  
           [0019]    In a logic LSI, particularly in a arithmetic logic unit, in order to increase the operation speed of the circuits, a circuit that operates in synchronization with the clock signal, e.g., the dynamic circuit, is often used instead of the static circuit. Hence, in the LSI, which is occupied with the circuits that operate in synchronization with the clock signal, the electric power consumption of the circuits connected to the clock signal increases in the entire electric power consumption. For this reason, even if the electric power consumption is reduced with use of the aforementioned conventional clock control method, it has been very difficult to satisfactorily suppress the electric power consumption.  
           [0020]    As described above, in the high-speed operating logic LSI, a problem lies in that, even if the electric power consumption is reduced with use of the aforementioned conventional clock control method, it has been very difficult to satisfactorily suppress the electric power consumption.  
         BRIEF SUMMARY OF THE INVENTION  
         [0021]    According to an aspect of the present invention, there is provided a semiconductor integrated circuit comprising a pre-charge type dynamic circuit; a static circuit which realizes the same logic as the dynamic circuit; a selection circuit which is connected to an input section of each of the dynamic circuit and the static circuit; a control circuit which controls the selection circuit to select either the dynamic circuit or the static circuit at the time of testing a semiconductor chip.  
           [0022]    According to another aspect of the present invention, there is provided a semiconductor integrated circuit comprising a clock control circuit which receives a clock signal and a low power-consumption mode control signal, outputs the clock signal retaining a logic level of the clock signal at the time when the power-consumption mode control signal is in an inactive state, and fixes the logic level of the clock signal at the time when the low power-consumption mode control signal is in an active state; and a logic circuit which receives an output signal of the clock control circuit as a control signal, and, when the control signal is the clock signal, operates in synchronization with the clock signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a circuit diagram showing a part of a logic LSI according to a first embodiment of the present invention;  
         [0024]    [0024]FIG. 2 is a graph showing an example of the relation between a threshold voltage Vth corresponding to process variation of the logic LSI and operation speed;  
         [0025]    [0025]FIG. 3 is a circuit diagram showing an example of a leak monitor circuit used for detecting process variation in a control circuit shown in FIG. 1;  
         [0026]    [0026]FIG. 4 is a circuit diagram showing a part of a logic LSI according to a second embodiment of the present invention;  
         [0027]    [0027]FIG. 5 is a timing diagram showing a signal waveform in a high-speed operation of a logic circuit in FIG. 4;  
         [0028]    [0028]FIG. 6 is a timing diagram showing a signal waveform in a low power-consumption operation of the logic circuit in FIG. 4;  
         [0029]    [0029]FIG. 7 is a circuit diagram showing a part of a logic LSI according to a third embodiment of the present invention;  
         [0030]    [0030]FIG. 8 is a circuit diagram showing a part of a logic LSI according to a modification of the second embodiment as shown in FIG. 4 of the present invention;  
         [0031]    [0031]FIG. 9 is a circuit diagram showing a part of a logic LSI according to a modification of the third embodiment as shown in FIG. 7 of the present invention;  
         [0032]    [0032]FIG. 10 is a circuit diagram showing a multi-input OR circuit as an example of a dynamic circuit;  
         [0033]    [0033]FIG. 11 is a circuit diagram showing an example of a circuit in which a sense amplifier circuit is provided in double scheme so as to stabilize an operation of the dynamic circuit in a DRAM; and  
         [0034]    [0034]FIG. 12 is a circuit diagram showing an example of a logic circuit provided by combining small input circuits in a multi-stage as a static circuit. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    Embodiments of the present invention now will be described in detail with reference to accompanying drawings.  
       First Embodiment  
       [0036]    [0036]FIG. 1 shows a part of a logic LSI according to a first embodiment of the invention.  
         [0037]    A circuit shown in FIG. 1 is applied to a memory peripheral circuit including a path critical with regard to operation speed in a logic in memory LSI, for example.  
         [0038]    A control circuit  15  generates an input-side select signal Select and an output-side select signal Select. The control circuit  15  also generates a power supply stop signal and a clock signal stop signal. A selection circuit  13  receives an input signal. The selection circuit  13  also receives the input-side selection signal Select from the control circuit  15  to select a dynamic circuit  11  or a static circuit  12  according to the input-side selection signal Select from the control circuit  15 , and outputs the received signal to the selected circuit. Output signals of the dynamic circuit  11  and the static circuit  12  are inputted to a selection circuit  14 . The selection circuit  14  receives the output-side selection signal Select from the control circuit  15  to select the dynamic circuit  11  or the static circuit  12  according to the output-side selection signal Select from the control circuit  15 , and outputs the output signal of the selected circuit.  
         [0039]    The dynamic circuit  11  and the static circuit  12  may be a small scale circuit such as a standard cell, or may be a large scale circuit block such as an ALU (arithmetic logic unit).  
         [0040]    [0040]FIG. 2 is a graph showing an example of the relation between a threshold voltage Vth corresponding to process variation and an operation speed of the logic LSI shown in FIG. 1.  
         [0041]    As shown in FIG. 2, when the threshold voltage Vth of a transistor (MOSFET) is increased due to variation of a manufacturing process of the logic LSI (the threshold voltage Vth shifts toward the “Slow” side in the abscissa in FIG. 2), the operation speed of the dynamic circuit slightly lowers. However, the operation speed of the static circuit greatly lowers. Therefore, in this case, it is preferable to operate the high-speed dynamic circuit  11  at the normal use of the logic LSI but not to operate the static circuit  12 .  
         [0042]    On the contrary to the above, when the threshold voltage Vth of the transistor (MOSFET) is decreased due to the variation of a manufacturing process of the logic LSI (the threshold voltage Vth shifts toward the “Fast” side in the abscissa in FIG. 2), the operation speed of the dynamic circuit reaches the fail point, and a malfunction occurs. In this case, the operation speed of the transistor itself is sufficiently high, so that even the low-speed static circuit can be operated relatively at high-speed. Therefore, in this case, at the normal use of the logic LSI, it is preferable to operate relatively high-speed static circuit  12  but not to operate the dynamic circuit  11 .  
         [0043]    By controlling in the manner as described above, the lowest operation speed for the LSI chip becomes the speed (fmin-d) of the dynamic circuit at the time when the threshold voltage Vth changes to the slow side or the speed (fmin-f) of the static circuit under the condition that a malfunction occurs in the dynamic circuit, whichever is lower. Besides, the lowest operation speed for the LSI chip is higher than the speed (fmin-s) of the static circuit at the time when the threshold voltage Vth moves toward the slow side.  
         [0044]    In order to detect process variation in the control circuit  15  shown in FIG. 1, it is possible to use a leak monitor circuit. The leak monitor circuit monitors a leak current in testing the LSI chip. When the leak current is large, the leak monitor circuit determines whether or not the dynamic circuit  11  operates under all the conditions. According to the determined result, the leak monitor circuit controls the selection circuits  13  and  14  to select the dynamic circuit  11  or the static circuit  12 .  
         [0045]    In this case, the leak monitor circuit is configured to be a circuit more unstable than a dynamic circuit, of dynamic circuits to which the selection method according to the invention is applied, whose operation is most unstable. As an example, the number or size of an input transistor is larger than the multi-input OR circuit described with reference to FIG. 8, or the size of the transistor of the keeper circuit is small or the gate length is short.  
         [0046]    In the control circuit  15 , when the leak current increases due to process variation and thus the operation of the dynamic circuit  11  becomes unstable, the static circuit  12  is selected. On the other hand, when the leak current is small and thus the dynamic circuit  11  operates stably, the dynamic circuit  11  is selected. Thus, it is possible to increase the operating frequency of the logic LSI.  
         [0047]    In this case, depending on the result of monitoring the leak current in testing the LSI chip, it is determined to select the dynamic circuit  11  or the static circuit  12 . In the normal mode, the logic level of the output of the control circuit  15  is fixed to a selecting logic level by which the selection of the circuits is carried out in accordance with the determination.  
         [0048]    Incidentally, in order to reduce wasteful power consumption and reduce the electric power consumption in operating, it is preferable that the selected circuit, which is selected from the dynamic circuit  11  and the static circuit  12  is operated, on the other hand the non-selected circuit is not operated. For this end, as a concrete example, a clock supply stop signal is generated from the control circuit  15  to stop supplying the clock signal to the non-selected circuit.  
         [0049]    As another concrete example for controlling not to operate the non-selected circuit, an electric power supply stop signal is generated from the control circuit  15 , and thus an electric power supply to the non-selected circuit is stopped. In such a case, it is also possible to reduce the electric power consumption in a stand-by mode.  
         [0050]    [0050]FIG. 3 shows an example of a leak monitor circuit used for detecting process variation in the control circuit  15  shown in FIG. 1.  
         [0051]    The leak monitor circuit is a pre-charge type seven-input OR circuit. A pre-charging PMOS transistor PT 1 , which is controlled by a clock signal CLOCK, is connected between a power supply (VCC) node and a dynamic node DN. Seven series circuits, each of which is connected to series-connected two NMOS transistors N 1  and N 2 , are connected in parallel to each other between the node DN and grounding (VSS) node. Further, an inverter circuit IV is connected between the node DN and an output node. A PMOS transistor PT 2  as a keeper circuit to whose gate an output of the inverter circuit IV is fed back, is connected between the VCC node and the node DN.  
         [0052]    The gate of the NMOS transistor N 1  in each of the series circuits is connected in common to the VSS node, and the gate of the NMOS transistor N 2  in each of the series circuits is connected in common to the VCC node.  
         [0053]    During a pre-charge period, the pre-charging transistor PT 1  becomes ON, and the dynamic node DN is pre-charged to the VCC. At this time, the logic level of the output node becomes “0”, which shows a Safe state.  
         [0054]    The pre-charge period ends and then an evaluation period (stand-by operation) starts. After that, when the electric potential of the dynamic node DN decreases lower than a certain value due to the channel leak current of the transistors N 1  and N 2  of the seven series circuits, the logic level of the output node becomes “1”, and shows a Fail state.  
         [0055]    During the period when the output of the leak monitor circuit is logic “0”, the dynamic circuit  11  shown in FIG. 1 operates properly. Therefore, the dynamic circuit  11  is selected and operated. On the other hand, when the output of the leak monitor circuit becomes logic “1”, it is in the Fail state in which an error has occurred in the leak monitor circuit. Therefore, it is controlled to operate the static circuit  12  instead of the dynamic circuit  11  shown in FIG. 1.  
         [0056]    As described above, in the logic LSI according to the first embodiment, the logic circuit is of double scheme and comprises two circuits, i.e. the dynamic circuit  11  and the static circuit  12 , both performing the same logic operation. By selecting one of the circuits, which is higher in operation speed than the other, against the variation of LSI manufacturing process, it is possible to suppress variation of the operation frequency due to the process variation, and increase the maximum operation frequency.  
         [0057]    Incidentally, in the present embodiment, when the leak current is large due to the process variation and thus the operation of the dynamic circuit  11  is unstable, it is controlled to select the static circuit  12 . However, it is also possible that, when the operation of the dynamic circuit  11  deteriorates due to the increase of the temperature in the use state and the dynamic circuit  11  cannot be operated any more, the control is changed to select the static circuit  12 .  
         [0058]    Further, in addition to the control to select the dynamic circuit  11  or the static circuit  12 , it is possible to change or switch power voltage of the operation power supply so as to increase the operation speed.  
       Second Embodiment  
       [0059]    [0059]FIG. 4 shows a part of the logic LSI according to a second embodiment of the present invention.  
         [0060]    In FIG. 4, a first logic circuit  41  is configured in that a PMOS logic circuit  42 , an NMOS logic circuit  43 , and an NMOS transistor NMOS 1  are connected in series between the power supply node and a grounding node.  
         [0061]    The PMOS logic circuit  42  and the NMOS logic circuit  43  constitute a multi-input NAND circuit, for example. In the NAND circuit, the PMOS logic circuit  42  includes a plurality of PMOS transistors, not shown, which are connected in parallel to each other and to whose gates a plurality of signals A 0  to An are inputted, respectively, and the NMOS logic circuit  43  includes a plurality of NMOS transistors, not shown, which are connected in series to each other and to whose gates a plurality of signals A 0  to An are inputted, respectively. A clock signal CLOCK  2  is inputted to the gate of the NMOS transistor NMOS 1 .  
         [0062]    An intermediate node B, to which the PMOS logic circuit  42  and the NMOS logic circuit  43  are connected, is connected to an output node Out via an inverter circuit  44 . Between the power supply node and the intermediate node B, the PMOS transistor PMOS 1  is connected. The clock signal CLOCK  2  is inputted to the gate of the PMOS transistor PMOS 1 .  
         [0063]    A clock signal CLOCK  1  and a low power-consumption mode control signal are inputted to a clock control circuit  40 , and the circuit  40  outputs the clock signal CLOCK  2 . In this case, when the low power-consumption mode control signal is in the inactive state, the clock signal  1  retaining the logic level is outputted as the clock signal CLOCK  2 . On the contrary, when the low power-consumption mode control signal is in the active state (low power-consumption mode), the clock signal CLOCK  2  is fixed at logic “1” level.  
         [0064]    In the circuit shown in FIG. 4, the first logic circuit  41  is selectively set to the normal high-speed operation state or to the electric power low consumption state by the clock signal CLOCK  2  inputted to the first logic circuit  41 , the operation thereof will be described below with reference to FIG. 5.  
         [0065]    [0065]FIG. 5 shows a timing diagram in a normal high-speed operation of the first logic circuit  41  shown in FIG. 4. In a normal high-speed operation, the clock signal CLOCK  1  with the current logic level is supplied to the first logic circuit  41  as the clock signal CLOCK  2 , and the first logic circuit  41  operates in synchronization with the clock signal CLOCK  2 .  
         [0066]    In this case, when the clock signal  2  is at logic “0” level, the operation is in a pre-charge period, and the PMOS transistor PMOS 1  is turned on and the NMOS transistor NMOS 1  is turned off, so as to set the logic level of the node B to logic “1” level.  
         [0067]    On the contrary to the above, when the clock signal CLOCK  2  is at logic “1” level, the operation is in an evaluation period, and the PMOS transistor PMOS 1  is turned off and the NMOS transistor NMOS 1  is turned on. Then, in accordance with the signal A 0  to An, the PMOS logic circuit  42  is turned on so as to hold the node B at logic “1” level, or the NMOS logic circuit  43  is turned on so as to invert the logic level of the node B to logic “ 0 ” level.  
         [0068]    In the circuit shown in FIG. 4, the state transition of the logic level of the clock signal in the first logic circuit  41  is one way (transition direction at the node B is logic “1” level→logic “0” level). Therefore, by enlarging the size Wn of the transistors (not shown) of the NMOS logic circuit  43  and reducing the size Wp of the transistors (not shown) of the PMOS logic circuit  42 , that is, by reducing Wp/Wn, the circuit shown in FIG. 4 operates at high-speed as in a dynamic circuit.  
         [0069]    In addition, the node B of the first logic circuit  41  will never be floating by the operations of the PMOS logic circuit  42  and the NMOS logic circuit  43 . Thus, the first logic circuit  41  is strong against noise in comparison with a dynamic circuit.  
         [0070]    [0070]FIG. 6 shows a timing diagram of the first logic circuit  41  shown in FIG. 4 at the time when the first logic circuit  41  does not need operate at high-speed so much and thus operates in low power-consumption.  
         [0071]    In this operation, the clock signal CLOCK  2  supplied to the first logic circuit  41  is fixed at “1” level. At this time, in the first logic circuit  41 , the PMOS transistor PMOS 1  is turned off and the NMOS transistor NMOS 1  is turned on, and thus the PMOS logic circuit  42  and the NMOS logic circuit  43  are operated as a static circuit.  
         [0072]    In addition, since the size Wp of the transistors (not shown) of the PMOS logic circuit  42  as described above is small, the time for transition of the node B from logic “0” level to logic “1” level is long. However, the operation frequency is originally low in the electric power low consumption operating, so that it does not matter.  
         [0073]    Further, since the clock signal CLOCK  2  is fixed to “1” level, then the electric power consumption for charging and discharging by the PMOS transistor PMOS 1  and the NMOS transistor NMOS 1 , in which the clock signal CLOCK  2  is inputted to the gate thereof, does not occur. Furthermore, the electric power consumption of the wiring conductor of the clock signal CLOCK  2  and the clock control circuit  40  in the charging and discharging is not generated. Thus, in a case where a process does not need high-speed operation so much, the low power-consumption mode is effective.  
         [0074]    As described above, in the logic LSI according to the second embodiment, slight parts of hardware such as the clock control circuit  40 , by which the logic level of the clock signal can be fixed in electric power low-consumption operation, is added. Then, it becomes possible to suppress variations of the operation frequency due to variation of manufacturing process, and reduce electric power consumption more than a logic circuit using the conventional clock control method.  
       Third Embodiment  
       [0075]    [0075]FIG. 7 shows a part of the logic LSI according to a third embodiment of the invention.  
         [0076]    In the circuit shown in FIG. 7, the first logic circuit  41  in the circuit shown in FIG. 4 according to the aforementioned second embodiment is changed to a second logic circuit  71 . In comparison with the first logic circuit  41 , the second logic circuit  71  is different in that a PMOS transistor PMOS 2  is inserted between the PMOS logic circuit  42  and the node B. A signal provided by inverting the low power-consumption mode signal by an inverter circuit  45  is inputted to the gate of the PMOS transistor PMOS 2 . The other parts or portions are the same as in the first logic circuit  41  and thus the same numerals or characters are used.  
         [0077]    According to the second logic circuit  71 , in the evaluation period of the normal high-speed operation, the PMOS transistor PMOS  2  is turned off, and a capacitive load on the PMOS logic circuit  42  side is electrically separated from the node B. Therefore, the capacitive load of the node B decreases and thus the operation can be carried out at more high-speed than in the second embodiment described above.  
         [0078]    In the electric power low-consumption operation, the PMOS transistor PMOS 2  is turned on, so that similar or the same operation and advantages as in the second embodiment can be obtained.  
         [0079]    Incidentally, in the first logic circuit  41  according to the aforementioned second embodiment and the second logic circuit  71  according to the third embodiment, when the operation relation between the PMOS logic circuit  42  and the NMOS logic circuit  43  is reversed (for example, if a NOR circuit is constructed), it functions equivalently to the embodiments described above.  
       Modification of Second Embodiment  
       [0080]    [0080]FIG. 8 is a circuit diagram showing a part of a logic LSI according to a modification example of the second embodiment as shown in FIG. 4 of the present invention;  
         [0081]    As shown in the logic circuit  41 a in FIG. 8, a PMOS transistor PMOS 3 , to whose gate the clock signal CLOCK 2  is inputted, is inserted between the VCC node and the PMOS logic circuit  42 , instead of the NMOS transistor NMOS 1  in the first logic circuit  41 . Furthermore, an NMOS transistor NMOS 2  for discharge operation, to whose gate the clock signal CLOCK 2  is inputted, is inserted between the intermediate node B and the VSS node, instead of the PMOS transistor PMOS 1  for the pre-charge operation. Also in this modification, the similar operation as in the second embodiment can be obtained.  
       Modification of Third embodiment  
       [0082]    [0082]FIG. 9 is a circuit diagram showing a part of a logic LSI according to a modification example of the third embodiment as shown in FIG. 7 of the present invention;  
         [0083]    As shown in the logic circuit  71   a  in FIG. 9, an NMOS transistor NMOS 3 , to whose gate the clock signal CLOCK 2  is inputted, is inserted between the intermediate node B and the NMOS logic circuit  43 , instead of the PMOS transistor PMOS 2  inserted between the PMOS logic circuit  42  and the intermediate node B.

Technology Classification (CPC): 6