Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of Japan Patent Application No. 2012-67561, filed on Mar. 23, 2012, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The disclosure relates generally to a semiconductor device using a level shift circuit, and a level shift circuit having a latch used in a semiconductor device, such as a NAND type flash memory. 
     2. Description of the Related Art 
     In semiconductor devices such as a NAND flash memory, for the requirement of versatility, one semiconductor device (chip device) is designed for operation with some external power supply voltages, such as 3.3V and 1.8V. 
       FIG. 22  is a block diagram illustrating a power supply voltage usage state of each circuit when the external power supply voltage VCC=3.3V is applied to the flash memory of the prior art. In addition,  FIG. 23  is a block diagram illustrating a power supply voltage usage state of each circuit when the external power supply voltage VCC=1.8V is applied to the flash memory of the prior art. In  FIGS. 22 and 23 , the NAND type flash memory consists of a cell array  1 , a page buffer  2 , a row decoder  3 , a power supply circuit  4  (a high voltage HV, a middle voltage MV), a power supply circuit  5  (a reference voltage Vref and a low voltage LV), a control logic  6 , a buffer and latch, etc.  7 , an input/output buffer  8 , and an input signal buffer  9 . 
       FIGS. 22 and 23  are the same NAND type flash memory, but different external power supply voltages VCC are applied thereto, and the power supply voltage usage state of each circuit are different. In the embodiment of  FIG. 22 , the internal power supply voltage VDD in the input/output buffer  8  and the input signal buffer  9  is 3.3V, the internal power supply voltage VDD in a part of page buffer  2 , a part of the row decoder  3 , the control logic  6  and the buffer and latch, etc.  7  is 1.9V, the internal power supply voltage VDD in another part of page buffer  2 , another part of the row decoder  3  and the power supply circuit  4  is 5V. In the embodiment of  FIG. 23 , the internal power supply voltage VDD in a part of page buffer  2 , a part of the row decoder  3 , the control logic  6  and the buffer and latch, etc.  7  is 1.8V, and the internal power supply voltage VDD in another part of page buffer  2 , another part of the row decoder  3 , the power supply circuit  4  the input/output buffer  8  and the input signal buffer  9  is 5V. Thus, for example, there was a need to provide a level shift circuit for level shifting the external voltage to the internal voltage, and level shifting the internal voltage to the external voltage in the internal flash memory. 
       FIG. 24  is a circuit diagram illustrating an embodiment of a level shift circuit according to the prior art. As shown in  FIG. 24 , the level shift circuit of the prior art embodiment comprises (1) a latch  10  configured by two inverters  11  and  12  cascaded to each other in a ring shape, (2) an inverter  13  inverting the output data of the latch  10  and outputting the output data signal DOUT (VCC), (3) NMOS transistors  31  and  32  being turned on in response to a latch signal with a high level for indicating a latching operation, (4) an NMOS transistor  21  being turned on in response to the input data signal DIN (VDD) with a high level, (5) an inverter  14  inverting the input data signal DIN (VDD), and (6) an NMOS transistor  22  being turned on in response to the output data signal of the inverter  14  with a high level. 
     In this embodiment, the sign in the parentheses of the input data signal DIN (VDD) indicates that the high level is the power supply voltage VDD with a high level, and the sign in the parentheses of the output data signal DOUT (VCC) indicates that the high level is the power supply voltage VCC with a high level. Therefore, the level shift circuit is provided with a latch  10  to temporarily hold the input data signal DIN (VDD), level shifts from the voltage VDD to the voltage VCC, and outputs the voltage VCC accordingly. In an embodiment of the NAND type flash memory, in order to output the data signal to an external device, it is necessary to level shift the internal VDD level data signal of the page buffer  2  to the external VCC level data signal. 
     BRIEF SUMMARY OF THE INVENTION 
     The Problem to be Solved 
     For the configuration of the level shift circuit described above, there is a problem where switching speed is relatively slow. 
       FIG. 25  is a table illustrating experimental results of the delay time in the level shift circuit of  FIG. 24 . For the case that the voltage VCC is same as the voltage VDD, the delay time between the input data signal DIN rises and when the output data signal DOUT falls, it is very slow. Thus, there is a problem that the time margin of the output cycle of the data signal is small. 
     In addition, in comparison with the conventional embodiment shown in  FIG. 24  which shows the input data signal DIN being applied to the gate electrode of the NMOS transistor  21 , if the input data signal DIN is connected to another inverter and its output is connected to the gate electrode of the NMOS transistor  21 , such that the input data signal DIN inputs the gate electrode of the NMOS transistor  22 , not the output data signal of the inverter  14  inputting the gate electrode of the NMOS transistor  22 , there is still the same problem that the delay time between the input data signal DIN falls and when the output data signal DOUT falls, it is very slow. 
     The purpose of the invention is to solve the above conventional problems for the level shift circuit, such as a level shift circuit of a flash memory, and to provide a level shift circuit and a semiconductor device using the level circuit which can reduce the delay time between the input data signal rises or falls and when the output data signal DOUT falls in comparison to that of prior art. 
     Solutions of the Problem 
     An embodiment of a level shift circuit according to the invention, for outputting a data output signal with a second level via an output inverter after a data input signal with a first level is stored in a latch and the level shift circuit comprises a level set circuit, wherein when the output data signal with a low level outputs, setting the output data signal to a low level in response to a change of the input data signal. 
     In an embodiment, the level set circuit is connected to an output terminal of the output inverter, and has an NMOS transistor having a drain electrode and a source electrode coupled to a ground, wherein the NMOS transistor turns on in response to the input data signal with a high level. 
     In an embodiment, the level set circuit further comprises a first inverter inverting the input data signal with a high level to an inverted signal, and outputting the inverted signal to the output terminal of the output inverter. 
     In an embodiment, the level set circuit further comprises: a second inverter, inverting the input data signal with a low level to an inverted signal; and an NMOS transistor, having a drain electrode and a source electrode coupled to a ground, wherein the NMOS transistor turns on in response to the inverted signal. 
     In an embodiment, the level set circuit outputs the input data signal with a low level to the output terminal of the output inverter. 
     In an embodiment, the latch has two inverters connected in cascade to each other. 
     In an embodiment, the latch has four MOS transistors, and the latch is a CMOS flip-flop type latch. 
     In an embodiment, the latch comprises two PMOS transistors respectively inserted between the two inverters and a power voltage, wherein the latch totally has six MOS transistors, and the latch is a CMOS flip-flop type latch. 
     In an embodiment, the latch comprises two PMOS transistors respectively inserted between the two inverters and a power voltage, and two NMOS transistors respectively inserted between the two inverters and a ground, wherein the latch totally has eight MOS transistors, and the latch is a CMOS flip-flop type latch. 
     In an embodiment, the latch and the output inverter comprise transistors driven by a high power voltage higher than the first level, and the second level is higher than the first level. 
     In an embodiment, the level shift circuit is a semiconductor device incapable of being driven by two power voltages with the first level and the second level. 
     An embodiment of a semiconductor device comprises the level shift circuit described above. 
     Effects of the Invention 
     Therefore, according to the present invention, for changing from a predetermined voltage to a same voltage, the delay time between the input data signal changes and when the output data signal DOUT falls can be much reduced in comparison to that of prior art. Thus, the time margin of the output cycle of the data signal can increase. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a circuit diagram illustrating a first embodiment of a level shift circuit according to the invention; 
         FIG. 1B  shows an embodiment of using simple symbol of inverters for the construction of the level shift circuit shown in  FIG. 1A ; 
         FIG. 2  is a circuit diagram illustrating a second embodiment of a level shift circuit according to the invention using the simple symbol of inverters. 
         FIG. 3  is a circuit diagram illustrating a third embodiment of a level shift circuit according to the invention using the simple symbol of inverters; 
         FIG. 4  is a circuit diagram illustrating a fourth embodiment of a level shift circuit according to the invention using the simple symbol of inverters; 
         FIG. 5  is a circuit diagram illustrating a fifth embodiment of a level shift circuit according to the invention using the simple symbol of inverters; 
         FIG. 6  is a circuit diagram illustrating a sixth embodiment of a level shift circuit according to the invention using the simple symbol of inverters; 
         FIG. 7  is a circuit diagram illustrating a seventh embodiment of a level shift circuit according to the invention using the simple symbol of inverters; 
         FIG. 8  is a circuit diagram illustrating an eighth embodiment of a level shift circuit according to the invention using the simple symbol of inverters; 
         FIG. 9  is a circuit diagram illustrating a ninth embodiment of a level shift circuit according to the invention using the simple symbol of inverters; 
         FIG. 10  is a circuit diagram illustrating a tenth embodiment of a level shift circuit according to the invention using the simple symbol of inverters; 
         FIG. 11  is a circuit diagram illustrating an eleventh embodiment of a level shift circuit according to the invention using the simple symbol of inverters; 
         FIG. 12  is a circuit diagram illustrating a twelfth embodiment of a level shift circuit according to the invention using the simple symbol of inverters; 
         FIG. 13  is a circuit diagram illustrating a thirteenth embodiment of a level shift circuit according to the invention using the simple symbol of inverters; 
         FIG. 14  is a circuit diagram illustrating a fourteenth embodiment of a level shift circuit according to the invention using the simple symbol of inverters; 
         FIG. 15  is a circuit diagram illustrating a fifteenth embodiment of a level shift circuit according to the invention using the simple symbol of inverters; 
         FIG. 16  is a circuit diagram illustrating the sixteenth embodiment of a level shift circuit according to the invention; 
         FIGS. 17   a  and  17   b  are diagrams showing symbols of the inverter and the MOS transistor using in the level shift circuit in  FIG. 16 ,  FIG. 18  and  FIG. 19 ; 
         FIG. 18  is a circuit diagram illustrating a seventeenth embodiment of a level shift circuit according to the invention; 
         FIG. 19  is a circuit diagram illustrating an eighteenth embodiment of a level shift circuit according to the invention; 
         FIG. 20  is a table illustrating the experimental results of the delay time of the level shift circuit of  FIG. 1A  in the worst state (100° C. temperature); 
         FIG. 21  is a table illustrating the experimental results of the delay time of the level shift circuit of  FIG. 1A  in the standard state (20° C. temperature); 
         FIG. 22  is a block diagram illustrating a power supply voltage usage state of each circuit when the external power supply voltage VCC=3.3V is applied to the flash memory of the prior art; 
         FIG. 23  is a block diagram illustrating a power supply voltage usage state of each circuit when the external power supply voltage VCC=1.8V is applied to the flash memory of the prior art; 
         FIG. 24  is a circuit diagram illustrating an embodiment of a level shift circuit according to the prior art; and 
         FIG. 25  is a table illustrating experimental results of the delay time in the level shift circuit of  FIG. 24 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Structures for Embodiments of the Invention 
     The embodiment of the invention will become more fully understood by referring to the following detailed description with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1A  is a circuit diagram illustrating a first embodiment of a level shift circuit according to the invention. The level shift circuit of  FIG. 1A  is used for a semiconductor chip device such as a flash memory, level-shifts an input data signal DIN (VDD) to an output data signal DOUT (VCC), and further comprises a level set circuit for forcing the output data signal DOUT set to a low level when the output data signal DOUT falls, and the level set circuit is configured with an NMOS transistor  23  with its drain electrode connected to ground, such that the delay time between when the input data signal DIN rises and when the output data signal DOUT falls can be much reduced in comparison to that of prior art. 
     The level shift circuit of  FIG. 1A  comprises (1) a latch  10  configured by two inverters  11  and  12  cascaded to each other in a ring shape, (2) an inverter  13  inverting the output data of the latch  10  and outputting the output data signal DOUT (VCC), (3) NMOS transistors  31 ,  32  and  33  being turned on in response to a latch signal with a high level for indicating a latching operation, (4) NMOS transistors  21  and  23  being turned on in response to the input data signal DIN (VDD) with a high level, (5) an inverter  14  inverting the input data signal DIN (VDD), and (6) an NMOS transistor  22  being turned on in response to the output data signal of the inverter  14  with a high level. 
     Also, the inverters  11 - 13  are driven by a power voltage VCC, and the inverter  14  is driven by a power voltage VDD. 
     For the level shift circuit of  FIG. 1A  configured as described above, when the latch signal LAT with a high level is inputted when a latching operation is being performed, the NMOS transistors  31 ,  32  and  33  are turned on. At this time, when the input data signal DIN (VDD) rises, and the output data signal DOUT (VCC) for outputting the data of the latch  10  falls, the NMOS transistor  23  forces the output data signal DOUT to be set to low level. Due to the NMOS transistor  23  is further added, the delay time between when the input data signal DIN rises and when the output data signal DOUT falls can be much reduced in comparison to that of prior art. Thus, the time margin of the output cycle of the data signal can be increased. The level shift circuit can be used in semiconductor devices such as a flash memory, for example. Experimental results of the present invention will be described in detail later. 
       FIG. 1B  shows an embodiment of using simple symbol of inverters for the construction of the level shift circuit shown in  FIG. 1A . In this embodiment, each of the inverters  11 - 14 , as shown in  FIG. 1A , is configured with the four MOS transistors, and form a well-known CMOS flip-flop type latch  10 . Also, to mark the simple symbol of inverters, P indicates that the inverter is driven by a voltage VCC, and L indicates that the inverter is driven by a voltage VDD. 
     Second Embodiment 
       FIG. 2  is a circuit diagram illustrating a second embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 2  with the level shift circuit of  FIG. 1B , this embodiment is characterized in that (1) the NMOS transistor  23  has been removed, and (2) the output voltage of the inverter  14  is applied to the predetermined electrode (the lower electrode as shown in  FIG. 2 , a source electrode or a drain electrode, and different from the electrode connected to the output of the inverter  13  and the gate electrode of NMOS transistor  33 ) of the NMOS transistor  33 . 
     The level shift circuit of  FIG. 2  described above operates as the same as the level shift circuits of  FIGS. 1A and 1B  do, particularly, the NMOS transistors  31 ,  32  and  33  are turned on when the latch signal LAT with a high level is inputted when a latching operation is being performed. At this time, when the input data signal DIN (VDD) rises, and the output data signal DOUT (VCC) for outputting the data of the latch  10  falls, the output data signal DOUT is forced to be set to a low level by the output voltage of the inverter  14 , such that a delay time between when the input data signal DIN rises and when the output data signal DOUT falls can be much reduced in comparison to that of prior art. Thus, a time margin of the output cycle of the data signal can increase. 
     Third Embodiment 
       FIG. 3  is a circuit diagram illustrating a third embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 3  with the level shift circuit of  FIG. 1B , this embodiment is characterized in that (1) the NMOS transistor  21  has been removed, and (2) the output voltage from the inverter  14  is applied to the predetermined electrode (the lower electrode as shown in  FIG. 3 , a source electrode or a drain electrode, and different from the electrode connected to the output terminal of the inverter  12  and the gate electrode of NMOS transistor  31 ) of the NMOS transistor  31 . 
     The level shift circuit of  FIG. 3  described above operates as the same as the level shift circuit of  FIG. 1B  does, with the same effects. 
     Fourth Embodiment 
       FIG. 4  is a circuit diagram illustrating a fourth embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 4  with the level shift circuit of  FIG. 2 , this embodiment is characterized in that (1) the NMOS transistor  21  has been removed, and (2) the output voltage from the inverter  14  is applied to the predetermined electrode (the lower electrode as shown in  FIG. 4 , a source electrode or a drain electrode, and different from the electrode connected to the output terminal of the inverter  12  and the gate electrode of NMOS transistor  31 ) of the NMOS transistor  31 . 
     The level shift circuit of  FIG. 4  described above operates as the same as the level shift circuit of  FIG. 2  does, with the same effects. 
     Fifth Embodiment 
       FIG. 5  is a circuit diagram illustrating a fifth embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 5  with the level shift circuit of  FIG. 1B , this embodiment is characterized in that (1) the NMOS transistor  22  and the inverter  14  have been removed, and (2) the input data signal DIN is applied to the predetermined electrode (the lower electrode as shown in  FIG. 5 , a source electrode or a drain electrode, and different from the electrode connected to the output terminal of the inverter  11  and the gate electrode of NMOS transistor  32 ) of the NMOS transistor  32 . 
     The level shift circuit of  FIG. 5  described above operates as the same as the level shift circuit of  FIG. 1B  does, with the same effects. 
     Sixth Embodiment 
       FIG. 6  is a circuit diagram illustrating a sixth embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 6  with the level shift circuit of  FIG. 2 , this embodiment is characterized in that (1) the NMOS transistor  22  has been removed, and (2) the input data signal DIN is applied to the predetermined electrode (the lower electrode as shown in  FIG. 6 , a source electrode or a drain electrode, and different form the electrode connected to the output terminal of the inverter  11  and the gate electrode of NMOS transistor  32 ) of the NMOS transistor  32 . 
     The level shift circuit of  FIG. 6  described above operates as the same as the level shift circuit of  FIG. 2  does, with the same effects. 
     Seventh Embodiment 
       FIG. 7  is a circuit diagram illustrating a seventh embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 7  with the level shift circuit of  FIG. 3 , this embodiment is characterized in that (1) the NMOS transistor  22  has been removed, and (2) the input data signal DIN is applied to the predetermined electrode (the lower electrode as shown in  FIG. 7 , a source electrode or a drain electrode, and different from the electrode connected to the output terminal of the inverter  11  and the gate electrode of NMOS transistor  32 ) of the NMOS transistor  32 . 
     The level shift circuit of  FIG. 7  described above operates as the same as the level shift circuit of  FIG. 3  does, with the same effects. 
     Eighth Embodiment 
       FIG. 8  is a circuit diagram illustrating an eighth embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 8  with the level shift circuit of  FIG. 4 , this embodiment is characterized in that (1) the NMOS transistor  22  has been removed, and (2) the input data signal DIN is applied to the predetermined electrode (the lower electrode as shown in  FIG. 8 , a source electrode or a drain electrode, and different from the electrode connected to the output terminal of the inverter  11  and the gate electrode of NMOS transistor  32 ) of the NMOS transistor  32 . 
     The level shift circuit of  FIG. 8  described above operates as the same as the level shift circuit of  FIG. 4  does, with the same effects. 
     Ninth Embodiment 
       FIG. 9  is a circuit diagram illustrating a ninth embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 9  with the level shift circuit of  FIG. 1B , this embodiment is characterized in that (1) the input data signal DIN is applied to the gate electrode of the NMOS transistor  22 , and (2) the input data signal DIN is inputted to the inverter  14 , and the output voltage from the inverter  14  is applied to each of the gate electrodes of the NMOS transistors  21  and  23 . 
     For the level shift circuit of  FIG. 9  described above, the NMOS transistors  31 ,  32  and  33  are turned on when the latch signal LAT with a high level is inputted when a latching operation is being performed. At this time, when the input data signal DIN (VDD) falls, and the output data signal DOUT (VCC) for outputting the data of the latch  10  falls, the NMOS transistor  23  forces the output data signal DOUT to be set to a low level, such that the delay time between when the input data signal DIN falls and when the output data signal DOUT falls can be much reduced in comparison to that of prior art. Thus, the time margin of the output cycle of the data signal can increase. 
     Tenth Embodiment 
       FIG. 10  is a circuit diagram illustrating a tenth embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 10  with the level shift circuit of  FIG. 9 , this embodiment is characterized in that (1) the NMOS transistor  23  has been removed, and (2) the input data signal DIN is applied to the predetermined electrode (the lower electrode as shown in  FIG. 10 , is a source electrode or a drain electrode, different from the electrode connected to the output terminal of the inverter  13  and the gate electrode of NMOS transistor  33 ) of the NMOS transistor  33 . 
     The level shift circuit of  FIG. 10  described above operates as the same as the level shift circuit of  FIG. 9  does, particularly, the NMOS transistors  31 ,  32  and  33  are turned on when the latch signal LAT with high level is inputted when a latching operation is being performed. At this time, when the input data signal DIN (VDD) falls, and the output data signal DOUT (VCC) for outputting the data of the latch  10  falls, the output data signal DOUT is forced to be set to a low level by the input data signal DIN, such that the delay time between when the input data signal DIN falls and when the output data signal DOUT falls can be much reduced in comparison to that of prior art. Thus, the time margin of the output cycle of the data signal can increase. 
     Eleventh Embodiment 
       FIG. 11  is a circuit diagram illustrating an eleventh embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 11  with the level shift circuit of  FIG. 9 , this embodiment is characterized in that (1) the NMOS transistor  21  has been removed, and (2) the input data signal DIN is applied to the predetermined electrode (the lower electrode as shown in  FIG. 11 , is a source electrode or a drain electrode, different from the electrode connected to the output terminal of the inverter  12  and the gate electrode of NMOS transistor  31 ) of the NMOS transistor  31 . 
     The level shift circuit of  FIG. 11  described above operates as the same as the level shift circuit of  FIG. 9  does, with the same effects. 
     Twelfth Embodiment 
       FIG. 12  is a circuit diagram illustrating a twelfth embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 12  with the level shift circuit of  FIG. 10 , this embodiment is characterized in that (1) the NMOS transistor  21  and the inverter  14  has been removed, and (2) the input data signal DIN is applied to the predetermined electrode (the lower electrode as shown in  FIG. 12 , is a source electrode or a drain electrode, different from the electrode connected to the output terminal of the inverter  12  and the gate electrode of NMOS transistor  31 ) of the NMOS transistor  31 . 
     The level shift circuit of  FIG. 12  described above operates as the same as the level shift circuit of  FIG. 10  does, with the same effects. 
     Thirteenth Embodiment 
       FIG. 13  is a circuit diagram illustrating a thirteenth embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 13  with the level shift circuit of  FIG. 10 , this embodiment is characterized in that (1) the NMOS transistor  22  has been removed, and (2) the input data signal DIN is inputted to the inverter  14 , and the output voltage from the inverter  14  is applied to the predetermined electrode (the lower electrode as shown in  FIG. 13 , is a source electrode or a drain electrode, different from the electrode connected to the output terminal of the inverter  11  and the gate electrode of NMOS transistor  32 ) of the NMOS transistor  32 . 
     The level shift circuit of  FIG. 13  described above operates as the same as the level shift circuit of  FIG. 10  does, with the same effects. 
     Fourteenth Embodiment 
       FIG. 14  is a circuit diagram illustrating a fourteenth embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 14  with the level shift circuit of  FIG. 11 , this embodiment is characterized in that (1) the NMOS transistor  22  has been removed, and (2) the input data signal DIN is inputted to the inverter  14 , and the output voltage from the inverter  14  is applied to the predetermined electrode (the lower electrode as shown in  FIG. 14 , is a source electrode or a drain electrode, different from the electrode connected to the output terminal of the inverter  11  and the gate electrode of NMOS transistor  32 ) of the NMOS transistor  32 . 
     The level shift circuit of  FIG. 14  described above operates as the same as the level shift circuit of  FIG. 11  does, with the same effects. 
     Fifteenth Embodiment 
       FIG. 15  is a circuit diagram illustrating a fifteenth embodiment of a level shift circuit according to the invention using the simple symbol of inverters. To compare the level shift circuit of  FIG. 15  with the level shift circuit of  FIG. 12 , this embodiment is characterized in that (1) the NMOS transistor  22  has been removed, (2) the inverter  14  has been added, and (3) the input data signal DIN is inputted to the inverter  14 , and the output voltage from the inverter  14  is applied to the predetermined electrode (the lower electrode as shown in  FIG. 14 , is a source electrode or a drain electrode, different from the electrode connected to the output terminal of the inverter  11  and the gate electrode of NMOS transistor  32 ) of the NMOS transistor  32 . 
     The level shift circuit of  FIG. 15  described above operates as the same as the level shift circuit of  FIG. 12  does, with the same effects. 
     Sixteenth Embodiment 
       FIG. 16  is a circuit diagram illustrating the sixteenth embodiment of a level shift circuit according to the invention. The level shift circuit of  FIG. 16  has a circuit for level-shifting an input data signal DIN (VDD) to an output data signal DOUT (VPP, in this embodiment, VPP is a middle voltage or high voltage higher than VDD and VCC, such as 5V). To compare the level shift circuit of  FIG. 16  with the level shift circuit of  FIG. 1A , this embodiment is characterized in that the level shift circuit comprises (1) a bias voltage circuit consisting of NMOS transistors  41 ,  42  and  43  being turned on in response to a bias signal BIAS with a high level (high level while the latch operation), (2) a middle voltage transistor group (MV Tr) consisting of a latch  210  and an output inverter  214 , and (3) a low voltage transistor group (LV Tr) consisting of NMOS transistors  31 ,  32  and  33  being turned on in response to a latch signal LAT, NMOS transistors  2 L  22 ,  23 , and an inverter  14 . 
       FIGS. 17   a  and  17   b  are diagrams showing a symbol of the inverter and the MOS transistor using in the level shift circuit in  FIG. 16 ,  FIG. 18  and  FIG. 19 .  FIG. 17   a  shows the inverter  201 , the NMOS transistor  202 , and the PMOS transistor  203  being configured to the middle voltage transistor group (MV Tr), Also,  FIG. 17   b  shows the inverter  101 , the NMOS transistor  102 , and the PMOS transistors  103  being are configured to the low voltage transistor group (LV Tr). 
     In the level shift circuit of  FIG. 16 , the latch  210  consists of inverters  11   a  and  12   a . The inverter  11   a  comprises PMOS transistors  211 ,  213  and an NMOS transistor  212 . The inverter  12   a  comprises PMOS transistors  221 ,  223  and an NMOS transistor  222 . In this embodiment, the inverters  11   a  and  12   a  comprise the PMOS transistors  213  and  223  respectively for preventing the break down of the MOS transistor, and form a PMOS transistor insertion flip-flop type latch. 
     The level shift circuit described above operates as the same as the level shift circuits of  FIGS. 1A and 1B  do, particularly, in the latching operation, wherein the NMOS transistors  41 ,  42  and  43  are turned on when the bias signal BIAS with a high level is inputted, and the NMOS transistor  33  is turned on when the latch signal LAT with high level is inputted. At this time, when the input data signal DIN (VDD) rises, and the output data signal DOUT (VPP) from the output inverter  214  for outputting the data of the latch  210  falls, the NMOS transistor  23  turns on in order to force the output level of the output inverter  214  to be set to a low level, such that the delay time between when the input data signal DIN rises and when the output data signal DOUT falls can be much reduced in comparison to that of prior art. Thus, the time margin of the output cycle of the data signal can increase. 
     Although the PMOS transistors  213  and  223  are inserted and connected to the power voltage VPP in the embodiment described above, the invention is not limited thereto. In order to get a higher withstand voltage, NMOS transistors can be inserted and connected to the ground. In this embodiment, the latch  210  may consist of eight MOS transistors. 
     Seventeenth Embodiment 
       FIG. 18  is a circuit diagram illustrating a seventeenth embodiment of a level shift circuit according to the invention. To compare the level shift circuit of  FIG. 18  with the level shift circuit of  FIG. 16 , this embodiment is characterized in that (1) the bias circuit has been removed, and (2) the latch  210  and the inverter  214  are formed by a latch  110  and an inverter  13 , and the latch  110  and the inverter  13  operates by low voltage level transistors. 
     In the level shift circuit of  FIG. 18 , the latch  110  consists of inverters  11   b  and  12   b . The inverter  11   b  comprises PMOS transistors  111 ,  113  and an NMOS transistor  112 . The inverter  12   b  comprises PMOS transistors  121 ,  123  and an NMOS transistor  122 . In this embodiment, the inverters  11   b  and  12   b  have the insertion of the PMOS transistors  113  and  123  respectively for preventing the break down of the MOS transistor, and form a PMOS transistor insertion flip-flop type latch. 
     The level shift circuit described above operates as the same as the level shift circuits of  FIGS. 1A and 1B  do, particularly, in the latching operation, wherein the NMOS transistor  33  is turned on when the latch signal LAT with high level is inputted. At this time, when the input data signal DIN (VDD) rises, and the output data signal DOUT (VPP) from the output inverter  13  for outputting the data of the latch  110  falls, the NMOS transistor  23  turns on in order to force the output level of the output inverter  13  to be set to a low level, such that the delay time between when the input data signal DIN rises and when the output data signal DOUT falls can be much reduced in comparison to that of prior art. Thus, the time margin of the output cycle of the data signal can increase. 
     Although the PMOS transistors  113  and  123  are inserted and connected to the power voltage VCC in the embodiment described above, the invention is not limited thereto. In order to get a higher withstand voltage, NMOS transistors can be inserted and connected to the ground. In this embodiment, the latch  110  may consist of eight MOS transistors. 
     Eighteenth Embodiment 
       FIG. 19  is a circuit diagram illustrating an eighteenth embodiment of a level shift circuit according to the invention. To compare the level shift circuit of  FIG. 19  with the level shift circuit of  FIG. 16 , this embodiment is characterized in that (1) an inverter  11   c  replaces the inverter  11   a , wherein the transistors  213  has been removed, (2) an inverter  12   c  replaces the inverter  12   a , wherein the PMOS transistors  223  has been removed, and (3) a latch  210   c  consists of the inverter  11   c  and  12   c.    
     The level shift circuit described above operates as the same as the level shift circuit of  FIG. 16  does, with the same effects. 
     Modified Embodiment 
     In the embodiments described above, although the level shift circuit has been described, these level shift circuits are further illustrated with reference to  FIGS. 22 and 23 , and are further configured in semiconductor devices such as a flash memory. In this embodiment, the semiconductor device is a semiconductor device which can be used for two supply voltages with a first level and a second level in the same device. 
     In the sixteenth to the eighteenth embodiments described above, various level shift circuits are illustrated according to the basic level shift circuit of the first embodiment, but the present invention is not limited thereto. The basic level shift circuit of the second to the fifteenth embodiments may be configured similar to the feature configurations (the latch and its peripheral circuit) of the embodiments of the sixteenth to eighteenth embodiments. 
     In the sixteenth to the eighteenth embodiments, the level-shift of the input data signal DIN (VDD) to the output data signal DOUT (VPP) has been described, but the present invention is not limited thereto. The circuit may be configured similarly to the level shift of the input data signal DIN (VDD) to the output data signal DOUT (high voltage, HV). 
     Embodiments 
     The inventors of the present invention performed simulations SPICE (Simulation Program with Integrated Circuit Emphasis) to the level shift circuit of  FIG. 1A  of the first embodiment, and measured delay times of data signals (the period time from the falling edge the rising edge of the data signal, or the period time from the rising edge to the falling edge of the data signal). 
       FIG. 20  is a table illustrating the experimental results of the delay time of the level shift circuit of  FIG. 1A  in the worst state (100° C. temperature),  FIG. 21  is a table illustrating the experimental results of the delay time of the level shift circuit of  FIG. 1A  in the standard state (20° C. temperature). For the condition where the VDD is the same as the VCC, the delay time between when the input data signal DIN rises and when the output data signal DOUT falls, has been reduced from 5.4 ns as in the prior art to 0.9 ns in the standard state. However, in particular, in the worst state, the delay time may be further reduced from 12.1 ns as in the prior art to 2.4 ns. Thus, the time margin of the output cycle of the data signal can increase. 
     INDUSTRIAL APPLICATIONS 
     As described above, in the present invention, the delay time between when the input data signal changes from the predetermined voltage to the same voltage and the output data signal falls can be much reduced in comparison to that of prior art. Thus, the time margin of the output cycle of the data signal can increase. The level shift circuit can be used in semiconductor devices such as a flash memory for example.

Technology Category: 3