Abstract:
An off-leak current cancel circuit includes an input protection circuit having a first protection transistor connected between a terminal and a high power potential, and a second protection transistor connected between the terminal and a low power potential. The first and second protection transistors flow first and second off-leak currents. A current cancel circuit has a first monitor transistor for flowing a third off-leak current that is smaller than the first off-leak current, and a cancellation circuit for flowing the first off-leak current to the low power potential responsive to the third off-leak current. A current providing circuit has a second monitor transistor for flowing a fourth off-leak current that is smaller than the second off-leak current, and a providing circuit for providing the second off-leak current from the high power potential responsive to the fourth off-leak current.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an off-leak current cancel circuit for canceling off-leak current of a MOS transistor in a CMOS semiconductor integrated circuit. 
     FIG. 2 shows a configuration example of an input portion of a conventional CMOS semiconductor integrated circuit. 
     In this input portion, in order to prevent destruction of an internal circuit by surge voltage such as static electricity applied to an input terminal  1 , between the input terminal  1 , a power source potential VDD and a ground potential GND, a P-channel MOS transistor (hereinafter, an MOS transistor will be referred to simply as MOS and the P-channel MOS will be referred to as PMOS)  2  and an N-channel MOS (hereinafter, referred to as NMOS)  3  are arranged so as to protect the inner circuit. 
     That is, the PMOS  2  has a gate a and a source connected to the power source potential VDD and a drain connected to the input terminal  1  so as to operate as a diode connected in the reverse direction. Moreover, the NMOS has a gate and a source connected to the ground potential GND and a drain connected to the input terminal  1  so as to similarly operate as a diode connected in the reverse direction. 
     In such an input portion, when a positive surge voltage is applied to the input terminal  1 , the PMOS  2  is turned on and electric current flows from the input terminal  1  via the PMOS  2  to the power source potential VDD. Moreover, when a negative surge voltage is applied to the input terminal  1 , the NMOS  3  is turned on and electric current flows from the ground potential GND via the NMOS  3  to the input terminal  1 . This controls the positive and negative potential increase of the input terminal  1  and protects the input terminal connected to the input terminal  1  from destruction by static electricity. 
     Since the PMOS  2  and the NMOS  3  are diode-connected in the reverse direction, they are off during a normal operation. However, in the MOS transistor, a current called off-leak current flows even in an off state. The off-leak current is a total of sub threshold current generated between the source and the drain and reverse-direction current in the silicon substrate and the drain pn junction diode, and the total value is very small. However, the off-leak current depends on the dimension of the gate of the MOS, varies depending on the ambient temperature, and especially the current value becomes large under a high temperature (for example, 100° C.). Moreover, in the PMOS  2  and the NMOS  3  in the input portion, a gate width W is made large as compared to a gate length L so as to increase the protection ability (for example, W/L=1000) and accordingly, the off-leak current becomes large. Furthermore, the off-leak current has become large because of lowering of a threshold value voltage due to the reduced voltage of the power source. 
     When an off-leak current flows to the PMOS  2  and NMOS  3  in the input portion, the off-leak current changes the potential of the input terminal  1  and affects the analog operation in the internal circuit. For example, in FIG. 2, the off-leak current IL flowing in the PMOS  2  divided to flow to the NMOS  3  and the signal source connected to the input terminal  1 . The current flowing into the signal source fluctuates the potential of the input terminal  1 , which disables normal analog operation in the internal circuit. 
     SUMMARY OF THE INVENTION 
     The present invention may provide an off-leak current cancel circuit for canceling an off-leak current in a MOS transistor. 
     An off-leak current cancel circuit of the present invention includes an input terminal, an input protection circuit, a current cancel circuit and a current providing circuit. The input protection circuit has a first protection transistor connected between the input terminal and a high power supply potential source, and a second protection transistor connected between the input terminal and a low power supply potential source. The first protection transistor flows a first off-leak current. The second protection transistor flows a second off-leak current. The current cancel circuit has a first monitor transistor for flowing a third off-leak current that is a first times smaller than the first off-leak current, and a cancellation circuit for flowing the first off-leak current to the low power supply potential source in response to the third off-leak current. The current providing circuit has a second monitor transistor for flowing a fourth off-leak current that is a second times smaller than the second off-leak current, and a providing circuit for providing the second off-leak current from the high power supply potential source in response to the fourth off-leak current. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows configuration of an off-leak current cancel circuit according to a first embodiment of the present invention. 
     FIG. 2 shows an example of an input portion in a conventional CMOS semiconductor integrated circuit. 
     FIG. 3 shows configuration of an off-leak current cancel circuit according to a second embodiment of the present invention. 
     FIG. 4 shows configuration of an off-leak current cancel circuit according to a third embodiment of the present invention. 
     FIG. 5 shows configuration of an off-leak current cancel circuit according to a fourth embodiment of the present invention. 
     FIG.  6 A and FIG. 6B show examples of level shift portions shown in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows configuration of an off-leak current cancel circuit according to a first embodiment of the present invention. 
     This off-leak current cancel circuit is a circuit for canceling an off-leak current of an input circuit protecting PMOS  2  and NMOS  3  connected between the input terminal  1 , a power source potential VDD, and a ground potential GND, and has cancel portions  10  and  20  formed on the semiconductor substrate of the PMOS  2  and NMOS  3 . 
     The cancel portion  10  cancels off-leak current of the PMOS  2  and includes a PMOS  11  and NMOS  12 ,  13 ,  14 . The PMOS  11  has a gate length identical to the PMOS  2  (for example, 0.2 micrometers) and a gate width about ⅕ (for example, 50 micrometers) of the gate width of the PMOS  2  (for example, 250 micrometers). The PMOS  11  has a source and a gate connected to the power source potential VDD and a drain connected to the node N 11 . That is, the PMOS  11  is diode-connected in the reverse direction like the PMOS  2  and configured so that ⅕ of the off-leak current flowing in the PMOS  2  flows. 
     The node N 11  is connected to the drain and the gate of the NMOS  12  whose source is connected to the ground potential GND. The NMOS  12  has a gate length and a gate width formed, for example, to be 1 micrometer. Furthermore, the node N 11  is connected to the gate of the NMOS  13  whose drain and source are connected to the input terminal  1  and to the ground potential GND, respectively. 
     The NMOS  13  has a gate length identical to the NMOS  12 , i.e., 1 micrometer and a gate width formed to be 5 micrometers which is the gate width of NMOS  12  multiplied by 5. That is, the NMOS  12  and  13  constitute a current mirror circuit and the current flowing in the NMOS  12  multiplied by 5 flows in the NMOS  13 . 
     Moreover, the node N 11  and the ground potential GND are connected to the drain and the source of the NMOS  14 , respectively, and the gate of the NMOS  14  is connected to the power source potential VDD. Accordingly, the NMOS  14  is always in on state. The NMOS  14  has a gate length of 100 micrometers and a gate width of 0.1 micrometers, so as to exhibit quite a high resistance. Thus, when almost no off-leak current is present in the PMOS  11 , the NMOS  14  makes the node N 11  the ground potential GND for stability of the operation. 
     On the other hand, the cancel portion  20  cancels off-leak current of the NMOS  3  and includes NMOS  21  and PMOS  22 ,  23 ,  24 . The NMOS  21  has a gate length identical to the NMOS  3  (for example, 0.2 micrometers) and a gate width about ⅕ (for example, 50 micrometers) of the gate width of the NMOS  3  (for example, 250 micrometers). The NMOS  21  has a source and a gate connected to the ground GND and a drain connected to the node N 21 . That is, the NMOS  21  is diode-connected in the reverse direction like the NMOS  3  and configured so that ⅕ of the off-leak current flowing in the NMOS  3  flows. 
     The node N 21  is connected to the drain and the gate of the PMOS  22  whose source is connected to the power source potential VDD. The PMOS  22  has a gate length and a gate width formed, for example, to be 1 micrometer. Furthermore, the node N 21  is connected to the gate of the PMOS  23  whose drain and source are connected to the input terminal  1  and to power source potential VDD, respectively. 
     The PMOS  23  has a gate length identical to the PMOS  22 , i.e., 1 micrometer and a gate width formed 5 micrometers which is the gate width of PMOS  22  multiplied by 5. That is, the PMOS  22  and  23  constitute a current mirror circuit and the current flowing in the PMOS  22  multiplied by 5 flows in the PMOS  23 . 
     Moreover, the node N 21  and the power source potential VDD are connected to the drain and the source of the PMOS  24 , respectively, and the gate of the PMOS  24  is connected to the ground potential GND. Accordingly, the PMOS  24  is always in on state. The PMOS  24  has a gate length of 100 micrometers and a gate width of 0.1 micrometers, so as to exhibit quite a high resistance. Thus, when almost no off-leak current is present in the NMOS  21 , the node N 21  is made to the power source potential VDD for stability of the operation. 
     Next, explanation will be given on operation. 
     For example, when the ambient temperature is a room temperature and there is almost no off-leak current, the NMOS  14  of the cancel portion  10  is in an ON state and accordingly, the node N 11  is almost ground potential GND and the NMOS  12  and  13  are in an OFF state. Similarly, the PMOS  24  of the cancel portion  20  is in an ON state and accordingly, the node N 21  becomes almost power source potential VDD and PMOS  22  and  23  become OFF. 
     Here, it is assumed that the ambient temperature has increased and off-leak current of 10 μA flows. The PMOS  2  and the PMOS  11  in the cancel portion  10  are formed on the same semiconductor substrate and have an identical gate length. Accordingly, off-leak current also flows in this PMOS  11  for monitoring. When the gate length is identical, the off-leak current flowing is proportional to the gate width and accordingly, the off-leak current flowing in the PMOS  11  becomes ⅕ of the PMOS  2 , i.e., 2 μA. The off-leak current flowing in the PMOS  11  flows into the node N 11 . 
     The node N 11  is connected to the NMOS  12  and  14  but since the NMOS  14  has quite a high resistance, almost no current flows. Accordingly, in the NMOS  12 , current almost identical to the PMOS  11 , i.e., 2 μA flows. The NMOS  12  is connected to the NMOS  13  constituting a current mirror circuit of the current ratio of 5 multiples. Thus, current of 10 μA flows via the NMOS  13  to the ground potential GND. 
     Thus, the off-leak current of 10 μA flowing in the PMOS  2  all flows into the ground potential GND via the NMOS  13  and no off-leak current flows into the signal source connected to the input terminal  1 . 
     Similarly, the off-leak current flowing in the NMOS  3  is detected by the NMOS  21  for monitoring of the cancel portion  20  and supplied from the power source potential VDD via the PMOS  23  to the NMOS  3 . Accordingly, no off-leak current flows to the signal source connected to the input terminal  1 . 
     As has been described above, the off-leak current cancel circuit of the first embodiment has a cancel portion including the PMOS  11  for monitoring the off-leak current intensity proportional to the off-leak current flowing from the power source potential VDD into the input circuit protecting PMOS  2  and the NMOS  13  for flowing off-leak current flowing in the PMOS  2  according to the current flowing in the PMOS  11 , to the ground potential GND. Moreover, the off-leak current cancel circuit has a cancel portion  20  for supplying the off-leak current flowing from the input circuit protecting NMOS  3  to the ground potential GND, from the power source potential VDD to the PMOS  23 . Thus, the off-leak current flowing in the PMOS  2  and the NMOS  3  is canceled and it is possible to prevent flowing of the off-leak current to the signal source connected to the input terminal  1 . 
     FIG. 3 shows configuration of an off-leak current cancel circuit according to a second embodiment of the present invention. Like components as in FIG. 1 are denoted by like reference symbols. 
     This off-leak current cancel circuit has an input circuit protecting PMOS  2   a  between the input terminal  1  and the power source potential VDD and a PMOS  2   b  connected in series to the PMOS  2   a . The input terminal  1  is connected to the drain of the PMOS  2   a  which has a source and a gate connected to the node N 1  and the power source potential VDD, respectively. The node N 1  is connected to the drain and the gate of the PMOS  2   b , and the source of the PMOS  2   b  is connected to the power source potential VDD. 
     Moreover, between the input terminal  1  and the ground potential GND, there are arranged an input circuit protecting NMOS  3   a  and an NMOS  3   b  connected in series to this. The input terminal  1  is connected to the drain of the NMOS  3   a  which has a source and a gate connected to the node N 2  and the ground potential GND, respectively. The node N 2  is connected to the drain of the NMOS  3   b  and the source of the NMOS  3   b  is connected to the ground potential GND. 
     Furthermore, this off-leak current cancel circuit has cancel portions  10 A and  10 B having configurations slightly different from those of cancel portions  10  and  20  in FIG.  1 . 
     The cancel portion  10 A, instead of the PMOS  11  for monitoring the off-leak current in the cancel portion  10 , includes a PMOS  15  constituting a current mirror circuit for the input circuit protecting PMOS  2   b . That is, the PMOS  15  has a source and a drain connected to the power source potential VDD and to the node N 11 , respectively and a gate connected to the node N 1 . 
     Similarly, instead of the NMOS  21  for monitoring the off-leak current in the cancel portion  20 , the cancel portion  20 A includes an NMOS  25  constituting a current mirror circuit for the input circuit protecting NMOS  3   b . The NMOS  25  has a source and a drain connected to the ground potential GND and to the node N 21 , respectively, and a gate connected to the node N 2 . The other configuration portion is identical to that of FIG.  1 . 
     Next, explanation will be given on operation. 
     When the ambient temperature is a room temperature and there is almost no off-leak current, the PMOS  2   a  and  2   b  are in an OFF state and ON state, respectively. The node N 1  is almost at the power source potential VDD, and no current flows in the PMOS  15  of the cancel portion  10 A. Similarly, the NMOS  3   a  and  3   b  are in an OFF state and ON state, respectively, the node N 2  has become the ground potential GND, and no current flows in the NMOS  25  of the cancel portion  20 A. 
     Here, when the ambient temperature increases and off-leak current flows in the PMOS  2   a , identical off-leak current also flows in the PMOS  2   b  connected in series to this. This generates a detection voltage corresponding to the off-leak current in the node N 1  and a current corresponding to this off-leak current flows in the PMOS  15  of the cancel portion  10 A, and identical current flows in the NMOS  12 . Furthermore, current identical to the off-leak current flows in the NMOS  13  constituting the current mirror circuit. Accordingly, the off-leak current flowing in the PMOS  2   a  flows via the NMOS  13  to the ground potential GND and no off-leak current flows to the signal source connected to the input terminal  1 . 
     Similarly, off-leak current flowing in the NMOS  3   a  is detected by the NMOS  25  of the cancel portion  20 A and a current corresponding to the off-leak current flows from the power source potential VDD via the PMOS  23  to this NMOS  3   a . Accordingly, no off-leak current flows to the signal line connected to the input terminal  1 . 
     As has been described above, the off-leak current cancel circuit according to the second embodiment includes the PMOS  2   b  for monitoring off-leak current flowing in the input circuit protecting PMOS  2   a  from the power source potential VDD and the cancel portion  10 A for detecting the current flowing in the PMOS  2   b  and flowing the off-leak current flowing in the PMOS  2   a  to the ground potential GND. Moreover, the off-leak current cancel circuit includes the NMOS  3   b  for monitoring the off-leak current flowing in the input circuit protecting NMOS  3   a  and the cancel portion  20 A for detecting the current flowing in the NMOS  3   b  supplying the off-leak current flowing in the NMOS  3   a  from the power source potential VDD. This cancels the off-leak current flowing in the PMOS  2   a  and NMOS  3   a , thereby preventing flow of the off-leak current to the signal source connected to the input terminal  1 . 
     FIG. 4 shows configuration of an off-leak current cancel circuit according to a third embodiment of the present invention. Like components as in FIG. 1 are denoted by like reference symbols in FIG.  3 . 
     This off-leak current cancel circuit has an input circuit protecting PMOS  2   a  and  2   c  between the input terminal  1  and the power source potential VDD. The input terminal  1  is connected to the drain of the PMOS  2   a  and the source of the PMOS  2   a  is connected to the node N 1 . The node N 1  is connected to the drain of the PMOS  2   c , and the source of the PMOS  2   c  is connected to the power source potential VDD. Moreover, gates of the PMOS  2   a  and  2   c  are connected to the power source potential VDD, so that power source potential VDD is applied to these bulk potentials. 
     Moreover, between the input terminal  1  and the ground potential GND, there are arranged an input circuit protecting NMOS  3   a  and  3   c  connected in series. The input terminal  1  is connected to the drain of the NMOS  3   a  and the source of the NMOS  3   a  is connected to the node N 2 . The node N 2  is connected to the drain of the NMOS  3   c  and the source of the NMOS  3   c  is connected to the ground potential GND. Moreover, the gates of the NMOS  3   a  and  3   c  are connected to the ground potential GND, so that the ground potential GND is applied to these bulk potentials. 
     Furthermore, this off-leak current cancel circuit has cancel portions  10 B and  20 B having configurations slightly different from the cancel portions  10  and  20  in FIG.  1 . 
     The cancel portion  10 B, instead of the NMOS  13  in the cancel portion  10 , includes a PMOS  16  and an NMOS  17 . The PMOS  16  has a source connected to the power source potential VDD and a gate and a drain connected to the node N 1 . Moreover, the NMOS  17  has a drain connected to the node N 1 , a gate connected to node N 11 , and a source connected to the ground potential GND. 
     Moreover, instead of the PMOS  23  in the cancel portion  20 , the cancel portion  20 B includes an NMOS  26  and a PMOS  27 . The NMOS  26  has a source connected to the ground potential GND and a gate and drain connected to the node N 2 . Moreover, the PMOS  27  has a drain connected to the node N 2 , a gate connected to the node N 21 , and a source connected to the power source potential VDD. The other configuration portion is identical to that of FIG.  1 . 
     Next, explanation will be given on the operation. 
     When the ambient temperature is a room temperature and there is almost no off-leak current, the NMOS  14  of the cancel portion  10 B is in an ON state and accordingly, the node N 11  is almost at the ground potential GND, and the NMOS  12  and  17  are in off state. Similarly, the PMOS  24  of the cancel portion  20 B is in an ON state and accordingly, the node N 21  is almost at the power source potential VDD, and the PMOS  22  and  27  are in an OFF state. 
     Here, when the ambient temperature increases and off-leak current flows in the PMOS  2   a  and  2   c , off-leak current flows in the PMOS  11  for monitoring the cancel portion  10 B. The off-leak current flowing in the PMOS  11  flows into the node N 11  and via the NMOS  12  to the ground potential GND. Since the NMOS  12  is connected to the NMOS  17  constituting the current mirror circuit, current proportional to the off-leak current also flows in this NMOS  17 . 
     Since the current flowing in the NMOS  17  is supplied from the power source potential VDD via the PMOS  16 , the potential of the node N 1  is lowered than the power source potential VDD. Accordingly, the voltage between the source and the drain of the PMOS  2   c  is reduced and the off-leak current flowing in this PMOS  2   c  is reduced. Furthermore, the potential of the node N 1  is applied to the source of the PMOS  2   a  and the bulk potential of this PMOS  2   a  has become the power source potential VDD. Thus, the threshold value voltage of the PMOS  2   a  is increased by the back gate effect and the off-leak current of the PMOS  2   a  is reduced. 
     Similarly, when an off-leak current flows in the NMOS  21  for monitoring the cancel portion  20 B, this off-leak current is supplied from the power source potential VDD via the PMOS  22  from the node N 21 . Since the PMOS  22  is connected to the PMOS  27  constituting the current mirror circuit, a current proportional to the off-leak current also flows in this PMOS  27 . 
     Since the current flowing in the PMOS  27  flows via the NMOS  26  to the ground potential GND, the potential of the node N 2  is increased higher than the ground potential GND. Accordingly, the voltage between the source and the drain of the NMOS  3   c  is reduced and the off-leak current flowing in the NMOS  3   c  is reduced. Furthermore, the potential of the node N 2  is applied to the source of the NMOS  3   a  and the bulk potential of this NMOS  3   a  has become the ground potential GND. Thus, the threshold value voltage of the NMOS  3   a  is increased by the back gate effect and the off-leak current of the NMOS  3   a  is reduced. 
     As has been described above, the off-leak current cancel circuit according to the third embodiment includes the cancel portion  10 B having the PMOS  11  for monitoring off-leak current and PMOS  17  and PMOS  16  for reducing the potential of the node N 1  according to the current flowing in the PMOS  11 . This can reduce the voltage between the drain and the source of the input circuit protecting PMOS  2   c  and reduce the off-leak current as well as increase the threshold value voltage by the back gate effect of the PMOS  2   a , thereby reducing the off-leak current. 
     Similarly, the off-leak current cancel circuit includes the cancel portion  20 B having the NMOS  21  monitoring the off-leak current and NMOS  27  and NMOS  26  for reducing the potential of the node N 2  according to the current flowing in this NMOS  21 . This can reduce the voltage between the drain and the source of the input circuit protecting NMOS  3   c  and reduce the off-leak current as well as increase the threshold value voltage by the back gate effect of the NMOS  3   a , thereby reducing the off-leak current. 
     FIG. 5 shows configuration of an off-leak current cancel circuit according to a fourth embodiment of the present invention. 
     In this off-leak current cancel circuit, by controlling the power source voltage VH, VL applied to the power source lines  31 ,  32  of the CMOS circuit block  30 , the off-leak current of the PMOS  33  and NMOS  34  is reduced. The PMOS  33  has a source connected to the power source line  31  so that the power source voltage VH is applied and the NMOS  34  has a source connected to the power source line  32  so that the power source voltage VL is applied. Power source potential VDD is applied to the bulk potential of the PMOS  33  and the ground potential GND is applied to the bulk potential of the NMOS  34 . 
     This off-leak current cancel circuit is provided on the same semiconductor substrate as the CMOS circuit block  30  and includes control blocks  40  and  60  for controlling the power source voltages VH and VL according to the state of the off-leak current of the PMOS  33  and the NMOS  34  in the CMOS circuit block  30 . 
     The control block  40  includes a PMOS  41  for monitoring the off-leak current. The PMOS  41  has a source and a drain connected to the power source potential VDD and the node N 41 , respectively, and a gate connected to the power source potential VDD so as to be in an OFF state. The node N 41  is connected to a drain and a gate of the NMOS  42 , and a source of the NMOS  42  is connected to the ground potential GND. The node N 41  is further connected to a gate of NMOS  43 , and this NMOS  43  has a drain and a source connected to the node N 42  and to the ground potential GND, respectively. 
     The node N 42  is connected to a drain and a gate of the PMOS  44 , and a source of the PMOS  44  is connected to the power source potential VDD. Moreover, the node N 41  and the ground potential GND are connected to a drain and a source of NMOS  45 , respectively, and a gate of the NMOS  45  is connected to the power source potential VDD. The NMOS  45  has a gate length and gate width formed to be, for example, 100 micrometers and 0.1 micrometer, respectively, so as to exhibit a very high resistance value. 
     The node N 41  is connected to an input side of an off-leak detector (for example, a level shift block)  50 . The level shift block  50  decides whether off-leak current is present according to the potential of the node N 41  and outputs a signal of level “H” or “L” according to the decision result. The level shift block  50  has an output side connected to the gate of the PMOS  46  for switching. The PMOS  46  has a source and a drain connected to the power source potential VDD and to the node N 42 , respectively. Power source voltage VH is output from the node N 42  to the power source line  31 . 
     Similarly, the control block  60  has an NMOS  61  for monitoring the off-leak current. The NMOS  61  has a source and a drain connected to the ground potential GND and the node N 61 , respectively, and a gate connected to the ground potential GND. The node N 61  is connected to a drain and a gate of a PMOS  62  and this PMOS  62  has a source connected to the power source potential VDD. The node N 61  is further connected to a gate of a PMOS  63  and this PMOS  63  has a drain and a source connected to the node N 62  and the power source potential VDD, respectively. 
     The node N 62  is connected to a drain and a gate of an NMOS  64  and this NMOS  64  has a source connected to the ground potential GND. Moreover, the node N 61  and the power source potential VDD are connected to a drain and a source of a PMOS  65 , respectively, and this PMOS  65  has a gate connected to the ground potential GND. The PMOS  65  has a gate length and a gate width formed, for example, to be 100 micrometers and 0.1 micrometer, respectively, so as to always exhibit a very high resistance value. 
     The node N 61  is connected to an input side of an off-leak detector (for example, level shift block)  70 . The level shift block  70  decides whether off-leak current is present according to the potential of the node N 61  and outputs a signal of level “H” or “L” according to the decision result. The level shift block  70  has an output side connected to the gate of the NMOS  66  for switching. The NMOS  66  has a source and a drain connected to the ground potential GND and to the node N 62 , respectively. Power source voltage VL is output from the node N 62  to the power source line  32 . 
     FIG.  6 A and FIG. 6B are circuit diagrams showing examples of the level shift block in FIG.  5 . FIG. 6A shows the level shift block  50  and FIG. 6B shows the level shift block  70 . 
     The level shift block  50  includes a PMOS  51   a  and an NMOS Sib constituting a CMOS inverter and potential of the node N 41  is applied to the gates of the PMOS  51   a  and the NMOS  51   b . The NMOS  51   b  has a source connected to the ground potential GND and the PMOS  51   a  has a source connected to the power source potential VDD via a PMOS  52  diode-connected in the forward direction. The drains of the PMOS  51   a  and the NMOS  51   b  are connected to the gates of PMOS  53   a  and NMOS  53   b  constituting an inverter. The source of the NMOS  53   b  is connected to the ground potential GND and the source of PMOS  53   a  is connected to the power source potential VDD via the PMOS  54  diode-connected in the forward direction. 
     The PMOS  53   a  and the NMOS  53   b  have drains connected to the gate of the NMOS  55  while the PMOS  51   a  and the NMOS  51   b  have drains connected to the gate of the NMOS  56 . The NMOS  55  and  56  have sources connected to the ground potential GND and drains connected to the power source potential VDD via the PMOS  57  and  58 , respectively. The PMOS  58  has a gate connected to a drain of PMOS  57  and the PMOS  57  has a gate connected to a drain of PMOS  58 . An output signal is output from the drain of the PMOS  58 . 
     In this level shift block  50 , a low level potential of the node N 41  is analog-amplified in two stages by inverters longitudinally connected, and output as differential signals from the inverter constituted from PMOS  51   a  and NMOS  51   b , and the inverter constituted from PMOS  53   a  and NMOS  53   b . The differential signals are applied to the gates of the NMOS  56  and  55  constituting a switching circuit and a digitized signal of “H” or “L” is output from the drain of the PMOS  58 . 
     Similarly, the level shift block  70  includes a PMOS  71   a  and NMOS  71   b  constituting an inverter and potential of the node N 61  is applied to the gates of the PMOS  71   a  and the NMOS  71   b . The PMOS  71   a  has a source connected to the power source potential VDD and the NMOS  71   b  has a source connected to the ground potential GND via an NMOS  72  diode-connected in the forward direction. The drains of the PMOS  71   a  and the NMOS  71   b  are connected to the gates of a PMOS  73   a  and an NMOS  73   b  constituting an inverter. The source of the PMOS  73   a  is connected to the power source potential VDD and the source of NMOS  73   b  is connected to the ground potential GND via the NMOS  74  diode-connected in the forward direction. 
     The PMOS  73   a  and the NMOS  73   b  have drains connected to the gate of the NMOS  75  while the PMOS  71   a  and the NMOS  71   b  have drains connected to the gate of the NMOS  76 . The NMOS  75  and  76  have sources connected to the ground potential GND and drains connected to the power source potential VDD via the PMOS  77  and  78 , respectively. The PMOS  78  has a gate connected to a drain of the PMOS  77  and the PMOS  77  has a gate connected to a drain of the PMOS  78 . An output signal is output from the drain of the PMOS  58 . 
     In this level shift block  70 , a high level potential of the node N 61  is analog-amplified in two stages by inverters longitudinally connected, and output as differential signals from the inverter constituted from PMOS ha and NMOS  71   b , and the inverter constituted from PMOS  73   a  and NMOS  73   b . The differential signals are applied to the gates of the NMOS  76  and  75  constituting a switching circuit and a digitized signal of “H” or “L” is output from the drain of the PMOS  78 . 
     Next, explanation will be given on operation. 
     When the ambient temperature is a room temperature and there is almost no off-leak current in the NMOS  61  for monitoring, the PMOS  65  in the control block  60  is in an ON state and accordingly, the node N 61  becomes almost power source potential VDD and the PMOS  62  and  63  are in an OFF state. The potential of the node N 61  is applied to the level shift block  70  and a signal “H” is output from this level shift block  70 . Thus, the NMOS  66  becomes ON and a power source voltage VL almost identical to the ground potential GND is output from the ground potential GND via the NMOS  66  to the node N 62 , i.e., the power source line  32 . 
     Here, if the ambient temperature increases and off-leak current flows in the PMOS  41 , the potential of the node N 41  increases. When the potential of the node N 41  exceeds a predetermined value, the signal output from the level shift block  50  becomes “H” and the PMOS  46  becomes OFF. The off-leak current flowing in the PMOS  41  flows into the ground potential GND via the NMOS  42  and the current mirror circuit constituted by this NMOS  42  and NMOS  43  operates to lower the potential of the node N 42 . Accordingly, the power source voltage VH of the power source line  31  becomes lower than the power source potential VDD. 
     In the PMOS  33  and the like in the CMOS circuit block  30 , the power source potential VDD is applied to the bulk potential and a power source voltage VH having potential lower than this is applied to the source. Thus, in the PMOS  33  and the like, the threshold value voltage is increased by the back gate effect and the off-leak current is reduced. 
     Similarly, when an off-leak current flows in the NMOS  61 , the potential of the node N 61  is lowered. When the potential of the node N 61  becomes lower than a predetermined value, the signal output from the level shift block becomes “L” and the NMOS  66  becomes OFF. The off-leak current flowing in the NMOS  61  flows to the power source potential VDD via the PMOS  62  and the current mirror circuit constituted by this PMOS  62  and the PMOS  63  operates to increase the potential of the node N 62 . Thus, the power source voltage VL of the power source line  32  becomes higher than the ground potential GND. 
     In the NMOS  34  and the like in the CMOS circuit block  30 , the ground potential GND is applied to the bulk potential and a power source voltage VL having potential higher than this is applied to the source. Thus, in the NMOS  34  and the like, the threshold value voltage is increased by the back gate effect and the off-leak current is reduced. 
     As has been described above, the off-leak current cancel circuit of the fourth embodiment has the PMOS  41  for monitoring the off-leak current of the PMOS and the control block  40  for controlling the power source voltage VH applied to the CMOS circuit block  30 , according to the potential of the node N 41  varying according to the current flowing in the PMOS  41 . Thus, it is possible to increase the threshold value voltage of the PMOS  33  and the like in the CMOS circuit block  30  and control the off-leak current of the PMOS. 
     Moreover, the off-leak current cancel circuit of the fourth embodiment has the NMOS  61  for monitoring the off-leak current of the NMOS and the control block  60  for controlling the power source voltage VL applied to the CMOS circuit block  30 , according to the potential of the node N 61  varying according to the current flowing in the NMOS  61 . Thus, it is possible to increase the threshold value voltage of the NMOS  34  and the like in the CMOS circuit block  30  and control the off-leak current of the PMOS. Furthermore, it is possible to reduce current consumption in vain by suppressing the off-leak current. 
     It should be noted that the present invention is not to be limited to the aforementioned embodiments but may be modified in various ways. For example, modifications as follows can be performed. 
     The off-leak current cancel circuit of FIG. 1 is not limited to an input protecting circuit of the CMOS semiconductor integrated circuit and can be applied to a circuit handling analog voltage in the integrated circuit. 
     The off-leak current cancel circuit of FIG. 3 is not limited to an input protecting circuit of the CMOS semiconductor integrated circuit and can be applied as an ordinary transistor power source control circuit in the integrated circuit. 
     The off-leak current cancel circuit of FIG. 4 is not limited to an input protecting circuit of the CMOS semiconductor integrated circuit and can be applied as an ordinary transistor power down control circuit in the integrated circuit. 
     The off-leak current cancel circuit of FIG. 5 controls the power source voltage VH, VL with respect to the CMOS circuit block  30  by using the PMOS  41  and the NMOS  61  for monitoring the off-leak current. However, it is also possible to provide an external control terminal and apply a control signal to this so as to suppress the off-leak current.