Patent Publication Number: US-2002000864-A1

Title: Semiconductor integrated circuit device using substrate bising and device control method thereof

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates generally to a semiconductor integrated circuit device and a control method thereof and, more particularly, to an input protection circuit and an output protection circuit in a CMOS semiconductor integrated circuit and a control method thereof.  
       [0002]FIG. 7 is a circuit diagram showing a conventional input protection circuit used in a CMOS semiconductor integrated circuit.  
       [0003] The input protection circuit in FIG. 7 is constructed of a P-channel MOS transistor MP in which a power source potential point V DD  is connected to a gate, a source and a substrate (back gate) thereof, and an input signal IN is supplied to a drain thereof, and of an N-channel MOS transistor MN in which a common potential point GND is connected to a gate, a source and a substrate (back gate), and the input signal IN is supplied to a drain thereof. The input protection circuit is connected via a buffer Buf to an internal circuit.  
       [0004] This input protection circuit, if the input signal IN having an excessively large amplitude is supplied, the P-channel MOS transistor M P  or the N-channel MOS transistor M N  is turned ON with the result that an electric current flows away to the power source potential point V DD  or the common potential point GND, thus performing a role of protecting a device constituting the internal circuit.  
       [0005] When an electric potential of the input signal IN is under the power source potential V DD , both of the gate and the source of the P-channel MOS transistor M P  are connected to the power source potential point V DD , and hence a gate/source voltage V GS  does not exceed a threshold voltage V thp . Consequently, no current flows across the P-channel MOS transistor M P . If the potential of the input signal IN becomes higher than the power source potential V DD  due to overshoot, however, the source and the drain of the P-channel MOS transistor are replaced with each other in their relationship, and the gate/source voltage V GS  becomes a negative value under the threshold voltage V thp , in which case the P-channel MOS transistor M P  is turned ON and the current flows to the power source potential point V DD  connected to the drain from an input terminal IN connected to the source, thereby restricting a peak voltage of the overshoot.  
       [0006] When the potential of the input signal IN is over the common potential GND, the gate/source voltage V GS  does not exceed a threshold voltage Vthn because of the common potential point GND being connected to both of the gate and the source of the N-channel MOS transistor MN, and therefore no current flows to the N-channel MOS transistor M N . If the potential of the input signal IN is lower than the common potential GND due to undershoot, however, the source and drain of the N-channel MOS transistor M N  are replaced with each other in their relationship, and the gate/source voltage V GS  becomes a positive value over the threshold value V thn , in which case the N-channel MOS transistor M N  is turned ON and the current flows to the input terminal IN connected to the source from the power source potential point V DD  connected to the drain, thereby restricting a peak voltage of the undershoot.  
       [0007] In the input protection circuit as shown in FIG. 7, the current transiently flows to a substrate and a well via a P N  junction between the source and the substrate (back gate) due to a delay time till the P-channel MOS transistor M P  or the N-channel MOS transistor M N  is turned ON since the input signal IN was supplied, or a current proportional to a source/drain current Ids flows to the substrate and the well after the P-channel MOS transistor M P  or the N-channel MOS transistor M N  has been turned ON. The current flowing across the substrate in the former state is the very current itself flowing through the PN junction in a forward direction from the source. The current flowing across the substrate in the latter state is a substrate current based on impact ionization, a magnitude of which is said to be on the order of {fraction (1/100)} to {fraction (1/10000)} of the source/drain current Ids. Problems inherent in the prior art input protection circuit in connection with the above currents will hereinafter be explained.  
       [0008]FIG. 8 is a sectional view showing a structure of the prior art input protection circuit shown in FIG. 1. Given herein is an example where a P-type substrate is provided with the above input protection circuit.  
       [0009] A P-type substrate  1  is provided with an N-type well  2 , and an N +  region  3  and P +  regions  4 ,  5  are provided in the vicinity of an internal surface of the N-type well  2 . Further, N +  regions  6 ,  7  and a P +  region  8  are provided in an area, outside the N-type well  2 , of the P-type substrate  1 . The P-channel MOS transistor M P  is constructed in such a way that the N +  region  3  serves as a substrate (back gate) B P , the P region  4  serves as a source S P , and the P +  region  5  serves as a drain D P . The N-channel MOS transistor M N  is constructed in such a way that the N +  region  6  serves as a drain D N  the N +  region  7  serves as a source S N , and the P +  region  8  serves as a substrate (back gate) B N . A gate G P ,  9  is provided via an insulating layer on between the source and drain of the P-channel MOS transistor M P , and a gate G N    10  is provided via an insulating layer on between the source and drain of the N-channel MOS transistor M N .  
       [0010] Then, as described above referring to FIG. 7, the power source potential point V DD  is connected to the gate GP 9 , the source S P   4  and the substrate (back gate) B P   3  of the P-channel MOS transistor M P , and the input signal IN is supplied to the drain D P   5 . Further, the common potential point GND is connected to the gate G N   10 , the source S N   7  and the substrate (back gate) B N   8  of the N-channel MOS transistor M N , and the input signal IN is supplied to the drain D N   6 .  
       [0011] If the potential of the input signal IN becomes higher than the power source potential V DD  due to the overshoot, the source S P  and the drain D P  are replaced with each other in their relationship, and the gate/source voltage V GS  of the P-channel MOS transistor M P  becomes a negative value. Since there is a delay till the P-channel MOS transistor MP is turned ON since the input signal IN was supplied, the current flows to the N-type well  2  from the input terminal IN via the PN junction between the source SP 5  and the substrate (back gate). Even when the gate/source voltage V GS  exceeds the threshold voltage V thp , and the P-channel MOS transistor is turned ON, it might happen that the current flows to the power source potential point V DD  connected to the drain DP 4  from the input terminal IN, and that an electric current approximate to 1 mA flows to the N-type well  2  on the assumption that the source/drain current I ds  is on the order of, e.g., 100 mA.  
       [0012] In the P-channel MOS transistor MP constituting a parasitic PNP bipolar transistor, the P +  region  5  of the source S P  serves as an emitter, the N-type well  2  serves as a base, and a P-type substrate  1  serves as a collector.  1  The current having flowed to the N-type well  2  becomes a base current, and the current flows to between the collector and the emitter, i.e., between the P-type substrate  1  and the p +  region  5  (the source S P , of the P-channel MOS transistor M P ). As a result, the potential of the P-type substrate  1  rises, and the current flows via the PN junction to between the P-type substrate  1  and the common potential point GND connected to the N +  region  7  of the source S N  of the N-channel MOS transistor M N .  
       [0013] At this time, all the N-type wells  2  constituting the parasitic NPN bipolar transistor serve as a collector, the P-type substrate  1  serves as a base, and all the N +  regions  7  of the source SN of the N-channel MOS transistor M N  serve as an emitter. The current having flowed to the P-type substrate  1  becomes a base current, and the current flows to between the collector and the emitter, i.e., between all the N-type wells  2  and the N +  regions  7  (the source S N  of the N-channel MOS transistor M N ). Thus, the parasitic PNP bipolar transistor and the parasitic NPN bipolar transistor makes them turned ON each other, and, even if there is no overshoot as a trigger, a large current flows to between the power source potential point VDD and the common potential point GND with the result that the device is damaged all the more. This is a well-known latch-up.  
       [0014] Further, when the potential of the input signal IN is lower than the common potential GND due to the undershoot, the source S N  and the drain D N  are replaced with each other in their relationship, and the gate/source voltage V GS  of the N-channel MOS transistor M N  becomes a positive value. Since there is a delay till the N-channel MOS transistor M N  is turned ON, the current flows to the P-type substrate  1  via the PN junction between the source SN 6  and the substrate (back gate). Even if the gate/source voltage VGS of the N-channel MOS transistor M N  exceeds the threshold voltage Vthn with the result that the N-channel MOS transistor M N  is turned ON, it might happen that the current flows to the input terminal IN connected to the source S N   6  from GND connected to the drain D N   7 , and that the current approximate to 1 mA flows to the P-type substrate  1  on the assumption that the source/drain current I ds  is, e.g., 100 mA.  
       [0015] In the N-channel MOS transistor M P  constituting a parasitic NPN bipolar transistor, the N +  region  6  of the source S N  serves as an emitter, the P-type substrate  1  serves as a base, and the N-type well  2  serves as a collector. The current having flowed to the P-type substrate  1  becomes a base current, and the current flows to between the collector and the emitter, i.e., between the N-type well  2  and N +  region  6  (the source S N  of the N-channel MOS transistor M N ). As a result, the potential of the N-type well  2  decreases, and the current flows via the PN junction to between the N-type well  2  and the power source potential point connected to the P +  region  4  of the source S P  of the P-channel MOS transistor M P . At this time, the P-type substrate  1  constituting the parasitic PNP bipolar transistor serves as a collector, the N-type well  2  serves as a base, and the P +  region  4  of the source S P  of the P-channel MOS transistor M P  serve as an emitter. The current having flowed to the N-type well becomes a base current, and the current flows to between the collector and the emitter, i.e., between the P-type substrate  1  and the P +  region  4 . Thus, the parasitic NPN bipolar transistor and the parasitic PNP bipolar transistor makes them turned ON each other, and, as in the case of the overshoot, a large current flows to between the power source potential point V DD  and the common potential point GND in the case of the undershoot also. Unlike the case where the overshoot is the trigger for the latch-up, however, in the case of the undershoot, a period for which the parasitic NPN bipolar transistor is allowed to remain ON is limited to a duration of the undershoot occurred. Hence, when the undershoot as the trigger disappears, the current between the power source potential point V DD  and the common potential point GND also disappears.  
       [0016] As a conventional countermeasure against the problems described above, the latch-up is prevented by forming at a structurally short pitch a substrate contact for connecting the N-type well  2  to the power source potential point VDD and a substrate contact for connecting the P-type substrate  1  to the common potential point GND, promptly collecting the currents flowed to the substrate and the well at the common potential point GND and the power source potential point V DD  via the substrate contacts, and thus restricting fluctuations in the potentials of the substrate and of the well.  
       [0017] In conventional countermeasure, however, though effective in the case where the potentials of the substrate and the well are supplied at a low output impedance as in the case of the power source such as the power source potential point V DD  and the common potential point GND, has a problem in which an area of a charge pump circuit is required to be taken large in terms of a constraint by the output impedance of the charge pump circuit in such a case as to bias the substrate using the charge pump circuit. Note that the input protection circuit has been described so far, however, an output protection circuit also presented the same problems.  
       SUMMARY OF THE INVENTION  
       [0018] It is a first object of the present invention to provide a semiconductor integrated circuit device capable of restricting a current inflow into a substrate from I/O terminals, which is a cause of a latch-up of an input protection circuit and an output protection circuit in a CMOS semiconductor integrated circuit.  
       [0019] It is a second object of the present invention to provide a method of controlling a semiconductor integrated circuit device.  
       [0020] According to one aspect of the present invention, there is provided a semiconductor integrated circuit device comprising: a CMOS-based input protection circuit or a CMOS-based output protection circuit constructed of a pair of a P-channel MOS transistor and an N-channel MOS transistor, wherein a back gate of said P-channel MOS transistor is biased at a voltage higher than a peak voltage of an overshooting input or output signal of said P-channel MOS transistor, or a back gate of said N-channel MOS transistor is biased at a voltage lower than a negative peak voltage of undershooting input or output signal of said N-channel MOS transistor.  
       [0021] According to an another aspect of the present invention, there is provided a method of controlling a semiconductor integrated circuit device having a CMOS-based input protection circuit or a CMOS-based output protection circuit constructed of a pair of a P-channel MOS transistor and an N-channel MOS transistor, said method comprising: a step of biasing the back gate of said P-channel MOS transistor at a voltage higher than a peak voltage of an overshooting of an input signal or an output signal of said P-channel MOS transistor, or biasing a back gate of said N-channel MOS transistor at a voltage lower than a negative peak voltage of an undershooting of the input signal or the output signal.  
       [0022] The semiconductor integrated circuit device and the control method thereof according to the present invention are characterized by restricting the current inflow into the substrate from the I/O signals which has hitherto been the cause of the latch-up, which involves, in an I/O cell of a CMOS semiconductor integrated circuit device, applying a voltage higher than a peak voltage of overshoot of the input signal or the output signal to a back gate (N-type substrate or N-type well) of a P-channel MOS transistor constituting an input protection circuit or an output protection circuit, or applying a voltage lower than a negative peak voltage of undershoot to a back gate (P-type substrate or P-type well) of an N-channel MOS transistor constituting an input protection circuit or an output protection circuit. This construction exhibits the greatest effect in stabilizing the potentials of the substrate and of the well, and it is feasible to largely reduce a possibility of causing the latch-up which has hitherto been treated as the problem in all CMOS circuits. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0023]FIG. 1 is a circuit diagram showing a semiconductor integrated circuit device (input protection circuit) in a first embodiment of the present invention;  
     [0024]FIG. 2 is a circuit diagram showing the semiconductor integrated circuit device (input protection circuit) in a second embodiment of the present invention;  
     [0025]FIG. 3 is a circuit diagram showing the semiconductor integrated circuit device (input protection circuit) in a third embodiment of the present invention;  
     [0026]FIG. 4 is a circuit diagram showing a semiconductor integrated circuit device (output protection circuit) in a fourth embodiment of the present invention;  
     [0027]FIG. 5 is a circuit diagram showing the semiconductor integrated circuit device (output protection circuit) in a fifth embodiment of the present invention; and  
     [0028]FIG. 6 is a circuit diagram showing the semiconductor integrated circuit device (output protection circuit) in a sixth embodiment of the present invention.  
     [0029]FIG. 7 is a circuit diagram showing a conventional input protection circuit;  
     [0030]FIG. 8 is a sectional view showing a structure of the conventional input protection circuit; 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0031] Embodiments of a semiconductor integrated circuit device and a control method thereof will hereinafter be described with reference to the accompanying drawings.  
     [0032]FIG. 1 is a circuit diagram showing a semiconductor integrated circuit device which is, to be more specific, an input protection circuit in a first embodiment of the present invention.  
     [0033] The input protection circuit in the first embodiment of the present invention is constructed of a P-cannel MOS transistor MP in which a power source potential point V DD  is connected to a gate and a source thereof, an N-type substrate or an N-type well defined as a substrate (back gate) is previously biased by a voltage V SUB+ (V SUB+ &gt;VIN Peak +≧V DD ) higher than a peak voltage of a predicted overshoot of an input signal IN, and the input signal IN is supplied to a drain thereof, and of an N-channel MOS transistor M N  in which a common potential point GND is connected to a gate, a source and a substrate (back gate) thereof, and the input signal IN is supplied to its drain. The input protection circuit is connected via a buffer Buf to an internal circuit.  
     [0034] A power source for biasing the substrate may be either a power source the power of which is suppled from outside or a self-supplied power source with a charge pump circuit mounted in the semiconductor integrated circuit device.  
     [0035] In the input protection circuit in the first embodiment of the present invention, even if the source and the drain are replaced with each other in their relationship because of the potential of the input signal IN becoming higher than the power source potential V DD  due to the overshoot, the voltage V SUB+  higher than the peak voltage of the previously predicted overshoot is applied to the substrate (back gate) of the P-channel MOS transistor M P , and hence it never happens that a PN junction between the source or the drain and the substrate (back gate) of the P-channel MOS transistor MP is biased in a forward direction. According to the prior art construction, there is a possibility in which the electric current flows into the substrate and the well via the PN junction. In the input protection circuit in the first embodiment of the present invention, however, the possibility described above is eliminated by the above construction.  
     [0036] A gate/source voltage V GS  of the P-channel MOS transistor MP becomes a negative value under a threshold value V thn  with the result that the P-channel MOS transistor MP is turned ON, in which case the current flows to the power source potential pint V DD  connected to the drain through the input terminal IN connected to the source. In the input protection circuit in accordance with the first embodiment of the present invention, however, if it is assumed that a source/drain current Ids at that time is, e.g., 100 mA, only the current on the order of 1 mA may be conceived as a substrate current.  
     [0037] If the substrate current is on the order of 1 mA, the power source for biasing the substrate can be easily ensured regardless of whether the power source may be the power source supplied with the power from outside or the self-supplied power source with the charge pump circuit mounted in the semiconductor integrated circuit device.  
     [0038] In the input protection circuit in accordance with the first embodiment of the present invention, it is feasible to largely reduce a possibility of causing a latch-up that has hitherto been treated as a problem in all the conventional CMOS circuits by restricting the substrate current.  
     [0039]FIG. 2 is a circuit diagram showing a semiconductor integrated circuit device which is, to be more specific, an input protection circuit in a first embodiment of the present invention.  
     [0040] The input protection circuit in the second embodiment of the present invention is constructed of a P-cannel MOS transistor MP in which a power source potential point V DD  is connected to a gate, a source and a substrate thereof, and of an N-channel MOS transistor M N  in which a common potential point GND is connected to a gate and a source thereof, a P-type substrate or a P-type well defined as a substrate (back gate) is previously biased by a voltage V SUB− (V SUB− &lt;VIN Peak− ≦GND) lower than a negative peak voltage of a predicted undershoot of an input signal IN, and the input signal IN is supplied to a drain thereof. The input protection circuit is connected via a buffer Buf to an internal circuit.  
     [0041] A power source for biasing the substrate may be either a power source supplied with power from outside or a self-supplied power source with a charge pump circuit mounted in the semiconductor integrated circuit device.  
     [0042] In the input protection circuit in the second embodiment of the present invention, even if the source and the drain are replaced with each other in their relationship because of the potential of the input signal IN becoming lower than the common potential GND due to the undershoot, the voltage V SUB−  lower than the peak voltage of the previously predicted undershoot is applied to the substrate (back gate) of the N-channel MOS transistor M N , and hence it never happens that a PN junction between the source or the drain and the substrate (back gate) of the N-channel MOS transistor M N  is biased in the forward direction. According to the prior art construction, there is a possibility in which the electric current flows into the substrate and the well via the PN junction. In the input protection circuit in the first embodiment of the present invention, however, the possibility described above is eliminated by the above construction.  
     [0043] A gate/source voltage V GS  of the N-channel MOS transistor M N  exceeds the threshold value V thn  with the result that the N-channel MOS transistor M N  is turned ON, in which case the current flows to the input terminal IN connected to the source from the common potential point GND connected to the drain. In the input protection circuit in accordance with the second embodiment of the present invention, however, if it is assumed that a source/drain current Ids at that time is, e.g., 100 mA, only the current on the order of 1 mA may be conceived as a substrate current.  
     [0044] If the substrate current is on the order of 1 mA, the power source for biasing the substrate can be easily ensured regardless of whether the power source may be the power source supplied with the power from outside or the self-supplied power source with the charge pump circuit mounted in the semiconductor integrated circuit device.  
     [0045] In the input protection circuit in accordance with the second embodiment of the present invention, it is feasible to largely reduce the possibility of causing the latch-up that has hitherto been treated as the problem in all the conventional CMOS circuits by restricting the substrate current.  
     [0046]FIG. 3 is a circuit diagram showing a semiconductor integrated circuit device which is, to be more specific, an input protection circuit in a third embodiment of the present invention.  
     [0047] The input protection circuit in the third embodiment of the present invention is constructed of a P-cannel MOS transistor MP in which a power source potential point VDD is connected to a gate and a source thereof, an N-type substrate or an N-type well defined as a substrate (back gate) is previously biased by a voltage V SUB+ (V SUB+ &gt;VIN Peak +≧V DD )) higher than a peak voltage of a predicted overshoot of an input signal IN, and the input signal IN is supplied to a drain thereof, and of an N-channel MOS transistor M N  in which a common potential point GND is connected to a gate and a source thereof, a P-type substrate or a P-type well defined as a substrate (back gate) is previously biased by a voltage V SUB− (V. SUB− &lt;VIN Pead− ≦GND) lower than a negative peak voltage of a predicted undershoot of an input signal IN, and the input signal IN is supplied to a drain thereof. The input protection circuit is connected via a buffer Buf to an internal circuit.  
     [0048] A power source for biasing the substrate may be either a power source the power of which is suppled from outside or a self-supplied power source with a charge pump circuit mounted in the semiconductor integrated circuit device.  
     [0049] In the input protection circuit in the third embodiment of the present invention, even if the source and the drain are replaced with each other in their relationship because of the potential of the input signal IN becoming higher than the power source potential V DD  due to the overshoot, the voltage V SUB+  higher than the peak voltage of the previously predicted overshoot is applied to the substrate (back gate) of the P-channel MOS transistor M P , and hence it never happens that a PN junction between the source or the drain and the substrate (back gate) of the P-channel MOS transistor M P  is biased in the forward direction. According to the prior art construction, there is a possibility in which the electric current flows into the substrate and the well via the PN junction. In the input protection circuit in the third embodiment of the present invention, however, the possibility described above is eliminated by the above construction.  
     [0050] A gate/source voltage V GS  of the P-channel MOS transistor M P  becomes a negative value under a threshold value V thn  with the result that the P-channel MOS transistor M P  is turned ON, in which case the current flows to the power source potential pint V DD  connected to the drain through the input terminal IN connected to the source. In the input protection circuit in accordance with the third embodiment of the present invention, however, if it is assumed that a source/drain current Ids at that time is, e.g., 100 mA, only the current on the order of 1 mA may be conceived as a substrate current.  
     [0051] While on the other hand, even if the potential of the input signal IN is lower than the common potential GND due to the undershoot, the voltage V SUB−  lower than the peak voltage of the previously predicted undershoot is applied to the substrate (back gate) of the N-channel MOS transistor M N . It therefore never happens that a PN junction between the source or the drain and the substrate (back gate) of the N-channel MOS transistor M N  is biased in the forward direction. According to the prior art construction, there is a possibility in which the electric current flows into the substrate and the well via the PN junction. In the input protection circuit in the third embodiment of the present invention, however, the possibility described above is eliminated by the above construction.  
     [0052] A gate/source voltage V GS  of the N-channel MOS transistor M N  exceeds the threshold value Vthn with the result that the N-channel MOS transistor M N  is turned ON, in which case the current flows to the input terminal IN connected to the source from the common potential point GND. In the input protection circuit in accordance with the third embodiment of the present invention, however, if it is assumed that a source/drain current I ds  at that time is, e.g., 100 mA, only the current on the order of 1 mA may be conceived as a substrate current.  
     [0053] If the substrate current is on the order of 1 mA, the power source for biasing the substrate can be easily ensured regardless of whether the power source may be the power source supplied with the power from outside or the self-supplied power source with the charge pump circuit mounted in the semiconductor integrated circuit device.  
     [0054] In the input protection circuit in accordance with the third embodiment of the present invention, the substrate current can be restricted in both cases of the overshoot and the undershoot of the input signal IN, and hence there is the greatest effect in stabilizing the potentials of the substrate and of the well. It is also feasible to largely reduce a possibility of causing a latch-up that has hitherto been treated as a problem in all the conventional CMOS circuits. FIG. 4 is a circuit diagram showing a semiconductor integrated circuit device which is, to be more specific, an output protection circuit in a fourth embodiment of the present invention.  
     [0055] The output protection circuit in the fourth embodiment of the present invention is a circuit to which the construction of the input protection circuit in the first embodiment of the present invention is applied. The output protection circuit in the fourth embodiment of the present invention is constructed of a P-cannel MOS transistor M P  in which a power source potential point V DD  is connected to a source thereof, an output terminal OUT is connected to a drain thereof, an N-type substrate or an N-type well defined as a substrate (back gate) is previously biased by a voltage V SUB+ (V SUB+ &gt;VIN Peak +≧V DD ) higher than a peak voltage of a predicted overshoot from the output terminal OUT, and of an N-channel MOS transistor M N  in which a common potential point GND is connected to a source and a substrate (back gate) thereof, and the output terminal OUT is connected to a drain thereof. A signal from an internal circuit is supplied to gates of the P- and N-channel MOS transistors M P  and M N .  
     [0056] A power source for biasing the substrate may be either a power source the power of which is suppled from outside or a self-supplied power source with a charge pump circuit mounted in the semiconductor integrated circuit device.  
     [0057] In the output protection circuit in the fourth embodiment of the present invention, even if the source and the drain are replaced with each other in their relationship because of the potential at the output terminal OUT becoming higher than the power source potential V DD  due to the overshoot, the voltage V SUB+  higher than the peak voltage of the previously predicted overshoot is applied to the substrate (back gate) of the P-channel MOS transistor M P , and hence it never happens that a PN junction between the source or the drain and the substrate (back gate) of the P-channel MOS transistor M P  is biased in the forward direction. According to the prior art construction, there is a possibility in which the electric current flows into the substrate and the well via the PN junction. In the output protection circuit in the fourth embodiment of the present invention, however, the possibility described above is eliminated by the above construction.  
     [0058] A gate/source voltage V GS  of the P-channel MOS transistor M P  becomes a negative value under a threshold value Vthn with the result that the P-channel MOS transistor M P  is turned ON, in which case the current flows to the power source potential pint V DD  connected to the drain through the output terminal OUT connected to the source. In the output protection circuit in accordance with the fourth embodiment of the present invention, however, if it is assumed that a source/drain current Ids at that time is, e.g., 100 mA, only the current on the order of 1 mA may be conceived as a substrate current.  
     [0059] If the substrate current is on the order of 1 mA, the power source for biasing the substrate can be easily ensured regardless of whether the power source may be the power source supplied with the power from outside or the self-supplied power source with the charge pump circuit mounted in the semiconductor integrated circuit device.  
     [0060] In the output protection circuit in accordance with the fourth embodiment of the present invention, it is feasible to largely reduce a possibility of causing a latch-up that has hitherto been treated as a problem in all the conventional CMOS circuits by restricting the substrate current.  
     [0061]FIG. 5 is a circuit diagram showing a semiconductor integrated circuit device which is, to be more specific, an output protection circuit in a fifth embodiment of the present invention.  
     [0062] The output protection circuit in the fifth embodiment of the present invention is a circuit to which the construction of the input protection circuit in the second embodiment of the present invention is applied. The output protection circuit in the fifth embodiment of the present invention is constructed of a P-cannel MOS transistor M P  in which a power source potential point V DD  is connected to a source and a substrate (back gate) thereof, and an output terminal OUT is connected to a drain thereof, and an N-channel MOS transistor M N  in which a common potential point GND is connected to a source thereof, an output terminal OUT is connected to a drain thereof, and a P-type substrate or a P-type well defined as a substrate (back gate) is previously biased by a voltage V SUB− (V SUB− &lt;VIN Peak− ≦GND) lower than a negative peak voltage of a predicted undershoot from the output terminal OUT. A signal from an internal circuit is supplied to gates of the P- and N-channel MOS transistors M P  and M N .  
     [0063] A power source for biasing the substrate may be either a power source the power of which is suppled from outside or a self-supplied power source with a charge pump circuit mounted in the semiconductor integrated circuit device.  
     [0064] In the output protection circuit in the fifth embodiment of the present invention, even if the source and the drain are replaced with each other in their relationship because of the potential at the output terminal OUT becoming lower than the common potential GND due to the undershoot, the voltage V SUB−  lower than the peak voltage of the previously predicted undershoot is applied to the substrate (back gate) of the N-channel MOS transistor M N , and hence it never happens that a PN junction between the source or the drain and the substrate (back gate) of the N-channel MOS transistor M N  is biased in the forward direction. According to the prior art construction, there is a possibility in which the electric current flows into the substrate and the well via the PN junction. In the output protection circuit in the fifth embodiment of the present invention, however, the possibility described above is eliminated by the above construction.  
     [0065] A gate/source voltage V GS  of the N-channel MOS transistor M N  exceeds a threshold value V thn  with the result that the N-channel MOS transistor M N  is turned ON, in which case the current flows to the output terminal OUT connected to the source from the common potential point GND connected to the drain. In the output protection circuit in accordance with the fifth embodiment of the present invention, however, if it is assumed that a source/drain current Ids at that time is, e.g., 100 mA, only the current on the order of 1 mA may be conceived as a substrate current.  
     [0066] If the substrate current is on the order of 1 mA, the power source for biasing the substrate can be easily ensured regardless of whether the power source may be the power source supplied with the power from outside or the self-supplied power source with the charge pump circuit mounted in the semiconductor integrated circuit device.  
     [0067] In the output protection circuit in accordance with the fifth embodiment of the present invention, it is feasible to largely reduce a possibility of causing a latch-up that has hitherto been treated as a problem in all the conventional CMOS circuits by restricting the substrate current.  
     [0068]FIG. 6 is a circuit diagram showing a semiconductor integrated circuit device which is, to be more specific, an output protection circuit in a sixth embodiment of the present invention.  
     [0069] The output protection circuit in the sixth embodiment of the present invention is a circuit to which the construction of the input protection circuit in the third embodiment of the present invention is applied. The output protection circuit in the sixth embodiment of the present invention is constructed of a P-cannel MOS transistor MP in which a power source potential point V DD  is connected to a source thereof, an output terminal OUT is connected to a drain thereof, an N-type substrate or an N-type well defined as a substrate (back gate) is previously biased by a voltage V SUB+ (V SUB+ &gt;VIN Peak+ ≧V DD ) higher than a peak voltage of a predicted overshoot from the output terminal OUT, and an N-channel MOS transistor MN in which a common potential point GND is connected to a source thereof, an output terminal OUT is connected to a drain thereof, and a P-type substrate or a P-type well defined as a substrate (back gate) is previously biased by a voltage V SUB− (V SUB− &lt;VIN Peak− ≦GND) lower than a negative peak voltage of a predicted undershoot from the output terminal OUT. A signal from an internal circuit is supplied to gates of the P- and N-channel MOS transistors M P  and M N .  
     [0070] A power source for biasing the substrate may be either a power source the power of which is suppled from outside or a self-supplied power source with a charge pump circuit mounted in the semiconductor integrated circuit device.  
     [0071] In the output protection circuit in the sixth embodiment of the present invention, even if the source and the drain are replaced with each other in their relationship because of the potential at the output terminal OUT becoming higher than the power source potential VDD due to the overshoot, the voltage VSUB+ higher than the peak voltage of the previously predicted overshoot is applied to the substrate (back gate) of the P-channel MOS transistor M N , and hence it never happens that a PN junction between the source or the drain and the substrate (back gate) of the P-channel MOS transistor M P  is biased in the forward direction. According to the prior art construction, there is a possibility in which the electric current flows into the substrate and the well via the PN junction. In the output protection circuit in the sixth embodiment of the present invention, however, the possibility described above is eliminated by the above construction.  
     [0072] A gate/source voltage VGS of the P-channel MOS transistor M P  becomes a negative value under a threshold value V thn  with the result that the P-channel MOS transistor M P  is turned ON, in which case the current flows to the power source potential point V DD  connected to the drain from the output terminal OUT connected to the source. In the output protection circuit in accordance with the sixth embodiment of the present invention, however, if it is assumed that a source/drain current Ids at that time is, e.g., 100 mA, only the current on the order of 1 mA may be conceived as a substrate current.  
     [0073] While on the other hand, even if the potential at the output terminal OUT is lower than the common potential GND due to the undershoot, the voltage VSUB− lower than the peak voltage of the previously predicted undershoot is applied to the substrate (back gate) of the N-channel MOS transistor M N . It therefore never happens that a PN junction between the source or the drain and the substrate (back gate) of the N-channel MOS transistor M N  is biased in the forward direction. According to the prior art construction, there is a possibility in which the electric current flows into the substrate and the well via the PN junction. In the output protection circuit in the sixth embodiment of the present invention, however, the possibility described above is eliminated by the above construction.  
     [0074] A gate/source voltage V GS  of the N-channel MOS transistor M N  exceeds the threshold value V thn  with the result that the N-channel MOS transistor M N  is turned ON, in which case the current flows to the output terminal OUT connected to the source from the common potential point GND. In the output protection circuit in accordance with the sixth embodiment of the present invention, however, if it is assumed that a source/drain current Ids at that time is, e.g., 100 mA, only the current on the order of 1 mA may be conceived as a substrate current.  
     [0075] If the substrate current is on the order of 1 mA, the power source for biasing the substrate can be easily ensured regardless of whether the power source may be the power source supplied with the power from outside or the self-supplied power source with the charge pump circuit mounted in the semiconductor integrated circuit device.  
     [0076] In the output protection circuit in accordance with the sixth embodiment of the present invention, the substrate current can be restricted in both cases of the overshoot and the undershoot from the output terminal OUT, and hence there is the greatest effect in stabilizing the potentials of the substrate and of the well. It is also feasible to largely reduce a possibility of causing a latch-up that has hitherto been treated as a problem in all the conventional CMOS circuits.  
     [0077] A method of controlling the semiconductor integrated circuit device according to the present invention, as discussed in each embodiment of the semiconductor integrated circuit device of the present invention, the back gate of the P-channel MOS transistor MP constituting the input protection circuit using CMOS, is biased by the voltage higher than the peak voltage of the predicted overshoot of the input signal, or the back gate of the N-channel MOS transistor MN is biased by the voltage lower than the negative peak voltage of the predicted undershoot of the input signal, or the back gate of the P-channel MOS transistor constituting the output protection circuit using CMOS, is biased by the voltage higher than the peak voltage of the predicted overshoot from the output terminal, or the back gate of the N-channel MOS transistor is biased by the voltage lower than the negative peak voltage of the predicted undershoot from the output terminal.  
     [0078] According to the method of controlling the semiconductor integrated circuit device of the present invention, the same effects as those described in the respective embodiments of the semiconductor integrated circuit device of the present invention can be obtained.  
     [0079] According to the semiconductor integrated circuit device and the control method thereof of the present invention, the back gate (the N-type substrate or well) of the P-channel MOS transistor constituting the input protection circuit or the output protection circuit using CMOS, is biased by the voltage higher then the peak voltage of the overshoot of the input signal or the output signal, or the back gate (the P-type substrate or well) of the N-channel MOS transistor constituting the input protection circuit or the output protection circuit,. is biased by the voltage lower then the negative peak voltage of the undershoot. Therefore, the substrate current is restricted, and, as a result, it is possible to largely reduce the possibility of causing the latch-up that has hitherto been treated as the problem in all the CMOS circuits.  
     [0080] The back gate (the N-type substrate or well) of the P-channel MOS transistor constituting the input protection circuit or the output protection circuit using CMOS, is biased by the voltage higher then the peak voltage of the overshoot of the input signal or the output signal, and the back gate (the P-type substrate or well) of the N-channel MOS transistor constituting the input protection circuit or the output protection circuit, is biased by the voltage lower then the negative peak voltage of the undershoot. In this case, the substrate current can be restricted in both of the cases of the overshoot and the undershoot of the input signal or the output signal, and hence there is the greatest effect in stabilizing the potentials of the substrate and of the well. It is also feasible to largely reduce the possibility of causing the latch-up that has hitherto been treated as the problem in all the CMOS circuits.