Abstract:
A semiconductor integrated circuit and power control method use one of a supply voltage of the circuit and a delay time of the circuit to control a substrate bias voltage applied to a substrate of an insulated gate field effect transistor. High speed operation, consuming a small amount of power, is achieved. A CMOS circuit has a widened operating voltage range, with reduced leak currents in a standby mode in a range of high supply voltage, reducing power consumption of the CMOS circuit, and increasing operating speed of the CMOS circuit in the range of low supply voltage.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 09/863,349 filed May 24, 2001 now U.S. Pat. No. 6,518,825. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a semiconductor integrated circuit device and more particularly to a semiconductor integrated circuit device operating at a high speed and consuming a small amount of electric power. 
     BACKGROUND OF THE INVENTION 
     The power consumed by a semiconductor integrated circuit device using a CMOS circuit consists of power consumed dynamically due to electric charge and discharge at the times of switching and power consumed statically due to subthreshold leak currents. Because dynamic consumption is proportional to the square of supply voltage VDD, dynamic consumption can be reduced effectively by lowering supply voltage VDD. Accordingly the supply voltage VDD of CMOS semiconductor integrated circuit devices of microprocessors, etc. is showing a tendency to lower. Some microprocessors are provided with a power-management mechanism, which enable the microprocessor to operate in two or more modes. In the standby mode of such a microprocessor, clock signals are not fed to the execution unit and, thereby, the dynamic power consumption of the non-operating execution unit is reduced significantly. On the other hand, the static consumption due to subthreshold leak currents has not been reduced. 
     The operating speed of a CMOS circuit lowers as the supply voltage VDD lowers. To prevent the operating speed from lowering, the threshold voltage of the MOS transistors has to be reduced as the supply voltage VDD lowers. However, when the threshold voltage is reduced, the subthreshold leak currents become significantly large. Accordingly the static consumption due to subthreshold leak currents has become salient as the supply voltage VDD has lowered. Thus hoped for is a semiconductor integrated circuit device of a microprocessor or the like which can operate at a high speed, consuming a small amount of power. 
     Proposed to solve the above problem is a method of controlling the threshold voltage of MOS transistors with variable substrate voltage [pp. 280-281, Digest of Technical Papers (February 1999), 1999 International Solid-State Circuits Conference]. In the active mode for the normal high-speed operation, the substrate voltage of the PMOS transistor (p-channel MOS transistor) is set to the supply voltage and that of the NMOS transistor (n-channel MOS transistor) is set to the ground voltage. In the standby mode in which high-speed operation is not required of the CMOS circuit, the substrate voltage of the PMOS transistor is raised over the supply voltage VDD and that of the NMOS transistor is lowered below the ground voltage (this operation is hereinafter referred to as “applying low substrate bias”). By applying low substrate voltage to the substrates of the MOS transistors in the standby mode, the threshold voltage of the MOS transistors constituting the CMOS circuit can be raised and, thereby, the static consumption due to subthreshold leak currents can be reduced. 
     To achieve a CMOS circuit capable of operating at a high speed and a low power-consumption level, the threshold voltages of the MOS transistors are lowered for high-speed operation in the active mode and raised to reduce the subthreshold leak currents in the standby mode. 
     On the other hand, a microprocessor is required to operate in a wide range of supply voltage. As indicated by the curve (A) in FIG. 2, the operating speed of a CMOS circuit decreases rapidly as the supply voltage lowers. Accordingly it is now difficult to run a CMOS circuit at a high speed under low voltage in the active mode just by setting the substrate voltage to the supply voltage and the ground voltage as described above. In the active mode, therefore, the substrate voltage of the PMOS transistor is lowered below the supply voltage VDD and that of the NMOS transistor is raised over the ground voltage (this operation is hereinafter referred to as “applying high substrate bias”) By applying high substrate bias to the substrates of the MOS transistors, their threshold voltage can be reduced and the operating speed of the CMOS circuit can be raised. 
     On the other hand, applying high substrate bias to the substrates of the MOS transistors means applying forward bias to the substrates in the direction of p-n junction, which increases the leak currents and may induce a latch-up phenomenon to damage the transistors. In the range of low supply voltage, however, the increase in the leak currents is limited and the latch-up phenomenon can be prevented. Therefore, it is preferable that the substrate bias of the PMOS transistor and that of the NMOS transistor are set to the supply voltage and the ground voltage, respectively, in the range of high supply voltage and high substrate bias is applied to the substrates for high-speed operation in the range of low supply voltage. In the standby mode, low substrate bias is applied to the substrates to hold down the leak currents. Thus a CMOS circuit operating at a high speed, consuming a small amount of power, can be achieved. 
     This invention achieves the following effects by applying low substrate voltage to the substrates in the standby mode in the range of high supply voltage and applying high substrate voltage to the substrates in the range of low supply voltage. 
     (1) To widen the voltage range in which a CMOS circuit can operate 
     (2) To reduce the leak currents of a CMOS circuit in the standby mode in the range of high supply voltage and, thereby, reduce the power consumption of the CMOS circuit 
     (3) To increase the operating speed of a CMOS circuit in the range of low supply voltage 
     SUMMARY OF THE INVENTION 
     This invention provides a semiconductor integrated circuit device comprising a main circuit which includes a PMOS transistor having a source-drain channel between a first operating-potential point and a second operating-potential point and a NMOS transistor having a source-drain channel between the first operating-potential point and the second operating-potential point and connected in series to the PMOS transistor. When the changing signal is in a first state, the first operating potential is fed as substrate potential of the PMOS transistor and the second operating potential is fed as substrate potential of the NMOS transistor. When the changing signal is in a second state, first substrate potential lower than the first operating potential is fed as substrate potential of the PMOS transistor and second substrate potential higher than the second operating potential is fed as substrate potential of the NMOS transistor. With such substrate potential, the main circuit operates at high speed. 
     Preferably, the state of the changing signal is changed over by the first operating potential or the operating speed of the main circuit. 
     In addition, an active mode and a standby more are provided, and reverse bias is applied to the substrates of MOS transistors in standby mode to reduce the power consumption further. 
     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred form of the present invention is illustrated in the accompanying drawings in which: 
     FIG. 1 is a block diagram of a first embodiment of the invention; 
     FIG. 2 shows that the delay time of a CMOS circuit has dependency on the supply voltage; 
     FIG. 3 shows waveforms of operations of the first embodiment of the invention; 
     FIG. 4 is a block diagram of a second embodiment of the invention; 
     FIG. 5 shows waveforms of operations of the second embodiment of the invention; 
     FIG. 6 shows waveforms of operations of the second embodiment of the invention; 
     FIG. 7 is a block diagram of a changeover circuit; 
     FIG. 8 is a block diagram of a comparator; 
     FIG. 9 is another block diagram of a changeover circuit; 
     FIG. 10 is yet another diagram of a changeover circuit; 
     FIG. 11 is a block diagram of a delay monitor; 
     FIG. 12 is another block diagram of a delay monitor; 
     FIG. 13 is a block diagram of a phase-frequency comparator; 
     FIG. 14 is a block diagram of an up-down counter; 
     FIG. 15 is a block diagram of an SR flip-flop; 
     FIG. 16 is a block diagram of a JK flip-flop; 
     FIG. 17 is a block diagram of a standby control circuit; 
     FIG. 18 is a block diagram of a level-up level converter; 
     FIG. 19 is a block diagram of a level-down level converter; 
     FIG. 20 is a block diagram of a charge pump for generating VWEL voltage; 
     FIG. 21 is a block diagram of a charge pump for generating VSUB voltage; 
     FIG. 22 is a block diagram of an active control circuit; 
     FIG. 23 is a block diagram of a standby control circuit; and 
     FIG. 24 is another block diagram of an active control circuit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to drawings, embodiments of the present invention will be described below. 
     FIG. 1 shows an embodiment of a semiconductor integrated circuit device of the present invention. The semiconductor integrated circuit device of the present invention comprises a main circuit LSI which is a semiconductor integrated circuit, such as a microprocessor, including a changeover circuit EXC, a substrate bias control circuit VFBB 1 , and a switching circuit SWC. The substrate bias control circuit VFBB 1  comprises a standby control circuit VBB 1  and an active control circuit FBB 1 . 
     The changeover circuit EXC outputs a changing signal N 1 . Upon receipt of the changing signal N 1 , the substrate bias control circuit VFBB 1  outputs a PMOS substrate bias signal N 2 , an NMOS substrate bias signal N 3 , a PMOS switch gate signal N 4 , and an NMOS switch gate signal N 5 . Besides, in the substrate bias control circuit VFBB 1 , the standby control circuit VBB 1  outputs the PMOS switch gate signal N 4 , the NMOS switch gate signal N 5 , and control signals N 01  and N 02  when it receives the changing signal N 1 . Moreover, the active control circuit FBB 1  in the substrate bias control circuit VFBB 1  outputs the PMOS substrate bias signal N 2  and the NMOS substrate bias signal N 3  when it receives the control signals N 01  and N 02 . 
     Upon receipt of the PMOS switch gate signal N 4  and the NMOS switch gate signal N 5 , the switching circuit SWC outputs the PMOS substrate bias signal N 2  and the NMOS substrate bias signal N 3  Upon receipt of the PMOS substrate bias signal N 2  and the NMOS substrate bias signal N 3 , the main circuit LSI gives the signals to the substrates of MOS transistors of the main circuit LSI respectively. 
     The main circuit LSI including a CMOS circuit changes its operating speed as the supply voltage changes. The delay time of a CMOS circuit has dependency on the supply voltage as is shown in FIG.  2 . As represented by the curve (A), the delay time increases as the supply voltage decreases. On the other hand, when 0.5-V forward bias is applied to the substrates of the CMOS circuit, the delay time is reduced compared to the curve (A) as represented by the curve (B) and the operating speed is raised. Forward bias means to apply high substrate bias to the substrate. For example, voltage lower than the supply voltage by 0.5 V is applied to the substrate of a PMOS transistor, and voltage higher than the ground voltage by 0.5 V is applied to the substrate of a NMOS transistor. As described above, applying forward bias to a CMOS circuit causes useless leakage currents in the circuit which increase the power consumption or can cause the circuit to misoperation. It tends to induce latch-up phenomena and can damage transistors. However forward bias does not bring about such problems in the case of low-voltage driving. Therefore, the operating speed of a CMOS circuit can be raised in the low-voltage area by applying forward bias to it when it is driven by voltage of, for example, 1 V or less and by applying usual substrate bias to it (applying the supply voltage to the substrate of the PMOS transistor and the ground voltage to the substrate of the NMOS transistor) when it is driven by voltage over 1 V. If the substrate bias is switched based on, for example, the supply voltage, the changeover circuit EXC measures the supply voltage and change the substrate bias to the usual substrate bias of the curve (A) in FIG. 2 when the supply voltage is higher than 0.8 V and to the forward bias of the curve (B) when the supply voltage is lower than 0.8 V. Alternatively, the changeover circuit EXC measures directly the delay time of the CMOS circuit and controls the substrate bias automatically so as to supply the usual substrate bias of the curve (A) when the delay time is shorter than 10 ns and the forward bias of the curve (B) when the delay time is longer than 10 ns. 
     In addition to the above methods, the changeover circuit EXC can be configured so as to change the substrate bias of the CMOS circuit based on instructions from the operation system, instructions from application software, external input signals, signals from a memory, or the like. 
     For the changeover circuit EXC to issue an instruction to supply the usual substrate bias, the changeover circuit EXC asserts the changing signal N 1 . Then the standby control circuit VEB 1  sets the PMOS switch gate signal N 4  to VSUB voltage (−1.5 V) and the NMOS switch gate signal N 5  to VWEL voltage (3.0 V). Upon receipt of the PMOS switch gate signal N 4 , the PMOS transistor of the switching circuit SWC turns on and outputs the supply voltage VDD (e.g., a source voltage) as a PMOS substrate bias signal N 2 . Similarly, upon receipt of the NMOS switch gate signal N 5 , the NMOS transistor of the switching circuit SWC turns on and outputs the ground voltage VSS (e.g., a source voltage) as the NMOS substrate bias signal N 3 . Thus the substrate bias of the main circuit LSI is set by supplying the supply voltage to the substrate of the PMOS transistor and the ground voltage to the substrate of the NMOS transistor. 
     On the other hand, for the changeover circuit EXC to issue an instruction to supply the forward bias, the changeover circuit EXC negates the changing signal N 1 . Then the standby control circuit VBB 1  sets the PMOS switch gate signal N 4  to VWEL voltage (3.0 V) and the NMOS switch gate signal N 5  to VSUB voltage (−1.5 V). Upon receipt of the PMOS switch gate signal N 4 , the PMOS transistor of the switching circuit SWC turns off and outputs 0.5-V forward bias as a PMOS substrate bias signal N 2  from the active control circuit FBB 1 . This 0.5-V forward bias equals to 1.0 V if the supply voltage is 1.5 V. Similarly, upon receipt of the NMOS switch gate signal N 5 , the NMOS transistor of the switching circuit SWC turns off and outputs 0.5-V forward bias as an NMOS substrate bias signal N 3  from the active control circuit FBB 1 . This voltage is 0.5 V because the ground voltage is 0 V. Thus 0.5-V forward bias is applied to the substrates of the main circuit LSJ by applying 1.0 V to the substrate of the PMOS transistor and 0.5 V to the substrate of the NMOS transistor. FIG. 3 shows the waveforms of the PMOS substrate bias signal N 2 , the NMOS substrate bias signal N 3 , the PMOS switch gate signal N 4 , and the NMOS switch gate signal N 5  while the changeover circuit EXC is issuing an assert signal and while it is issuing a negate signal. 
     In the above description, although the supply voltage VDD, the ground voltage VSS, the VWEL voltage, and the VSUB voltage are assumed to be 1.5, 0.0, 3.0, and −1.5 V, those voltages are not limited to these values. It will do if their values are as follows: VWEL&gt;VDD&gt;VSS&gt;VSUB. The same holds true of the description below. 
     FIG. 4 shows another embodiment of a semiconductor integrated circuit device of the present invention. 
     The semiconductor integrated circuit device of the invention comprises a main circuit LSI which is a semiconductor integrated circuit, such as a microprocessor, including a changeover circuit EXC, a substrate bias control circuit VFBB 2 , and a switching circuit SWC. The substrate bias control circuit VFBB 2  comprises a standby control circuit VBB 2  and an active control circuit FBB 2 . 
     The changeover circuit EXC outputs a changing signal N 1 . When the changing signal N 1  and a mode signal ACT/STB are inputted in the substrate bias control circuit VFBB 2 , it outputs a PMOS substrate bias signal N 2 , an NMOS substrate bias signal N 3 , a PMOS switch gate signal N 4 , and an NMOS switch gate signal N 5 . The standby control circuit VBB 2  in the substrate bias control circuit VFBB 2  outputs the PMOS switch gate signal N 4 , the NMOS switch gate signal N 5 , the PMOS substrate bias signal N 2 , and the NMOS substrate bias signal N 3  when it receives the changing signal N 1  and the mode signal ACT/STB. The active control circuit FBB 2  in the substrate bias control circuit VFBB 2  outputs the PMOS substrate bias signal N 2  and the NMOS substrate bias signal N 3  when it receives the changing signal N 1  and the mode signal ACT/STB. 
     Upon receipt of the PMOS switch gate signal N 4  and the NMOS switch gate signal N 5 , the switching circuit SWC outputs the PMOS substrate bias signal N 2  and the NMOS substrate bias signal N 3 . Upon receipt of the PMOS substrate bias signal N 2  and the NMOS substrate bias signal N 3 , the main circuit LSI gives the signals to the substrates of MOS transistors of the main circuit LSI respectively. 
     By applying forward bias to the substrates of the CMOS circuit, its operating speed is raised as indicated by the curve (B) in FIG.  2 . On the contrary, if reverse bias, or low substrate bias, is applied to the substrates of the CMOS circuit, the operating speed and the leakage currents of the CMOS circuit are reduced, reducing the power consumption of the CMOS circuit. In addition, while the main circuit LSI is in its standby mode, the CMOS circuit does not function; therefore the power consumption of the whole circuit can be reduced by applying low substrate bias to the substrates of the CMOS circuit and, thereby, holding down the leakage currents. Accordingly, a semiconductor integrated circuit device operating at a higher speed and consuming less electric power can be made by adding a function to apply reverse bias to the substrates of the CMOS circuit during the standby mode to the function of the changeover circuit EXC to switch the substrate bias between usual substrate bias and forward bias described in the embodiment of FIG.  1 . The main circuit LSI is switched between the standby mode and the active mode by the mode signal ACT/STB. 
     FIG. 5 shows the waveforms of the PMOS substrate bias signal N 2 , the NMOS substrate bias signal N 3 , the PMOS switch gate signal N 4 , and the NMOS switch gate signal N 5  in the active and standby modes while the changeover circuit EXC asserts the changing signal N 1  for the usual substrate bias. While the mode signal ACT/STB is asserted, the main circuit LSI is in the active mode and the standby control circuit VBB 2  sets the PMOS switch gate signal N 4  to VSUB voltage (−1.5 V) and the NMOS switch gate signal N 5  to VWEL voltage (3.0 V) and outputs them. Then the PMOS and NMOS transistors of the switching circuit SWC turn on and the supply voltage VDD (1.5 V) and the ground voltage VSS (0.0 V) are supplied to the PMOS substrate bias signal N 2  and the NMOS substrate bias signal N 3 , respectively, for the main circuit LSI to operate with usual substrate bias. 
     When the mode signal ACT/STB is negated, the main circuit LSI shifts into the standby mode and the standby control circuit VBB 2  sets the PMOS switch gate signal N 4  to VWEL voltage (3.0 V) and the NMOS switch gate signal N 5  to VSUB voltage (−1.5 V) and outputs them. Then the PMOS and NMOS transistors of the switching circuit SWC turn off and, in turn, the standby control circuit VBB 2  supplies VWEL voltage (3.0 V) and VSUB voltage (−1.5 V) to the PMOS substrate bias signal N 2  and the NMOS substrate bias signal N 3 , respectively, to apply back bias to the substrates of the main circuit LSI and, thereby, reduce the standby leakage currents. 
     FIG. 6 shows the waveforms of the PMOS substrate bias signal N 2 , the NMOS substrate bias signal N 3 , the PMOS switch gate signal N 4 , and the NMOS switch gate signal N 5  in the active and standby modes while the changeover circuit EXC negates the changing signal N 1  for forward bias. While the changing signal N 1  is negated, the standby control circuit VBB 2  fixes the PMOS switch gate signal N 4  and the NMOS switch gate signal N 5  to VWEL voltage (3.0 V) and VSUB voltage (−1.5 V), respectively, to turn off each transistor of the switching circuit SWC. While the mode signal ACT/STB is asserted, the main circuit LSI is active and the active control circuit FBB 2  supplies 1.0 V and 0.5 V to the PMOS substrate bias signal N 2  and the NMOS substrate bias signal N 3 , respectively, and, thereby, the main circuit LSI operates with forward bias at a high speed. When the mode signal ACT/STB is negated, the main circuit LSI shifts into the standby mode and the active control circuit FBB 2  turns off. In turn, the standby control circuit VBB 2  supplies VWEL voltage (3.0 V) and VSUB voltage (−1.5 V) to the PMOS substrate bias signal N 2  and the NMOS substrate bias signal N 3 , respectively, so as to apply back bias to the substrates of the main circuit LSI and reduce the standby leakage currents. 
     FIG. 7 shows an embodiment of a changeover circuit EXC. 
     In the case that the changeover circuit EXC is to detect the change of voltage, it comprises a comparator CMP. Supply voltage VDD and reference voltage VREF are inputted in the comparator CMP, which asserts N 1  output when supply voltage VDD is higher than reference voltage VREF and negates N 1  output when supply voltage VDD is lower than reference voltage. For example, if reference voltage VREF is set to 0.8 V, N 1  is asserted for usual substrate bias control when supply voltage VDD is 0.8 V or higher and N 1  is negated for forward bias control when supply voltage VDD is lower than 0.8 V. In this way the changeover circuit EXC detects drops in the supply voltage. FIG. 8 shows an example of specific circuit configurations of the comparator CMP. 
     FIG. 9 shows another embodiment of changeover circuit EXC. The changeover circuit EXC comprises a delay monitor DMON 1 , a phase-frequency comparator PFD, and an up-down counter UDC. The delay monitor DMON 1  outputs a clock signal N 10  of which the frequency corresponds to the supply voltage. Upon receipt of the clock signal N 10  and a reference clock signal CLK, the phase-frequency comparator PFD outputs an up signal N 11  or a down signal N 12 . Upon receipt of the up signal N 11  or the down signal N 12  as the case may be, the up-down counter UDC outputs a changing signal N 1 . The phase-frequency comparator PFD outputs an up signal N 11  when the frequency of the clock signal N 10  is higher than that of the reference clock signal CLK and a down signal N 12  when the former is lower than the latter. The up-down counter UDC counts up upon receipt of an up signal N 11  and counts down upon receipt of a down signal N 12 . When the countdown becomes minimum, that is to say, the frequency of the clock signal N 10  becomes lower than that of the reference clock signal CLK, the up-down counter UDC negates the N 1  output. With the above configuration, the changeover circuit EXC measures the operating speed of the CMOS circuit and detects drops in the operating speed. 
     FIG. 10 shows yet another embodiment of changeover circuit EXC. The changeover circuit EXC comprises a delay monitor DMON 2 , a phase-frequency comparator PFD, and an up-down counter UDC. The delay monitor DMON 2  has a delay time corresponding to the supply voltage and transmits a clock signal with the predetermined delay time to N 13 . Upon receipt of the delay signal N 13  and an input clock signal CLK, the phase-frequency comparator PFD outputs an up signal N 11  or a down signal N 12 . Upon receipt of the up signal N 11  or the down signal N 12  as the case may be, the up-down counter UDC outputs a changing signal N 1 . The phase-frequency comparator PFD outputs an up signal N 11  when the delay time of the delay signal N 13  is shorter than that of the input clock signal CLK and a down signal N 12  when the former is longer the latter. The up-down counter UDC counts up upon receipt of an up signal N 11  and counts down upon receipt of a down signal N 12 . When the countdown becomes minimum, that is to say, the delay time of the delay signal N 13  becomes longer than that of the input clock signal CLK, the up-down counter UDC negates the N 1  output. With the above configuration, the changeover circuit EXC measures the operating speed of the CMOS circuit and detects drops in the operating speed. 
     FIG. 11 shows an example of configurations of the delay monitor DMON 1 . The delay monitor DMON 1  comprises a ring oscillator which is a loop of inverters. The frequency of the clock signal N 10  of the ring oscillator is determined by the supply voltage fed to the inverters and the substrate bias. 
     FIG. 12 shows an example of configurations of the delay monitor DMON 2 . The delay monitor DMON 2  comprises a delay circuit which is a series of inverters. The delay time of the delay signal N 10  of the delay monitor is determined by the supply voltage fed to the inverters and the substrate bias. 
     FIG. 13 shows an example of configurations of the phase-frequency comparator PFD. The phase-frequency comparator PFD compares the phases and the frequencies of two input signals and outputs the results of comparison through N 11  and N 12 . The phase-frequency comparator PFD outputs an up signal N 11  when the phase and the frequency of the input signal N 10  are ahead of and higher than those of the clock signal CLK and a down signal N 12  when the former are behind and lower than the latter. 
     FIG. 14 shows an example of configurations of the up-down counter UDC. The up-down counter UDC comprises an SR flip-flop, a counter CNT, a clock generator CKGEN, and an OR circuit. The counter CNT comprises a JK flip-flop, an inverter circuit, an AND circuit, and an OR circuit. The clock generator CKGEN comprises an OR circuit, an AND circuit, and a NAND circuit. The SR flip-flop receives an up signal N 11  or a down signal N 12 . Upon receipt of an up signal N 11 , the SR flip-flop causes the counter CNT to count up the count outputs Q 0  and Q 1 . Upon receipt of a down signal N 12 , the SR flip-flop causes the counter CNT to count down the count outputs Q 0  and Q 1 . Upon receipt of a Q 0  signal and a Q 1  signal, the OR circuit outputs an N 1  signal. Therefore N 1  is negated only when both the Q 0  and Q 1  signals are “0”. When both the Q 0  and Q 1  signals become “0”, the clock generator CKGEN stops the counter CNT from counting down. When both the Q 0  and Q 1  signals become “1”, the clock generator CKGEN stops the counter CNT from counting up. FIG. 15 shows an example of configurations of the SR flip-flop; FIG. 16, an example of configurations of the JK flip-flop. 
     FIG. 17 shows an example of configurations of the standby control circuit VBB 1 . The standby control circuit VBB 1  comprises an inverter circuit, a level-up level converter LC 1 , a level-down level converter LC 2 , PMOS transistors, and NMOS transistors. When a changing signal N 1  for switching the substrate bias between the usual substrate bias and forward bias is inputted, the NMOS switch gate signal N 5  and the PMOS switch gate signal N 4  become VWEL voltage (3.0 V) and VSUB voltage (−1.5 V), respectively, if N 1  is asserted. Accordingly the MOS transistors of the switching circuit SWC turn on so as to apply the usual substrate bias of supply voltage and ground voltage to the substrates of MOS transistors of the main circuit. On the other hand, when N 1  is negated, the NMOS switch gate signal N 5  becomes VSUB voltage (−1.5 V) and the PMOS switch gate signal N 4  becomes VWEL voltage (3.0 V). Accordingly the MOS transistors of the switching circuit SWC turn off. At the same time, the NMOS switch gate signal N 5  and the PMOS switch gate signal N 4  are outputted as a control signal N 01  and a control signal N 02 , respectively, to the active control circuit FBB 1 . 
     A charge pump CHP 1  and a charge pump CHP 2  generate VWEL voltage and VSUB voltage from the supply voltage VDD and the ground voltage VSS. The level-up level converter LC 1  raises the input voltage of 0.0-1.5 V to 0.0-3.0 V. The level-down level converter LC 2  lowers the input voltage of 0.0-1.5 V to −1.5 to +1.5 V. FIGS. 18 and 19 show examples of configurations of the level-up and -down level converters LC 1  and LC 2 . FIG. 20 shows an example of configurations of the charge pump CHP 1  for generating VWEL voltage; FIG. 21, an example of configurations of the charge pump CHP 2  for generating VSUB voltage. 
     FIG. 22 shows an example of configurations of the active control circuit FBB 1 . The active control circuit FBB 1  comprises a substrate bias generator FBNGEN, a substrate bias generator FBPGEN, amplifiers AMP 1  and AMP 2 , switches MOS 1  and MOS 2 , and current limiters CLCs. The substrate bias generator FBNGEN outputs forward bias substrate potential 0.5 V for NMOS. The substrate bias generator FBPGEN generates bias of 1.0 V when the supply voltage is 1.5 V because the same bias as the substrate potential for NMOS is used for PMOS. The outputs of the substrate bias generators FBPGEN and FBNGEN undergo current amplification by the amplifiers AMP 1  and AMP 2 , respectively. The amplifiers AMP 1  and AMP 2  receive N 4  and N 5  signals to hold down the leakage currents while the active control circuit FBB 1  is not functioning. The output currents of the amplifiers AMP 1  and AMP 2  are held down by the two current limiters CLCs, respectively. Each current limiter CLC may utilize the channel impedance of the MOS transistor or use an ordinary resistor. Each current limiter CLC prevents the leakage currents from growing too large during the application of forward bias. Finally, the outputs of the current limiters CLCs are outputted through the switches MOS 1  and MOS 2 , respectively, as the PMOS substrate bias signal N 2  and the NMOS substrate bias signal N 3 , respectively. 
     FIG. 23 shows an example of configurations of the standby control circuit VBB 2  The standby control circuit VBB 2  comprises a substrate bias generator VBGEN and a circuit utilizing the standby control circuit VBB 1 . Upon receipt of a mode signal ACT/STB, the substrate bias generator VBGEN outputs a PMOS substrate bias signal N 2  and a NMOS substrate bias signal N 3 . When the mode signal ACT/STB is asserted, the output signals ceases. When the mode signal ACT/STB is negated, or the main circuit LSI shifts into its standby mode, the output signal N 2  becomes VWEL voltage and the output signal N 3  becomes VSUB voltage. Upon receipt of a changing signal N 1  and the mode signal ACT/STB, the standby control circuit VBB 1  outputs an NMOS switch gate signal N 5  and a PMOS switch gate signal N 4  through an AND circuit. When both the changing signal N 1  and the mode signal ACT/STB are asserted, that is to say, only when the main circuit LSI is under the usual substrate bias and in its active mode, the NMOS switch gate signal N 5  and the PMOS switch gate signal N 4  become VWEL voltage and VSUB voltage, respectively; otherwise N 5  and N 4  become VSUB voltage and VWEL voltage, respectively. 
     FIG. 24 shows another example of configurations of the active control circuit FBB 2 . The active control circuit FBB 2  receives the changing signal N 1  and the mode signal ACT/STB, and the standby control circuit VBB 1  receives a signal which is made by inverting the N 1  signal through an inverter and a signal which is made when a NAND of the ACT/STB signal is taken. When the active control circuit FBB 1  receives what is outputted accordingly, the active control circuit FBB 2  can output the PMOS substrate bias signal N 2  and the NMOS substrate bias signal N 3 . The active control circuit FBB 2  applies forward bias of 1.0 V and 0.5 V to N 2  and N 3 , respectively, when the signal N 1  is negated and the signal ACT/STB is asserted, namely, only when the main circuit LSI is under the forward bias and in its active mode. In other modes, no outputting is made. 
     The substrate bias control has been described on the ground that there is one control system for the main circuit LSI. However, the main circuit LSI may be divided into at least two or more sections and above-described substrate bias control may be carried out in each section independently. 
     In the above embodiments, since voltage higher than the supply voltage VDD is applied to the standby control circuits VBB 1  and VBB 2 , and the MOS transistor of the switching circuit SWC, a transistor having withstand voltage of the VWEL voltage maybe used A transistor having withstand voltage of the supply voltage VDD may be used as a MOS transistor for other circuits. 
     The foregoing invention has been described in terms of preferred embodiments. However, those skilled, in the art will recognize that many variations of such embodiments exist. Such variations are intended to be within the scope of the present invention and the appended claims.