Substrate bias switching unit for a low power processor

The feature of the present invention consists in: a processor main circuit for executing program instruction strings on a processor chip; a substrate bias switching unit for switching voltages of substrate biases applied to a substrate of the processor main circuit; and an operation mode control unit for controlling, in response to the execution of an instruction to proceed to a stand-by mode in the processor main circuit, the substrate bias switching unit in such a way that the biases are switched over to voltages for the stand-by mode, and for controlling, in response to an interruption of the stand-by release from the outside, the substrate bias switching unit in such a way that the biases are switched over to voltages for a normal mode, and also for releasing, after the bias voltages switched thereto have been stabilized, the stand-by of the processor main circuit to restart the operation.

TECHNICAL FIELD

The present invention relates to a semiconductor integrated circuit device such as a processor, and more particularly to a microprocessor which is capable of realizing the high speed operation as well as the low power consumption by controlling substrate biases of a processor circuitry constituted by MOS transistors in accordance with an operation mode of the processor.

At the present time, for realization of a microprocessor, an integrated circuit employing CMOSs is widely used. The power consumption of the CMOS circuit is classified into the dynamic power consumption due to charge and discharge during the switching, and the static power consumption due to a leakage current. Out of them, since the dynamic power consumption is proportional to a power, source voltage Vdd squared and hence occupies the large power consumption, in order to promote the low power consumption, it is effective to reduce the power source voltage. Then, in recent years, the power source voltages of many microprocessors have been reduced.

As for the present low power consumption type microprocessor, there is known the microprocessor which includes the power management mechanism and which has a plurality of operation modes provided therein and in accordance therewith, stops the supply of a clock to execution units during the stand-by. By stopping the clock supply, the dynamic power consumption due to the switching in the unnecessary units can be reduced as much as possible. However, the static power consumption due to the leakage current can not be reduced and hence still remains.

Since the operation speed of the CMOS circuit is decreased along with reduction of the power source voltage, in order to prevent the degradation of the operation speed, the threshold voltage of the MOS transistor needs to be reduced in conjunction with the reduction of the power supply voltage. However, since if the threshold voltage is reduced, then the leakage current is remarkably increased, along with the reduction of the power source voltage, the increase of the static power consumption due to the leakage current which was not conventionally large so much becomes remarkable. For this reason, it becomes a problem to realize a microprocessor in which the high speed is compatible with the low power consumption.

As for a method of solving the problem associated with both the operation speed and the leakage current of the MOS transistor circuit, a method wherein the threshold voltage of the MOS transistor is controlled by setting variably the substrate biases is disclosed in JP-A-6-53496.

The description will hereinbelow be given with respect to the device structure for use in setting variably the substrate biases with reference toFIG. 2.FIG. 2shows a cross sectional view of a circuit having the CMOS structure. As shown in the figure, an n type well205is formed in a part of a surface layer of a p type well (p type substrate)201, an n-channel MOS transistor consisting of an n+type source/drain region202, a gate oxide film203and a gate electrode204is formed on a surface of the p type well201, and a p-channel MOS transistor consisting of a p+type source/drain region206, a gate oxide film207and a gate electrode208is formed on a surface of the n type well205.

Normally, the source of the p-channel MOS transistor and the source of the n-channel MOS transistor are respectively connected to the power source voltage (hereinafter, referred as Vdd) and the ground electric potential (hereinafter, referred as Vss), and the drains of the n-channel MOS transistor and the p-channel MOS transistor are connected to the output signal. As for terminals through which the substrate biases are given, Vbp209is provided in the n type well205of the p-channel MOS transistor, and Vbn210is provided in the p type well201of the n-channel MOS transistor.

While when employing the device as shown inFIG. 2, normally, Vbp209is connected to Vdd and Vbn210is connected to Vss, during the non-operation of the circuits, these substrate biases are switched so that Vbp209is connected to the higher electric potential and Vbn210is connected to the lower electric potential, whereby the threshold voltages of the MOS transistors can be increased and hence the leakage current can be reduced.

DISCLOSURE OF THE INVENTION

In order to realize a microprocessor in which the high speed operation is compatible with the low power consumption, it is required that for the processor circuitry, the variable control of the substrate biases as described above is carried out, and during the operation of the processor, the threshold voltages of the MOS transistors are decreased to maintain the high speed operation, while during the stand-by thereof, the threshold voltages are increased to reduce the leakage current. However, in order to control variably the substrate biases of the processor, the timing of reactivating the processor in the proceeding of the operation mode of the processor when switching the substrate biases, in particular in the proceeding of the operation mode from the stand-by state to the operation state is accurately controlled, whereby the malfunction of the processor must be prevented.

The present invention was made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a high speed and low power consumption processor by realizing the above-mentioned substrate bias control, on a processor chip, which is applied to the various operation modes of the processor.

In order to solve the above-mentioned problems, a feature of the present invention is provided by providing: a processor main circuit for executing program instruction strings on a processor chip; a substrate bias switching unit for switching voltages of substrate biases applied to a substrate of the processor main circuit; and an operation mode control unit for controlling, in response to the execution of an instruction to proceed to a stand-by mode in the processor main circuit, the substrate bias switching unit in such a way that the biases are switched over to voltages for the stand-by mode, and for controlling, in response to an interruption of the stand-by release from the outside, the substrate bias switching unit in such a way that the biases are switched over to voltages for a normal mode, and also for releasing, after the bias voltages switched thereto have been stabilized, the stand-by of the processor main circuit to restart the operation.

In addition, another feature of the processor according to the present invention is that a semiconductor device of the processor chip has a triple well structure, and also the processor main circuit is formed on a well region different from those of the substrate bias switching unit and the operation mode control unit.

In addition, still another-feature of the processor according to the present invention is that the operation mode control unit includes, as means for waiting, before restarting the operation of the processor main circuit when switching the biases, until the bias voltages switched thereto are stabilized, either an on-chip timer for measuring a lapse of the time period required for stabilizing the biases, or a sensor for detecting that the biases have been stabilized to predetermined voltages.

In addition, yet another feature of the processor according to the present invention is provided by providing: the processor main circuit in which the semiconductor device of the processor chip has a triple well structure and is divided into a plurality of functional modules which are respectively formed on the different wells; a substrate bias switching unit for switching the substrate biases to the substrate of the respective functional modules; a operation mode control unit for controlling, in response to execution to make stand-by one functional module or the plurality of functional modules in the processor main circuit, the substrate bias switching unit in such a way that the substrate biases of the one functional module or the plurality of functional modules are switched over to the voltages for the stand-by mode, and for controlling, when having received a signal to release the stand-by mode of the one functional module or the plurality of functional modules from the outside or the processor main circuit, the substrate bias switching unit in such a way that the biases are switched over to the voltages for a normal mode, and also for informing, after the bias voltages switched thereto have been stabilized, the processor main circuit of that the stand-by of the one functional module or the plurality of functional modules has been released.

In addition, a further feature of the processor according to the present invention is provided by providing: means for switching dynamically the operation speed of the processor main circuit; and an operation mode control unit for controlling, in response to execution of an instruction to change the operation frequency in the processor main circuit, the substrate bias switching unit in such a way that the substrate biases of the processor main circuit or the functional modules are switched to voltages which are suitable for the operation frequency thereof, and for informing, after the bias voltages switched thereto have been stabilized, the processor main circuit of that the switching of the operation speed has been completed.

Further, an even further feature of the processor according to the present invention is that the substrate bias switching unit is constituted by a substrate bias generating circuit for generating therein the voltages of the substrate biases.

In addition, the present invention also proposes a control method contributing to the promotion of the low power consumption of the device. That is, since while the transistor having the low threshold is operated at a high speed, the leakage current passing between the source and the drain is large to increase the power consumption, it is important to prevent the large leakage current therebetween.

As for the construction therefor, there is provided a control method of controlling the power consumption of a semiconductor integrated circuit device including a plurality of element circuit blocks having transistors formed on a semiconductor substrate and being operated on the basis of a clock signal, wherein a first mode in which all the element circuit blocks are operated on the basis of the clock signal, a second mode in which the supply of the clock signal to at least one of the element circuit blocks is stopped, and a third mode in which the supply of the clock signal to all the element circuit blocks is stopped and also substrate biases of at least part of the transistors formed on the semiconductor substrate are controlled to increase thresholds of the associated transistors are switched to be used.

A main circuit is, for example, a processor including a CPU and the like. The first mode is a mode wherein the main circuit carries out the normal operation (computing, storage or the like).

The second mode is a state in which the supply of the clock to a part of the processor is stopped, and is called a sleep mode, a deep sleep mode or the like for example. By selecting the range in which the clock is stopped, it is possible to promote the low power consumption while maintaining only the necessary functions.

The third mode is a mode wherein the substrate biases are controlled for the circuits of the processor so as to increase the thresholds of the transistors constituting the circuits to reduce the power consumption due to the sub-threshold leakage current, and is referred to as a stand-by mode or a hardware stand-by mode for example. While the operation mode can be returned from the stand-by mode to the normal state by the interruption control, in the hardware stand-by mode, the operation mode can be returned thereto by only the reset. In the third mode, the functions of the main circuit are stopped.

As for the construction of the overall circuitry, the element circuit blocks are included in a first circuit block, and the clock signal is formed from an oscillation circuit included in a second circuit block, and the clock signal and the information signals which are to be processed in the first circuit block are inputted from the second circuit block to the first circuit block. In addition to the oscillation circuit, an I/O circuit, and a control circuit for controlling the substrate biases are included in the second circuit block. Normally, the high speed operation is not required for the second circuit block so much as for the first circuit block. Then, it is desirable that the thresholds of the transistors constituting the second circuit block are larger than those of the transistors constituting the first circuit block and also the operation voltages of the former are higher than those of the latter. In addition, the transistors constituting the main circuit of the first circuit block are formed on the well different from those of other circuits, whereby the influence of other circuits thereupon can be reduced.

When the operation voltages of the first circuit block are different from those of the second circuit block, level conversion circuits are required to be provided between the first and second circuit blocks. For example, in order to carry out the conversion of the signal level, a level-down circuit is provided in the first circuit block, while a level-up circuit is provided in the second circuit block.

Since in the present invention, by switching the mode of the interest over to another mode, the substrate bias voltages are dynamically switched, in order to ensure the reliability, the operation sequence thereof is important.

When switching the operation mode from the first or second mode to the third mode, firstly, the clock signal which is inputted from the second circuit block to the first circuit block, and the information signals which are inputted to the first circuit block in order to be processed therein are stopped, and next, the substrate biases of at least part of the transistors formed on the semiconductor substrate are controlled to increase the thresholds of the associated transistors. As a result, the input to the first circuit block in the state in which the operation of the first circuit block is unstable can be blocked and also the malfunction of the first circuit block can be prevented.

For this operation, the procedure may be adopted in which after the signal inputs to the first circuit block are stopped and the device waits for a predetermined time period (e.g., 60 μsec. or so) through a timer or the like, the substrate biases are controlled. The timer for waiting is provided in the outside of the first circuit block, e.g., either in the second circuit block or in the outside of the device.

In addition, when switching the operation mode from the third mode (stand-by mode) to the first mode, the substrate biases of at least part of the transistors formed on the semiconductor substrate are controlled to decrease the thresholds of the associated transistors, and next, the input of the above-mentioned clock signal which is inputted from the second circuit block to the first circuit block and the information signals which are to be processed in the first circuit block is started. That is, in order to prevent the malfunction of the first circuit block, after the substrate voltages of the first circuit block have been stabilized, the input of the signals is started.

For this reason, when switching the operation mode from the third mode to the first mode, after the substrate biases of the first circuit block are controlled to decrease the thresholds of the associated transistors and the device waits for a predetermined time period by the timer so that the operation is stabilized, the input of the clock signal which is to be inputted to the first circuit block and other signals is started.

Another method is such that after the state of the thresholds of the transistors have been confirmed by a voltage monitor or the like, the signal input to the first circuit block is started. Or, on the basis of the state of a substrate bias generating circuit for controlling the substrate voltages, in accordance with the signal which is outputted from the substrate bias generating circuit in order to report the stand-by release, the input of the clock signal and other signals which are to be inputted to the first circuit block is started.

As for a method of stopping the information signals and the clock signal to the first circuit block, it is considered that the signal levels are fixed by an output fixing circuit (level holding circuit) provided in the second circuit block. In the first mode, while the signals are inputted to the level-down circuit through the output fixing circuit, in the third mode, the inputs to the level-down circuit are fixed.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1is a block diagram showing an example of a configuration of a processor chip for realizing a first embodiment of the present invention. InFIG. 1, a processor chip101is an LSI having a circuit of a CMOS structure, and includes a processor main circuit102, an operation mode control unit103, and a substrate bias switching unit104. To the substrate bias switching unit104, voltages Vdd and Vss in the normal mode, and voltages Vddb and Vssb in the stand-by mode are inputted through a signal110. In accordance with a signal107outputted by the operation mode control unit, the substrate bias switching unit104selects, as the substrate bias for a p-channel MOS transistor constituting the processor main circuit102, between Vdd and Vddb to output the selected one to a signal Vbp111, and also selects, as the substrate bias for an n-channel MOS transistor, between Vss and Vssb to output the selected one to a signal Vbn112. As for the voltage values for the substrate bias selection, for example, Vdd=1.5V, Vddb=3.0V, Vss=0.0V and Vssb=−1.5V.

Incidentally, as will be described later, a well302on which the processor main circuit102is formed is formed separately, independently of wells on which the substrate bias switching unit104and the operation mode control unit are respectively formed.

FIG. 3is a cross sectional view showing a device structure of the processor chip101. A point of difference ofFIG. 3fromFIG. 2is that a p type well302is formed in an n type substrate301and the n type well205is formed in a part of the surface layer of the p type well302, i.e., the device has a triple well structure. An n-channel MOS transistor is formed on the surface of the p type well302and a p-channel MOS transistor is formed on the surface of the n type well205, thereby to constitute a CMOS circuit. In addition, a point that as for terminals through which the substrate biases are given, Vbp209is provided in the n type well205of the p-channel MOS transistor and Vbn210is provided in the p type well302of the n-channel MOS transistor is the same as inFIG. 2. In the present embodiment, the processor main circuit102is formed in the p type well302different from those of the operation mode control unit103and the substrate bias switching unit104. As a result, the substrate bias control influences only the processor main circuit102, and hence both the operation mode control unit103and the substrate bias switching unit104can avoid that influence.

The description will hereinbelow be given with respect to the operation of the processor chip101in the present embodiment with reference toFIG. 4. The operation modes of the processor main circuit102are classified into the normal mode in which the normal instruction execution is carried out, and the stand-by mode in which the instruction execution is not carried out.FIG. 4is a flow chart showing the processing on the processor chip101in the case where the operation mode of the processor main circuit102is changed from the normal mode to the stand-by mode and then is changed from the stand-by mode to the normal mode.

Firstly, the processor main circuit102is operated in the normal mode. At this time, the sub-strate bias switching unit104selects Vdd and Vss for the substrate biases Vbp111and Vbn112, respectively. For the voltage values of the substrate biases in the normal mode in this example, Vbp=1.5V and Vbn=0V (Step401).

After the processor main circuit102outputs, after having executed the sleep instruction, “stand-by request” to the signal105and then informs the operation mode control unit103of this fact, the processor main circuit102stops the operation of executing the instruction and then proceeds to the stand-by mode (Step402).

After having received the signal105from the processor main circuit, the operation mode control unit103outputs the signal107in order for the substrate biases of the processor main circuit102to be switched over to the voltages for the stand-by mode. Then, in response to the signal107, the substrate bias switching unit104selects Vddb and Vssb, out of the input voltages110, for the substrate biases Vbp111and Vbn112, respectively, to output Vddb and Vssb (Steps403and404). In this example, for the voltage values of the substrate biases in the stand-by mode, Vbp=3.0V and Vbn=−1.5V.

When the operation mode control unit103detects that when the processor main circuit102is in the stand-by state, “stand-by release interruption” is asserted from the outside to a signal108(Step405), the unit103outputs the signal107in order for the substrate biases of the processor main circuit102to be switched over to the voltages for the normal mode. Then, in response to the signal107, the substrate bias switching unit104switches the substrate biases Vbp111and Vbn112over to Vdd (1.5V) and Vss (0.0V), respectively (Step406).

Since there is the possibility that a lapse of some time period is required until the biases are stabilized after having switched the substrate biases, if the operation of the processor main circuit102is immediately restarted, then the malfunction may occur. In order to avoid this possibility, before switching the operation mode of the processor main circuit102, the operation mode control unit103sets a sufficient time period required for stabilization of the substrate bias voltages switched thereto in an on-chip timer109and then restarts the processor main circuit102(Step407) and then waits until time-out (Step408). Then, after time-out, the operation mode control unit103outputs “stand-by release” to the signal106and then informs the processor main circuit102of this fact. In response to the signal106, the processor main circuit102proceeds to the normal mode and restarts the operation of executing an instruction (Step409).

In such a way as described above, the substrate biases Vbp111and Vbn112of the processor main circuit102are controlled such that during the operation, the threshold voltages of the MOS transistors constituting the processor main circuit are decreased to cope with the high speed operation, while during the stand-by, the threshold voltages thereof are increased to able to reduce the leakage current.

FIG. 5is a block diagram showing a configuration of the processor chip in a second embodiment of the present invention. In the present embodiment, the operation mode control unit103includes a sensor501for detecting the bias voltages which are applied to the substrate of the processor main circuit102. When the operation mode of the processor main circuit102is changed from the normal mode to the stand-by mode, the processing procedure in the above-mentioned first embodiment is applied to the present embodiment. On the other hand, when the operation mode of the processor main circuit102is changed from the stand-by mode to the normal mode, similarly to the above-mentioned embodiment, after the operation mode control unit103has controlled the substrate bias switching unit104so as to switch the substrate biases to the voltages for the normal mode, the unit103waits until the sensor501outputs the signal relating to the fact that the voltages of the substrate biases switched thereto are stabilized to the predetermined values, i.e., Vbp=1.5V and Vbn=0.0V in the present embodiment to a signal502. When the sensor501outputs the stabilization of the substrate biases to the signal502, then the operation mode control unit103outputs “stand-by release” to the signal106in order to restart the operation of the processor main circuit102.

FIG. 6is a block diagram showing a configuration of a processor chip in a third embodiment of the present invention. As for the basic device structure of a processor chip601, the triple well structure as shown inFIG. 3is assumed. In the processor chip601ofFIG. 6, the processor main circuit includes a CPU604, and a plurality of functional modules such as a module A606and a module B608. The functional modules are present separately on the respective different well regions and hence one functional module is not influenced by the substrate bias control for other functional modules. The functional module includes the elements, each having the smaller scale unit, such as a CPU, an FPU, a cache, or a computing element. Substrate bias switching units605,607and609are respectively provided so as to correspond to the functional modules604,606and608, and can switch, similarly to the above-mentioned embodiments, the substrate biases of the corresponding functional modules. The execution of the instruction is carried out with the CPU, as one of the functional modules, as a center, and hence if any instruction to make stand-by any unnecessary functional module for execution is executed, then the operation mode control unit602is informed of that the functional module of interest is in the stand-by state.

Next, the description will hereinbelow be given with respect to the operation of the processor chip601in the present embodiment. Firstly, it is assumed that all the functional modules are operated in the normal mode. After having executed the instruction to make stand-by the module A, the CPU604outputs the stand-by request to a signal610, and thereafter, it is impossible to use that module until the stand-by of the module A606is released. After having received the signal610, the operation mode control unit602outputs a signal612to the substrate bias switching unit607and then switches the substrate biases of the module A606over to the voltages for the stand-by mode. When the module A606is in the stand-by state, after the operation mode control unit602has received the signal610from the CPU604or a signal relating to the stand-by release of the module A606from the signal613outside of the processor chip601, the unit602outputs the signal612to the substrate bias switching unit607and then switches the substrate biases of the module A over to the voltages for the normal mode. Then, similarly to the first embodiment of the present invention, the operation mode control unit602waits the stabilization of the substrate biases switched thereto using an on-chip timer603, and after the stabilization thereof, informs the CPU604through a signal611of that the stand-by of the module A is released. After the CPU604has received this signal611, it becomes possible to execute the instruction using the module A.

The foregoing is applied to the stand-by control for the module B608as well as other functional modules. In addition, the CPU604itself is an object of the stand-by control. In this case, the functional module B608and other functional modules are controlled similarly to the case of the above-mentioned module A604except that after having proceeded to the stand-by mode, the CPU604stops all the instructions from being executed, and when the signal relating to the stand-by release of the CPU604has been asserted to the external signal613, the operation mode control unit602asserts the stand-by release of the CPU604to the signal611after completion of the switching of the substrate biases of the CPU604, thereby restarting the execution of the instructions of the CPU604.

By the stand-by control in functional modules in the present embodiment, it is possible to reduce the leakage current of any functional module which is unnecessary during the operation of the processor.

FIG. 7is a block diagram showing a configuration of a processor chip in a fourth embodiment of the present invention. A point of difference of the present embodiment from the first embodiment is that voltages701which are supplied from the outside to the substrate bias switching unit104are increased in kind so that the substrate bias switching unit104can select, as the substrate biases, the suitable voltages among these voltages701to apply them to the processor main circuit102. In the present embodiment, it is assumed that means for changing dynamically the operation speed of the processor main circuit102, i.e., the operation frequency thereof on the basis of an instruction, and the operation modes of the processor main circuit102are classified into a high speed mode and a low speed mode. In the present embodiment, Vdd (for the p-channel MOS transistor) and Vss (for the n-channel MOS transistor) are selected as the substrate biases corresponding to the high speed mode. Vddb2 (for the p-channel MOS transistor) and Vssb2 (for the n-channel MOS transistor) are selected as the substrate biases corresponding to the low speed mode, and Vddb1 (for the p-channel MOS transistor) and Vssb1 (for the n-channel MOS transistor) are selected as the substrate biases corresponding to the stand-by mode.

Next, the description will hereinbelow be given with respect to the operation of the processor chip101in the present embodiment. Now, it is assumed that the operation mode of the processor main circuit102is switched from the high speed mode over to the low speed mode. While the processor main circuit102is being operated in the high speed mode, as the substrate biases for the processor main circuit, the substrate switching unit104selects Vdd and Vss for Vbp111and Vbn112, respectively. After having executed the instruction to proceed to the low speed mode, the processor main circuit102outputs this request to the signal105to suspend the operation of executing the instruction. A clock which is supplied to the processor main circuit102is switched over to a low frequency on the basis of execution of the instruction to proceed to the low speed mode. After having received the signal105, the operation mode control unit103outputs the signal107in order to switch the substrate biases of the processor main circuit102over to the voltages for the low speed mode. In response to the signal107, the substrate bias switching unit104switches the substrate biases Vbp111and Vbn112over to Vddb2 and Vssb2, respectively. Similarly to the above-mentioned embodiments, the operation mode control unit103maintains the stability of the substrate biases switched thereto using the on-chip timer109, and informs the processor main circuit102through the signal106of that the proceeding to the low speed mode has been completed. After having received the signal106, the processor main circuit102restarts the suspended operation of executing the instruction in the low speed mode.

Since the operation in switching the operation mode from the low speed mode to the high speed mode, in switching the operation mode from the high speed mode or the low speed mode to the stand-by mode, or in switching the operation mode from the stand-by mode to the high speed mode or the low speed mode in the present embodiment is also similar to the foregoing, the details thereof will be omitted here. In the present embodiment, it is also possible that the operation speed is further subdivided and the substrate bias control corresponding thereto is carried out. In addition, it is also possible as in the third embodiment, the processor main circuit102is separated in functional modules by utilizing the triple well structure of the device, and for every functional module, the substrate biases are controlled in conjunction with the switching of the operation frequency thereof.

As in the present embodiment, the substrate bias control which is suitable for the operation frequency of the processor is carried out, whereby it is possible to reduce the leakage current in the low speed operation mode. In addition, since in the low speed mode, the range of the input voltages by which both the p-channel MOS transistor and the n-channel MOS transistor of the CMOS circuit are caused to conduct at the same time is narrower than that in the high speed operation mode, there is also provided the effect that the passing through current during the switching is reduced.

FIG. 8is a block diagram showing a configuration of a processor chip in a fifth embodiment of the present invention. A point of difference of the present embodiment from the above-mentioned first embodiment is that the above-mentioned substrate bias switching unit is constituted by a substrate bias generating unit801. The substrate bias generating circuit801is controlled by an output signal802of the operation mode control unit103so that it generates in the inside the voltages of the substrate biases to output these voltages to Vbp111and Vbn112, respectively. The voltage values of the substrate biases Vbp111and Vbn112which are generated in correspondence to the operation mode of the processor main circuit102under the control by the operation mode control unit103are the same values as those in the first embodiment. Since the operations of the processor main circuit102and the operation mode control unit103are the same as those in the first embodiment, the details thereof will be omitted here. In addition, similarly to the present embodiment, the substrate bias switching unit in the second, third and fourth embodiments is constituted by the substrate bias generating circuit801, whereby the substrate biases can be generated in the inside of the processor chip to switch the substrate biases thus generated in accordance with the operation mode.

As described above, according to these embodiments, since the timing of reactivating the processor in the proceeding from the stand-by state to the operation state is accurately controlled using either the timer or the sensor, the optimal substrate bias control corresponding to the operation mode of the processor becomes possible. As a result, the leakage current can be reduced in the stand-by mode while maintaining the high speed when the operation mode of the processor is the normal mode. In addition, the substrate bias control is carried out in accordance with the operation mode by the functional module, whereby even when the processor is in operation, the leakage current of any functional module which is unnecessary for the execution can be reduced. Further, the substrate bias control which is suitable for the operation frequency of the processor is carried out, whereby in addition to the reduction of the leakage current in the low speed mode, there is also obtained the effect that the passing through current in the switching can be reduced.

As a result, the reduction of the power consumption can be effectively realized and also it is possible to provide a microprocessor in which the high speed operation is compatible with the low power consumption.

Hereinbelow, as an embodiment of a microcomputer, the operation mode in which the substrate biases are controlled will be described concretely. Then, it is assumed that the microcomputer has two power sources, i.e., a 1.8V power source and a 3.3V power source, and the substrate bias control is carried out by only the 1.8V power source. It is desirable that the circuit for supplying 1.8V is constituted by a MOS transistor having a relative low threshold (e.g., Vth<0.4V or so).

FIG. 9shows one example of the operation modes of the microcomputer. The operation modes are classified into a normal operation mode981in which the microcomputer is normally operated, and a reset mode982. The modes in each of which the microcomputer is operated with the low power consumption are classified into a sleep mode983, a deep sleep mode984, a stand-by mode985, a hardware stand-by mode986, and an RTC (real time clock) battery back-up mode. In addition, as the test mode, there is an IDDQ measurement.

Since the high speed operation is required during the normal operation982, no control for the substrate biases is carried out. Since all the functions need to be reset during the reset981, no control for the substrate biases is carried out. While in the low power consumption modes, no control for the substrate biases is carried out during the sleep983and the deep sleep984each having a short time period required for return from each of the low power consumption modes, in the case of the stand-by985and the hardware stand-by986in each of which emphasis is put on that the power consumption is reduced rather than the return time period, the substrate bias control is carried out. The RTC battery back-up mode is a mode wherein the voltage from only the power source for the RTC circuit operating at 3.3V is supplied. Since to the RTC battery back-up mode, the transition is made from the low power consumption mode, the substrate bias control is carried out. In addition, since the IDDQ measurement is a mode wherein the stand-by current is measured to measure the passing through current due to the short-circuit or the failure of the transistor, in this case, it is required that the substrate biases are necessarily controlled so as to reduce the leakage electric power of the chip to make the discovery of the failure easy.

Prior to description of the low power consumption operation modes, the description will hereinbelow be given with respect to a configuration of internal blocks of a processor main circuit902with reference toFIG. 10. This figure is one example of the main constituent blocks of the processor main circuit. As for computing circuits, there are a CPU (central computing processing unit)971and an FPU (floating-point computing unit)972. In addition thereto, there are a cache973as a memory self contained in the chip, a BSC (bus control unit)974for carrying out the interface with an external memory, a DMAC (DMA control unit)975for carrying out the DMA (direct memory access), an SCI (serial control unit)976for controlling a serial port, an INTC (interruption control unit)977for controlling an interruption input, a CPG (clock control unit)978for controlling a clock, and the like.

The description will hereinbelow be given with respect to the sleep983, the deep sleep984and the stand-by985as the low power consumption modes with reference toFIG. 11.

In the sleep983, only the clock for the computing units such as the CPU971, the FPU972, and the cache973is stopped and also the substrate bias control is not carried out. Therefore, though the power consumption can not be greatly reduced, the DMA transfer through the DMAC975, and the normal refresh (refresh at the rate of 102 times/16 msec.) for the DRAM (dynamic RAM) and the SDRAM (synchronous dynamic RAM) through the BSC974are possible. Since the CPG978is in operation and the substrate bias control is not carried out, the time period required for return from the sleep983to the normal operation mode982is short.

Since in the stand-by985mode, all the operating clocks are stopped and also the substrate bias control is carried out, the power consumption is very small. Also, since all the clocks are stopped, it is impossible to carry out the DMA transfer. In addition, with respect to the refresh for the DRAM and the SDRAM, it is required that the control signals (RAS signal, CAS signal) for the memories are set using the BSC974in such a way that before entering into the stand-by985, the mode becomes the self-refresh mode wherein the memories carry out the refresh by themselves. But, the time period required for return from the stand-by985to the normal operation982becomes long due to waiting for stability of the clock oscillation and a lapse of the time period required for return from the substrate biasing state since all the clocks are stopped.

The deep sleep984mode is the low power consumption mode between the sleep983and the stand-by985.

The differences in operation modules between the sleep983and the deep sleep984are shown inFIG. 12. Since the BSC973, the DMAC974and the SCI975which are operated during the sleep983are stopped during the deep sleep984, the power consumption can be reduced so much.

But, in the deep sleep984mode, the DMA transfer can not be carried out and also the refresh of the memories becomes the self-refresh. The time period required for return from the deep sleep984to the normal operation982is, similarly to the sleep mode, short.

In such a way, the three kinds of low power consumption modes are provided, whereby the fine low power consumption control can be carried out in accordance with the application.

FIG. 13shows a state transition diagram of the operation modes in order to give the description thereof. On the basis of a RESET#952(or, a power-on reset) pin input from a state980in which all the power sources are turned off, the processor chip makes transition to a reset state981. When RESET#952is negated, the processor chip makes transition to the normal operation982. Then, the processor chip makes transition from this state to the low power consumption operation mode.

There are two transition methods. One transition method is the transition based on an instruction. The CPU971executes a sleep instruction, thereby making this transition. A mode register is set in executing the sleep instruction, whereby the selection can be made among the sleep983, the deep sleep984and the stand-by985, and the processor chip can make transition to the selected one of these modes. The return from each of these modes to the normal operation mode982is carried out on the basis of an instruction958.

The other transition method is the transition based on a HARDSTB#951pin. When having asserted this pin, the processor chip makes transition to a hardware stand-by state986. This state is a state wherein similarly to the stand-by985, all the clocks are stopped and also the substrate bias control is carried out too.

If in this mode, the impedance of an I/O buffer is made high, then no transistor having the passing through current flowing therethrough is present in the 3.3V system circuit, and hence the IDDQ measurement becomes possible.

In addition, if an input buffer of an RTC circuit provided in the 3.3V system circuit is fixed, even when the power sources for the constituent elements other than the RTC circuit are turned off, the input signal to the RTC circuit does not become at floating (at an intermediate level). Therefore, the malfunction of the RTC circuit can be prevented and only the RTC circuit can be operated.

Next, the description will hereinbelow be given with respect to an application example of the hardware stand-by.

FIG. 14shows configurations of a processor chip901and a power source control circuit in which the hardware stand-by is applied to enable a power source (battery)904of the processor chip901to be exchanged.

The processor chip901is constituted by a 1.8V region circuit930which is operated at 1.8V and a 3.3V region circuit931which is operated at 3.3V. The 1.8V region circuit930includes a processor main circuit902, and level-down circuits905and906each of which carries out the level conversion from 3.3V down to 1.8V. The 3.3V region circuit931includes a substrate bias generating circuit903, a clock oscillation circuit908, an I/O circuit909, an operation mode control unit913, an RTC circuit914, level-up circuits904and910each of which carries out the level conversion from 1.8V up to 3.3V, and output fixing circuits907and911each of which fixes a signal from 3.3V to 1.8V.

A control circuit for a power source system includes a power source904, a power source monitoring circuit921, a display921, and a voltage producing circuit920for producing a voltage for a 1.8V system.

The operation will hereinbelow be described. When the processor chip901is in the normal operation mode982, the substrate bias generating circuit903holds the normal substrate levels (e.g., the electric potential VDD for the p-channel MOS transistor, and the electric potential VSS for the n-channel MOS transistor) without carrying out the subtraction with respect to the substrate biases. The clock generating circuit908includes a PLL (phase-locked loop) and the like, and produces a clock for the internal operation to send it to the processor main circuit902through the output fixing circuit907and the level-down circuit905. The I/O circuit909fetches in a signal from the outside to send it to the processor main circuit902through the output fixing circuit907and the level-down circuit905. In addition, the I/O circuit909outputs a signal from the processor main circuit902to the outside through the level-up circuit904. The RTC circuit914is operated at 3.3V, and receives a control signal from the processor main circuit902through the level-up circuit910to transmit a control signal to the processor main circuit902through the level-down circuit906and the output fixing circuit911. The operation mode control unit913carries out, in particular, the control for the substrate bias generating circuit903.

The power source monitoring circuit921monitors the voltage level of the power source904. When the voltage level has been decreased down to a level lower than a predetermined level (When having detected the exhaustion state of the battery), the circuit921makes HARDSTB#951the low level. At the same time, the circuit921displays the alarm for the battery exhaustion on the display922to inform a user of this fact. Even in the state in which the voltage level has been decreased, the voltage holding circuit923can hold the voltage level for a predetermined time period (ranging from several minutes to several hours). For this time period, a user can exchange the power source.

The description will hereinbelow be given with respect to a power source exchanging sequence with reference toFIG. 15.

(1) HARDSTB#951becomes the low level, whereby the operation mode enters into the hardware stand-by state986. Now, 1.8V signal fixing953is outputted from the operation mode control unit913to fix the signal from 3.3V to 1.8V and also to stop a 1.8V system clock. As a result, even when carrying out the subtraction with respect to the substrate biases, the signal of 1.8V system is not operated. Therefore, the malfunction of the 1.8V system circuit in the state of carrying out the subtraction with respect to the substrate biases (the state in which since the threshold voltages of the MOS transistors are increases, the operation speed thereof is low and hence the substrate electric potentials are unstable) is prevented. In this state, a substrate bias control starting signal955is outputted to the substrate bias producing circuit903.

(2) Thereafter, on the basis of the timing of the 1.8V signal fixing953, the substrate bias control starting signal955is outputted to the substrate bias producing circuit903. In actual, the signal is fixed between the signal fixing953and the substrate bias control start955, and hence a time difference until the supply of the signals to the 1.8V region is stopped is set therein. This time difference can be measured by the timer bases on the RTC clock of the RTC circuit914.

(3) In response to the substrate bias control starting signal955, the substrate bias generating circuit903starts carrying out the subtraction with respect to the substrate biases for the 1.8V system substrate. For a time period of carrying out the subtraction with respect to the substrate biases, a substrate bias in-control956signal is returned back to the operation mode control unit913.

(4) In the state of carrying out the sub-traction with respect to the substrate biases, the processor main circuit902is not operated. In addition, since the leakage current is small, the consumption quantity of current is small. As a result, the hold time of the voltage holding circuit923becomes long.

(5) Under this state, the power source904is exchanged.

(6) Since after having exchanged the power source, the power source voltage recovers the normal level, HARDSTB#951returns to the high level.

(7) Thereafter, the power-on reset circuit is operated and RESET#952is inputted thereto. On the basis of this reset input, the substrate bias control starting signal955which is outputted from the operation mode control unit913is released.

(8) In response to release of the substrate bias control starting signal955, the substrate bias generating circuit903starts returning the substrate biases of the substrate to the electric potentials in the operation state (e.g., the electric potential VDD for the p-channel MOS transistor, and the electric potential VSS for the n-channel MOS transistor). A predetermined time period is required until recovery of the substrate biases, and after completion of the recovery of the substrate biases, the substrate bias in-control signal956is released to inform the operation mode control unit913of this result.

(9) In response to release of the substrate bias in-control signal956, the 1.8V signal fixing953which is outputted from the operation mode control unit913is released, and then the signals are inputted to the 1.8V system circuits such as the processor main circuit902and the like.

(10) After completion of the reset state981, the operation mode enters into the normal state982, and the processor main circuit902starts the normal operation.

As described above, by utilizing the low power consumption mode by the hardware stand-by, the exchange of the power source904becomes possible.

Next, the description will hereinbelow be given with respect to a second application example of the hardware stand-by.

FIG. 16shows an example of a configuration of realizing the RTC power source back-up mode. The RTC circuit914is called a real time counter and is provided for realizing the function such as a clock or a calendar. For this reason, the function of a clock can not be realized if the circuit914is not operated at all times. Even if the power source904is shut-off, the RTC circuit914needs to be operated.

In the embodiment shown here, in order to realize the RTC power source back-up mode, the 3.3V region is divided into a normal 3.3V region991and a region992in which the associated circuits are operated at 3.3V of the RTC. In addition, in the region of 3.3V of the RTC, both an input fixing circuit912and an input fixing level-up circuit960are added to the input circuit so that even when in the state in which other power sources (1.8V, the normal 3.3V power source) are shut-off, the input signal becomes at floating, the signal of an intermediate level is not transmitted to the region992in which the associated circuits are operated at 3.3V of the RTC. In such a way, the malfunction is prevented.

The control circuit for the power source system includes a back-up battery962, and diodes963and964in addition to the power source904, the power source monitoring circuit921, the display922, and the voltage producing circuit920for producing the voltage of 1.8V system.

The operation will hereinbelow be described. In the normal operation mode982, the substrate bias generating circuit903holds the normal substrate levels without carrying out the subtraction with respect to the substrate biases. The clock oscillation circuit908includes a PLL (phased-locked loop) and the like, and produces a clock for the internal operation to send it to the processor main circuit902through both the output fixing circuit907and the level-down circuit905. The I/O circuit909fetches in the signal from the outside and sends the signal thus fetched in to the processor main circuit902through both the output fixing circuit907and the level-down circuit905. In addition, the circuit909outputs the signal from the processor main circuit902to the outside through the level-up circuit904. The RTC circuit914is operated at 3.3V and receives the control signal from the processor main circuit902via the input fixing level-up circuit960to transmit the control signal to the processor main circuit902via both the level-down circuit906and the output fixing circuit911. The operation mode control unit913receives the control signal via the input fixing circuit912to in particular carry out the control for the substrate bias generating circuit903.

The voltage monitoring circuit921monitors the voltage level of the power source904. When the voltage level has been decreased down to a level lower than a predetermined level (When having detected the state in which the battery is exhausted up), the circuit921makes HARDSTB#951a low level, and fixes the inputs to the RTC 3.3V region992to prevent the malfunction of the RTC circuit914. At the same time, the circuit921displays the alarm of exhaustion of the battery on the display922. Thereafter, the voltage level continues to be decreased so that the voltages of 3.3V and 1.8V systems will not be supplied to the processor chip901. At this time, the voltages (VDD-RTC, VSS-RTC) are supplied to only the 3.3V region of the RTC from the back-up battery962via the diode963, and hence even when the power source904is exhausted up, only the RTC circuit (the counter circuit for a calendar)914is normally operated. The diode964serves to prevent the current from being caused to flow through the circuits other than the RTC circuit914.

The RTC power source back-up sequence will hereinbelow be described in detail with reference toFIG. 17.

(1) HARDSTB#951becomes a low level, whereby the operation mode enters into the hardware stand-by state986. Then, the 1.8V signal fixing953is outputted from the operation mode control unit913to fix the signal from 3.3V to 1.8V and also to stop the clock of 1.8V system. As a result, since even when carrying out the subtraction with respect to the substrate biases, the signals of 1.8V system are not operated, the malfunction of the circuits of 1.8V system in the state of carrying out the subtraction with respect to the substrate biases is prevented. At the same time, the input fixing signal954to the RTC circuit914is outputted to fix the input signal. As a result, when other power sources are shut-off, the unstable signal of the intermediate level is prevented from entering into the RTC circuit914.

(2) Thereafter, on the basis of the timing of the 1.8V signal fixing953, the substrate bias control starting signal955is outputted to the substrate bias producing circuit903. In actual, the signal is fixed between the signal fixing953and the substrate bias control state955, and hence a time difference until the supply of the signals to the 1.8V region is stopped is set therein. This time difference can be measured by the timer based on the RTC clock of the RTC circuit914.

(3) In response to the substrate bias control starting signal955, the substrate bias generating circuit903starts carrying out the subtraction with respect to the substrate biases of the substrate of 1.8V system. For a time period of carrying out the subtraction with respect to the substrate biases, the substrate bias in-control956signal is returned to the operation mode control unit913.

(4) In the state of carrying out the subtraction with respect to the substrate biases, the processor main circuit902is not operated. In addition, since the leakage current is small, the consumption quantity of current is small.

(5) The shut-off time period of the power source904may be long. In addition, the power source904can be exchanged.

(6) Since after return from the shut-off of the power source904(or after exchange of the power source904), the power source voltage recovers the normal level, HARDSTB#951is returned to the high level.

(7) Thereafter, the power-on reset circuit is operated and RESET#952is inputted. On the basis of this reset input, the substrate bias control starting signal955is released.

(8) In response to release of the substrate bias control starting signal955, the substrate bias generating circuit903starts returning the substrate biases of the substrate of 1.8V system to the electric potentials in the operation state (e,g., the electric potential VDD for the p-channel MOS transistor, and the electric potential VSS for the n-channel MOS transistor). A predetermined time period is required until recovery of the substrate biases, and after completion of the recovery of the substrate biases, on the basis of release of the substrate bias in-control signal956, the operation mode control unit913is informed of the completion of the recovery.

(9) In response to release of the substrate bias in-control signal956, the 1.8V signal fixing953which is outputted from the operation mode control unit913is released, and the signals are inputted to the circuits of 1.8V system such as the processor main circuit902and the like.

(10) After completion of the reset state981, the operation mode enters into the normal state982, and the processor main circuit902starts the normal operation.

In the above-mentioned sequence, a power source switch is provided in the power source904so that for a time period when the power source is turned off, only the RTC circuit914can be operated.

As described above, by utilizing the hardware stand-by, only the RTC circuit914can be operated on the basis of the back-up by the back-up battery.

The description will hereinbelow be given with respect to the sequence in which by utilizing a normal sleep instruction959, the operation mode enters into a stand-by state985, and then on the basis of an interruption signal958, the operation mode returns to the normal state982with reference toFIG. 18.

(1) On the basis of the sleep instruction959, the operation mode enters into the stand-by state985. Then, the 1.8V signal fixing953is outputted from the operation mode control unit913to fix the signal from 3.3V to 1.8V and also to stop the clock of 1.8V system. As a result, the malfunction of the circuits of 1.8V system when carrying out the subtraction with respect to the substrate biases is prevented.

(2) Thereafter, on the basis of the 1.8V signal fixing953, the substrate bias control starting signal955is outputted to the substrate bias producing circuit903. In actual, the signal is fixed between the signal fixing953and the substrate bias control state955, and hence a time difference until the supply of the signals to the 1.8V region is stopped is set therein. This time difference can be measured by the timer based on the RTC clock of the RTC circuit914.

(3) In response to the substrate bias control starting signal955, the substrate bias generating circuit903starts carrying out the subtraction with respect to the substrate biases of the substrate of 1.8V system. For a time period of carrying out the subtraction with respect to the substrate biases, the substrate bias in-control956signal is returned to the operation mode control unit913.

(4) In the state of carrying out the subtraction with respect to the substrate biases, the processor main circuit902is not operated. In addition, since the leakage current is small, the consumption quantity of current is small.

(5) Under this state, after having received the interruption signal958from the control signal957(external pin) via the I/O circuit909, the operation mode control unit913releases the substrate bias control starting signal955.

(6) In response to release of the substrate bias control starting signal955, the substrate bias generating circuit903starts returning the substrate biases of the substrate of 1.8V system to the electric potentials in the operation state (e.g., the electric potential VDD for the p-channel MOS transistor, and the electric potential VSS for the n-channel MOS transistor). A predetermined time period is required until recovery of the substrate biases, and after completion of the recovery of the substrate biases, on the basis of release of the substrate bias in-control signal956, the operation mode control unit913is informed of the completion of the recovery thereof.

(7) In response to release of the substrate bias in-control signal956, the operation mode control unit913releases the 1.8V signal fixing953. The 1.8V signal fixing953is released after having released the substrate bias in-control signal, whereby the malfunction of the circuits of 1.8V system is prevented.

(8) The signals are inputted to the circuits of 1.8V system such as the processor main circuit902and the like so that the operation mode enters into the normal state982and the processor main circuit902starts the normal operation.

On the basis of the foregoing, the processor chip901enters into the low power consumption mode and also can return thereto by the interruption.

The description will hereinbelow be given with respect to the sequence in which by using the normal sleep instruction959, the operation mode enters into the stand-by state985and then returns to the normal state982by RESET#952with reference toFIG. 19.

(1) On the basis of the sleep instruction959, the operation mode enters into the stand-by state985. Then, the 1.8V signal fixing953is outputted from the operation mode control unit913to fix the signal from 3.3V to 1.8V and also to stop the clock of 1.8V system. As a result, the malfunction of the circuits of 1.8V system when carrying out the subtraction with respect to the substrate biases is prevented.

Thereafter, it is measured that on the basis of the 1.8V signal fixing953, the signal fixing has been completed, and then the substrate bias control starting signal955is outputted to the substrate bias producing circuit903.

(2) In response to the substrate bias control starting signal955, the substrate bias generating circuit903starts carrying out the subtraction with respect to the substrate biases of the substrate of 1.8V system. For a time period of carrying out the subtraction with respect to the substrate biases, the substrate bias in-control956signal is returned to the operation mode control unit913.

(3) In the state of carrying out the subtraction with respect to the substrate biases, the processor main circuit902is not operated. In addition, since the leakage current is small, the consumption quantity of current is small.

(4) Under this state, the operation mode control unit913receives RESET#952to release the substrate bias control starting signal955.

(5) In response to release of the substrate bias control starting signal955, the substrate bias generating circuit903starts returning the substrate biases of the substrate of 1.8V system to the electric potentials in the operation state. After completion of the return of the substrate biases, the operation mode control unit913is informed of the completion of the return using the substrate bias in-control signal956.

(6) In response to this release signal, the 1.8V signal fixing953is released.

(7) After completion of the reset state981, the signals are inputted to the circuits of 1.8V system such as the processor main circuit902and the like, and the operation mode enters into the normal state982and also the processor main circuit902starts the normal operation.

On the basis of the foregoing, the processor chip901enters into the low power consumption mode and also can return thereto by the reset.

As set forth hereinabove, the processor chip901has a section to which 1.8V is supplied as the power source voltage, and a section to which 3.3V is supplied as the power source voltage. The section to which 1.8V is supplied includes the processor main circuit902and the like for example. This section is a section wherein the circuit scale is large and the high speed operation is required. Since the circuit scale is large and also the high speed operation is required, the power consumption in this section becomes large. In the present embodiment, the power source voltage is reduced in order to reduce that power consumption.

In addition, since if the power source voltage is decreased (e.g., 1.8V), then the operation speed becomes slow, the threshold voltages of the MOS transistors are decreased (e.g., Vth<0.4V or so). In addition, in the present embodiment, the substrate voltage control is carried out in order to reduce the sub-threshold leakage-current due to the decrease of the threshold voltage.

On the other hand, the section to which 3.3V is supplied as the power source voltage includes the RTC circuit914and the like for example. Since these circuits are small in scale and are operated at the low speed, the power consumption is small. Therefore, for such circuit blocks, the power source voltage does not need to be decreased. For example, the relation of Vth>0.5V or so can be established. Thus, since the threshold voltage of the MOS transistor does not need to be decreased, there is obtained the advantage that the current measure by the substrate control is not required in order to reduce the sub-threshold leakage current.

The processor chip901of the present embodiment uses both the power source voltages appropriately. That is, for the section requiring the large scale high speed operation, the MOS having the low threshold voltage is used by controlling the substrate, and also the MOS transistor having the high threshold voltage is used without controlling the substrate. While the method of manufacturing the MOS transistors having the different threshold values is not limited in particular, it can be realized by changing the channel implantation quantity. In addition, it can be realized by changing the thickness of the gate oxide film. In the latter, the technique may be adopted wherein for the construction of the MOS transistor, the oxide film is thickened to increase the threshold voltage. This reason is that since the MOS transistor having the high threshold voltage is operated at a high voltage, the oxide film b needs to be thickened. If the threshold voltage can be increased by thickening the oxide film, then the process can be simplified.

In addition, since the I/O circuit909needs to transmit/receive the external signal amplitude of 3.3V, if the MOS transistor which is the same as the MOS transistor having the high threshold voltage is employed therefor, then the process can be desirably made common thereto.