In the semiconductor integrated circuit device configured as described, a set value for the power supply VINT, which is an internal step-down voltage, i.e., the reference voltage VREF, is set to a value near the minimum value (VCCmin) of the voltage of the external power supply VCC. If the voltage of the external power supply VCC drops for some reason, the first power supply circuit 11 will not be able to supply sufficient current to the load circuit 14 connected to the power supply node VINT during its operation. However, when the potential of the power supply node VINT becomes below the reference voltage VREF-ΔV, the second power supply circuit 12 is turned on and the step-up voltage power supply VPP is supplied to the power supply node VINT. This power supply circuit 12 has sufficient current supply capability and is capable of maintaining at least the voltage of the power supply node VINT at the reference voltage VREF-ΔV by having the step-up voltage power supply VPP with a voltage higher than the voltage of the external power supply VCC supply power to the power supply node VINT.
Next, the operation waveforms of the power supply voltage generating circuit 10 will be described.
On the other hand, in the case where the second power supply circuit 12 does not exist, when the potential difference between the voltages of the external power supply VCC and the power supply VINT becomes small and the current supply capability of the first power supply circuit 11 decreases, the first power supply circuit 11 cannot sufficiently provide for the current consumed by the circuit group connected to the power supply node VINT during their operation. In this case, the IR drop at the power supply node VINT becomes large and the return to the reference voltage is slow. As a result, a malfunction may occur and the required operation speed may not be realized (B in
As described above, in the power supply voltage generating circuit 10, when the IR drop of the voltage of the power supply VINT occurs during the operation of the load circuit 14 connected to the power supply node VINT, the second power supply circuit 12 immediately brings the voltage back to the reference voltage VREF-ΔV. Therefore, the load circuit 14 is less likely to malfunction and a higher speed operation is possible. The power supply generating circuit will be further described in detail using examples.
In the first power supply circuit 11 configured as described above, the NMOS transistors N11 and N12, having the PMOS transistor P11 and the PMOS transistor P12 as a load respectively, constitute a differential amplifier to which the voltage of the power supply node VINT is fed back, and the PMOS transistor P13 forms an output stage. The external power supply VCC supplies current to the power supply node VINT so that the voltage of the power supply node VINT is equal to the reference voltage VREF.
Further, the second power supply circuit 12 comprises PMOS transistors P21, P22, and P23, and NMOS transistors N21, N22, and N23. In the second power supply circuit 12, the PMOS transistors P21, P22, and P23, and the NMOS transistors N21, N22, and N23, respectively, correspond to the PMOS transistors P11, P12, and P13, and the NMOS transistors N11, N12, and N13 in the first power supply circuit 11 and are configured identically. However, the reference voltage VREF-ΔV is applied instead of the reference voltage VREF, and the step-up voltage power supply VPP is applied instead of the external power supply VCC, in the second power supply circuit 12.
In the second power supply circuit 12 configured as described above, the NMOS transistors N21 and N22, having the PMOS transistor P21 and the PMOS transistor P22 as a load respectively, constitute a differential amplifier to which the voltage of the power supply node VINT is fed back, and the PMOS transistor P23 forms an output stage. When the voltage of the power supply node VINT is equal to the reference voltage VREF, the PMOS transistor P23 is turned off and there is no current flowing from the step-up voltage power supply VPP to the power supply node VINT. On the other hand, when the voltage of the power supply node VINT is below the reference voltage VREF-ΔV, the step-up voltage power supply VPP supplies current to the power supply VINT so that the voltage of the power supply VINT is equal to the reference voltage VREF-ΔV.
The power supply voltage generating circuit configured as described above is capable of maintaining the minimum power supply voltage for the load circuit because it steps down the voltage of the step-up voltage power supply VPP and supplies it to the power supply node VINT of the load circuit when the voltage of the external power supply VCC is below the required minimum value.
In the power supply voltage generating circuit configured as described above, the reference voltage VREFa and the reference voltage VREFa-ΔV can be set lower than the voltage of the power supply VINT by setting the resistance ratios between the resistances R1 and R2 and between the resistances R3 and R4. For instance, when a desired voltage of the power supply node VINT is Vint and VREFa=Vint/2, Vint=VREFa×2 can be obtained by setting R1=R2. In the power supply circuit 12a, when a reference voltage ΔVa lower than VREFa is supplied, and by configuring the power supply circuit 12a with the ratio between the resistances R3 and R4 so that it outputs a predetermined step-down voltage (VREFa−ΔVa), Example 2 operates identically to Example 1 and the same effects can be obtained. In the power supply voltage generating circuit described above, the voltage of the power supply node VINT can be set to a desired voltage by setting the reference voltage VREFa low even in cases where it is difficult to generate a stable reference potential VREFa very close to the voltage of the external power supply VCC.
In Examples 1 and 2, transistors that function as the driver for the output stage of the power supply voltage generating circuit are PMOS transistors, however, the same effects as Examples 1 and 2 can be obtained when NMOS transistors are used as shown in
It should be noted that other objects, features and aspects of the present invention will become apparent in the entire disclosure and that modifications may be done without departing the gist and scope of the present invention as disclosed herein and claimed as appended herewith.
Also it should be noted that any combination of the disclosed and/or claimed elements, matters and/or items may fall under the modifications aforementioned.
Number | Date | Country | Kind |
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2006-288692 | Oct 2006 | JP | national |