Reference supply voltage circuit using more than two reference supply voltages

Abstract

A reference supply voltage circuit includes a detecting device for detecting a first reference voltage, a comparator, and a preventing circuit for preventing any false operation during pre-operation indefinite time interval. The comparator outputs a signal which controls an operation circuit whose supply voltage is a second reference voltage equal to or lower than the first reference voltage. The preventing circuit maintains the second reference voltage to a circuit reference potential when the first reference voltage is lower than a first predetermined voltage, sets the second reference voltage to a voltage equal to the first reference voltage when the first reference voltage is equal to or higher than the first predetermined voltage and lower than a second predetermined voltage, and sets the second reference voltage to a voltage proportional to the first reference voltage when the first reference voltage is equal to or higher than the second predetermined voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings throughout which like parts are designated by like reference numerals, and in which:

FIG. 1 is a circuit diagram showing a configuration of a semiconductor device provided with a reference supply voltage circuit 3 according to a preferred embodiment 1 of the present invention;

FIG. 2 is a correlation diagram showing a correlation between voltages at a VCC terminal 11 and a VDD terminal 12 on start-up of the reference supply voltage circuit 3 shown in FIG. 1;

FIG. 3 is a circuit diagram showing a configuration of a semiconductor device provided with a reference supply voltage circuit 3A according to a preferred embodiment 2 of the present invention;

FIG. 4 is a correlation diagram showing a correlation between voltages at the VCC terminal 11 and the VDD terminal 12 on start-up of the reference supply voltage circuit 3A shown in FIG. 3;

FIG. 5 is a circuit diagram showing a configuration of a semiconductor device provided with a reference supply voltage circuit 3B according to a preferred embodiment 3 of the present invention; and

FIG. 6 is a correlation diagram showing a correlation between voltages at the VCC terminal 11 and the VDD terminal 12 on start-up of the reference supply voltage circuit 3B shown in FIG. 5.

Claims

1. A reference supply voltage circuit, comprising: a detecting device for detecting a first reference voltage of a first reference voltage source;a comparator for outputting a signal which controls an operation state and a stop state of an operation circuit whose supply voltage is a second reference voltage of a second reference voltage source that is equal to or lower than the first reference voltage, by comparing the first reference voltage detected by said detecting device with a predetermined reference detection voltage; anda circuit for preventing any false operation during a pre-operation indefinite time interval for maintaining the second reference voltage to a circuit reference potential when the first reference voltage is lower than a first predetermined voltage, for setting the second reference voltage to a voltage equal to the first reference voltage when the first reference voltage is equal to or higher than the first predetermined voltage and lower than a second predetermined voltage, and for setting the second reference voltage to a voltage proportional to the first reference voltage when the first reference voltage is equal to or higher than the second predetermined voltage.

2. The reference supply voltage circuit as claimed in claim 1, wherein the first predetermined voltage is equal to or higher than a voltage at which an operation circuit whose supply voltage is the second reference voltage can be stably operated; andwherein the second predetermined voltage is equal to or higher than a voltage at which an operation circuit whose supply voltage is the first reference voltage can be stably operated.

3. The reference supply voltage circuit as claimed in claim 1, wherein said circuit for preventing any false operation during the pre-operation indefinite time interval comprises:a diode section having a cathode electrode connected to the circuit reference potential, for supplying a forward voltage that is the second predetermined voltage;a first resistor connected between said first reference voltage source and an anode electrode of said diode section;a first switching device having one side electrode connected to said first reference voltage source, the other side electrode connected to the circuit reference potential via a second resistor, and a control electrode connected to the anode electrode of said diode section; anda second switching device having one side electrode connected to the first reference voltage source, the other side electrode connected to the second reference voltage source, and a control electrode connected to a connecting node between said second resistor and said first switching device.

4. The reference supply voltage circuit as claimed in claim 2, wherein said circuit for preventing any false operation during the pre-operation indefinite time interval comprises:a diode section having a cathode electrode connected to the circuit reference potential, for supplying a forward voltage that is the second predetermined voltage;a first resistor connected between said first reference voltage source and an anode electrode of said diode section;a first switching device having one side electrode connected to said first reference voltage source, the other side electrode connected to the circuit reference potential via a second resistor, and a control electrode connected to the anode electrode of said diode section; anda second switching device having one side electrode connected to the first reference voltage source, the other side electrode connected to the second reference voltage source, and a control electrode connected to a connecting node between said second resistor and said first switching device.

5. The reference supply voltage circuit as claimed in claim 3, wherein said diode section comprises a plurality of diodes connected in series with each other.

6. The reference supply voltage circuit as claimed in claim 4, wherein said diode section comprises a plurality of diodes connected in series with each other.

7. The reference supply voltage circuit as claimed in claim 3, wherein said diode section comprises a plurality of bipolar transistors connected in series with each other.

8. The reference supply voltage circuit as claimed in claim 4, wherein said diode section comprises a plurality of bipolar transistors connected in series with each other.

9. The reference supply voltage circuit as claimed in claim 3, wherein said first and second switching devices are P-type transistors, respectively.

10. The reference supply voltage circuit as claimed in claim 4, wherein said first and second switching devices are P-type transistors, respectively.