JPH06308171A - Power supply-voltage detecting circuit - Google Patents

Abstract

PURPOSE:To detect the drop of a power supply voltage with a single power supply by outputting the first signal corresponding to a varying resistance value from the first circuit, which is connected to the power supply, outputting the second signal corresponding to the specified resistance value from the second circuit, and comparing the first and second signals with respect to the voltage with a comparing circuit. CONSTITUTION:Diffused resistors R1, R2 and R3 are formed on one transistor resistor RT and the fluctuation of a power supply voltage. An output terminal Y, a +input terminal and a -input terminal are provided in the comparator 1. The result of the detection of the power supply voltage is outputted from the output terminal Y. The gate of the resistor RT is connected to GND. The source is connected to VDD. The drain is connected to the diffused resistor R1 and the +input terminal of the comparator 1. The opposite-side terminal of the resistor R1 is connected to GND. The -input of the comparator 1 is connected to the resistors R2 and R3. When the difference between the first signal and the second signal becomes the specified value, the signal corresponding to the specified value is outputted. Therefore, the drop of the power supply voltage can be detected with a single power supply.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply voltage detecting circuit, and more particularly, to a comparator and a transistor resistance which are composed of a semiconductor integrated circuit, and a resistance which can obtain a stable resistance value than the transistor resistance on the semiconductor integrated circuit (here, as an example. The present invention relates to a power supply voltage detection circuit in which a diffusion resistance) is formed on one semiconductor chip.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional semiconductor integrated circuit (hereinafter referred to as IC
Is a block diagram showing the circuit configuration of the reference voltage V which can supply a stable voltage to the first power supply having the power supply voltage VDD1, the comparator 2 and the outside of the IC.
It is composed of a second power supply having a DD2 and resistors r1 and r2. The comparator 2 is provided with a + input terminal, a − input terminal and an output terminal Y of the comparator 2, and the detection result of the power supply voltage VDD1 is output to the Y output. The + side input of the comparator 2 is connected to the first power source of the IC, and the − side input of the comparator 2 is connected to the resistors r1 and r2 outside the IC.
Thus, the resistance-divided input voltage of the reference voltage VDD2 of the second power supply is applied. Therefore, when VDD1 which is the power supply voltage of the IC drops and becomes lower than the voltage of the-side input of the comparator 2, the output level of the comparator 2 is inverted and it is detected that VDD1 has dropped. It was That is, since it is difficult to detect the voltage effect with only a single power supply voltage supplied to the conventional IC, it goes without saying that the comparator 2 is built in the IC.
Even if a voltage drop of the voltage VDD1 of the first power supply supplied to the IC occurs, the negative input terminal for the comparison voltage is provided in the comparator 2 in the comparator 2 and the first power supply is connected to the + input terminal. Was connected to this input terminal.

[0003]

However, it is difficult to permanently supply a stable voltage with the second power source, and it is necessary to secure an area for mounting the second power source and replace the power source. It was

It is an object of the present invention to provide a power supply voltage detection circuit in a semiconductor integrated circuit which does not require a second power supply and can reduce the number of external parts outside the IC and at the same time reduce the number of terminals of the IC.

[0005]

A first circuit connected to a power supply and having a resistance value that changes in response to a change in the power supply voltage and outputting a first signal corresponding to the changing resistance value is connected to the power supply. A second circuit having a predetermined resistance value and outputting a second signal corresponding to the predetermined resistance value, a first signal supplied from the first circuit, and a second signal supplied from the second circuit. And a comparator circuit that compares the voltages and outputs a signal according to the predetermined value when the difference between the voltages of the first signal and the second signal reaches a predetermined value.

[0006]

The resistance value of the first circuit connected to the power supply changes in response to the fluctuation of the power supply voltage, and the first circuit corresponding to the changing resistance value.
The second circuit, which outputs a signal, has a predetermined resistance value and has a predetermined resistance value, outputs a second signal corresponding to the predetermined resistance value, and the comparison circuit outputs the first signal and the first signal supplied from the first circuit. The second signal supplied from the two circuits is compared with respect to the voltage, and when the difference between the voltages of the first signal and the second signal reaches a predetermined value, a signal corresponding to the predetermined value is output. Can detect a drop in the power supply voltage.

[0007]

1 is a block diagram of an embodiment of a power supply voltage detecting circuit comprising a semiconductor integrated circuit according to the present invention. In the figure, 1 is a comparator, VDD is a power supply voltage of a power supply, GN
D is ground, R1, R2, and R3 are resistors whose resistance values do not fluctuate much, such as diffusion resistors, RT is a P-channel transistor resistor, VM is the input voltage of the + input terminal of the comparator,
VREF indicates the negative input voltage of the comparator 1.

This circuit includes a diffusion resistance R for the comparator 1, a P-channel type transistor resistance RT (or an N-channel type transistor resistance may be used), and a variation in the power supply voltage.
IC in which 1, R2 and R3 are formed on one semiconductor chip
Therefore, the comparator 1 is provided with the output terminal Y, the + input terminal, and the − input terminal of the comparator 1, and the power supply voltage detection result is output from the Y output terminal.

The gate of the P-channel transistor resistance RT is connected to GND, the source is connected to VDD, the drain is connected to the diffusion resistor R1 and the + input terminal of the comparator 1, and the opposite terminal of the diffusion resistor R1 is connected to GND. ing. Further, the minus input of the comparator 1 is a diffusion resistor R2,
It is connected to the connection point of R3, and the opposite terminals of the diffused resistors R2 and R3 are connected to VDD and GND.

When RT <R1 and R2 = R3, VM = R1.VDD / (RT + R1)> VDD / 2 VREF = R3.VDD / (R2 + R3) = VDD /
2 Therefore, the comparator + side voltage> the comparator-side voltage, and the Y = “high (HIGH)” level is output.

In the above state, the P-channel type transistor resistance RT gradually increases as the power supply voltage VDD drops. This P-channel type transistor resistance R
Using the characteristics of T, when RT> R1, VM = R1.VDD / (RT + R1) <VDD / 2 Therefore, comparator + side voltage <comparator−side voltage, and Y = “low (LOW)” The level is output. That is, it indicates that the voltage level drops below a certain reference (VDD / 2 in this case). This makes it possible to detect that the power supply voltage is lower than VDD / 2.

In the present embodiment, the number of terminals of the IC can be reduced by tackling even the external resistance outside the IC inside the IC.

[0013]

The first circuit connected to the power supply changes the resistance value according to the fluctuation of the power supply voltage, outputs the first signal corresponding to the changing resistance value, and the second circuit connected to the power supply operates. A second signal having a predetermined resistance value and corresponding to the predetermined resistance value is output, and the comparison circuit supplies a first signal and a second signal supplied from the first circuit.
The second signal supplied from the circuit is compared with respect to the voltage, and when the difference between the voltages of the first signal and the second signal reaches a predetermined value, a signal corresponding to the predetermined value is output, so that a single signal is output. The power supply can detect a drop in the power supply voltage.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a power supply voltage detection circuit including a semiconductor integrated circuit according to the present invention.

FIG. 2 is a block diagram showing a circuit configuration of a conventional semiconductor integrated circuit.

[Explanation of symbols]

 1 Comparator RT P-channel transistor resistance R1, R2, R3 Diffusion resistance

Claims (1)

[Claims] 1. A first value which is connected to a power supply and whose resistance value changes in response to fluctuations in the power supply voltage and which corresponds to the changing resistance value.
A first circuit that outputs a signal, a second circuit that is connected to the power supply, that outputs a second signal that has a predetermined resistance value and that corresponds to the predetermined resistance value, and that is supplied from the first circuit The first signal and the second signal supplied from the second circuit are compared with respect to voltage, and when the difference between the voltages of the first signal and the second signal reaches a predetermined value, a signal corresponding to the predetermined value is detected. A power supply voltage detection circuit including a comparison circuit for outputting.