JPH0353612A - Comparing circuit - Google Patents

Abstract

PURPOSE:To prevent malfunction due to noise by causing a constant current to flow to a resistive element corresponding to the output of a comparator circuit to set a Schmitt width optionally depending on a noise level from an equipment itself employing the comparator circuit or from a peripheral equipment. CONSTITUTION:The comparator circuit is constituted by adding an inverter 21 whose noninverting input terminal 2 is connected to a resistive element 8 with respect to gate of MOSFETs 12, 15, and whose input terminal is connected to an output terminal 23, a P-channel MOSFET 6 whose gate is connected to a gate of a MOSFET 3, an a P-channel MOSFET 7 whose gate is connected to the output terminal of the inverter 21 and which is inserted between the P-channel MOSFET 6 and a resistive element 8. The Schmitt width is set optionally depending on a noise level from an equipment itself employing an integrated circuit incorporating the comparator circuit or from a peripheral equipment by causing a constant current to flow to the resistive element 8 in response to the logic level of the output of the comparator circuit.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention includes a first differential amplifier whose first stage is composed of an N-channel MOSFET, and a first stage composed of a P-channel MOSFET.
The present invention relates to a comparator circuit in which second differential amplifiers configured with the following are connected in parallel.

[Conventional technology]

FIG. 3 is a circuit diagram showing a conventional example of this type of comparison circuit.

This comparison circuit is a P-channel MOSFET 3.9.11
．． 14.15.16.19 and N-channel MOSFE
T5.10.12.13.17, 18.20 and resistance 4
, and power is supplied from power supply terminals 22 and 24.

Since the input signal is applied between the non-inverting input terminal 2 and the inverting input terminal 1, the first stage is set to P so that the input range can be widened.
Channel MOSFETs 15.16 and a differential amplifier whose first stage is composed of an N-channel MOSFET I0.12 are connected in parallel. The input signal applied between the non-inverting input terminal 2 and the inverting input terminal 1 is an N-channel MOS
The signal is amplified by a differential amplifier composed of FETs 10 and 12 and a differential amplifier composed of P-channel MOSFETs 15 and 16, and the output signal thereof is outputted to output terminal 23.

This output level is the same as that of the inverting input terminal 1 for the non-inverting input terminal 2.
When the level of is low, it becomes a high level (hereinafter referred to as H level), and when the level of inverting input terminal 1 is higher than that of non-inverting input terminal 2, it is a low level (hereinafter referred to as L level)
becomes.

[Problems to be Solved by the Invention] The conventional comparator circuit described above has a very high impedance because the input terminal is the gate of a MOS FET, and when an integrated circuit containing this comparator circuit is incorporated into a device, etc. The disadvantage is that noise generated by peripheral devices or the noise generated by the device itself that uses an integrated circuit that incorporates this comparison circuit is applied to the input terminal and tends to cause errors in the output, causing the device to malfunction. There is.

SUMMARY OF THE INVENTION In view of the above drawbacks, it is an object of the present invention to provide a comparison circuit that is less susceptible to disturbances such as noise.

[Means to solve the problem]

The comparison circuit of the present invention includes: a resistance element connected in series to at least one input terminal of the comparison circuit; and a constant current supply circuit that supplies a constant current to the resistance element in accordance with the logic level of the output of the comparison circuit. has.

[Effect]

When a constant current supply circuit causes a constant current to flow through a resistive element, the logic level of the output will not change unless the input level is correspondingly large.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the comparison circuit of the present invention.

In this embodiment, the non-inverting input terminal 2 of the conventional example shown in FIG. 3 and the MOS
A resistor 8 is inserted between the gates of FETs 12 and 15, an inverter 21 whose input terminal is connected to the output terminal 23, and a P-channel M whose gate is connected to the gate of MOSFET 3.
It is configured by adding an OSFET 6 and a P-channel MOSFFT 7 whose gate is connected to the output terminal of the inverter 21 and inserted between the P-channel MOSFET 6 and the resistor 8.

Next, the operation of this embodiment will be explained.

The input signal applied between the non-inverting input terminal 2 and the inverting input @i1 is amplified by a differential amplifier composed of an N-channel MOSFET 10.12 and a P-channel MOSFET 15.16, and its output is The signal is output to the output terminal 23. This output level becomes H level when the level of inverting input terminal 1 is lower than that of non-inverting input terminal 2, and becomes L level when the level of inverting input terminal 1 is higher than that of non-inverting input terminal 2.

Here, when the output level becomes H level, inverter 2
1 output becomes 1- level, P channel MOSFE
T7 is turned on and the current shown in equation (1) flows.

However, Voo... Power supply voltage Vcsa...
Gate-source voltage VGS3 of N-channel MOSFET 5... Gate-source voltage R4 of P-channel MOSFET 3... Resistance value of resistor 4 Therefore, a voltage drop LLXRa (Ra is the resistance value of resistor 8) occurs across resistor 8. .

This voltage drop IL XR8 becomes the Schmitt width of the input, and the voltage drop IL
The output will not go to L level unless the voltage of XRa is lowered. This Schmidt width can be arbitrarily set by arbitrarily selecting a resistor R4.8. In other words, the Schmitt width can be arbitrarily set depending on the level of noise caused by the device itself using the integrated circuit in which the comparator circuit is built, or by the peripheral devices, so malfunctions due to noise can be prevented. Furthermore, by making the resistor R4 that constitutes the constant IR current source and the resistor R8 that sets the Schmitt width from the same type of resistor when integrated into a circuit, it is possible to provide a comparison circuit with less variation in the Schmitt width.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

The operation is similar to the embodiment shown in FIG. 1, and the current ILL flowing through the resistor 3o is expressed by equation (2).

1LL=Voo-VGS5-VGS3. ．． ．． ．． ．．
．． (2) R4 Therefore, the Schmidt width is L LL X R 30, and by arbitrarily selecting a resistance of 4.30, the Schmidt width can be set arbitrarily. In other words, the Schmitt width can be arbitrarily set depending on the level of noise from the device itself using the integrated circuit in which the comparison circuit is built, or from peripheral devices, so malfunctions due to noise can be prevented. By making the resistor 4 and the resistor 30 for setting the Schmitt width using the same type of resistor when integrated into a circuit, it is possible to provide a comparison circuit with less variation in the Schmidt width. In addition, the comparator circuit has a resistive element connected to both the non-inverting input and the inverting input, and a constant current source connected to both the non-inverting input terminal and the inverting input terminal by a switch element controlled by the output of the comparator circuit. The same effect can be obtained.

〔Effect of the invention〕

As explained above, the present invention connects a resistive element to at least one of the non-inverting input terminal and the inverting input terminal, and flows a constant current through the resistive element in accordance with the output of the comparator circuit. Since the Schmidt width can be arbitrarily set depending on the device used or the level of noise caused by the surrounding 'lfiff, malfunctions due to noise can be prevented.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a comparison circuit of the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and FIG. 3 is a circuit diagram showing a conventional example. 1... Inverting input end, 2... Non-inverting input end, 2
3... Output end, 22.24... Power supply end,
21.33...Inverter, 4.7.30...Resistor

Claims (1)

[Claims] 1. The first stage is composed of an N-channel MOSFET.
A comparison circuit in which a differential amplifier and a second differential amplifier whose first stage is composed of a P-channel MOSFET are connected in parallel, a resistive element connected in series to at least one input terminal of the comparison circuit; A comparison circuit comprising: a constant current supply circuit that causes a constant current to flow through the resistance element in accordance with a logic level of an output of the comparison circuit.