JPH0550366U - Voltage comparison circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] In a voltage comparison circuit that compares a reference voltage with an input voltage, these voltages are accurately compared to prevent chattering of the output voltage. A positive feedback loop is formed by connecting a switching means 2 and a resistor R8 in series between a non-inverting input terminal + and an output terminal of a comparator 1. The control means 7 is configured to supply the control signal to the switching means only for a predetermined time immediately after the output signal of the comparator 1 is inverted. Since the switching means short-circuits the positive feedback loop of the comparator 1 while the control signal is being supplied and positively feeds back the output voltage to the non-inverting input terminal, hysteresis can be imparted to the threshold and chattering of the output voltage is prevented. Can be prevented
Since the reference voltage Vs can be set to the threshold after a predetermined time, the reference voltage and the input voltage can be accurately compared.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a voltage comparison circuit, and more particularly to a voltage comparison circuit suitable for electronically controlled cameras and other electronic devices, or inspection devices for electronic devices.

[0002]

[Prior Art]

 There is a conventional voltage comparison circuit that uses a comparator. In this case, the comparator has a voltage level input to the inverting input terminal − and a voltage level input to the non-inverting input terminal +. And output voltage of either high or low is generated at the output terminal according to the magnitude relation. It is known that in such a comparator, the output voltage is likely to chatter due to the noise superimposed on the input voltage.

Therefore, in the above-described conventional circuit, a positive feedback loop is formed by providing a resistor between the output terminal and the non-inverting input terminal +, and the threshold is provided with hysteresis, thereby chattering the output voltage. I try to suppress the occurrence of. However, by providing a hysteresis, the threshold with respect to the input voltage shows a different value depending on the polarity, so that the desired result cannot always be obtained particularly in an application in which highly accurate voltage comparison is desired. This greatly affects the inversion cycle of the output voltage, which hinders the improvement of the accuracy of the voltage comparison circuit. Further, since it has hysteresis, there is a problem that accurate level detection becomes extremely difficult when it is desired to calibrate and adjust the threshold level.

[0004]

[Problems to be solved by the device]

 In view of such problems of the conventional art, a main object of the present invention is to provide a voltage comparison circuit capable of accurately comparing a reference voltage with an input voltage and preventing chattering of an output voltage.

[0005]

[Means for Solving the Problems]

 The above-mentioned object is according to the present invention, a comparator, a switching means for opening and closing a positive feedback loop of the comparator, and a control signal for turning on the switching means only for a predetermined time immediately after the switching of the output signal of the comparator. Is provided to the switching means, and a voltage comparison circuit is provided.

[0006]

【Example】

 Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is an electric circuit diagram showing a voltage comparison circuit to which the present invention is applied. An inverting input terminal − of a comparator 1 as a comparator has an input voltage which is one of the voltages to be compared. Vin is supplied, and the non-inverting input terminal + of the comparator 1 is connected to the anode of the power supply Vs as the reference voltage which is the other of the voltages compared via the resistor R3, and the anode thereof is grounded. There is. A positive feedback loop formed by connecting the switching means 2 and the resistor R8 in series is formed between the output terminal of the comparator 1 and the non-inverting input terminal +.

The output terminal of the comparator 1 is connected to the power source E via the capacitor C, one via the resistor R1, and the other is grounded via the resistor R2. The differentiating circuit 3 is composed of the capacitor C and the resistors R1 and R2. The non-inverting input terminal + of the comparator 4 is connected to the node of the capacitor C and the resistor R2, and the inverting input terminal − of the comparator 5 is further connected.

The above-mentioned power source E is connected to the inverting input terminal-of the comparator 4 via a resistor R5, and is also grounded via a resistor R6 and further via a resistor R7. The non-inverting input terminal + of the comparator 5 is connected to the node of the resistors R6 and R7.

The output terminals of the comparators 4 and 5 are connected to the input terminals of the OR gate 6, respectively, and the output terminal of the OR gate 6 is connected to the switching means 2. The differentiating circuit 3, the comparators 4 and 5, and the OR gate 6 constitute the control means 7, and the switching means 2 short-circuits the positive feedback loop of the comparator 1 by the output signal of the OR gate 6 as a control signal. Do or open.

Next, the operation procedure of the present invention will be described with reference to the waveform diagram of FIG. Each Va to Vi in the figure shows the voltage level of each node a to i in FIG. 1, and for example, the voltage at the node a is shown at Va.

First, when the relationship between the voltage Vin input to the inverting input terminal − of the comparator 1 and Vs as the reference voltage input to the non-inverting input terminal + is Vin> Vs, that is, j in FIG. The case indicated by will be described. A low level output voltage of the power supply voltage E is generated at the output terminal of the comparator 1. Then, this output voltage is waveform-shaped by the differential circuit 3, and is supplied to the non-inverting input terminal + of the comparator 4 and the inverting input terminal-of the comparator 5, respectively.

In the comparator 4, a negative differential waveform is supplied to the non-inverting input terminal +, and a voltage Vh [Vh = {which is obtained by dividing the power supply voltage E by the resistors R5, R6, and R7 is supplied to the inverting input terminal −. Since (R6 + R7) / (R5 + R6 + R7)} · E] is supplied, the output voltage of the comparator 4 becomes low level. Further, in the comparator 5, a negative differential waveform is supplied to the non-inverting input terminal −, and the non-inverting input terminal + is divided by the resistors R5, R6, and R7 to obtain a voltage Vi [Vi = {R7 / (R5 + R6 + R7)} · E] is supplied, the output voltage of the comparator 5 becomes high level.

In the OR gate 6 to which the output voltages having the respective states from the comparators 4 and 5 are supplied, the high level output signal of the comparator 5 causes the switching means 2 to have a high level as a control signal. Supply a pulse signal of. When the switching means 2 is turned on, the output terminal of the comparator 1 and the resistor R8 are short-circuited to form a positive feedback loop, so that the switching means 2 and the resistor R8 are connected to the non-inverting input terminal +. Low-level output voltage is positively fed back via. The wavelength of the pulse signal supplied to the switching means 2 at this time is determined by the differentiating circuit 3, and for example, by changing the time constants of the capacitor C and the resistors R1 and R2, as desired. Can change.

Next, a description will be given of the time point when the relationship between the input voltage Vin and the reference voltage Vs becomes Vin <Vs, that is, the case indicated by k in FIG. Is output. The output voltage is wave-shaped by the differentiating circuit 3 and supplied to the non-inverting input terminal + of the comparator 4 and the inverting input terminal-of the comparator 5.

In the comparator 4, since the positive differential waveform is supplied to the non-inverting input terminal + and the above-mentioned Vh is supplied to the inverting input terminal −, the output voltage of the comparator 4 becomes a high level. Further, in the comparator 5, the positive sub-waveform is supplied to the inverting input terminal − and the above-mentioned Vi is supplied to the non-inverting input terminal +, so that the output voltage of the comparator 5 is low level. Becomes

In the OR gates supplied with the output voltages having the respective states from the comparators 4 and 5, the high-level output signal of the comparator 4 causes the switching means 2 to output a high-level signal as a control signal. Supply a pulse signal. When the switching means 2 is turned on, the output terminal of the comparator 1 and the resistor R8 are short-circuited to form a positive feedback loop, so that the switching means 2 and the resistor R8 are connected to the non-inverting input terminal +. The high-level output voltage is positively fed back via and.

As is apparent from the above-described two operations, the output voltage of the comparator 1 is superimposed on the reference voltage Vs by opening the output terminal of the comparator 1 and the resistor R8 by the switching means 2 in the steady state. Therefore, when the input voltage Vin is compared, it can be compared with the single reference voltage Vs. When the input voltage Vin crosses the reference voltage Vs, the switching means 2 short-circuits the output terminal of the comparator 1 and the resistor R8 for a predetermined time to form a positive feedback loop in the comparator 1. Since the reference voltage Vs can have a hysteresis, the output signal of the comparator 1 does not chatter.

[0019]

[Effect of the device]

 As is clear from the above description, according to the voltage comparison circuit of the present invention, the switching means is turned on for the predetermined time only immediately after the input voltage crosses the reference voltage, thereby preventing the chattering of the output voltage. Can be compared with a single reference voltage at all times, and even when comparing input voltages whose amplitude varies for each polarity, the problem that the output voltage differs for each polarity does not occur. Further, since the accurate reference voltage level can be detected, the reference voltage level can be easily compared. Therefore, the conventional hysteresis comparator is simply provided with switching means and control means for operating the switching means. It is possible to provide a highly accurate voltage comparison circuit having analog rigor.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a preferred embodiment of the present invention.

2 is a voltage waveform diagram at each node of the electric circuit diagram of FIG. 1. FIG.

[Explanation of symbols]

 1, 4, 5 Comparator 2 Switching means 3 Differentiating circuit 6 OR gate 7 Control means

Claims (1)

[Scope of utility model registration request] 1. A comparator, switching means for opening and closing a positive feedback loop of the comparator, and a control signal for turning on the switching means only for a predetermined time immediately after switching of the output signal of the comparator is supplied to the switching means. A voltage comparison circuit having a control means.