JPH0276317A - Voltage comparison circuit - Google Patents

Abstract

PURPOSE:To improve the stability of the comparison discriminating operation of an operational amplifier against an input noise in the vicinity of a reference voltage by forming a flowout path of a constant current to the earth side via a constant current source through a resistor at the time of energizing a current switch. CONSTITUTION:If a level of an input voltage waveform b111 is lower than a level of a reference voltage waveform a11, an output voltage waveform c11 is inverted from an L level to an H level based on the comparison discrimination operation of an operational amplifier 4. A current switch 5 is made into an energized state by using it as a control signal and a constant current flows from an input terminal 1 to the earth side. If a level of a voltage waveform b112 at a connecting point A is higher than the level of the reference voltage waveform a11, the output voltage waveform c11 is inverted from an H level to an L level. The current switch 5 is made into an energized state by using it as a control signal and a constant current flowing to the earth side is interrupted. That is, the circuit acts like a voltage comparison circuit having two stable points and a hysteresis effect with a voltage V1 is provided in the transmission characteristic between the input and output.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voltage comparison circuit that compares an input voltage with a reference voltage and outputs the comparison result.

(Conventional technology) FIG. 4 shows a typical example of this type of voltage comparison circuit.

That is, the input voltage applied to the positive phase input terminal (non-inverting input terminal) of the operational amplifier 11 via the input terminal 9 is set to its negative phase input terminal (inverting input terminal) via the reference voltage input terminal 10. It is compared with a reference voltage, and the comparison result is obtained from the output terminal 12 as a negative phase output voltage.

FIG. 5 shows the basic operation of this voltage comparison circuit, where a□ is a reference voltage waveform, b21 is an input voltage waveform, and C21 is an output voltage waveform. That is, the reference voltage waveform a21 is set as the threshold voltage, and the reference voltage waveform a! The difference voltage between I and the input voltage waveform btt is amplified, and the waveform bz+ becomes the waveform a! When the voltage falls below l, the output voltage waveform cz+ is set to the rHJ level.

[Problem to be solved by the invention]

However, according to such a conventional voltage comparison circuit, since the comparison circuit uses an operational amplifier, the input voltage waveform b! When noise is superimposed on I, the comparison and determination operation is repeated in the amplifier 11, causing a problem that the comparison result obtained as the output voltage waveform C□ becomes unstable. That is, when noise is superimposed on the waveform bat, resulting in a waveform bzz as shown in FIG. The output voltage waveform becomes unstable as shown in the figure ('b).

[Means to solve the problem]

The present invention was made to solve such problems, and it compares the input voltage applied to the first input terminal via the resistor with the reference voltage applied to the second input terminal, and compares the input voltage applied to the first input terminal through the resistor. an operational amplifier that outputs a result; a current switch whose conduction or non-conduction is determined based on the comparison result output from the operational amplifier; and a first input terminal of the operational amplifier and the resistor when the current switch is conductive. and a constant current source connected between the connection point and the ground side.

[Effect]

Therefore, according to the present invention, when the current switch is turned on, an outflow path for the constant current flowing to the ground side via the resistor and the constant current source is formed.

〔Example〕

Hereinafter, the voltage comparison circuit according to the present invention will be explained in detail.

FIG. 1 is a circuit diagram showing an embodiment of this voltage comparison circuit. In the figure, 1 is an input terminal, 2 is a reference voltage input terminal, 3 is a resistor connected between the input terminal 1 and the positive phase input terminal of the operational amplifier 4, and 5 is the negative phase output of the operational amplifier 4. A current switch which receives an output voltage as a control signal, becomes conductive when the reverse phase output voltage is reversed from rLJ level to rHJ level, and becomes non-conductive when reversed from rHJ level to rLJ level, 6 is this current switch. A constant current source is connected between the connection point A between the resistor 3 and the positive-phase input terminal of the operational amplifier 4 through 5 and the ground, and 7 is the negative-phase output voltage output from the operational amplifier 4 as a comparison result. This is the output terminal for obtaining. Note that when the current switch 5 is non-conductive, the voltage drop due to the input current of the resistor 3 and operational amplifier 4 is set to a value that can be ignored.

FIG. 2 shows the basic operation of this voltage comparison circuit, and a represents the reference voltage waveform forming the dark value voltage of this circuit.

b Ill is the input voltage waveform + bl11 is the voltage waveform at the connection point A + C11 is the output voltage waveform.

Now, if we consider the case where the input voltage waveform b Ill is about to fall below the reference voltage waveform all, waveform b Ill becomes waveform a
In the region exceeding ll, the output voltage waveform CIl is rL
J level, and the current switch 5 maintains a non-conducting state. In such a state, when the input voltage waveform b Ill falls below the reference voltage waveform a, the output voltage waveform C, , is inverted from the rLJ level to the rHJ level based on the comparison and determination operation in the operational amplifier 4. This output voltage waveform CI
By reversing l from the rLJ level to the rHJ level, the current switch 5 becomes conductive using this as a control signal.
A constant current flows from the input terminal 1 through the resistor 3, the current switch 5, and the constant current source 6 to the ground side. Now, assuming that the resistance value of the resistor 3 is R1+the value of the constant current is 2, a voltage drop of V,=R,XI occurs in the voltage at the connection point A. In other words, the voltage waveforms S and 2 at the connection point A drop by Vl with respect to the input voltage waveform b Ill, and the reference voltage waveform a becomes equivalent to shifting and amplifying the input voltage waveform b Ill by V, and henceforth. ,
In the region where the waveform b112 is below the a-th waveform, the output voltage waveform CI+ is reliably at the rHJ level.

On the other hand, considering the case where the voltage waveform b11g at the connection point A tries to exceed the reference voltage waveform all, the waveform b1
In the region where 12 is lower than waveform a, the output voltage waveform CI1 is at the rHJ level, so the current switch 5 maintains the conductive state. From this state, the voltage waveform b1
12 exceeds the reference voltage waveform a, based on the comparison judgment operation in the operational amplifier 4, the output voltage waveform CIl becomes rH.
Inverts from J level to "L" level. By inverting the output voltage waveform C1l from the rHJ level to the rLJ level, the current switch 5 is brought into a non-conducting state using this as a control signal, and the constant current flowing to the ground side in the above-mentioned outflow path is cut off. That is, the voltage waveform bl at the connection point A
l! increases by ■, returns to input voltage waveform b Ill, and becomes equivalent to the reference voltage waveform a shifting down by V with respect to waveform b++z, and henceforth, waveform b III
The output voltage waveform C0 is reliably at the "L" level in the region where the voltage exceeds the waveform a.

That is, the voltage comparison circuit according to this embodiment is a voltage comparison circuit having two stable points, and has a hysteresis effect of voltage 1 in the input/output transfer characteristic.

In Figure 3, noise is superimposed on the input voltage waveform, for example waveform b.
111, and due to the hysteresis effect of this voltage comparator circuit, the reference voltage waveform al! which forms the threshold voltage is Even when the voltage is close to cl!, the operational amplifier 4 performs a stable comparison/judgment operation, and the output voltage waveform as a result of the comparison is shown in the figure). It can be stably obtained as follows. [Effects of the Invention] As explained above, according to the voltage comparison circuit according to the present invention, the input terminal applied to the first input terminal via the resistor is compared with the reference voltage applied to the second input terminal. an operational amplifier that outputs the comparison result; a current switch whose conduction or non-conduction is determined based on the comparison result output from the operational amplifier; and when the current switch is conductive, a first input terminal of the operational amplifier and the Since it is equipped with a constant current source connected between the connection point with the resistor and the ground side,
If the comparison result is reversed in the operational amplifier, based on this comparison result (conduction and non-conduction of the current switch), the reference voltage is geometrically shifted up or down relative to the input voltage, and hysteresis is applied to the input/output transfer characteristics. This has the effect of increasing the stability of the operational amplifier's comparison/determination operation with respect to input noise near the reference voltage.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an embodiment of the voltage comparison circuit according to the present invention, FIG. 2 is a voltage waveform diagram of each part showing the basic operation of this voltage comparison circuit, and FIG. 3 is a diagram showing the voltage waveforms of each part in this voltage comparison circuit. A voltage waveform diagram of each part showing the operation when noise is superimposed on the input voltage waveform, Figure 4 is a circuit configuration diagram showing a typical example of a conventional voltage comparison circuit, and Figure 5 shows the basic operation of this voltage comparison circuit. FIG. 6 is a voltage waveform diagram of each part showing the operation of this voltage comparator circuit when noise is superimposed on its input voltage waveform. l...Input terminal, 2...Reference voltage input terminal, 3...
-Resistor, 4... operational amplifier, 5... current switch, 6... constant current source, 7... output terminal.

Claims (1)

[Claims] an operational amplifier that compares an input voltage applied to its first input terminal via a resistor with a reference voltage applied to its second input terminal and outputs the comparison result; a current switch whose conduction and non-conduction are determined based on the current switch; and a constant current source connected between a connection point between the first input terminal of the operational amplifier and the resistor and a ground side when the current switch is conductive. A voltage comparison circuit equipped with