JPH0414311A - Comparator circuit - Google Patents

Abstract

PURPOSE:To increase the input impedance and to easily control a hysteresis width accurately based on a product between a constant current and a resistance of a resistor by providing a 2nd constant current source and generating the hysteresis width with a supply current from the constant current source. CONSTITUTION:An anode of a 1st diode 8 connects to a noninverting input terminal 7, a cathode of the diode 8 connects to a source side of a 1st constant current source 10 together with a cathode of a 2nd diode 9 whose anode connects to an output terminal 11 of a comparator 1. Furthermore, the terminal 11 connects to the input of an inverter 12, the output side of the inverter 12 connects to a cathode of a 4th diode 13, and an anode of the diode 13 connects to a sink side of the 2nd constant current source 15 together with the anode of a 3rd diode 14. Since the hysteresis width is not generated by an input signal like a conventional circuit but generated by the constant current source 15, the input impedance is more increased, the hysteresis width is easily controlled accurately by the product between a constant current and a resistance of a resistor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a comparator circuit with hysteresis whose hysteresis width can be controlled by a constant current circuit and whose input impedance is very high.

2. Description of the Related Art A conventional comparator circuit with hysteresis whose hysteresis width can be controlled is shown in FIG. The configuration and operation will be described below with reference to the drawings. A resistor 6 is connected to the non-inverting input terminal 7, and the other end of the resistor 6 is used as the positive input terminal 5 of a comparator with hysteresis. The non-inverting input terminal 7 is further connected to the anode of the first diode 8. 1st
The cathode of the diode 8 is connected to the cathode of the second diode 9 and further connected to the source side of the constant current source 10 . The anode of the second diode 9 is connected to the output terminal 11 of the comparator 1. In the above circuit configuration, if the inverting input terminal 4 is the negative input terminal, the voltage input to the negative input terminal 4 is V2 (hereinafter referred to as V2), and the voltage input to the positive input terminal 5 is V2 (hereinafter referred to as V2). The voltage is V+ (hereinafter referred to as Vl), the voltage Vo output to the output terminal 11 (hereinafter referred to as Vo), and the voltage at the non-inverting input terminal 7 of the comparator is Vs (hereinafter referred to as Vs). ), then Vs decreases from the state of V2 to V
When the state changes to s>V2, Vs is the constant current source 10
The current is Io (hereinafter referred to as IO), and the resistance value is R(
Hereinafter, it will be referred to as R. ), then V s = Vl −RX I o ...(I
). Further, when the state of Vs>V2 changes to the state of Vs<V2, Vs is Vs=V1. Therefore, the hysteresis width is RXIo, and even if you want to make the hysteresis width smaller, I.

The hysteresis width can be controlled by the size of .

Problems to be Solved by the Invention In such a conventional comparator circuit, in order to draw a constant current 1o from the positive input terminal 5 of the comparator,
If the impedance of the signal source connected to the positive input terminal is not sufficiently low, there is a problem that the input voltage value will deviate.

The present invention solves these conventional problems by supplying a current that causes a hysteresis width from another constant current source, so that even if a signal source with high output impedance is connected, the input voltage value will not deviate. It is an object of the present invention to provide a comparator that can generate a hysteresis width with a small number of elements by switching the constant current using a diode switch.

Means for Solving the Problems In order to achieve the above object, the comparator of the present invention has the following features:
A positive power source is connected to the positive power terminal of the comparator, a negative power source is connected to the negative power terminal of the comparator, and a resistor is connected to the non-inverting input terminal of the comparator.
The other end of the resistor is a positive input terminal of a comparator with hysteresis, and the inverting input terminal of the comparator is a negative input terminal of the comparator with hysteresis. The non-inverting input terminal of the comparator is further connected to the anode of the first diode, the cathode of the first diode is connected to the cathode of the second diode, and the source side of the first constant current source is connected to the non-inverting input terminal of the comparator. connected to. The anode of the second diode is connected to the output terminal of the comparator. The output terminal of the comparator is further connected to the input of an inverter. The output of the inverter is connected to the cathode of the fourth diode, and the anode of the fourth diode is connected to the anode of the third diode and the sink side of the second constant current source. The cathode of the third diode is connected to the positive input terminal of the comparator with hysteresis. The output terminal of the comparator is configured to be the output terminal of the comparator with hysteresis.

Effect With this configuration, the hysteresis width is not created by the input signal as in the conventional case (but is created by another constant current source), so the input impedance is very high (and it is the product of the constant current and the size of the resistance, It becomes possible to easily and accurately control the hysteresis width.

Embodiment A comparator circuit according to an embodiment of the present invention will be described below with reference to FIG.

In the figure, elements having the same functions as those in the conventional example shown in FIG. The anode of the first diode 8 is connected to the non-inverting input terminal 7, and the cathode of the diode 8 is connected to the cathode of the second diode 9 whose anode is connected to the output terminal 11 of the comparator 1. The output terminal 11 of the comparator 1 is further connected to the input terminal of an inverter 12, and the output side of the inverter 12 is connected to the cathode of a fourth diode 13. The anode of the diode 13 is connected to the sink side of the second constant current source 15 together with the anode of the third diode 14, and the cathode of the third diode 14 is connected to the non-inverting input terminal 7. It is connected to the other end of the resistor 6.

To explain the operation of the comparator circuit with hysteresis configured as above, the input voltage v1 of the positive input terminal 5 is
, <v2 to the state of Vl >V2 (and the voltage Vs of the non-inverting input terminal 7 changes the resistance value of the resistor 6 to R
6. The first constant current source current and the first constant current source current are I
When O, V s = V −1o X Rs ・・・・・・(2
), so when the value of V+ becomes higher than V2 by IoXRs, the output voltage V of the output terminal 11 of the comparator 1
o switches from low level VOt to high level VO)I, the second diode 9 is turned on, and the first diode is turned off. At this time, since V o = VOH, the fourth diode 13 is turned on and the third diode 14 is turned off, so the second constant current source current is equal to the fourth diode 13.
The current flows through the diode 13 and the second diode 9 to the first constant current source 10. During this time, the relationship Vs=V1 holds true.

Next, V, > V2 (from D state v, < V2 (7
) state, when V, = Vs = v2,
Vo is the fourth in order to switch from VO)I to voL.
diode 13 and second diode 9 are turned off,
The first diode 8 and the third diode 14 are turned on, resulting in the state of formula C).

At this time, the current Io flowing from the second constant current source through the resistor R6 decreases because the first constant current source is pulling the current IO. Therefore, the input impedance of comparator 1 is very high (and the hysteresis width is IoXR
6, and even if the hysteresis width is set small, I
O can be accurately controlled, and R6 can be made small.

Effects of the Invention As described above, according to the present invention, even when the hysteresis width is set small, the resistance R6 can be made small, and the input impedance is such that the hysteresis width can be accurately controlled at a current of 1o. It is possible to provide a highly practical comparator that can be configured as a comparator with extremely high human teresis.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a comparator circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional comparator circuit. 1...Comparator, 2...Positive side power terminal, 3...Minus side power terminal, 4...
...Inverting input terminal, 5...Positive input terminal, 6...Resistor (R6), 7...Non-inverting input terminal, 8...・First diode, 9...
...Second diode, 10...First constant current source, 11...Output terminal, 12...
Inverter, 13...Fourth diode, 14
...Third diode, 15...Second
constant current source. Name of agent: Patent attorney Shigetaka Awano and one other person Figure 1 Conhalrator Figure 2

Claims (1)

[Claims] In a comparator in which a resistor is connected to a non-inverting input terminal and the other end of the resistor is a positive input terminal, an anode of a first diode is connected to the non-inverting input terminal, and an anode of a second diode is connected to the output terminal. further, the cathode of the first diode and the cathode of the second diode are connected to the source side of the first constant current source, and the output terminal is connected to the input of the inverter, and the output terminal of the inverter is connected to the source side of the first constant current source. and connect the cathode of the fourth diode,
Further, the anode of the fourth diode and the anode of the third diode are connected to a sink source of a second constant current source,
Furthermore, the comparator circuit has a circuit configuration in which the cathode of the third diode is connected to the positive input terminal.