JPH1174767A - Comparator having hysteresis - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate effects of an output voltage value and to improve the accuracy by comparing voltages of 1st and 2nd voltages divided by resistors in a 1st differential circuit and making the lower voltage as a comparative voltage with an input voltage. SOLUTION: Inside a current supplying part 15, an NPN transistor Q7 is on and current I of a current source 15 is supplied to a dividing voltage point A through transistors Q8 to Q11 when an output of an outputting part 14 is on a high level. A differential circuit 11 compares voltages of the point A and of a dividing voltage point B and the lower voltage is supplied to a differential circuit 13. The circuit 13 compares fall threshold voltage with input voltage Vin and a low level is outputted. In this way, the part 15 makes the fall threshold voltage higher than rise threshold voltage according to whether output voltage Vout is on low or high level, the circuit 11 compares voltages of dividing voltage resistance, and the lower voltage is made as comparative voltage with input voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly accurate comparator with hysteresis.

[0002]

2. Description of the Related Art Since a comparator detects a small voltage difference between inputs, if there is a slight noise near a threshold value, it responds to the noise. For this reason, a hysteresis characteristic is provided so as not to react to noise, and the noise is enhanced. Such an apparatus is shown in FIG.

In FIG. 1, reference numeral 2 denotes an operational amplifier, which receives a comparison voltage Vref at a negative terminal and outputs a comparison result Vout. R7 is a resistor having one end to which the input voltage Vin is input and the other end connected to the + terminal of the operational amplifier 2. R8 is a resistor having one end connected to the + terminal of the operational amplifier 2 and the other end connected to the output terminal of the operational amplifier 2.

[0004] The operation of such an apparatus will be described. FIG. 5 is a diagram for explaining the operation of the device of FIG. (A) shows the input voltage Vin, and (b) shows the output voltage Vout. Operational amplifier 2
Is determined by the power supply voltage of the operational amplifier 2. Here, the high level is Vh, and the low level is Vl.

The rising threshold voltage Vth +
Is as follows. Vth + = (1 + R7 / R8) .Vref-R7 / R8.Vl The falling threshold voltage Vth- is as follows. Vth − = (1 + R7 / R8) · Vref−R7 / R8 · Vh

[0006]

As described above, the threshold voltage is affected by the output voltage Vout.
The output voltage Vout is likely to fluctuate under the influence of a load or the like, which is a major factor of a threshold voltage error. That is, the accuracy of the comparator is deteriorated.

An object of the present invention is to realize a highly accurate comparator with hysteresis without being affected by the output voltage.

[0008]

According to the present invention, there is provided a first voltage dividing resistor for dividing a comparison voltage and defining a falling threshold voltage, and a first voltage dividing resistor for dividing the comparison voltage and defining a rising threshold voltage. 2, a first differential circuit that compares a divided voltage of the first divided resistor with a divided voltage of the second divided resistor, and outputs a lower voltage; A second differential circuit for comparing an output of the first differential circuit with an input voltage; and a current flowing to a voltage dividing point of the first voltage dividing resistor based on an output of the second differential circuit. Supply,
A current supply unit for setting the falling threshold voltage to a voltage higher than the rising threshold voltage, wherein the output of the second differential circuit is used as a comparison result.

In the present invention, the current supply unit supplies the current to the voltage dividing point of the first voltage dividing resistor based on the output of the second differential circuit, and raises the falling threshold voltage. Set the voltage higher than the threshold voltage. Then, the first differential circuit compares the threshold voltages generated by the first and second voltage-dividing resistors, and uses the lower voltage as the voltage to be compared with the input voltage.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of the present invention. In the figure, R1 is a resistor, one end of which is a comparison voltage Vref.
Connect to R2 is a resistor having one end connected to the other end of the resistor R1 and the other end grounded. That is, the resistors R1 and R2 are the first voltage-dividing resistors, which divide the comparison voltage Vref and define the falling threshold voltage Vth-.

R3 is a resistor having one end connected to the comparison voltage Vref. R4 is a resistor having one end connected to the other end of the resistor R4 and the other end grounded. That is, the resistors R3 and R4 are connected to the second
The reference voltage Vref is divided by the voltage dividing resistor to define the rising threshold voltage Vth +.

Reference numeral 1 denotes a comparator, which includes an input voltage, a resistance R,
1 and the voltage at the voltage dividing point A of the resistor R2, and the resistors R3 and R4.
, And outputs the comparison result Vout. The specific configuration of the comparator 1 will be described with reference to FIG.

In the comparator 1, reference numeral 11 denotes a first differential circuit which compares the voltage at the voltage dividing point A between the resistors R1 and R2 with the voltage at the voltage dividing point B between the resistors R3 and R4, Output voltage. Then, the PNP transistors Q1,
It comprises Q2 and current source I1. The PNP transistor Q1 has the base connected to the voltage dividing point A of the resistors R1 and R2, the emitter connected to the current source I1, and the collector grounded. The PNP transistor Q2 has resistors R3 and R
4 is connected, the current source I1 is connected to the emitter, and the collector is grounded.

Reference numeral 12 denotes a buffer, and a PNP transistor Q
3 and a current source I2, and inputs an input voltage Vin.
In the PNP transistor Q3, the input voltage Vin is input to the base, the current source I2 is connected to the emitter, and the collector is grounded.

A second differential circuit 13 compares the output of the first differential circuit 11 with the input voltage Vin. And PN
P-transistors Q4, Q5, current source I3, resistors R5, R
And 6. The PNP transistor Q4 has the base connected to the emitters of the PNP transistors Q1 and Q2, the emitter connected to the current source I3, and the collector connected to the resistor R.
Ground through 5. The PNP transistor Q5 has the base connected to the emitter of the PNP transistor Q3, the emitter connected to the current source I3, and the collector grounded via the resistor R6.

An output unit 14 is an NPN transistor Q6.
And a current source I4, which amplifies the output of the second differential circuit 13 and outputs an output voltage Vout as a comparison result. The NPN transistor Q6 has a base connected to the collector of the PNP transistor Q5 and a collector connected to the current source I4.
And connect the emitter to ground. Then, the output of the collector of the NPN transistor Q6 is set as the comparison result Vout of the comparator 1.

Reference numeral 15 denotes a current supply unit, which outputs resistors R1 and R2 based on the output of the second differential circuit 13 via the output unit 14.
Current is supplied to the voltage dividing point A, and the falling threshold voltage is made higher than the rising threshold voltage. The current supply unit 15 includes NPN transistors Q7 to Q9, PNP transistors Q10, Q11
And a current source I5. NPN transistor Q
Reference numeral 7 connects the collector of the NPN transistor Q6 to the base, connects the current source I5 to the collector, and grounds the emitter. The NPN transistors Q8 and Q9 are current mirror circuits. The NPN transistors Q8 and Q9 supply the same amount of current as the current supplied from the current source I5 connected to the collector of the NPN transistor Q8.
The current flows between the collector and the emitter of the PN transistor Q9.
Similarly, the PNP transistors Q10 and Q11 are current mirror circuits, and a current flows between the collector and the emitter of the NPN transistor Q9 connected to the PNP transistor Q10, and the same amount of current flows through the PNP transistor Q11.
Flow between the emitter and the collector. PNP transistor Q
11 is connected to the collector of the base of the PNP transistor Q1.

The operation of such a device will be described below.
FIG. 3 is a diagram for explaining the operation of the apparatus shown in FIGS.
(A) is the input voltage Vin, (b) is the voltage at the voltage dividing points A and B,
(C) shows the output voltage Vout. When the current I from the current source I5 of the current supply unit 15 is not supplied, the falling threshold voltage Vth- (off) determined by the voltage dividing resistors of the resistors R1 and R2 is as follows. Vth− (off) = R2 / (R1 + R2) · Vref

When the current I of the current source I5 of the current supply unit 15 is supplied, the falling threshold voltage Vth- (on) determined by the voltage dividing resistors R1 and R2 is as follows. Vth− (on) = R2 / (R1 + R2) · Vref + R1 · R2
/ (R1 + R2) · I

The rising threshold voltage Vth + determined by the voltage dividing resistors R3 and R4 is as follows. Vth + = R4 / (R3 + R4) · Vref The relationship of the above equation is as follows. Vth- (off) <Vth + <Vth- (on)

At time t1, the output of the output unit 14 is at a low level. As a result, inside the current supply unit 15, the NPN transistor Q7 is turned off, and the current I of the current source I5 is supplied to the voltage dividing point A via the transistors Q8 to Q11.
Supplied to Therefore, the voltage at the voltage dividing point A is Vth- (on)
Becomes The voltage at the voltage dividing point A and the voltage at the voltage dividing point B are compared by the differential circuit 11, and the lower voltage (Vth +) is
3 is supplied. The differential circuit 13 compares the rising threshold voltage Vth + with the input voltage Vin via the buffer 12, and outputs a high level. As a result, the NPN transistor Q6 turns on, and the output voltage V
out goes low.

At time t2, the output of the output unit 14 is at a high level. As a result, inside the current supply unit 15, the NPN transistor Q7 is turned on, and the current I of the current source I5 is supplied to the voltage dividing point A via the transistors Q8 to Q11.
Not supplied to Therefore, the voltage at the voltage dividing point A is Vth- (of
f). The voltage at the voltage dividing point A and the voltage at the voltage dividing point B are compared by the differential circuit 11, and the lower voltage (Vth− (off)) is supplied to the differential circuit 13. The differential circuit 13 compares the falling threshold voltage Vth- (off) with the input voltage Vin via the buffer 12 and outputs a low level. As a result, the NPN transistor Q6 turns off,
Vout goes high.

As described above, depending on whether the output voltage Vout is the low level or the high level, the current supply unit 15 makes the falling threshold voltage generated by the voltage dividing resistor higher than the rising threshold voltage, and the differential circuit 11 The voltages of the piezoresistors are compared, and the lower voltage is used as the comparison voltage with the input voltage. Therefore, there is no influence of the output voltage value, and the accuracy is good.

In the case of a MOS transistor, a configuration in which a voltage divided by a voltage dividing resistor is switched by a MOS switch can be considered. However, when a bipolar transistor is used, there is no configuration in which a switch is used.
This is particularly effective when a comparator with hysteresis is created in bipolar.

The present invention is not limited to this, but may be as follows. In the embodiment. Although an example using a bipolar transistor has been described, a MOS transistor may be used. The output unit 14 is not an essential requirement of the present invention, but is generally required in circuit design.

Then, the output of the second differential circuit 13 is
The output from the collector of the NP transistor Q4 may be used. In this case, it is natural that the configuration must be changed so that the relationship between the output unit 14 and the current supply unit 15 is established.

In addition, although the configuration in which the falling threshold voltage is varied by the current I has been described, a configuration in which the rising threshold voltage is varied by the current may be employed. In this case, based on the output of the second differential circuit, the current supply unit draws current from the voltage dividing point of the resistors R3 and R4, and sets the rising threshold voltage to a voltage lower than the falling threshold voltage. .
Then, the first differential circuit outputs the higher voltage to the second differential circuit as a threshold voltage.

[0028]

According to the present invention, the following effects can be obtained. According to the first aspect, depending on whether the output voltage is low level or high level, the current supply unit sets the falling threshold voltage generated by the first voltage dividing resistor higher than the rising threshold voltage, and sets the first differential voltage. The circuit compares the voltages of the first and second voltage dividing resistors, and uses the lower voltage as the comparison voltage with the input voltage. Therefore, there is no influence of the output voltage value, and the accuracy is good.

According to the second aspect, depending on whether the output voltage is low level or high level, the current supply unit sets the rising threshold voltage generated by the voltage-dividing resistor lower than the falling threshold voltage, and performs the first differential operation. The voltage of the first and second voltage dividing resistors is compared by a circuit, and the higher voltage is used as a comparison voltage with the input voltage. Therefore, there is no influence of the output voltage value, and the accuracy is good.

According to the third aspect, in the case of a MOS transistor, a configuration in which a voltage divided by a voltage-dividing resistor is switched by a MOS switch is conceivable. This is particularly effective when the comparator with hysteresis is formed by bipolar transistors.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a specific configuration of a comparator 1 of the device of FIG.

FIG. 3 is a diagram for explaining the operation of the apparatus of FIGS.

FIG. 4 is a diagram illustrating a configuration of a conventional comparator with hysteresis.

FIG. 5 is a diagram for explaining the operation of the device of FIG. 4;

[Explanation of symbols]

 R1, R2, R3, R4 Resistance 11 First differential circuit 13 Second differential circuit 15 Voltage supply unit

Claims (3)

[Claims] A first voltage dividing resistor that divides a comparison voltage and defines a falling threshold voltage; a second voltage dividing resistor that divides the comparison voltage and defines a rising threshold voltage; A first differential circuit that compares the divided voltage of the first voltage dividing resistor with the divided voltage of the second voltage dividing resistor and outputs a lower voltage; Second to compare output and input voltage
A current is supplied to the voltage dividing point of the first voltage dividing resistor based on the output of the second differential circuit, and the falling threshold voltage is increased to a voltage higher than the rising threshold voltage. A current supply unit that performs the comparison, and uses the output of the second differential circuit as a comparison result. 2. A first voltage dividing resistor that divides a comparison voltage and defines a falling threshold voltage, a second voltage dividing resistor that divides the comparison voltage and defines a rising threshold voltage, A first differential circuit that compares the divided voltage of the first voltage dividing resistor with the divided voltage of the second voltage dividing resistor and outputs a higher voltage; Second to compare output and input voltage
And a current that draws a current from the voltage dividing point of the second voltage-dividing resistor to make the rising threshold voltage lower than the falling threshold voltage based on the second differential circuit. And a supply section, wherein the output of the second differential circuit is used as a comparison result. 3. The comparator with hysteresis according to claim 1, wherein said comparator comprises a bipolar transistor.