JPH09243671A - Hysteresis comparator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the hysteresis characteristic of a hysteresis comparator. SOLUTION: A comparator 12 compares an input signal VI with a reference signal VA so as to output a signal V0. The ratio of the emitter area of a transistor T11 to that of a transistor T12 at a hysteresis circuit 13 is 1:n. A switch 15 is turned on and off by the signal V0 so as to supply and cut off a current to the transistors from a constant-current source 14. A voltage source V1 and a resistance R1 are connected to the emitter of the transistor T11, a resistance R2 is connected to the emitter of the transistor T12, and a resistance R3 is connected to a voltage source V2. The reference signal VA is output from the connection point of the resistances R1 to R3. The collector and the base of the transistor T11 are connected, and the collector and the base of the transistor T12 are connected. The current of the constant-current source 14 is set at (n+1)/n times as large as a current flowing in the transistor T12 so that the emitter voltage of the transistor T12 becomes equal to the voltage source V1.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to hysteresis comparators. With the increase in accuracy of electronic equipment systems using semiconductor devices in recent years, the accuracy of hysteresis comparators used in these systems is also required to be improved. Therefore, it is necessary to improve the hysteresis characteristic of the hysteresis comparator.

[0002]

2. Description of the Related Art FIG. 7 shows a circuit configuration of a conventional hysteresis comparator. The hysteresis comparator 1 includes a comparator 2 and a hysteresis circuit 3. The comparator 2 is supplied with a high potential power supply V _CC and a low potential power supply V _SS as operating power supplies. The comparator 2 inputs the input signal VI to the + side input terminal (non-inverting input terminal) and inputs the reference signal VD of the hysteresis circuit 3 to the − side input terminal (inverting input terminal) as a reference signal. When the voltage of the input signal VI is higher than the voltage of the reference signal VD, the comparator 2 outputs the signal VO of the power supply V _CC level (H level), and the voltage of the input signal VI is lower than the voltage of the reference signal VD. In this case, the signal VO of the power supply V _SS level (L level) is output.

The hysteresis circuit 3 has three resistors R4.
R5 and R6 and npn transistor T as a switch
1 is provided. One end of the resistor R6 is connected to the high potential power supply V _CC , and the other end is connected to one end of the resistor R4. Resistance R
The other end of 4 is connected to the low potential power supply V _SS . Resistance R5
Is connected to the node D between the resistors R6 and R4, and the other end is connected to the collector of the npn transistor T1. The emitter of the npn transistor T1 is a low potential power supply V
_It is connected to _SS , and the output signal VO of the comparator 2 is input to the base.

The hysteresis circuit 3 has resistors R6 and R based on whether the npn transistor T1 is on or off.
The reference signal VD is output from the node D between the four. That is, when the npn transistor T1 is off,
Since a current flows from the power supply V _CC to the power supply V _SS via only the resistors R6 and R4, the voltage VD1 of the reference signal VD is expressed by the following mathematical expression 1.

[0005]

[Equation 1]

On the other hand, when the npn transistor T1 is turned on, along with the current flows to the power supply V _SS from the power supply V _CC through a resistor R6, R4, current to the power supply V _SS via the resistor R5 and the npn transistor T1 Flowing. At this time, the voltage of the reference signal VD is set to VD2, and the resistors R6 and R6 are
The currents flowing in 4 and R5 are I1, I2 and I3, respectively, and the voltage of the node E (collector of the npn transistor T1) is VE. The voltage VE is the collector-emitter voltage V of the npn transistor T1 with respect to the low potential power supply V _SS.
It is the value with _CE added. Then

[0007]

[Equation 2]

Voltage across the resistor R6 (V _CC -VD2)
Is

[0009]

(Equation 3)

[0010] Therefore, transposing each side and rearranging

[0011]

(Equation 4)

## EQU1 ## Therefore,

[0013]

(Equation 5)

As can be seen from the equation (5), the voltage VD2 of the reference signal VD when the npn transistor T1 is on is influenced by the collector-emitter voltage V _CE of the npn transistor T1. The collector-emitter voltage V _CE of the npn transistor T1 is, for example, 0.1 V (volt) to 0.3 V (volt).

FIG. 8 shows a conventional hysteresis circuit 3 in which a constant current source 4 is connected to the base of an npn transistor T1 and the voltages of power supplies V _CC and V _SS are 12 V and -12, respectively.
V, and the resistance values of the resistors R4, R5, and R6 are 2.
The characteristics of the reference signal VD when 4 kΩ (kΩ), 2.67 kΩ, and 8 kΩ are shown.

As shown in FIG. 8B, when the current of the constant current source 4 is 0 A (ampere), that is, when the npn transistor T1 is off, the voltage of the reference signal VD is-.
Although it can be set to 8.0 V, even if the current of the constant current source 4 is increased, the collector-emitter voltage V _CE of the npn transistor T1 cannot be set to 0 V, so that the voltage of the reference signal VD is -V _. It cannot be 10.0V.

[0017]

Therefore, in the conventional hysteresis comparator 1, the npn transistor T
The voltage of the reference signal VD when 1 is on is influenced by the collector-emitter voltage V _CE of the npn transistor T1 and cannot be determined by the resistors R4, R5 and R6. As a result, highly accurate hysteresis characteristics could not be obtained.

The present invention has been made to solve the above problems, and an object thereof is to provide a hysteresis comparator having a highly accurate hysteresis characteristic.

[0019]

FIG. 1 is a diagram for explaining the principle of the invention of claim 1 including claim 2. The comparator 12 is supplied with a high potential power supply V _CC and a low potential power supply V _SS as operating power supplies. The comparator 12 compares the input signal VI with the reference signal VA, and when the voltage of the input signal VI is higher than the voltage of the reference signal VA, outputs the signal VO of the voltage of the high potential power supply V _CC ,
When the voltage of the input signal VI is lower than the voltage of the reference signal VA, the signal VO of the voltage of the low potential power supply V _SS is output.

The hysteresis circuit 13 outputs to the comparator 12 the reference signal VA of the first voltage and the second voltage having different voltage values based on the output signal of the comparator 12. Constant current source 14
Supplies a constant current.

First and second transistors T11, T1
Reference numeral 2 denotes a current flowing from the constant current source 14, and the ratio of the emitter areas of the first and second transistors T11 and T12 is 1: n (n is a positive number).

The switch 15 is an output signal VO of the comparator 12.
Is to be turned on / off based on the above, and to supply and cut off the current from the constant current source 14 to the first and second transistors T11 and T12.

The first voltage source V1 is the first transistor T
11, the first resistor R1 has one end connected to the emitter of the first transistor T11.
One end of the second resistor R2 is connected to the emitter of the second transistor T12. One end of the third resistor R3 is the second
Of the voltage source V2. First to third resistors R1
~ Reference signal VA from the connection point where the other ends of R3 are connected to each other
Is output.

The collector and base of the first transistor T11 are connected to each other, and the collector and base of the second transistor T12 are connected to each other. And
The current supplied by the constant current source 14 is the second transistor T
It is set to (n + 1) / n times the current flowing through the second transistor T12 so that the voltage of the 12th emitter becomes equal to the voltage of the first voltage source V1.

FIG. 2 is a diagram for explaining the principle of the invention of claim 1 including claim 3. The hysteresis circuit 17 outputs to the comparator 12 the reference signal VA of the first voltage and the second voltage having different voltage values based on the output signal of the comparator 12.

The collector and base of the first transistor T11 are connected to each other, and the second transistor T12 is current-mirror connected to the first transistor T11. Regarding the current supplied by the constant current source 14, the voltage of the emitter of the second transistor T12 is the first voltage source V1.
Of the second transistor T12 so that it is equal to the voltage of
It is set to 1 / n times the current flowing through.

(Operation) Therefore, in the inventions of claims 1 and 2, when the current from the constant current source 14 to the first and second transistors T11 and T12 is cut off by the switch 15, the first signal of the reference signal VA is changed. The voltage of 1 is represented only by the values of the first and third resistors R1 and R3. Further, the switch 15 allows the constant current source 14 to move the first and second transistors T
When a current is supplied to 11 and T12, the potential of the emitter of the second transistor T12 becomes the same potential as the potential of the first voltage source V1, and the second voltage of the reference signal VA changes to that of the second transistor T12. It is not affected by the collector-emitter voltage and is represented only by the values of the first to third resistors R1, R2 and R3. Therefore, a highly accurate hysteresis characteristic can be obtained.

Also, in the third aspect of the invention, the first voltage and the second voltage of the reference signal VA are resistors R1, R2 and R2.
It is represented only by the value of R3, and it is possible to obtain an accurate hysteresis characteristic and to reduce the current consumption of the constant current source 14 to reduce the current consumption.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] A first embodiment of the present invention will be described below with reference to FIGS.

FIG. 3 shows a circuit configuration of the hysteresis comparator 21 of this embodiment. Hysteresis comparator 21
Includes a comparator 12, a hysteresis circuit 22, and an output circuit 25. The comparator 12 has a high potential power source (hereinafter referred to as a high power source) V _CC and a low potential power source (hereinafter referred to as a low power source) V _SS.
And are supplied as operating power. The comparator 12 inputs the input signal VI to the + side input terminal (non-inverting input terminal),
-The reference signal VA of the hysteresis circuit 22 is input to the input terminal (inverting input terminal).

When the voltage of the input signal VI is equal to or higher than the voltage of the reference signal VA, the comparator 12 outputs the signal VC1 of H level (high power supply V _CC level), and the voltage of the input signal VI is the voltage of the reference signal VA. L level (low power supply V
The signal VC1 of _SS level) is output.

The output circuit 25 includes constant current sources 26 and 27, resistors 28 and 33, an npn transistor 30 for input, an npn transistor 31 for output, and a diode 32.

The input npn transistor 30 inputs the collector connected to the high power supply V _CC , the emitter connected to the low power supply V _SS , and the output signal VC1 of the comparator 12 via the constant current source 26. And a base. The npn transistor 30 is turned on based on the H-level signal VC1 and turned off based on the L-level signal VC1.

The diode 32 has an anode connected to the high power supply V _CC via the constant current source 27, and a cathode connected to the low power supply V _SS via the resistor 33. N for output
The pn transistor 31 is connected to the high power source V _CC via the resistor 28.
, A collector connected to the low power supply V _SS , and a base connected to the collector of the input npn transistor 30.

The npn transistor 31 outputs an output signal VO based on the input signal VI from its collector. That is, when the npn transistor 30 is turned on based on the H-level signal VC1, the base potential of the npn transistor 31 drops to the L level.
1 turns off and outputs an output signal VO of H level (high power supply V _CC level). On the contrary, when the npn transistor 30 is turned off based on the L-level signal VC1, the base potential of the npn transistor 31 rises to the H level.
The n-transistor 31 is turned on and outputs the output signal VO of L level (low power supply V _SS level).

The hysteresis circuit 22 includes an npn transistor T11 as a first transistor, an npn transistor T12 as a second transistor, and a first to a first transistor.
Third resistors R1, R2, R3 and np as a switch
The n-transistor 23, the resistor 24, and the constant current source 14 are provided. The ratio of the emitter areas of the npn transistors T11 and T12 is set to 1: n (n is a positive number).

The constant current source 14 is connected to the high power source V _CC and supplies a constant current I. The collector and the base of the npn transistor T11 are connected to each other and to the constant current source 14. npn
The collector and the base of the transistor T12 are connected to each other, and are connected to the constant current source 14 in parallel with the first npn transistor T11. The emitter of the first npn transistor T11 is connected to the ground GND as the first voltage source (V1).

The npn transistor 23 has a collector connected to the collectors of the npn transistors T11 and T12, an emitter connected to the base of the output npn transistor 31 via a resistor 24, and a constant current source 27.
And a base connected to the node between the diodes 32.

When the npn transistor 30 is turned on to turn on the npn
When the base potential of the transistor 31 drops to L level, the npn transistor 23 turns on and the constant current source 14
Current to the npn transistors T11 and T12 is cut off. On the contrary, the npn transistor 30 is turned off and the npn
When the base potential of the transistor 31 rises to the H level, the npn transistor 23 turns off and the constant current source 14
To supply current to the npn transistors T11 and T12.

The first resistor R1 is connected to the emitter of the first npn transistor T11 and the ground GND, and one end of the second resistor R2 is connected to the second npn transistor T12.
Connected to the emitter. One end of the third resistor R3 is connected to the power supply V _SS as the second voltage source (V2). The other ends of the first to third resistors R1 to R3 are connected to each other at a connection point A, and the reference signal VA is output from the connection point A.

The current supplied by the constant current source 14 is
It is set to (n + 1) / n times the current flowing through the npn transistor T12 so that the voltage of the emitter of the npn transistor T12 becomes equal to the voltage of the ground GND.

Therefore, the hysteresis circuit 22 outputs the reference signal VA of the first voltage and the second voltage having different voltage values based on the conduction state and the non-conduction state of the npn transistor 23.

That is, when the npn transistor 23 is turned on, the ground GND (first voltage source V
1) via the resistors R1 and R3 only to the low power supply V _SS (second
Since a current flows through the voltage source V2) of the above, the voltage VA1 of the reference signal VA is expressed by the following Expression 6.

[0044]

(Equation 6)

On the other hand, when the npn transistor 23 is off, the current I of the constant current source 14 flows through the first and second npn transistors T11 and T12. The voltage of the reference signal VA at this time is VA2, and the resistors R1, R2,
The currents flowing through R3 are I1, I2 and I, respectively, and np
The voltage of the emitter of the n-transistor T12 is VB.
Then

[0046]

(Equation 7)

Is as follows. From number 7,

[0048]

(Equation 8)

Is as follows. Therefore, transposing each side and rearranging

[0050]

[Equation 9]

Is as follows. At this time, the current I is

[0052]

(Equation 10)

Is as follows. When the current I of the constant current source 14 is set to a value of the equation 10, the base-emitter voltages of the npn transistors T11 and T12 become equal, so VB = V1
Becomes Therefore, the second voltage VA2 is

[0054]

[Equation 11]

And the constant current I is

[0056]

(Equation 12)

Is as follows. In this embodiment, the ground GND
Is the first voltage source V1 and the low power supply V _SS is the second voltage source V2.

[0058]

(Equation 13)

Is as follows. Since the low power supply V _SS has a negative voltage, VA2> VA1. The constant current I is

[0060]

[Equation 14]

It becomes Next, the operation of the hysteresis comparator 21 configured as above will be described.

Now, the voltage of the input signal VI is the reference signal VA.
When the voltage is lower than the voltage of, the comparator 12 outputs an L level signal VC1. The npn transistor 30 is turned off based on the signal VC1 of L level, and the base potential of the npn transistor 31 becomes H level. Then n
The pn transistor 31 is turned on and the L level output signal V
Output O.

At this time, since the base voltage of the npn transistor 31 is at the H level, the npn transistor 23
Is turned off, and the npn transistor T1 from the constant current source 14 is turned off.
Supply of current to T1 and T12 is permitted. Therefore, the voltage of the reference signal VA of the hysteresis circuit 22 is VA2 (> V
A1).

Next, the voltage of the input signal VI rises to VA
When it becomes 2 or more, the signal VC of H level is output from the comparator 12.
1 is output. Np based on H level signal VC1
The n-transistor 30 turns on, and the npn-transistor 31
The base potential of the L level becomes L level. Then, the npn transistor 31 is turned off and the H level output signal VO is output.

At this time, since the base voltage of the npn transistor 31 is at the L level, the npn transistor 23
Turns on, and the constant current source 14 turns on the npn transistor T1.
1, the current to T12 is cut off. Therefore, the voltage of the reference signal VA of the hysteresis circuit 22 becomes VA1.

After this, the voltage of the input signal VI drops and V
When it becomes lower than A1, the signal VC1 becomes L level,
The npn transistor 30 is turned off, the npn transistor 31 is turned on, and the L-level output signal VO is output.

At this time, the npn transistor 23 is turned off, and the constant current source 14 causes the npn transistors T11, T
Current is supplied to 12, and the voltage of the reference signal VA of the hysteresis circuit 22 returns to VA2.

Incidentally, the resistance values of the resistors R1, R2 and R3 are set to 4 kΩ, 2.67 kΩ and 8 kΩ, respectively, and the voltages of the high power supply V _CC and the low power supply V _SS are 12 V and -12 V, respectively.
FIG. 4 shows the output characteristic of the hysteresis circuit 22 when the ratio of the emitter areas of the npn transistors T11 and T12 is set to 1: 1. As shown in FIG. 4B, when I = 0 (A), VA1 = -4 (V),
When the constant current I is, VA2 = -2 (V). At this time, I = 1.5 (mA).

The present embodiment has the following effects. (1) In the present embodiment, when the current from the constant current source 14 to the npn transistors T11 and T12 is cut off by turning on the npn transistor 23 of the hysteresis circuit 22, the first voltage VA1 of the reference signal VA becomes the first voltage. And the third
It is represented only by the values of the resistors R1 and R3. Further, when the current is supplied from the constant current source 14 to the npn transistors T11 and T12 by turning off the npn transistor 23, the potential of the emitter of the npn transistor T12 becomes equal to the potential of the ground GND, and the second potential of the reference signal VA is exceeded.
Voltage VA2 of the collector of npn transistor T12
The first to third resistors R are not affected by the voltage between the emitters.
It is represented only by the values of 1, R2 and R3. Therefore, a highly accurate hysteresis characteristic can be obtained.

[Second Embodiment] Next, a second embodiment of the present invention will be described.
The embodiment will be described with reference to FIGS. In order to avoid redundant description, the same elements as those described in FIG. 3 are denoted by the same reference numerals.

FIG. 5 shows a circuit configuration of the hysteresis comparator 41 of this embodiment. Hysteresis comparator 41
Includes the comparator 12, a hysteresis circuit 42, and an output circuit 46.

The output circuit 46 includes constant current sources 47 and 48, resistors 49 and 52, an input pnp transistor 50, an output pnp transistor 51, and a diode 52.

The input pnp transistor 50 inputs the emitter connected to the high power supply V _CC , the collector connected to the low power supply V _SS via the constant current source 47, and the output signal VC1 of the comparator 12. And a base. The pnp transistor 50 turns on based on the L level signal VC1 and turns off based on the H level signal VC1.

The diode 52 has an anode connected to the high power supply V _CC via the resistor 53 and a cathode connected to the low power supply V _SS via the constant current source 48. P for output
The np transistor 51 has an emitter connected to the high power supply V _CC , a collector connected to the low power supply V _SS via the resistor 49, and a base connected to the collector of the input pnp transistor 50.

The pnp transistor 51 outputs an output signal VO based on the input signal VI from its collector. That is, when the pnp transistor 50 is turned on based on the L-level signal VC1, the base potential of the pnp transistor 51 rises to the H level, so the pnp transistor 5
1 turns off and outputs the L-level output signal VO. On the contrary, when the pnp transistor 50 is turned off based on the H-level signal VC1, the base potential of the pnp transistor 51 drops to the L level.
Turns on and outputs the H-level output signal VO.

The hysteresis circuit 42 includes a pnp transistor T13 as a first transistor, a pnp transistor T14 as a second transistor, and a first to a first transistor.
Third resistors R1, R2, R3 and np as a switch
The n-transistor 23, the resistor 45, and the constant current source 43 are provided. The ratio of the emitter areas of the pnp transistors T13 and T14 is set to 1: n (n is a positive number).

The constant current source 43 is connected to the low power source V _SS and supplies a constant current I. The collector and base of the pnp transistor T13 are connected to each other and to the constant current source 43. pnp
The emitter of the transistor T13 is the first voltage source (V1)
Is connected to the ground GND. The base of the pnp transistor T14 is connected to the base of the pnp transistor T13, and the pnp transistor T14 is current-mirror connected to the pnp transistor T13. The collector of the pnp transistor T14 is connected to the low power supply V _SS .

The pnp transistor 44 has a collector connected to the bases of the pnp transistors T13 and T14, an emitter connected to the base of the output pnp transistor 51 via a resistor 45, a constant current source 48 and a diode 52. And a base connected to the node in between.

The pnp transistor 50 is turned on to turn on the pnp
When the base potential of the transistor 51 rises to the H level, the pnp transistor 44 turns on and the constant current source 43
To pnp transistors T13 and T14 are cut off. Conversely, the pnp transistor 50 turns off and the pnp
When the base potential of the transistor 51 drops to L level, the pnp transistor 44 turns off and the constant current source 43
To supply current to the pnp transistors T13 and T14.

The first resistor R1 is a pnp transistor T1.
3 and the ground GND, and one end of the second resistor R2 is connected to the emitter of the pnp transistor T14. One end of the third resistor R3 is connected to the high power source V _CC as the second voltage source (V2). First to first
The other ends of the third resistors R1 to R3 are connected to each other at a connection point A, and the reference signal VA is output from the connection point A.

The current supplied by the constant current source 43 is
It is set to 1 / n times the current flowing through the pnp transistor T14 so that the voltage of the emitter of the pnp transistor T14 becomes equal to the voltage of the ground GND.

Therefore, the hysteresis circuit 42 outputs the reference signal VA of the first voltage and the second voltage having different voltage values based on the conduction state and the non-conduction state of the pnp transistor 44.

That is, when the pnp transistor 44 is on, a current flows from the high power supply V _CC (second voltage source V2) to the ground GND (first voltage source V1) via only the resistors R3 and R1. Therefore, the voltage VA1 of the reference signal VA is represented by the following Expression 15 only by the resistance values of the resistors R3 and R1.

[0084]

(Equation 15)

On the other hand, when the pnp transistor 44 is off, the current I of the constant current source 43 flows through the first and second pnp transistors T13 and T14. At this time, the voltage of the reference signal VA is VA2, the currents flowing through the resistors R1 and R2 are I1 and I2, respectively, and the emitter voltage of the pnp transistor T14 is VB. Then

[0086]

(Equation 16)

It becomes At this time, the current flowing through the resistor R3 is

[0088]

[Equation 17]

## EQU11 ## Substituting equation 16 into equation 17,

[0090]

(Equation 18)

It becomes Therefore, transposing each side and rearranging

[0092]

[Equation 19]

Is obtained. At this time, the current I2 is

[0094]

(Equation 20)

Is obtained. When the current I2 is set to the value of the equation 21, the base-emitter voltages of the pnp transistors T13 and T14 become equal, so VB = V1. Therefore, the current I2 and the constant current I are

[0096]

(Equation 21)

Therefore, the second voltage VA2 is

[0098]

(Equation 22)

## EQU10 ## In this embodiment, the ground GND
Is the first voltage source V1 and the high power source V _CC is the second voltage source V2, so the first and second voltages V1 and V2 of the reference voltage VA are
A1 and VA2 are

[0100]

(Equation 23)

Is obtained. Since the high power supply V _CC has a positive voltage, VA2 <VA1. The constant current I is

[0102]

(Equation 24)

Is obtained. Next, the operation of the hysteresis comparator 41 configured as described above will be described.

Now, the voltage of the input signal VI is the reference signal VA.
When the voltage is lower than the voltage of, the comparator 12 outputs an L level signal VC1. The pnp transistor 50 is turned on based on the L-level signal VC1 and the base potential of the pnp transistor 51 becomes H level. Then p
The np transistor 51 is turned off, and the L level output signal V
Output O.

At this time, since the base voltage of the pnp transistor 51 is at the H level, the pnp transistor 44
Is turned on, and the pnp transistor T1 is turned on from the constant current source 43.
3, the current to T14 is cut off. Therefore, the voltage of the reference signal VA of the hysteresis circuit 42 is VA1 (> VA2).
It has become.

Next, the voltage of the input signal VI rises to VA
When it is 1 or more, the H-level signal VC1 is output.
The pnp transistor 5 based on the H level signal VC1
0 is turned off, and the base potential of the pnp transistor 51 is L
Become a level. Then, the pnp transistor 51 is turned on and outputs the L level output signal VO.

At this time, since the base voltage of the pnp transistor 51 is at the L level, the pnp transistor 44
Is turned off, and the pnp transistor T1 from the constant current source 43 is turned off.
3, the supply of current to T14 is allowed. Therefore, the voltage of the reference signal VA of the hysteresis circuit 42 becomes VA2.

After that, the voltage of the input signal VI is lowered to V
When it becomes lower than A2, the signal VC1 becomes L level,
The pnp transistor 50 is turned on, the pnp transistor 51 is turned off, and the L-level output signal VO is output.

At this time, the pnp transistor 44 is turned on, and the constant current source 14 causes the pnp transistors T13, T
The current to 14 is cut off, and the voltage of the reference signal VA of the hysteresis circuit 42 returns to VA1.

By the way, the resistance values of the resistors R1, R2 and R3 are set to 4 kΩ, 2.67 kΩ and 8 kΩ, respectively, and the voltages of the high power supply V _CC and the low power supply V _SS are 12 V and -12 V, respectively.
6 shows the output characteristic of the hysteresis circuit 42 in such a case. FIG. 6B shows pnp transistors T13 and T14.
Shows the output characteristics when the ratio of the emitter area of is set to 1: 1. When I = 0 (A), VA1 = 4 (V), and when the constant current I is 750 (μA), VA2 = 2.
(V). Further, FIG. 6C shows the output characteristics when the ratio of the emitter areas of the pnp transistors T13 and T14 is set to 1: 5, and when I = 0 (A), VA1 =
4 (V), and when the constant current I is 150 (μA), V
A2 = 2 (V).

The present embodiment has the following effects. (1) In the present embodiment, when the current from the constant current source 43 to the pnp transistors T13 and T14 is cut off by turning on the pnp transistor 44 of the hysteresis circuit 42, the first voltage VA1 of the reference signal VA changes to the first voltage VA1. And the third
It is represented only by the values of the resistors R1 and R3. When current is supplied to the pnp transistors T13 and T14 from the constant current source 43 by turning off the pnp transistor 44, the potential of the emitter of the pnp transistor T14 becomes equal to the potential of the ground GND, and the second potential of the reference signal VA is exceeded.
Voltage VA2 of the collector of the pnp transistor T14
The first to third resistors R are not affected by the voltage between the emitters.
It is represented only by the resistance values of 1, R2 and R3. Therefore, a highly accurate hysteresis characteristic can be obtained.

(2) The pnp transistor T1 of this embodiment
Since the current mirrors 3 and T14 are connected to each other, the current value I of the constant current source 43 can be reduced, and the current consumption can be reduced.

[0113]

As described in detail above, the present invention can provide a hysteresis comparator having highly accurate hysteresis characteristics.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the invention of claims 1 and 2.

FIG. 2 is an explanatory view of the principle of the invention of claims 1 and 3;

FIG. 3 is a circuit diagram showing a hysteresis comparator of a first form.

FIG. 4 is an explanatory diagram showing output characteristics of the hysteresis circuit of FIG.

FIG. 5 is a circuit diagram showing a hysteresis comparator of a second form.

6 is an explanatory diagram showing the output characteristics of the hysteresis circuit of FIG.

FIG. 7 is a circuit diagram showing a conventional hysteresis comparator.

FIG. 8 is an explanatory diagram showing output characteristics of the hysteresis circuit of FIG.

[Explanation of symbols]

12 comparators 13 and 17 hysteresis circuit 14 constant current source 15 switches R1 to R3 first to third resistors T11 and T12 npn transistors as first and second transistors V1 first voltage source V2 second voltage source VA Reference signal V _CC High potential power supply VI Input signal VO Output signal V _SS Low potential power supply

Front Page Continuation (72) Inventor Hisao Suzuki 1844-2, Kozoji-cho, Kasugai-shi, Aichi Prefecture Fujitsu Viels-E Co., Ltd. (72) Inventor Yoshiaki Sano 2-844, Kozoji-cho, Kasugai-shi, Aichi Share In the company

Claims (3)

[Claims] 1. A high-potential power supply and a low-potential power supply are supplied as operating power supplies, and an input signal and a reference signal are compared. When the voltage of the input signal is higher than the voltage of the reference signal, the high-potential power supply or the low-potential power supply is used. A comparator that outputs an output signal of the voltage of the potential power supply and outputs an output signal of the voltage of the low potential power supply or the high potential power supply when the voltage of the input signal is lower than the voltage of the reference signal, and an output signal of the comparator A hysteresis circuit for outputting a reference signal of a first voltage and a second voltage having different voltage values to the comparator based on the above-mentioned, wherein the hysteresis circuit supplies a constant current. Of the constant current source and the first and second transistors for flowing the current of the constant current source, the ratio of the emitter areas of the first and second transistors is 1: n (n is a positive number) And ON / OFF based on the output signal of the comparator, and
A switch for supplying and blocking a current from the constant current source to the first and second transistors; a first voltage source connected to an emitter of the first transistor; A second voltage source different from the voltage source, a first resistor whose one end is connected to the emitter of the first transistor, and a second resistor whose one end is connected to the emitter of the second transistor, A third resistor having one end connected to the second voltage source, and outputting the reference signal from a connection point where the other ends of the first to third resistors are connected to each other. A hysteresis comparator in which the current supplied by a current source is set to a value such that the voltage of the emitter of the second transistor becomes equal to the voltage of the first voltage source. 2. The collector and base of the first transistor are connected to each other, the collector and base of the second transistor are connected to each other, and the current supplied by the constant current source is the second transistor. The hysteresis comparator according to claim 1, wherein the current is (n + 1) / n times the current flowing through the hysteresis comparator. 3. The collector and base of the first transistor are connected to each other, the second transistor is current-mirror connected to the first transistor, and the current supplied by the constant current source is The hysteresis comparator according to claim 1, which is 1 / n times the current flowing through the second transistor.