JP2537748B2 - Comparison circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a comparison circuit having a hysteresis characteristic, and more particularly to a comparison circuit capable of setting a hysteresis voltage with high accuracy.

[0002]

2. Description of the Related Art A comparator circuit is a circuit for comparing an input voltage and a reference voltage to obtain a magnitude relationship between the input voltage and the reference voltage, and is used in various electronic circuits such as a trigger circuit. By the way, in recent years, noise sources have been increasing with the sophistication and miniaturization of electronic devices, and in order to stabilize the operation of the comparison circuit, the comparison circuit is provided with a hysteresis characteristic.

FIG. 4 shows a conventional general comparison circuit with a hysteresis characteristic. The inverting input terminal of the comparator 10 receives the input voltage from the input terminal 12 via the resistor 14.
The resistor 1 is provided between the output terminal of the comparator 10 and the output terminal 16.
Connect 8. A series circuit of resistors 20 and 22 is connected between the output terminal 16 and the reference voltage terminal 24, and its common connection point is connected to the non-inverting input terminal of the comparator 10. In addition,
The resistor 14 is used to limit the input current and adjust the offset voltage, and the resistor 18 is used to limit the output current and adjust the output impedance.

When the input voltage of the input terminal 12 is lower than the voltage of the non-inverting input terminal of the comparator 10, the output voltage of the output terminal 16 is Voh (positive voltage), and the input voltage is higher than the voltage of the non-inverting input terminal. The output voltage when it is high is Vol (negative voltage). Further, the voltage at the non-inverting input terminal (upper trip voltage) of the comparator 10 when the output voltage is Voh is Vth, and the voltage at the non-inverting input terminal (lower trip voltage) when the output voltage is Vol is Assuming Vtl, the results are as follows. Vth = (R20.Vr + R22.Voh) / (R20 + R22) Vtl = (R20.Vr + R22.Vol) / (R20 + R22) R20 and R22 are resistance values of the resistors 20 and 22, and Vr is a terminal 24 voltages.

Since Voh is positive and Vol is negative, the hysteresis reference voltage is between the upper trigger voltage and the lower trip voltage. Therefore, from these two equations, the hysteresis reference voltage is R20.Vr / (R20 + R22), and the upper hysteresis voltage (difference between the upper trip voltage and the hysteresis reference voltage) is R22.Voh / (R20 +
R22), and the lower hysteresis voltage (the difference between the lower trip voltage and the hysteresis reference voltage) is R22.Vol.
/ (R20 + R22)

From these points, it can be seen that the hysteresis reference voltage depends not on the voltage Vr at the terminal 24 but on the values of the resistors 20 and 22. The values of these resistors 20 and 22 must be determined not only by considering the hysteresis characteristics but also by the influence of impedance and offset, which complicates the design of the comparison circuit. Further, the hysteresis voltage is influenced by the voltage Vol or Voh of the output terminal 16. Since the voltage Vol or Voh varies, in order to make the hysteresis voltage highly accurate,
The design of the comparison circuit becomes more complicated.

Therefore, in order to solve these drawbacks,
A comparison circuit that supplies an input voltage to one of the input terminals of a comparator and selectively supplies one of two different reference voltages to the other input terminal of the comparator according to the output voltage of the comparator is disclosed. JP-A-58-210714, JP-A-62-21319
JP-A-64-20711 and JP-A-4-20711.
It is disclosed in Japanese Patent No. 132410. In the prior arts disclosed in these publications, in order to generate two different reference voltages, two different voltages are simply switched by a switch, the configuration of the voltage divider is changed by the switch, or the voltage division ratio is changed. I'm wondering. However, in any case, it requires two different voltages. Also, in order to make the trip voltage, the hysteresis reference voltage or the hysteresis voltage highly accurate, these two different voltages must also be highly accurate.

[0008]

When a comparator circuit having a hysteresis characteristic is used as a trigger circuit, it is often the case that only one of the two trip voltages needs to be highly accurate. But,
Even in such a case, in the above-described conventional technique, two voltages with different high precision are required. Therefore, the circuit configuration becomes complicated and expensive.

Further, in the above-mentioned conventional technique, the switch is switched when the trip voltage is switched, but the signal path to the input end of the comparator is temporarily cut off as the switch is switched. Therefore, noise may occur, the comparison operation may become unstable, and the next-stage circuit may be adversely affected.

Therefore, an object of the present invention is to provide a comparator circuit with a hysteresis characteristic which is capable of highly accurately adjusting one trip voltage with an inexpensive structure.

Another object of the present invention is to provide a comparator circuit with a hysteresis characteristic that does not generate noise when the trip voltage is switched.

[0012]

As shown in FIG. 1, a comparator circuit according to the present invention includes a comparator 10 receiving an input voltage at one input terminal and an output terminal of the comparator and the other input terminal. Depending on the series circuit of the connected switch means 30 and the first resistor 26, the second resistor 22 connected between the other input terminal of the comparator 10 and the reference potential source 24, and the output voltage of the comparator 10. Control means 32, 34 for controlling conduction and non-conduction of the switch means 30. Switch means 30
When is non-conducting, the voltage of the reference potential source 24 is directly supplied to the other input terminal of the comparator. Therefore, the trip voltage at this time is determined only by the reference potential source voltage. When the switch means 30 is conductive, it is determined by the reference potential source voltage, the output voltage of the comparator, and the values of the first and second resistors. Therefore, if only the reference potential source voltage is made highly accurate, one of the trip voltages can be made highly accurate.

[0013]

Further, the comparator circuit of the present invention, as shown in FIG. 3, has a comparator 10 receiving an input voltage at one input terminal.
A first resistor 26 connected between the output terminal and the other input terminal of the comparator, and a second resistor 22 connected between the other input terminal of the comparator 10 and the reference potential source 24, The switch means 30 is connected in parallel with the second resistor 22, and the control means 32 and 34 for controlling conduction and non-conduction of the switch means 30 according to the output voltage of the comparator 10. When the switch means 30 is conducting, the trip voltage becomes the reference potential source voltage. When the switch means 30 is non-conductive, the trip voltage is determined by the reference potential source voltage, the output voltage of the comparator, and the values of the first and second resistors.
Therefore, if only the reference potential source voltage is made highly accurate, one of the trip voltages can be made highly accurate. Also, the switch means 3
Since current always flows through the first and second resistors 22 and 26 regardless of the conduction or non-conduction state of 0, even if the switch means 30 is switched, noise is not generated thereby.

[0015]

1 is a circuit diagram of a first preferred embodiment of the present invention. The comparator 10 has a resistor 14 at its inverting input terminal.
The input voltage from the input terminal 12 is received via. The non-inverting input terminal of the comparator 10 is connected to the reference potential source terminal 24 via the resistor 22, and the output terminal of the comparator 10 is connected to the output terminal 16 via the resistor 18. Resistor 14
The functions of 18 and 18 are the same as in the case of the conventional example of FIG.
A series circuit of a resistor 26 and a switch means 30 is connected between the output terminal 16 and the non-inverting input terminal of the comparator 10.
The switch means 30 may be a semiconductor switching element such as a field effect transistor or a reed relay. The sense circuit 32 detects the value (for example, high level or low level) of the output voltage of the comparator 10. The drive circuit 34 controls conduction and non-conduction of the switch means 30 according to the output of the sense circuit 32. The sense circuit 32 and the drive circuit 34 constitute control means.

When the lower trip voltage requires high accuracy, when the output voltage of the comparator 10 is at a low level, that is,
When the input voltage value of the input terminal 12 is higher than the non-inverting input terminal voltage of the comparator 10, the drive circuit 34 makes the switch means 30 non-conductive. Therefore, the voltage at the non-inverting input terminal of the comparator 10, which is the trip voltage at this time, is determined only by the voltage at the reference potential source terminal 24. If the reference potential source voltage has high accuracy, the trip voltage at this time also has high accuracy.

When the input voltage drops below the lower trip voltage, the output voltage of the comparator 10 goes high and the drive circuit 34 causes the switch means 30 to conduct. Therefore,
The voltage at the inverting input terminal of the comparator 10 at this time, that is, the upper trip voltage is determined by the voltage of the output terminal 16 and the reference potential source voltage of the terminal 24 and the values of the resistors 22 and 26. At this time, since the voltage of the output terminal 16 is not highly accurate,
The upper trip voltage is not accurate, but it is okay as the detection when the input voltage falls below the lower trigger voltage is important. It should be noted that since it is only necessary to supply a high-precision voltage to the terminal 24, two different high-precision voltages as in the above-described conventional case are unnecessary.

In the embodiment shown in FIG. 1, the inverting input terminal and the non-inverting input terminal of the comparator 10 are reversed so that the input voltage from the input terminal 12 is supplied to the non-inverting input terminal of the comparator 10 and the resistance is increased. The common connection point of the devices 22 and 26 may be connected to the inverting input terminal of the comparator 10. Further, the input end of the sense circuit 32 may be connected to the output terminal 16. Further, the relationship between the output level of the drive circuit 34 and the conduction / non-conduction of the switch means 30 may be reversed.

FIG. 2 is a circuit diagram of the second embodiment of the present invention. Elements similar to those in FIG. 1 are designated with the same reference numbers. The difference from the embodiment of FIG. 1 is that the right end of the resistor 26 is a constant voltage source 28.
And the switch means 30 is connected in parallel with the resistor 22. That is, a series circuit of resistors 22 and 26 is connected between different reference potential sources.

The trip voltage, which is the non-inverting input terminal voltage of the comparator 10, is applied to the terminal 2 when the switch means 30 is conducting.
4 and the switch means 30 is non-conducting, the reference potential source voltage of the terminal 24 and the constant voltage source 28.
And the values of resistors 22 and 26. Comparator 10
Whether the switch means 30 is conductive or non-conductive depending on whether the output voltage is high level or low level can be arbitrarily set according to design conditions. In any case, regardless of whether the switch means 30 is conductive or non-conductive, a current is constantly flowing through the parallel circuit of the resistor 22 and the switch means 30 and the resistor 26. Does not change to Therefore, it should be noted that even if the switching means 30 is switched, the noise generated at that time can be significantly reduced.

In the embodiment of FIG. 2 as well, as in the embodiment of FIG. 1, the inverting input terminal and the non-inverting input terminal of the comparator 10 are reversed and the input voltage from the input terminal 12 is applied to the comparator 10. It may be supplied to the non-inverting input terminal and the common connection point of the resistors 22 and 26 may be connected to the inverting input terminal of the comparator 10. Further, the input end of the sense circuit 32 may be connected to the output terminal 16. Further, the switch means 30 may be connected in parallel with the resistor 26 instead of the resistor 22. Further, the relationship between the output level of the drive circuit 34 and the conduction / non-conduction of the switch means 30 may be reversed.

FIG. 3 is a circuit diagram of the third embodiment of the present invention. Elements similar to those of FIGS. 1 and 2 are designated with the same reference numerals. The difference from the embodiment of FIG. 2 is that the right end of the resistor 26 is connected to the output terminal 16. The trip voltage, which is the non-inverting input terminal voltage of the comparator 10, becomes the reference potential source voltage of the terminal 24 when the switch means 30 is conductive, and the reference potential source voltage of the terminal 24 when the switch means 30 is non-conductive. And the voltage at output terminal 16 and the values of resistors 22 and 26.

In this embodiment, similar to the embodiment of FIG.
If the reference potential source voltage of the terminal 24 is highly accurate, the trip voltage when the switch means 30 is conducting can be highly accurate. Further, as in the embodiment of FIG. 2, regardless of whether the switch means 30 is conductive or non-conductive, current always flows through the parallel circuit of the resistor 22 and the switch means 30 and the resistor 26. Noise when switching can be significantly reduced.

In the embodiment shown in FIG. 3, the inverting input terminal and the non-inverting input terminal of the comparator 10 may be reversed or the input terminal of the sense circuit 32 may be reversed, as in the embodiment shown in FIGS. May be connected to the output terminal 16. In addition, the drive circuit 34
The relationship between the output level and the conduction and non-conduction of the switch means 30 may be reversed.

[0025]

As described above, according to the present invention, one of the trip voltages can be highly accurate by one highly accurate reference potential source, so that the comparison circuit with hysteresis characteristics can be realized with an inexpensive structure. Further, since the current is supplied to the resistor regardless of whether the switch means is conductive or non-conductive, noise generated due to the switching of the trip voltage due to the operation of the switch means can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first preferred embodiment of a comparison circuit of the present invention.

FIG. 2 is a circuit diagram of a second preferred embodiment of a comparison circuit of the present invention.

FIG. 3 is a circuit diagram of a third preferred embodiment of a comparison circuit of the present invention.

FIG. 4 is a circuit diagram of a conventional comparison circuit.

[Explanation of symbols]

 10 comparator 12 input terminal 22, 26 resistor 24 reference potential source terminal 28 constant voltage source 30 switch means 32, 34 control means

Claims (2)

(57) [Claims] 1. A comparator which receives an input voltage at one input terminal, a series circuit of a switch means and a first resistor connected between an output terminal of the comparator and the other input terminal, and a comparator of the comparator. A comparison circuit comprising a second resistor connected between the other input terminal and the reference potential source, and control means for controlling conduction and non-conduction of the switch means according to the output voltage of the comparator. 2. A comparator that receives an input voltage at one input terminal, and a first terminal connected between the output terminal of the comparator and the other input terminal.
A resistor, a second resistor connected between the other input terminal of the comparator and the reference potential source, a switch means connected in parallel to the second resistor, and an output voltage of the comparator. A comparison circuit comprising control means for controlling conduction and non-conduction of the switch means.