JPH0888546A - Comparator and proximity sensor - Google Patents

Abstract

PURPOSE: To hold the hysteresis of output of a differential amplification comparator for a fixed time. CONSTITUTION: Transistors Q13, Q14 comprise a voltage comparator circuit, and reference voltages V1, V2 (V1<V2) are set, respectively. Only the AC component of an input voltage is superimposed on the reference voltage V1 via a capacitor C2. When the voltage exceeds the reference voltage V2 and the transistor Q13 is turned on and the transistor Q14 is turned off, a transistor Q12 is turned on, and the voltage V1 increases, and also, parasitic capacitance between the base and emitter of the transistor is charged. When input goes lower than the reference voltage V2, the transistor Q13 is turned off. The transistor Q12 is held in an on-state untill the parasitic capacitance is discharged via a resistor R14 and the hysteresis is held.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a comparator for holding a comparison level hysteresis when an AC signal is input by using a differential amplifier circuit, and a proximity sensor using the comparator.

[0002]

2. Description of the Related Art A comparator circuit is widely used in various electronic circuits such as photoelectric sensors and proximity sensors. The comparator circuit is used as a circuit that outputs an object detection or the like by discriminating an input signal with a predetermined threshold value.
FIG. 6 is a circuit diagram showing an example of such a conventional comparator circuit. In this figure, the power source Vcc is resistors R1 and R
The voltage is divided by 2, R3 and R4, and the reference voltages V1 and V2 are obtained respectively. The bases of the transistors Q1 and Q2 forming the differential amplifier circuit are connected to these voltage dividing circuits. The collectors of the transistors Q1 and Q2 are connected to the power source Vcc through the transistors Q3 and Q4, respectively, and the emitters are connected together and connected to the collector of the transistor Q5. The transistor Q5 and the transistor Q6 form a current mirror circuit, and a resistor R5 is configured so that a constant current flows through the differential amplifier circuit via the current mirror circuit. The transistors Q3 and Q4 are current-mirror connected, and the collector of the transistor Q3 and the collector of the transistor Q1 are commonly connected,
It is connected to the base of the transistor Q7. The emitter of the transistor Q7 is connected to the power supply Vcc, and the collector is connected to the middle point of the resistors R1 and R2 via the resistor R6. The collector of the transistor Q1 is connected to the base of the transistor Q5. The emitter of the transistor Q8 is the power supply Vcc
Is a PNP-type transistor connected to, and constitutes an output circuit.

Here, it is assumed that the reference voltage V2 is set higher than the reference voltage V1, and the input signal is input via the coupling capacitor C1 with only the AC component superimposed on the reference voltage V1. Therefore, if there is no input signal, the transistors Q2 to Q4 are turned on and the transistors Q1 and Q7, Q are turned on.
8 is in the off state. When an input signal is applied, the base voltage of the transistor Q1 becomes a reference voltage V1 with an AC component superimposed, and when the superimposed voltage exceeds the reference voltage V2, the transistor Q1 turns on and the transistors Q2 to Q4 turn off. .

[0004]

In such a conventional comparator, the differential amplifier circuit has hysteresis, but when the input signal is an AC signal, the AC component of the input signal is compared with the comparison level as shown in FIG. If V2−V1 is exceeded, hysteresis is added and the level decreases. Then, when the AC signal falls below this level, the comparison level returns to the original state again. Therefore, there is a drawback that the comparison level changes for each waveform of the input signal and the output also changes. In order to avoid this, it may be considered that the AC signal is once rectified, converted into a DC level corresponding to its amplitude, and then input to the comparator.
Since a CR circuit is used for this rectifying / smoothing circuit, there is a drawback in that the response to the output when the level of the input signal changes is poor and it is easily affected by noise.

The present invention has been made in view of the above-mentioned conventional problems, and a comparator for stabilizing an output by holding a hysteresis with a time constant corresponding to the frequency of an input signal, Another object of the present invention is to provide a proximity sensor that can detect an object by stabilizing the output using the sensor.

[0006]

The invention of claim 1 of the present application has a voltage comparison circuit comprising a differential amplifier circuit including first and second transistors, and the first and second voltage comparison circuits are provided. First and second reference voltages V1 and V2 (V1 <
V2) is set, is input to the first input terminal, and the reference voltage V
A comparator for providing a discrimination output by comparing a voltage level superimposed on 1 and a second reference voltage, wherein a first and a second reference voltage are respectively applied to first and second input terminals of a voltage comparison circuit. And a voltage input to the first input terminal of the voltage comparison circuit that is superimposed on the first reference voltage exceeds the second reference voltage, and the output of the differential amplifier circuit is inverted. At this time, a hysteresis latch circuit for changing the difference between the first and second reference voltages of the comparison level setting circuit to be small and holding the change for a predetermined time is provided.

In the invention of claim 2 of the present application, the hysteresis latch circuit has a series connection body of a resistor and a third transistor connected in parallel to the voltage dividing resistor forming the comparison level setting circuit, When the voltage input to the first input terminal of the comparison circuit by being superimposed on the first reference voltage exceeds the second reference voltage, the base of the third transistor
It is characterized in that the parasitic capacitance between the emitters is charged, and when the output of the second transistor is inverted, the hysteresis is maintained while the parasitic capacitance is discharged.

According to a third aspect of the present invention, an oscillating circuit including a detecting coil, a comparator according to the first or second aspect in which an alternating current component of the oscillating circuit is input, and the detection coil is approached based on the output of the comparator. And a signal processing circuit for determining the presence or absence of an object.

[0009]

In the comparators according to claims 1 and 2 of the present application having such characteristics, the voltage comparison circuit is configured by the differential amplifier circuit including the first and second transistors.
The first and second reference voltages are set to the respective input terminals, and the input signal is applied to the first input terminal. The level at which the input signal is superimposed on the first reference voltage is the second
If the reference voltage is exceeded, the transistor of the voltage comparison circuit is inverted. At this time, the hysteresis latch circuit changes the comparison level setting circuit so that the difference between the first and second reference voltages becomes small, and the change in hysteresis is held for a certain period of time. Therefore, even if the input level is below the threshold, the output is not immediately inverted. Therefore, when the input signal has an AC component, the output does not change for each waveform and is stabilized.

According to the third aspect of the invention, by applying this comparator to a proximity sensor, it is possible to discriminate a change in the amplitude of oscillation at high speed, and to detect passage of an object at high speed.

[0011]

1 is a block diagram showing the basic configuration of a comparator of the present invention. In the figure, the voltage comparison circuit 2 is connected to the input terminal 1. The voltage comparison circuit 2 is composed of a differential amplifier circuit, and a first reference voltage is set by the comparison level setting circuit 3 on the input terminal 1 side and a second reference voltage is set on the other input terminal. And A comparison level setting circuit 3 that defines the comparison level is connected to the voltage comparison circuit 2. A hysteresis latch circuit 4 for changing its hysteresis is connected to the comparison level setting circuit 3 based on the output of the voltage comparison circuit 2.
The hysteresis latch circuit 4 reduces the difference between the first and second reference voltages of the comparison level setting circuit 3 when the input signal changes over the second reference voltage based on the output of the voltage comparison circuit 2. And holds the change of the reference voltage for a certain period of time, and its output is given to the comparison level setting circuit 3. The output terminal of the voltage comparison circuit 2 is connected to the output terminal 5.

FIG. 2 is a circuit diagram of a comparator embodying such a comparator according to the first embodiment of the present invention. In this figure, resistors R11 and R12 and a transistor Q11 are connected in series between a power source Vcc and a ground terminal as shown in the figure, and a transistor Q12 is connected between both ends of the resistor R11.
And resistor R13 are connected. A resistor R14 is connected between the base of the transistor Q12 and the power supply Vcc, and the collector of the transistor Q13 is connected. The transistors Q13 and Q14 form a differential amplifier circuit, the emitters of which are commonly connected to the collector of the transistor Q15. The transistors Q11 and Q15 form a current mirror circuit. Also transistor Q15
Resistors R15 and R16 are connected to the base of the power supply Vcc. Further, similarly to the conventional example, the collector of the transistor Q13 which constitutes the differential amplifier circuit is the output transistor Q16.
Connected to the base of. The transistor Q16 is an output transistor whose emitter is connected to the power supply Vcc and whose collector is connected to the output terminal. In this embodiment, the voltage comparison circuit 2 includes transistors Q14, Q15, Q16 and a resistor R1.
It is composed of four. The comparison level setting circuit 3 is composed of resistors R11, R12, R15 and R16, and the hysteresis latch circuit 4 is composed of a resistor R13 and a transistor Q12.

Next, the operation of this embodiment will be described. FIG. 3 is a time chart showing the operation of this embodiment. In this figure, if there is no input voltage, transistors Q13 and Q1
4 is turned on or off depending on the relationship between the resistors R11, R12 and R15, R16. If the voltage dividing ratio is set so that the first reference voltage V1 at the midpoint of the resistors R11 and R12 is lower than the second reference voltage V2 of the resistors R15 and R16,
The transistor Q14 is turned on and the transistor Q13 is turned off. Therefore, the transistors Q12, Q16
Is also off, and the collector current flowing through the transistor Q14 has a current value defined by the resistors R11 and R12 and the power supply voltage Vcc. And this reference voltage V1
And V2 is the threshold value Vth1 (= V2-V1). Since the reference voltage V1 changes depending on whether the transistor Q13 is turned on or off, the voltage when the transistor Q13 is turned off is V1of
f, and the voltage when it is on is V1on.

The input signal is a coupling capacitor C.
Only the AC component is input to the differential amplifier circuit via 2.
This peak value is the threshold value Vth1 (V
2-V1off) or less, the transistor Q13 remains off and the transistor Q14 remains on.

When the AC component of the input signal exceeds the threshold value Vth1, the transistor Q13 enters the active region and its collector current starts to increase. Therefore, the transistor Q12
Also, the base current and collector current start to flow, and the resistor R11
The transistor Q12 and the resistor R13 are connected to both ends of the. Therefore, the current flowing through the transistor Q11 through the resistor R12 increases, and the collector current of the transistor Q15, that is, the emitter current of the transistor Q13 or Q14 also increases due to the current mirror circuit. In this way, the positive current feedback is applied and the transistors Q13 and Q1 are
4 reverses in a short time. At this time, the resistor R1 is connected to the resistor R1.
Since 3 is connected in parallel, resistors R11 and R1
The reference voltage V1 at the midpoint of 2 is higher than the original voltage V1off,
V1 on. Therefore, the threshold value Vth2 changes from Vth1 to Vth2 (V2-V1on) lower than Vth1 as shown in FIG. All such changes are caused by the transistor Q1.
It works to turn 3 on and Q14 off. Therefore, the transistor Q13 is turned on at high speed, and the transistor Q14
Is turned off. At this time, the base current of the transistor Q16 also rapidly increases, so that the delay time of the transistor Q16 can be shortened and the output can be inverted in a short time.

Now, as shown in FIG. 4, the transistor Q12
Has a parasitic capacitance C3 between the base and the emitter. When the transistor Q12 is in the off state, the parasitic capacitance C3 is in a discharged state, but when the transistor Q12 is in the on state, the parasitic capacitance C3 is charged. Therefore, when the input signal is an AC component and its level becomes equal to or lower than the threshold value Vth2, the transistor Q13 is turned off and the transistor Q14 is turned on. However, at this time, the base-emitter parasitic capacitance C3 of the transistor Q12 is discharged in the direction indicated by the arrow via the resistor R14, so that the transistor Q12 remains on for a certain period of time. Therefore, the transistor Q16 is also shown in FIG.
As shown in (b), the ON state will continue. If the input signal is inverted and exceeds the threshold value Vth2 again during this period, the transistor Q13 is turned on and the transistor Q14 is turned off, so that the parasitic capacitance C3 is charged. Thus, when the input signal is an AC waveform, the change in the threshold value is held for a certain period of time, and the output obtained from the transistor Q16 is as shown in FIG. 3 (b). Therefore, the output becomes stable, and it is not necessary to provide a rectifying circuit for rectifying the pulse waveform after the comparator, and the configuration can be extremely simplified.

FIG. 5 is a block diagram showing the configuration of a proximity sensor using this comparator. In the figure, an oscillator circuit 11 is provided with a detection coil L1 and oscillates at a constant frequency. Then, the oscillation output of the oscillation circuit 11 is directly input to the comparator 12. The comparator 12 is the comparator according to the embodiment described above, and only the AC component of the comparator 12 is the coupling capacitor C2.
Is input to one input terminal of the differential amplifier circuit.
The output of the comparator 12 is given to the signal processing circuit 13. The signal processing circuit 13 outputs an object detection signal via the output circuit 14 when the output of the comparator changes continuously for a predetermined time. The power supply circuit 15 is a power supply circuit that supplies a constant voltage to each of these blocks.
With such a configuration, the comparator 12 can be operated at high speed, so that the object is detected at high speed by the detection coil L.
When passing the vicinity of 1, the effect that the change in the amplitude can be detected at high speed is obtained.

[0018]

As described in detail above, according to the present invention, the change in the threshold value can be held for a certain period of time when the comparator is inverted. Even when an AC signal is input, the output is not inverted for each AC waveform, and the output can be stabilized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a comparator according to the present invention.

FIG. 2 is a circuit diagram showing a comparator according to an embodiment of the present invention.

FIG. 3 is a time chart showing the operation of the comparator of this embodiment.

FIG. 4 is a diagram showing a parasitic capacitance of a comparator of the present embodiment and its discharge path.

FIG. 5 is a block diagram showing an example of a proximity sensor to which a comparator according to the present invention is applied.

FIG. 6 is a circuit diagram showing an example of a conventional comparator.

FIG. 7 is a graph showing output characteristics of a conventional comparator.

[Explanation of symbols]

 1 voltage comparison circuit 2 comparison level setting circuit 3 bias current control circuit 11 oscillation circuit 12 comparator 13 signal processing circuit 14 output circuit 15 power supply circuit C3 parasitic capacitance

Claims (3)

[Claims] 1. A voltage comparison circuit comprising a differential amplifier circuit including first and second transistors, wherein first and second reference voltages are respectively provided at first and second input terminals of the voltage comparison circuit. V
1, V2 (V1 <V2) are set, and the voltage level which is input to the first input terminal and is superimposed on the reference voltage V1 and the second
A comparison level setting circuit for setting first and second reference voltages to the first and second input terminals of the voltage comparison circuit, respectively, and When the voltage input to the first input terminal of the comparison circuit by being superimposed on the first reference voltage exceeds the second reference voltage and the output of the differential amplifier circuit is inverted, the comparison level setting circuit And a hysteresis latch circuit that changes the difference between the first and second reference voltages to be small and holds the change for a predetermined time. 2. The hysteresis latch circuit has a series connection body of a resistor and a third transistor connected in parallel to a voltage dividing resistor forming a comparison level setting circuit, and the first voltage comparison circuit has a first connection. The base-emitter parasitic capacitance of the third transistor is charged when the voltage superimposed on the first reference voltage and input to the input terminal of the second reference voltage exceeds the second reference voltage, and the output of the second transistor is output. 2. The comparator according to claim 1, which holds hysteresis while the parasitic capacitance is discharged when is inverted. 3. An oscillation circuit including a detection coil, a comparator according to claim 1 or 2 to which an AC component of the oscillation circuit is input, and the presence or absence of an object in proximity to the detection coil based on the output of the comparator. A proximity sensor, comprising: a signal processing circuit for determining.