JP2587677Y2 - Waveform shaping 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 waveform shaping circuit, and more particularly to a waveform shaping circuit using a comparator integrated circuit (hereinafter abbreviated as a comparator IC) to shape an input signal.

[0002]

2. Description of the Related Art Hitherto, a waveform shaping circuit as shown in FIG. 3 has been used for a speedometer for displaying a running speed of an automobile or the like. In a speedometer, an AC signal having a frequency proportional to the speed of an automobile is input, the AC signal is shaped into a rectangular pulse by using a comparator IC, and a waveform shaping for supplying the pulse to a meter driving circuit is performed. Although a circuit is used, the signal generation source that generates an AC signal having a frequency corresponding to the vehicle speed is a pickup sensor including an AC generator (not shown) that generates a single-shot signal as shown in FIG. The generated voltage range is wide, and a signal with a high peak value is generated as the vehicle speed increases.

When a high voltage is applied to an input signal, a current flows through a parasitic diode during a negative cycle of an AC signal, and a waveform of a negative cycle starts to be clamped by the parasitic diode. As a result, the bias potential of the input signal fluctuates, which causes a fluctuation in the period of the pulse obtained by the waveform shaping circuit, which may cause a wobble of the pointer.

Hereinafter, the operation will be described with reference to FIG.
As shown in FIG. 3, an AC signal composed of a single-shot signal generated by an AC generator in response to the rotation of a rotating body that rotates according to the vehicle speed is input to an input terminal 1, and a comparator IC 3 is connected via a coupling capacitor 2. Is input to the non-inverting input terminal. When this input signal is larger than the comparison reference voltage V _REF supplied to the inverting input terminal of the comparator IC3, the state of the output terminal of the comparator IC3 is saturated (ON), and when the input is small, it is cut off (OFF). Become. That is, the comparator IC3 shapes the waveform of the input AC signal into a rectangular pulse signal and supplies it to the subsequent meter drive circuit. 4 to 7 are resistors, and 8 is a bypass capacitor.

[0005]

The amplitude of the AC signal actually applied to the non-inverting input terminal of the comparator IC3 increases in proportion to the vehicle speed. Therefore, when an input signal having a large amplitude is applied, the parasitic diode shown by the dotted line in the comparator IC3 turns on near the negative cycle peak, the negative cycle peak is clamped, and the forward voltage of the parasitic diode is compared with the comparator. IC
3, the bias potential of the non-inverting input terminal is increased, and the phenomenon that the comparison reference voltage V _REF is relatively lowered occurs.

[0006] Therefore, when an alternating signal as shown in FIG. 4 (a) is inputted to the input terminal 1, while the smaller the parasitic diode of the amplitude to the time point t ₁ is not to be turned on, proper wave shaping Are performed, and as shown in FIG.
It is converted into a pulse signal of T3. However, the amplitude of the AC signal increases, a negative cycle peak parasitic diode is turned on at time t ₂ is to be clipped, non-potential of the inverting input terminal rises, the time t ₂ after the subsequent comparator IC3 Is shifted upward.

When such a phenomenon occurs, when the AC signal is a single-shot signal as shown in FIG.
Time of greater than _REF is, cause malfunction that occurs in a very early time point t ₃ than the original time t _4,
The period of the pulse signal obtained at the output terminal of the comparator IC3 transiently becomes extremely small as T4. When the cycle T4 of the small pulse signal is supplied to the subsequent meter drive circuit, the meter drive circuit recognizes that a high-frequency pulse signal has been input, and causes the meter pointer to instantaneously swing in the positive direction. Will be caused.

In order to solve such a problem, a zener diode 9 is connected in parallel with the bypass capacitor 8 as shown by a dotted line in FIG. It is conceivable to cut the cycle peak. However, in this case, the zener diode operates even for a signal having a small amplitude, so that the bias potential is reduced and the input sensitivity is reduced as shown in FIG.
In addition to the deterioration shown in FIG. 6A from FIG. 6A, the insertion of a zener diode causes another problem that the temperature characteristics also deteriorate as shown in FIG. 5B to FIG. 6B.

Therefore, in view of the above-mentioned conventional problems, the present invention inputs an input signal from a pickup sensor including an AC generator that generates an AC signal including a single-shot signal via a coupling capacitor, and receives the input signal. Is compared with a comparison reference voltage to convert the signal into a pulse signal.In the waveform shaping circuit, an AC signal whose amplitude fluctuates in a wide range while maintaining desired characteristics without deteriorating sensitivity frequency characteristics and temperature characteristics. It is an object of the present invention to provide a waveform shaping circuit that does not malfunction even when input.

[0010]

In order to achieve the above-mentioned object, a waveform shaping circuit according to the present invention inputs an input signal from a pickup sensor comprising an AC generator for generating an AC signal through a coupling capacitor. A waveform shaping circuit including a comparator for comparing the input signal with a comparison reference voltage and converting the input signal into a pulse signal, wherein a zener diode for clamping a positive / negative cycle peak of the input signal is connected to a stage preceding the coupling capacitor. Features.

[0011]

In the above construction, since the Zener diode is connected at the preceding stage of the coupling capacitor, the Zener diode is separated from the comparator in a DC manner, and does not adversely affect the frequency characteristic and the temperature characteristic of the sensitivity of the comparator.

In addition, since the positive cycle peak of the AC input signal is clamped (limited) to the Zener voltage and the negative cycle peak is clamped to the forward voltage by the Zener diode, and then applied to the non-inverting input terminal of the comparator. The signal input to the inverting input terminal does not swing to the negative side, and does not turn on the parasitic diode.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a circuit diagram showing an embodiment of a waveform shaping circuit according to the present invention. In FIG. 1, parts that are the same as the conventional ones described above with reference to FIG. Detailed description is omitted.

In the waveform shaping circuit according to the present invention, a zener diode 10 is connected in parallel with a bypass capacitor 8 in a preceding stage of the coupling capacitor 2 so that the zener diode 10 is connected to the comparator IC 3 by AC coupling.
Is connected to a position separated from the DC. Therefore,
The adverse effect of the Zener diode 10 on the frequency characteristic and the temperature characteristic of the sensitivity of the comparator IC3 is eliminated.

With the above configuration, the input terminal 1 is connected to the terminal shown in FIG.
When an AC signal as shown in FIG. 2A is input, the AC signal is clamped (limited) by the Zener diode 10 so that the positive cycle peak is changed to the Zener voltage and the negative cycle peak is changed to the forward voltage. The signal is converted into a signal as shown in FIG. The AC signal whose positive and negative cycle peaks are clamped is AC-coupled to the non-inverting input terminal of the comparator IC3 via the coupling capacitor 2, and the bias potential is applied to the non-inverting input terminal of the comparator IC3 as shown in FIG. Is applied. The signal applied to the non-inverting input terminal of the comparator IC3 is compared with the comparison reference voltage _VREF, and a pulse signal as shown in FIG.

That is, even if the amplitude of the input signal is large,
Since the signal input to the non-inverting input terminal of the comparator IC3 does not swing to the negative side and does not turn on the parasitic diode, it does not cause a malfunction by changing the bias potential of the comparator IC3.

Further, since the AC signal level is clamped before the AC coupling, the generation of a differential wave of the input signal in the CR coupling circuit can be suppressed, and malfunction due to the differential wave can be eliminated.

[0018]

As described above, according to the present invention, since the Zener diode is connected at the preceding stage of the coupling capacitor, desired characteristics can be maintained without impairing the frequency characteristics and the temperature characteristics of the sensitivity. .

The zener diode clamps (limits) the positive cycle peak of the AC input signal to the zener voltage and clamps the negative cycle peak to the forward voltage, and then applies the same to the non-inverting input terminal of the comparator. Input signal varies over a wide range,
There is no possibility that the parasitic diode in the comparator is turned on and malfunctions.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a waveform shaping circuit according to the present invention.

FIG. 2 is a waveform chart showing waveforms at various parts in FIG.

FIG. 3 is a circuit diagram showing an example of a conventional waveform shaping circuit.

FIG. 4 is a waveform chart for explaining the operation of the circuit of FIG. 3;

FIG. 5 is a graph showing frequency characteristics and temperature characteristics of sensitivity of the circuit of FIG. 3;

FIG. 6 is a graph corresponding to the characteristic of FIG. 5 deteriorated in another conventional circuit example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input terminal 2 Coupling capacitor 3 Comparator IC 10 Zener diode

Claims (1)

(57) [Scope of request for utility model registration] 1. A comparator for inputting an input signal from a pickup sensor comprising an AC generator for generating an AC signal through a coupling capacitor, comparing the input signal with a comparison reference voltage, and converting the signal into a pulse signal. In the waveform shaping circuit, a zener diode for clamping a positive / negative cycle peak of the input signal is connected in a stage preceding the coupling capacitor.