JPS62168420A - Inputting circuit - Google Patents

Abstract

PURPOSE:To convert exactly a fundamental wave signal to a square wave by connecting a comparator for comparing a signal and a peak detector for detecting the upper and lower peaks of this signal, to each set and reset terminal of a flip-flop. CONSTITUTION:By a peak detector constituted of diodes 11, 12 and capacitors 13, 14 and amplifiers 15, 16, the upper and lower levels of an input signal are detected, and two DC voltages +VP, -VP being proportional to its voltage levels are outputted. Comparators 21, 22 compare input signals from a buffer 1 by using this DC voltage as a reference voltage, and this compared output is inputted to a set terminal and a reset terminal of a flip-flop 23 of the next stage. Accordingly, the flip-flop 23 is set and reset by the output of the comparator 21 and an output of the comparator 22, respectively, therefore, even if the outputs of the comparators 21, 22 contain plural pulses by noise, the output of the flip-flop 23 converts exactly a fundamental wave to a square wave.

Description

[Detailed Description of the Invention] A. ``Objective of the Invention'' [Industrial Application Field] The present invention is directed to converting the fundamental wave signal of alternating current containing noise into a square wave accurately without being affected by the noise. It concerns an input circuit that can be converted.

[Conventional technology]

Since the input circuit according to the present invention is often used in frequency counters, the following description will be given assuming that it is applied to this field. Since a frequency counter measures the frequency and period of the fundamental wave of an input alternating current signal, the fundamental wave is generally converted into a square wave for measurement.

However, since the alternating current waveform to be measured is usually irregular and contains noise, converting this noise component into a square wave will result in a measurement error. Therefore, an input circuit is required that converts only the fundamental wave into a square wave without being affected by noise components.

In view of the above points, conventional means have been developed to provide an attenuator, an amplifier III, and a Schmitt circuit in an input circuit, sequentially control the attenuator according to the amplitude of the input waveform, and apply an input signal of constant amplitude to the Schmitt circuit. was.

According to this method, the attenuator and amplifier are adjusted so that the fundamental wave of the input signal applied to the Schmitt circuit has an amplitude slightly larger than the hysteresis voltage width, so the noise component superimposed on the fundamental wave is , is a sufficiently small value, and one square wave can be output for one period of the fundamental wave.

[Problem that the invention seeks to solve]

However, the above-mentioned means are broadband (DC~GHz>
The problem is that it is not possible to accurately convert an input signal over a wide range into a square wave. The reason is that it is difficult to realize an attenuator with linear attenuation characteristics over such a wide band.

SUMMARY OF THE INVENTION An object of the present invention is to provide an input circuit that can accurately convert even a wideband input signal containing noise into a square wave without using an attenuator to solve the above problems.

In order to solve the above problems, the present invention provides two peak detectors for detecting upper and lower peaks of an input signal, and an output level of the peak detectors. This system includes two comparators that introduce a signal and compare the signal level with the input signal, and a flip 70 tab that is set and reset by the outputs of these two comparators.

(Example) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the present invention in blocks, and FIG. 3 is a time chart.

In Figures 1 and 2, 1 is a buffer, which is used to ensure isolation between the signal source that generates the AC signal to be measured and the frequency counter, or high input impedance (for example, 1 MΩ or more). be. This buffer has wideband frequency characteristics. Although the present invention will be described assuming that the amplification degree of the buffer 1 is 1, the present invention is not limited to this.

10 is a peak detector, which detects the upper and lower levels (g, lower, explained in terms of voltage levels in this text) of the input signal introduced via buffer 1, and generates two DC voltages proportional to the voltage levels. (+Vp) and (-Va) are output to the next stage. This peak detector 10 is composed of a diode 11.12, a capacitor 13.14, and an amplifier 15.16, for example, as shown in FIG. Diodes 11 and 12 rectify the output voltage of buffer 1, charging capacitor 13 with +Vp and charging capacitor 14 with (-Vp). This voltage (+Vp)
, (-Vp) is V from the peak voltage of the input signal.
o (on-voltage of diodes 11 and 12). The voltages of these two capacitors 13 and 14 are transferred to and controlled by the next stage Schmitt circuit 20 via voltage follower (high input impedance) amplifiers 15 and 16, respectively.

20 is a Schmitt circuit, the hysteresis voltage of which is controlled by a signal from the peak detector 10. Specifically, the fundamental wave of the input signal introduced through the buffer 1 is converted into a square wave and output. This Schmitt circuit 20 is composed of comparators 21, 22 and a flip-flop 23, as shown in FIG. 1, for example. The comparator 21.22 uses the voltage +V p +-p introduced from the amplifier 15.16 as a reference, and compares this voltage with the input signal from the buffer 1 introduced at the other terminal. The outputs of these two comparators:)1.22 are introduced into the set and reset terminals of the flip-flop 23.

The operation of the apparatus shown in FIGS. 1 and 2 constructed as above will be explained with reference to FIG. 3.

(1) in FIG. 3 shows an input signal waveform in which noise n is superimposed on the fundamental wave υ. When such a signal is applied via the buffer 1, the peak detector 10 detects it and adjusts the voltages (+Vp) and (-Vp) by the operation described above.
p) to occur. Comparator 21 is (+Vp)
A comparison is made between the input signal waveform and the input signal waveform, and a logic level signal shown in FIG. 3 (11) is output. Further, the comparator 22 compares (Vp) with the input signal waveform and outputs a logic level signal shown in FIG. 3 (till).

Since the flip-flop 23 is set by the output of the comparator 21 and reset by the output of the comparator 22, ?
71II, steresis occurs and forms a Schmidt circuit. Because of this configuration, the outputs of the comparators 21 and 22 are <Il+ and <Il+ in FIG.
Even if the waveform includes multiple pulses due to the influence of the noise component n, the output waveform of the flip-flop 23 is a square wave equal to the frequency of the fundamental wave υ1 as shown in FIG. becomes.

Note that when the amplitude of the input signal waveform applied to the buffer 1 changes, the voltage charged to the capacitors 13 and 14 of the peak detector 10 also responds, so (+Vp) in FIG.
, (-Vp) changes and becomes a new hysteresis voltage.

FIG. 4 shows another embodiment of the invention. The difference between this figure and FIG. 1 is that a clamp circuit consisting of a capacitor 30, a resistor 31, a diode 32, and a power supply 33 is provided, and at the same time, one of the peak detectors in FIG. 1 is removed. The rest of the configuration is the same as that in FIG. 1, so the same element numbers are given and the explanation thereof will be omitted.

The circuit shown in FIG. 4 attempts to eliminate the influence of low frequency noise by using a newly provided clamp circuit.

An input signal with low frequency noise is, for example, the fifth factor. When such an input signal waveform is applied from the signal source 34, the DC component is cut by the capacitor 30,
Only the AC component is applied to the diode 32, power source 33, and resistor 31. Then, at the moment when the input signal is about to exceed (VR+VD), the diode 32 turns on, and the voltage of the input signal does not exceed VR.Here, VR is the voltage of the power supply 33, and VD is the voltage of the diode 32 turned on. It is voltage.

As a result, as shown in FIG. 6, a peak detector on the positive side is not required, and operation can be performed only on the negative side. That is, the positive side steresis voltage is (VR+VC+ >
The negative side hysteresis voltage is (-Vp +
Vo).

C. "Effects of the Present Invention" As described above, according to the present invention, the following effects can be obtained.

■ The hysteresis voltage of the comparator is automatically adjusted according to the amplitude of the input signal, so you can manually adjust the attenuation amount wA! ! ! Noise can be suppressed without

■ Since the positive and negative hysteresis levels are set independently, an appropriate trigger level can be obtained even if a DC component is superimposed on the input signal.

■ Since there is no need to provide a 7-tensioner before the Schmitt circuit, there is no disturbance in frequency characteristics.

[Brief explanation of drawings]

Fig. 1 is a diagram showing one embodiment of the present invention, Fig. 2 is a diagram showing the present invention in block form, Fig. 3 is a time chart, and Fig. 4 is a diagram showing another configuration example of the present invention. Figures 5 and 6 are diagrams showing the input jM waveform. 1...Buffer, 10...Peak detector, 11
．． 12゜32...Diode, 13.14...Capacitor, 15.16...Amplifier, 20...Schmitt circuit, 21.22...Comparator, 23...Flip-flop. Figure 4 Figure 5

Claims (1)

[Claims] Two peak detectors that detect upper and lower peaks of an input signal; two comparators that introduce an output level signal of the peak detector and compare the signal level of this level with the input signal; An input circuit comprising: a flip-flop that is set and reset by the outputs of the two comparators;