JPS6232717A - Waveform shaping circuit - Google Patents

Abstract

PURPOSE:To obtain a pulse train having 50% duty from a comparator by inputting a pulse string to one input terminal of the comparator and inputting a voltage obtained by smoothing the output of said comparator to the other input terminal. CONSTITUTION:A square pulse train having repeating frequency (f) is inputted to one input of the comparator. The output of the comparator 3 is branched and inputted to a low pass filter 4 through a buffer 5. Since the interruption frequency fc of the low pass filter 4 is smaller than the repeating frequency (f) of the input square pulse train, the input of the low pass filter is smoothed and an average DC voltage is obtained. The average DC voltage is inputted to the other input terminal of the comparator 3 as a reference signal VR, so that the pulse train of 50% duty can be obtained.

Description

[Detailed description of the invention] [Low quality of the invention] A waveform shaping circuit that corrects changes in duty ratio used in the fields of communication, control, and information processing using rectangular pulse transmission technology, etc., and a low-frequency P wave generator having a cutoff frequency fcyx. and a rectangular pulse train 4 with a repetition frequency f greater than the cutoff frequency fc.
It has first and second input terminals for inputting the output t from the No. 1 and low-frequency P-wave generators, respectively, and is composed of a comparator that feeds back a part of the output signal to the low-frequency P-wave generator. The output smoothed signal from the P wave generator is used as a reference signal and compared with the original rectangular pulse train signal input to the first input terminal, and in the region where the duty ratio is >0.5, the output pulse width is compressed and the duty ratio is <0. In the region of .5, the output pulse width is expanded and a rectangular pulse train signal with a duty ratio of approximately 50% is shaped.

[Industrial application field]

The present invention relates to a waveform shaping circuit used in the communication, control, and information processing fields using rectangular pulse transmission technology, and more particularly to a waveform shaping circuit with a feedback loop configuration that corrects changes in duty ratio and forms a rectangular pulse train with a duty ratio of 50%. It is something.

[Conventional technology]

In this type of rectangular pulse transmission technology, normally, as shown in Fig. 5, in the case of a rectangular pulse width W and a repetition period T, it is necessary to transmit a rectangular pulse train with a duty ratio of 50%, that is, W/T = Q, 5. be. However, due to interference in the transmission path, the duty ratio of the transmitted rectangular pulse train may not be 50%, as shown in FIG. 6C-2. In the pulsed frequency modulation method used for the transmission of general C2 analog video signals, the transmission signal waveform is a rectangular wave with a duty ratio of 50% as shown in Figure 7. Change in ratio, i.e. 5
A deviation from 0% results in signal distortion.

[Problem that the invention seeks to solve]

Conventionally, waveform distortion due to shift in duty ratio of this type of transmission rectangular pulse train signal! The correction circuit requires a frequency counter, a pulse generation circuit, etc., and there is a problem in that it generally has a complicated configuration.

[Means for solving problems]

In order to solve the conventional problems, the present invention includes a waveform shaping circuit that includes a low-frequency P-wave generator having a cut-off frequency few and a cut-off frequency f.
The first . It is characterized by having a second input terminal and comprising a comparator which feeds back a part of the output signal to the low-frequency P-wave device.

[For production]

The present invention provides a duty ratio key 50 input to the comparator.
% rectangular pulse train signal is compared with the smoothed signal output from the low frequency fI wave generator as a reference signal, and the duty ratio is 50%.
By compressing or expanding the pulse width of the output of the comparator in each region below 1 or 50%, the signal is shaped into a rectangular pulse train signal with a duty ratio of approximately 50% and output. This will be explained using drawings.

〔Example〕

FIG. 1 shows the circuit configuration of the first embodiment of the present invention.
This is a case of one person outputting. The operating principle of the first embodiment will be explained with reference to FIGS. 2(α) and (A).

A rectangular pulse train signal with a duty ratio of 50% shown in FIG. A part of the output signal of the comparator 3 is sent to the other input terminal of the comparator 3 via a passbubber 54 and then passed through a low frequency filter (LPF) 4 as shown in Fig. 2 (α
) is smoothed and input as shown by the broken line. In other words, the circuit configuration forms a feedback loop.

- The comparator 5 uses the smoothed signal from the low-pass P wave generator 4 as a reference signal Vj and compares it with the original rectangular pulse train input signal with a duty ratio of 50% input to the first input terminal. Here, since the rise and fall times of the rectangular pulse train signal of the input signal are finite, the pulse width of the output of the comparator 3 is compressed, and conversely the duty ratio <
In the region of 0.5, the pulse width of the output of the comparator 3 is expanded, and as a result, the output of the comparator 3 becomes a rectangular pulse train signal with a duty ratio of approximately 50%, as shown in FIG. 2(b). Shaped.

Figure 6 shows the circuit configuration of the second embodiment of the present invention! In the diagram shown,
This is an example applied to the case of two-person output. The differential signal input of the rectangular pulse train signal input to the input terminal 52 and the input terminal 31 is terminated as shown in the figure, and a differential line receiver is used as the comparator 35 to output the signal to the output terminal 33. The non-inverted output, which is a part of the output signal of the rectangular pulse train signal, is sent to the buffer 37. Low frequency door wave device (LP
F) 36 to the second input terminal of the differential line receiver 35.

In the circuit configuration of each of the embodiments described above, the cutoff frequency fc of the low-pass F wave generators 4 and 36 must be selected sufficiently lower than the repetition frequency f of the rectangular pulse train signal of the input signal.

FIG. 4 shows an example of a specific circuit configuration of the present invention.

This example is an example of a shaping circuit for a pulsed frequency modulated differential signal with a repetition frequency of around 30 MHz. Rμ
, RcL is a pull-up/down resistor for termination and DC bias determination, IC1 is for example used as a differential line receiver with comparator function (DECL-IC(
IC2 is, for example, an operational amplifier (using National Semiconductor LF357) having the functions of a buffer and a low-frequency P wave generator. In this circuit example, the cutoff frequency fc of the low-frequency F-wave device is as follows. By doing so, it is possible to obtain a waveform shaping circuit that corrects changes in duty ratio of a rectangular pulse train signal with a simple circuit.Furthermore, since the present invention has a feedback loop circuit configuration, it is possible to obtain a waveform shaping circuit that corrects changes in duty ratio of a rectangular pulse train signal. less affected by

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a first embodiment of the present invention, Fig. 2 is a diagram explaining the operating principle of the present invention, Fig. 3 is a block diagram of a second embodiment of the present invention, and Fig. 4 is a block diagram of a second embodiment of the present invention. Examples of specific circuit configurations of the present invention, FIG. 5 shows a transmission rectangular pulse with a duty ratio of 0.5, FIG. 6 shows a noise-mixed pulse with a duty ratio of 0.5, and FIG. 7 shows a transmission using a pulsed frequency modulation method. It is a signal waveform diagram. 1.31.52...Input terminal, 2, 55, 34
...Output terminal, 5...Comparator, 4,56...
・Low frequency F wave device, 5, 37...Buffer, 35...Comparator or differential line receiver

Claims (1)

[Claims] A low-pass filter having a cut-off frequency f_c; a first input terminal into which a rectangular pulse train signal having a repetition frequency f greater than the cut-off frequency f_c is input; and an output of the low-pass filter is input. A waveform shaping circuit comprising a comparator having a second input terminal that feeds a part of the output signal back to the low-pass filter.