JPH02121519A - 4-multiplying circuit for wide band signal - Google Patents

Abstract

PURPOSE:To attain a theoretically perfect pulse counting action by using a VCR, etc., to differentiate an input signal, obtaining the doubled pulse trains of the differentiated signal and the input signal, and securing an OR of these pulse signals. CONSTITUTION:The noises produced at reproduction are eliminated by a BPF 13 for the regenerative signals. These signals are inputted to a 1st edge detecting circuit 15 and a differentiation circuit 17 via the buffer circuit 14 and 16. The circuit 15 converts the regenerative signals into the density of the doubled pulse. While the circuit 17 differentiates the regenerative signal and a 2nd edge detecting circuit 18 converts the differentiation waveform signal into the density of the doubled pulse. Thus an OR is secured via a 2-OR circuit 20 between the pulse trains obtained through both circuits 15 and 18. Therefore the regenerative signal is converted into the density wave of a qudrupled pulse. This pulse train integrated via an LPF 4 and converted into the change of amplitude.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is used in VCRs (νTR), etc., and when demodulating reproduced video signals etc. using the pulse count method, the wideband main signal is multiplied by 4. The present invention relates to a wideband signal quadrupling circuit that obtains pulse train compression waves.

[Conventional Example] Conventionally, in many VCRs and the like, a pulse counting method is used as a method of demodulating a reproduced video signal.

An example of the pulse counting method will be explained based on FIGS. 4 and 5.

In these figures, a reproduction signal from a video head 1 is amplified by a reproduction amplification circuit 2 (shown in FIG. 5(c)), this coarse and dense pulse train is integrated by a low-pass filter (LPF) 4 and converted into a change in amplitude, which is amplified to a predetermined value by an amplifier 5 (shown in FIG. 5(d)).
). Therefore, the doubler circuit 3 includes a comparator 3a that detects the zero-crossing point of the reproduced signal and outputs the rectangular wave signal (shown in FIG. 5(b)), a delay circuit 3b that delays the rectangular wave, and a delay circuit 3b that delays the rectangular wave. It is composed of a logic circuit 3C that calculates the exclusive OR of rectangular wave signals.

By the way, with the development of high-definition television in recent years, V
CR and the like are being developed, and the pulse counter method is also used as a method for demodulating high-definition television signals (for example, wideband FM signals) in VCR and the like.

This example will be explained based on FIGS. 6 and 7. In FIG. 1, the same parts as in FIG. 4 are designated by the same reference numerals, and redundant explanation will be omitted.

In these figures, the reproduced signal (broadband FM signal) obtained by the reproduced amplifier circuit 2 is transmitted through the buffer circuit 6 to the 2
The signal is input to the multiplier circuit 7 and also to the π/2 phase shift circuit 9 via the buffer circuit 8 . The reproduced signal phase-shifted by the π/2 phase shift circuit 9 is output to the equalizer circuit 1.
The signal is waveform-shaped at 0 and input to the doubling circuit 11. Note that the doubler circuits 7 and 11 have the same structure as the doubler circuit 3 shown in FIG.

Then, as shown in FIGS. 7(a) and (b),
The reproduced signal passed through the buffer circuit 6 is made into a compression wave of double pulses. On the other hand, regarding the reproduced signal whose phase is shifted by π/2, the reproduced signal is similarly made into a compression wave of double pulses. Since these pulse trains are input to the 2-OR circuit 12, a compression wave of quadrupled pulses is obtained in the 2-OR circuit 12, as shown in FIG. 7(e). This compression wave pulse train is integrated by a low pass filter (LPF) 4 and converted into a change in amplitude (as shown in FIG. 7(f)).

[Problems to be Solved by the Invention] Incidentally, in the quadrupling circuit for wideband signals described above, the π/2 phase shift circuit 9 that shifts the phase of the input signal by π/2 is constituted by a resistor/capacitor (C, R) circuit. and filter operations were performed. However, although the pulse counting method using the quadrupling circuit described above does not actually cause any problems, it can be said to be incomplete in principle because it does not utilize the peak points in the signal.

This invention was made in view of the above-mentioned problems, and its purpose is to obtain quadrupled pulses by using the peak points of a broadband signal as a human signal, and to realize a complete pulse counting method in principle. An object of the present invention is to provide a quadrupling circuit for a wideband signal that can perform the following functions.

[Means for Solving the Problems] In order to achieve the above object, four of the broadband signals of the present invention are provided.
When a wideband FM signal such as a video signal is demodulated by the pulse counting method, the multiplier circuit converts the wideband FM signal into a compression wave of quadrupled pulses. detect,
A first edge detection circuit outputs a pulse at the edge timing, a differentiation circuit differentiates the broadband FM signal, and a second edge detection circuit detects the zero-crossing point of the differentiated signal and outputs a pulse at the edge timing. an edge detection circuit; and an OR circuit for ORing the pulse trains obtained by the first and second edge detection circuits; The gist is that the compression wave is a multiplied pulse.

[Function] With the above configuration, the zero-crossing point of the differential wideband FM signal (differential reproduction signal) corresponds to the peak point of the reproduction signal. That is, the zero-crossing point is detected by the second edge detection circuit, and a pulse is output at the timing of that point. On the other hand, in the first edge detection circuit,
The zero-crossing point of the reproduced signal is detected, and a pulse is output at the timing of that point. The pulses obtained by the first edge detection circuit are double pulses of the reproduction signal, and the pulses obtained by the second edge detection circuit are double pulses of the differential reproduction signal. The sum is taken in the above-mentioned OR circuit to obtain a quadrupled pulse. Moreover, since this quadrupling pulse is obtained by using the peak point of the reproduced signal, the pulse counting method using the quadrupling circuit described above can be said to be perfect in principle.

[Embodiments] Hereinafter, embodiments of the present invention will be described based on the drawings. Note that in the figure, the same parts as in FIGS. 4 and 6 are denoted by the same reference numerals, and redundant explanation will be omitted.

In FIG. 1, the reproduction signal (broadband FM signal) from the video head 1 is amplified by the reproduction amplifier circuit 2, and its noise is removed by a low-pass filter (LPF) 13.
The signal is input to the first edge detection circuit 15 via the buffer circuit 14. On the other hand, the reproduced signal is also input to the differentiation circuit 17 via the buffer circuit 16, and this differentiated reproduction signal is input to the second edge detection circuit 18. The first edge detection circuit 15 detects the zero crossing point of the reproduced signal and outputs a pulse (compression wave obtained by doubling the reproduced signal) at that point. Furthermore, the second edge detection circuit 18 similarly detects the zero-crossing point of the differential reproduction signal and outputs a pulse (compression wave obtained by multiplying the reproduction signal by two) at that point.

The pulse train obtained by the first edge detection circuit 15 is finely adjusted by the delay circuit 19, and then the pulse train obtained by the first edge detection circuit 15 is finely adjusted by the delay circuit 19.
Together with the pulse train obtained in step 8, the pulse train is input to the 2-OR circuit 20. The pulse train logically summed by the 2-OR circuit 20 is input to a low-pass filter (LPF) 5.

Note that as the differentiating circuit 17 and the second edge detecting circuit 18, a circuit shown in FIG. 2 can be considered.

Next, the operation of the broadband signal quadrupling circuit with the above configuration will be explained in the third section.
The explanation will be based on the time chart shown in the figure.

First, if the video signal obtained by the video head 1 is a high-definition television signal, for example, it can be said to be a wideband FM signal (reproduction signal). As shown in FIG. 3(a), the reproduced signal is passed through a low-pass filter 13 to remove noise generated during reproduction, and then sent to the first edge via buffer circuits 14 and 1.6. The signal is input to the detection circuit 15 and the differentiation circuit 17. Then, in the first edge detection circuit 15, the
Similar to the doubler circuit shown in the figure, the reproduced signal is converted into coarse and finer double pulses. On the other hand, as shown in FIG. 3(b), the differential circuit 17 differentiates the reproduced signal, and the second edge detection circuit 18 converts this differentiated waveform signal into a double pulse.

In this way, the first and second edge detection circuits 15, 1
The pulse train obtained at step 8 is logically summed by a 2-OR circuit 20 (shown in (e) of the same figure). Therefore, as in the example shown in FIG. 6, the reproduced signal is converted into a compression wave of quadrupled pulses, and this pulse train is integrated by the low-pass filter 4 and converted into a change in amplitude (see FIG. 3). f)). Moreover, since the peak point of the reproduced signal is used for the demodulated signal obtained by the conversion, it is possible in principle to obtain a perfect quadrupled pulse. Further, as shown in FIG. 2, the differentiator circuit 17 and the second edge detection circuit 18 have the advantage that they can have simple circuit configurations and do not need to be adjusted.

[Effects of the Invention] As explained above, according to the wideband signal quadruple multiplier circuit of the present invention, as a method of converting an input signal into a compression wave of a pulse train that is quadrupled, the input signal is differentiated and the differentiated signal is Since the pulse train is obtained by multiplying the input signal by two times and by performing the logical sum of these pulse signals, it is possible to obtain a pulse by four times the reproduced wideband signal by using the peak point of the wideband FM signal as the input signal. This can be said to be a complete pulse counting method in principle.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a wideband signal quadrupling circuit showing an embodiment of the present invention, FIG. 2 is a partial circuit diagram of the quadrupling circuit, and FIG. 3 explains the operation of the quadrupling circuit. Figure 4 is a schematic block diagram of a doubling circuit using the conventional pulse counting method.
FIG. 6 is a schematic block diagram of a quadruple multiplier circuit using the conventional pulse counting method.
FIG. 3 is a time chart diagram for explaining the operation of the multiplier circuit. In the figure, 15 is a first edge detection circuit, 17 is a differentiation circuit,
18 is a second edge detection circuit, and 20 is a 2-OR circuit (OR circuit).

Claims (1)

[Claims] (1) When demodulating a wideband signal such as a video using the pulse counting method, in a wideband signal quadrupling circuit that converts the wideband signal into a compression wave of quadrupled pulses, detecting the zero crossing point of the wideband signal, a first edge detection circuit that outputs a pulse at the edge timing; a differentiation circuit that differentiates the broadband signal; and a second edge detection circuit that detects the zero-crossing point of the differentiated signal and outputs a pulse at the edge timing. a detection circuit; and an OR circuit for ORing the pulse trains obtained by the first and second edge detection circuits, and the pulse train output from the OR circuit is a quadruple pulse of the broadband signal. A wideband signal quadrupling circuit characterized by a compression wave.