JPS6044735B2 - Signal distortion improvement circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal distortion improvement circuit that is applied to a signal transmission system in which a clipper performs clip processing and transmits a signal to compensate for waveform distortion of a signal caused by the above-mentioned clip processing. .

For example, a video tape recorder (hereinafter referred to as a VTR) records and plays video signals.

), since the transmission band of the signal transmission system used is limited, the input video signal is pre-emphasized and then subjected to white clip processing before magnetic recording. For this reason, when the input video signal has an excessive signal level or a large level, the above-mentioned white clipping process causes distortion in the signal waveform, resulting in the problem that it becomes impossible to obtain a reproduced image with good image quality. ing. SUMMARY OF THE INVENTION Therefore, the present invention aims to compensate for the waveform distortion of signals caused by the above-mentioned clip processing in a signal transmission system such as a VTR that performs signal transmission by performing clip processing, thereby making it possible to transmit signals with high fidelity. The present invention provides a signal distortion improvement circuit. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings showing one embodiment. FIG. 1 shows a block diagram of an embodiment of the present invention configured to be applied to a VTR.

In addition, a waveform diagram for explaining the operation of this embodiment is shown in the second section.
Shown in Figures A to J. In this embodiment, a signal distortion improvement circuit 3 according to the present invention is provided between a demodulation circuit 1 and a de-emphasis circuit 2 in a block of circuits of a reproduction system of a VTR.

In this embodiment, pre-emphasis is applied to the input video signal in a recording system circuit block of the VTR (not shown), so that the input video signal is set at a predetermined clip level L.

After being subjected to clip processing, a reproduced signal of the recording signal magnetically recorded using the frequency modulation recording method is supplied to the demodulation circuit 1 from the signal input terminal 4. Here, the above input video signal has a waveform shown in FIG. 2A, and is changed to a waveform as shown in FIG. 2B by pre-emphasis,
Furthermore, it is assumed that the signal is magnetically recorded as a recording signal in a state where the waveform becomes as shown in FIG. 2c through clip processing. That is, the reproduced signal supplied to the signal input terminal 4 is a portion of the input video or image signal that has reached an excessive signal level due to pre-emphasis (the triangular waveform indicated by diagonal lines in FIG. 2B). This includes waveform distortion caused by the clipping.
The reproduced signal containing the waveform distortion as described above is frequency modulated by the demodulation circuit 1 and then supplied to the signal distortion improvement circuit 3 having the configuration as described below, where the waveform distortion is compensated. That is, the demodulated signal obtained by the demodulation circuit 1 is supplied to the voltage comparator 5 in the signal distortion improvement circuit 3, and is delayed by a predetermined delay time T1 in the first delay circuit 6, and then sent to the signal mixing circuit 7. is supplied to.

The voltage comparator 5 has a comparison level L that is a predetermined clip level L in the recording system circuit block described above.

The reference voltage RIE1P from the reference voltage input terminal 8 is set to a level slightly lower than the reference voltage input terminal 8. This voltage comparator 5 is obtained by performing a voltage comparison between the demodulated signal and the reference voltage VR, and performs level discrimination on the signal level of the demodulated signal using the comparison level L. Outputs a comparison output signal.
This comparison output signal has a pulse waveform with a pulse width corresponding to the width of the waveform distortion portion (that is, the triangular wave-shaped portion indicated by diagonal lines in FIG. 2B) caused by the above-mentioned clipping process. The signal has a waveform as shown in FIG. 2D. Note that if no waveform distortion occurs due to the clipping process described above, the signal level of the comparison output signal from the voltage comparator 5 will be at a constant level. That is, the voltage comparator 5 described above performs an operation of generating waveform distortion by clipping processing. The comparison output signal obtained by the voltage comparator 5 is supplied to the first input terminal 9a of the charging/discharging circuit 9, and is transmitted through the second delay circuit 10 as shown in FIG. 2E. Predetermined delay time T2. The second input terminal 9b1 of the charging/discharging circuit 9 is supplied to the set pulse generator 11 and the AND circuit 12 with a delay of .times.

Note that the reset pulse generator 11 is similar to the second reset pulse generator 11.
In response to the above comparison output signal supplied through the delay circuit 10 of ! The reset pulse obtained by the same operation is supplied to the third input terminal 9c of the charge/discharge circuit 9. The charging/discharging circuit 9 performs a charging operation according to the pulse waveform of the comparison output signal supplied to its first input terminal 9a, converts the pulse width of the pulse waveform into a DC level, and holds it. and a second delay circuit 1 is connected to its second input terminal.
It has a function of performing a discharging operation in accordance with the pulse waveform of the comparison output signal supplied via 0.

Therefore, this charging/discharging circuit 9 creates an output signal having a trapezoidal waveform as shown in FIG. 2F from the signals supplied to each input terminal, and supplies this output signal to the AND circuit 12.
The AND circuit 12 outputs an analog AND output signal between the comparison output signal delayed by the predetermined delay time T2 by the second delay circuit 10 and the output signal from the charge/discharge circuit 9. , outputs a triangular waveform signal as shown in FIG. 2G.

In this way, the AND output signal obtained from the AND circuit 12 includes a portion of the input video signal clipped by the clipping process described above, that is, a portion of the triangular waveform shown with diagonal lines in FIG. 2B. , minutes, and is supplied to the signal mixing circuit 7 and superimposed on the demodulated signal delayed by the predetermined delay time T1 in the first delay circuit 6. That is, the signal mixing circuit 7 described above
2H is a diagram in which the demodulated signal indicated by the dashed line in FIG. Signal distortion is improved by superimposing the triangular wave-shaped AND output signal on the portion indicated by the middle broken line.Here, the first and second delay circuits 6 and 10 are In order to obtain an AND output signal with a triangular waveform that approximates the waveform distortion caused by clip processing, and to superimpose the above AND output signal at the correct position on the portion of the demodulated signal where waveform distortion occurs, each delay is Time Tl and T2 are determined.

In this way, the signal obtained by the signal mixing circuit 7 has the waveform distortion in the demodulated signal compensated for, and the waveform of the input video signal that has been pre-emphasized in the recording system circuit block described above (see FIG. It has a waveform as shown in FIG. 2, which is similar to the waveform shown in FIG. This signal is subjected to de-emphasis via the de-emphasis circuit 2 to form a waveform as shown in FIG. 2J, and is then outputted from the signal output terminal 13 as a reproduced video signal. The reproduced video signal outputted from the signal output terminal 13 is obtained by applying de-emphasis to the demodulated signal whose waveform distortion due to the clipping process has been compensated as described above, and therefore has high fidelity to the input video signal. It will be possible to play back images with good quality.

Therefore, in this embodiment, even if a reproduced signal with waveform distortion caused by clip processing in the circuit block of the recording system of the VTR is supplied to the signal input terminal 13, the signal distortion improvement circuit 3 according to the present invention Since waveform distortion is compensated for, a reproduced video signal that can always be reproduced with good image quality can be output from the signal output terminal 13.

In addition, in a VTR, since the duplication, carrier frequency, and white clip level are specified by frequency, the clip level can be set from the demodulated signal obtained by frequency demodulation, so that it is also possible to perform clip correction. As described above, according to the present invention, the discrimination output signal obtained by level-discriminating the signal level of the transmission signal that has been subjected to clip processing at a level slightly lower than the clip level in the clip processing. By synthesizing a correction signal and superimposing this correction signal on the transmission signal, the waveform distortion caused by clipping in the transmission signal is compensated for. It becomes possible to perform correction and high-fidelity signal transmission, and for example, by applying it to a VTR, it is possible to obtain effects such as obtaining reproduced images with good image quality, and the intended purpose can be fully achieved. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment in which the present invention is applied to a VTR. FIGS. 2A to 2J are waveform diagrams for explaining the operation of the above embodiment. 3... Signal distortion improvement circuit,
5...Voltage comparator, 6,10...Delay circuit, 7...
- Signal mixing circuit, 9...Charging/discharging circuit, 12...AND circuit.

Claims (1)

[Claims] 1 For the transmission signal that has been subjected to clip processing, a correction signal is synthesized from the discrimination output signal obtained by level-discriminating the signal level of the transmission signal at a discrimination level slightly lower than the clip level in the clip processing, and this correction signal is 1. A signal distortion improvement circuit comprising: compensating for waveform distortion occurring in the transmission signal due to clip processing by superimposing the same on the transmission signal.