JPH0325345Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field The present invention relates to a clip partial compensation circuit, for example.
The present invention relates to a compensation circuit used in a VTR playback system to compensate for and extract a portion of a waveform that is clipped by a clip circuit in a recording system.

BACKGROUND TECHNOLOGY In the brightness signal reproducing circuit of a VTR, so-called triangular noise is generated when demodulating an FM signal recorded on a magnetic tape. As a circuit for reducing this triangular noise, a pre-emphasis circuit that emphasizes the high frequency range of a modulated wave during recording and a de-emphasis circuit that reduces the high frequency range during playback are generally used.

By the way, the larger the amount of emphasis in the pre-emphasis circuit, the higher the SN after de-emphasis.
Although it is possible to improve the ratio, this increases the spikes that occur when the video signal rises from black to white, leading to overmodulation and causing problems such as inversion. A clip circuit is used to limit this spike portion to a certain amplitude or less.

When the high range of the video signal shown in FIG. 3A is emphasized by a pre-emphasis circuit and this emphasized portion is clipped at a certain clip level, as shown in FIG. 3B, a clipped portion m ₁ and an unclipped portion m ₂ are created. and give rise to. When this signal is reduced in high frequency by a de-emphasis circuit having characteristics opposite to the pre-emphasis characteristics, a portion m ₃ where the reproduced waveform deteriorates and a portion m ₄ where the reproduction waveform does not deteriorate as much are generated as shown in FIG.

Problems to be solved by the invention In the conventional device, the reproduced waveform _m5 of the clipped part as shown in Fig. 4 is improved by not making the de-emphasis characteristic the inverse of the pre-emphasis characteristic. , the reproducibility of the reproduced waveform _m6 of the unclipped portion deteriorates, and
Since both of the above characteristics are not reversed, SN
There was a problem that the ratio was not sufficient.

The present invention provides a clipped partial compensation circuit that can obtain an output signal with approximately the same waveform as the output of the pre-emphasis circuit, and can obtain a signal with a high signal-to-noise ratio by using a subsequent de-emphasis circuit with characteristics opposite to that of the pre-emphasis circuit. The purpose is to

Means for solving the problem In Figure 1, 2 is an emphasis circuit that emphasizes the high frequency range of the input signal, 6 is a comparator that detects the clip period of the input signal, and 5 is a circuit that connects the output of the emphasis circuit and the input signal. This is a switching circuit.

Function The emphasis circuit 2 emphasizes the high frequency range of the input signal, the comparator 6 detects the clip period of the input signal, and the output of the comparator 6 is used to obtain the output of the clip period emphasis circuit 2, while inputting other periods. Take out the signal.

Embodiment FIG. 1 shows a block diagram of an embodiment of the circuit of the present invention. In the figure, terminal 1 is connected to a video signal a (Figure 2A) whose spike portions with particularly large amplitudes are limited by a clip circuit (not shown) in the recording system.
comes in. The high frequency range of the video signal a is emphasized by an emphasis circuit 2, which has substantially the same characteristics as the emphasis characteristics of a pre-emphasis circuit (not shown) in the recording system, and becomes the signal b shown in FIG. 2B.
The attenuator 3 attenuates the output level to the same level as the output level of the delay circuit 4, which will be described later.
is supplied to terminal a of.

In this case, since the characteristics of the emphasis circuit 2 are the same as those of the pre-emphasis circuit in the recording system, the slopes of portions b ₁ and b ₂ of the signal b are the signals before clipping by the clip circuit in the recording system (i.e., the pre-emphasis circuit's characteristics). The slope is approximately the same as the slope of the output signal).

On the other hand, the video signal a is delayed in the delay circuit 4 by the same amount as the delay time in the emphasis circuit 2, and is supplied to the terminal b of the switch circuit 5.

6 is a window comparator (comparator, clip period detection circuit) having two types of reference potentials V _HC and V _LC , which determines the clip level of the video signal a to V _H , V _L
Then, V _HC <V _H , V _LC >V _L are selected (note that the differences between V _HC and V _H and between V _LC and V _L are extremely small). The video signal a is compared with reference potentials V _HC , V _LC in a comparator 6, and the level is determined as the potentials V HC , V _LC .
A signal c (C in the same figure) which is at H level only during a period greater than V _LC and at L level during a period smaller than V LC is taken out and supplied to the switch circuit 5 as a switching signal.

The movable contacts of the switch circuit 5 are configured to be connected to the terminal a when the output signal c of the comparator 6 is at the H level, and to the terminal b when the output signal c is at the L level. A signal d shown in FIG. D is taken out from the terminal 7. The signal d is a signal obtained by delaying parts b ₁ and b ₂ of the signal b during the clipping period of the video signal a, and is a delayed signal of the video signal a during other periods, and can have substantially the same waveform as the output of the pre-emphasis circuit in the recording system.

Note that if the delay time in the emphasis circuit 2 can be ignored, it is not necessary to provide the delay circuit 4.

Effects of the invention The circuit of the invention consists of an emphasis circuit which is supplied with an input signal in which a part of the period of the waveform of the output of the pre-emphasis circuit is clipped and which emphasizes the high frequency range with substantially the same characteristics as the characteristics of the pre-emphasis circuit; This is because it consists of a clip period detection circuit that detects the period in which the clip is being clipped, and a switching circuit that outputs the output of the clip period emphasis circuit from the output of the clip period detection circuit, while switching to extract the input signal for periods other than the clip period. , it is possible to extract an output signal with approximately the same waveform as the output of the pre-emphasis circuit, thereby allowing the subsequent de-emphasis circuit to have characteristics opposite to those of the pre-emphasis circuit. Both of them have the advantage of being able to extract signals with good reproducibility, being relatively simple to construct and therefore inexpensive, and being constructed of circuits capable of digital signal processing.

[Brief explanation of the drawing]

Figures 1 and 2 are a block system diagram and a signal waveform diagram for explaining the operation of an embodiment of the circuit of the present invention, respectively, and Figure 3 is a signal waveform diagram when the pre-emphasis circuit has characteristics opposite to those of the de-emphasis circuit. , FIG. 4 is a signal waveform diagram after de-emphasis by a conventional circuit. 1...Video signal input terminal, 2...Emphasis circuit, 5...Switch circuit, 6...Comparator, 7...
...Output terminal.

Claims (1)

[Scope of utility model registration request] An emphasis circuit that is supplied with an input signal in which a partial period of a waveform of an output of a pre-emphasis circuit is clipped and emphasizes the high range thereof with substantially the same characteristics as the pre-emphasis circuit, and detects the clipped period of the input signal. A clip partial compensation circuit comprising a clip period detection circuit and a switching circuit configured to extract the output of the emphasis circuit during the clip period from the output of the clip period detection circuit, and to extract the input signal during periods other than the clip period. .