JPH0937295A - Recording and playback device - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To prevent noise by reducing a signal level when there is no color signal. A reproduction signal is input to a low-pass filter 12 via a reproduction amplifier 11. Low-pass filter 1
2 extracts a color signal from the reproduction signal. ACC circuit 13
Keeps the color signal level constant. Frequency conversion circuit 14
Converts the frequency of the color signal output from the ACC circuit 13 into a predetermined value. The bandpass filter 15 and the comb filter 16 remove unnecessary components from the signal output from the frequency conversion circuit 14. The killer detection circuit 22 detects whether or not the output signal of the comb filter includes a color signal. When the killer detection circuit 22 determines that the color signal is included, the maximum gain of the ACC circuit 13 becomes small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for recording or reproducing a video signal.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional recording / reproducing apparatus. Reference numeral 11 is a reproduction amplifier. Reproduction amplifier 11
Is a reproduction signal of a minute level (including color signal and luminance signal)
Has the function of amplifying. 12 is a low-pass filter (LPF). The low-pass filter 12 has a function of separating the low-pass converted color signal (629 kHz) and the FM-modulated luminance signal (4 MHz) and outputting only the color signal.

13 is an ACC (Automatic C)
Roma Control) circuit. ACC circuit 1
3 has a function of keeping the level of the color signal constant.
Reference numeral 14 is a frequency conversion circuit. Frequency conversion circuit 14
Has a function of converting a color signal into a carrier color signal of 3.58 MHz.

Reference numeral 15 is a bandpass filter. The bandpass filter (BPF) 15 has a function of removing unnecessary components generated by frequency conversion. 16 is a comb filter. The comb filter 16 has a function of removing a noise component from the carrier color signal.

Reference numeral 17 is a burst extraction circuit, and 18 is
The 3.5 MHz oscillator, 19 is a phase comparator. The phase comparator 19 compares the phase of the burst signal with the phase of the oscillator 18, and outputs an output signal according to the phase difference between the two.

Reference numeral 20 is a voltage controlled oscillator. The voltage controlled oscillator (VCO) 20 has a function of outputting a signal of a predetermined frequency based on the output signal of the phase comparator 19.
21 is a frequency conversion circuit. Frequency conversion circuit 21
Has a function of receiving the horizontal sync separation signal and the output signal of the voltage controlled oscillator 20 and giving a signal of a predetermined frequency to the frequency conversion circuit 14.

Reference numeral 22 is a killer detection circuit. The killer detection circuit 22 receives a signal from the output signal of the comb filter 16 and outputs a signal.
The strike component is extracted to detect whether or not a color signal is recorded, and if a color signal is recorded, a predetermined output signal is output.

Reference numeral 23 is a killer circuit. Killer circuit 2
3 has a function of receiving the output signal of the killer detection circuit 22 and turning off when there is no color signal, and blocking the output signal of the comb filter 16.

The recording / reproducing apparatus described above is described in, for example, "NHK home video technology" written by Katsuya Yokoyama, published by Japan Broadcasting Corporation, p. 93-96 (7.4 Color Process Circuit Implementation).

[0010]

In the above-described recording / reproducing apparatus, for example, when a video tape in which a color signal is not recorded is reproduced, the ACC circuit 13 keeps the noise level constant, that is, noise is generated. There is a drawback that the maximum gain is amplified.

As a result, the killer detection circuit 22 initially judges that the color signal is not recorded, but thereafter,
When the noise is amplified, the color signal is erroneously determined to be recorded, so that the killer circuit 23 is turned on and only the amplified noise is output.

The present invention has been made to solve the above-mentioned drawbacks, and an object thereof is to provide a function for immediately reducing the maximum gain of the ACC circuit when the killer detection circuit judges that there is no color signal, thereby reducing noise. It is to prevent the situation where only the output is made.

[0013]

In order to achieve the above object, a recording / reproducing apparatus of the present invention has a first filter for extracting a color signal from an input signal and a level of a color signal output from the filter. At least one ACC circuit, a frequency conversion circuit that converts the frequency of the color signal output from the ACC circuit to a predetermined value, and a second filter that removes unnecessary components from the signal output from the frequency conversion circuit, A killer detection circuit for detecting whether or not a color signal is included in a signal output from the second filter; and a killer detection circuit which is turned on when the killer detection circuit detects a color signal and is output from the second filter. A killer circuit for outputting an output color signal, and for reducing the level of the input signal when the input signal does not include a color signal,
The output signal of the killer detection circuit is fed back to at least one of the first filter, the ACC circuit, the frequency conversion circuit, and the second filter.

The output signal of the killer detection circuit is converted into the AC signal.
When it is fed back to the C circuit, the maximum gain of the ACC circuit is reduced when the killer detection circuit determines that the input signal does not include a color signal.

When there are a plurality of ACC circuits, the maximum gain of at least one of the plurality of ACC circuits is the maximum gain when the killer detection circuit determines that the input signal does not include a color signal. It is configured to be small.

When the output signal of the killer detection circuit is fed back to the frequency conversion circuit or the second filter, when the killer detection circuit determines that the input signal does not include a color signal. The level of the output signal of the frequency conversion circuit or the level of the output signal of the second filter is reduced.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a recording / reproducing apparatus according to an embodiment of the present invention. The reproduction amplifier 11 amplifies a reproduction signal of a minute level (including a color signal and a luminance signal). Low-pass filter 12
Separates the low-pass converted color signal (629 kHz) from the FM-modulated luminance signal (4 MHz) and outputs only the color signal.

The ACC circuit 13 has a function of keeping the color signal level constant. Further, the ACC circuit 13 has
The output signal of the killer detection circuit 22 is input. AC
The C circuit 13 receives the output signal of the killer detection circuit 22,
The maximum gain is reduced when there is no color signal.

The ACC circuit 13 may be composed of two or more ACC circuits connected in series. In this case, when the killer detection circuit 22 determines that there is no color signal, the maximum gain of at least one ACC circuit is reduced.

The frequency conversion circuit 14 converts the color signal to 3.58.
Converted to MHz carrier color signal. The bandpass filter (BPF) 15 removes unnecessary components generated by frequency conversion. The comb filter 16 removes noise components from the carrier color signal.

The phase comparator 19 compares the phase of the burst signal with the phase of the oscillator 18, and outputs an output signal according to the phase difference between the two. The voltage controlled oscillator (VCO) 20 outputs a signal of a predetermined frequency based on the output signal of the phase comparator 19.

The frequency conversion circuit 21 receives the horizontal sync separation signal and the output signal of the voltage control oscillator 20, and gives a signal of a predetermined frequency to the frequency conversion circuit 14. The killer detection circuit 22 extracts the burst component from the output signal of the comb filter 16 to detect whether or not a color signal is recorded, and when the color signal is recorded, a predetermined value is determined. Output the output signal.

The killer circuit 23 receives the output signal of the killer detection circuit 22, and when the color signal does not exist, the killer circuit 23 is turned off and cuts off the output signal of the comb filter 16.
According to the recording / reproducing apparatus having the above-described configuration, for example, when a video tape in which a color signal is not recorded is reproduced, the killer detection circuit 22 initially determines that the color signal is not recorded and the killer circuit is detected. The output signal that turns off 23 is
It is given to the circuit 23. At the same time, the killer detection circuit 22 is
The output signal for reducing the maximum gain of the CC circuit 13 is AC
It is given to the C circuit 13.

As a result, since the ACC circuit 13 does not amplify the noise to the maximum gain, the killer detection circuit 22 does not mistakenly judge the noise as a color signal. Therefore, the killer circuit 23 does not malfunction,
It is also possible to prevent a situation in which only amplified noise is output.

In the recording / reproducing apparatus described above, the maximum gain of the ACC circuit is reduced when there is no color signal. However, the circuit constituting the recording / reproducing system (from the low-pass filter 12 to the comb). Shape filter 16)
It is also possible to reduce the level of the output signal of any one or two or more of the circuits. Even in such a case, it is possible to avoid the situation in which the killer detection circuit 22 erroneously determines noise as a color signal, and thus the object of the present invention is achieved.

[0026]

As described above, the recording / reproducing apparatus of the present invention has the following effects. When a playback signal with no color signal recorded is input, the
The detection circuit correctly determines that the color signal is not recorded, and turns off the killer circuit. At the same time, the killer detection circuit provides the ACC circuit with an output signal that reduces the maximum gain of the ACC circuit, for example.

Therefore, the ACC circuit does not amplify the noise to the maximum gain, and thereafter the killer detection circuit does not make an erroneous decision. Therefore, it is possible to prevent a situation in which the killer circuit malfunctions and only amplified noise is output.

[Brief description of drawings]

FIG. 1 is a block diagram showing a recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional recording / reproducing apparatus.

[Explanation of symbols]

 11 ... Reproduction amplifier, 12 ... Low-pass filter, 13 ... ACC circuit, 14, 21 ... Frequency conversion circuit, 15 ... Band pass filter, 16 ... Comb type filter, 17 ... Burst extraction circuit, 18 ... Oscillator, 19 ... phase comparator, 20 ... voltage controlled oscillator, 22 ... killer detection circuit, 23 ... killer circuit.

Claims (1)

[Claims] 1. A first filter for extracting a color signal from an input signal, at least one ACC circuit for making a level of a color signal output from the filter constant, and the ACC.
A frequency conversion circuit for converting the frequency of the color signal output from the circuit to a predetermined value, a second filter for removing unnecessary components from the signal output from the frequency conversion circuit, and a signal output from the second filter. A killer detection circuit for detecting whether or not a color signal is included, and a killer for outputting a color signal output from the second filter when the killer detection circuit detects a color signal and is turned on. A circuit, the second circuit if the input signal does not include a color signal
In order to reduce the level of the signal output from the filter, the output signal of the killer detection circuit is fed back to at least one of the first filter, the ACC circuit, the frequency conversion circuit and the second filter. A recording / reproducing apparatus characterized by the above.