JPS6339157B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise reduction device for SECAM color signals in a magnetic recording/reproducing device.

The SECAM color television system is a system in which color difference signals R-Y and B-Y are alternately FM modulated for each scanning line and multiplexed with a luminance signal. The recording and reproduction of SECAM color television signals will be briefly explained based on the circuit diagram of the conventional device shown in FIG. First, the recording system shown in a will be explained. Luminance signal is NTSC
and PAL format. That is, the SECAM input signal from terminal 1 is LPF2 → AGC circuit 3 → FM modulation circuit 4 →
Through the HPF 5, the signal is mixed and amplified with a color signal processed as described later in a recording amplifier 9, and recorded on a magnetic tape 20 by a video head 10. The color signal is supplied to a 1/4 countdown circuit 7 via the BPF 6, and the carrier wave frequency is counted down to 1/4 in the countdown circuit 7.
That is, the FM-modulated color signal in the 4 MHz band is converted to the low frequency side in the 1 MHz band by the 1/4 countdown circuit 7 described above. converted to low frequency side
The upper limit frequency of the FM color signal is limited by the LPF 8, and the FM color signal is mixed with the above-mentioned FM luminance signal and recorded by the recording amplifier 9.

Next, the reproduction system shown in b will be explained.
The pick-up signal from the video head 10 is passed through the playback amplifier 11 → switching circuit 12.
The luminance signal passes through the HPF 13 and demodulation circuit 14, is mixed with a color signal processed as described later in a mixing circuit 18, and is taken out from a terminal 19 as a SECAM output signal. On the other hand, the color signal converted to a low frequency band during recording is separated by the LPF 15, and further quadrupled by the quadruple wave generation circuit 16, which multiplies the carrier wave to 4 times the frequency to obtain the carrier wave frequency (4MHz) of the original color signal.
band). Then, the required band is extracted by the BPF 17, mixed with the luminance signal that has passed through the demodulation circuit 14 described above in the mixing circuit 18, and taken out from the terminal 19 as a SECAM output signal.

As mentioned above, the 1/4 countdown method is used for magnetic recording of the color signal of the SECAM color television signal, but in the case of the SECAM method, the color subcarrier is FM modulated and there is no line correlation. , it is difficult to use it as a countermeasure for reducing noise caused by crosstalk using line correlation, as in the case of the NTSC and PAL systems. For this reason, the influence of crosstalk appears greatly during playback, resulting in an extremely unsightly playback screen, especially when tracking is off.
In addition, the low frequency converted color signal is approximately 1.1MHz.
Although it is an FM signal, there is a limit to crosstalk removal due to the azimuth effect, and furthermore, in the case of long-term recording, it is necessary to take measures to reduce noise caused by some crosstalk due to the H shift of the color signal. .

The present invention has been made in view of the above-mentioned circumstances.
-Y line sequential color difference signal, and the above R-Y,
At the stage of converting to a B-Y line sequential color difference signal, noise components are removed using line correlation, and then the process is performed again.
In a configuration that cancels and reduces the noise of the SECAM reproduced color signal by FM modulating it and returning it to the SECAM FM signal, the free-running frequency of the FM modulation circuit is kept constant during the above FM modulation. By changing the clamp voltage of the modulation signal every 1H, SECAM
The present invention provides a noise reduction device for SECAM color signals in a magnetic recording/reproducing device, which has a simple circuit configuration by extracting FM signals.

An embodiment of the present invention will be described below with reference to FIG.

The SECAM reproduced color signal supplied to the terminal 21 in FIG.
2, where it is once demodulated and converted into R-Y,B
-Y line-sequential color difference signals, and noise components are removed here using line correlation. The SECAM reproduced color signal supplied to the terminal 21 is supplied to the first demodulation circuit 23 and also supplied to the second demodulation circuit 25 via the 2H delay line 24, respectively. Y
is demodulated into a line-sequential color difference signal. The output from the first demodulation circuit 23 and the output from the second demodulation circuit 25 are each supplied to a first difference circuit 26, and a noise component is obtained from the output of the first difference circuit 26. . The output of the first difference circuit 26 is appropriately limited by a limiter circuit 27 and is supplied to a second difference circuit 28. The second difference circuit 28 is also supplied with the output from the first demodulation circuit 23 described above. That is, in the noise reduction circuit 22 described above, in order to utilize line correlation,
The SECAM reproduced color signal is first converted into R-Y, B-Y main line sequential color difference signals by a demodulation circuit, and the difference is taken between this and a 2H delayed sub line sequential color difference signal similar to the above. By subtracting the sub signal from the above main signal, a color signal with reduced noise is obtained.

The color signal whose noise has been reduced in the noise reduction circuit 22 described above is supplied to the FM modulation circuit 30 via the clamp circuit 29, where the SECAM
It is converted to a color signal and sent from terminal 31 to SECAM.
Extracted as FM signal. The above FM modulation circuit 30 has a reference subcarrier of 4.40M for R-Y.
Reference subcarrier for Hz and B-Y
Although the modulation operation is performed alternately every 1H at 4.25MHz, the free-running frequency of the FM modulation circuit 30 is constant, and the clamp voltage of the clamp circuit 29 interposed in the previous stage is supplied to the terminal 32. The FM modulation circuit 30 changes the clamp voltage of the modulation signal every 1H using the horizontal synchronization pulse generated.
It operates at the above-mentioned 4.25MHz and 4.40MHz every 1H to produce a SECAM FM signal.

Since the center frequency of the SECAM color television signal is switched between 4.25MHz and 4.40MHz every 1H, an oscillation circuit is required to oscillate each of the above frequencies, but according to the present invention, the above oscillation circuit is not necessary, and the configuration of the FM modulation circuit is also simplified.

As described above, according to the present invention, the first FM demodulator 2 inputs the SECAM reproduced color video signal.
3, a delay element 24 for two horizontal periods to which the SECAM reproduced color video signal is input, a second FM demodulator 25 to which the output of the delay element is input;
a first difference circuit 26 that outputs the difference between the output of the FM demodulator 23 and the output of the second FM demodulator 25;
, a limiter 27 that inputs the output of the first difference circuit 26 to limit the amplitude, and a second difference circuit 28 that subtracts the output of the limiter 27 from the output of the first FM demodulator 23 and outputs the result. and the second difference circuit 2
FM modulator 30 that inputs the output of 8 and performs FM modulation.
SECAM in magnetic recording and reproducing equipment equipped with
In the color signal noise reduction device, the second
A clamp circuit 29 whose clamp voltage is switched according to the horizontal synchronizing pulse is inserted between the difference circuit 28 and the FM modulator 30, and the frequency of FM modulation is switched every horizontal period. of
Even in the case of the SECAM method that uses FM modulation, noise reduction can be achieved with a simple circuit configuration, and furthermore, a SECAM reproduced color video signal with a stable FM modulation frequency can be output without the need for a separate oscillator. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional magnetic recording and reproducing apparatus for SECAM color television signals, in which a is a schematic circuit diagram of the recording system, b is a schematic circuit diagram of the reproducing system, and FIG.
The figure is a circuit configuration diagram of a noise reduction device according to the present invention. 23, 25: demodulation circuit, 26, 28: difference circuit,
24: 2H delay line, 27: Limiter circuit,
29: Clamp circuit, 30: FM modulation circuit.

Claims (1)

[Claims] 1 1st input for SECAM playback color video signal
an FM demodulator, a delay element for two horizontal periods to which the SECAM reproduced color video signal is input, a second FM demodulator to which the output of the delay element is input, an output of the first FM demodulator and the a first difference circuit that outputs the difference between the output of the second FM demodulator; a limiter that inputs the output of the first difference circuit and limits the amplitude; and a limiter that inputs the output of the first difference circuit and limits the amplitude; A second difference circuit that subtracts from the output of the device and outputs it, and an FM that inputs the output of the second difference circuit and performs FM modulation.
In a magnetic recording/reproducing device equipped with a modulator
In the SECAM color signal noise reduction device,
A clamp circuit whose clamp voltage is switched according to a horizontal synchronization pulse is inserted between the second difference circuit and the FM modulator, and the frequency of FM modulation is switched every horizontal period. Noise reduction device for SECAM color signals in magnetic recording and reproducing devices.