JPS6339155B2 - - 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 → FA 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 1/4 countdown circuit 7. In other words, the 4MHz band FM modulated color signal is converted to 1M by the above 1/4 countdown circuit 7.
Converted to the lower side of the Hz band. The upper limit frequency of the FM color signal converted to the lower frequency side is limited by the LPF 8, and mixed with the above-mentioned FM luminance signal by the recording amplifier 9 and recorded.

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. Therefore, during playback, the influence of noise caused by crosstalk appears significantly, and especially when tracking is deviated, the playback screen becomes very unsightly. In addition, although the low frequency converted color signal is an FM signal of approximately 1.1MHz, there is a limit to crosstalk removal due to the azimuth effect, and furthermore, there is some crosstalk due to the H shift of the color signal when recording for a long time. It is necessary to take measures to reduce noise caused by crosstalk.

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.
The present invention provides a noise reduction device for a SECAM color signal in a magnetic recording/reproducing device, which cancels and reduces noise in a SECAM reproduced color signal by FM modulating the signal and returning it to a SECAM FM signal. .

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3.

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 above terminal 21 is supplied to the first demodulation circuit 23 and is also supplied to the second demodulation circuit 23 via the 2H delay line 24.
are supplied to the demodulation circuit 25 of R-Y and B-, respectively.
It is demodulated into a Y line sequential color difference signal. The output from the first demodulation circuit 23 and the second demodulation circuit 25
The outputs from the two 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 converted into a SECAM color signal in the FM modulation circuit 29, and is outputted from the terminal 30 as a SECAM FM signal. FIG. 3 shows an example of the configuration of the FM modulation circuit 29 described above. The terminal 31 is supplied with the R-Y, BY-line sequential color difference signals that have passed through the noise reduction circuit 22 described above, and this signal is further supplied to the FM modulation circuit 29. The FM modulation circuit 29 is supplied with a signal from a phase comparator circuit 29D, and is a reference subcarrier for the R-Y signal.
The modulation operation is performed at 4.40 MHz and a reference subcarrier of 4.25 MHz for the BY signal. SECAM color television signal is
Since the center frequency is switched between 4.25MHz and 4.40MHz every 1H, the 4.25MHz oscillation circuit 29A and
The reference oscillation output of the 4.40MHz oscillation circuit 29B is alternately supplied to the phase comparison circuit 29D every 1H via a switch circuit 29E driven by a horizontal synchronizing pulse supplied from the terminal 32. . On the other hand, the burst signal portion of the output of the FM modulation circuit 29 is supplied to the phase comparison circuit 29D via the burst gate circuit 29C based on the burst gate pulse supplied from the terminal 33. Therefore, the above phase comparator circuit 29
An error voltage is taken out from the output of D, and based on the error voltage, the FM modulation circuit 29
Modulation operations are performed at alternating center frequencies of 4.25 MHz and 4.40 MHz.

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 29 that inputs the output of 8 and performs FM modulation.
The color signal is FM modulated because it is equipped with
Even in the case of the SECAM method, noise reduction can be achieved with a simple circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional magnetic recording and reproducing device 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 diagram of a noise reduction device according to the present invention.
FIG. 3 is a diagram showing an example of the configuration of the FM modulation circuit. 23, 25: demodulation circuit, 26, 28: difference circuit,
24: 2H delay line, 27: Limiter circuit,
29: 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.
A noise reduction device for SECAM color signals in a magnetic recording and reproducing device, characterized by comprising a modulator.