JPS5828795B2 - Eizou Shingo no Saisei Souchi - Google Patents

Description

[Detailed Description of the Invention] When recording a color video signal with a VTR, the luminance signal is converted to an FM signal that occupies the high frequency side of the recordable band, and the recorded color signal is converted into a low frequency signal of the FM luminance signal. For frequency conversion, the carrier frequency is, for example, 688 kHz, and a frequency multiplexed signal of the FM luminance signal and the carrier color signal is recorded on the magnetic tape.

Furthermore, when recording a black and white video signal, it is recorded in the same way as a color video signal, only without the carrier color signal.

However, in this case, a part of the low-frequency sideband of the FM luminance signal falls into the frequency band occupied by the low-band-converted carrier color signal, so when a monochrome video signal is recorded and played back, the FM luminance signal A part of the low-frequency sideband of the signal is supplied to the carrier color signal system.

When the sideband component is supplied to the carrier color signal system in this way, the color killer circuit treats this sideband component as a carrier color signal (burst signal) and malfunctions, resulting in no longer performing color killer. , a colornoid appears on the black and white screen where the sideband components are regenerated, making it unsightly.

Furthermore, even when a color video signal is recorded and reproduced, its sideband components mix with the carrier color signal as crosstalk, resulting in poor S/N ratio of the carrier color signal.

Therefore, in the past, a bypass filter was provided at the next stage of the FM modulation circuit that converts the luminance signal into the FM luminance signal, and a part of the lower side band of the FM luminance signal was cut, and this filter was used to transmit the low-frequency converted signal. This is done so that it does not fall within the frequency band occupied by the color signal.

However, when a part of the low-frequency sideband of the FM luminance signal is cut in this way, the resolution of the reproduced screen decreases because the low-frequency sideband corresponds to the high-frequency component of the luminance signal.

SUMMARY OF THE INVENTION In view of these points, it is an object of the present invention to provide a VTR that can prevent color noise from occurring during monochrome playback without reducing the resolution of the playback screen.

Therefore, in the present invention, the VTR is equipped with an APC circuit, and the signal obtained from the APC circuit is used to perform color killer during monochrome reproduction.

That is, in FIG. 1, reference numeral 1 indicates a magnetic tape, on which color video signals (or black and white video signals) are frequency-multiplexed and recorded as described at the beginning.

In this case, in the multiplexed signal, a part of the lower side band of the FM luminance signal may fall into the frequency band occupied by the carrier color signal which has been low-band converted.

Then, the multiplexed signal is reproduced from this tape 1 by a rotating magnetic head 2, and this is supplied to a bypass filter 4 through an amplifier 3, where an FM luminance signal is extracted.
This FM luminance signal is supplied to a demodulation circuit 6 through a limiter 5 to demodulate the original luminance signal, and this luminance signal is supplied to an addition circuit 7.

Also, the multiplexed signal from the amplifier 3 is filtered through the low-pass filter 11.
The carrier color signal that has been low-pass converted is taken out and supplied to the frequency converter 2, where it is frequency-converted to a carrier color signal in the original frequency band.The carrier color signal is then passed through a C-shaped comb filter. 13→amplifier 14→color killer circuit 15, which will be described later, and is supplied to the adder circuit 7.

Therefore, since the carrier color signal is added to the luminance signal in the adder circuit 7, the original color video signal is taken out at the terminal 8.

In this case, if the carrier frequency of the FM luminance signal is f1, and the horizontal frequency is fh, the sideband components of the FM luminance signal are concentrated at (f, ±mf h), and the carrier chrominance signal that has been low-band converted is The carrier frequency is generally (nshiji) fh
(This value is, for example, 688 kHz), so by selecting the carrier frequency f, the low-frequency sideband components of the FM luminance signal will be frequency interleaved with the carrier color signal that has been low-frequency converted. .

If the low frequency sideband component of the FM luminance signal is frequency interleaved with the carrier color signal that has been low frequency converted in this way, then the carrier color signal is
When the frequency is converted to the original frequency band in step 2, the lower side band components of the FM luminance signal are frequency interleaved even in the carrier color signal after the conversion.

Therefore, when the converted carrier color signal is supplied to the next stage C-shaped comb filter 13, the low-frequency sideband component of the FM luminance signal that is frequency interleaved with the carrier color signal is removed. Therefore, the carrier color signal from the filter 13 does not include the sideband component.

Further, for frequency conversion in the converter 12, an oscillation circuit 21 and a variable frequency oscillation circuit 22 are provided.

That is, the oscillation signal from the oscillation circuit 21 (the frequency is, for example, 3.
58 MHz) and an oscillation signal (center frequency is 688 kHz, for example) from the oscillation circuit 22 are supplied to the frequency converter 23 and converted into an alternating signal with a frequency that is the sum of these oscillation signals, and this signal is sent to the converter 12 for frequency conversion. It is supplied as a signal.

Further, an AFC circuit 30 and an APC circuit 40 are provided to prevent the phase of the carrier color signal from changing due to chic or the like.

That is, the luminance signal from the demodulation circuit 6 is supplied to the synchronization separation circuit 31 to extract the horizontal synchronization pulse, this pulse is supplied to the frequency discrimination circuit 32 for frequency discrimination, and the discrimination output is sent to the oscillation circuit 22 to determine the oscillation frequency. The AFC circuit 30 is configured by being supplied as a control signal.

Further, the carrier color signal from the amplifier 14 is supplied to the burst gate circuit 41 to extract a burst signal, and this burst signal and the oscillation signal from the oscillation circuit 21 are supplied to the phase comparator circuit 43 to perform phase comparison. The comparison output is supplied to the oscillation circuit 22 as a control signal for its oscillation frequency, and the APC circuit 40 is configured.

In this way, when the carrier frequency or phase of the carrier color signal from the head 2 changes due to jitter or the like, the oscillation frequency of the oscillation circuit 22 changes accordingly due to the outputs of the discrimination circuit 32 and the comparison circuit 43, and the carrier color signal from the converter 12 changes accordingly. The carrier frequency or hue of is held constant.

By the way, in this case, when a black and white video signal is recorded on tape 1, a part of the 0 low frequency side band of the FM luminance signal enters the occupied frequency of the low frequency converted carrier color signal, so at this time burst A sideband component of the burst signal is obtained from the gate circuit 41 instead of the burst signal and is supplied to a comparison circuit 43.

Comparing the time when the sideband components are supplied to the comparator circuit 43 in this way and the time when the burst signal is supplied to the comparator circuit 43 from the burst gate circuit 41 during color reproduction, the output of the comparator circuit 43 is Levels vary greatly.

That is, when a burst signal is supplied to the comparator circuit 43, the APC circuit 40 operates so that the frequency and phase of this burst signal match the oscillation signal and phase from the oscillation circuit 21. The output level of the comparator circuit 43 is, for example, small.

However, when the sideband component is supplied to the comparison circuit 43, the frequency and phase of this sideband component are significantly different from the frequency and phase of the oscillation signal from the oscillation circuit 21, so the APC circuit 40 cannot follow it, and the comparison circuit 43 cannot follow the frequency and phase of the sideband component. circuit 4
For example, the output level of No. 3 becomes large.

The present invention performs color killer by determining the difference in the output level of the comparison circuit 43.

That is, the burst signal (or sideband component) from the burst gate circuit 41 is supplied to the switch circuit 51, and the comparison output of the comparison circuit 43 is supplied to the level discrimination circuit 54.
Based on the level difference between the comparative outputs, it is determined whether color reproduction or monochrome reproduction is being performed, and the determination output is supplied to the switch circuit 51 as its control signal.

In this way, during color reproduction, the switch circuit 51 is turned on, and the burst signal from the burst gate circuit 41 is supplied to the detection circuit 52 through the switch circuit 51 and detected, and the detection output is supplied to the integration circuit 58 to reach the burst level. A DC voltage of a corresponding level is provided, and this DC voltage is supplied to the amplifier 14 as a control signal for its gain, and is also supplied to the color killer circuit 15 as a control signal for its color killer.

Therefore, during color reproduction, the gain of the amplifier 14 is controlled by the DC voltage from the integrating circuit 53 so that the level of the burst signal from the burst gate circuit 41 is constant, so that at the same time, the carrier color signal from the amplifier 14 is The level of is also controlled to be constant, that is, ACC is performed.

Moreover, if the level of the burst signal is small, the integrating circuit 53
The DC voltage of the carrier is also small, which turns on the color killer circuit 15, so that when the level of the carrier color signal is small, color killer is performed and a noisy color reproduction screen is prevented.

On the other hand, during black and white playback, the switch circuit 51 is turned off by the discrimination output of the discrimination circuit 54, so the integration circuit 53
Since the color killer circuit 15 performs color killing, the low-frequency sideband components of the FM luminance signal are not supplied to the adder circuit 7, and the sideband components are not reproduced. It does not appear as color noise on a black and white screen.

Thus, according to the present invention, it is possible to prevent the low frequency sideband component of the FM luminance signal from being reproduced as color noise during monochrome reproduction.

Furthermore, in this case, there is no need to cut out the sideband components during recording, so a high-resolution image can be reproduced.

Furthermore, during color reproduction, even if the sideband components of the FM luminance signal enter the frequency band occupied by the low-pass converted carrier color signal, they are removed by the filter 13, so that the S
The APC circuit 4 has a good IN and can reproduce high-resolution color images, and the SIN of the burst signal is also good.
0 and ACC operations are ensured.

In addition, the phase fluctuation of the carrier color signal is large and the AFC circuit 30 and A
When the PC circuit 40 cannot correct it, the level of the comparison output of the comparison circuit 43 is large enough to turn off the switch circuit 51 and perform color killer, so that an image whose color has changed due to the phase fluctuation is reproduced. Never.

FIG. 2 shows a specific connection example of the switch circuit 51 and the discrimination circuit 54.

That is, the output terminal of the burst gate circuit 41 and the detection circuit 52
A resistor 61 is connected between the input end of the detection circuit 52 and the collector-emitter of a switching transistor 62 is connected between the input end of the detection circuit 52 and ground, thereby configuring the switch circuit 51.

In addition, the comparison output of the comparison circuit 43 is an FET with a common source.
71 and the emitter-grounded transistor 72 to the rectifier circuit 73 whose rectified output is the emitter follower transistor 74):j: through the transistor 62
A discriminating circuit 54 is configured by being supplied to the base of the discriminating circuit 54.

Therefore, during color reproduction, since the comparison output of the comparator circuit 43 is small, the rectified output of the rectifier circuit 74 is also small, the transistor 62 is turned off, and the burst signal is supplied from the burst gate circuit 41 to the detection circuit 52, so that color killer is not performed. Not possible.

However, during black-and-white reproduction, the comparison output of the comparison circuit 43 is large, so the rectification output of the rectification circuit 73 is large, the transistor 62 is turned on, and the low-frequency sideband component from the burst gate circuit 41 is bypassed through the transistor 62. Therefore, color killing is performed.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of one example of the present invention, and FIG. 2 is a connection diagram of another part of the present invention. 4, 11, and 13 are filters, 12 is a converter, 30 is an AFC circuit, and 40 is an APC circuit.

Claims (1)

[Claims] 1 Reproduction from a recording medium in which a frequency multiplexed signal of an FM luminance signal FM modulated by a luminance signal and a carrier chrominance signal whose frequency is converted from a standard carrier frequency to the lower frequency side of the FM luminance signal is recorded. a frequency converter that converts the carrier color signal reproduced from the recording medium into a carrier color signal having the standard carrier frequency; a C-shaped comb filter to which the output signal of the frequency converter is supplied; An amplifier to which the output signal of this C-shaped comb filter is supplied, a gate circuit for extracting the burst period signal from the output signal of this amplifier, a color killer circuit to which the output signal of the amplifier is supplied, and a burst signal frequency It has an oscillation circuit that forms a reference signal, a phase comparison circuit that compares the phase of the signal extracted by the gate circuit and the reference signal, and a level discrimination circuit that discriminates the level of the comparison output of the phase comparison circuit. The color killer circuit is controlled by the discrimination output of this level discrimination circuit, and only when the carrier color signal is reproduced from the recording medium at a predetermined level or higher, the color killer circuit causes the carrier color signal to be transmitted at the standard carrier frequency. A video signal reproducing device that extracts color signals.