JPS587116B2 - Irosingou Shiyori Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides, for example, a color television signal of the SECAM system and a
The present invention relates to a color signal processing circuit applied to a color VTR capable of recording and reproducing any AL type color television signal.

The SECAM method uses the (R-Y) component and (B-
The carrier wave is FM modulated by the (R-Y) component, and both are transmitted line-sequentially.The PAL system uses quadrature two-phase balanced modulation by the (R-Y) and (B-Y) axes, and the (R-
This is a method of transmitting data by inverting the Y) axis every horizontal period.

The horizontal and vertical frequencies of both are equal to each other.

When recording or reproducing a PAL color television signal on a VTR, the level of the carrier color signal is
It is set to a predetermined value by the C circuit (automatic saturation adjustment circuit).

Also, since the carrier color signal of the color TV signal of the SECAM system is an FM modulated wave, normally it is sufficient to keep the amplitude constant with a limiter, but it is not possible to insert a limiter into the color signal system common to the PAL system. The level is then controlled by the ACC circuit.

In the case of the PAL system, this level control is performed based on detecting the level fluctuation of the burst signal, and the SECAM
In the case of this method, it is based on detecting level fluctuations of an unmodulated carrier wave inserted within the horizontal blanking period.

That is, if the horizontal synchronizing signal Ph with a width of 4.7 [μS] is shown as shown in FIG. 1A, the PAL system burst signal Sb
i As shown in Figure 1B, about 10 cycles occur from the time (5.6 ± 0.1) [μs] delayed from the leading edge of the horizontal synchronization signal PhO (time t1), and the non-modulated S pressure AM method The carrier wave Sf is generated from a time point delayed by (5.7±0.3) (μS) from time point t1, and is generated during the horizontal planking period (to-t
2) occurs continuously until the end.

The above numbers are standardized. Note that the carrier wave S
When the (R-Y) component is a modulated wave, f is the frequency fr(4-
40625 (MHz)), and when the (BY) component is a modulated wave, the frequency is fb (4-250 (MHz)).

When the burst signal Sb and the carrier wave Sf start from the center point of the standard, the burst signal Sb obtained by gating with the common gate pulse Pg
b1 or carrier wave Sf1 is shown in Fig. 2,
By detecting these signals through, for example, a narrow band filter and an integrating circuit, the control signal for the ACC can be formed.

However, even if the burst signal Sb and the carrier wave Sf are within the standard, when the starting point of the burst signal Sb and the carrier wave Sf are shifted from the center, for example, as shown in FIG. In the worst case where the carrier wave Sf is generated with a delay of 6 [μS] from the time t1, the energy of the burst signal Sb2 and the carrier wave Sf2 extracted by the common gate pulse Pg is extremely reduced, especially in the case of Sf2. Therefore, when this is detected, the level of the carrier color signal is detected to be lower than the original level.

As in the numerical example above, the carrier wave Sf is the burst signal Sb
Unlike in the case of the PAL system, since the standards are lenient, the starting point varies considerably, and as a result, the expected ACC operation cannot be expected depending on the gate pulse Pg, which is common to the PAL system.

The present invention takes the above-mentioned points into consideration, and by varying the time point at which the unmodulated carrier wave Sf of the SECAM system is generated, the AC
This is to prevent the C operation from being affected.

Hereinafter, an embodiment in which the present invention is applied to a rotating two-head type color VTR will be described with reference to the drawings. FIG. 4 shows its recording system, and FIG. 5 shows its reproducing system.

In FIG. 4, 1 indicates a terminal to which a SECAM or PAL color television signal is supplied, 3 is a low-pass filter, and 4 is a band-pass filter.

The method for recording a color television signal in this example is to separate the color television signal into a luminance signal Y and a carrier color signal Sc, and FM-modulate the carrier wave with the luminance signal Y to produce a modulated luminance signal YF.
At the same time as forming the carrier color signal Sc at 700 CKHz.
) to obtain a low-pass converted carrier color signal Cc, and these signals S.

and Cc are mixed and supplied to the rotating magnetic heads 2a and 2b to record on the magnetic tape.

That is, the luminance signal Y separated by the low-pass filter 3 is supplied to the FM modulator 5, and further passed through the high-pass filter 6 to obtain the modulated luminance signal YFM, which is supplied to the adder circuit 7.

The carrier color signal S is still separated by a low-pass filter 4.

is supplied to converter 9 and gate circuit 13 via ACC circuit 8 .

The ACC circuit 8 is configured as a level control circuit such as a variable gain amplifier.

For example, a carrier wave from a fixed oscillator 10 is supplied to the converter 9, and an unnecessary signal component 7% included in the output of the converter 9 is removed by an o-bus filter 11 to obtain a low-pass conversion carrier color signal Cc, which is added. Signal YFM in circuit 7
It is further supplied to the rotary magnetic heads 2a and 2b via the recording amplifier 12.

A gate signal is supplied to the gate circuit 13 from the output terminal 15a of the switch 14.

The switch 14 is switched between recording a SECAM color television signal and a PAL color television signal, and the input terminal 15s on the SECAM side is connected to a predetermined DC power supply 16, and the input terminal 15p on the PAL side is connected to a predetermined DC power supply 16. is connected to the output terminal of the gate pulse generator 17.

The gate pulse generator 17 generates a gate pulse Pg (
burst flag).

Further, the gate circuit 13 is always turned on when a DC voltage is applied from the DC power supply 16, and is configured to provide a carrier color signal of the SECAM system to the narrow band filter 19 at the next stage.

The output of the narrow band filter 19 is detected by an integrating circuit 20 and further supplied to the ACC circuit 8 via a DC amplifier 21 as its control signal.

Due to this ACC looseness, the level of the carrier color signal Sc is controlled to a predetermined level.

When recording a PAL color television signal, the terminals 15a and 15p of the switch 14 are connected, the burst signal Sb is gated by the gate circuit 13, and the ACC operation is performed by detecting the level fluctuation of the burst signal Sb. .

In this case, the time point at which the burst signal Sb occurs is within the standard (
Even if it fluctuates by ±0.1μS), it is hardly affected.

Furthermore, when recording a SECAM color television signal to which the terminals 15a and 15s of the switch 14 are connected,
Since the ACC operation is performed by detecting the level fluctuation of the carrier color signal itself, it is not affected by fluctuations in the time point at which an unmodulated carrier wave is generated within the horizontal blanking period.

In this case, the carrier color signal of the SECAM system includes an unmodulated carrier wave in its black and white portion, so it is necessary to avoid compromising compatibility with a black and white receiver on the image sending side, as shown in Figure 6. A bell-shaped filter is inserted that has a center frequency fo (=4.4286 MHz) and attenuates carrier wave (frequency fr and fb) components, and the envelope of the carrier color signal, which is an FM modulated wave, varies depending on the content of the color signal. It ends up.

Therefore, when detecting a carrier color signal, it is preferable to increase the time constant of the integrating circuit 200. Even in the reproduction system shown in FIG. are indicated with the same reference numerals.

During reproduction, the signals sequentially reproduced from the rotating magnetic heads 2a and 2b are supplied to the high frequency switch circuit 32 via the regenerative amplifiers 31a and 31b, respectively, and a continuous reproduced signal is obtained from the high frequency switch circuit 32. It is supplied to filter 34.

Modulated luminance signal YFM separated by high-pass filter 33
is supplied to the FM demodulator 35, and unnecessary signal components in the demodulated output are removed by the low-pass filter 36 to obtain the luminance signal Y.

The low-pass conversion carrier color signal Cc separated by the low-pass filter 34 is kept at a constant level by the ACC circuit 8 and is supplied to the converter 37, where it is converted to the original carrier frequency and further passed through the band-pass filter 38. By this, the carrier color signal S.

is obtained. This carrier color signal S. The signal is mixed with the luminance signal Y in the adder circuit 39, and a reproduced color television signal appears at its output terminal 40.

The carrier color signal Sc is also supplied to the gate circuit 13 of the ACC loop.

Also, when converting the frequency in the converter 37, S
When reproducing an ECAM system signal, a carrier wave is supplied from the AFC circuit 43 through the terminals 42a and 42s of the switch 41, while when reproducing a PAL system signal, a carrier wave is supplied from the AFC and APC circuit 44 through the terminals 42a and 42p of the switch 41. is supplied so that time axis fluctuations caused by VTR jitter, etc., are canceled.

In the embodiment of the present invention described above, the time constant when detecting the carrier color signal of the SECAM method is increased so that the envelope is not affected by fluctuations depending on the content of the color signal. By inserting a bell-shaped filter with a frequency characteristic opposite to that shown in FIG. 6 at the location shown by the broken line in FIGS. 4 and 5, and supplying the carrier color signal of the SECAM method to this bell-shaped filter, Detection may be performed after the characteristics are approximately flattened, that is, after the envelope curve does not vary depending on the content of the color signal.

FIG. 7 shows a case in which it is applied to a recording system, in which the output of the ACC circuit 8 is supplied to the converter 9 and also to the switch 45.

In the case of PAL system, the input terminal 46a of the switch 45 is
It is connected to the output terminal 46p, and in the case of the SECAM method, it is connected to the output terminal 46s.The output terminal 46p is directly connected to the input terminal of the gate circuit 130, and the A bell-shaped filter 47 which produces a carrier color signal whose output has a substantially flat frequency characteristic with a frequency characteristic opposite to that shown in FIG. 6.
is connected.

When applied to a reproduction system, a circuit having the same configuration as that shown in FIG. 7 may be inserted at the position indicated by the broken line in FIG. 5.

In this way, the envelope of the carrier color signal in the SECAM system can be prevented from being affected by fluctuations depending on the content of the color signal, and therefore the time constant during detection, such as the time constant of the integrating circuit 20, can be made particularly large. In addition, there is an advantage that a responsive ACC operation can be expected because the level fluctuation of the carrier color signal is detected almost constantly rather than every horizontal period.

The above explanation is based on the case where the present invention is applied to color television signals of SECAM and PAL systems. Similar benefits apply when the circuit controls the level of its carrier color signal.

[Brief explanation of drawings]

Figures 1 to 3 are waveform diagrams showing the horizontal planking period and the temporal relationship of gate pulses in SECAM and PAL color television signals, and Figure 4 is a waveform diagram showing the temporal relationship of gate pulses in color television signals of the SECAM and PAL systems. FIG. 5 is a system diagram of the recording system of one embodiment, FIG. 5 is a system diagram of its reproduction system, FIG. 6 is a diagram showing the characteristics of the filter inserted on the image sending side, and FIG. 7 is another embodiment of the present invention. It is a main part system diagram of. 1 is a supply terminal for color television signals to be recorded, 2a, 2
b is a rotating magnetic head, 8 is an ACC circuit, 13 is a gate circuit, 17 is a gate pulse generator, 19 is a narrow band filter, 20 is an integrator circuit, 47 is a bell-shaped filter, 14, 41
, 45 are switches that can be switched between the SECAM system and the PAL system.

Claims (1)

[Claims] 1. A first wave including a burst signal within the horizontal planking period and in which the carrier wave is quadrature two-phase balanced modulated by the color signal.
The carrier color signal and the collapse of the second carrier color signal, which includes an unmodulated carrier wave within the horizontal blanking period and is obtained by FM modulating this carrier wave by the color signal, are selected and transmitted on the signal path. A level leg circuit is inserted, and when transmitting the first carrier color signal, extracts and detects the burst signal, and when transmitting the second carrier color signal, detects the second carrier color signal, and detects these signals. A color signal processing circuit whose output controls the above level control circuit. 2. The color signal processing circuit according to claim 1, wherein when transmitting the second carrier color signal, the frequency characteristics of the second carrier color signal are substantially flattened before detection.