JPH0642741B2 - Video tape recorder playback circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing circuit of a video tape recorder, and more particularly to improving the level fluctuation of the color signal generated when the reproducing head hits the tape.

[Background technology and its problems]

Conventionally, a reproducing circuit of a video tape recorder (VTR) is constructed as shown in FIG. That is, the magnetic tape 1
The video signal recorded above is reproduced by a reproducing head 2 which is a rotating head, is amplified by a reproducing amplifier circuit 3, and is then supplied to a luminance signal reproducing circuit 10.
In the high frequency filter 11, the FM luminance signal component is taken out, the FM luminance signal is demodulated through the limiter 12 and the FM demodulation circuit 13, and the luminance signal thus obtained is given to the luminance / color signal synthesizing circuit 30. Further, the reproduction signal is given to the color signal reproduction circuit 20, and the low frequency conversion color signal component COL which is AM-modulated by the low frequency filter 21 is taken out, and then ACC
APC circuit 24 fed to frequency conversion circuit 23 via circuit 22
A color signal obtained by frequency conversion by the color subcarrier from is supplied to the luminance / color signal synthesis circuit 30. Thus, the luminance signal and the color signal are combined in the luminance / color signal combining circuit 30 and sent to the next stage as an image signal.

The ACC circuit 22 is fed back with a level detection signal indicating the signal level of the color burst detected by the ACC detection circuit 25 based on the color signal, and ACC control is performed so that the color signal component level given to the frequency conversion circuit 23 becomes constant. To do. Therefore, for example, the level fluctuation or the like caused in the color signal due to the characteristic difference between the A and B heads is eliminated through the closed loop.

In the reproducing circuit of the VTR having the above construction, when the reproducing head hits the tape 1, the envelope of the reproduced signal varies, and the variation of the envelope has a great influence on the AM-modulated color signal. On the other hand, the luminance signal is FM
Since it is modulated, the fluctuation of the envelope appears as the fluctuation of the amplitude in the amplitude of the carrier as it is, but the influence does not occur in the luminance signal.

By the way, the insertion section of the color burst is short, and the video signal reproduced at the timing of the start and end of the reproduction head is the start portion of the signal for one field (that is, vertical as shown in FIG. 3A). Since it is in the blanking interval), there is the following problem that the influence of the color signal due to the fluctuation of the reproduced signal envelope cannot be removed by the ACC loop of FIG.

That is, first, the follow-up speed of the ACC loop including the ACC circuit 22 is short (about 2.8 [μ] when the insertion period of the color burst CB, which is the reference for level control, is as shown in FIG. 3 (B).
s]), it is not possible to select too quickly because the noise is large relative to the amount of information, but since the fluctuation of the envelope is faster than the tracking speed of the ACC loop, the fluctuation of the envelope should be compensated by the ACC loop. It is difficult.

Secondly, since the color burst CB is inserted only in the latter half 11H as shown in FIG. 3 (A) during the vertical blanking period at the beginning and at the time of hitting the head of the tape, the follow-up by the ACC loop is performed. It is difficult to eliminate envelope variations during the vertical blanking period because of the delayed onset of operation.

[Object of the Invention]

The present invention has been made in consideration of the above points, and an object of the present invention is to provide a video tape recorder capable of surely removing the level fluctuation of the color signal due to the tape contact at the head entrance / exit.

[Summary of the Invention] In order to achieve the above object, according to the present invention, a level fluctuation detecting means for detecting a fluctuation of an envelope of a reproduction signal from an envelope of a carrier of an FM luminance signal, and a level of a color signal according to the detected value. And a correction control means for correcting the correction of the color signal level to improve the compensation accuracy of the color signal level with respect to the level fluctuation.

〔Example〕

In the following, the same reference numerals are given to portions corresponding to those in FIG.
An embodiment of the present invention will be described in detail with reference to the drawings.

The VTR shown in FIG. 1 is the FM luminance signal Y from the high frequency filter 11.
A level at which the level fluctuation detection signal SS is sent to the combining circuit 50 which inputs the FM and the luminance signal Y demodulated from the FM demodulation circuit 13 and gives the ACC correction signal AC to the ACC circuit (automatic color signal control circuit) 22. It has a fluctuation detection circuit 40.

The envelope detection circuit 41 of the level fluctuation detection circuit 40 is FM
The luminance signal YFM is envelope-detected and the envelope signal SE is given to the gate circuit 42. Also, level fluctuation detection circuit
The horizontal sync separation circuit 43 for 40 changes the luminance signal Y to the horizontal sync signal.
HSY is extracted and given to the gate circuit 42.

The gate circuit 42 opens while the horizontal synchronizing signal HSY is being applied, allows the envelope signal SE to pass, and supplies it to the integrating circuit 44.

The integrator circuit 44 integrates and averages the envelope signal SE for each horizontal synchronizing signal HSY period and gives it to the high-frequency filter 45. The high-frequency filter 45 passes only the AC component of the averaged signal through the variable resistor VR. The level fluctuation detection signal SS is given to the synthesizing circuit 50.

The synthesis circuit 50 outputs the level fluctuation detection signal SS to the deviation signal SVB of the color burst level from the ACC detection circuit 25.
To the ACC circuit 22 as a correction signal AC.

In the configuration shown in FIG. 1, when a reproduced video signal is input, an envelope signal SE which varies according to the variation of the FM carrier envelope is output from the envelope detection circuit 41 based on the output signal YFM of the high frequency filter 11. Given to.

In the envelope signal SE, the horizontal synchronizing signal HSY extracted from the luminance signal Y by the horizontal synchronizing separating circuit 43 is the gate circuit 4
While being input to 2, it passes through the gate circuit 42 and is given to the integrating circuit 44.

Thus, the gate output representing the level of the envelope signal SE at the timing of the horizontal synchronizing signal HSY is
At 44, it is averaged, and only the variation is taken out by the high-pass filter 45, and then it is combined as a level fluctuation detection signal SS.
Given to 50.

Here, the color signal COL and the FM luminance signal YFM exhibit a fluctuation in the envelope such that the signal level gradually increases as shown in FIGS. 4A and 4B when the tape is hit, but the level is large. The AC component is large in the output of the integration circuit 44 during the changing period, and the AC component is small in the period in which the level fluctuation is small. Therefore, a large signal is given to the synthesizing circuit 50 when the level fluctuation is large, and a minute signal is given when the level fluctuation is small (fine fluctuation within the screen).

This level fluctuation detection signal is combined with the ACC deviation signal SVB by the ACC detection circuit 25, and the correction signal AC obtained at the combined output terminal is given to the ACC circuit 22. As a result, the ACC circuit 22
The output of is controlled in gain, and finally a stabilized color signal C as shown in FIG. 4 (C) is sent to the luminance / color synthesizing circuit 30.

Thus, according to the circuit of FIG. 1, the horizontal synchronization signal HSY
Since the level fluctuation is detected based on the FM luminance signal YFM for each time and the level of the color signal is corrected by the detected signal, the color burst CB is inserted in the vertical blanking period (Fig. 3 (A)). It is possible to continuously respond to the level fluctuation during the period of 9H which is not performed. Also, not only the color burst period (about 2.8 [μs]), but also Fig. 3 (B))
Since the information of the period (about 5 [μs]) of the horizontal synchronizing signal HSY shown in (3) is also used, the tracking accuracy can be improved. Further, by selecting the time constant of the integrating circuit 44, it is possible to adjust not only the response to the variation component due to the head entrance / exit of the tape but also the response to the fine variation component in the screen.

Incidentally, as a method of compensating for the level fluctuation of the color signal at the time of hitting the tape, a method of applying AGC to the reproduction signal can be considered, but in this case, the wavelengths of the FM luminance signal component and the low-frequency conversion color signal component are significantly different. Therefore, regarding the color signal, unlike the case of the luminance signal (Fig. 5 (A)), overcompensation occurs as shown in Fig. 5 (B), and the AGC
Although there is a drawback that spurious is generated by the cross modulation of 1 and an oblique beat is generated, these drawbacks do not occur in the case of FIG.

The present invention is not limited to the embodiment shown in FIG. 1 having the correction control means configured to add the level fluctuation detection signal SS to the deviation signal SVB of the ACC detection circuit 24, but as shown in FIG. A signal having a correction control means for controlling the color signal level by giving the detection signal of 40 to the AM modulation circuit 60 provided in the preceding stage of the ACC circuit 22, and as shown in FIG. Color signal reproduction circuit for detection signal SS
It may have a correction control means for controlling the level of the color signal by giving it to the AM modulation circuit 70 provided in the final stage of 20. In short, the level fluctuation detection signal SS detected based on the luminance signal level is used. Any configuration may be used as long as it can be used to compensate the level of the color signal C.

〔The invention's effect〕

As described above, according to the present invention, the level fluctuation is detected based on the envelope signal of the FM luminance signal, and the color signal level is corrected based on the detected signal. Level fluctuations can be reliably removed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration according to an embodiment of the present invention, FIG. 2 is a block diagram showing a configuration of a conventional device, FIG. 3 is a schematic diagram showing a signal configuration of a reproduced video signal, and FIG. (A) and (B) are schematic diagrams for explaining the level reduction state of the color signal and luminance signal when hitting the tape, and (C) are schematic lines for explaining the state in which the level fluctuation of the color signal is removed. FIGS. 5 (A) and 5 (B) are schematic diagrams for explaining the output state of the luminance signal and the chrominance signal when the reproduced video signal is passed through the AGC circuit, and FIGS. 6 and 7 are main diagrams, respectively. FIG. 9 is a block diagram showing a partially extracted configuration of another embodiment of the invention. 10 ... Luminance signal reproduction circuit, 20 ... Chromatic signal reproduction circuit, 40 ... Level fluctuation detection circuit, 50 ... Synthesis circuit, 60, 70 ... AM modulation circuit.

Claims (1)

[Claims] 1. An envelope detecting means for receiving an FM luminance signal extracted from a reproduced video signal and detecting an envelope of the FM luminance signal, and a reproduced horizontal synchronizing signal is detected from the luminance signal obtained by demodulating the FM luminance signal. Horizontal synchronizing signal detecting means, gate means for gating the level of the envelope signal output from the envelope detecting means based on the reproduction horizontal synchronizing signal output from the horizontal synchronizing signal detecting means, and the reproducing video signal. The automatic color signal control means for correcting the signal level of the extracted low-frequency conversion color signal and the gain control signal for controlling the gain of the automatic color signal control means superimpose the envelope signal output from the gate means. And a superimposing means for outputting the envelope output from the gate means based on the reproduction horizontal synchronizing signal. Reproducing circuit of a video tape recorder which is characterized in that so as to correct the signal level of the I connexion the low-band converting chrominance signal into-loop signal.