JPH0134519B2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention is directed to a β
This paper relates to an improvement of a color burst insertion circuit used for special playback of a video tape recorder (hereinafter abbreviated as VTR).

(b) Prior Art In VTRs, phase fluctuations that occur during recording and reproduction cause time axis fluctuations (jitter) in the reproduction output, which adversely affects color reproduction. Therefore, a jitter correction circuit has conventionally been provided in the color signal processing circuit on the reproduction side to eliminate jitter due to frequency conversion. This jitter correction circuit usually detects fluctuations in the horizontal synchronization period to form an AFC circuit, and detects color carrier wave phase fluctuations to form an APC circuit. If the color burst signal has a constant phase, such as an NTSC color signal, the color burst can be used as is in the APC circuit, but if the color burst has a phase inversion, such as with a PAL color video signal, the color burst can be used as is. is not available. Therefore, in a β-type video tape recorder, a constant-phase pilot burst is inserted into the horizontal synchronizing signal portion for recording, and during playback, this pilot burst is used to activate the APC circuit.

When performing special playback using such a VTR,
When the video head crosses a recording track, the playback output is attenuated and the SN is degraded. Also
The VTR is equipped with an ACC circuit on the playback side to correct the color signal level according to fluctuations in the burst signal level, and the color signal level is corrected so that the burst signal level is constant. Therefore, at the timing when recording tracks are crossed, there is a problem in that the signal to noise (SN) is significantly degraded and the color signal component is amplified.

Therefore, in beta-type VTRs, a fixed-level color burst signal is reinserted during special playback, and the ACC
Undesirable operation of the circuit is prohibited. This inserted color burst uses an output obtained by converting and shifting the phase of a pilot burst, which should originally be specified at the intermediate phase of the color burst, and the phase-shifted output is superimposed on the burst insertion section.

However, the width of the actual soft tape may contain a pilot burst whose phase does not match the intermediate phase of the color burst.
When special reproduction is performed on such a soft tape, the phase of the reinsertion burst is shifted from the phase of the color carrier wave, and a color shift occurs only during special reproduction.

(c) Purpose of the Invention Therefore, the present invention proposes a new and effective color burst reinsertion circuit that serializes the pilot burst during special reproduction and defines its phase as the center phase of the reproduced color burst.

(d) Structure of the Invention Therefore, in this embodiment, a continuous wave having the same phase as the pilot burst is input to a phase shift circuit, and its phase is shifted so that the phase shift output matches the intermediate phase of the reference reproduced color burst. It controls the amount.

(e) Embodiment The figure shows a circuit block diagram of a color signal processing circuit on the reproduction side according to an embodiment of the present invention. In this embodiment, a pilot burst with the same frequency and constant phase as the color burst is low-frequency converted and recorded together with the color signal in the horizontal synchronization signal portion, and the low-frequency converted color component to be reproduced is passed through the ACC circuit 1. Second
It is input to the frequency conversion circuit 2, converted back to the original high frequency color signal, and then passed through the second band pass filter 3.
and is derived through the comb filter 4. The output of the comb filter 4 is input to a pilot burst gate 5 which uses a horizontal synchronizing signal as a gate control input, and the high frequency converted pilot burst is separated. This pilot burst is phase-compared with the output of a reference oscillation circuit 7 in the APC circuit 6. The APC output obtained by the comparison is used as a control input of a VCO (voltage controlled oscillator circuit) 8. The VC08 also has an AFC that compares the horizontal synchronization signal and the VCO output.
The comparison output of circuit 9 is also input. AFC output and
The VCO controlled by APC output
The oscillation frequency of 8 corresponds to the low-pass conversion color carrier. A first frequency conversion circuit 10 which receives the VCO output and the output of the reference oscillation circuit 7 inputs a high-frequency conversion carrier corresponding to the sum frequency to the second frequency conversion circuit 2 via a first bandpass filter 11. are doing.

In the comb filter output, the color burst switching order becomes discontinuous every time a recording track is crossed during special playback. Therefore, in the latter stage of the comb-shaped filter 4,
A 1H delay circuit 12 is provided, and the 1H delayed output and non-delayed output are input to the first analog switch 13 to make the color burst switching order continuous. The flip-flop 14 which controls the first analog switch 13 operates as follows.

The burst flag pulse generation circuit 15, which inputs the horizontal synchronization signal, generates a burst flag pulse, and synchronizes the phase between the reinsertion burst, which will be described later, and the color burst after switching, which are input to the phase comparator circuit 16 in synchronization with this pulse. I'm comparing. The level of the comparison output is determined by a threshold hold circuit 17, and when the comparison output level is large, that is, when the phase difference exceeds ±90°, the flip-flop 14 is inverted.

Therefore, the output of the analog switch 13 is
The color burst phase switching order is made continuous. However, with color burst, the level attenuates at the timing when the recording track is crossed, and the S/
N also deteriorates. Therefore, when the ACC circuit of the TV receiver is activated, an image with significant noise is recorded at the timing when the recording track is crossed. Therefore, it becomes necessary to reinsert a constant level burst signal. Conventionally, the reinsertion burst is derived by shifting the phase of a reference oscillation output that is in phase with the pilot burst. However, as described above, the pilot burst may not be specified at the intermediate phase of the color burst, and it is necessary to control the amount of phase shift of the reference oscillation output in accordance with the reproduced color burst.

Therefore, in this embodiment, the reference oscillation output is
is input to the phase shift circuit 18 that allows the phase shift circuit 18 to derive a plurality of phase shift outputs with slightly different phase shift amounts, and these outputs are selected by the analog multiplexer 19 to almost match the intermediate phase of the color burst. Derive the reference phase output. The selection of the analog multiplexer 19 is made as follows. The reference phase output is input to the multiplication circuit 20 and multiplied by the color burst at the burst generation timing. This multiplication output is converted to a DC level with the phase difference averaged through the low-pass filter 21. The first and second Schmitt trigger circuits 22 and 23 judge this DC level, and if a phase difference of more than a certain amount occurs, the first or second Schmitt trigger circuit
Schmitt trigger output is derived. This output allows the up/down counter 2 to be set during special playback.
4 is activated, and the analog multiplexer 19 is selected in accordance with the count output.

The reference phase output derived in this manner is sequentially input to a 315° shift circuit 25 and a 90° shift circuit 26, and is converted into a continuous wave having the same phase as the two types of color bursts. This converted output is input to the second analog switch 28, and is alternately selected by the output of the 1/2 frequency divider circuit 27 which receives the horizontal synchronizing signal as input. The reinsertion burst derived from this selection is input to the third analog switch 29, and only during special playback, a fixed level reinsertion burst is inserted in place of the color burst in synchronization with the generation of the burst flag pulse. .

(F) Effects of the Invention Therefore, according to the present invention, since the reference phase output, which is the reference for the reinsertion burst, is made to match the intermediate phase of the color burst, color shift can be avoided even if a phase shift occurs in the pilot burst. It is possible to obtain a correct reproduced image, and the effect is great.

[Brief explanation of drawings]

The figure shows a circuit block diagram of a color signal processing circuit according to an embodiment of the present invention. Explanation of main figure numbers, 18...Phase shift circuit, 19
...Analog multiplexer, 7...Reference oscillation circuit,
29...Third analog switch.

Claims (1)

[Scope of Claims] 1. A constant phase pilot burst signal is inserted into the horizontal synchronization signal portion of a PAL color video signal, the color component is converted to low frequency and recorded, and upon playback, the color component is converted to high frequency based on the pilot burst signal. In addition, in a video tape recorder that reinserts a color burst at a constant level during special playback, a reference oscillation circuit that makes the oscillation phase the same as that of the pilot burst, and a reference phase output is derived by transferring the oscillation output. a phase circuit; a control circuit that adjusts the amount of movement of the phase circuit so that the reference phase output matches the average phase of the color burst; and a control circuit that shifts the phase of the reference phase output and reinserts the same phase as the color burst. A color burst insertion circuit comprising a circuit for switching and deriving bursts, and a switching circuit for replacing the color burst in the color component with a reinsertion burst.