JPS625515B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a subcarrier signal reproducing circuit that reproduces a subcarrier signal based on a color burst signal of a PAL color television signal.

FIG. 1 is a diagram showing an example of a conventional subcarrier signal reproducing circuit, in which the composite video signal from terminal 1 enters the burst gate circuit 2, where the composite video signal is burst based on the burst gate pulse from terminal 3. A signal is extracted. The burst signal extracted by the gate circuit 2 enters the phase comparator circuit 4, where it is phase-compared with the reproduced subcarrier signal from the voltage controlled oscillator VCO5. Phase comparison circuit 4
The output is sampled and held by the sample and hold circuit 6 as a comparison output while there is a burst signal, and is sent to the VCO 5 via the filter 7. In the PAL system, the burst phase of the input burst signal changes by 90 degrees every horizontal period, so the output of the sample and hold circuit 6 is a signal that changes in the form of a rectangular wave of one horizontal period. For this reason, it was necessary for the filter 7 to remove the frequency component of the horizontal period, and as a result, the response of the loop was slow and sufficient performance could not be achieved.

In another conventional example, the phase comparator circuit 4 in FIG.
Insert a 90° phase delay device into one of the two inputs and switch it in a horizontal period to prevent the signal from the sample and hold circuit from becoming a rectangular wave, and make the filter quick in response. This method has also been used, but there have been cases where synchronization cannot be achieved reliably.

Therefore, an object of the present invention is to provide a subcarrier signal reproducing circuit that has a fast response speed and reliably synchronizes with a reference phase axis. Furthermore, another object of the present invention is to provide a subcarrier signal regeneration circuit that reliably synchronizes with the reference phase axis even if the burst phases differ by 90 degrees from line to line in the PAL system. That's true.

According to the present invention, two sample-and-hold circuits are provided to sample and hold the output of the phase comparison circuit, and these are driven with sample pulses every two horizontal periods according to the phase of the input burst, so that the outputs of the two sample-and-hold circuits are A subcarrier signal regeneration circuit is obtained which synthesizes the subcarrier signals and uses them as a control voltage for the VCO.

Next, the present invention will be described in detail with reference to the drawings showing one embodiment of the present invention. FIG. 2 is a diagram showing an embodiment of the present invention, in which the burst gate circuit 11 receives the signal supplied to the composite video signal input terminal 9 and the gate pulse supplied to the burst gate pulse input terminal. Separate the color burst from the received composite video signal. The phase comparison circuit 12 is
The phase of the reproduced subcarrier signal from the voltage controlled oscillator VCO 17 and the output signal of the burst gate circuit 11 is compared. At the output of the phase comparison circuit 12, phase detection outputs corresponding to, for example, +45° and -45° are generated depending on the phase of the color burst. The output of the phase comparator circuit 12 is sent to two sampling and hold circuits 1.
3 and 14. The outputs of the two sampling and holding circuits 13 and 14 become control signals for the VCO 17 via an adder circuit 15 and a filter circuit 16.

The sampling pulse generation circuit 19 distributes the signal from the burst detection circuit 18 with the signal from the flip-flop circuit 20, generates two-phase sampling pulses, and drives the two sampling and hold circuits 13 or 14. The flip-flop circuit 20 receives signals from the horizontal synchronizing signal input terminal 21 and the phase comparison circuit 12, and sends a PAL (Ident) signal indicating lines having different burst phases to the sampling pulse generation circuit 19 and the output terminal 23. A reproduced subcarrier signal from the VCO 17 is sent to the output terminal 22.

Next, the operation of the present invention will be explained with reference to FIG. FIG. 3A is a diagram showing the output of the phase comparator circuit 12 of FIG. 2, and the comparison output is output in reverse for each line. B represents the detection output from the burst detection circuit 18. C and D indicate the outputs of the sample pulse generation circuit 19, and only lines having burst signals of the same phase are sampled and held. E, F are sample and hold circuits 13, 1
4, and outputs +V ₁ and -V ₂ phase comparison outputs, respectively.

In the present invention, since a phase comparison output on a rectangular wave is not output, a filter with a small time constant can be used, and a subcarrier signal reproducing circuit with a fast response speed can be obtained. Also, the vertical blanking period (approximately
9H), there is no burst signal, but a constant control voltage is obtained during this period as well. In the present invention, since the input bursts are coupled to the center phase only after the phase difference of 90 degrees, phase coupling with less jitter is possible even if the burst phase difference is, for example, 80 degrees.

[Brief explanation of the drawing]

FIG. 1 shows a conventional subcarrier regeneration circuit. FIG. 2 shows an embodiment of the present invention. FIG. 3 shows waveforms of the main parts of FIG.

Claims (1)

[Claims] 1 A circuit for reproducing a subcarrier signal synchronized with a burst signal included in a PAL color television signal, comprising: means for extracting the burst signal from an input color television; a voltage controlled oscillator for generating the subcarrier signal; a phase comparator that compares the phase of the burst signal and the subcarrier signal from the voltage controlled oscillator;
Two sample and hold circuits each sample and hold the output of the phase comparator at the timing of two horizontal periods determined according to the phases of two types of bursts in the horizontal scanning period, and the outputs of the sample and hold circuit are added together to obtain an addition result. a subcarrier signal regeneration circuit, comprising: an adder circuit that uses the voltage controlled oscillator as a control voltage.