JPS5923146B2 - Synchronous sampling device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a synchronous sampling device for a composite color television signal in which a luminance signal, a subcarrier-modulated color signal, and a burst signal are multiplexed.

Conventionally, as a method for realizing sampling in phase synchronization with a burst signal of a color television signal, a method has been used, such as adjusting the phase of a sampling pulse obtained by multiplying the burst signal.

However, in this method, not only is the sampling frequency limited to an integer multiple (usually 3 or 4 times) of the subcarrier frequency, but also the phase of the burst signal and the sampling pulse is kept precisely in a fixed state. However, the disadvantages were that the adjustment was delicate and the stability was poor. For example, in the case of an NTSC color television signal, the subcarrier frequency is approximately 3.58M
H2, the time corresponding to phase 10 is approximately 0.
．． 8 nanoseconds, and the delay time of transistor circuits and A/
Since the sampling pulse width (aperture time) of the D converter is much larger, sophisticated techniques are required to adjust the phase error to within a few degrees. SUMMARY OF THE INVENTION An object of the present invention is to provide a synchronous sampling device that can significantly relax limitations on sampling frequencies, do not require sophisticated adjustment techniques, and can automatically perform stable phase synchronization.

A synchronous sampling device according to the present invention includes an A/D converter for sampling and encoding a television signal, a means for generating a local subcarrier as a digital code string from the sampling pulse, and a means for generating a local subcarrier as a digital code string from the sampling pulse. means for multiply detecting the burst signal with a local subcarrier, and controlling the phase of the burst signal and the local subcarrier by changing the relative phase of the burst signal and the sampling pulse using the detection output so that the phase of the burst signal and the local subcarrier has a predetermined relationship. means for sampling in phase synchronization with the burst signal.

According to the present invention, the relative phase between the A/D-converted burst signal and the local subcarrier of known phase created by the sampling pulse is automatically controlled to a predetermined value. Stable and accurate synchronous sampling without the influence of phase delay or aperture time in the D converter can be achieved.

In addition, as described later, the sampling frequency is the subcarrier frequency (
m/n) times, the limitations on the sampling frequency are greatly relaxed. Although the target color television signal will be described below as a jNTSC signal, the present invention can also be applied to other television signals such as PAL and SECAM.

Figure 1 is a block diagram showing the synchronous sampling device of the present invention.
The NTSC signal 1 is sampled and encoded by an A/D converter 2.

The A/D converter output is guided to a bandpass filter (BPF) 3, where components near the subcarrier frequency are extracted and multiplied by a local subcarrier generated by a local subcarrier generator 5 in a detector 4. The product is detected. The sampling frequency Fs of the A/D converter is the subcarrier frequency Fsc. m. n (m>n)
When is an integer, choose so that .

The relationship between the horizontal synchronization frequency FH and Fsc of the NTSC signal is as follows:
Therefore, the relationship (1) becomes as follows, which provides a wide degree of freedom in selecting the sampling frequency within a practically possible range.

In the figure, 6 is a synchronous separation circuit, and 7 is a voltage controlled oscillator, which is used to generate a frequency-related sampling pulse as shown in equation (3) based on a horizontal synchronous signal that is synchronously separated from the NTSC signal 1. It is a circuit. Further, 8 is a variable phase shifter for changing the phase of the sampling pulse. The local subcarrier generator 5 includes, for example, an address generator 12 and a read-only memory (ROM) 13. The local subcarrier can be obtained by storing a continuous number of sine function values in the ROM13 and reading out these values by periodically scanning the storage address of the ROM.

On the other hand, if the envelope of the color burst inserted into the back pouch is B(t), the burst signal is continuous,
S2(t)-B(t)Sin(2πFsct+θ)(6
), the product detection output with the local subcarrier is CO
It is proportional to sθ.

Therefore, if you want the phase difference θ to be 00, set the detection output to the maximum, and if you want θ to be 900, set the detection output to O, θ
If you want to set it to 1800, just minimize the detection output.

In this case, the phase difference is defined between the two inputs of the detector 4, but the delays in the BPF 3 and local subcarrier generation circuit 5 are known, so if these delays are taken into account in advance, the A/D The sampling phase at the converter output can be set to a desired value, and if this is branched and output, it can be used for various purposes. To achieve this kind of control,
First, the detection output is extracted only during the burst period of the back porch by the gate 9, and integrated by the integrator 10.The result is led to the judgment circuit 11 to judge the magnitude and direction of the deviation from a predetermined phase difference. The result may be fed back to the phase shifter 8 and the local subcarrier generation circuit 5, and automatic control may be performed so that the deviation becomes zero. When a large phase shift of one cycle or more of the sampling pulse is detected, rough phase control is performed by controlling the address generator 12 of the local subcarrier generation circuit 5. When a small phase shift is detected, Fine phase control is performed by the variable phase shifter 8. The address generator is controlled by, for example, stopping address scanning momentarily and generating the same address twice, or momentarily skipping the address and generating it by skipping the first address. At the initial stage of phase pull-in, the rough phase is adjusted by this address control, and then the remaining minute phase shift is adjusted by controlling the variable phase shifter. Furthermore, fine phase control can be performed by inserting a variable delay line in front of the A/D converter instead of the variable phase shifter to control the amount of delay of the input NTSC signal. The detector 4 generally consists of a multiplier and a low-pass filter, but one input of the multiplier is a local subcarrier and takes only m finite values expressed by equation (5). , the multiplier and the ROM for local subcarrier generation can all be replaced by one read-only memory.

For example, if you want to obtain an 8-bit precision multiplication result for the output of an 8-bit 256-level A/D converter, 8×25
The multiplication result is stored in a 6×m bit ROM, and the R
All you have to do is specify the storage address of OM and take out the multiplication result.
When m=3, the ROM has a capacity of 6 kilobits and can be constructed from several integrated circuits. In addition, in the case of PAL system, (2)
Although the relationship between equation and equation (3) is different, the basic principle is the same, so the present invention can be applied. Furthermore, in the SECAM system, since the back porch burst has a different frequency for each line, the present invention can be applied by focusing on only one of the bursts, that is, by opening the gate 9 only during one burst period.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a periodic sampling device according to the present invention, in which 2 is an A/D converter, 3 is a bandpass amplifier, 4 is a detector, 5 is a local subcarrier generator, and 6 is a Synchronous separation circuit, 7
is a voltage controlled oscillator, 8 is a variable phase shifter, 9 is a gate, 10
is an integrator, 11 is a judgment circuit, 12 is an address generator, 1
3 is a read-only memory.

Claims (1)

[Claims] 1 A composite color television signal in which a luminance signal, a subcarrier-modulated color signal, and a subcarrier burst signal are multiplexed is transmitted at a frequency that is (m/n) times the subcarrier (m, n (m>n) is an integer). means for sampling and encoding with a sampling pulse; means for generating a local subcarrier having a frequency equal to the subcarrier as a digital code string based on the sampling pulse; and generating a back porch burst signal using the local subcarrier. A synchronous sample comprising means for performing multiplicative detection, means for monitoring the output of the multiplicative detection, and means for changing the relative phase of the burst signal and the sampling pulse based on the output of the monitoring means. conversion device.