KR0141113B1 - Carrier generator for decoding chroma signal - Google Patents

Abstract

The present invention relates to a demodulation carrier generator for use in a color signal demodulator of a video device, wherein the carrier generator for color signal demodulation can be used in various digital color signal demodulators having different color carrier frequencies without modification of hardware without any hardware modification.

According to the present invention, a demodulated carrier value corresponding to a plurality of cases is stored in a ROM table, and the phase value detection unit compares the phase value of the color burst with the phase value of the currently occurring carrier and compares the demodulated carrier value corresponding to the phase difference according to the comparison result. Overcoming the limitations of analog color signal demodulation carrier generator by supplying color signal demodulation carrier in digital way by generating color burst signal and demodulation carrier that is exactly phase-constructed. It was made possible.

Description

Carrier Generator for Color Signal Demodulation

1 is a block diagram of a conventional color signal carrier generator,

2 is a block diagram showing an embodiment of a carrier generator for color signal demodulation according to the present invention;

3 is a partial detailed view of FIG.

* Explanation of symbols for main parts of the drawings

1: Burst gate 2,20: Phase difference detector

10: phase detection unit 30: demodulated carrier generating unit

31: Register 32: Rom Dable

33: address generator VCD: voltage controlled oscillator

INV1: Inverter

The present invention relates to a demodulation carrier generator for use in a color signal demodulator of an imaging apparatus. More particularly, the present invention relates to a carrier generator for demodulating a color signal which can be used in various digital color signal demodulators having different color carrier frequencies without modification of hardware without changing hardware. will be.

In general, in order to demodulate a color signal input in a modulated state, a demodulation carrier that is exactly phase synchronized with a color burst of a color signal is required.

FIG. 1 is a block diagram of a conventional color signal demodulation carrier generator. The conventional color signal demodulation carrier generator is an analog type, and the color signal of the composite video signal inputted by Y / C separation and sampling is inputted by the burst gate 1. Only the color burst signal is output.

The color burst signal output from the burst gate 1 is input to the gas difference detector 2, and the BY signal which is a partial output of the low voltage controlled oscillator VCO at the rear stage is compared with the signal inverted by the inverter INV1. The phase difference according to the comparison result is output as a voltage.

The reason for the phase inversion of the B-Y signal, which is the output of the voltage controlled oscillator VCO, by using the inverter INV1 is that there is an 18 ° difference between the B-Y signal and the color carrier signal on the frequency axis.

The voltage controlled oscillator VCO receives a voltage corresponding to the phase difference output to the phase difference detector 2 and oscillates at 358 MHz, which is a frequency of the color carrier, to output a demodulated carrier.

However, in the conventional color signal demodulation carrier generator as described above, if the phase difference detection unit 2 detects a phase difference between the output of the burst gate 1 and the output of the voltage controlled oscillator VCO, the carrier voltage generator corresponds to the detected voltage. As a result, the VCO oscillates at 3.58MHz, which is the frequency of the color carrier, to correct the demodulated carrier.It can only be corrected after many hours, and it is corrected by the analog method. There was a problem.

The present invention solves this problem, and an object of the present invention is to digitally demodulate the carrier by directly comparing the phase of the phase difference demodulation carrier of the color burst and outputting the value according to the comparison result from the ROM table for carrier generation. The present invention provides a carrier generator for demodulating a color signal.

A feature of the present invention for achieving the above object is that a burst gate for outputting only a color burst signal of an input modulation color signal, a phase value detector for detecting a phase value of the color burst signal from the burst gate, and in the phase value detector A phase difference detector which outputs the phase difference by comparing the detected phase value of the color burst signal with the phase value of the currently occurring carrier, and a demodulated carrier generator which corrects and outputs the demodulated carrier with the phase error detected by the phase difference detector. There is provided a carrier generator for demodulating color signals.

Hereinafter, a preferred embodiment of the color signal demodulation generator according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram of a carrier generator for color signal demodulation according to the present invention.

A phase value detector 10 for detecting the phase value of the color burst signal from the burst gate 1 is connected to a burst gate 1 which outputs only the color burst signal of the input modulation color signals.

The phase value detector 10 is connected to a phase difference detector 20 which compares the phase value of the color burst signal detected by the phase value detector 10 with the phase value of the carrier currently occurring and outputs the phase value. The demodulation carrier generator 30 is connected to the phase difference detector 20 to correct and output the demodulated carrier with the amount of phase error detected by the phase difference detector 20.

3 is a detailed block diagram of the demodulation carrier generator 30 of FIG.

A register 31 for storing a phase change value of the color carrier signal per clock, a ROM table 32 for storing a plurality of demodulation carrier values corresponding to the weft error detected by the weft error detector 20, The address generator 33 is connected to the register 31 and the ROM table 32, and supplies an address to the ROM table 32.

In the present invention configured as described above, the principle of detecting the phase value of the sample point by using the sampled value of the color signal will be described based on NTSC method. The color signal is a balanced signal of 3.58 MHz, especially in the color burst period. The RY component is zero and only the BY component is present with constant amplitude. If this is expressed vertically, it is as follows.

Where C (n): column burst signal,

R (n): color burst is amplitude,

C (n + 1): color burst signal after 1 clock

θs: Phase change of 3.58MHz signal per clock,

Fsc: color carrier frequency (3.58MHz),

Fs: sampling frequency.

Since R (n) = R (n + 1), the equations (1) and (2) can be summarized with respect to θ (n) using color burst signals.

In Equation (4), if two values of C (n + 1) and C (n) are known, the phase value θ (n) at that time can be known.

On the other hand, only the color burst signal is input to the phase value detection unit 10 by the burst gate 1 for the Y / C separated and sampled composite video signal, that is, the modulated color signal. The phase value detection unit 10 may use a ROM table using the above equation (4), and averages and uses data of several lines in order to reduce the influence of noise.

The phase value detector 10 detects a phase value θ (n) corresponding to a sample point of the color bus signal sampled by the above-described formulas (1), (2) and (4), and then detects the phase difference. Will output Accordingly, the phase difference detector 20 compares the phase difference θ (n) of the input color burst with the carrier phase value supplied from the subcarrier generator 30 at the next stage, detects the phase difference corresponding to the difference, and demodulates the carrier generator. It supplies to 30.

In addition, the demodulation carrier generator 30 generates a carrier accurately phase-locked to the input color signal by adding the phase difference detected by the phase difference detector 20 to the carrier signal currently generated.

On the other hand, the demodulation carrier generator 30 stores the value θs of the equation (3) corresponding to the color carrier of the color signal to be demodulated in the register 31 and stores this value in synchronization with the drive clock in the address generator 33. Integrate and generate an address. This address becomes the address of the carrier (SIN) and cosine (COS) table for the generation of the ROM table 32, and generates a carrier which is phase-synchronized to the input signal exactly in this sign and cosine table.

As described above, the present invention stores a demodulated carry value corresponding to a plurality of cases in a ROM table and stores a demodulated carrier value corresponding to a phase difference according to a result of comparing a phase value of a color burst with a phase value of a carrier that is currently occurring. By outputting from the table and generating the demodulated carrier precisely phase-constructed with the color burst signal of the inputted color signal, the color signal demodulation carrier is supplied digitally, so it is the deterioration and distortion of image quality which is the limit of the analog signal demodulation generator. There is an effect that can be prevented.

Claims (3)

A burst gate 1 that outputs only a color burst signal of the modulated color signals to be input, a current sample value [C (n + 1)] of the color burst signal output from the burst gate 1, and the current sample value [C a phase value detector 10 for detecting a delay sample value C (n) having a clock delay of (n + 1)] and a current sample value C of the color burst signal detected by the phase value detector 10; (n + 1)] and the delay sample [C (n)], (Where θ s is a phase change value of 3.58 MHz signal per clock), and the phase difference detector 20 detects the phase difference θ, and the detected phase difference θ at the phase difference detector 20. And a demodulation carrier generator (30) for demodulating and demodulating the demodulated carrier. The demodulation carrier generating unit (30) according to claim 1, wherein the demodulation carrier generating unit (30) includes a register (31) storing a phase change value of a color carrier signal per clock and a plurality of phase differences (θ) detected by the phase difference detecting unit (20). A ROM table 32, which stores a demodulated carrier value, and an address generator 33 which is connected to the register 31 and the ROM table 32 and supplies an address to the ROM table 32. Carrier generator for color signal demodulation. The carrier for demodulating color signals according to claim 1 or 2, wherein the demodulation carrier generator 30 modulates the coefficient by an external control signal according to the frequency of the color carrier so that a frequency such as a nuclear carrier is generated. generator.