JPS6080385A - Apc circuit - Google Patents

Abstract

PURPOSE:To lock accurately an output of a voltage controlled oscillator to a burst phase by extracting a burst part in an R-Y signal with a gate pulse obtained based on burst information in a B-Y signal so as to apply phase discrimination. CONSTITUTION:The R-Y signal is supplied to a burst gate 16 of an APC circuit and a color burst part is extracted and the result is fed to a comparator 17. A gate pulse Pg is formed based on the burst information of the B-Y signal. The comparator 17 compares an output of the burst gate 16 with a reference value (equivalent to a pedestal level), and gives a count decrement signal to the next up-down counter 18 when the burst gate output is higher than a reference value and gives a count increment signal when lower than the reference value. An output of a counter 18 is given to a VCO21 via a D/A converter 19 and an LPF20 to control an oscillated frequency 4fsc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to an APO (Automatic Pbase) used in a system for digitally processing video signals.
0ontorol) circuit.

Background Art and Problems In digital television receivers and the like that digitally process input video signals, APO circuits that generate continuous wave oscillation output (4S) based on colorverse signals are also digitized.In the case of digital televisions , the output of the A20 circuit is, for example, four times the frequency of the subcarrier (143 NIHZ).
This clock pulse is used as a reference pulse (system clock) for A/D conversion on the input side, D/A conversion on the output side, and other timing signals of the system.

The phase comparison between the burst signal and the oscillation output in the A20 circuit is performed based on the RY information shown in FIG. 1, which is obtained separately from the digitized video signal. In other words, when the A20 circuit is phase-locked, the digital value of the R-Y information in the burst period is equal to [100000], and when the phase shifts, the value becomes larger or smaller than this value as shown by the dotted line in Figure 1. The 6th A detection circuit, which utilizes the generation of digital values, uses the reference value (100000) and R-Y information in the burst interval (burst Kate Hals B).
It is composed of a magnitude comparator that compares the magnitude at GP (7) width), and controls the output frequency (phase) of a VCO (voltage controlled oscillator) based on its output.

The burst gate pulse BGP shown in FIG. 1 is generated with a delay from the horizontal gate signal. Since the phase of the burst signal relative to the synchronization signal changes by 1W1 depending on the transmission path of the video signal, the burst gate pulse BGP is made wide as shown in FIG. 1 with sufficient phase margin. Therefore, the phase detection circuit of the APO circuit also discriminates the level of the pedestal portion of the R and -T information as burst phase information.

The digital value of this pedestal level is originally (1000
00) (the intermediate value of the 6-bit quantization level), it is exactly the same as the RY node information when the APO circuit is locked, and therefore the phase detection circuit malfunctions and the locked phase is not reached. There is a risk of errors occurring.

OBJECTS OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to perform phase discrimination based only on burst information in the RY signal to prevent the A20 circuit from malfunctioning.

Summary of the Invention The APO circuit of the present invention converts an input video signal into a digital signal to obtain an RY signal and a BY signal, extracts a color burst portion of the RY signal using a gate circuit, The output of the gate circuit is compared with a reference value by a first comparator, and the voltage controlled oscillator is controlled based on the error information of the output, and the gate pulse given to the gate circuit is B-Y. It is characterized in that it is formed by comparing the color burst information in the signal with a certain level using a second comparator.

With this configuration, it is possible to discriminate the phase error between the color burst and the vCO output based only on the burst information.

Example The present invention will be explained below based on examples.

FIG. 2 is a block diagram of main parts of a digital television receiver to which the present invention is applied, and FIG. 6 is a waveform diagram of each part of FIG. In Fig. 2, the input signal from the antenna (1) passes through the tuner +21, is detected as a video signal at the VIP (3+), and is converted into a digital signal by the A/D converter (4). The video signal is Y/
In the C (luminance/chroma) separation circuit (5), the luminance signal Y
and chroma signal C. The luminance signal is sent to the subsequent processing circuit, and the chroma signal is sent to the ACC circuit (6
) (automatic chroma control circuit) to the demosulator (7
), the R-Y signal (Figure 1) and the B-Y signal (
It is separated into Figure 3A). Each 1'(, -Y, B-Y signal is adjusted or controlled as necessary, and then converted to an analog chroma signal by a D/A converter +81 +91, and output to a subsequent circuit. .

The R-Y signal shown in FIG. 1 is applied to the burst gate (llil) of the APO circuit as in the conventional case, and after the curler burst portion is extracted and Jly is applied to the comparator On. - It is formed based on the burst information of the Y signal.

In the comparator aη, the burst gate (Lfi
The output of I is compared with a reference I (100000) (corresponding to the pedestal level). As is well known, the chroma signal is transmitted after being subjected to complex modulation, and the detection axes for R and -Y are perpendicular to the burst axis. Therefore, v of A20 circuit
While the output phase of a o +an is locked to the color burst of the input video signal, the output of burst game 1-11Fil for -Y signal is the above reference value cio
oooo). That is, the burst information is not originally included in the R-Y detection output.

The comparator aη compares the reference value with the burst gate output, and if the burst gate output is higher than the reference value, the next U/D (up/down) counter (up/down) gives a counting reduction signal to the burst gate output and the burst gate output becomes the reference value. If it is lower than the value, a counter increase signal is given.U/D counter (I8)
The output is D/A converter 5 (19J), low pass filter (2
(It is given to VCOf21+ as a control voltage via υ, and its oscillation frequency 4 fsc is controlled.V 001
2++ output frequency (phase) change is burst game)
(This is carried out until the output of 161 matches the reference value and a stable state is reached c!: V CO (The output of 211 and the color burst signal match in phase.

In order to compare only the reference value and burst information in the kPc circuit (7) comparator (17), the burst gate (1('N) gate is A pulse Pg is formed.The detection axis for BY is in phase with the burst axis, and as shown in FIG. 6A, the burst information in the BY signal exhibits a constant value different from the pedestal level. Therefore, based on this burst information, it is possible to obtain the gate pulse Pg shown in FIG. 3C, which accurately represents the position of the first burst signal.

In Fig. 2, the output B-Y of the demosimulator (7)
The signal is sent to a burst gate (10) 11, and a burst portion is extracted based on the burst gate pulse BGP shown in FIG. 6B. This burst gate pulse takes into consideration the phase shift of the burst signal due to the transmission path of the video signal.
It is made wide. This burst gate pulse is generated by separating and extracting a synchronization signal from the video signal output from the VIFi3+ in a synchronization separation circuit (14), giving this synchronization signal to a timing counter (15) as a reset pulse, and It can be created by extracting a pulse having the phase and pulse width shown in Figure 6B. Note that the timing counter (15) is V CO
The output 4 fsc of f21) is counted to form various timing signals along the time axis of the video signal.

The output of the burst gate (IO) is given to a comparator (group), and compared with reference level 1 (lower than reference level I (.L) shown in Fig. 6A), the burst portion is clipped. Therefore, from the output of the comparator (10), a gate pulse Pg corresponding to the burst signal shown in FIG. -Stogate 1- (1G+ cannot be given. Therefore, -Stogate (16) accurately extracts only the burst Ml (minute) in the R and -Y signals, and the next comparator (in case of itching, the pedestal level is Accurate phase discrimination is performed based only on burst information that is not included.

In addition, when the electric field is weak or there is a lot of noise, B- in Figure 6A
The burst information level in Y(m) may rise near the reference level RL. In such a case, if clipping is performed at the reference level RL in the comparator (11), a whisker as shown in the third figure may occur. A signal containing such noise pulses is not suitable as the burst gate pulse Pg. The burst gate pulse BGP (FIG. 6B) is used.

The LJJ switching control of the changeover switch (13) uses a counter (12) to count the number of data exceeding the reference level RL based on the output of the comparator (11), and when the number exceeds a certain level, the This is not done based on the switching control signal. This counter (12) is reset 11 every vertical scanning section, for example.

As described above, the present invention is applied to a digital television receiver.
Although the explanation has been made based on one example, the present invention 6 uses a shield of the gods that digitally processes an audio video signal, such as a frame memory,
It can be applied to frame synchronizers, time base collectors, etc.

Effects of the Invention As described above, the present invention compares the burst portion of the Il, -Y signal detected in the form of digital information with the reference signal to obtain a phase error and control the voltage '+ljt control oscillator, thereby generating a color burst. While obtaining a phase-locked oscillation output,
The burst information in the B-Y signal is compared with a certain level to obtain a gate pulse corresponding to the burst part, and based on this gate pulse, the burst part in the R and -Y signals is extracted, and the above-mentioned phase error is calculated. It is designed to perform a comparison to obtain the following. Therefore, phase discrimination can be performed based on the R and -Y information of only the burst portion without including unnecessary information, and the output of the heavy pressure control oscillator can be accurately locked to the burst phase without error.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram of the 67r video (l[(, -Y information not obtained from issue A), FIG. 2 is a block diagram of the main parts of a digital television receiver showing an example of the first page of the present invention, FIG. is a waveform diagram of the trough in Figure 2. In the symbols used in the drawing, (1)......Antenna (2)
・・・・・・・・・・・・・・・Tuner (3) ・
・・・・・・・・・・・・・・・ VIF(4)・・・
......A/D converter (5)...
......Y10 separation circuit (61...
・・・・・・・・・−・AOO circuit (7j・・・・・・・
・・・・・・Demosimulator+8)191・・・・
......D/A converter α01...
・・・・・・Burst Kate (11)・・・・・・
......Comparator (121...
・・・・・・・・・Counter (13)・・・・・・・・・
......Choice switch 114J...
......Synchronization separation circuit (15)...
...Timing counter (16)...
・・・・・・・・・Burst Kate+171・・・・・・
......Conno 1° rater (18)...
......-...U/D counter (19)...
・・・・・・・・・・・・D/A converter (201...
......Low pass filter (21)...
・・・・・・・・・・・・ ■00. 1st plan 11 plates - 11

Claims (1)

[Claims] A circuit that converts an input video signal into a digital signal to obtain a R-Y signal and a B-Y signal, a gate circuit that extracts a color burst portion in the R-Y signal, and an output of this gate circuit and a reference value. a first comparator that compares
A voltage controlled oscillator controlled according to the error information of the output of the first comparator and a second comparator that compares the color burst information of the B-Y signal with a constant level to obtain a gate pulse to be applied to the gate circuit. An APO circuit comprising a comparator.