JPS60150394A - Apc color synchronism circuit of pal color video signal - Google Patents

Abstract

PURPOSE:To attain the phase comarison sensitivity and lock in range on synchronization similar to those of the NTSC system by allowing an APC synchronism circuit to change alternately the 1st and 2nd phase comparator circuit inputs at each 0 deg., 90 deg., 180 deg. and one horizontal scanning period so as to prevent a phase error of 45 deg. with different polarity at each horizontal scanning to an output of the phase comparator circuit from being generated. CONSTITUTION:A color burst signal and an outut signal of a control oscillator 12 are compared at the 1st phase comparator circuit 13 with nearly 90 deg. of phase difference at the synchronism state the same as the NTSC system by using the 1st phase shift circuit 19 and they are compared at almost in-phase by the 2nd phase comparator circuit 21 provided separately from the 1st phase comparator circuit by using the 2nd phase shift circuit 20. Moreover, a polarity discriminating circuit 23 and a polarity switching circuit 24 switch the polarity of an output of a frequency divider circuit 22 so that the phase shift amount of the 1st and 2nd phase shift circuits is 0 deg. and 90 deg. when the phase of a color burst signal is +135 deg., and 90 deg. and 180 deg. when the phase of the color burst signal is -135 deg., and the phase of the PAL color burst signal is discriminated using the output of the said 1st and 2nd phase discriminating circuits 13, 21.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a PAL magnetic recording/reproducing device that converts the frequency of a carrier color signal during recording, and converts the frequency-converted carrier color signal back to the original frequency during playback. The present invention relates to an APC color synchronization circuit for a PAL color video signal, which is used to return the PAL color video signal back to its original position and to reduce phase fluctuations in a conveyed color signal due to time axis fluctuations caused by mechanical vibrations, uneven contact between a tape and a head, and the like.

The present invention can also be applied to an APC color synchronization circuit that demodulates a carrier color signal in a PAL color television receiver.

Conventional configuration and its problems In recent years, APC color synchronization circuits for PAL color video signals have been used in magnetic recording and reproducing devices based on the same principle as the APC color synchronization circuits used in PAL color television receivers. It will be done.

An APC color synchronization circuit for a PAL color video signal used in a conventional magnetic recording/reproducing device will be described below.

In a simple magnetic recording and reproducing device that records and reproduces PAL color video signals, the luminance signal is generally angularly modulated (for example, FM modulated), the carrier color signal is frequency-converted to a lower frequency band, and the carrier color signal is converted to a lower frequency band. The signal and the angle-modulated luminance signal in the high frequency band are mixed and recorded on the recording medium. During reproduction, the angle modulation signal is demodulated to reproduce the luminance signal, and the low frequency converted carrier color signal is frequency-converted to return it to its original frequency. Here, the APC color synchronization circuit is used to obtain a frequency conversion signal for converting the frequency of a carrier color signal during recording and reproduction. That is, during recording, the APC color synchronization circuit compares the phase of the color burst signal of frequency fsc in the carrier color signal separated from the color video signal with the oscillation signal of the control oscillator, and uses the phase comparison error signal to determine the oscillation frequency of the control oscillator. is varied to obtain a frequency fs that is synchronized in frequency and phase with the color burst signal.
I am getting a signal of c. Further, during recording, an AFC circuit is provided to obtain a signal of frequency fL, which is the subcarrier frequency of the low-frequency conversion carrier color signal, which is proportional to the horizontal scanning frequency fH. Here, fL=(40100) fH in PAL and VH8 type magnetic recording and reproducing apparatuses. Note that the horizontal scanning frequency fH of the PAL system is 15
, 625KHz, color subcarrier frequency fsc is approximately 4.4
It is 3MHz. Frequency fs obtained as above
The signal of c and the signal of frequency fL are supplied to a frequency converter to obtain a signal of sum frequency fsc10fL, which can be used as a frequency conversion signal for low frequency conversion of the carrier color signal.

At the time of recording, by providing the A20 circuit and the AFC circuit, the subcarrier frequency of the low-pass conversion carrier color signal can be accurately set to a frequency fL proportional to the horizontal scanning frequency fH.

On the other hand, even during playback, conventionally the A20 circuit and AF
The A20 circuit compares the phase of the color burst signal in the reproduced carrier color signal and the signal of the subcarrier frequency of the reference oscillator, and the control oscillator is controlled by the phase comparison error signal, and the AFC circuit performs reproduction horizontal synchronization. A signal with a frequency proportional to the frequency of the signal is created from the signal, the signal from the control oscillator of the A20 circuit and the signal from the A20 circuit are supplied to a frequency converter, and the output signal is converted into a carrier color signal that has been low frequency converted. It was used as a frequency conversion signal to return to the original frequency.

By the way, in comparison with the NTSC system, the PAL system color video signal has one color signal component, for example, the phase of the color subcarrier associated with the color difference signal RY signal, which is inverted by 180 degrees per horizontal scanning period. On the other hand, color difference in number B-Y
The phase of the color subcarrier for the signal is the co-phase for each horizontal scan period. A color burst signal is used to identify the phase of the color subcarrier for the R-Y signal, and the color burst signal phase is a burst whose phase is 136 degrees ahead of the phase of the color subcarrier of the B-Y signal. Bursts with a phase delay of 136°, in other words, burst signals with a relative phase difference of 90° are transmitted alternately every horizontal period.

When such a PAL carrier color signal is processed by the A20 circuit, that is, when the phase comparator directly compares the PAL color burst signal with the control oscillator or reference oscillator output, the output of the phase comparator has a characteristic peculiar to the PAL system. Since the color burst signal shifts by 90 degrees per horizontal scan, a 450 phase error with a different sign occurs per horizontal scan, so conventionally the time constant of the A20 circuit was made thicker so that it did not respond to this phase error. In this way, the occurrence of phase fluctuations in the output of the controlled oscillator was prevented.

However, with the above configuration, there is a limit to increasing the time constant of the A20 circuit during recording with the magnetic recording/reproducing device, and phase fluctuations remain, causing phase fluctuations in the low frequency conversion carrier color signal. The phase comparison sensitivity of the phase comparison circuit is 1/r2, that is, about s dB smaller than that of the NTSC system, which is disadvantageous for noise, etc., and when the phase comparison signal is used to discriminate between color and black and white, this discrimination sensitivity is also about 3 dB smaller. , during playback, especially special playback AFC
The circuit has drawbacks, such as the need to reduce the time constant if only the A20 circuit is used, the synchronization pull-in range of the A20 circuit is limited to the NTSC system, and the low phase comparison sensitivity makes it susceptible to noise. It had a point.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned problems of the conventional technology. Phase fluctuation does not occur even if the time constant of the A20 circuit is reduced, the phase comparison sensitivity and synchronization pull-in range are comparable to those of the NTSC system, and the AP
An object of the present invention is to provide an APC color synchronization circuit for a PAL color video signal that can stably discriminate between color and black and white.

Structure of the Invention The present invention provides a method for adjusting the phases of the color burst signal and the oscillation signal of the frequency oscillator relative to 0 and 90, and 900 and 1800.
, the first phase is compared by changing the phase alternately every horizontal scanning period.
．． the second phase comparison means, and the first degree obtained by the second phase comparison means. An APC color synchronization circuit for a PAL color video signal, comprising means for switching the alternating polarity using a second phase comparison error signal, the first. By alternating the input of the second phase comparator circuit between 00°, 90°, and 1800° every horizontal scanning period, 40 phase errors with different signs are generated in the output of the phase comparator circuit every horizontal scanning period. This prevents the phase comparison sensitivity and synchronization pull-in range from
This method can be used at the same level as the TSC method.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 shows a block diagram of an APC color synchronization circuit for PAL color video signals in a first embodiment of the present invention. In FIG. 1, a PAL color video signal input from an input terminal 1 is processed by a low-pass P-wave filter (hereinafter referred to as LPF) 2. The signal is supplied to a bandpass filter (hereinafter referred to as BPF) 3, where it is separated into a luminance signal and a carrier color signal. The luminance signal extracted by the LPF 2 is supplied to an FM modulator 4 and subjected to FM modulation, and then a high-pass filter (hereinafter referred to as HPF) 5 removes low-frequency components. The carrier color signal of the color subcarrier fsc taken out from the BPF 3 is supplied to the frequency converter 6 where it is frequency converted, unnecessary components are removed by the LPF 7, and the above FM
The modulated luminance signal is converted into a low frequency carrier color signal having a frequency band lower than the modulated luminance signal band.

Then, the FM modulated luminance signal from which the low frequency component has been removed by the HPF 6 and the low frequency converted carrier color signal are added and superimposed in the synthesizer 8, amplified by the recording amplifier 9, and recorded on the recording medium by the magnetic head 10. be done.

Here, in order to obtain a frequency conversion signal from the frequency converter 60, the carrier color signal taken out from the BPF 3 is supplied to the burst gate circuit 11 without being switched, and a color burst signal of frequency fsc is taken out. The signal and the oscillation signal from the control oscillator 12 are transferred to the first phase comparator circuit 1.
3 to obtain a first phase comparison error signal, and by controlling the controlled oscillator 12, a signal having a frequency fsc whose frequency and phase are synchronized with the color burst signal is outputted from the controlled oscillator 12. get as. Here, the controlled oscillator 12 and the first phase comparator circuit 13 are A2
0 circuit is configured. On the other hand, 14 is a sync signal separation circuit that separates a sync signal from a video signal, and 16 is a pulse signal with a horizontal scanning frequency fH (hereinafter H
16 is an HD signal generation circuit that obtains the H signal (called the D signal).
Fff, -Zurosoku circuit that is phase synchronized with the D signal (hereinafter P
It is a circuit that stably outputs a signal with a frequency fL proportional to the horizontal scanning frequency fH even if the horizontal synchronizing signal is absent or noise is mixed in. The PAL color video signal is also supplied to the synchronization signal separation circuit 14 to separate the synchronization signal, and the HD signal generation circuit 16 obtains an HD signal at a horizontal scanning frequency of fH.
A PLL circuit 16 obtains a signal with a frequency fL proportional to fH. Here, the PLL circuit 16 constitutes an AFC circuit.

In the end, as described above, the oscillation signal with the frequency fsc of the output of the controlled oscillator 12 and the frequency fL of the output of the PLL circuit 16 are obtained.
The signal of B is supplied to the frequency converter 17 for frequency conversion.
PF18 takes out the signal with the sum frequency fsc + fL,
It can be used as a frequency conversion signal for the frequency converter 6.

By the way, as explained in the conventional configuration and its problems, the PAL color burst signal
135 and -135 (i.e. 1225) and phase difference 9
It changes alternately between 0 and 0.

Therefore, if the phase of the signal from the controlled oscillator 12 is also changed alternately with a large phase difference of 90 degrees, the phase comparator 13 can always compare the phases at a constant phase, and the phase comparison can be performed every horizontal scan, which is unique to various conventional PAL signals. The phenomenon in which the phase comparison error signal fluctuates by ±46 minutes is eliminated. Reference numeral 19 denotes a first phase shift circuit that alternately changes the phase of the signal every Qo and every 900.1 horizontal scanning period. It's a sword, 2
0 is the second phase shift circuit, which changes the phase of the signal by 90
0 and 180' are alternately changed every horizontal scanning period. In this way, the first phase shift circuit 19
In the first phase comparator circuit 13, the color burst signal and the output signal of the controlled oscillator 12 are compared in a synchronous state with a phase difference of approximately 900, as in the case of the NTSC system, and the second phase shift circuit 2o A second phase comparator circuit 21 provided separately from the phase comparator circuit compares the signals in substantially the same phase.

By the way, No. 1. The signal for switching the phase of the second phase shift circuit is obtained by frequency-dividing the signal from the PLL circuit 16 using a frequency dividing circuit 22 to create a signal with a frequency of ifH, which is half the horizontal scanning frequency. however,
The horizontal synchronization signal in the video signal does not have information for determining the phase of the color burst signal, and the phase of the frequency dividing circuit 22 output is as follows.
1゜The phase shift amount of the second phase shift circuit is O',
Polarity determination circuit 23. It is unclear whether the polarity will be 900, 90o, or 180'. The polarity switching circuit 24 selects the first polarity when the phase of the color burst signal is +135°. This is for switching the polarity of the output of the frequency dividing circuit 22 so that the phase shift amount of the second phase shift circuit becomes 900 and 180 degrees when the phase of the large power rarburst signal is 1135 degrees. The feature of the present invention is that the phase determination of the PAL color burst signal is performed in the above-mentioned first. This is done using the output of the second phase discrimination circuit 13.21.

Hereinafter, one embodiment of the polarity discrimination circuit 23 and the polarity switching circuit 24 will be described using the block diagram of FIG. 2.

In general, a phase comparator circuit can be composed of a multiplier and LP'F, but in this case, a signal having the same frequency but differing in phase by 01 v1 = As1n (OJt + θ1) 7) 2 = B sin ((IJ t ) Here, A,
When B is the amplitude of vl and v2, and 0 is the angular frequency, the multiplier output is 1) 1XZ72-=-zABcoSθ1-7 ABco
s (2to t +f)1), high-frequency components are removed from the LPF output, and a phase comparison error signal of -A B Cos θ1 is obtained. Now, the phase of the output signal of the controlled oscillator 12 is θ, and the phase of the color burst signal is -1-135.
°, +226°, and the first phase shift circuit 19 is operating correctly and outputs θ, θ+90°, the color burst signal and the phase shift circuit 1
The phase difference between the outputs of 9 is always θ-135°, and the phase comparison error signal is YABCos(θ-135·). At this time, the output of the second phase shift circuit 21 is θ+900, θ
-1-1800 is output, the phase difference with the color burst signal is always θ-450, and the phase comparison error signal is A
B cos (θ-450). On the other hand, the first. If the polarity of the second phase shift circuit 21 is reversed and θ'-90°, θ is output to the first phase shift circuit 19, the phase difference with the color burst signal is one horizontal scanning. The phase comparison error signals are -AB-Cos (θ-45°) and 7 ABcos.
(θ−226°)=−T ABcos (θ−45°
), the second phase shift circuit 20 output has θ+180',
θ+900 is fully output, and the phase difference with the color burst signal is θ+46° and θ-135° for each horizontal scan, and the phase comparison error signal is 2 A B Co5 (θ+45°).
, 7 ABcos (θ-1360)=T A Bc
os (θ+45°). Therefore, the first. If the second phase shift circuit 19 is operating correctly, each phase comparison error signal is always constant, but if the polarity is reversed, the outputs are equal in absolute value and opposite in sign for each horizontal scan.

In Figure 2, 25°26 is the 1st. A 1H delay circuit 27°28 delays the output of the second phase comparator circuit 13.21 by one horizontal scanning period. Second phase comparison circuit 13.21
The 1st and 2nd adders 29.30 add the outputs of the 1H delay circuit 26.26 and the 1H delay circuit 26.26; The first one to square the output of the second adder or obtain the absolute value. The second square value circuit is an absolute value circuit, and 31 is the first square value circuit. Second square value or absolute value circuit 29
．． 30 is a third adder that adds the outputs; 32 is a reference value generation circuit that generates a predetermined reference value; 33 is a third adder 31;
The output is compared with the output of the reference value generation circuit 32, and the first. Second
A comparison circuit 26 to 33 constitute a polarity discrimination circuit 23, which generates a polarity discrimination output to determine whether the polarity of the phase shift circuit is correct or incorrect. 34 is a flip-flop circuit (hereinafter referred to as an FF circuit) which has two states in its output and inverts its state when triggered by the output of the comparator circuit 33.
5 is a phase inversion circuit that inverts the phase of the output of the frequency dividing circuit 22;
36 is a switching circuit that is controlled by the FF circuit 34 output and switches between the frequency divider circuit 22 output and the phase inversion circuit 35 output,
34 to 36 constitute a polarity switching circuit 24. Now, the first and second phase shift circuits are switched to the correct polarity by the polarity switching circuit 24.
is set, the first. Second phase comparison circuit 13.
The output of 21 is always 1 AB cos (θ-1360) AB
cos (θ-45°), so the first. The second 1H delay circuits 25 and 26 are also equal to these, and the first . The outputs of the second adders 27 and 28 are respectively ABcos(θ-136°)
, AB cos (θ-46°), and when p, 29.30 is a square circuit, the output of the third adder 31 is cos (θ
-1350)=sin (θ-450), so A
2B20O52(θ-1350) 10A2B2cos(θ
-469A2B 2 Also, when 29.30 is an absolute value circuit, AB <AB 1sin (θ-45°) l +AB
1cos(θ-' 60)1g2AB. on the other hand,
1st. When the polarity of the second phase shift circuit is reversed, the polarity of the first phase shift circuit is reversed. The output of the second phase comparison circuit 13.21 has the same absolute value and opposite sign for each horizontal scan, so the first
．． The output of the second adder 27,28 is always zero, and the output of the third adder is also zero. That is, the third adder 31
1. When the polarity of the polarity switching circuit 24 is correct, li force life is θ
Regardless of the value of , it becomes a constant value A2 B 2 , l, or a constant value AB or more, and when the polarity is reversed, it becomes zero regardless of the value of θ, and the output of the reference generation circuit 32 is set to an appropriate value. ”: The comparator circuit 33 can determine whether the polarity is correct or incorrect, and if the polarity is incorrect, a trigger pulse for the FF circuit 34 is generated, the state of the FF circuit 34 is reversed, and the switching circuit 36 switches the polarity. will be in the correct state.

As described above, according to this embodiment, the first . The second phase comparison circuit and the first phase comparison circuit. By providing a second phase shift circuit, a polarity discrimination circuit, and a polarity switching circuit, even if a color burst signal whose phase shifts by 90 degrees per horizontal scan, which is unique to the PAL system, is input to the APC circuit, the phase comparison can be performed. The circuit output has 4 signals with different signs for each horizontal scan.
A stable frequency conversion signal can be obtained without a 6° phase error. In addition, since the phase comparison sensitivity is always compared in the same phase, the same sensitivity as in the case of the NTSC system can be obtained, and in the case of the PAL system, the sensitivity does not decrease by approximately 3 dB compared to the NTSC system, and the APC circuit is stabilized. Furthermore, when the output of the second phase comparator circuit is used to determine whether a color burst signal exists, that is, to determine whether the input video signal is color or monochrome, the sensitivity is comparable to that of the NTSC system, and the PAL system The drawback of being easily affected by specific noise is also eliminated.

FIG. 3 shows a block diagram of an APC color synchronization circuit for PAL color video signals in a second embodiment of the present invention. The same parts as in the first embodiment shown in FIG. 1 are indicated by the same reference numerals, and detailed explanation will be omitted. In Figure 3,
The reproduction signal reproduced from the recording medium by the magnetic head 10 is amplified by the reproduction amplifier 37 and then sent to the HPF 38 and the LPF 3.
9 and is separated into an FM modulated luminance signal and a low frequency conversion carrier color signal. The FM modulated luminance signal separated by the HPF 38 is supplied to the FM demodulator 41 via the limiter 40 and demodulated into a reproduced luminance signal.On the other hand, the low frequency conversion carrier color signal of the color subcarrier fL separated by the LPF 39 is The signal is supplied to a frequency converter 42 and subjected to frequency conversion, and a BPF 43 removes unnecessary frequency components and converts it into a reproduced carrier color signal of the color subcarrier fsc, which is the original frequency. Then, the reproduced luminance signal and the reproduced carrier color signal are added and mixed in a synthesizer 44, and an output terminal 45 is also taken out.

Here, in order to obtain the frequency conversion signal of the frequency converter 42, first, the carrier color signal taken out from the BPF 43 is supplied to the burst gate circuit 11 to take out the color burst signal, and this burst signal and color Carrier number fs
The reference signal from the reference oscillator 46 of c is phase-compared by the first phase comparison circuit 13 via the first phase shift circuit 19 to obtain a first phase comparison error signal, which is reproduced by controlling the control oscillator 12. A signal having the same frequency as the color subcarrier fL of the low-pass converted carrier color signal is obtained, and the reference oscillator 46 is generated by the frequency converter 1γ.
Frequency conversion is performed with the reference signal of frequency fsc. As a result, a signal having a sum frequency fsc is obtained as a frequency conversion signal at the BPF 18 output. Now, the reproduced low-pass conversion carrier color signal has jitter, and its subcarrier is fL+
When ΔfL, the output to the controlled oscillator is also fL + ΔfL
Therefore, the frequency conversion signal becomes fsc + fL + ΔfL, and the carrier color signal whose frequency is returned to its original value always becomes fsc, and jitter correction is performed.

Here, frequency converter 42 - BPF 43 - burst gate circuit 11 - phase comparison circuit 13 - controlled oscillator 12 - frequency converter 17 - BPF 18 - frequency converter 42 is A20.
A feedback loop of the circuit is configured, and the output of the control oscillator 12 is controlled so that the frequency and phase of the color burst signal output from the BPF 43 have a constant relationship with the output of the reference oscillator, and the frequency converter 42 converts the reproduced low-frequency conversion carrier color signal. changing the frequency and phase of In this embodiment, the first. The second phase shift circuit shifts the reference oscillator 46 output to 00, 90° and 90°.
It is provided to have a phase shift of 00.1800.

1st. The signal for switching the second phase shift circuit is sent to the combiner 4.
The synchronization signal separation circuit 14 obtains a synchronization signal from the reproduced video signals of the four outputs, and the HD signal generation circuit obtains an H signal with a horizontal scanning frequency fH.
D signal is obtained, and the PLL circuit 16 generates a stable f for the nozzle, etc.
A signal proportional to H is obtained, and the frequency dividing circuit 22 divides the first . A switching signal for the second phase shift circuit is obtained.

The first thing to check is whether the polarity of this switching signal is correct. The polarity discrimination circuit 23 uses the output of the second phase comparison circuit 13.21 to discriminate, and if it is incorrect, the polarity switching circuit uses the frequency division circuit 22
Switching the output polarity.

As described above, according to this embodiment, the first . The second phase comparison circuit and the first phase comparison circuit. By providing a second phase shift circuit, a polarity discrimination circuit, and a polarity switching circuit, even if a color burst signal whose phase shifts by 90' for each horizontal scan is input to the A20 circuit, the output from the phase comparison circuit is Since a 45° phase error with a different sign does not occur every horizontal scan, a stable frequency conversion signal can be obtained even if the time constant of the A20 circuit is made small. In addition, the phase comparison sensitivity is improved by approximately s dB compared to the conventional case, and N
As the A20 circuit becomes stable and becomes comparable to the TSC method, the A20 circuit becomes stable.
The synchronous pull-in range of 20 circuits is twice that of the conventional system, and the maximum fH = 17, 625KHZ, which is equivalent to the NTSC system.

Further, the detection sensitivity of color and black and white using the output of the second phase comparator circuit is improved to the same level as that of the NTSC system.

Effects of the Invention The APC color synchronization circuit for PAL color video signals of the present invention is as follows:
A20 circuit is used to compare the phases of the color burst signal and the oscillation signal of the frequency oscillator (controlled oscillator or reference oscillator) by alternating the relative phases of 00 and 900 and 900 and 180 every horizontal scanning period. 1. a second phase comparison means; a first phase comparison means; The first phase obtained by the second phase comparison means. Second
Using the phase comparison error signal of
and 900 and 900 and 180" By providing a means for determining and switching the polarity which is alternately changed every horizontal scanning period, a color burst signal whose phase shifts every horizontal scanning is input to the A20 circuit. Also, since a 45° phase error with a different sign does not occur in the phase comparator output for each horizontal scan, a stable frequency conversion signal can be obtained during recording, and when playing back quickly, it is possible to obtain a stable signal for frequency conversion. It is possible to configure an A20 circuit with a fast response by reducing the constants.In addition, the phase comparison sensitivity is on par with NTSC, which is about 3d13 larger than the conventional one, and the synchronization pull-in range of the A20 circuit is on par with NTSC, which is about 3d13 larger than the conventional one. By doubling the output, the color and black-and-white detection sensitivity using the output of the second phase comparator circuit can also be improved by about 3 dB to the same level as NTSC, which has a great practical effect.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an APC color synchronization circuit for a PAL color video signal in a first embodiment of the present invention; FIG. 2 is a block diagram of a polarity discrimination circuit and a polarity switching circuit in the same embodiment;
FIG. 3 is a block diagram of an APC color synchronization circuit for PAL color video signals in a twentieth embodiment of the present invention. 3.18.43・River・・BPF, 7.39・River・・LP
F, 6, 17, 42... Frequency converter, 11.
... Burst gate circuit, 12 ... Controlled oscillator, 13°21 ... Phase comparison circuit, 19.
20... Phase shift circuit, 14... Synchronization signal separation circuit, 15... HD signal generation circuit,
16... PLL circuit, 22... Frequency dividing circuit, 23... Polarity discrimination circuit, 24... Polarity switching circuit, 25.26... 1H delay circuit, 27,2
8゜31... Adder, 29.30...
Square or absolute value circuit, 32... Reference value generation circuit, 33... Comparison circuit, 34... FF circuit, 35... Phase inversion circuit, 36・・・・・・
Switching circuit, 46...Reference oscillator. Name of agent: Patent attorney Toshio Nakao and one other name
1 Figure man? (2) 2.5

Claims (2)

[Claims] (1) First phase comparison in which the phases of the color burst signal in the carrier color signal of the PAL color video signal and the oscillation signal of the frequency oscillator are changed relatively to 0 and 90, alternately for each horizontal scanning period, and the phases are compared. a second phase comparison means for comparing the phases of the color burst signal and the second oscillation signal by alternatingly changing the phases of 90 and 180 degrees for each horizontal scanning period; and the first phase comparison means. means for changing the frequency of the oscillation signal of the frequency oscillator or the frequency of the carrier color signal including the color burst signal -3 using the first phase comparison error signal obtained by the means; Using the first and second phase comparison error signals obtained by the second phase comparison means, the phases of the color burst signal and the oscillation signal are relatively determined at 0°, 9o0, 900 and 1800 for each horizontal scanning period. 1. An APC color synchronization circuit for a PAL color video signal, comprising means for switching polarity to alternately change it. (2) The means for switching the polarity which is alternately changed every horizontal scanning period adds the means for generating a signal whose polarity is inverted every horizontal scanning period and the first phase comparison error signal over at least two horizontal scanning periods. means for summing the second phase comparison error signal over at least two horizontal scanning periods; and means for summing the squared value or absolute value of the first and second phase comparison error signals summed over at least two horizontal scanning periods. , means for comparing with a predetermined value, and means for controlling the phase of a signal whose polarity is inverted every horizontal scanning period in the signal obtained by the comparing means. APC color synchronization circuit for color video signals.