JPS6362157B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a video tape recorder or the like that records and plays back PAL color video signals.
The present invention relates to an APC circuit provided to reduce phase fluctuations of a carrier color signal caused by jitter.

In addition, the present invention provides approximately 45 times the output of the phase comparator constituting the APC circuit has a different sign for each horizontal scan.
A phase comparison error component of half the horizontal scanning frequency that occurs because the reference signal and the average phase of the color burst are phase synchronized. offset,
This provides an APC circuit that prevents hue variation within a line (hereinafter referred to as DP) from occurring and has a quick response.

Now, in a simple video tape recorder that records and plays PAL color video signals, the luminance signal is generally angularly modulated (for example, FM modulated), the carrier color signal is frequency-converted to the lower frequency band, and the carrier color signal is frequency-converted to the lower frequency band. The carrier color signal of the band and the angle-modulated luminance signal of the high frequency band are mixed and recorded on the tape. During reproduction, the angle modulation signal is demodulated to reproduce the luminance signal, and the carrier color signal in the low frequency band is returned to its original frequency by a frequency converter.

During playback, it is necessary to correct phase fluctuations in the carrier color signal due to jitter, so conventionally
An AFC circuit and an APC circuit are provided, and the AFC circuit creates a signal with a frequency that is, for example, an integer multiple of the frequency of the reproduced horizontal synchronization signal, and the APC circuit compares the phases of the reproduced burst signal and the reference subcarrier signal. Control a variable frequency oscillator at the output and
The signal from the AFC circuit and the signal from the variable frequency oscillator of the APC circuit are supplied to a frequency converter, and the output signal is used as a frequency conversion signal for returning the carrier color signal to its original frequency.

When doing this, the color burst phase shifts 90 degrees every horizontal scan, which is unique to the PAL method, so the output of the phase comparator that makes up the APC circuit has a different sign every horizontal scan.
Since a 45 degree phase error occurs, the time constant of the APC circuit is increased so that it does not respond to this phase error, thereby preventing the occurrence of DP. However, when the AFC circuit is affected by noise bands or skew that occur during high-speed playback, such as 10x speed, the AFC circuit acts as a disturbance to the APC circuit, and the time constant of the APC circuit is large. The hue and color saturation were likely to change over time.

The present invention solves the problems of the conventional configuration, and even if the time constant of the loop filter is small,
This provides an APC circuit that does not generate DP.

If the APC circuit of the present invention is used, the conventional AFC circuit is basically unnecessary, and a novel and high-performance playback circuit for a PAL video tape recorder can be realized.

The present invention will be described in detail below using an example in which the APC circuit of the present invention is applied to a video tape recorder.

The block diagram in FIG. 1 shows one embodiment of the present invention.
The playback circuit configuration of a video tape recorder is shown.

In FIG. 1, a mixed signal of a FM-modulated luminance signal and a carrier color signal in a low frequency band, which is reproduced from a magnetic tape by a head 1, is sent to a reproduction amplifier 2.
The FM-modulated luminance signal is extracted and supplied to the FM demodulator 5 via the limiter 4, and the demodulated luminance signal is supplied to the synthesizer 6.

The reproduced signal is also supplied to a low-pass filter 7 to extract a carrier color signal in a low frequency band, which is passed through an ACC circuit 8 to a frequency converter 9.
is supplied to

In this case, the color video signal recorded on the magnetic tape is a PAL signal, and the subcarrier frequency _L when frequency converted to the low frequency band is _L = 321/8 _H = (40 + 1/8) _H ... Suppose (1). However, _H is the horizontal scanning frequency.

Then, the signal of the reference subcarrier number frequency _S from the reference oscillator 10 is supplied to the frequency converter 11, while the frequency from the variable frequency oscillator 12 is (160
+1/2) _H signal is supplied to the 1/4 frequency divider 13, and the frequency is divided into 1/4 to obtain a signal with a frequency of _L. This is supplied to the frequency converter 11. A frequency conversion signal with a frequency of _S + _L can be obtained. This frequency conversion signal is then supplied to the frequency converter 9, and the carrier color signal in the low frequency band is returned to its original frequency.

The carrier color signal restored to its original frequency is supplied to the synthesizer 6, so that a reproduced color video signal is obtained at the output terminal 14.

A portion of the reproduced carrier color signal output from the frequency converter 9 is supplied to the phase comparator 15. The phase comparator 15 performs a phase comparison operation with the reference signal of the reference oscillator 10 only during the burst period, and is controlled by the burst gate pulse obtained from the output synchronization signal of the synchronization separation circuit 16 through the burst gate pulse generation circuit 17. . The phase comparison output is then supplied to the variable frequency oscillator 12 via the mixer 18, loop filter 19 and mixer 20,
Control its oscillation frequency. Therefore, the frequency of the frequency conversion signal supplied to the frequency converter 9 is controlled. i.e. by color burst
APC circuit is configured.

By the way, the APC circuit is a phase lock circuit that uses color burst, which is an intermittent signal.
In the configuration described so far, when the variable frequency oscillator 12 is an oscillator with a relatively wide frequency variable range, such as an unstable multivibrator, the color burst frequency supplied to the phase comparator 15 is is the reference subcarrier frequency
There is a phenomenon in which APC locks even at a frequency that is an integer multiple of _H from _S (hereinafter referred to as pseudo-lock).
At this time, the oscillation frequency of the variable frequency oscillator 12 is a frequency that is an integral multiple of _4H different from the normal lock frequency 4×(40+1/8) _H .

Therefore, in order to prevent this false lock, the oscillation frequency of the variable frequency oscillator 12 is controlled by providing a feedback loop separate from the APC.
is configured to oscillate near the frequency in the regular lock. 21 is a frequency detection circuit that detects the oscillation frequency of the variable frequency oscillator. 22 uses the output of the frequency detection circuit 21 to determine whether the oscillation frequency of the variable frequency oscillator 12 is close to the frequency during normal locking, and also determines whether the frequency is higher than the frequency during normal locking or not. This is a discrimination circuit that discriminates whether the temperature is low or not. 23 is an integrating circuit that integrates the discrimination output. For example, the oscillation frequency of the variable frequency oscillator 12 is 1/2 from the oscillation frequency 4 × (160 + 1/2) _H at the time of normal lock.
When the frequency is higher than _H , a control voltage that lowers the oscillation frequency of the variable frequency oscillator 12 is supplied to the variable frequency oscillator 12 via the mixer 20, and the oscillation frequency of the variable frequency oscillator 12 is
When the frequency is 1/2 _H or more lower than (160+1/2) _H , a control voltage is supplied to the variable frequency oscillator 12 to increase the oscillation frequency of the variable frequency oscillator 12. Therefore variable frequency oscillator 12
The oscillation frequency of the lock is controlled close to the oscillation frequency during normal lock, and false locks do not occur.

With the configuration explained above, pseudo locks do not occur.
The APC circuit will operate stably, but the APC circuit will be able to operate stably. The APC operates in phase synchronization with the oscillation signal.
In a steady state, this corresponds to a phase difference of approximately 45 degrees, and a phase error with a different polarity for each horizontal flux is obtained at the output of the phase comparator. The output current of this phase comparator 15 is shown in FIG. 2b. FIG. 2a shows a carrier color signal, and A shows a burst signal.
This phase comparison output is directly passed through the low-pass filter 19,
Since DP is generated when the signal is supplied to the variable frequency oscillator 12, the configuration described below prevents the generation of DP.

24 is a pulse signal (hereinafter referred to as an HD signal) having a horizontal scanning frequency, which is obtained by removing the vertical synchronizing signal and the equivalent pulse from the output signal of the synchronizing separation circuit 16, and which is phase-synchronized with the horizontal synchronizing signal. ) is a pulse generation circuit that obtains the following. Reference numeral 25 denotes a phase lock circuit that is phase-locked to this HD signal, and stably outputs the pulse _S1 at the horizontal scanning frequency even if the horizontal synchronizing signal is absent due to, for example, dropout. 26 is a 1/2 frequency divider circuit which divides the frequency of _S5 and outputs a continuous signal having a frequency of 1/ _2H . The output signal of the frequency dividing circuit 26 is the switch circuit 2
7 to obtain a signal S 5 having the same phase or an inverted phase, and supplying the signal S ₅ to the current supply circuit 28 . A specific configuration of this current supply circuit 28 is shown in FIG.
A signal _S5 is input between terminals 281 and 282 in FIG. 3, and transistors 283 and 2 are differentially connected.
Operate the switch 84. transistor 285
and 286 constitute a current mirror circuit. A transistor 287 serving as a current source is connected to the common emitters of the differentially coupled transistors 283 and 284, and a burst gate pulse input from a terminal 288 causes the burst period transistor 28 to
7 is electrically conductive. Therefore, if the current flowing through this transistor 287 is I ₀ , the polarity changes depending on the state of _the input signal S ₅ as shown by the arrow in FIG.
This is what you get.

The output of the current supply circuit 28 is then output to the mixer 18.
and is mixed with the phase comparison output current.

Therefore, with this configuration, the current of the opposite polarity shown in FIG. Therefore, the output current I ₀ of the current supply circuit 28 is
If the output current of the current supply circuit 28 has a different polarity than the phase comparison output current, as shown in FIG. The currents cancel out as shown in . Furthermore, when the output current of the current supply circuit 28 has the same polarity as the phase comparison output current, the output of the mixer 18 has a different polarity for each horizontal scan, as shown in FIG. Twice the current will flow.

Incidentally, the frequency components of the output current of the current supply circuit 28 are components of 1/2 _H and odd multiples thereof, and are at a constant level. Therefore, the output current of the current supply circuit 28 has an influence only on the frequency components of 1/2 _H or more of the phase comparison output.
It does not unlock the APC circuit,
For example, the current shown in FIG.
Even if the output voltage becomes as shown in FIG. 2G, the DP of the carrier color signal only increases.

Therefore, the APC circuit is always locked, and the output voltage of the loop filter 19 is either almost constant and no DP occurs, or a large voltage fluctuation occurs every two horizontal scans as shown in Figure 2G. It will be one of the following.

Therefore, the configuration is such that this state is determined and the polarity of the output current of the current supply circuit 28 is controlled so that the state is always such that DP does not occur. This consists of a high-pass filter 29, a half-wave rectifier circuit 30, and
It consists of a pulse shaping circuit 31, a counter 32 whose output changes from "0" to "1" when counting four pulses, a 1/2 frequency divider 33, and a T flip-flop 34, and the output current of the phase comparator 15. When the polarity of the output current of the current supply circuit 28 matches and the output voltage of the loop filter 19 fluctuates by two horizontal scanning periods as shown in FIG. 2G and FIG. 4, this AC component becomes a high-pass component. The signal passes through a filter 29 and is half-wave rectified by a half-wave rectifier circuit 30, and the output signal is supplied to a pulse shaping circuit 31 where it is converted into pulses as shown in FIG. counter 32
is reset when the output signal _S2 of the 1/8 frequency divider ₃₃ is "1". Therefore, as shown in FIG. The output signal _S3 changes from "0" to "1" as shown in FIG. 4 when four pulses are counted. Therefore, the output signal S ₄ of the T-flip-flop 34 to which the output signal S ₃ of the counter 32 is supplied changes from "0" to "1", switching the switch 27 and thus the switch input to the current supply circuit 28. 27 output signal S ₅
The phase of is reversed as shown in FIG. 4, and therefore the output current of the current supply circuit 28 changes from D to C as shown in FIG.
The output current of the phase comparator 15 is canceled out, and the state shifts to a state where DP does not occur. Furthermore, when the output current of the current supply circuit 28 has a polarity that cancels out the output current of the phase comparator 15 as shown in FIG. No, half wave rectifier circuit 3
Unless the output level of 0 is sufficiently large, the pulse shaping circuit 31 cannot generate a pulse. Therefore, in this case, as shown in FIG. 4, no pulse can be obtained from the output of the pulse shaping circuit 31, and the current supply circuit The polarity of the output current of 28 does not change.

That is, the average phase of the color burst and the output signal of the reference oscillator 10 are controlled to be phase-locked, so that phase comparison errors having different polarities for each horizontal scan are canceled out.

As explained above using the examples, the present invention
The output of the phase comparator constituting the APC circuit is configured to supply a voltage or current corresponding to a phase difference of approximately 45 degrees with a different sign for each horizontal scan, and the polarity of this supplied current is controlled by, for example, a loop filter. 1
The AC component of the output signal of No. 9 is detected and controlled, and the standard signal and the average phase of the color burst are phase-synchronized, resulting in half of the horizontal scanning frequency.
This is to cancel out the phase comparison error component.

Therefore, as shown in FIG.
If the playback circuit of a videotape recorder is configured using this circuit, phase fluctuations due to jitter in the carrier color signal can be corrected at high speed without generating DP.
A good reproduction image can be reproduced.

Also, even if the polarity of the output current of the current supply circuit is
Even if the polarities of the phase comparison output currents that make up the APC circuit match, the APC loop will not be unlocked.
The carrier frequency of the output carrier color signal does not vary greatly, and when the APC circuit of the television receiver is unlocked, the color killer is activated and colors are less likely to disappear on the screen.

Further, only one expensive crystal resonator is required for the subcarrier frequency oscillator, and since there are many digital circuits, it is suitable for semiconductor integration.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a playback circuit of a video tape recorder which is an embodiment of the present invention, FIG. 2 is a waveform diagram explaining the same operation, FIG. This figure is a waveform diagram illustrating the operation of the configuration shown in FIG. 1. 1... Head, 2... Regenerative amplifier, 3, 29... High pass filter, 4... Ritter, 5... FM demodulator,
6, 18, 20... Synthesizer, 7, 19... Low pass filter, 8... ACC circuit, 9, 11... Frequency converter, 10... Reference oscillator, 12... Variable frequency oscillator, 13, 26, 33... Frequency divider, 15... Phase comparator, 16... Synchronization separation circuit, 17... Burst gate pulse generation circuit, 21... Frequency detection circuit, 22...
Discrimination circuit, 23... Integrating circuit, 24... Pulse generation circuit, 27... Switch circuit, 28... Current supply circuit,
30...half-wave rectifier circuit, 31...pulse shaping circuit, 3
2...Counter, 34...T flip-flop.

Claims (1)

[Claims] 1. A phase comparator that compares the phase of a color burst in a carrier color signal of a PAL color video signal and an oscillation signal of a reference oscillator at a subcarrier frequency, a signal source whose polarity is inverted every horizontal scanning period, and the signal source. means for mixing the output signal of the phase comparator with the output signal of the phase comparator, and a variable frequency oscillator controlled by a control signal formed based on the output of the mixing means, A signal for frequency conversion of the carrier color signal was obtained.
In the PAL color video signal processing device, a detection means for substantially detecting the magnitude of the alternating current component of the control signal is provided, and the output signal of the detection means is used to control the polarity of the signal source. Characteristic PAL color video signal processing device.