JPS6229394A - Processing device for pal color video signal - Google Patents

Abstract

PURPOSE:To prevent color vanishment of a monitor television set by using the 2nd switch means to select one of signals being the result of one horizontal period delay from a reproduced color signal, adding the signal to a demodulated luminance signal to form a reproduced color video signal. CONSTITUTION:A clock counter 43 has the 1st and 2nd counters CNT1, CNT2 giving an output by several different counts in the inside and one of the outputs of the counters CNT1, CNT2 is selected by the 1st switch 51 in interlocking with the changeover for normal play and trick play mode. The 2nd counter CNT2 connected to the 2nd monostable multivibrator 44 at the trick play has fewer counts than the of the 1st counter CNT1 to give an output at, e.g., '2' counts of the pulses from a ripple detector 37 thereby decreasing the discontinuous part of color and preventing color vanishment.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a PAL color video signal processing device used in a video tape recorder or the like for recording and reproducing PAL color video signals. In particular, for the 8mm video standard, the NTSC system is α11=1. In the PAL system, α11=2 is the standard mode. Therefore PAL
In this method, in trick play modes such as search and still, the phase of the burst signal becomes discontinuous, causing the monitor's color killer circuit to operate, causing color to disappear. The present invention relates to a PAL color video signal processing device that can correct such color fading.

Conventional technology In recent years, processing devices for PAL color video signals have been integrated into integrated circuits.
To reduce costs, a high-performance PAL video tape recorder playback circuit has been realized using only an APC circuit that does not require an AFC circuit.

FIG. 7 shows a conventional PAL color video signal processing device in a video tape recorder playback circuit.

In FIG. 7, a mixed signal of an FM-modulated luminance signal and a carrier color signal in a low frequency band obtained by reproduction from a magnetic tape by the head 1 is supplied to a bypass filter 3 through a reproduction amplifier 2. This is supplied to the FM demodulator 5 via the limiter 4, and the demodulated luminance signal is supplied to the synthesizer 6.

Further, the output signal of the regenerative amplifier 2 is supplied to a low-pass filter to extract a carrier color signal in a low frequency band, and this is supplied to the main frequency converter 9 through an ACC circuit 8.

In this case, the color video signal recorded on the magnetic tape is P
Assume that the subcarrier frequency fL of the AL signal when the frequency is converted to the low frequency band is . However, f) is the horizontal scanning frequency. Then, the signal of the reference subcarrier frequency fS from the reference oscillator 10 is supplied to the side frequency converter 11, while the voltage controlled variable oscillator 12 [hereinafter referred to as ■CO
A signal with a frequency of 375·fu from 172
The signal is supplied to the frequency divider 13 to become a signal of (187+1/2)·fo, which is further divided by 174 by the 174 frequency divider 14 to obtain a signal with a frequency of fL, which is supplied to the side frequency converter 11. As a result, a frequency conversion signal of frequency fg+fL is obtained as the output of the side frequency converter 11. This frequency conversion signal is supplied to the main frequency converter 9, and the carrier color signal in the low frequency band is returned to its original frequency.The carrier color signal returned to its original frequency is demodulated by a synthesizer 6. A reproduced color video signal is obtained at the output terminal 15 by being added to the luminance signal.

A portion of the reproduced carrier color signal output from the frequency converter 9 is supplied to a phase comparator 16. The phase comparator 16 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 17 through the burst gate pulse generation circuit 18. . The output of the phase comparator 16 is supplied to the VCO 12 via a mixer 19, a low-pass filter 20, and a mixer 21 to control the oscillation frequency, and the frequency of the frequency conversion signal supplied to the frequency converter 9. There is. That is, APC (
(automatic phase control) circuit is configured.

By the way, the APC circuit is a phase lock circuit that uses a color burst signal that is an intermittent signal, and in the configuration described so far, if the VCO 12 is an oscillator with a relatively wide frequency variable range, such as an unstable multivibrator, , even if the color burst frequency supplied to the phase comparator 16 is different from the reference subcarrier frequency fs by an integral multiple of fH, there is a phenomenon in which the APC is locked (hereinafter).

This is called a pseudo lock. ) At this time, the oscillation frequency of vC○12 is the normal lock frequency 4X (47-1/8
) f ) The frequency differs from I by an integer multiple of 4·fH.

Therefore, in order to prevent this false lock, the oscillation frequency of the vCO 12 is controlled by providing a feedback loop separate from the APC so that the VCO 12 oscillates near the frequency at normal lock. 22 detects the oscillation frequency of vC012. A frequency detection circuit 23 determines whether the oscillation frequency of VC○12 is the normal lock frequency based on the output of the frequency detection circuit 22, and also determines whether or not the oscillation frequency of VC○12 is the normal lock frequency. A discrimination circuit 24 discriminates whether the frequency is high or low, and 24 is an integrating circuit that integrates the discrimination output. For example, when the oscillation frequency of the VCO 12 is higher than the oscillation frequency during normal locking by 1/2 f 11 or more, a control voltage that lowers the oscillation frequency of the VCO 12 is supplied to the vC○ 12 via the mixer 21. Further, when the oscillation frequency of vC○12 is lower than 1/2 fu, a control voltage that increases the oscillation frequency of VCO12 is supplied to vC○12. Therefore, VCO1
The oscillation frequency of No. 2 is controlled close to the oscillation frequency during normal locking, and false locking does not occur.

With the configuration explained above, pseudo-lock does not occur and A.
The PC circuit will operate stably, but A2
6 circuits operate so that the average phase of the color burst, whose phase changes approximately 90 degrees for each horizontal scan input to the phase comparator 15, and the oscillation signal of the reference oscillator 10 are phase-synchronized. In the steady state, 45
Equivalent to a phase difference of degrees.

Phase errors with different polarities are obtained at the output of the phase comparator 16 for each horizontal scan. The output current of this phase comparator 16 is
Shown in Figure (B). FIG. 8(A) shows a burst signal in the carrier color signal. If the output of the phase comparator 16 is directly supplied to the vCO 12 via the low-pass filter 20, a differential phase phenomenon (hereinafter referred to as DP) will occur, so the configuration described below prevents the occurrence of this DP. There is.

25 is a pulse generation circuit which removes the vertical synchronization signal and equivalent pulses from the output signal of the synchronization separation circuit 17 to obtain a pulse signal (hereinafter referred to as HD signal) having a horizontal scanning frequency that is phase-synchronized with the horizontal synchronization signal; A phase lock circuit that synchronizes the phase with the HD signal, so even if the horizontal synchronization signal is missing due to dropout, the horizontal scanning frequency pulse S
Outputs □ stably. 27 is a 172 frequency divider circuit which divides the frequency of the pulse S1 and outputs a continuous signal having a frequency of 1/2fu. The output signal of the frequency dividing circuit is applied to a switch circuit 28 to obtain a signal S having the same phase or an inverted phase, and is supplied to a current supply circuit 29. The output of the current supply circuit 29 is mixed with the output current of the phase comparator 16 in a mixer 19.

Therefore, with this configuration, the current of the opposite polarity shown in FIG. 8(C) or (D), which differs in polarity for each horizontal scan during the burst period, is combined with the output current of the phase comparator 16. Become. Therefore, the output current of the current supply circuit 29. If is equal to the phase comparison output current of the phase comparator 16 at a 45 degree phase difference, as shown in FIG. 8(C),
When the output current of the current supply circuit 29 has a different polarity from the output current of the phase comparator 16, the output currents of the mixer 19 are canceled as shown in FIG. 8(E). Furthermore, when the output current of the current supply circuit 29 has the same polarity as the output current of the phase comparator 16, the output of the mixer 19 has a different polarity for each horizontal scan as shown in FIG. A current approximately twice the error current will flow.

Incidentally, the frequency components of the output current of the current supply circuit 29 are components of 1/2 fu and odd multiples thereof, and are at a constant level. Therefore, 1/2 fu of the output of the phase comparator 26
It affects the output current of the current supply circuit 29 only for the above frequency components, and does not unlock the A26 circuit. For example, the current shown in FIG. through.

Even if the output voltage becomes as shown in FIG. 8(G), the DP of the carrier color signal only increases.

Therefore, the A26 circuit is always locked, and the output voltage of the low-pass filter 20 is either almost constant and no DP occurs, or there is a large voltage fluctuation every two horizontal scans as shown in FIG. 8(G). Either condition occurs.

So let's take a look at this situation.

The current supply circuit 2 is configured so that no DP occurs at all times.
The configuration is such that the polarity of the output current of No. 9 is controlled.

This consists of a bypass filter 30, a half-wave rectifier circuit 31, a pulse shaping circuit 32, and a counter 33. which outputs from "0" to "1" when counting four pulses shown in FIG.
It consists of a 178 frequency divider 34 and a T-type flip-flop 35, and the polarity of the output current of the phase comparator 16 and the output current of the current supply circuit 29 match, and the output voltage of the low-pass filter 20 is as shown in FIG. As shown in FIG. 9, when a voltage fluctuation of two horizontal scanning periods occurs, this AC component passes through a bypass filter 30, is half-wave rectified by a half-wave rectifier circuit 31, and its output signal is supplied to a pulse shaping circuit 32. te 9th
It is converted into a pulse as shown in the figure. The counter 33 divides the output of the phase lock circuit 26 by 172 and further divides it by 1/1.
It is reset when the signal S2 divided by 6 is 4 "1", and as shown in FIG. 9, when the signal S2 is "0", the counter 33 counts the output signal of the pulse shaping circuit 32, and its output The signal S1 changes from "0" to 0171 as shown in FIG. 9 when four pulses are counted. Therefore, the output signal S4 of the T-type flip-flop 35 to which the output signal S3 of the counter 33 is supplied changes from "O" to "1", and the switch 28 is switched. Therefore, the phase of the output signal S of the switch 28 input to the current supply circuit 29 is reversed as shown in FIG. 9, and the output current of the current supply circuit 29 changes from (D) to (C) shown in FIG. The output current of the phase comparator 16 is canceled out, and the state shifts to a state where DP does not occur.

Furthermore, as shown in FIG. 8(C), when the output current of the current supply circuit 29 has a polarity that cancels out the output current of the phase comparator 16, the output voltage of the low-pass filter 20 is If there is no fluctuation and the output level of the half-wave rectifier circuit 31 is sufficiently large, the pulse shaping circuit 32 cannot generate a pulse. Therefore, in this case, a pulse can be obtained at the output of the pulse shaping circuit 31 as shown in FIG. First, the polarity of the output current of the current supply circuit 29 does not change, that is, the average phase of the color burst and the reference oscillator 1
Control is performed so that the phase comparison error, which differs in polarity in each horizontal scan and occurs due to phase locking of the 0 output signal, is canceled out.

Also, even if the polarity of the output current of the current supply circuit 29 and the AP
Even if the polarities of the phase comparison output currents that make up the C circuit match, the APC loop will not be unlocked, so even if, for example, a color video signal that has been edited with a discontinuous field order is played back, the output will still be output. The carrier frequency of the carrier color signal does not vary greatly, and it is unlikely that the color killer will operate due to the APC circuit becoming unlocked in the television receiver, causing colors to disappear on the screen.

Problems to be Solved by the Invention In the PAL format standard for 8mm video, αo = 2 is the standard mode, and in trick play modes such as search and still, the phase of the burst signal becomes discontinuous and the color killer circuit of the monitor is activated. This causes color fading.

SUMMARY OF THE INVENTION An object of the present invention is to provide a PAL color video signal processing device that compensates for burst discontinuity and prevents color fading on a monitor television even when track jumps are made with the same head during search, still, etc.

Means for Solving the Problems The PAL color video signal processing device of the present invention supplies 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 to a phase comparator. A control loop formed to obtain a phase comparison error signal, control a variable frequency oscillator with a control signal obtained using this phase comparison error signal, and obtain a signal for frequency conversion of the carrier color signal; a signal source that generates a signal whose polarity is inverted, and a detection means for detecting the magnitude of the AC component of the control signal obtained using the phase comparison error signal, is configured to control the polarity of the signal source and mix the output signal of the signal source with the comparison error signal of the phase comparator, and the detection means is configured to include a first detector that counts ripples of the phase comparison error signal during normal reproduction. The polarity of the signal source is controlled by switching and outputting the output of a second counter that counts the ripple during multi-speed playback in which the output of the counter is searched and track jumps with the same head as in stills. The output signal of the second counter is used during multi-speed reproduction to select one of the reproduced color signal and a signal obtained by delaying the reproduced color signal by one horizontal period using the second switch means, and demodulate the luminance. It is characterized in that it is configured to be added to the signal to produce a reproduced color video signal.

Function: According to this configuration, during trick play modes such as search and still, an APC error that occurs when the same head performs a track jump is detected, the detected pulses are counted, and a command signal is issued when the number of error pulses exceeds a certain level. The configuration is such that the IH delay signal and through signal are switched according to this command signal, and the count number during normal playback and the count number during trick play modes such as search and still are set to the first. By setting the second counter separately and setting the count number during trick play mode to be smaller than the count number of APC error detection pulses during normal playback, it is possible to detect APC errors at an early timing. , it is possible to compensate for burst discontinuity and prevent color fading from occurring.

Embodiment Hereinafter, one embodiment of the PAL color video signal processing apparatus of the present invention will be described with reference to the drawings. In addition.

Components having the same functions as those in FIG. 7 are given the same reference numerals.

FIG. 1 is a schematic diagram of an APC system illustrating the present invention. In FIG. 1, 9 is a main frequency converter, 10 is a reference oscillator, 11 is a side frequency converter, 12 is a voltage controlled variable oscillator, 16 is a phase comparator, and 36 is a loop filter. The present invention is a processing device used for reproduction based on the APC system described in the conventional example, in which a color burst outputted to the outside as a video output is compared with the output of a reference crystal oscillator 10 by a phase comparator 16. Its output is VCO12
, and the VCO 12 is used to generate a frequency for frequency conversion of the reproduced color signal. In order to keep the phase error of the output color signal small, the loop filter 36 must be very fast. For PAL signals, the alternating burst phases result in ripples on the APC loop filter, and phase changes in the line are seen as hue changes on the monitor television screen.

FIG. 3 In the DP correction circuit in the processing device of the present invention, the second
Figure (a) shows the error current waveform of the phase comparator 16, and Figure 2 (b) shows the error current waveform of the phase comparator 16.
) is the corrected current waveform of the current supply circuit 29 in Fig. 3, (C)
indicates the voltage at the APC loop filter, the dotted line indicates the slicing level, and signals within the dotted line are not detected. (d) and (C) indicate the output signal of the ripple detector 37 in Fig. 3. .

FIG. 3 shows that the aforementioned ripple can be corrected by current. It is necessary to ensure that the correction current always has the correct phase. This is because the ripple becomes larger when corrected with an opposite phase.

This is achieved by controlling a phase detector 38 for changing the phase of the correction current using a ripple detector 37 when ripple occurs. Ripple detector 3
7 reaches a very stable and precisely defined slicing level, the ripple is detected by a dual comparator directly connected to the loop filter 36, and the exact phase of the correction is adjusted according to the output signal of this ripple detector 37. Ru.

In the search and still case, each change from one track to the next same head (during the presence of the noise bar) is a change in burst phase, depending on the choice of criteria. This is shown in FIG. Rev represents head scanning. Since the PAL chrominance signal switches each line to an alternating conjugate complex, rotating the output phase by 180 degrees is not sufficient and would create a conjugate complex signal again. One way to achieve this is with the aid of an IH delay.
This is to replace the chrominance signal using the signal one line before. The burst phase varies by ±45 degrees depending on the chroma signal imaginary part. As a result, the correction current phase is changed using the switching signal, and the LH delay line is directly turned ON-OFF. During normal play, it is necessary to always turn off the IH delay line and avoid moving the color one line below. Furthermore, since the IH delay line has a narrow band, it is necessary to prevent the normal image quality from deteriorating.

FIG. 5 shows the configuration of the present invention including the above-mentioned contents.

17 is a reproduction signal synchronization separation circuit, 26 is a phase lock circuit, 39 is a 1/2 line first monostable multivibrator, 40 is a 1/2 divider, 41 is a 0 degree/180 degree phase switch, and 42 is a phase lock circuit. A correction current output circuit, 18 a burst gate pulse generation circuit, and 43 a clock counter.

44 is the second monostable multivibrator, 45 is 1/2
Divider 51.46 is the 1st .46 during normal playback and trick playback. The second changeover switch 47 is a one-delay line changeover circuit.

The operation of the embodiment configured in this way will be explained. The refreshed synchronization signal is divided into two with the aid of the phase lock circuit 26 to obtain an alternating current for each line. The output signal of the phase lock circuit 26 comes almost simultaneously with the burst gate pulse of the burst gate pulse circuit 18 and has a jitter component, which provides a noise bar in addition to the skew, so that the phase lock signal is at the point at which the skew continues. can cause incorrect phasing for current correction. For this reason, the first monostable multivibrator 39 phase lock signal is moved to the middle of the next line. The 172 divider 40 provides a phase to the correction current output circuit 42 that is active during burst times during playback and trick play, but not in record mode.

In the case of incorrect phase correction, the ripple detector 37 exhibits an eutoroidal output signal, which is sampled by the burst error selector switch.

Combined with correction phase. As a result, all ripples having other shapes on the loop filter can be effectively removed.

The clock counter 43 internally has first and second counters CNT and CNT that output due to several erroneous counts.
In this Karatan CNT, one of the outputs of the CNT2 is selected by the first switch 51 in conjunction with switching between normal play mode and trick play mode. The first counter CNT□ connected to the second monostable multivibrator 44 during normal play has a higher count than the second counter CNT2, for example,
The pulse from the ripple detector 37 is set to be output at rt 8 +7 counts to prevent hue shifts on the television screen due to malfunctions such as dropouts and skews. However, if a trick play is performed in this state, the response will be slow and the discontinuous portion of color will become long, resulting in a color killer operation and color fading on the television screen. Therefore, a second counter CNT connected to the second monostable multivibrator 44 during trick play,
For example, if the count number is smaller than the first counter CNT, the pulse from the ripple detector 37 is #(
It is set to output at 2It counts to shorten the discontinuous portion of one color and prevent color fading. J, is a reset signal for the clock counter 43, and J2 is a mask signal, which instructs the counting operation to be performed only during the period when the output signal is generated from the first monostable multivibrator 39. The 1/2 divider 45 changes the phase of the correction current, which is supplied to the IH delay line switching circuit 47 via the trick play mode switch 46 to switch the IH delay line ON-OF.
Switch to F. If there are only error pulses due to other forms of ripple on the APC loop, i.e., error pulses due to malfunction, the clock counter 43 is set and counts up between the error pulses, etc. to prevent unnecessary correction phase changes. doesn't happen. The output signal of the clock counter 43 is delayed by a second monostable multivibrator 44, and the output signal of the clock counter 43 is delayed by a second monostable multivibrator 44.
Stops counting about 0 lines. Therefore, it is avoided that switching occurs more than once after the noise bar.

Having explained the detection means for detecting the discontinuity of the burst signal, the IH delay line switching circuit 47 will now be explained with reference to FIG. 48 is a reproduced color signal processing circuit including the above-mentioned APC loop, 52 is an IH delay line circuit 49 is a trick play detection circuit, and 50 is a changeover switch for normal play/trick play and trick play. The color signal from the reproduced color signal processing circuit 48 is supplied to one contact side of the changeover switch 50 and the 1H delay line circuit 52, and the IH delayed signal is supplied to the other contact side of the changeover switch 50.

During normal play, the changeover switch 50 is connected to the one contact side, and during trick play, it is switched to the other contact side by a control voltage from the trick play detection circuit 49.

Effects of the Invention As described above, the PAL color video signal processing device of the present invention can perform variable processing according to the phase comparison error signal between the color burst in the carrier color signal of the PAL color video signal and the oscillation signal of the reference oscillator of the subcarrier frequency. A control loop is formed to control a frequency oscillator to obtain a signal for frequency conversion of the carrier color signal, and a detection means for detecting the magnitude of the alternating current component of the phase comparison error signal is connected to the detection means for detecting the magnitude of the AC component of the phase comparison error signal during normal reproduction. The output of the first counter that counts the ripples and the output of the second counter that counts the ripples during multi-speed playback that jumps tracks with the same head, such as search and still, are switched by the first switch means. The output signal of the detection means is used to control the polarity of a signal source whose polarity is inverted every horizontal scanning period, and the output signal of this signal source is mixed with the comparison error signal of the phase comparator. During reproduction, the output signal of the second counter is used to select either a reproduced color signal or a signal obtained by delaying the reproduced color signal by one horizontal period using a second switch means, and adds the selected signal to the demodulated luminance signal to produce a reproduced color image. Since it is configured to be a signal, in trick play mode, it is possible to quickly detect the error signal of the APC loop, detect discontinuity in the burst signal due to track jump with the same head, and correct the discontinuity in the burst signal. It is possible to obtain an excellent effect of preventing color fading on a monitor TV.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an APC system according to an embodiment of the present invention, and FIG. 2 is a waveform diagram of a DP correction circuit according to an embodiment of the present invention.
FIG. 3 is a block diagram of a DP correction circuit according to an embodiment of the present invention, FIG. 4 is an explanatory diagram of tape pattern scanning in the case of search and still, and FIGS. 5 and 6 are blocks showing an embodiment of the present invention. 7 are block diagrams of a conventional PAL color video signal processing apparatus, and FIGS. 8 and 9 are waveform diagrams illustrating the conventional example. 16... Phase comparator, 36... Loop filter, 3
7... Ripple detector, 39, 44... 1st. 2nd monostable multivibrator, 43... Clock counter, 45... 112 divider, 46... Normal play/trick play switch, 47... IH delay line switching circuit, 48... Regeneration Color signal processing circuit, 50.
... Selector switch [second switch means], 51...
First switch [first switch means], 52...I
H delay line circuit, CNT□, CNT2...1st and 2nd counter agent Yoshihiro Morimoto

Claims (1)

[Claims] 1. A phase comparison error signal was obtained by supplying the color burst in the carrier color signal of the PAL color video signal and the oscillation signal of the reference oscillator at the subcarrier frequency to a phase comparator, and using this phase comparison error signal. a control loop formed to control a variable frequency oscillator with a control signal to obtain a signal for frequency conversion of the carrier color signal, a signal source that generates a signal whose polarity is inverted every horizontal scanning period, and the phase comparison error. A detection means for detecting the magnitude of an alternating current component of a control signal obtained using a signal is provided, the output signal of the detection means is used to control the polarity of the signal source, and the output signal of the signal source is transmitted to the phase comparator. The detecting means is configured to be mixed with the comparison error signal of the phase comparison error signal during normal playback, and the detection means is connected to the output of the first counter that counts ripples in the phase comparison error signal during normal playback. The output of the second counter that counts the ripples is switched and outputted by a first switch means to control the polarity of the signal source, and the output signal of the second counter is configured to control the polarity of the signal source during multi-speed playback. A PAL color video signal configured to use a second switch means to select one of a reproduced color signal and a signal obtained by delaying the reproduced color signal by one horizontal period and add it to the demodulated luminance signal to obtain a reproduced color video signal. Processing equipment.