JPH0783464B2 - Rotating head type video signal reproducing device - Google Patents

Description

The present invention relates to a rotary head type video signal reproducing device, and more particularly to a TB
The present invention relates to a combination of C (time base compensation device) and a dropout compensation circuit.

[Outline of Invention]

The present invention compares the phase of a horizontal synchronizing signal in a reproduced video signal with the phase of a reference horizontal synchronizing signal to form a phase error signal and a delay amount of a first analog variable delay circuit, for example, a first CCD delay line. TBC controlled by phase error signal
And a dropout detection circuit that detects a dropout in the reproduction signal and generates a dropout detection signal, and a dropout detection signal is supplied, and a delay amount is controlled by a phase error signal common to TBC. A CCD delay line and a dropout compensation circuit that is supplied with the reproduced video signal output from the first CCD delay line and that uses the dropout detection signal that has passed through the second CCD delay line to compensate for the dropout period. , Equipped with a servo circuit for controlling the rotation of the drum motor by a common phase error signal to remove the time base fluctuation of the reproduced video signal, and to detect the dropout detection signal and the dropout compensation circuit detected from the reproduced signal. The phase of the reproduced video signal supplied is made uniform.

[Conventional technology]

Time-axis fluctuation component (called jitter) in the reproduced signal
As a TBC that removes, a digital memory (RAM) used in combination with a VTR for a broadcasting station is known. However, since TBC using a digital memory has a large scale of hardware and is expensive, a consumer video signal reproducing device, for example, a video disc reproducing device, uses a simple analog variable delay circuit, for example, a CCD delay line. The configuration TBC is being used. In the TBC in the video disc reproducing apparatus, the time of 1H (1 horizontal cycle) is detected from the phase of the burst signal in the reproduced color video signal. The phase of this burst signal is ± 20 (μ
sec] width window.

Rotary head type VTR for consumer use CCD delay line
With the TBC, fine fluctuations due to jitter in the reproduced image can be removed, and therefore the quality of the reproduced image can be improved.

However, the conventional VTR has a drawback that a lot of jitter is included in the reproduced video signal. In the conventional VTR servo circuit, since the drum motor is controlled by the servo error signal detected in the vertical cycle, the reproduced video signal has a very large jitter, for example, a jitter of 60 to 70 (μsec) is reproduced video signal. Was included in.

[Problems to be solved by the invention]

Since the jitter contained in the reproduced video signal of the conventional rotary head type VTR is larger than that of the reproducing apparatus of the video disk, it is not possible to use the TBC in which the allowable range of the time axis fluctuation of the input signal is narrow.

Further, in the method of separately processing the luminance signal and the carrier color signal, there is a problem that the time base fluctuation of the reproduced video signal cannot be detected from a predetermined one wave of the burst signal, unlike the conventional TBC.

Therefore, an object of the present invention is to enable the use of a TBC configured to control the delay amount of an analog variable delay circuit,
It is an object of the present invention to provide a rotary head type video signal reproducing device capable of obtaining a high quality reproduced image from which jitter caused by jitter is removed.

Further, in the conventional VTR, a dropout compensation circuit is provided. In the dropout compensation circuit, the output signal of one horizontal period delay line is embedded in the dropout period. As the dropout compensation circuit, there are a system using a reproduction signal (high frequency signal) and a system using a reproduction video signal after demodulation. In the former case, the switching noise appears as noise in the FM demodulation output, so the latter method is preferable. However, as mentioned above, when TBC is provided, the playback video signal is delayed by TBC, so during dropout compensation, there is a phase shift between the dropout detection signal detected from the playback signal and the playback video signal. ,
There was a problem that the dropout could not be compensated accurately.

Another object of the present invention is to provide a rotary head type video signal reproducing apparatus capable of delaying a dropout detection signal by a phase error signal in a reproduced video signal and accurately performing dropout compensation of the reproduced video signal. It is in.

[Means for solving problems]

The present invention compares the phases of a horizontal synchronizing signal in a reproduced video signal and a reference horizontal synchronizing signal to form a phase error signal, and a delay amount of a first analog variable delay circuit is a phase error signal. Controlled by the time axis compensator for removing the time axis error of the reproduced video signal, the dropout detection circuit for detecting the dropout period in the reproduced signal and generating the dropout detection signal, and the dropout detection signal Is supplied to the second variable delay circuit whose delay amount is controlled by the phase error signal, and the reproduced video signal output from the first variable delay circuit is supplied to the second variable delay circuit.
Rotary head type video signal reproduction provided with a dropout compensation circuit for compensating the dropout period by using the dropout detection signal passed through the variable delay circuit of No. 3, and a servo circuit for controlling the rotation of the drum motor by the phase error signal. It is a device.

[Action]

A phase error between the horizontal synchronizing signal included in the reproduced video signal and the reference horizontal synchronizing signal is detected. This phase error is TBC
Are removed by. The rotation of the drum motor is controlled by the phase error signal, and the time axis error included in the reproduced video signal is sufficiently reduced. Further, the dropout detection signal detected from the reproduction signal is supplied to the second CCD delay line, and the delay amount of the second CCD delay line is changed by the phase error signal for controlling the first CCD delay line of TBC. Controlled.
Therefore, the phase of the reproduced video signal and the dropout detection signal supplied to the dropout compensation circuit provided in the subsequent stage of the TBC can be aligned, and the dropout can be compensated accurately.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. The description of this embodiment will be made in accordance with the following items.

a. Overall configuration bY Comb-shaped filter / dropout compensation circuit c. Modified example a. Overall configuration In FIG. 1, reference numeral 1 indicates a drum motor having, for example, a DC motor configuration. The drum motor 1 rotates at the frame frequency, and the head disk is rotated integrally with the drum motor 1. A pair of rotary heads 2A and 2B are attached to the head disk at angular intervals of 180 °. The extension directions of the gaps of the rotary heads 2A and 2B are made different. The rotary heads 2A and 2B are alternately in contact with the magnetic tape 3 wound around the peripheral surface of the tape guide drum.

Although not shown, a pulse generator that generates a pulse synchronized with the rotation phase of the drum motor 1 is provided, and the detection pulse from this pulse generator is supplied to the speed servo circuit and the phase servo circuit 4. In the speed servo circuit, the cycle of the detection pulse is measured, and a speed error signal corresponding to the deviation between the measured cycle and the reference cycle is generated. The phase servo circuit 4 generates a phase error signal corresponding to the phase difference between the phase of the detection pulse and the servo reference signal. This phase error signal is supplied to one input terminal r of the switch circuit 5. The switch circuit 5 selects the input terminal r during recording and variable speed reproduction, and also selects the input terminal p during normal reproduction. Variable speed playback means slow motion playback operation and high speed playback operation.

Speed error signal from speed servo circuit and switch circuit 5
Is mixed in the mixing amplifier 6 and the output signal of the mixing amplifier 6 is supplied to the drum motor 1 via the driver 7. The speed servo and the phase servo of the drum motor 1 during recording and variable speed reproduction are
It is similar to the VTR servo circuit.

Although the signal reproduced from the magnetic tape 3 by the rotary heads 2A and 2B alternately is not shown, the high pass filter 12, the low pass filter 13 and the dropout detection circuit 14 are passed through the rotary transformer, (not shown) and the reproduction amplifier 11. Is supplied to.
The FM modulated luminance signal is separated by the high pass filter 12,
The low-pass filter 13 separates the low-pass conversion color signal.

The FM modulated luminance signal is FM demodulated by the FM demodulator 15. The reproduced video signal from the FM demodulator 15 is CCD (charge coupled device)
It is supplied to the delay line 16. A clock pulse formed by a VCO (voltage controlled oscillator) 34 is supplied to the CCD delay line 16. The delay amount of the CCD delay line 16 is proportional to the number of stages and inversely proportional to the frequency of the clock pulse. In this example,
The delay amount of the CCD delay line 16 is varied within a range of ± 20 [μsec] centered at 70 [μsec] according to the frequency of the clock pulse from the VCO 34.

The low frequency conversion color signal is supplied to the CCD delay line 17. Further, the dropout detection signal from the dropout detection circuit 14 is supplied to the CCD delay line 18. Dropout detection circuit 1
4 detects a period in which the envelope of the reproduction signal is below a predetermined level as a dropout period.

The reproduced video signal from the CCD delay line 16 is supplied to the equalizer 20 via the buffer circuit 19, and the output signal of the equalizer 20 is supplied to the low pass filter 21. Low pass filter
Reference numeral 21 is provided to remove the clock frequency component and the folding component included in the output signal of the CCD delay line 16, and has a cutoff frequency of 4.5 [MHz] as an example. The equalizer 20 is provided to compensate for the phase shift generated in the low pass filter 21. The video signal from the low-pass filter 21 is passed through the buffer amplifier 22 to Y
It is supplied to the comb filter / dropout compensation circuit 23 and the phase error detection circuit 32.

The Y-comb filter / dropout compensation circuit 23 uses a 1H delay line common to the Y-comb filter and the dropout compensation circuit for removing the crosstalk component in the reproduced luminance signal, as described later. Is. The output signal of the Y comb filter / dropout compensation circuit 23 is supplied to the noise removal circuit 24, and the output signal of the noise removal circuit 24 is supplied to the mixing circuit 25. The reproduction color signals are mixed in the mixing circuit 25, and the reproduction color video signal is obtained at the output terminal 26.

Similarly to the luminance signal, the time-axis-compensated low-frequency converted color signal output from the CCD delay line 17 passes through the buffer circuit 27, the equalizer 28, and the low-pass filter 29, and the frequency converter 3
Supplied to 0. In the frequency converter 30, the carrier frequency is converted into the original value (3.58 MHz) by the carrier signal for conversion formed by the APC circuit. The output signal of the frequency converter 30 is supplied to the C-comb filter 31, and the C-comb filter 31 removes the crosstalk component. C
The reproduction color signal from the comb filter 31 is supplied to the mixing circuit 25 and mixed with the reproduction luminance signal.

The dropout detection signal from the dropout detection circuit 14 is the CCD delay line 18, the buffer circuit 35, and the waveform shaping circuit 36.
Through Y comb filter / dropout compensation circuit 23
Is supplied to. This dropout detection signal is, for example, a signal that becomes high level during the dropout period. The Y comb filter / dropout compensation circuit 23 is
Compensation operation is performed to embed the output signal of the 1H delay line in the dropout period when the dropout detection signal becomes high level.

The CCD delay line 16 to which the reproduction luminance signal is supplied, the CCD delay line 17 to which the reproduction low frequency conversion color signal is supplied, and the CCD delay line 18 to which the dropout detection signal is supplied are equivalent to the clock pulse formed by the VCO 34. Controlled by. The VCO 34 changes the frequency of the output signal according to the phase error signal from the phase error detection circuit 32.

The phase error detection circuit 32 is supplied with the reference luminance synchronizing signal from the terminal 33 together with the reproduction luminance signal from the buffer amplifier 22. The reference horizontal sync signal is supplied from a sync signal generation circuit (not shown). The reference horizontal synchronizing signal and the horizontal synchronizing signal synchronously separated from the reproduction luminance signal are supplied to the phase comparing circuit of the phase error detecting circuit 32. The phase error signal obtained in the phase comparison circuit is supplied to the VCO 34.

At the same time, the phase error signal from the phase error detection circuit 32 is supplied to the input terminal p of the switch circuit 5. Therefore, during reproduction, the phase error signal is supplied to the mixing amplifier 6 as a servo error. In this case, a phase compensation amplifier having a gain characteristic and a phase characteristic for stabilizing the loop of the servo circuit is provided as needed. Thus, during normal reproduction, the phase error signal is used as the phase error signal of the drum motor 1. Therefore, the rotation phase of the drum motor 1 is locked so that the phase of the reproduction horizontal synchronizing signal has a predetermined phase relationship with the reference horizontal synchronizing signal. By this phase servo, the jitter of the reproduced video signal is significantly reduced as compared with the conventional servo circuit.

Since the clock pulse from the VCO 34 is supplied to the CCD delay line 16, the reproduction video signal is delayed by the CCD delay line 16 so that the reproduction horizontal synchronizing signal and the reference horizontal synchronizing signal have a predetermined phase difference. Therefore, the reproduced video signal taken out to the output of the buffer amplifier 22 through the CCD delay line 16 becomes a signal locked to the reference horizontal synchronizing signal, and the jitter in the reproduced video signal is greatly reduced.

A capstan motor for driving the magnetic tape 3 is also provided (not shown). A speed servo circuit and a phase servo circuit are also provided for the capstan motor, and the cycle (or frequency) of the detection signal from the frequency generator is set.
Is measured by the speed servo circuit to form a speed error signal for the capstan motor. Also, during normal reproduction, the servo reference signal and the reproduction control signal are supplied to the phase servo circuit.

The phase error detector 32 is provided with a sync separation circuit for separating the sync signal from the reproduced video signal. The horizontal sync signal separated by sync is delayed by a predetermined amount, and the waveform is shaped to form a gate pulse. Also, input terminal 33
Is supplied to the trapezoidal wave generation circuit via the duty adjustment circuit, and the trapezoidal wave signal from the trapezoidal wave generation circuit is sampled by the gate pulse in the sample hold circuit. Therefore, the output signal (phase error signal) of the sample hold circuit has a level corresponding to the phase difference between the reference horizontal synchronizing signal and the reproduced horizontal synchronizing signal.

bY comb filter / dropout compensation circuit Figure 2 shows the Y comb filter / dropout compensation circuit.
23 shows an example of the configuration. In FIG. 2, the reproduction video signal from the buffer amplifier 22 (see FIG. 1) is supplied to the input terminal indicated by 41. This reproduced video signal is supplied to one input terminal N of the switch circuit 44 via the buffer circuit 42 and the clamp circuit 43.

The switch circuit 44 is controlled by the dropout detection signal from the terminal 36a, the input terminal N is selected in the normal period in which the dropout detection signal is low level, and the dropout detection signal in the dropout period in which the dropout detection signal is high level. , The input terminal D is selected. The CCD delay line 18 gives the dropout detection signal the same delay amount as the reproduced video signal.

The video signal appearing at the output of the switch circuit 44 is supplied to the AM modulator 50, and, for example, a carrier signal of 10.7 [MHz] is modulated by the video signal. The output signal of the AM modulator 50 is supplied to a 1H delay line 51 using a glass delay line, for example. 1H delay line
The output signal of 51 is supplied to the AGC amplifier 52, and the output signal of the AGC amplifier 52 is supplied to the AM detection circuit 53. The detection output of the AM detection circuit 53 is fed back to the AGC amplifier 52 via the hold circuit 54, and the level of the output signal of the 1H delay line 51 is controlled to a predetermined level. The output signal of AM detection circuit 53 is a low-pass filter.
It is supplied to the clamp circuit 56 via 55, and the clamp circuit 56
Is supplied to the input terminal D of the switch circuit 44.

During the dropout period, the switch circuit 44 receives the input terminal D
, The video signal via the 1H delay line 51 is selected,
The dropout period is compensated. The output signal of the switch circuit 44 is supplied to the adder circuit 45, and the output signal of the adder circuit 45 is taken out to the output terminal 46.

The 1H delay line 51 is used both for the above-mentioned dropout compensation and for the Y comb filter. The detected crosstalk component is supplied to the adder circuit 45 in the opposite phase, and the reproduced luminance signal from which the crosstalk is removed is obtained at the output terminal 46.

The output signal of the clamp circuit 43 and the output signal of the clamp circuit 56 are supplied to the limiter amplifier 57. The limiter amplifier 57 has a differential structure for extracting a difference signal between two input signals, and also has a limiter structure for limiting the amplitude of the difference signal. Since the luminance signal has horizontal correlation, the difference signal between the input luminance signal and the signal obtained by delaying the input luminance signal by 1H is a non-correlation signal. This decorrelation signal is regarded as a crosstalk component.

The output signal of the limiter amplifier 57 is supplied to the adder circuit 45 in reverse phase via the low-pass filter 58, the attenuator 59, the limiter amplifier 60, the switch circuit 61, and the attenuator 62. Only the small-amplitude noise component is passed by the limiter amplifiers 57 and 60. Therefore, the crosstalk component is canceled in the adder circuit 45. The switch circuit 61 is
The dropout detection signal is turned off during the high level period, and the operation of the Y-comb filter is prohibited during the dropout period when the video signal disappears. This Y-comb filter is provided after the TBC composed of the CCD delay line 16, and the video signal from which the time-axis fluctuation component has been removed is supplied to the Y-comb filter, so that crosstalk suppression can be performed well. .

Similarly for the C-shaped filter 31 for color signals, CC
The D delay line 17 supplies the color signal from which the time-axis fluctuation component is removed, and crosstalk can be suppressed well.

FIG. 3 is a waveform diagram showing the dropout compensation operation. The dropout detection signal shown in FIG. 3B is formed in the dropout detection circuit 14 from the fluctuation of the envelope of the reproduction signal shown in FIG. 3A. The period Td during which the dropout detection signal is at high level is the dropout period. This dropout detection signal is delayed by Th by the CCD delay line 18, and the dropout detection signal shown in FIG. 3C is Y-comb filter / dropout compensation circuit.
Supplied to 23. The delay amount of the CCD delay line 18 is controlled by the CCD delay lines 16 and 17 to a value such that the time base fluctuation is removed. In FIG. 3, the delay amount is set to the central value 1H (= Th).

The reproduced video signal shown in FIG. 3D is supplied to the input terminal 41 of the Y comb filter / dropout compensation circuit 23. Since this reproduced video signal is delayed by Th by the CCD delay line 16, the delayed dropout detection signal shown in FIG. 3C and the video signal shown in FIG. 3D have the same phase relationship. Have. This video signal is 1H delay line 51
Is delayed for a time Th by the clamp circuit 56.
The video signal shown in FIG. E is obtained.

The switch circuit 44 is controlled by the dropout detection signal shown in FIG. 3C from the input terminal 36a, and selects the delayed video signal from the input terminal D in the dropout period Td. Therefore, as shown in FIG. 3F, an output signal in which the delayed video signal is embedded in the dropout period is obtained from the switch circuit 44.

c. Modified Example In the present invention, a variable delay circuit other than the CCD delay line can be used as the analog variable delay circuit.

Further, not limited to a VTR that records a signal obtained by mixing an FM-modulated luminance signal and a color signal converted to a low-frequency carrier frequency,
The present invention can be applied to a method of FM-modulating a composite color video signal.

〔The invention's effect〕

In the present invention, the phase error signal is formed by comparing the phase of the reproduced horizontal synchronizing signal and the reference horizontal synchronizing signal. The phase error signal controls the delay amount of the TBC CCD delay line and the rotation phase of the drum motor. Therefore, a common phase error detection unit may be provided between the TBC and the servo circuit of the drum motor, and the circuit configuration can be simplified. Further, since the drum motor is phase-locked with the reference horizontal synchronizing signal, the jitter of the reproduced video signal is significantly reduced, and it becomes possible to use a simple TBC using a CCD delay line.

Further, since the dropout detection signal is delayed for a time equal to the delay amount given in the TBC, it is possible to match the phase between the reproduced video signal and the dropout detection signal in the dropout compensating circuit, and the accurate Dropout compensation can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of a Y-comb filter / dropout compensation circuit in an embodiment of the present invention, and FIG. 3 is used for explaining a dropout compensation operation. It is a waveform diagram. Description of main symbols in the drawings 1: Drum motor, 2A, 2B: Rotary head, 4: Phase servo circuit, 14: Dropout detection circuit, 16, 17, 18: CCD delay line, 23: Y comb filter / drop Out compensation circuit, 3
2: Phase error detector, 34: VCO, 44: Switch circuit, 51: 1H
Delay line.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04N 9/89

Claims (1)

[Claims] 1. A circuit for comparing the phases of a horizontal synchronizing signal and a reference horizontal synchronizing signal in a reproduced video signal to form a phase error signal, and a delay amount of a first analog variable delay circuit depends on the phase error signal. A time axis compensator for controlling a time axis error of the reproduced video signal, means for detecting a dropout period in the reproduced signal and generating a dropout detection signal, and the dropout detection signal The second variable delay circuit whose delay amount is controlled by the phase error signal and the reproduced video signal output from the first variable delay circuit are supplied and passed through the second variable delay circuit. A dropout compensating circuit for compensating the dropout period by using the dropout detection signal and a rotation of the drum motor are controlled by the phase error signal. Rotary head type video signal reproducing apparatus characterized by comprising a servo circuit.