JP2502613B2 - Time axis error correction device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time axis correction device for reproducing a home video tape recorder (VTR) which records a color signal by frequency converting it into a low frequency band.

2. Description of the Related Art In various recording / reproducing devices such as a VTR or a video disc, a time-axis fluctuation occurs in a reproduced video signal due to a relative speed fluctuation between a signal detection medium and a recording medium. A time axis error correction device (TBC) is used as a method of correcting a reproduced video signal accompanied by such a time axis fluctuation. This time-axis error correction device, for example, used in 3 / 4-inch professional VTRs (see TV Society Journal, Vol. 35, No. 6 (1981) P495, "Magnetic Recording (VII) Time-axis Variation and its Correction Method") ) Is conventionally known.

In the above-mentioned conventional example, the luminance signal component is extracted from the reproduced video signal by the high-pass filter, and the low-pass conversion color signal is extracted by the low-pass filter. The low-pass conversion color signal is frequency-converted by an APC loop phase-synchronized with the synchronization signal from the luminance signal, added to the luminance signal, and then sequentially written in the memory. The write clock is created based on the sync signal of the luminance signal, and the read clock is created by a fixed reference signal generator. Therefore, the reproduced video signal whose time axis is corrected by the write clock and the read clock is output. Further, as an example of a time axis error correction device used for a home VTR, the one disclosed in Japanese Patent Laid-Open No. 61-28289 is known.

In the above-mentioned conventional example, the phase of the clock created based on the horizontal synchronizing signal obtained from the luminance signal is used as a write clock by using a memory that separately stores the luminance signal and the low-frequency conversion color signal separated from the reproduced video signal. , The low-pass conversion color signal is converted according to a timing error between a carrier color signal and a luminance signal, which have been frequency-converted, and the timing of writing to the two memories is controlled by using this phase conversion clock, and further the color signal read from the memories Is subjected to frequency conversion to be returned to the carrier color signal, is then passed through a comb filter to remove adjacent crosstalk, and is added to the luminance signal to output a reproduced video signal whose time axis is corrected.

Problems to be Solved by the Invention In the time axis error correction device as described above, one is complicated and expensive because it is for business use, and in a home VTR, the influence of adjacent crosstalk due to the azimuth recording method is large and sufficient. The accuracy cannot be expected and the comb filter cannot be constructed. On the other hand, although these problems are solved, since the luminance signal component and the chrominance signal component are processed independently, two systems of analog-digital converter, digital, analog converter, memory, etc. are required. Therefore, it is difficult to use for a home VTR because of the cost.

In view of the above point, the present invention provides a circuit configuration that can configure a comb filter that removes the influence of adjacent crosstalk, and that can use an analog-digital converter, a digital-analog converter, a memory, etc. in only one system. The purpose is to provide.

Means for Solving the Problems The time base error correction apparatus of the present invention stores a reproduction head output signal including a low frequency conversion color signal and a reproduction FM signal directly in a memory. A write clock that is controlled to follow the phase of the synchronizing signal that is demodulated and taken out is generated, and the reproducing head output signal converted into a digital signal by the analog-digital converter is written in the memory by the write clock.
The reproduction head output signal read from the memory at a constant read clock by the reference signal generator and converted by the digital-analog converter is separated into the luminance signal and the low-frequency conversion color signal by the separation circuit, and the low-frequency conversion color signal is obtained. After frequency conversion and returning to the specified carrier color signal, this is filtered through a comb filter to remove crosstalk components from adjacent tracks, and synthesized into the above luminance signal to obtain a time-axis corrected reproduced video signal. It is configured.

The present invention is a time axis error correction device having the above-described configuration, in which a reproduced FM signal is FM demodulated and directly stored in a memory with a write clock that phase-follows a sync signal extracted and read with a fixed read clock. Since it is an error correction device, it is possible to perform time axis correction while maintaining the phase-synchronized relationship between the luminance signal in the reproduction head output signal and the low-frequency conversion color signal. The frequency-converted carrier color signal can be passed through a comb filter that removes adjacent crosstalk, and the analog-digital converter, digital-analog converter, and memory can be used for only one system.

Embodiment An embodiment of the present invention will be described with reference to FIG.
The reproduction head output signal reproduced from the reproduction head 1 is amplified by the first stage amplifier 2, and then one is input to the analog-digital converter 3 and the other is input to the high-pass filter 6. The luminance signal component output from the high-pass filter 6 is demodulated by the FM demodulator 7 and then synchronized signal separation circuit 8
The sync signal is separated by. The write clock is generated by the write clock generator 9 which is controlled so as to be phase-locked with the separated sync signal. The digital signal output from the analog-digital converter 3 is written in the memory 4 according to the write clock. A read clock output from the reference signal generator 10 is input to the memory 4, and a digital signal is read from the memory 4 at a constant timing according to the read clock and sent to the digital-analog converter 5. The reproducing head output signal output from the digital-analog converter 5 is input to the high pass filter 11 and the low pass filter 13. The luminance signal component output from the high pass filter 11 is input to the FM demodulation circuit 12 and then output to the adder 16. On the other hand, the low-pass conversion chrominance signal component output from the low-pass filter 13 is converted into a carrier chrominance signal by the frequency converter 14 and input to the comb filter 15, and then added by the adder 16 with the luminance signal to reproduce the video signal. Is output as.

Next, the specific operation of this embodiment will be described in more detail. The frequency range of the playback head output signal is, for example, VH
Since S is about 6 MHz, the sampling frequency in the analog-digital converter 3 needs to be about 12 MHz or more. The write clock is generated by the write clock generation circuit 9 that follows the phase of the sync signal separated by the sync separation circuit 8 from the luminance signal obtained by FM demodulating the reproduced FM signal. Write clock generation circuit 9
For example, a phase locked loop circuit as shown in FIG. 2 can be considered.

The write clock generation circuit shown in FIG. 2 outputs the synchronization signal extracted from the signal separation circuit 8 shown in FIG.
The signal detected by the reference signal generator 21 shown in the figure is input to the phase detector 19 from the input terminal 18 and is phase-shifted by the phase shift circuit 20 into n signals each having a phase difference of 2π / n. Input to device 19. Further, the n signals output from the phase shifter 20 are input to a clock signal selector 22, the phase detector 19 selects a signal having a phase closest to the synchronization signal, and is output from an output terminal 23 as a write clock. .

The write clock generated by the write clock generating circuit as described above is used as the write clock in FIG. Memory 4 whose memory address is reset by the sync signal
Then, the digital signal of the reproducing head output signal converted by the analog-digital converter 3 is written in accordance with the write clock. The read clock output from the reference signal generator 10 does not change with time, and is read from the memory 4 by this clock and converted into a reproducing head output signal by the digital-analog converter 5. Therefore, the time axis of the reproduction head output signal is constant, and the time axis error is corrected. This playback head output signal is a low pass filter
The low-frequency conversion color signal separated in 13 is processed by the frequency converter 14.
Converted to 58MHz carrier color signal, and further comb filter 15
Then, the adjacent crosstalk is removed and output. The playback signal output from the playback head is separated into a luminance signal component by a high-pass filter 11, demodulated by an FM demodulator 12, and then added by the previous carrier color signal by an adder 16 to form a composite playback image without a time axis error. It is output as a signal.

According to this embodiment, since the reproduced carrier color signal can be passed through the comb filter, it is possible to remove crosstalk from the adjacent tracks, and the azimuth recording system for home use can be used.
Even when used in a VTR, time axis correction can be performed with sufficient accuracy. In addition, since the time axis correction is performed with the playback head output signal as it is, only one line of analog-digital converter, digital-analog converter, memory, etc. is required, and the playback head output signal is converted into the luminance signal component and the low-frequency conversion color signal component. Since the time axis correction can be performed before separation, a circuit configuration that does not require an APC loop for color signals is possible.

Next, another embodiment of the present invention will be described with reference to FIG.

The configuration of FIG. 3 differs from the configuration of FIG. 1 in that the signal read from the memory 4 is processed as a digital signal before being passed through the digital-analog converter 5. In the figure, the digital signal read from the memory 4 is separated into a luminance signal component and a low-pass conversion color signal by the digital high-pass filter 24 and the digital low-pass filter 26, and the luminance signal component is demodulated by the digital FM demodulator 25. Output to the adder 29, and the low-frequency conversion color signal component is frequency-converted by the frequency converter 27,
The digital comb filter 28 removes the adjacent crosstalk, and then outputs it to the adder 29. Therefore, at the output of the adder 29, a digital reproduction video signal whose time axis error has been corrected is obtained, and by passing this signal through the digital-analog converter 30, an analog reproduction video signal is obtained.

With the circuit configuration as described above, it becomes possible to collectively perform digital signal processing on the signal processing circuit during reproduction.

Further, another embodiment of the present invention will be described with reference to FIG.

The configuration of FIG. 4 differs from the configuration of FIG. 1 in the case where the signal reproduced from the reproducing head 1 includes FM audio such as 8 mm VTR, and time axis correction including FM audio can be performed. Is. In the figure, the digital signal read from the memory 4 is converted into an analog reproducing head output signal by the digital-analog converter 5, and this analog reproducing head output signal is passed through the band pass filter 31.
The FM demodulator 32 demodulates the FM audio signal by FM demodulation. With the above-described configuration, the FM audio signal can be corrected on the time axis at the same time, and the skew phenomenon due to the switching noise can be eliminated, so that the FM audio with lower distortion can be reproduced. As a matter of course, the above-described configuration can collectively perform digital signal processing as shown in the above-described embodiment.

Still another embodiment of the present invention will be described with reference to FIG.

The difference between the configuration of FIG. 5 and the configuration of FIG. 1 is that the residual time axis error is further reduced by adding an APC loop to the frequency converter 14 that frequency-converts the time-axis corrected low-frequency conversion color signal. It was made.

In the figure, the carrier color signal converted by the frequency converter 14 is passed through the comb filter 15 and the burst gate circuit 34 extracts only the burst signal and inputs it to the APC loop. On the other hand, the reference signal is input to the APC loop from the reference signal generator 10, and the output signal is fed back to the frequency converter 14. By adding the configuration described above, it is possible to correct even higher-speed time-axis error components that cannot be removed by time-axis correction using only the synchronization signal, and it is possible to improve the DP of color signals.

The time-axis error correction device according to the present invention is configured as described above, and is capable of performing time-axis correction with a reproduction head output signal including a low-frequency conversion color signal and a reproduction FM signal. , The carrier color signal separated and converted from the output signal of this reproducing head can be passed through a comb filter to remove crosstalk from adjacent tracks, and the time axis is sufficiently accurate even if it is used in a home VTR of azimuth recording system. Since the correction can be performed and the analog-digital converter, the digital-analog converter, the memory, and the like can be performed by only one system, the time axis correction can be performed at a lower cost with a simpler circuit configuration.

[Brief description of drawings]

FIG. 1 is a block diagram of a time axis error correction apparatus according to one embodiment of the present invention, FIG. 2 is a block diagram of a write clock generator according to one embodiment of the present invention, and FIG. 3 is another embodiment of the present invention. Block diagram of an example time axis error correction device,
FIG. 4 is a block diagram of a time axis error correction device according to another embodiment of the present invention, and FIG. 5 is a block diagram of a time axis error correction device according to another embodiment of the present invention. 1 ... Playback head, 2 ... First stage amplifier, 3 ... Analog-digital converter, 4 ... Memory, 5,30 ... Digital-analog converter, 6,11,24 ... High-pass filter, 7,12,
25, 32 …… FM demodulator, 8 …… Sync signal separation circuit, 9 ……
Write clock generator, 10, 21 ... Reference signal generator, 1
3,26 …… Low-pass filter.

Claims (5)

(57) [Claims] 1. A time-axis error correction apparatus for a reproduced video signal in a video tape recorder for converting a color signal into a low frequency band of a frequency-modulated luminance signal for recording and performing FM demodulation of a reproduced FM signal including a time-axis fluctuation. A means for separating the synchronizing signal, a writing clock generating means controlled so that the phase follows the synchronizing signal, a reading clock generating means for generating a fixed reading clock, and a low frequency conversion according to the writing clock. A means for sampling a reproducing head output signal including a color signal and a reproducing FM signal and writing the same in a memory; a means for reading the reproducing head output signal from the memory in accordance with the read clock; Means for separating into a converted color signal, and color signal frequency conversion for frequency-converting the low-pass converted color signal into a carrier color signal Stage and the time base error correcting apparatus characterized by comprising comprises at least a video signal combining means to said frequency-converted synthesizing the reproduced video signal a carrier chrominance signal into the luminance signal. 2. A reproducing head output signal read by a means for reading a reproducing head output signal from a memory is separated into a luminance signal and a low frequency conversion color signal in a digital signal state, and the luminance signal is digitally FM demodulated. 2. The time according to claim 1, wherein the low-pass conversion color signal is digitally frequency-converted, then added again, and output as an analog reproduction video signal by a digital-analog converter. Axis error correction device. 3. A reproducing head output signal for time axis correction is FM
A means for separating the FM audio signal into a means for separating the reproduction head output signal written in the memory by the write clock and read by the read clock with a signal including an audio signal into a luminance signal and a low frequency conversion color signal. The time axis error correction device according to claim 1, wherein the time axis error correction device is added. 4. A clock obtained by phase-modulating a fixed read clock of the read clock generation means is used as a write clock from the write clock generation means controlled so that the phase follows the signal. The time axis error correction device according to claim 1, wherein 5. A color signal frequency conversion means for frequency-converting a low-pass conversion color signal into a carrier color signal, gates a burst signal of the carrier color signal whose frequency has been converted, and compares the phase with a reference signal from a reference signal generator. The time axis error correction device according to claim 1, wherein the frequency conversion means includes a so-called APC loop that feeds back to the frequency conversion means.