JPS623978Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a slow motion reproduction circuit that synthesizes successive reproduction signals with respect to a horizontal synchronization period.

A video tape recorder configured to obtain a slow-motion reproduced image while reproducing and scanning a recording track a predetermined number of times may perform reproduction scanning across tracks in the middle of scanning. Therefore, unless adjacent tracks record horizontal synchronization signals side by side in the track width direction, the horizontal synchronization period will be disrupted the moment scanning is performed across tracks. Therefore, most conventional devices have performed so-called H-alignment recording in which horizontal synchronizing signals are stored side by side in the width direction of the track. However, many video tape recorders that perform high-density recording due to the demand for long-time recording and playback do not employ the H alignment recording method, and are inevitably subject to disturbances in the horizontal synchronization period during slow-motion playback.

Therefore, in view of the above-mentioned points, the present invention aims to propose a slow motion reproduction circuit that does not disturb the horizontal synchronization period even during slow motion reproduction.

The present invention will be described below with reference to an illustrative embodiment.

In this embodiment, a pair of rotating magnetic heads with different azimuths are used to sequentially record video signals for one field per scan on the same track.
During playback, the recording tracks formed with a difference of 0.75H (H is one horizontal synchronization period) are run at 1/3 the speed of recording, and the tracks recorded by each rotating magnetic head are shifted by 1/3. This is a slow motion playback circuit for a video tape recorder that performs 3x slow motion playback.

FIG. 1 is a diagram schematically showing the relationship between recording scanning traces and reproduction scanning traces, where the horizontal line indicates the center line of the recording scanning trace, and the diagonal line indicates the center line of the reproduction scanning trace, respectively.
The solid line indicates the center line of the scan trace of the A head, and the dotted line indicates the center line of the scan trace of the B head. FIG. 2 is a diagram schematically showing changes in the output level of the reproduction head. Therefore, as is clear from both figures, the first scan SA1 of the A head during reproduction
The first track TA1 of the A head is reproduced by the first scan SB1 of the B head, and the point P is reproduced by the first scan SB1 of the B head.
1st track TB1 of head B in the first half
However, the 0th track (not shown) of the second half B head is reproduced, and the second scan SA2 of the A head is also reproduced.
The first track TA1 of the A head is reproduced, and the second track TA1 of the B head is reproduced by the second scan SB2 of the B head.
The first track TB1 of the head is played, and the following A
By the third scan SA3 of the head, the second track TA2 of the first half of the A head and the first track TA1 of the second half are reproduced from the point q.

Therefore, in this embodiment, the recording track to be reproduced is changed every three scans in the middle of the scan (point p, point q, point r...), and due to the change, the horizontal synchronization period of the reproduction output becomes discontinuous. Become. Since the difference in the horizontal synchronization period is 0.75H for adjacent tracks, the difference in horizontal synchronization period is 1.5H for A track and B track, or 1.5H for each track.
It is 0.5H.

Therefore, in this embodiment, the playback output with continuous horizontal synchronization periods is synthesized by alternately switching and deriving the playback output delayed by 0.5H and the non-delayed playback output at points p, q, r, etc. ing.

Hereinafter, the circuit operation of this embodiment will be explained with reference to the circuit blocks shown in FIG. 3. In this embodiment, the reproduced FM signals alternately reproduced and derived from the A head H _A and the B head H _B are input to the head output switching circuit 3 via the first and second head amplifiers 1 and 2, respectively, to rotate the head. successive reproduction outputs are synthesized and derived by switching pulses associated with
The luminance component of the FM video signal is separated and derived from the low-pass filter 5 as a low-pass converted color signal. The derived FM video signal luminance component is input to the high frequency conversion circuit 7 via the limiter 6, converts the carrier's center frequency from 3.6MHz to 7.2MHz, and relatively halves the ratio of frequency deviation with respect to the center frequency. The signal is input to the first switching circuit 8 and the first delay circuit 9. The luminance component that has been subjected to double high-frequency conversion is
Without damaging frequency characteristics in delay circuit 9
The signal is input to the first switching circuit 8 with a delay of 0.5H. The switching circuit 8 derives a luminance component with a continuous horizontal synchronization period by a switching pulse P derived in synchronization with the time when the rotating magnetic heads H _A and H _B change and scan the recording track, and outputs luminance components that are continuous in the horizontal synchronization period to the demodulation circuit 10 . and derive the luminance signal. The derived luminance signal is amplified by the video amplification circuit 11 and then input to the mixing circuit. On the other hand, the 688KHz low-pass conversion color signal derived from the low-pass filter 5 is input to the ACC circuit 13, where the output level is adjusted, and then input to the next stage frequency conversion circuit 14, where the 3.58MHz High-frequency conversion is performed to a color signal. The derived color signal is inputted to a second switching circuit 16 and a second delay circuit 17 through a 3.58MHz first bandpass filter 15.
The 0.5H delay output and the bandpass filter output derived by the second delay circuit 17 are switched and derived by the second switching circuit 16 based on the switching pulse P, and a continuous color signal with respect to the horizontal synchronization period is synthesized. Furthermore, the output is passed through a comb filter 18 to eliminate the luminance component left in the color signal, and then sent to the next stage rectifier circuit 19 and gain control circuit 22.
is input. The envelope signal input to the rectifier circuit 19 and further derived via the low-pass filter 20 is input to the level comparison circuit 21 which sets a predetermined level, and when the envelope output detects a noise level below the predetermined level, The gain control circuit 22 is closed to prevent noise components that exist alone from being derived. The color signal from which the noise signal existing alone has been blocked is input to the mixing circuit 12, and a video signal including the color signal is derived. On the other hand, the horizontal synchronization signal to be input to the ACC circuit 15 is obtained by inputting the output of the mixing circuit 12 to the horizontal synchronization separation circuit 23, and inputting the horizontal synchronization signal obtained to the third switching circuit 24 and the third delay circuit 25. A switching signal obtained by switching and deriving a horizontal synchronizing signal and a 0.5H delayed horizontal synchronizing signal using a switching pulse P is used.

Also input to the frequency conversion circuit 14
The 4.72MHz signal is transmitted to a balanced modulation circuit 28 by combining the output of the first variable oscillation circuit 26 whose center frequency is 44 times the horizontal synchronization frequency and the output of the second variable oscillation circuit 27 whose center frequency is 3.57MHz. The signal is input to the second band pass filter 29 in the next stage and is synthesized with a signal of 4.27 MHz, which is the addition frequency. The control signal of the first variable oscillation circuit 26 is a reference signal obtained by inputting the first variable oscillation output to a 1/44 frequency divider circuit 30 and a horizontal synchronization separation output (comparison signal). The control signal of the second variable oscillation circuit 27 is the output obtained by inputting the 3.58 MHz oscillation circuit 32 output (reference signal) and the burst output of the burst separation circuit 33 which receives the mixing circuit output as input. (comparison signal)
This is the output obtained by inputting it to the APC detection circuit 34.

It is assumed that the switching pulse P is derived by detecting the attenuation point of the reproduced output, which is also shown in FIG. That is, the switching pulse generation circuit shown in FIGS. 4 and 5 first inputs the continuous reproduced output a to the envelope detection circuit 35 to derive an envelope output, and then derives the envelope output from a section corresponding to a predetermined level or lower. A comparison output b that becomes a low level is derived from the level comparison circuit 36 in the next stage, and a delayed output c that coincides with the track change point in the center of the low level region of the comparison output b is derived from the phase shift circuit 37 in the subsequent stage. , the delayed output is input to a flip-flop circuit 38 to derive a switching pulse P.

As shown in FIGS. 6 and 7, another switching pulse generation circuit for deriving such a switching pulse P delays the control signal d by 1.5 fields in a transfer circuit 39, and outputs the delayed output e. As shown in FIGS. 8 and 9, the AFC phase detection circuit 31 derives the output from a monostable multi-circuit 40 with a metastable period of 3 fields and outputs it as a switching pulse P, as shown in FIGS. 8 and 9. The phase fluctuation detection output is derived through the low-pass filter 41, and only the high-level phase fluctuation detection output derived when the horizontal synchronization period is disturbed by 0.5H is detected by the pulse separation circuit 42, and this output is used for shaping in the next stage. There is a circuit that shapes the waveform in a circuit 43 and then inputs it to a flip-flop circuit 44 to form a switching pulse.

As described above, according to this embodiment, the delayed output and non-delayed output of the video signal are alternately selected and derived at the timing of changing the track during scanning, thereby making the horizontal synchronization period continuous. The synchronization disorder is eliminated, and the effect is great.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between recording scanning traces and reproduction scanning traces, Fig. 2 is a diagram showing changes in reproduction output, Fig. 3 is a block diagram of an implementation circuit of the present invention, and Fig. 4 is a diagram showing the main parts. Circuit block diagram, Figure 5 is an explanatory diagram of the same waveforms, Figure 6
The figure shows another embodiment of the main part circuit block diagram, FIG. 7 shows the same waveform explanatory diagram, FIG. 8 shows still another embodiment of the main part circuit block diagram, and FIG. 9 shows the same waveform explanatory diagram. Explanation of main drawing numbers, 9, 17, 25...delay circuit, 8, 16, 24...switching circuit, P...
...Switching pulse.

Claims (1)

[Claims for Utility Model Registration] On a recording track formed by changing the scanning area by 0.25 (1+2n)H [H is the horizontal synchronization period, n is an integer] in the scanning direction by a pair of rotating magnetic heads with different azimuths. In order to play back at low speed a videotape on which a recording signal formed by frequency multiplexing an FM luminance signal and a low-frequency conversion color signal is recorded, the rotating magnetic head moves the same azimuth recording track during playback scanning during slow motion playback. A switching pulse generation circuit that generates a switching pulse in synchronization with the time of change scanning, a high-frequency conversion circuit that converts the reproduced FM luminance signal into a high-frequency converted luminance signal, and a 0.5H delay for the high-frequency converted luminance signal. a first delay circuit that derives a delayed high-frequency converted luminance signal based on the switching pulse; and a first switching circuit that selects and derives a continuous luminance signal from the delayed high-frequency converted luminance signal and the high-frequency converted luminance signal based on the switching pulse. a demodulation circuit for FM demodulating the output of the first switching circuit; a frequency conversion circuit for frequency converting the reproduced low frequency converted color signal to the reproduced color signal at the original frequency; a second delay circuit for deriving a delayed reproduced color signal; and a second delay circuit for selectively deriving a continuous color signal corresponding to the continuous luminance signal based on the switching pulse from the delayed color signal and the reproduced color signal.
a switching circuit; a horizontal synchronization separation circuit that separates the continuous horizontal synchronization signal from the continuous luminance signal; a third delay circuit that delays the continuous horizontal synchronization signal by 0.5H to derive the delayed synchronization signal; and the delayed synchronization signal. a third switching circuit for selectively deriving the discontinuous horizontal synchronizing signal from the continuous horizontal synchronizing signal based on the switching pulse; A slow motion reproduction circuit consisting of an ACC circuit that controls the level of the converted color signal.