JPH0140555B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a helical scan type magnetic recording and reproducing apparatus (hereinafter referred to as VTR) that sequentially records and reproduces color video signals as a recording trajectory inclined with respect to the longitudinal direction of a magnetic tape using a rotating magnetic head. This is especially true for VTRs that have multiple rotating video heads with different azimuth angles.
The horizontal synchronizing signal H in the color video signal is recorded with a predetermined amount of deviation between adjacent tracks of the magnetic tape on which the color video signal is recorded.
A horizontal synchronization signal that occurs when recording is performed without so-called H alignment and is played back at a tape running speed different from that at the time of recording to obtain special playback images such as still images, slow motion, fast motion, and reverse. The automatic frequency control circuit (hereinafter referred to as "automatic frequency control circuit"), which constitutes a part of the time axis fluctuation correction circuit of the reproduced color signal, detects the discontinuous part of the time interval, that is, the part with an error of 0.5H or an odd number multiple thereof. The purpose of this system is to instantly stabilize the time axis fluctuations of the reproduced color signal in the horizontal synchronization signal discontinuous generation section by controlling the variable frequency oscillator of the AFC (referred to as AFC), thereby obtaining a good reproduced image. .

Generally, in order to record a color video signal on a magnetic tape or the like, a VTR uses a method of FM modulating the luminance signal and converting the frequency of the color signal to the lower frequency side. During reproduction, the luminance signal is demodulated and the original frequency signal of the color signal is restored. In this case, the color signal frequency conversion signal may have a constant frequency and therefore a constant phase during recording, but during playback, it is necessary to correct time axis fluctuations in frequency or phase using a synchronization signal in the reproduced color video signal. be. For this reason, conventionally
AFC circuit and color automatic phase control circuit (APC)
In the AFC circuit, the first variable frequency oscillator is controlled by the horizontal synchronization signal obtained by synchronously separating the horizontal synchronization signal included in the reproduced video signal, and the frequency that follows the reproduced horizontal synchronization signal is controlled by the AFC circuit. The APC circuit compares the phase of the reproduced color synchronization signal, that is, the reproduced burst signal, and the color reference oscillator signal, and outputs the comparison output.
controlling the second variable frequency oscillator of the APC circuit;
A signal from the first variable frequency oscillator of the AFC circuit and a signal from the second variable frequency oscillator of the APC circuit are supplied to a frequency converter to obtain a signal for frequency conversion during reproduction. Normally, for the time axis correction range during playback, the APC circuit is in charge of ±90° phase correction of the color signal, and the AFC circuit is used for anything beyond that, and either one of these two circuits is sufficient. If it does not function, stable reproduced color signals will not be obtained. In particular, recording tapes in which the horizontal synchronizing signals H between adjacent tracks on the magnetic tape are not arranged in H order (for example, in the case of FIG. 1, the H deviation amount α between adjacent tracks is set to 0.25) are recorded. In the discontinuous part of the time interval of the horizontal synchronization signal that occurs during so-called special playback, where the tape is played back at a tape running speed different from the current time, the consecutive horizontal synchronization signals are shifted by 0.5H every horizontal synchronization period (referred to as 1H). In other words, a condition of 1.5H occurs,
There is a frequency change of 1:1.5, or about 30%, as the horizontal synchronization frequency, but since the synchronization pull-in range of the AFC circuit is generally about 13%, the pull-in will be defective, and the reproduced color video signal as it is will not be received by the monitor television. When the image was received on a television receiver, significant color jitter occurred, degrading the image quality, or the color killer of the television receiver malfunctioned, resulting in color fading. The present invention solves these drawbacks and provides a means for instantaneously stabilizing the time axis fluctuation of the reproduced color signal at the discontinuous occurrence portion of the horizontal synchronizing signal.

In addition, with the above special playback, 0.5H
However, conventional methods require a horizontal synchronization signal discontinuity detection circuit and a reproduction color video signal skew.
Skew is improved by installing a 0.5H delay circuit and switching between the signal that has passed through the 0.5H delay circuit of the reproduced color video signal and the normal signal that does not, using the signal from the detection circuit in the horizontal synchronization signal discontinuity generation section. are doing. The VTR to which the present invention relates is also based on this method, but since the purpose of the invention is different, it will not be described in detail.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 shows recording track trajectories on a magnetic tape of a helical scanning VTR having two rotating video heads with different azimuth angles. In particular, horizontal synchronization signal positions (marked as Hsync on the drawing) between adjacent tracks are not aligned.
This shows the state in which H is not lined up, and the UHS method is used.
For VTR (VHS is a trademark), in 4-hour recording mode, the drum diameter is 62 mm and the tape running speed is 16.7 mm/s.
This corresponds to the case where an NTSC color video signal is recorded, and in this case, the Hsync deviation amount αH between adjacent tracks is α=0.25. Also, A ₀ and A ₁ are head A
B ₀ and B ₁ indicate tracks recorded by head B having a different azimuth angle from head A.

FIG. 2 shows the scanning locus of the playback video head when the recording track pattern shown in FIG. This figure explains the state in which a discontinuous portion occurs in the time interval (indicated as Hss output in the figure), and at the same time illustrates the output of the horizontal synchronization signal discontinuity detection circuit (indicated as AFC trigger pulse in the figure). A ₀ and A ₁ indicate tracks recorded by video head A,
B ₀ is head B which has a different azimuth angle from head A.
The track recorded by is shown. If we consider the playback scanning trajectory of head A during special playback, as shown by the diagonal lines in the figure, head A does not scan only one recorded track, but scans the adjacent track A ₁ →B ₀ →A ₀ . Scanning is performed so as to straddle adjacent tracks, but the Hsync recorded on tracks A ₁ and A ₀ is reproduced because the azimuth angles are the same between recording and reproduction with playback head A, but the Hsync of track B ₀ is
Hsync is not reproduced because the azimuth angle is different between head A and recording and reproduction. Therefore, Hss output is usually
It is reproduced every 1H, but when head A scans from track A ₁ to A ₀ , just at the point where it straddles track B ₀ , the H deviation between adjacent tracks is 0.25H.
A discontinuity in the time interval of the horizontal synchronization signal occurs, which is a 0.5H shift. As mentioned above, this discontinuity causes a frequency pull-in failure in the AFC circuit that constitutes a part of the color signal time axis fluctuation correction circuit, so this discontinuity is detected and the AFC circuit is forced to pull in the frequency instantly. A control signal is required. At the bottom of FIG. 2, the output pulse (AFC trigger pulse) of the horizontal synchronization signal discontinuity detection circuit, which is this control signal, is shown. Although only the reproducing head A has been described in FIG. 2, it goes without saying that the discontinuous occurrence of the horizontal synchronizing signal can also be explained for the head B by making the azimuth angles for recording and reproducing correspond to each other as described above. FIG. 3 shows a block system diagram of one example of creating the horizontal synchronization signal discontinuity detection circuit. Reference numeral 1 denotes a voltage controlled oscillator having a free-running frequency approximately twice the horizontal synchronizing signal frequency _H , and a synchronizing signal synchronously separated by a synchronizing separation circuit 4 from a reproduced video signal inputted to an input terminal 3 and the voltage controlled oscillator. The phase comparison circuit 2 compares the phase with the output of the oscillator 1 in the phase comparator circuit 2, supplies the voltage according to this phase difference to the voltage controlled oscillator 1, and sets the oscillation frequency _2H of the oscillator 1 to the horizontal synchronizing signal frequency in the reproduced video signal. Lock the phase. The output of the oscillator 1 is divided by the flip-flop circuit 5 to return it to the standard horizontal synchronizing signal frequency _H , and the output Q of the flip-flop circuit 5 with different polarity and the horizontal synchronizing signal separated in synchronization are sent to the first AND circuit. A gate is applied by the gate 6 and the second AND circuit gate 7, and a horizontal synchronization signal is alternately output from the first gate 6 and the second gate 7 every time the horizontal synchronization signal as explained in FIG. 2 occurs discontinuously. It is configured so that This output triggers the next flip-flop circuit 8,
The output of the flip-flop circuit 8 alternately outputs high and low levels every time a discontinuous portion occurs. The next differentiating circuit 9 is configured to generate a pulse every time the output level of the flip-flop circuit 8 switches, and the horizontal synchronizing signal discontinuity detection circuit output shown in FIG. 2 is obtained at the output terminal 10. be able to.

FIG. 4 is a block system diagram showing a configuration including peripheral parts of a color signal time axis fluctuation correction circuit using the present invention. The luminance signal in the color video signal reproduced by the video head 11 is sent to the FM demodulator 1.
2. The horizontal synchronization signal is extracted by the synchronization separation circuit 13 and supplied to the AFC detection circuit 14 of the AFC circuit. In the AFC circuit, a signal obtained by dividing the output of the first variable frequency oscillator 15 to 1/160 by a 1/4 frequency dividing circuit 16 and a 1/40 frequency dividing circuit 17 is sent to an AFC detection circuit 14.
The frequency difference with the previously reproduced horizontal synchronizing signal is detected and compared, and a voltage corresponding to the comparison output is supplied to the first variable frequency oscillator 15, and the voltage is supplied to the first variable frequency oscillator 15. The frequency applied from 16 to the color signal frequency conversion signal generator 18 is 40 times the frequency that follows the horizontal synchronizing signal frequency. At the same time, in the present invention, 0.5H of horizontal synchronization signal
In order to prevent synchronization failure of the AFC circuit at the discontinuity generating portion, the oscillation frequency of the variable frequency oscillator 15 may be controlled by the output of the horizontal synchronization signal discontinuity detection circuit 19 explained in FIG. Make it possible. Generally, it is sufficient to vary the control range of the oscillation frequency by about 20% based on the capabilities of current AFC circuits. On the other hand, in the APC circuit, a reproduced burst signal extracted by a burst gate circuit 21 from a frequency converter 20 of a color signal subjected to low frequency conversion is supplied to an APC detection circuit 22. And this
The phase of the burst signal and the signal from the color reference oscillator 23 are compared in the APC detection circuit 22, and a voltage corresponding to the phase difference is applied to the second variable frequency oscillator 24, so that the phase of the oscillation frequency of the variable frequency oscillator is color-coded. The phase of the oscillation frequency of the reference oscillator 23 is made to follow. Then, the output signal synchronized with the reproduction burst signal of this variable frequency oscillator 24 is
In addition to the frequency conversion signal generator 18, the AFC
By balanced modulation with the signal from the circuit, 2
It is configured to create a sum of the frequencies of two signals and apply this to the frequency converter 20 as a frequency converted signal.

FIG. 5 shows an embodiment in which the oscillation frequency of the variable frequency oscillation circuit of the AFC circuit is controlled by the output pulse of the horizontal synchronization signal discontinuity detection circuit of the present invention. The current of the constant current source 26, which is controlled by the error voltage of the AFC detection circuit, flows to GND through the resistor R while charging the capacitor C, but the voltage at point a rises and reaches the level of _E1 . Then, due to the operation of the Schmidt circuit 27, the switch 2
9 is closed, and the charging voltage of capacitor C is constant current source 2.
8 and discharged to GND. When the voltage at point a drops to the level of _E2 , the Schmitt circuit 27 operates again to open the switch 29, and the capacitor C is charged by the current from the constant current source 26, and the above operation is repeated to oscillate. do. The oscillation frequency is approximately expressed as =/2C(V ₀ −2IR) (V ₀ =E ₁ −E ₂ ). In FIG. 5, when the oscillation frequency of the oscillator is determined, the resistor R, which is one of the constants, is switched by the transistor 30 using the output of the horizontal synchronization signal discontinuity detector 19, thereby oscillating the variable frequency oscillator according to the present invention. An example of a frequency control method is shown. That is, to be more detailed,
In Fig. 5, block 25 is the AFC of Fig. 4.
This is a filter block located at a portion connecting the detection circuit 14 and the variable frequency oscillator 15. For example, in the part where the AFC trigger pulse is generated in Figure 2, due to the discontinuity of H, the output of the AFC detection circuit 14, that is, point a in Figure 5, tends to output a large error signal, but the CR time constant It only responds. Therefore, as a result, the variable frequency oscillator 15 transmits the discontinuous detection pulses from the discontinuity detection circuit 19 to the transistor 3.
0, turns on the transistor 30, rapidly charges the capacitor, and increases the potential at point a from the solid line to the dotted line as shown in Figure 6, causing the discontinuity of H. Immediately realizes a change in the oscillation frequency of the variable frequency oscillator 15 according to the
This is intended to perform AFC operation. As other control examples, the present invention can of course be implemented by controlling the bias voltage of the terminal 25, the capacitance value of the capacitor C, the values of E ₁ and E ₂ , the trigger level of the Schmitt circuit 27, etc. is omitted.

As described above, the present invention can record still images, slow motion, fast motion, and
A circuit is installed to detect large time axis fluctuations in the reproduced color signal that occur during special reproduction such as reverse, as well as discontinuities in the time interval of the horizontal synchronization signal, and this output controls the variable frequency oscillator of the color AF circuit. This is an extremely simple structure that instantly improves the defects in the discontinuous portion of the horizontal synchronizing signal, and is highly effective.

[Brief explanation of drawings]

Fig. 1 is a diagram schematically showing the track locus of the non-H and recording magnetic tape of a helical scanning VTR having multiple rotating video heads, and Fig. 2 is a special reproduction of the recording track shown in Fig. 1. FIG. 3 is a block diagram showing one embodiment of the horizontal synchronization signal discontinuity detection circuit used in the present invention, and FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 5 is a block diagram showing the main structure of an embodiment of the present invention, and FIG. 6 is a waveform diagram for explaining the same operation. 1... _H voltage controlled oscillator, 2... Phase comparator,
4... Synchronous separation circuit, 5... Flip-flop circuit, 6... Gate, 7... Gate, 8... Flip-flop circuit, 9... Differential circuit, 11...
Video head, 12...FM demodulator, 13...Sync separation circuit, 14...AFC detection circuit, 15...
Variable frequency oscillator, 16...1/4 frequency divider circuit, 17
...1/40 frequency dividing circuit, 18... Frequency conversion signal generator, 19... Horizontal synchronization signal discontinuity detection circuit, 20
... Frequency converter, 21 ... Burst gate circuit, 22 ... APC detection circuit, 23 ... Color reference oscillator, 24 ... Variable frequency oscillator, 26,
28...constant current source, 27...Schmitt circuit, 2
9...Switch, 30...Transistor, C...
Capacitor, R...resistance.

Claims (1)

[Claims] 1 A variable frequency oscillator is synchronously driven by a horizontal synchronizing signal separated from the reproduced color video signal, and a signal related to the output of the oscillator is used to detect the time axis fluctuation component of the reproduced color signal in the reproduced color video signal. In a magnetic recording/playback device for correcting the horizontal synchronization signal, the horizontal synchronization signal discontinuity detection circuit generates a detection pulse at a portion where the time interval of the reproduction horizontal synchronization signal is discontinuous, and instantaneously changes the oscillation frequency of the oscillator by the detection pulse. A magnetic recording and reproducing device characterized by comprising: