JPS6244470B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to provide an FM recording method and a playback device thereof, which are devised so as to be able to accurately detect the synchronous leading edge and/or trailing edge positions of FM recorded video signals. It is something.

When a video signal is recorded on a recording medium such as a tape or a disk and played back and displayed on a television receiver, jitter due to time axis errors may be observed on the screen. Various methods have been used to solve this problem, but in any case, it is necessary to accurately know the time axis error of the reproduced video signal. Conventionally, the time axis error was known from the horizontal synchronization signal of the demodulated video signal, but in addition to the required time axis error, this included fluctuations due to carrier time fluctuations, making the accuracy less accurate. It had some disadvantages. For example, if the reproduced FM signal is sent to a discrimination circuit to detect the change in frequency of the frequency modulated wave from the black level to the sync tip or vice versa, the position (phase) of the change will be at the frequency equivalent to the black level. Alternatively, it may fluctuate by a time corresponding to the reciprocal of the synchronization tip equivalent frequency. To alleviate this, in a TED video disk system with a low carrier frequency, for example, the FM carrier is stopped after each horizontal blanking, and then the FM carrier is oscillated in synchronization with a new horizontal synchronization signal ( See Figure 7. Note that T _p is the carrier oscillation stop period). In this case, the phase difference between the zero-crossing point of the FM carrier (which is P in Figure 7, which is the intersection point of the carrier and the level of DC O) and the frequency change point corresponding to the front and trailing edges of the horizontal synchronization signal is constant. However, since the difference is not zero, if a logic circuit is used to discriminate between the leading and trailing edges, the error due to the phase difference will not be sufficiently eliminated.

The present invention aims to provide a new FM recording method and a reproducing device thereof suitable for detecting accurate time axis fluctuations that do not include carrier time fluctuations. That is, in the present application, in order to stop the carrier for each horizontal blanking and synchronize with a new horizontal synchronization signal to oscillate the FM carrier,
At a fixed point of each horizontal sync signal, that is, in this application, when frequency modulating a carrier with a composite video signal, the carrier is reset at a fixed point of each horizontal sync signal. The invention of a method for recording the modulated signal on a medium so that the change in carrier frequency corresponding to the position coincides with the zero crossing point of the frequency modulated wave, and the invention of a method for reproducing the modulated signal recorded by this method and reproducing the reproduced signal. It is an object of the present invention to provide two inventions: a video signal reproducing device in which a pulse corresponding to the transition point is extracted based on the zero crossing point, and the extracted pulse is used as a jitter detection signal for a recording/reproducing system.

First, the first invention will be explained. This refers to the leading edge and/or trailing edge of the horizontal synchronizing signal (as shown in Figure 8, when the size of the synchronizing signal part is 100, the point approaching the black level by 50 from the synchronizing tip is referred to as the leading edge). The main point of this method is to match the transition point of the carrier frequency corresponding to the position of the leading edge of the horizontal synchronizing signal with the zero crossing point of the frequency modulated wave. (b) A method of aligning the transition point of the carrier frequency corresponding to the position with the zero-crossing point of the frequency modulated wave; (b) A method of aligning the transition point of the horizontal synchronization signal corresponding to the trailing edge with the zero-crossing point; (c) There is a method of making each transition point coincide with the zero crossing point. In order to realize the method (a) above, the interval between the reset position (fixed point) and the leading edge of the horizontal synchronization signal, which is reset at a fixed point immediately before each horizontal synchronization signal, is τ _B , the carrier frequency is _B during that period, and n Let be a positive integer, and _B and τ _B should be selected so as to satisfy 1/2・1/ _B・n=τ _B …….

In order to realize the method (c) above, in addition to the conditions related to (b) above, it is necessary to set the pulse width of the horizontal synchronization signal to τ _S
Let _S be the carrier frequency during that period, and furthermore, let m be a positive integer, and _S and τ _S should be selected so as to satisfy 1/2・1/ _S・m=τ _S .

Furthermore, in order to realize the method ( _b ) above, it is not necessary to align the transition point of the frequency corresponding to the leading edge of the horizontal synchronization signal with _the zero _- crossing _point ; It is only necessary to make only the transition point of the frequency corresponding to the edge coincide with the zero crossing point.

The above description is based on an ideal case in which the change from the pedestal level to the horizontal synchronization tip level is considered to occur at time zero. In reality, this change requires a finite amount of time, so using the formula it is not possible to exactly match the change in frequency corresponding to the front and trailing edges with the zero crossing point.

Strictly speaking, it can be considered as follows.
In the TED method, the frequency corresponding to the black level is 3.2M
Hz and the frequency corresponding to the sync tip is 2.8MHz
It is. In FIG. 9, it is assumed that the time required to change from the black level to the synchronization tip is T, and that this change occurs linearly. Then, if time t=0 at the leading edge, the period -τ _B ~-a
is a 3.2MKz signal, and the frequency modulation signal E ₁ is E ₁ =Asim2π _B t... On the other hand, during period -a to a, assuming that the waveform can be expressed as V(t), E ₂ =Asim {2πct÷2πm
[∫V(t)dt] ^t _−a +θ}... Here, _C is the center frequency of the carrier, and m is the modulation index. At t=-a, _E1 = _E2 .

Then, when t=0, if θ+2πm[∫V(t)dt] ⁰ _−a =0..., the frequency modulation signal can be set to zero cross when t=0.

In other words, if _B is determined first, the leading edge can be made to coincide with the zero crossing point by changing τ _B. Also, the above (b) and (c) can be considered in the same way.

Next, the second invention will be explained. The recording method is the method (c) above, and an embodiment in which the trailing edge is extracted will be described.

FIG. 1 is a block diagram showing the main structure of the present invention. This will be explained below with reference to FIG. 2 (schematically shown) showing waveforms at various parts in the same figure. Playback signal a extracted by pick-up 1
is supplied to an FM demodulation circuit 4 and a gate circuit 5 via a preamplifier 2 and a limiter 3. The FM demodulation circuit output b (N is the noise generated corresponding to the carrier stop period To) is transmitted from the terminal 6 to the video signal processing circuit (not shown), while being applied to the synchronization separation circuit 7. The output horizontal synchronization signal is input to a flywheel oscillator 8, and a control signal c for controlling the gate circuit is derived as its output. The signal d taken out from the gate circuit under this control signal is provided to the synchronization position detection circuit 9. As an output, a detection signal delayed by a certain period of time from the trailing edge of the horizontal synchronization signal can be obtained.

FIG. 3 shows a specific example of this detection circuit. In the same figure, 10 is an IC (product number)
SN74123N) is a monostable multivibrator, and 11 is also an IC (product number SN7474N).
It is a flip-flop using Monostable multivibrator 10 includes resistor 12 and capacitor 13
The metastable time τ is 1/2 _B < τ < 1/2 _S
4a corresponding to the signal in FIG. 2d (according to the synchronization signal shown in FIG. 4, the frequency _S corresponding to the synchronization tip to the frequency _B corresponding to the black level Between ₁ , ₂ , ₃ ,
₄ and ₅ , the frequency gradually increases. For the sake of explanation, this is
A gated FM carrier as shown in FIG.
The flip-flop 11 which introduces the output signal from this monostable multivibrator into the D terminal, the FM carrier into the CK terminal, and the control signal (Fig. 2c) into the reset terminal has a truth value shown in Fig. 5. As is clear from the diagram showing the horizontal synchronizing signal, the terminal output is inverted as shown in FIG. This output signal is delayed by a certain period of time from the zero-crossing point of the reproduced FM carrier, which corresponds to the frequency change point corresponding to the trailing edge of the horizontal synchronization signal. It contains only the fluctuations of the video signal, without any accents or the like. Therefore, the jitter detected from this output signal completely matches the jitter contained in the video signal.

Note that the circuit shown in FIG. 3 can also be used when extracting the leading edge of the synchronization signal. In this case, the signal corresponding to the above control signal must be a pulse that includes the vicinity of the leading edge, and the input to this detection circuit is an inverted version of the FM carrier, and the flip-flop clear and reset terminals are By appropriately selecting the signal to be supplied to the flip-flop, it is possible to operate this flip-flop as shown in the diagram showing the truth value shown in Figure 6. It can be reversed to positive at a position delayed by a certain period of time, and this can be used as a detection signal.

As described above, the present invention provides a method for frequency modulating a carrier, which is reset at a fixed point immediately before each horizontal synchronizing signal, with a composite video signal. Since the transition point coincides with the zero-crossing point of the frequency modulated wave and it is recorded, the recorded signal is reproduced, the pulse corresponding to the transition point is extracted based on the zero-crossing point, and the jitter is detected. The jitter detection signal contains only the time fluctuation of the video signal that existed in the recording and reproducing system, without any time fluctuation or waveform distortion caused by FM modulation and demodulation. Therefore, jitter compensation can be performed accurately.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main structure of a regenerator according to the present invention. FIG. 2 is a waveform diagram of each part. FIG. 3 shows a specific example of the synchronous position detection circuit. FIG. 4 is a waveform diagram of each part. Figures 5 and 6 are diagrams showing the truth of flip-flops. Also, Fig. 7 is a waveform diagram showing the carrier, and Fig. 8 is a waveform diagram showing the carrier.
The figure is a waveform diagram showing a horizontal synchronization signal. FIG. 9 is a waveform diagram for explaining frequency changes. 9... Synchronous position detection circuit, 10... Monostable multivibrator, 11... Flip-flop.

Claims (1)

[Claims] 1. When frequency modulating a carrier that is reset at a fixed point immediately before each horizontal synchronization signal with a composite video signal, a change in the carrier frequency corresponding to a specific position of the horizontal synchronization signal is a frequency modulation wave. A method in which the modulated signal is recorded on the medium so that it coincides with the zero-crossing point of the modulated signal. 2. The coincidence between the transition point of the carrier frequency corresponding to the position of the leading edge of the horizontal synchronization signal and the zero-crossing point of the frequency modulated wave is determined by the interval between the fixed point and the leading edge being τ _B , and the carrier frequency during that period _{being B.} year,
Furthermore, the first claim obtained by setting n to a positive integer and satisfying 1/2・1/ _B・n=τ _B
FM recording method described in section. 3. The coincidence between the transition point of the carrier frequency corresponding to the position of the trailing edge of the horizontal synchronization signal and the zero-crossing point of the frequency modulated wave is defined by the pulse width of the horizontal synchronization signal being τ _S , the carrier frequency during that period being _S ,
Furthermore, the second claim obtained by setting m as a positive integer and satisfying 1/2・1/ _S・m=τ _S
FM recording method described in section.