JPS6349974Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is a playback circuit for a VTR (video tape recorder). In particular, tapes with a recording system in which a guard band and a recording section for signals in other modulation modes such as PCM audio signals are formed between video RF signal recording sections are played back using a playback device capable of low-speed playback, etc. This relates to a circuit for doing so.

In general, VTR recording systems are broadly divided into those in which a guard band (non-recording band) is formed between the video RF signal recording sections and those in which a guard band (non-recording band) is formed between the video RF signal recording sections. P.C.M.
In cases where a recording section is formed using a modulation mode other than video, such as recording, video is recorded in a biased manner on the tape surface T by recording heads (not shown) with different azimuth angles, as shown in Figure 1.
Between the RF signal bands SL and SR, a guard band G is formed to improve the separation of the recording bands WL and WR, which are recorded in a biased manner on the tape surface T by a recording head (not shown), and other signals. ing. A tape recorded using this method can be played back at low speed, fast forward playback A, or rewind playback B.
Then, the trace band V of the playback head (not shown) crosses the video RF signal band diagonally, passing through the recording bands WL, WR and guard band G, and is not played back from the playback head. The recording bands WL, WR and guard band G, which have no meaning as a video signal, are output as a noise component N together with the video RF signal. This noise component N is outputted to a video device or the like through a reproduction circuit, and is a major inconvenience as it causes a significant deterioration of the reproduced image quality.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the conventional method, and to prevent the above-mentioned conventional method even when playing back a tape with a guard band and a recording section of signals by other modulation modes formed between video RF signals at low speed. It is an object of the present invention to provide a reproduction circuit for a VTR which can obtain good reproduction image quality without outputting noise.

Embodiments of the present invention will be described below with reference to FIGS. 2 to 4.

In the figure, reference numeral 1 denotes a detection circuit for detecting the presence or absence of a video RF signal from a reproduction head (not shown) and a recording signal in another modulation mode.

Reference numeral 2 denotes a sample-and-hold circuit which outputs a voltage corresponding to the frequency of the horizontal synchronizing signal separated from the demodulated video signal. 3
is a VCO that is controlled by the output voltage from the sample-and-hold circuit 2 and generates a pseudo horizontal synchronization signal.

Reference numeral 4 denotes a switching circuit that changes the operating state of the sample and hold circuit 2 into a closed loop using the video RF signal from the detection circuit 1 or a signal with a recording signal in another modulation mode. The sample-and-hold circuit 2 is put into an open loop by the video RF signal from the RF signal and the signal without recording signal due to other modulation modes.
They are now working properly.

Reference numeral 5 denotes a pseudo decoupling synchronization signal generation circuit and a clamp circuit, in which the playback head is connected to the video RF when the sample-and-hold circuit 2 is in open-loop operation.
It includes a pseudo-decoupled synchronization signal for the scanning period that scans the guard band part G between the signals, and clamps the video output level to a constant level.

6 is a switching circuit configured to time-divisionally select and output the signal from the clamp circuit and the video demodulated signal. Reference numeral 7 denotes a control circuit, which is provided between the switching circuit 6 and the detection circuit 1, and controls the operating timing of the switching circuit according to a playback mode such as fast-forward playback or rewind playback. I'm starting to do that.

Part 3 regarding the operation example of the reproducing circuit configured as above.
To explain based on the figure, first, a video RF signal RF as shown in I is input from the input section VIN of the detection circuit 1.
The detection circuit 1 detects the video RF signal RF and the recording signal W, and outputs these signals RF as shown in J. A switching pulse J that repeats ON and OFF in synchronization with , W is output. On the other hand, input HIN of sample and hold circuit 2
A horizontal synchronization signal from a horizontal synchronization signal separation circuit (not shown) is input from the horizontal synchronization signal separation circuit (not shown), but the horizontal synchronization signal is a video RF signal RF and a recording signal W by PCM.
Since it is included only in guard band G and not included in guard band G, the horizontal synchronizing signal is missing as shown in K. Sample-and-hold circuit 2 supplements this missing part, and the video RF
A PLL (phase-locked loop) consisting of a sample-and-hold circuit 2 and a VCO 3 is operated in a closed loop only in the time domain where the signal RF or the recording signal W exists, and the timing of the horizontal synchronization signal is sampled. In the time period where neither the RF nor the recording signal W exists, that is, the time period during which the guard band is scanned, the above PLL is operated in an open loop and a pseudo horizontal synchronization signal is outputted according to the already sampled timing. It works to fill in the missing parts mentioned above. Therefore, the horizontal synchronization signal has the regular timing as shown in M,
The signal is input to a decoding synchronization signal generation circuit and a clamp circuit 5 at the next stage. In the decoding synchronization signal generation circuit, M
The mono multivibrator is triggered by the pulse to obtain a horizontal synchronization signal, and the time constant of the mono multivibrator is changed by the control signal of the drum servo system to obtain a vertical synchronization signal. The outputs from the decoding synchronization signal generation circuit and the clamp circuit 5 include regular horizontal and vertical synchronization signals, and the output level thereof is set to correspond to the vicinity of the gray level in image brightness. The switching circuit 6 selects and outputs the pseudo video signal P from the clamp circuit 5 and the video demodulated output signal in the signal shown in A in a time-sharing manner, but the timing of its operation is delicate and the playback It varies depending on the mode.
For example, in fast-forward playback (Figure 1A), recording bands WL and WR are located behind the video RF signal bands SL and SR, respectively, while in fast-reverse playback (Figure 1B), the video RF signal bands are located behind the video RF signal bands SL and SR. Recording band on the front side of SL and SR
WR and WL are located respectively, and the above-mentioned recording band WL and WR signals are the signals that should be erased, but the detection circuit 1
Since the recording bands WL and WR are detected in the same way as video RF signals, it is necessary to detect the presence or absence of the recording bands WL and WR, as well as their generation positions, and to control the switching circuit 7 appropriately. Therefore, the control circuit 8 controls the pulse width of the switching pulse inputted from the detection circuit using the control signal C from the reproduction mode switching section (not shown), and outputs the control signal U.
By controlling the switching circuit 6 according to We are making adjustments.

In the embodiment, the control circuit 7 has a configuration as shown in FIG. 4, where MV ₁ and MV ₂ are mono multivibrators, A ₁ and A ₂ are AND gates N ₁ and N ₂ are NAND gates, IV ₁ and IV ₂ represent inverters, respectively, and MV ₁ and MV ₂ are designed so that when an input signal is applied, the output is inverted for a certain period of time, and the phase of the output relative to the input is Q. There is.

Here, examples of its operation are stop generation, rewind play,
To explain each fast-forward playback mode, first, in stop playback, the recording signal W is placed at the front of the video RF signal.
exists, it is necessary to delay switch _S3 to turn it on. In this case, the signal input from the detection circuit 1 is at a high level (hereinafter abbreviated as H), the signal input terminal RW is at a low level (hereinafter abbreviated as L) which becomes H only during rewind playback, and becomes H only during fast forward playback. Since the signal input end FF becomes L, switch _S1 turns off and the mono multivibrator
The operating time constant of MV ₁ is determined by variable resistor VR ₁ , and the signal pull and the output of MV ₁ are AND gated.
Multiplied by A ₂ yields an output that truncates the front of the signal. Therefore, from the output 32 of the NAND gate _N3 , the video RF signal from the detection circuit 1 is output.
A signal that becomes H is output only in a time range where the signal exists.

Therefore, the switch _S3 is turned on and the demodulated video signal A is output from the input section IN to the output section OUT, and in the time period when no video RF signal is present, the switch _S3 is turned on by the inverter _IV2 . The switching _S2 , which operates in phase, is turned on, and the pseudo video signal P is output to the output section OUT.

Next, in rewind playback, the signal input terminal RW
only becomes H, switch _S1 is turned on, and variable resistors _VR1 and _VR2 are connected in parallel. The operating time constant of the mono multi-vibrator MV ₁ is determined by the variable resistor VR ₂ , but this is because the relative speed between the tape and the playback head is different between stop playback and rewind playback. The aim is to fine-tune the operating time constant of the vibrator MV ₁ to correspond to each.

Therefore, the output section 32 outputs a control signal suitable for rewind playback.

Next, during fast-forward playback, only the signal input terminal FF becomes H, and one input 3 of the NAND gate _N1
The levels of one input 34 of NAND gate N2 and NAND gate _N2 are inverted and become H and L, respectively. Therefore, the output from the mono multivibrator MV ₁ is blocked by the NAND gate N ₂ , and the mono multivibrator MV ₂ causes the output section 32 to rise simultaneously with the detection signal from the detection circuit 1 and fall quickly. A signal is output. Therefore, the recording signal W present at the rear of the video RF signal is not output to the output section OUT, but is replaced by the above-mentioned pseudo video signal P.

As mentioned above, the output section OUT of the switching circuit 6 receives only the video demodulated output signal A in the input signal shown in A during the time range where the video RF signal RF exists, and also during the time when the video RF signal RF does not exist. In other words, the video signal P is output in each of the time regions where the noise component N exists, and a waveform shown in X is obtained. Therefore, no noise components are output to the output section OUT, and the video RF signal RF
In between, the image signal P near the gray level, which has no risk of adversely affecting the image quality, is supplemented, so an image with no deterioration in image quality can be obtained. In addition, since the predetermined decoding synchronization is obtained as described above, image distortion cannot occur.

According to the VTR playback circuit according to the present invention, a VTR tape including a video RF signal recording section, a recording section based on another modulation mode, and a guard band section is played back by a playback device capable of low-speed playback, etc. Even in the case of You can get the image. Furthermore, by controlling the operation timing of the switching circuit according to the reproduction mode, uniform characteristics can be obtained in both forward and reverse reproduction.

[Brief explanation of drawings]

Figure 1 is a plan view showing the distribution of recording bands on a recording tape, and Figures 2 to 4 are related to the present invention.
An embodiment of a reproducing circuit for a VTR is shown in which FIG. 2 is a basic block diagram, FIG. 3 is an explanatory diagram of operation, and FIG. 4 is a concrete example of the circuit. 1: Detection circuit, 2: Sample and hold circuit, 3: VCO, 4: Switching circuit, 5: Clamp circuit, 6: Switching circuit, 7: Control circuit.

Claims (1)

[Claims for Utility Model Registration] To reproduce a tape using a recording method in which a guard band and a recording section for signals in other modulation modes are formed between video RF signal recording sections using a reproducing device capable of low-speed, high-speed reproduction, etc. The reproducing circuit includes a detection circuit for detecting the presence or absence of a video RF signal and a recording signal in other modulation modes, and a sampling circuit that outputs a voltage corresponding to the frequency of the horizontal synchronization signal separated from the demodulated video signal. A VCO controlled by the output voltage from the hold circuit and the sample-and-hold circuit to generate a pseudo-decoupled synchronization signal, and a signal with a signal from the detection circuit to close the sample-and-hold circuit. A switching circuit for operating the sample-and-hold circuit in an open loop by a signal without a signal from the detection circuit, and a video output during a scanning period when the playback head scans a portion other than the video RF signal section. A clamp circuit for clamping the level to a certain level,
A switching circuit that selects and outputs the signal from the clamp circuit and the video demodulated signal in a time-divisional manner, and a switching circuit that is provided between the switching circuit and the detection circuit, and that controls the operating timing of the switching circuit according to the playback mode. and a control circuit for controlling the video output level, and is configured to replace noise components caused by other modulation modes and noise components caused by the guard band section with a signal that includes a pseudo-decoupled synchronization signal and clamps the video output level to a constant level. A VTR playback circuit characterized by: