JPH0441662Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application The present invention relates to a television receiver in which a horizontal AFC circuit operates well even during special playback of a VTR.

(b) Conventional technology The horizontal AFC circuit of a television receiver is designed to have low sensitivity so that it operates stably without being affected by noise when a video signal is input, and to draw in quickly when no video signal is input. It is well known to increase sensitivity.

This sensitivity switching is performed by using the phase comparison output of the flyback pulse and horizontal synchronization pulse in the horizontal AFC circuit, and detecting the synchronization/asynchronous state with an H killer circuit (Japanese Patent Publication No. 61-51828). reference).

By the way, the video signal input from the VTR also contains many jitter components, so if the television receiver is equipped with a circuit similar to the one described above, it will detect an asynchronous state and increase the accuracy of the horizontal AFC circuit. (Refer to Utility Model Publication No. 54-20920). However, VTR
Due to its improved performance, the jitter component during playback has been reduced, reducing the need for switching the detection level of the horizontal AFC circuit.

However, as is well known, one of the improvements in performance of VTRs is
It now has a high-speed search function.

A so-called helical scan type home VTR
Now, if a tape recorded at a normal tape running speed is played back at a faster tape running speed, special playback such as high-speed playback can be performed.

When special reproduction is performed, the scanning locus of the rotary head on the tape is at a different angle from the recording locus as shown in FIG. 4, so that two or more recording loci are reproduced.

Note that the reproduction horizontal synchronization signal during high-speed reproduction is shown in the following equation.

nHN=262.5−αH×(m−1) ……(0) nHN: Number of horizontal synchronization signals in one field during playback αH: H deviation from adjacent track (β=0.75,
β=0.5) m: Gear ratio with standard regeneration (+m...forward direction, -
m...reverse direction) The recording horizontal synchronizing signals between two adjacent recording trajectories of the same azimuth are out of phase. Therefore, when the rotating head moves to an adjacent recording locus, this phase shift occurs in the reproduction horizontal synchronization signal. Although this deviation is corrected on the VTR side, it is not sufficient.

When a VTR special reproduction signal is reproduced on a television receiver or the like, when the rotating head moves to an adjacent recording locus, the horizontal oscillation frequency is disturbed and a noise band is generated on the screen. In addition to this noise band, image head curvature and image shaking occur, making it impossible to obtain a good reproduced image.

Automatic frequency control (AFC) of television receivers
By reducing the time constant of the rotation integrator and increasing the response speed so as to quickly respond to the phase shift, image head curvature and image shaking can be improved.

Therefore, in the H killer circuit, the input signal is
It is sufficient to detect whether or not it is a VTR special playback signal. However, the VTR special reproduction signal is an asynchronous signal when the noise band (N) in FIG. 5 occurs, but the normal image portions (A, B) are in a synchronous state. In other words,
Conventional H-killer circuits that simply detect synchronization/asynchrony are difficult to detect and design, and require improvement.

For this reason, some types of television receivers are equipped with a switch that changes the time constant of the horizontal AFC circuit, and the switch can be switched to produce a good reproduced image when receiving VTR special playback, when receiving normal playback, and when receiving on-air broadcasting. I am trying to make it visible.
However, since this switch is manual, it is difficult to operate.

(b) Purpose of the invention This invention was made in view of the above points, and aims to improve the signal supplied to the television receiver.
To provide a television receiver that distinguishes between a normal television signal such as a normal reproduction signal of a VTR or a special reproduction signal (non-standard television signal) of a VTR, and switches the time constant of a horizontal AFC circuit.

(c) Structure of the invention In this invention, the counting operation is reset by a vertical synchronization signal, and a gate period of a specific width is set by a counter output that counts pulses synchronized with a horizontal synchronization signal, and during this gate period, the vertical A detection means detects whether or not a synchronization signal is present, and when a vertical synchronization signal is present outside the gate period, the response speed is changed by the output of the detection means, so that the video during special playback from the VTR is The present invention is characterized by comprising a horizontal AFC circuit that increases the response speed when a signal is input.

(d) Embodiment The frequency H of a horizontal pulse signal output from a horizontal oscillation circuit synchronized with a horizontal synchronizing signal in a television signal supplied to a television receiver;
In the case of the NTSC system, the relationship between the vertical synchronizing signal v in the television signal supplied to the television receiver can be expressed by the following equation.

v = 2 × H / 525 ... (1) H = 262.5v ... (1') However, when the television signal during special playback of the VTR is supplied to the television receiver,
The above equation (1) does not hold due to lack of synchronization due to the noise band and disturbances in the horizontal oscillation frequency and vertical oscillation frequency (see equation 0).

In other words, when equation (1) holds true, a normal television signal is being supplied where the phase of the horizontal synchronizing signal supplied to the television receiver does not change midway through.

The present invention is a television receiver that utilizes the above relationship and includes a detection circuit that determines whether a signal supplied to the television receiver is a normal television signal or not.

An embodiment of the present invention will be described with reference to FIG. In Figure 1, 1 is a terminal to which a horizontal pulse signal is supplied, 2 is a terminal to which a vertical synchronizing signal is supplied, and 3 is a terminal that is reset by the vertical synchronizing signal and outputs a pulse when 261 horizontal pulse signals are counted. a first counting means for outputting; 4 a second counting means for outputting a pulse when it is reset by a vertical synchronizing signal and counts 264 horizontal pulse signals;
5 and 6 are RS flip-flops, and 7 is an AND circuit. A gate period setting means is formed for outputting a gate signal during the period until the vertical synchronizing signal from the terminal 2 is applied to the RS flip-flops 5 and 6. Reference numeral 8 denotes a D flip-flop, which is a detection means for detecting whether or not a vertical synchronizing signal is present at terminal C during the gate signal generation period. That is, when the rising signal is applied to the terminal C, the D flip-flop 8 outputs the signal applied to the terminal D from the terminal Q, and maintains the output state until the rising signal is applied to the terminal C again. Reference numeral 9 is an output terminal, which is normally at a high level when receiving a television signal.

The operation of the above circuit will be explained with reference to FIGS. 2a, b, and c. First, the counting means 3, 4 and the RS flip-flops 5, 6 are set to a predetermined initial state by a vertical synchronizing signal applied to the terminal 2.
And the horizontal pulse signal applied to terminal 1 is 261
The counting means 3 generates a pulse at the time of counting. This pulse changes the RS flip-flop 5 from low level to high level. Since the initial state of the RS flip-flop 6 is at a high level, the output of the AND circuit 7 is at a high level. Then, when the counting means 4 counts 264 horizontal pulse signals, the counting means 4
generates a pulse, which causes the output of the RS flip-flop 6 to go low. Sideways
The output of the AND circuit 7 also becomes low level. In other words,
A gate signal is output from the AND circuit 7 from the time when 261 horizontal pulse signals are counted until the time when 264 horizontal pulse signals are counted. When a vertical synchronizing signal is input to the terminal c of the D flip-flop 8 during this gate signal generation period (see FIG. 2C), the output of the D flip-flop 8 becomes high level. but,
As shown in FIGS. 2a and 2b, when the vertical synchronizing signal is applied to the D flip-flop 8 earlier than counting 261 horizontal pulse signals [see FIG. 2 b], and when it is later than counting 264 horizontal pulse signals [ Refer to FIG. 2a], the output of the D flip-flop 8 becomes low level.

As described above, in the detection circuit of this embodiment, when the supplied signal is a normal television signal, the terminal Q of the D flip-flop 8 becomes high level. Normally, in the case of special playback of a VTR, the vertical synchronization signal does not exist during the period of 261 to 264, so the output of the D flip-flop 8 is at a low level, and this low level causes the connection to the television receiver. It is detected that the VCR is in special play mode. Therefore, by using this output to switch the time constant of the integrating circuit of the horizontal AFC circuit in a color television receiver, it is possible to prevent screen image shaking and image head curvature.

In this embodiment, the gate signal generation period is between 261 and 264 horizontal pulse signals, but is not limited to this.

Also, since the PAL television signal is v=2×H/625 (2), when applying the present invention to a PAL television receiver, the gate signal period must be changed from 310 to 315. This can be done while counting the number of pieces.

Further, in this embodiment, the gate pulse signal period width is determined by the counting means 3 and the counting means 4, but it may be determined by, for example, a monostable multivibrator triggered by the pulse signal from the counting means 3. The gate signal period may be set by generating a pulse with a fixed period width.

Furthermore, the detection circuit of this embodiment detects whether or not a vertical synchronizing signal is input within a predetermined period when a gate signal is generated. A judgment circuit that determines which is faster, counting 261 pulses or inputting the subsequent vertical synchronization signal, and determining which is faster, counting 264 horizontal pulse signals or inputting the vertical synchronization signal. and a circuit that determines that the signal is a regular television signal based on the output signals of the two determination circuits, for example, when the vertical synchronization signal is slow in the former and early in the latter. good.
Note that the two determination circuits also function as a gate period setting circuit.

FIG. 3 shows a specific example of the circuit of the present invention shown in FIG. 1, and 10 is a frequency dividing circuit that functions similarly to the counting means 3 and 4 of FIG. or,
Transistors Q3, Q4 and Q5, Q6 form a flip-flop.

(f) Effects of the invention According to the invention, when the signal supplied to the television receiver is a non-standard television signal, the time constant of the horizontal AFC circuit is automatically changed to a smaller value to quickly compensate for the phase shift. I can do it.

[Brief explanation of the drawing]

Figure 1 is a schematic block diagram showing an embodiment of the present invention, and Figure 2a shows a system in which the vertical synchronizing signal is connected to the horizontal synchronizing signal.
When the input is slower than counting 264 (VTR
Figure 2b shows the waveform diagram of the detection circuit when the vertical synchronization signal is input earlier than counting 261 horizontal pulse signals (during VTR special playback). The waveform diagram in Figure 2c for explaining the operation shows that the vertical synchronizing signal is slower than counting 261 horizontal pulse signals and 264
FIG. 3 is a waveform diagram for explaining the operation of the detection circuit when an input is received earlier than counting (when receiving a regular television signal), and FIG. 3 is a schematic diagram showing a specific example of the circuit shown in FIG. 1. . Figure 4 shows the general
FIG. 3 is a diagram for explaining a high-speed search of a VTR.
FIG. 5 is a diagram showing a television screen during high-speed search. 3...Counting means, 5, 6, 7...Gate signal generation means, 8...Detection means.

Claims (1)

[Claims for Utility Model Registration] The counting operation is reset by the vertical synchronization signal, and the pulses synchronized with the horizontal synchronization signal are counted, and the count output is used to calculate the horizontal A gate period of a certain width is set before and after the count output time of the number of synchronization signals, and a detection means detects whether or not a vertical synchronization signal exists during this gate period, and the response speed is increased by the output of the detection means. What is claimed is: 1. A television receiver comprising: a horizontal AFC circuit which is changed, and which increases the response speed of the horizontal AFC circuit when a vertical synchronization signal during special playback from a VTR exists outside the gate period.