JPH0253385A - Television receiver - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a television receiver, particularly a beam index type television receiver.

[Summary of the invention]

This invention includes a detection circuit for detecting the presence or absence of a television signal in a television receiver, and fixing the oscillation frequency of a horizontal synchronous oscillator to a predetermined value when the detection circuit detects the absence of a television signal. By providing a signal generating means to generate a signal, it is possible to prevent synchronization disturbances and color disturbances from occurring even when characters are displayed when there is no television signal.

[Conventional technology]

A television that uses a conventional relatively small color picture tube and can selectively switch between receiving and displaying television broadcasts and displaying characters such as the channel and current time on the entire surface of the picture tube. John has a receiver.

[Problem to be solved by the invention]

In this type of television receiver, when a television signal is not supplied during character display, such as when an empty channel is selected, the synchronization circuit may mistakenly use noise as a synchronization signal. In such a case, there is a problem that synchronization disorder occurs. In particular, in beam index type television receivers such as those disclosed in Japanese Patent Publication No. 61-61314, when synchronization disturbance occurs, the index servo may become disconnected, causing the timing of color switching to shift and causing color disturbance. There was a problem with it being put away.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a television receiver that can prevent synchronization disturbances and display characters well even when there is no television signal.

[Means to solve the problem]

In this invention, in a television receiver in which a television signal and a character signal are switched and supplied to a picture tube, there is provided a detection circuit for detecting the presence or absence of a television signal, and a detection circuit for detecting the presence or absence of a television signal. The configuration includes signal generating means for fixing the oscillation frequency of the horizontal synchronous oscillator to a predetermined value when the absence of the horizontal synchronization oscillator is detected.

[Operation] A television signal can be detected by the detection circuit. If there is no television signal, a detection signal is supplied from the detection circuit to the synchronous oscillator of the synchronous deflection circuit.

The oscillation frequency of the synchronous oscillator is fixed to a predetermined frequency, for example, a free run frequency, based on the above-mentioned detection signal.

The character generation circuit generates a character signal in synchronization with the horizontal frequency signal from the synchronous oscillator and supplies it to the picture tube.

Since the synchronous oscillator stably generates a horizontal frequency signal without malfunctioning due to noise, it is possible to prevent synchronization disturbances from occurring during character display.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. In this embodiment, the present invention is applied to a beam index type television receiver. The explanation will be given in the following order.

(A) Overall circuit configuration and operation (B) Example of screen display (A) Overall circuit configuration and operation FIG. 1 shows the configuration of a television receiver according to this embodiment.

In FIG. 1, input terminal 1 is for inputting an external video signal, and input terminal 2 is for inputting a television signal. The video signal input to the input terminal 1.2 is decomposed into three primary color signals R, G, and B, which are input in parallel.

The video signals inputted to the input terminals 1.2 are selected by a changeover switch 3 and supplied to a no-signal detection circuit 4, a synchronous deflection circuit 5, and a television/character switching circuit 6, respectively.

The no-signal detection circuit 4 detects that no video signal is input based on, for example, the presence or absence of a horizontal synchronization signal. When no video signal is input, the no-signal detection circuit 4 transmits the detected signal to the synchronization circuit 7 of the synchronization deflection circuit 5. supply to.

The synchronization circuit 7 of the synchronization deflection circuit 5 includes a horizontal synchronization separation circuit, a horizontal oscillator, a vertical synchronization separation circuit, and a vertical oscillator. When the detection signal is supplied, the operation of the synchronization separation circuit is turned off and the oscillation frequency of the oscillator is fixed to the free run frequency.

As described above, when the video signal is not supplied, this synchronization circuit 7 generates a horizontal frequency signal and a vertical frequency signal fixed to a free run frequency that is equal to the horizontal frequency and the vertical frequency, and generates the horizontal frequency signal and the vertical frequency signal. , and vertical frequency signals to the character generation circuit 8, respectively. on the other hand,
When a video signal is being supplied, a horizontal frequency signal and a vertical frequency signal synchronized with the horizontal and vertical synchronizing signals in the signal are generated and supplied to the character generation circuit 8.

This can prevent noise from being mistakenly used as a synchronization signal, and can prevent synchronization disturbances even if characters are displayed when there is no video signal.

Further, since the occurrence of synchronization disturbance is prevented, the index servo will not go out of order, and even when characters are displayed, the occurrence of color disturbance can be prevented.

Further, the deflection circuit 9 of the synchronous deflection circuit 5 forms a deflection signal in synchronization with the signal supplied from the synchronous circuit 7, and supplies this deflection signal to the deflection device 11 of the picture tube 10.

A microcomputer 12 (hereinafter referred to as microcomputer) controls this television receiver, and is connected to operation keys 13.

By controlling the microcomputer 12 via the operation keys 13, desired modes, channels, video conditions, volume, etc. are selected and adjusted. Signals output from the operation keys 13 are converted into various control signals by the microcomputer 12 and supplied to the character generation circuit 8, the television/character switching circuit 6, and the drive circuit 14, respectively.

In the character generation circuit 8, when a display command is issued from the microcomputer 12, when there is no video signal, a character signal is generated in synchronization with a horizontal frequency signal and a vertical frequency signal, which are fixed at a predetermined free-run frequency. This character signal is output to the television/character switching circuit 6. On the other hand, when there is a video signal, the character generation circuit 8
A character signal is formed according to a horizontal frequency signal and a vertical frequency signal synchronized with the horizontal synchronization signal and vertical synchronization signal of the video signal supplied from the synchronization circuit 7, respectively, and this character signal is output to the television/character switching circuit 6.

The television/character switching circuit 6 selects either a video signal or a character signal in response to a switching pulse supplied from the microcomputer 12. The signal exposed by the television/character switching circuit 6 is supplied to a drive circuit 14.

The drive circuit 14 changes the video signal to black level during the video signal switching period according to the drive mute signal supplied from the microcomputer 12. The video signal that has passed through this drive circuit 14 is supplied to a color switching circuit 15.

The color switching circuit 15 performs color switching by outputting only a specific primary color signal defined by the gate pulse supplied from the gate pulse generation circuit 16. That is, when the electron beam scans the red color-changing light stripe, it uses the red primary color signal, when it scans the green color-changing light stripe, it uses the green primary color signal, and when it scans the green color-changing light stripe, it uses the green primary color signal. During scanning, density modulation is performed using the blue primary color signal. The primary color signals output from the color switching circuit 15 are supplied to the first grid 18 of the picture tube 10 via a video amplifier 17.

The picture tube 10 has a single electron beam, and although the fluorescent surface of the picture tube 10 is not shown, color-changing light stripes of three primary colors are arranged repeatedly in the horizontal scanning direction. Inside, index phosphor stripes are arranged in the horizontal scanning direction.

When the electron beam scans the index phosphor strip by the deflection device 11, the photomultiplier 19
The index signal can be obtained by: This index signal is fed back to the gate pulse generation circuit 16.

The gate pulse generation circuit 16 forms gate pulses corresponding to each primary color signal based on the above-mentioned index signal, and is composed of a bandpass filter for separating the index signals, a PLL, and a ring counter.

(B) Example of screen display FIG. 2 shows an example of the screen display.

Until time 10 shown in FIG. 2, normal television signals are being received, and the switching pulse from the microcomputer 12,
The drive mute signal, the detection signal from the no-signal detection circuit 4, etc. are all at low level.

The television signal is transmitted through the television/character switching circuit 6.
, a drive circuit 14, a color switching circuit 15, and a video amplifier 17 before being supplied to the picture tube 10.

On the other hand, the above-mentioned television signal is supplied to the synchronous deflection circuit 5, and from the deflection circuit 9 of the synchronous deflection circuit 5 to the picture tube 1.
A deflection signal is supplied to the deflection device 11 of No. 0, and scanning of the electron beam is performed.

When the electron beam horizontally scans the index phosphor stripe by the deflection device 11, the index signal obtained by the photomultiplier 19 is fed back to the gate pulse generation circuit 16 to perform appropriate color switching. .

At time 10, when the time display mode is selected using the operation key 13, a time display mode signal is supplied to the microcomputer 12, and the character generation circuit 8 is supplied from the microcomputer 12.
A display command is output for the

The character generation circuit 8 outputs a character signal for time display to the television/character switching circuit 6 based on a display command from the microcomputer 12.

At time L1, the drive circuit 14 from the microcomputer 12
The drive mute signal is output for a predetermined period of time (from time t1 to t4), and the drive mute signal rises during this period. As a result, in the picture tube 10, the video signal is kept at a black level for a predetermined period of time (times 1 to t4), and the display on the picture tube 10 is entirely black, as shown in the second diagram.

If a regular television signal is available, no synchronization disturbance will occur in the character display even if the display is switched to character display. However, there is no television signal when an empty channel is selected, such as at the end of VTR playback, or when a clock is displayed after the end of television broadcasting.

In such a state, at time t2, the no-signal detection circuit 4 detects that there is no video signal, and the no-signal detection circuit 4 outputs a detection signal to the synchronization circuit 7. Therefore, this detection signal rises at time L2. As a result, the synchronization circuit 7 supplies the character generation circuit 8 with a horizontal frequency signal and a vertical frequency signal that are fixed at a free run frequency that is equal to the horizontal frequency and the vertical frequency, respectively.

At time t3, the microcomputer 12 outputs a switching pulse to the television/character switching circuit 6. Therefore, the switching pulse rises at time t3, and the switching pulse causes the TV/character switching circuit 6 to switch to the character signal side.

At time t4, the aforementioned drive mute signal is no longer output, so a character signal is supplied to the picture tube 10, and a character is displayed.

This character display is, for example, a time display as shown in the second diagram, and this display is a time display for a certain period of time [time t4
to time L5].

At time t5, the drive circuit 14 from the microcomputer 12
Meanwhile, the drive mute signal is supplied again from time 5 to L8, and during this period, the drive mute signal rises.

As a result, in the picture tube 10, the predetermined time [time t5 to L]
8], the video signal is set to the black level, and the display on the picture tube 10 is completely black, as shown in the second diagram.

At time L6, character display ends, so the switching pulse falls and becomes low level, as shown in FIG. 2A. Therefore, the television/character switching circuit 6 is switched to the video signal side.

After the character display is completed, the operation for displaying the image of the television signal is automatically performed under the control of the microcomputer 12.

At time L7, the detection signal from the no-signal detection circuit 4 falls and becomes low level, so the synchronization separation operation is turned on in the synchronization circuit 7, and the synchronization separation is output.

The oscillation output is locked to the force.

At time t8, the supply of the drive mute signal is stopped. The television signal includes a television/character switching circuit 6, a drive circuit 14, and a color switching circuit 15.
, and is again supplied to the picture tube 10 via the video amplifier 17. After time t8, the television signal is received as before time 10, and the image of the television signal is displayed.

Although this embodiment describes an example in which both horizontal synchronization and vertical synchronization are controlled, the present invention is not limited to this, and it is also possible to control only horizontal synchronization.

〔Effect of the invention〕

According to the present invention, by providing a signal generating means for fixing the oscillation frequency of the horizontal synchronous oscillator to a predetermined value when the absence of a television signal is detected, a character is displayed even when no video signal is supplied. Even if this is done, it has the effect of preventing the occurrence of comradeship disorder. Since synchronization disturbances can be prevented, it is possible to prevent the index servo from coming off in beam index type television receivers, and it is possible to prevent deviations in the timing of color switching when displaying characters, thereby preventing color disturbances. There is an effect that it can be done.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a timing chart for explaining the embodiment of the invention. Explanation of main symbols in the drawings 4: No-signal detection circuit, 5: Synchronous deflection circuit, 7: Synchronous circuit, 10: Picture tube.

Claims (1)

[Claims] A television receiver configured to switch between a television signal and a character signal and supply the same to a picture tube, comprising: a detection circuit for detecting the presence or absence of the television signal; 1. A television receiver comprising signal generating means for fixing the oscillation frequency of a horizontal synchronous oscillator to a predetermined value when the absence of a television signal is detected.