JPS58166384A - Crt display unit - 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 The present invention provides a cathode ray display device that selectively displays two types of image information on a screen, such as television teletext broadcasting, or normal television broadcasting by combining a television receiver and a telephone network. The present invention relates to a cathode ray tube display device that selectively displays images of characters, figures, etc. on a screen.

Recently, we have focused on home television receivers, which have become widely used for receiving broadcasts, and researched a new image information system that can individually respond to multiple information by using them as display devices for text and graphics. being developed. In such an image information system, for example, image information consisting of characters and figures is multiplexed and transmitted in the form of a digital signal onto television broadcast radio waves, and on the receiving side, this is converted into a video signal by a decoder and then received on the television. An example of this is an image information system called teletext that is displayed on a machine. In addition, by utilizing the television receiver and telephone network, the television receiver is connected to the telephone line via a modem, etc., and receives text and graphic information sent from the image information center in response to requests from the keypad. There is an image information system that takes the video signal, converts it into a video signal, and displays it on a television receiver.

As mentioned above, the user terminal of this image information system connects a television receiver to a telephone line via a modem, and transmits image information from the image information center to an RF multiplied signal similar to television broadcast waves. An adapter type that displays image information on a television receiver after conversion, and a decoder that is built into the television receiver to directly display image information from an information center.
- There is a built-in type that converts into three primary color signals of LGB, amplifies this in the video output circuit of the television receiver, and adds it to the picture tube for display. Similarly, in teletext broadcasting, there are two types: adapter type and built-in type. By the way, when switching the display from images of general television broadcasts to images of text and graphics, or conversely from images of characters and graphics to images of general television broadcasts, depending on the timing of this switching, the normal television broadcast There is a phase difference between the synchronizing signal of the signal or the synchronizing signal of the image information of characters and graphics and the sawtooth wave signal of the horizontal output circuit of the horizontal deflection circuit, and for this reason, the sawtooth wave signal is output by the AFC circuit of the receiver. It is controlled so that the phase difference becomes zero by drawing in the synchronization signal. However, from immediately after switching until the phase difference becomes zero, blanking is not applied to the screen, resulting in a phenomenon in which a blanking line appears.

The present invention was proposed in view of the above-mentioned problems, and selects two types of image information in which the image is not displayed on the screen until the horizontal AFC circuit stabilizes when the display image is switched. An object of the present invention is to provide a cathode ray tube display device that displays images on a screen.

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

FIG. 1 relates to an embodiment of the present invention, in which a decoder is incorporated into a normal television receiver, and image information of normal television broadcasting and image information such as characters and figures sent through a telephone line, for example. FIG. 2 is a circuit diagram of a main part of a cathode ray tube display device that selectively displays one of the following.

A tuner extracts the signal of the channel to be received from among the television signals applied to the antenna terminal, amplifies it, and converts it into an intermediate frequency signal.

This is a video intermediate frequency amplification circuit that amplifies the video and audio intermediate frequency signals extracted by a 2-digit tuner. The video intermediate frequency signal and the audio intermediate frequency signal amplified by the three video intermediate frequency amplification circuits are detected and the difference between them is 'I, , ! ;
This is an audio FM detection circuit that extracts an MHz audio intermediate frequency signal. Hiro is an audio amplification circuit that amplifies audio intermediate frequency signals. It's a bonus speaker. B is a video detection and amplification circuit that detects the video intermediate frequency signal amplified by the video intermediate frequency amplification circuit 2, extracts and amplifies a composite video signal. 7 is a synchronization circuit that removes the video signal from the composite video signal branched from the video detection amplifier circuit B and extracts only the synchronization signal; or is a vertical deflection controlled by the vertical synchronization signal obtained from the synchronization circuit 7; This is a vertical deflection circuit that passes current through the vertical deflection coil of the picture tube/J. This is a horizontal deflection circuit that causes a horizontal deflection current controlled by a horizontal synchronization signal obtained from the synchronization circuit 7 to flow through the horizontal deflection coil of the picture tube 12. This horizontal deflection circuit compares the frequency of the sawtooth wave signal, which is the horizontal deflection current, and the horizontal synchronization signal, corrects any deviation, and maintains the frequency of the sawtooth signal stably at the frequency of the synchronization signal. A horizontal AFC circuit is provided. IQ
The carrier color signal component and the luminance signal are extracted from the composite video signal branched from the video detection amplifier circuit B, and the RGB
This is a color signal reproducing circuit that demodulates and amplifies the first three primary color signals of the color signal. /lad) This is a video output circuit that receives the first three primary color signals of LGB and drives the picture tube 12.

A decoder 13 converts image information sent from an image information center via a telephone line, for example, into second three primary color signals. This decoder 13 also extracts a synchronization signal included in the image information and applies it to the synchronization circuit 7.

/4L is a display image changeover switch for switching the image displayed on the picture tube 12 between television broadcasting and telephone line or the like. lj is an input signal changeover switch that works in conjunction with the display image changeover switch /j7 to change the connection on the input side of the synchronization circuit 7 to either the output of the video detection amplifier circuit B or the output of the decoder /3.

lB is a display screen identification signal that is at a high level when a television broadcast image is being received, and is a low level when an image from a telephone line, etc. is being received, according to the display screen changeover switch/iJ selection switch. This is a display screen identification signal generation circuit that generates a display screen identification signal. 17 is an inverter circuit that inverts the signal level of the display image identification signal. This is an AND circuit that performs a logical product of the horizontal synchronizing signal outputted from the /f synchronizing circuit 7 and the horizontal AFC pulse outputted from a well-known AFC circuit included in the horizontal deflection circuit 7. 19 is an AND circuit/
This is a retriggerable monostable multivibrator with the output pulse of g as the trigger pulse and the pulse width set in advance to a value slightly larger than the horizontal scanning period (3.sμm 11eC). Reference numeral 20 denotes a first end circuit which takes the AND of the display image identification signal and the inverted output signal of the monostable multivibrator 12. This is a second AND circuit which performs the logical product of the display image identification signal whose signal level has been inverted by the inverter circuit 17 and the inverted output signal of the monostable multivibrator.

2.2 is the low level of the output signal of the first AND circuit θ,
. . . 23 is the low level of the output signal of the AND circuit 21. The seventh switch circuit controls the connection between the N color signal reproduction circuit IO and the video output circuit // according to the level. , a second switch circuit that controls connection or disconnection between the decoder 13 and the video output circuit // in accordance with the high level.

Next, the operation of the i/circuit surrounded by the dashed line, which is the main part of the present invention, will be explained. First, display image changeover switch l
Assume that ≠ is on the television broadcasting side. At this time, the 1 display image identification signal is at a high level. This high level signal is inverted to low level by the inverter circuit 77 and input to the second AND circuit 21, so the output signal of the second AND circuit 21 becomes low level and the second switch circuit 23 is turned off. Therefore, the path between the decoder 13 and the video output circuit 1/ is cut off, and the image information of characters and graphics output from the decoder 13 is not displayed on the picture tube 12.

Assuming that sufficient time has passed since the display image changeover switch/4 was switched to the television broadcasting side, the horizontal AFC pulse given from the horizontal deflection circuit is in phase with the horizontal synchronization signal, so Stable multivibrator 19
The inverted output signal of becomes high level. Therefore, the first end circuit, l! The output signal of 0 is at a high level, and the 7th switch circuit 22 is turned on, and the path between the color signal reproduction circuit IO and the video output circuit /l is connected, and the image information of the television broadcast is displayed on the picture tube 1.2. be done.

Next, when the display image changeover switch l≠ is switched to the side sent from the image information center, the display image identification signal changes from high level to low level. Therefore, the output signal of the first AND circuit 20 becomes low level, the first switch circuit 22 is turned off, and the path between the color signal reproduction circuit IO and the video output circuit II is cut off. That is, the image information of the television broadcast is displayed on the picture tube 12 and looks great.

On the other hand, at the moment when the display image changeover switch/4Z is switched to the image information center side, the horizontal AFC is
There is a phase difference between the pulse and the horizontal synchronization signal.

As a result, the output signal of the AND circuit lf triggers the monostable multivibrator 1 at the 1 level. The monostable multivibrator 19 outputs a low-level inverted output signal to the second AND circuit 21 . Since the monostable multivibrator 19 is a re-triggered monostable multivibrator, until the horizontal AFC pulse is drawn into the horizontal synchronization signal, that is, until the phase difference between the horizontal synchronization signal and the horizontal AFC noculus becomes zero. Monostable Martino (
The inverted output of the iblator becomes a low level. Therefore, during this time, the output signal of the second AND circuit 21 is at a low level, the path between the decoder 13 and the video output circuit // is cut off, the picture tube 12 is blanked, and an image is not displayed on the picture tube 12. Very popular. Note that the time required for this blanking varies depending on the phase difference between the horizontal synchronizing signal and the horizontal AFC pulse, and the larger the phase difference, the longer it takes. Then, when the phase difference between the horizontal synchronizing signal and the horizontal AFC pulse becomes zero, the output signal of the AND circuit uig is inverted to a low level, so that the inverted output signal of the monostable multivibrator 15;' becomes a high level. As a result, the output signal of the second AND circuit 21 becomes high level and the second switch circuit 23 is turned on, and the same is true when switching to the decoder 13.

As explained above, the present invention prevents the image from being displayed on the screen in proportion to the period until the f1 horizontal AFC circuit stabilizes when the image information to be displayed is switched, so that blanking is performed during the retrace period. It is possible to efficiently prevent problems such as a return line appearing on the screen or an incomplete image being displayed.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, in which a decoder is built into a standard broadcasting television receiver, and a cathode ray tube is used to selectively display text, graphics, and other image information. Circuit diagram of display device, Figure 2 is AND circuit it
FIG. 2 is a waveform diagram of input and output signals of FIG. itt, H...display image identification signal generation means, /7...
・-inverting circuit, 1g...phase difference detection circuit, 17...monostable multivibrator, co0...first
gate circuit. 21...Second gate circuit 1. 2.2...First switch circuit 1. 23...Second switch circuit. Patent applicant ShinNippon Electric Co., Ltd.

Claims (1)

[Scope of Claims] Receiving first image information and second image information including vertical and horizontal synchronization signals, separating the vertical and horizontal synchronization signals to drive the vertical and horizontal directions of the picture tube; The cathode ray tube display device displays on the screen of the picture tube by selectively applying either the first image information or the second image information to a video output circuit. a signal generating means for generating a display image identification signal whose signal level is inverted in response to switching of image information to be displayed on a screen; an inverting circuit for inverting the display image identification signal provided from the means; The horizontal synchronization signal and the horizontal AFC pulse output from the horizontal AFC circuit are input, and the horizontal synchronization signal and the horizontal AFC pulse are logically ANDed.
A phase difference detection circuit that outputs a pulse only when there is a phase difference between it and the C pulse, and the output pulse of this phase difference detection circuit is used as a trigger pulse,
a retriggerable monostable multivibrator having a time constant preset to a value slightly larger than a horizontal scanning period and outputting an inverted output signal having a phase opposite to the triggered pulse; a first gate circuit that ANDs the inverted output signal of the monostable multivibrator; a second gate circuit that ANDs the signal output from the inverting circuit and the inverted output signal of the monostable multivibrator; a first switch circuit that controls supply or cutoff of the first image information to the video output circuit according to the output given from the first gate circuit; and an output given from the first gate circuit. A cathode ray tube display device comprising: a second switch circuit that controls supply or cutoff of the second image information to the video output circuit according to the above.