JPS5864873A - Picture tube driving circuit - Google Patents

Abstract

PURPOSE:To efficiently display a picture having double density of a digital signal on a picture tube, by using two independent input signals to drive the cathode and 1st grid of the picture tube separately. CONSTITUTION:In case of normal TV display, a signal turning on an analog gate circuit 20 and turning off a digital signal gate circuit 21 is outputted from a display gate output terminal 12 of a character multiplex signal processing circuit 10, and a color signal is inputted to the cathode of a picture tube CRT6 from an analog CPT drive circuit 5. Next, in case of a character multiplex broadcast, a signal turning off the circuit 20 and turning on the circuit 21 is outputted from the terminal 12 of the circuit 10. A digital character signal is inputted as a positive polarity to the 1st grid of a CPT6 with a digital CPU drive circuit 22 having a frequency band possible for double density display through the circuit 21 from a character output terminal 11 of the circuit 10.

Description

Detailed Description of the Invention The present invention provides a picture tube (hereinafter sometimes abbreviated as CPT) that enables selective display of two mutually independent signals on the screen.
This relates to a drive circuit.

In recent years, there has been a gradual movement toward the practical use of new information systems that use television receivers to display digital information such as character and graphic information tables.
, p58, There is a teletext broadcast described in "Teletext" by Murasaki, which transmits text information converted into a digital signal by superimposing it on the direct retrace period of the television signal, and transmits it to the home TV. This is a system that displays characters on a screen of about 15 characters horizontally x 8 lines vertically.

Below, Figure 1 describes the teletext receiver.
FIG. 2 is a block diagram showing a conventional example of such a teletext broadcasting receiver. FIG. 2 is a circuit diagram showing the CTP drive circuit in FIG. 1.

In FIG. 1, 1 is a tuner for receiving television signals, 2 is an IF circuit, 3 is an Eirin signal detection circuit, 4 is a video amplification color reproduction circuit, 5 is a CPT drive circuit, and 6 is a picture tube. .about.6 constitute a video reproducing circuit network that reproduces a video signal from a normal television broadcast signal and supplies it to a picture tube. 10 extracts the character signal superimposed on the television signal, decodes it into a predetermined coded digital character signal, stores this in a display memory (not shown), and synchronizes with the beam scanning of the picture tube 6. 11 in the block 10, which is a character multiplex signal processing circuit that outputs a character signal.
is a character signal output terminal. Further, the text multiplex signal processing circuit 10 outputs a display gate signal for switching between a television image and a text broadcast screen, and its output terminal is designated by 12 in FIG. Reference numeral 15 denotes a signal switching circuit for switching between a TV screen and a teletext screen using a display gate signal from the terminal 12. In such conventional teletext receivers,
The digital character signal is converted to an analog operation level signal and passed through the signal switching circuit 13.
As described in 54215 "Television Teletext Receiving Apparatus", the CPT 6 is driven by the same CPT driving circuit 5 as the analog television video signal. However, in such teletext receivers, as mentioned above, 15 horizontal characters x 8 vertical lines (pixel drive frequency 5.73 MHz
) can only display a total of 120 characters, which limits the number of displayed characters, so a large amount of information cannot be displayed all at once. As an improvement method for this purpose, the density is twice this (50 characters horizontally and 1 character vertically).
A method of displaying in 6 lines) is also being considered. In this case, the configuration is similar to that of the CPT drive circuit described above, and
In order to display characters (pixel drive frequency a115 MHz), the frequency characteristics of the CPT drive circuit are doubled compared to the conventional one.
The band was expanded to MHz.

However, in such a wideband CPT drive circuit, it is necessary to reduce the value of the load resistance & of the drive circuit shown in Figure 2, and for this reason, a large current flows through the transistor (Tr), which causes heat generation in the transistor. As a result, a heat sink is added to dissipate heat, which increases the circuit scale, increases the price, and deteriorates stability due to heat. In addition, since the television signal is peaked in advance in anticipation of the attenuation of the frequency characteristics at the CPT drive stage to raise the high frequencies, a correction circuit is required to attenuate the high frequencies of the frequency characteristics of the television signal. The problem was complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive CPT driving circuit for displaying a double-density screen of one digital signal on a CPT by eliminating the drawbacks of the prior art described above.

In order to achieve the above object, the present invention provides a CPT grid drive circuit exclusively for digital signals in addition to the conventional CPT grid drive circuit, and furthermore provides an analog signal gate circuit and a digital signal gate circuit to connect the television screen and the digital signal. The signal (character signal) screen can now be switched independently. As a result, it is no longer necessary to correct the frequency characteristics of the television signal to attenuate the high range or to convert the digital signal to an analog operating level signal.

Hereinafter, the present invention will be explained in detail using Examples. FIG. 3 is a block diagram showing an embodiment of the present invention, and shows an example of a block diagram of a teletext receiver. Further, FIG. 4 shows the main part of the present invention shown in FIG. 6. In FIGS. 3 and 4, 20 is a character multiplex signal processing circuit 1.
0 is an analog signal gate circuit that turns on and off the analog TV signal from the Eirin amplifier circuit 4 using the display gate signal output from the output terminal 12, and similarly, 21 is a digital signal gate circuit that turns on and off the digital character signal using the display gate signal. and 22 is C for digital character signal.
The PT driving circuit 0 and other symbols are the same as those in the block diagram of FIG.

First, the case of normal television display will be explained. At this time, the analog signal gate circuit 20 is turned on from the display gate signal output terminal 12 of the character multiplex signal processing circuit 10.
A signal that turns off the digital signal gate circuit 21 is output. Therefore, the analog television signal is transmitted from the video amplification circuit 4 through the analog signal gate circuit 20 to the conventional analog CPT drive circuit 5 to be converted to red (abbreviated as R).

Green (abbreviated as G) and blue (abbreviated as B') color signals are CPT.
The digital character signal is input to the cathode of CP for
No digital signal is input to the T drive circuit 22, and the first grid of the CPT 6 to which the digital CPT drive circuit 22 is connected is zero-biased. Therefore, the same TV screen as before is displayed on the CPT 6, and in this case, the analog CPT drive circuit 5 operates in a frequency band of 0.7.
A device with a small circuit size and a small amount of heat dissipation, such as about MILz, may be sufficient.

Next, the case of teletext display will be explained.

At this time, the display gate signal output terminal 12 of the character multiplex signal processing circuit 10 outputs a signal that turns off the analog signal gate circuit 20 and turns on the digital signal gate circuit 21. Therefore, an analog TV signal is applied from the video amplifier circuit 4 to the analog signal gate circuit 20, but since the analog signal gate circuit 20 is turned off, the analog TV signal is not input to the analog CPT drive circuit 5 at the next stage. , CPT6 cathodes are kept at a certain constant potential. However, for digital character signals, the character multiplex signal processing circuit 1
The positive polarity is input from the character signal output terminal 11 of 0 to the first grid of the CPT 6 through the digital signal gate circuit 21 by the digital CPT drive circuit 22 which has a frequency band capable of displaying double density. Therefore, CP for digital
The T drive circuit 22 is input with digital signals up to 1, and the CP
A double density digital character signal is displayed on T6. The operating frequency of this digital CPT drive circuit 22 is 05M1l.
However, since the signals to be handled are digital signals, it is possible to switch the drive transistor with extremely little heat dissipation. If so, when double-density display of a character signal is performed, there is no need to do anything on the TV signal side, and there is no need to convert the digital character signal to an analog operation level.
Although the teletext receiver has been described above, the present invention also applies to other information systems that display digital information such as character and graphic information using a television receiver, as described above. Since the CPT drive section has a similar configuration, it is possible to apply the present invention in which two independent input signals are used to drive the cathode and the first grid separately.

In addition, even in the case of super display, in which the TV signal is displayed on the TV receiving aircraft and a digital signal is superimposed on it, when looking at the detailed table time, the analog TV signal and digital signal are switched. Application of the present invention is possible.

As described above, the CPT drive circuit according to the present invention eliminates the need to treat character signals, which are originally digital signals, as analog signals in order to display double-density digital signals. There is no need to perform preprocessing for region attenuation correction. In addition, since the digital signal can be directly input to the digital CPT drive circuit, there is almost no attenuation of frequency characteristics in front of the drive circuit compared to analog, and digital CPT drive circuits with broadband frequency characteristics dissipate more heat than analog ones. Since the circuit size is small, the circuit size can be reduced and the cost can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional example of a teletext receiver, FIG. 2 is a circuit diagram showing a picture tube drive circuit in FIG. 1, and FIG. 5 is a block diagram showing an embodiment of the present invention. FIG. 4 is a detailed block diagram of the main parts in FIG. Code explanation 1... Tuner 2... IF circuit 5... Eirin detection circuit 4... Eirin amplifier circuit 5... Analog C
P'I' drive circuit 6-CPT 10...Character multiplex signal processing circuit 11...Character signal output terminal 12...
・Display gate signal output terminal 13...Signal switching circuit 2
0...Analog signal gate circuit 21...Digital signal gate circuit 22...Digital CPT drive circuit side A""A+"thin 64"" section 1st marking 2 diagram

Claims (1)

[Scope of Claims] 1) a picture tube having a cathode input terminal and a grid input terminal; when a first signal to be displayed on the picture tube is inputted, the cathode input terminal is driven in accordance with the signal; a cathode driving means that drives the cathode input terminal with a constant output when no input is received; when a second signal to be displayed on the picture tube is input, the cathode drive means drives the grid input terminal in accordance with the signal; a grid driving means for driving the grid input terminal with a constant output; a first selection switching means for selectively inputting the first signal to the cathode driving means; and a first selection switching means for selectively inputting the first signal to the grid driving means. and when the first selection switching means is in a state of inputting a first signal to the cathode drive means, the second selection switching means selectively inputs the grid signal. When the second selection switching means is not in a state of inputting the second signal to the driving means and, conversely, the second selection switching means is in a state of inputting the second signal to the grid driving means, the first selection switching means control means for controlling the first and second selection switching means so that the first signal is not inputted to the cathode drive means, A picture tube drive circuit characterized in that drive and drive of a grid input terminal by a second signal can be performed independently of each other. 2. In the picture tube drive circuit according to claim 1, one of the cathode drive means and the grid drive means is a drive means for analog operation, and the other one is a drive means for digital operation. A picture tube drive circuit characterized by: