JPH0369117B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a synchronization signal input device for a personal computer connected to a television receiver.

Conventional configurations and their problems Recently, television receivers with terminals to which a personal computer can be connected have been developed.

Personal computers have an RGB output and horizontal and vertical synchronization signal outputs, and many systems use a method in which the horizontal and vertical synchronization signals are combined in the television receiver and added as input to the video signal processing circuit. There is. However, in television receivers whose video signal processing circuits lock onto burst signals, synchronization can be achieved both horizontally and vertically when this synchronization signal is input; , there was jitter in the vertical synchronization signal, which appeared on the screen as horizontal jitter, and when characters were output, the characters wobbled finely in the horizontal direction, making the screen extremely difficult to read. .

Purpose of the invention The present invention solves the above-mentioned conventional problems.
An object of the present invention is to provide a synchronization signal input device capable of obtaining a television receiver without horizontal shaking of characters when displaying characters of a personal computer.

Structure of the Invention A synchronization signal input device according to the present invention combines horizontal synchronization signals and vertical synchronization signals of a personal computer using an AND gate, and outputs the combined output from a resonant circuit having a resonant frequency equal to the burst frequency (3.58MHz). A composite synchronization signal with a 3.58MHz ringing waveform is created through the 3.58MHz ringing frequency, and this composite synchronization signal is input to the video signal processing circuit. It is possible to synchronize and eliminate horizontal jitter in the horizontal period.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a specific circuit of a synchronizing signal input device in an embodiment of the present invention. In FIG. 1, 1 is a television receiver, 2 is an antenna, 3 is a tuner, 4 is a VFI circuit, and 5 is a circuit for switching between a video signal from tuner 3 and a composite synchronization signal from personal computer 38. , 6 and 7 are emitter follower circuits, 8 is a coupling capacitor, 9 and 10 are clamp resistors, 11 is a video signal processing circuit, 12 is a clamp circuit, and 13 is an RGB output signal from the video signal processing circuit 11. and external connection terminals RiN, GiN,
14 is an RGB switching circuit for switching each RGB input signal from BiN, and 14 is a cathode ray tube (hereinafter referred to as CRT).
), 15, 16, 17, and 18 are capacitors, resistors, and diodes constituting a clip circuit for clipping the lower level of the video input signal or the composite synchronization signal from the personal computer 38; 10Ω with input protection resistance
20 and 22 are pull-down resistors with a value of approximately 1KΩ. 23 is an AND gate for synthesizing the horizontal synchronization signal and vertical synchronization signal from the personal computer 38;
24 and 25 are dividing resistors for dividing the TTL level output of the AND gate 23, and 26 and 27 are dividing resistors.
28 is a coupling capacitor, 29 and 30 are bias resistors for DC bias, 31 and 32 are emitter follower circuits, 33 is an input terminal for a horizontal synchronizing signal from a personal computer 38, 34 is an input terminal for a vertical synchronizing signal from the personal computer 38, and 35, 36, and 37 are also personal computer 38 input terminals.
An input terminal 39 for R, G, and B signals from the computer 38 is a keyboard section of the personal computer 38. Also, Figure 2 shows H, V,
It shows waveforms corresponding to each part of a, b, and c.

The operation of the above configuration will be explained next.

First, the graphic and character information signals input from the personal computer 38 and the keyboard section 39 are
The synchronizing signals are input to RGB input terminals 35, 36, and 37, and the horizontal synchronizing signal is input to the input terminal 33, and the vertical synchronizing signal is input to the input terminal 34, respectively.

Here, it goes without saying that the television receiver 1 has the function of receiving original broadcast radio waves and displaying the information as an image on the CRT 14, and the video input changeover switch 5 is the one that receives the original broadcast radio waves and displays the information as an image on the CRT 14. When the RGB switching circuit 13 is on the output terminal side of the video signal processing circuit 11, it is the mode for receiving broadcast radio waves, and the opposite case is when the RGB switching circuit 13 is on the output terminal side of the video signal processing circuit 11.
This is a mode in which a device with an RGB output terminal is connected and its text and graphic information is displayed.

Here, the video input switch 5 is set to the lower side, that is, to the synthetic synchronization signal side of the personal computer.
A case will be described in which the RGB changeover switch 13 is also on the lower side, that is, on the RGB input side of the personal computer. In the opposite case, the mode is for receiving television broadcast waves, so a description thereof will be omitted. Horizontal and vertical synchronizing signals H and V from the personal computer 38 are inputted from terminals 33 and 34, respectively, and are sent to the AND gate 23 via protective resistors (approximately 10Ω) 19 and 21 and pull-down resistors (approximately 1KΩ) 20 and 22. A composite synchronizing signal is obtained by combining horizontal and vertical synchronizing signals a as shown in FIG. 2 at its output terminal.

In the conventional system, as shown by the dotted line X in FIG. In this case, it is assumed that the video signal processing circuit 11 employs a burst lock method. The burst lock method operates by locking the circuit system to the color burst signal. Especially when digital processing is being performed, the oscillation frequency of the clock generator used to operate the video signal processing system is locked to the color burst signal. A method is adopted that detects the signal and automatically locks.

In this case, this clock generator is designed to oscillate at a constant frequency when a video input signal without a color burst signal is input, but if a high-frequency sync signal is used as a synchronization signal like a personal computer, When a signal containing a noise component is input to the video signal processing circuit 11, the circuit tries to lock on the noise component close to the burst signal, and if the frequency component of the noise is fluctuating,
It works to try to follow it. That is, although not shown here, the horizontal synchronizing signal obtained by synchronously separating the output of the video signal processing circuit 11 causes jitter. This jitter occurs when graphics and text information from the personal computer 38 is displayed on the CRT 14, causing the characters and graphics to sway,
It appears as a fine trailing phenomenon.

In order to eliminate this phenomenon, the device shown in FIG. 1 synchronizes the clock that operates the video signal processing circuit 11 with this pseudo burst component by adding a color burst frequency (3.58MHz) component to the composite synchronization signal. It was designed to make it possible.
For this purpose, the output signal a of the AND gate 23 is divided by a resistor 24 and a resistor 25, and this is applied to the capacitor 2.
6 and coil 27 resonant circuit (resonance frequency 3.58M
Hz) to obtain the waveform shown in Fig. 2b. This is supplied via a coupling capacitor 28, a DC bias is applied by resistors 29 and 30, and is supplied to the video input selector switch 5 at low impedance via an emitter follower circuit consisting of a resistor 31 and a transistor 32, and then from a transistor 6 and a resistor 7. The signal is input to the video signal processing circuit 11 via an emitter follower circuit and a coupling capacitor 8. The reason why the signal applied to the video signal processing circuit 11 has the waveform shown in FIG. Here, the clamp circuit 12 is a pedestal clamp driven by pulses.

As described above, by adding the 3.58 MHz ringing waveform to the composite synchronization signal, the operation of the video signal processing circuit 11 is locked to this ringing frequency, so that a stable horizontal output can be obtained.

In addition, the clip circuit connected to the input section of the video signal processing circuit 11 clips large changes in the signal at the input section when switching the video input changeover switch 5 at a constant level, so that synchronization from the time of switching is stable. The time it takes for the screen to change is shortened, and the instability of the screen due to input signal switching is eliminated. Also, depending on the division ratio of the resistors 24 and 25, the amplitude of the composite synchronization signal (Fig. 2c) is made larger (approximately 3V) than the amplitude of the video signal supplied from the VIF circuit 4 (approximately 2Vp-p). By doing so, the output of the clamp circuit 12 is outputted every (every) H (horizontal period). This prevents the integral level of the clamp pulse from fluctuating greatly.
(When a synchronization signal with a small amplitude is input from a personal computer, the clamp circuit 12 works to maintain a constant level, so a clamp pulse is not generated for each H, resulting in a ripple, and the pedestal level clamp operation is interrupted. Effects of the Invention As described above, according to the present invention, the combined output of the horizontal synchronization signal and the vertical synchronization signal is passed through a resonant circuit having a resonant frequency approximately equal to the color burst frequency of the television receiver. By supplying the signal to the video signal processing circuit, the operation of the video signal processing circuit is locked to the resonant frequency, and a stable horizontal output can be obtained.

Additionally, by using a clip circuit to clip large changes in the signal at the input section of the video signal processing circuit at a constant level when the video input selector switch is switched, the time from when the switch is switched until synchronization becomes stable is shortened. Also, instability of the screen due to switching of input signals does not occur.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a television receiver including a synchronization signal input device according to an embodiment of the present invention, and FIG.
The figure is a waveform diagram showing waveforms of various parts for explaining the operation of FIG. 1. 1... Television receiver, 2... Antenna,
3... Tuner, 4... VIF circuit, 5... Video input selection switch, 11... Video signal processing circuit, 13... RGB switching circuit, 14... CRT, 2
3...and gate, 26, 27...3.58MHz
Capacitors, coils, 38... that make up the resonant circuit
...Personal computer, 39...keyboard.

Claims (1)

[Claims] 1. A horizontal synchronizing signal and a vertical synchronizing signal are combined, and the combined output is supplied to a video signal processing circuit through a resonant circuit having a resonant frequency approximately equal to the color burst frequency of a television receiver. Synchronous signal input device. 2. The synchronization signal input device according to claim 1, wherein the lower waveform of the synthesized synchronization signal passed through the resonance circuit is flipped at a constant voltage value before being supplied to the video signal processing circuit. .