JPH0133075B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image receiving apparatus that obtains an image by scanning the screen of a cathode ray tube with an electron beam.

Monitor receivers that utilize some of the circuit functions of television receivers are commonly used. For example, as shown in Figure 1, a cathode ray tube drive circuit 2 sends video output to a cathode ray tube (CRT) 1, a vertical oscillation circuit 3 generates a vertical deflection signal, and a vertical deflection coil is driven in accordance with the deflection signal. A vertical output circuit 4, a horizontal oscillation circuit 5 that generates a horizontal deflection signal, a horizontal output circuit 6 that drives a horizontal deflection coil with the horizontal deflection signal, and a high voltage rectifier that rectifies the high voltage of this horizontal output circuit and supplies it to the cathode ray tube anode. The video signal input to the drive circuit 2, the vertical synchronization signal input to the vertical oscillation circuit 3, and the horizontal synchronization signal input to the horizontal oscillation circuit 5 are transmitted to a source external to the monitor receiver, such as a television camera or a video tape recorder. , and further from a game control logic circuit of a television game machine or the like. Then, during one cycle of the vertical deflection current, horizontal scanning is performed, for example, 525 times to obtain an image on the screen. In this case, the horizontal deflection current is 1 as shown in Figure 2A.
Scanning is performed at a cycle of 63.5 μS, including a retrace period for performing the next scan. In order to prevent the retrace of each scan from appearing on the video screen, a blanking pulse consisting of an internal retrace signal 10 as shown in FIG. 2B is supplied to the cathode ray tube drive circuit 2 to cut off the video output during the retrace period. and blanking is performed. The same goes for vertical blanking.

The vertical retrace signal is obtained from the vertical output circuit 4, and the horizontal line signal is obtained from the horizontal output circuit 6, which is generated when the sawtooth horizontal deflection current decreases, for example, by providing a tertiary winding in a flyback transformer. A pulse voltage (FIG. 2B) induced by the back electromotive voltage is obtained and used as a horizontal retrace signal. The retrace period _T2 based on this signal is determined by the circuit constants of the horizontal output circuit 6, so the effective scanning period
T ₁ becomes T ₁ =63.5−T ₂ μS. For example T ₂ = 12μS
Then, T ₁ =51.5μS. That is, the ratio T ₂ /T ₁
is necessarily determined depending on the circuit constants.

This retrace signal is applied to the cathode ray tube drive circuit 2, so that a video output is supplied to the cathode ray tube cathode only during the effective scanning period _T1 .

By the way, as shown by N in FIG. 2C, at the beginning and end of the video signal input to the cathode ray tube drive circuit 2,
Noise may appear on both sides of the screen and degrade the image quality. This is similar to the control circuit of a television game machine, etc.
This phenomenon is often seen in cases where the oscillation circuit itself contains an oscillation circuit and generates various signals. Furthermore, when the internal blanking signal is supplied to the cathode ray tube drive circuit 2, the period during which the circuit 2 is cut off may be shorter than the blanking period due to passing through an integrating circuit, etc. As a result, there was an inconvenience that the image was folded or shadows appeared on both sides of the image screen.

The present invention solves the above-mentioned drawbacks, and provides a video receiving device that can lengthen the retrace period by receiving a retrace signal from the outside without using the retrace signal inside the monitor receiver. It is something.

Embodiments of the present invention will be described in detail below with reference to FIG. 3 and the following drawings. Note that the same parts as in FIG. 1 are given the same reference numerals and their explanations will be omitted. In FIG. 3, the external signal source 8 is a game control logic circuit of a television tuner, television camera, video tape recorder, computer equipment, television game machine, etc., and includes at least a color signal, a vertical synchronization signal, and a horizontal synchronization signal. A signal source that can send out signals. Signal source 8
has a built-in oscillator and generates various signals, but the present invention, as shown in FIG. 4, extracts the horizontal scanning period (T ₁ + T ₂ ) and A pulse having the same period and a pulse width Tr wider than the horizontal retrace period _T2 of the monitor receiver is extracted and used as the external retrace signal 11,
By using a changeover switch 9, it is possible to use the horizontal retrace signal 10 of the monitor receiver itself. It goes without saying that the waveform of the external retrace signal 11 can be appropriately shaped by a waveform shaping circuit. still,
The changeover switch 9 may be a semiconductor switch circuit.

The retrace period Tr based on the external retrace signal 11 is T ₂ <Tr
Therefore, the effective scanning period is T ₁ + T ₂ −Tr (<T ₁ )
So, if Tr=14μS, it becomes 49.5μS. That is,
The effective scanning period becomes shorter. Therefore, the video noise N located near the retrace signal is blanked out and does not appear on the video screen. Furthermore, even if the external retrace signal 11 passes through an integrating circuit or the like, the drive circuit 2 is cut off for a period that is the same as or longer than the retrace period of the monitor receiver's own retrace signal, so there is no loopback or aliasing of the video. Shadows never appear on the screen. Although only horizontal blanking has been illustrated above, the same applies to vertical blanking.

Since the present invention has the above-mentioned configuration, when a defect occurs in the vertical and horizontal retrace lines as in the conventional example, the internal retrace signal of the monitor receiver itself is switched to the external retrace signal. The receiver can be used commonly for different types of external signal sources.

Furthermore, when blanking is performed by applying a blanking signal to the grid of a cathode ray tube, the same configuration as described above can be used.
Furthermore, when the external signal source 8 is one that sends out a video signal, the cathode ray tube drive circuit 2 includes all the circuits necessary to project an image on the screen, such as a video amplification circuit, a color demodulation circuit, and a color demodulation circuit. It shall include a synchronous circuit, etc. In this case, the retrace signal is given as conventionally known, and the vertical and horizontal synchronizing signals are not sent from the external signal source 8, but from the video amplification circuit via the synchronization separation circuit as before, and are sent to both the vertical and horizontal oscillation circuits. can be entered.

Furthermore, although an example has been shown in which the vertical and horizontal retrace signals are mixed as the external retrace signal, when they are separated, separate switching switches may be provided for processing.

[Brief explanation of drawings]

1 is a wiring diagram of a conventional monitor receiver, FIG. 2 is a waveform diagram, FIG. 3 is a wiring diagram of a video receiver according to the present invention, and FIG. 4 is a waveform diagram in FIG. 3. In the figure, 1 is a cathode ray tube, 2 is a video amplification circuit, 6 is a horizontal output circuit, 8 is an external signal source, 9 is a changeover switch, 10 is a retrace signal of the monitor receiver itself, 11 is an external retrace signal, N is video noise.

Claims (1)

[Claims] 1. A video receiver that includes a cathode ray tube drive circuit, a vertical output circuit, a horizontal output circuit, and a high-voltage rectifier circuit, obtains a video signal and a synchronization signal from an external signal source, and projects the image on a cathode ray tube screen. The apparatus includes a switch means for selectively switching between an external retrace signal extracted from the external signal source and an internal retrace signal of the video receiving device itself, and the retrace signal obtained from the switch means is used to 1. A cathode ray tube image receiving apparatus, characterized in that blanking is performed and the blanking period of the external blanking signal is made longer than the blanking period of the internal blanking signal.