JPS63142773A - Device for generating vertical blanking signal - Google Patents

Abstract

PURPOSE:To delete an unnecessary video appearing on the top part of a screen by using an oscillation circuit to which the differential signal of a first vertical blanking signal which has the time width of a conventional vertical fly-back time is set to a trigger input, and generating a second vertical blanking signal which has the desired time width. CONSTITUTION:A first vertical blanking signal generation circuit 3 generates the first vertical blanking signal (d) from a vertical output (b) from a vertical deflection output circuit 2 and an output (a) from a vertical oscillation circuit 1. The signal (d) is inputted to a differential circuit 5 in a second vertical blanking generation circuit 4 and the differential signal (e) is obtained. In the differential signal (e), only a part in which the vertical fly-back time starts is sampled and is inputted to the oscillation circuit 6, whereby the differential signal (e) is oscillated as the trigger. Since the time constant of the duty in the oscillation circuit 6 is variably constituted, the second blanking signal (f) with the optional time width can be generated with changing the time constant. Thus, the video is not projected on the top part of the peripheral frame of a projection screen.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vertical blanking signal generation circuit for, for example, a projection type reflection type television receiver (hereinafter referred to as a "video projector").

[Prior art] A block circuit diagram showing the configuration of the book and its surroundings. Figure 2 shows the output of each component. In the waveform diagram, (1) is a vertical oscillation circuit that uses the synchronization signal S as a trigger and oscillates at that period, and (2) is the signal a output from the vertical oscillation circuit (1) (see Fig. 3 (a).
) The vertical deflection output signal b(shown) is synchronized with the timing of the vertical deflection output signal b(
A vertical deflection output circuit (3
) is a vertical blanking signal generation circuit, and (7) is a video circuit that outputs a video signal C on which a vertical blanking signal d is superimposed.

The conventional vertical blanking signal generation circuit (3) generates six direct oscillation signals a shown in FIG. From the vertical output signal (b) shown in Figure (b), when ITiI
A vertical SYI line period of width T is extended to generate a vertical blanking signal d, and this vertical blanking signal d is superimposed on the video signal by the video circuit (7) to produce the video signal shown in FIG. 3(c). C, so that no video is displayed during the vertical retrace period T.

[Problems to be Solved by the Invention] In the vertical blanking signal generation circuit as described above, the time width of the blanking signal d is the same as the vertical retrace period T, and the blanking signal d is on the front porch of the video signal C. It is not possible to erase signals other than video signals such as teletext broadcasting, so when a text report is received, signals other than the video signal of the text report are projected on the top of the frame around the projection screen of the video projector. Therefore, there was a problem that it was unsightly.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a vertical blanking signal generator capable of erasing signals other than video signals appearing on the front porch.

[Means for Solving the Problems] A vertical blanking generation device according to the present invention includes a first vertical blanking signal generation circuit that generates the same signal as a conventional vertical blanking signal, and a first vertical blanking signal generation circuit that generates the same signal as a conventional vertical blanking signal. A second vertical blanking signal generating circuit generates a second vertical blanking signal having a predetermined time width using the differential signal as a trigger input.

[Operation] The first vertical blanking generation circuit in this invention has the following features:
A vertical blanking signal having the same time width in synchronization with the retrace period T of the video signal is generated.

The second vertical blanking signal generation circuit generates a second vertical blanking signal having a desired time width using the differentiated signal of the six-direction blanking signal as a trigger, and transmits this second vertical blanking signal to the video circuit. Output to and superimpose. Therefore, video signals other than those on the front porch can be erased, and when a text message or the like is received, it is possible to prevent unnecessary video from being displayed around the image.

[Embodiment of the Invention] FIG. 1 is a block circuit diagram showing an embodiment of the present invention. In FIG.
) is the same as the conventional vertical blanking signal generating circuit (3) shown in FIG.

(4) is a second vertical blanking generation circuit, which includes a differentiation circuit (5) for differentiating the first (7) vertical blanking signal d output from the first vertical retrace signal generation circuit (3); It is comprised of an oscillation circuit (6) that oscillates a pulse signal of a desired time width using the starting portion of the differential signal e as a trigger.

Next, the operation of this embodiment will be explained.

First, from the vertical output b of the vertical deflection output circuit (2) or the output a of the vertical oscillation circuit (i), the first vertical blanking signal generation circuit (3) generates the first vertical blanking signal with the same waveform as the conventional one. Generate signal d.

This signal d is input to the differentiation circuit (5) of the second vertical blanking generation circuit (4) to obtain a differential signal e, and only the portion where the vertical retrace period begins is extracted from this differential signal e to generate an oscillation circuit. (6) and uses this differential signal e as a trigger to oscillate.The duty time constant of the zero oscillation circuit (6) is configured to be variable, so by changing this time constant, the second vertical blanking signal f can be generated. Therefore, the period can be set to a desired time width from the video circuit (7), and it is possible to eliminate the problem of the video being projected on the top of the frame around the projection screen.

[Effects of the Invention] As explained above, the present invention uses an oscillation circuit whose trigger input is a differential signal of a first vertical blanking signal having a time width of the conventional vertical retrace period to generate a desired time width. Since the second vertical blanking signal is generated, an effect can be obtained in which unnecessary images appearing at the top of the screen can be erased.

[Brief Description of the Drawings] Fig. 1 is a block circuit diagram showing one embodiment of the present invention, Fig. 2B is a block circuit diagram showing the configuration of a conventional vertical blanking signal generation circuit and its peripheral circuits, and Fig. 3 are waveform diagrams of output signals of each component thereof. (3)...first vertical blanking signal generation circuit, (
4)...Second vertical blanking signal generation circuit, (5
)...Differential circuit, (8)...)r8 Editing circuit In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] (1) A first vertical blanking signal generation circuit that generates a first vertical blanking signal having a time width of a vertical retrace period from a vertical synchronization signal of a video signal, and a differential signal of this first vertical blanking signal. a second vertical blanking signal generating circuit that generates a second vertical blanking signal having a time width that erases a video signal on a front porch using the trigger as a trigger.