JPH05207315A - Television receiver - Google Patents

Abstract

PURPOSE:To stably hold a raster size by automatically turning the raster size to the state of an overscan when an input signal is absent in the state of an underscan. CONSTITUTION:This device is equipped with a horizontal deflection amplitude control circuit 2 which controls the B voltage of a horizontal deflection outputting circuit 3 for controlling the raster size. The output of a synchronous signal detecting circuit 7 provided on the output side of a synchronism separator circuit 5 is added to a horizontal deflection amplitude control circuit 2 and the output of the horizontal deflection output circuit is controlled so that the raster size is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for stabilizing the raster size when a television receiver or a monitor display receives no signal.

[0002]

2. Description of the Related Art Generally, in a monitor display for broadcasting,
The raster size can be switched because it is necessary to display all of the video signals on the CRT, and the raster size is slightly larger than the effective screen of the CRT (hereinafter referred to as overscan).
Then, any of the raster sizes (hereinafter referred to as underscan) in which the four corners of the raster are inscribed within the four corners of the CRT can be selected.

A conventional horizontal raster size switching device will be described below with reference to the drawings. FIG. 2 shows an example of the configuration of a conventional horizontal raster size switching device. 1 is a raster size changeover switch, 2 is a horizontal deflection output circuit power supply voltage control device, 3 is a horizontal deflection output circuit, 4 is a CRT, 5
Is a sync separation circuit, and 6 is a horizontal oscillation circuit.

With respect to the horizontal raster size switching device including the above components, the relationship and operation of each component will be described below. The case where the raster size is switched from underscan to overscan will be described.

First, when the raster size changeover switch 1 is switched to the overscan side, the output voltage of the horizontal deflection output circuit power supply voltage control device 2 is controlled to the value at the time of overscan, and the output of the horizontal deflection output circuit 3 is output. The amplitude outputs the amplitude at the time of overscan, and the raster size of the CRT 4 becomes overscan.

When no signal is input, the sync separation circuit 5
Therefore, the synchronizing signal is not output from the horizontal oscillation circuit 6, and the horizontal oscillation circuit 6 is free-oscillating. Since the oscillation frequency at this time is higher than that at the time of normal signal input, the output amplitude of the horizontal deflection output circuit 3 becomes small.

[0007]

As described above, the horizontal deflection amplitude is reduced when no signal is input, as compared to when a normal signal is input. This decrease in amplitude does not appear on the CRT during overscan, but it appears as a reduction in the horizontal raster size on the CRT during underscan. That is, there is a problem that the raster size becomes unstable when the non-signal state and the signal state are switched during the underscan.

In view of the above problems, the present invention provides a raster size stabilizing device capable of eliminating a reduction in raster size due to the presence or absence of an input signal.

[0009]

In order to solve the above problems, a raster size stabilizing device of the present invention uses a sync signal detection circuit for detecting the presence or absence of a sync signal, and an output from the sync signal detection circuit as a control input. A horizontal deflection amplitude control circuit for controlling the B voltage of the horizontal deflection output circuit is provided. If there is no synchronization signal, the synchronization signal detection circuit detects it and the horizontal deflection amplitude control circuit detects the B voltage of the horizontal deflection output circuit. To increase the output current of the horizontal deflection output circuit, that is, the raster size in the horizontal direction.

[0010]

According to the present invention, the horizontal deflection amplitude control circuit, which detects the presence or absence of the sync signal and switches the raster size in the horizontal direction when there is no signal by the above-described structure, can be used for underscan and overscan for the image frame Nevertheless, the present invention realizes a raster size stabilizing device that performs forced overscan operation and prevents fluctuations in raster size.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram of a raster size stabilizing device according to a first embodiment of the present invention. The same components as those in the conventional example are designated by the same reference numerals. 1 is a raster size changeover switch, 2 is a horizontal deflection amplitude control circuit,
Reference numeral 3 is a horizontal deflection output circuit, 4 is a CRT, 5 is a sync separation circuit, 6 is a horizontal oscillation circuit, and 7 is a sync signal detection circuit.

With respect to the raster size stabilizing apparatus composed of the above-described constituent elements, the relationship and operation of each constituent element when the signal state changes to the non-signal state during underscan will be described with reference to FIG.

First, when the signal-existing state is changed to the no-signal state, the output of the sync separation circuit 5 becomes zero, which is detected by the sync signal detection circuit 7, and the horizontal deflection amplitude control circuit 2 is then output by the horizontal deflection output circuit 3. B voltage is increased, and this B voltage value is raised to the B voltage value at the time of overscan regardless of the position of the raster size changeover switch 1. As a result, the output current of the horizontal deflection output circuit 3 becomes the same value as when there is no signal overscan, and the raster size of the CRT 4 becomes overscan.

[0015]

As is apparent from the above description of the embodiments, according to the present invention, when a signal input state is changed to a signalless input state by adding a synchronizing signal detection circuit to the conventional raster size switching device. Also in the above, it is possible to easily realize a raster size stabilizing device that keeps the raster size stable.

[Brief description of drawings]

FIG. 1 is a block diagram of a raster size stabilizing device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional raster size switching device.

[Explanation of symbols]

 1 raster size selector switch 2 horizontal deflection amplitude control circuit 3 horizontal deflection output circuit 5 sync separation circuit 6 horizontal oscillation circuit 7 sync signal detection circuit

Claims (1)

[Claims] 1. A synchronization separation circuit, a horizontal oscillation circuit, a horizontal deflection output circuit, a raster size changeover switch, a horizontal deflection amplitude control circuit of a B voltage supply circuit of the horizontal deflection output circuit, and the synchronization separation circuit. A synchronization signal detection circuit is provided between the horizontal deflection amplitude control circuits, and when there is no input signal, the synchronization signal detection circuit detects that there is no synchronization signal, and its output enters the horizontal deflection amplitude control circuit and The deflection amplitude control circuit raises the B voltage of the horizontal deflection output circuit to the B voltage value at the time of overscan to increase the horizontal deflection output, and when there is no input signal regardless of the position of the raster size changeover switch. A television receiver designed to be in an overscan state.