JPS6326591B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION When a pattern such as characters or symbols is displayed on the screen of a television receiver separately from the received broadcast, the present invention generates a trigger signal for determining the vertical position of the display pattern. This relates to the trigger circuit that generates the signal.

When displaying a display pattern, for example, numbers indicating the time, on the screen of a television receiver separately from the received broadcast, it is necessary to determine its horizontal and vertical positions.

As a reference trigger signal for determining the above vertical position, there are cases where a vertical reference signal such as a so-called vertical pulse generated in a vertical deflection circuit and synchronized with the vertical deflection output is used, and a vertical synchronization signal included in the television signal is used. However, in the former case, by adjusting the vertical synchronization adjustment knob called V-HOLD, the position of the vertical reference signal is moved, so a horizontal interference signal is present at the moved position. This has the disadvantage that jitter occurs in the vertical reference signal, that is, the trigger signal, and the display pattern vibrates up and down.In addition, in the latter case, the trigger signal is not generated when the television signal is not being received, so the trigger is There is a disadvantage that the display pattern no longer appears on the screen.

As a trigger signal serving as a reference for determining the above-mentioned horizontal position, a horizontal reference signal such as a horizontal pulse generated in a horizontal deflection circuit may be used as it is, and the drawbacks mentioned in the former case do not occur. This is because the horizontal deflection circuit uses a phase discriminator to perform automatic frequency control (AFC) of the horizontal synchronization signal, so there is no knob for horizontal synchronization adjustment, and therefore the horizontal This is because the position of the reference signal never moves.

This invention was made in view of the above circumstances,
By using the vertical synchronization signal when a television signal is being received and the vertical reference signal when not receiving a television signal as a trigger signal, a trigger signal is constantly supplied and the television signal is It is an object of the present invention to provide a trigger circuit that supplies a stable trigger signal without jitter when receiving a signal.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, a switching circuit 1 receives a vertical synchronizing signal a of a television signal from its first input terminal 2 and a vertical reference signal b from its second input terminal 3, and outputs both signals a and b. It is now possible to selectively pass the . The vertical reference signal b is generated by a vertical deflection circuit (not shown) and synchronized with the vertical deflection output, and is composed of an oscillating pulse used to generate a sawtooth vertical deflection output signal, for example. Just take out the pulse signal as it is and use it.

4 is a control circuit that detects the presence or absence of the vertical synchronization signal a, and when the vertical synchronization signal a is present, passes the vertical synchronization signal a; when the vertical synchronization signal a is not present, it passes the vertical reference signal b. The switching circuit 1 is controlled to allow the signal to pass through. The vertical synchronizing signal a or the vertical reference signal b that has passed through the switching circuit 1 is delayed by a predetermined time through the delay circuit 5, and is output as a trigger signal d.

The output trigger signal d triggers a display circuit (not shown) that generates a display pattern of video signals, such as numeric signals representing the time, to position the display at a predetermined vertical position on the screen of the television receiver.
Display the above display pattern. The above delay circuit 5
By appropriately changing and setting the predetermined delay time, the display pattern can appear at a desired vertical position on the screen.

In the above configuration, when a television signal is present, the vertical synchronization signal a included in this television signal is used as the trigger signal d;
This vertical synchronization signal a does not change its position even if the viewer adjusts the vertical synchronization adjustment knob (not shown), so it is generated in the horizontal deflection circuit in advance during the manufacturing stage of the television receiver. A horizontal interference signal such as a horizontal pulse is a vertical synchronization signal a
If the setting is made so that the trigger signal d is not superimposed on the vertical synchronizing signal a during reception of the television signal, jitter will not occur in the trigger signal d due to movement of the position of the vertical synchronizing signal a, and the trigger signal d will be stabilized.

When there is no television signal, the vertical reference signal b synchronized with the vertical deflection output is the trigger signal d.
used as. At this time, when the vertical synchronization adjustment knob is adjusted, the cycle of the vertical deflection output signal changes and the position of the vertical reference signal b moves, so it is possible to avoid jitter from occurring in the trigger signal due to the horizontal interference signal mentioned above. However, in this case, since there is no video of the television program on the screen, the vertical vibration of the display pattern does not make the video difficult to view, and in reality does not cause any major problems.

As explained above, according to the present invention, a trigger signal can be obtained at all times regardless of whether or not a television signal is being received, and a stable trigger signal without jitter can be obtained when a television signal is being received. It will be done. Therefore, this trigger signal can be used to always determine the vertical position of the display pattern on the screen, and especially when a television signal is being received, the vertical position is stable and an easy-to-read display can be obtained. Can be done.

[Brief explanation of the drawing]

The drawing is a block diagram showing one embodiment of the present invention. 1...Switching circuit, 4...Control device, 5
...Delay circuit, a...Vertical synchronization signal, b...Vertical reference signal, d...Trigger signal.

Claims (1)

[Claims] 1. A switching circuit that selectively passes a vertical reference signal synchronized with the vertical deflection output and a vertical synchronization signal of a television signal, and detects the presence or absence of the vertical synchronization signal, and when the vertical synchronization signal is present,
a control circuit that controls the switching circuit to pass the vertical synchronization signal and to pass the vertical reference signal when the vertical synchronization signal is not present;
A trigger circuit comprising: a delay circuit that delays the signal from the switching circuit for a predetermined time and outputs the delayed signal as a trigger signal.