JPH0748809B2 - Pedestal clamp circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pedestal clamp circuit of a display device for displaying an input video signal, and more specifically, to either a separate synchronization input method or a superposition synchronization input method. A pedestal that automatically generates a clamp pulse at an appropriate timing for the video signal of the sync signal input method.
Regarding the clamp circuit.

[Conventional technology]

In the output formation of the sync signal of the video signal output from the conventional personal computer, the device for business and the device for measurement, etc., the separate sync input method in which the video signal and the sync signal are output as separate lines, There is a superposition synchronization input method in which a synchronization signal is superposed on a video signal.

For this reason, the display device is provided with a pedestal clamp circuit according to the input method of the synchronization signal in order to align the pedestal level to a constant potential, and determines the pedestal position for displaying the screen accurately. The generation timing of the clamp signal is individually designed by the display device, and when a device other than a dedicated device is connected, it may not be possible to project an image with an accurate pedestal level.

[Problems to be solved by the invention]

The present invention has been made to solve such a problem. Regardless of the synchronization signal input method, a clamp pulse is automatically generated at an appropriate timing, and an accurate pedestal is obtained. -The purpose is to obtain a pedestal clamp circuit that can display an image even at a level.

[Means for solving problems]

A pedestal clamp circuit according to the present invention includes a sync signal separation circuit for separating a horizontal sync signal from an input video signal,
A synchronizing signal detection circuit for generating a switch switching signal according to the presence or absence of the separated horizontal synchronizing signal, and a horizontal synchronizing signal selected when the horizontal synchronizing signal is separated from the input video signal controlled by the switch switching signal. And a first switch for selecting and outputting a separate input type horizontal synchronizing signal which is separately input when it is not separated, and a first switch which is synchronized with the timing and the back porch of the synchronizing signal of the horizontal synchronizing signal selected by this switch. 1, second
And a clamp pulse generating circuit for generating a clamp pulse for selecting the second clamp pulse when the horizontal synchronizing signal is separated from the input video signal by being controlled by the switch switching signal, and when not separating, the first clamp pulse is selected.
The second switch for selecting and outputting the clamp pulse and the clamp circuit to which the clamp pulse selected by the switch is input.

[Action]

The horizontal sync signal separation circuit separates and outputs the horizontal sync signal when the input video signal is superimposed. The sync signal detection circuit generates a switch switching signal according to the presence / absence of the separately output horizontal sync signal. The first switch is controlled by the switching signal and selects the horizontal synchronizing signal when there is a separated horizontal synchronizing signal, and selects the horizontal synchronizing signal which is separately input when there is not and outputs it. The clamp pulse generating circuit generates first and second clamp pulses synchronized with the timing of the synchronizing signal of the horizontal synchronizing signal input from the first switch and the back porch.

The second switch is controlled by a switch switching signal. When the horizontal synchronizing signal is separated from the input video signal, the second clamp pulse is selected, and when it is not separated, the first clamp pulse is selected and output. The clamp circuit reproduces the input DC-free video signal by the clamp pulse input from the second switch.

Example of Invention

FIG. 1 is a circuit diagram of an embodiment of the present invention, in which (1) is an input terminal for a video signal of a superposition synchronous input system and a video signal of a separate synchronous input system, and (2) is a sync signal of a separate synchronous input system. Input terminal, (3) a sync signal separation circuit that separates the horizontal sync signal from the input video signal, (4) integrates the separated horizontal sync signal, and is a binary value of L and H depending on the presence or absence of the horizontal sync signal Of the sync signal detecting circuit for outputting the switch signal of the switch, (5) is a first switch which is switched by the switch signal, and (6) is the timing of the sync signal of the horizontal sync signal input from the switch (5) and It is a clamp pulse generation circuit that generates first and second clamp pulses respectively synchronized with the back porch.

(7) is a second switch that selectively outputs the first and second clamp pulses output from the clamp pulse generation circuit (6) by a switch switching signal, and (8) is a second switch ( This is a clamp circuit for reproducing the DC component of the video signal having no DC component input by the clamp pulse selected in 7).

Next, the operation when the video signal of the superposition synchronization input system of this embodiment is input will be described.

FIG. 2 is a timing chart in this case. When the negative video signal a on which the horizontal synchronizing signal H shown in FIG. 2 (a) is superimposed is input from the input terminal (1), the synchronizing signal separation circuit ( 3) is a negative horizontal synchronizing signal b shown in FIG.
Is output. The sync signal detection circuit (4) integrates the horizontal sync signal b and outputs the L level switch switching signal c shown in FIG. 2 (c). The input terminal A of the first switch (5) is connected to the input terminal (2), the input terminal B is connected to the output terminal of the sync separation circuit (3), and when the switch switching signal c is at the L level. Since it is switched to the terminal B side, the separated synchronizing signal b is supplied to the clamp pulse generating circuit (6).
Input to 1B and 2A terminals. The clamp pulse generating circuit (6) is a first pulse synchronizing with the synchronizing signal of the horizontal synchronizing signal b.
Second clamp pulse e (see FIG. 2 (e)) is output from the 2Q terminal and synchronized with the back porch of the horizontal synchronizing signal b.
The clamp pulse d (see FIG. 2 (d)) is output from the 1Q terminal. The first clamp pulse e is input to the input terminal A of the second switch (7), the second clamp pulse d is input to the input terminal B, and the input terminal A is switched to the B input terminal by the switch switching signal c. The second clamp pulse d is selected and output. The clamp circuit (8) clamps the video signal z having no DC component (see FIG. 2 (z)) by the second clamp pulse d and outputs a video signal in which the DC component is reproduced.

As described above, in the case of the superposition synchronization signal input method, the second synchronization in synchronization with the back porch of the superposed horizontal synchronization signal H is performed.
Since the video signal z is clamped by the clamp pulse d of
Accurate DC reproduction can be performed without the clamp position overlapping the horizontal synchronizing signal.

Next, the operation in the case of the separate synchronous input method will be described.

FIG. 3 is a timing chart in this case, in which the negative video signal shown in FIG. 3 (a) is input from the input terminal (1),
The horizontal synchronizing signal shown in FIG. 3 (f) is input from the input terminal (2). Since there is no output from the sync signal separation circuit (3), the level of the switch switching signal c output from the sync signal detection circuit (4) becomes H level as shown in FIG. Switches (5) and (7) are switched to the A terminal side, respectively. Clamp pulse generation circuit (6)
Outputs a first clamp pulse (see FIG. 3 (h)) synchronized with the synchronization signal of the input horizontal synchronization signal and a second clamp pulse synchronized with the back porch, and the second switch (7 ) Selects the first clamp pulse and inputs it to the clamp circuit (8). The clamp circuit outputs a video signal in which a DC component is reproduced by the clamp pulse.

As described above, in the case of the separate sync signal input, the first clamp pulse synchronized with the separate horizontal sync signal is selected and clamped, so that the DC signal does not overlap with the video signal component V and the like, and the accurate DC reproduction operation is performed. It can be performed.

〔The invention's effect〕

The present invention discriminates whether the input video signal is the superposition synchronization input method or the separate synchronization input method, and in the case of the superposition synchronization input method, a clamp pulse synchronized with the back porch of the horizontal synchronization signal is used. The clamp operation is performed, and in the case of the separate sync input method, the clamp operation is performed with the clamp pulse synchronized with the horizontal sync signal. It is possible to obtain a pedestal clamp circuit capable of performing direct current regeneration.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a timing chart for explaining the operation when a video signal of the superposition synchronous input system of this embodiment is input, and FIG. It is a timing diagram at the time of a video signal of a synchronous input system. (3) ... Sync signal separation circuit, (4) ... Sync signal detection circuit, (5) ... First switch, (6) ... Clamp pulse generation circuit, (7) ... Second switch, (8) ...
… Clamp circuit.

Claims (1)

[Claims] 1. A horizontal synchronizing signal separating circuit to which a video signal is input, a synchronizing signal detecting circuit which outputs a switch switching signal according to the presence or absence of the separated horizontal synchronizing signal, and a switch which is controlled by the switch signal. A first switch for selecting the separated horizontal synchronizing signal when there is the separated horizontal synchronizing signal, and selecting a separate input horizontal synchronizing signal which is separately input when there is no separated synchronizing signal; Clamp pulse generation circuit for generating the first and second clamp pulses respectively synchronized with the timing of the synchronizing signal of the horizontal synchronizing signal selected in step 1 and the back porch, and the separated horizontal synchronizing circuit controlled by the switch switching signal. When there is a signal, the second clamp pulse synchronized with the back porch is selected. First second switch and the pedestal clamp circuit clamps the pulse selected by the switch is provided with a clamp circuit to be input for selecting and outputting a clamp pulse coincident with the timing of the.