JPH0346617Y2 - - Google Patents

Description

[Detailed description of the invention] This invention inserts a reference level signal into the input signal and executes polarity control in order to reproduce the reference DC level that changes during the polarity control process in the polarity control circuit of the television video signal. The present invention relates to a device that can easily and stably restore a normal video signal by regenerating the DC component using the reference level signal and inserting a reference blanking signal.

A television video signal is composed of a positive polarity video signal, a blanking signal, and a synchronization signal, but in order to create an inverted video signal by polarity control, the blanking and synchronization signal components of the video signal components must be polarized. Therefore, only the video signal components must be converted. To carry out such control, a gain control circuit is used that is controlled to variably mix a positive polarity television video signal and a negative polarity television video signal, and at the same time output the positive polarity video signal component during blanking. is sometimes used. In such a gain control circuit, the two input video signals must be clamped and applied while maintaining the specified DC level, and a video signal inversion circuit, clamp circuit, etc. are required, and the DC level stability There were problems with this. On the other hand, when polarity conversion is performed continuously using a multiplier, the blanking DC level also fluctuates during control, making it difficult to reproduce the DC component of the video signal using a clamp circuit.

The purpose of this invention is to use the multiplier method,
An object of the present invention is to provide a device that can easily and stably perform DC component regeneration after polarity control by applying a reference pulse whose level does not change during the polarity control process to an input signal. That is, the present invention is a video signal polarity control device that continuously varies the polarity of a television video signal between positive polarity and negative polarity. a first clamp circuit whose clip level is a black level, and a black clip circuit and a white clip circuit which output a video signal within an amplitude range specified by the black level and a specified white level;
A negative NAM circuit generates a reference pulse that has a reference level that is uniquely determined from the signal range from the black clip circuit and the white clip circuit and whose level does not change during the polarity control process, and a negative NAM circuit that generates a reference pulse at an arbitrary timing during blanking. A positive NAM circuit generates a composite video signal by inserting a pulse into the video signal from the black clip circuit and the white clip circuit, and a positive NAM circuit that generates a composite video signal by inserting a pulse into the video signal from the black clip circuit and the white clip circuit, A polarity control circuit that performs polarity control to obtain a video signal including a reference signal in which the DC component does not fluctuate; a second clamp circuit that regenerates the DC component of the video signal after polarity control by clamping it to an intermediate voltage, inserts a regular blanking signal into the video signal after reproducing the DC component, and removes the reference pulse; It is characterized by having a blanking gate circuit and a synchronization addition circuit that inserts a synchronization signal into the output of the blanking gate circuit.

Next, embodiments of the present invention will be described in detail with reference to the drawings.

In FIG. 1, the device of the present invention includes an input terminal 1 for a video signal, a clamp circuit 2 that clamps this input signal, a black clip circuit 3 that clips the output signal of the clamp circuit, a white clip circuit 4, and a white clip circuit 4. The output signal of the clip circuit 4 and the output signal of the negative NAM circuit 7 are
A positive NAM circuit 5 for mixing, a polarity control circuit (multiplier) 6 to which the output signal of the NAM circuit 5 is supplied, a clamp circuit 8 to which the output of the polarity control circuit 6 is supplied, and the clamp circuit 8
blanking gate circuit 9 to which the output of
, a synchronous addition circuit 10 to which the output of the gate circuit 9 is supplied, an output terminal 14 from which a video signal is taken out from the addition circuit 10, a reference voltage applied to the clamp circuit 2, the clip circuits 3 and 4, and the NAM circuit 7. and a reference voltage generating circuit 11 that supplies the respective reference voltages.

The input video signal is keyed clamped by the clamp circuit 2 to the reference potential EC ₁ applied through the terminal C ₁ at the back porch portion. Since the same reference potential is also given to the black clip circuit 3 in the subsequent stage,
The synchronizing signal component is clipped at the output of the clipping circuit 2. The white peak component of the black clipped video signal is clipped by the white clip circuit 4 at the subsequent stage, so that the output video signal becomes a signal that appears only within the amplitude range defined by the white clip level and the black clip level. Both clip levels are
It is generated by a reference voltage generating circuit 11 as shown in one embodiment of the figure. That is, the potential EC ₂ appearing at the terminal C ₂ defines the white clip level, and the potential EC ₁ appearing at the terminal C ₁ defines the black clip level. terminal C ₃
A resistor R ₂ = R ₃ is used so that the potential EC ₃ appearing in is an intermediate potential between EC ₂ and EC ₁ . In FIG. 2, TR ₁ to TR ₃ represent transistors, and R ₁ to _{R 6} represent resistors, respectively. Next, the operation of the positive NAM circuit 5 in FIG. 1 will be explained in detail with reference to FIGS. 3 and 4. In Figure 3, the video signal input terminal
A transistor is applied to the clamped, white and black clipped video signals provided by V _I.
At TR ₁ and TR ₂ , the reference pulse is mixed in the blanking by positive NAM operation. This reference pulse is applied to the gate signal input terminal by the negative NAM circuit 7, that is, transistors TR _{3, 4, 5} .
It is generated by negative NAM operation based on the reference pulse given from V _G and the reference potential EC ₃ given from the reference level input terminal _VE for reference pulse signals. 12 is a gate signal input terminal of the negative NAM circuit 7. This operating waveform is shown in FIG. As explained above, the reference potential EC ₃ is the intermediate potential between EC ₁ (the black clip level of the video signal) and EC ₂ (the white clip level of the video signal).
In the V _O waveform shown in FIG. 4, the potential of the reference pulse within blanking is the intermediate potential between the white peak and black peak (pedestal) of the video signal. When the polarity control circuit 6 controls the polarity of the video signal synthesized in this way using the reference pulse signal portion as a reference potential, the reference pulse portion is always output as a signal at a constant level, regardless of the polarity of the output video signal. Therefore, by clamping the pulse portion to an intermediate potential between the prescribed white peak and black peak levels in the subsequent clamp circuit 8, the DC component of the video signal can be reproduced even after polarity control.

A normal blanking signal is inserted into the video signal after the DC component reproduction using a blanking signal supplied from a blanking signal input terminal 13 to the blanking gate circuit 9. Through this operation, the reference pulse is removed and a regular video signal is obtained, but the synchronization signal component is added by the synchronization addition circuit 10 in the subsequent stage, and a composite video signal is output from the terminal 14.

As explained above, in the present invention, a reference pulse is generated during blanking in conjunction with the white clip and black clip levels of the video signal, and is inserted, so that the polarity of the video signal containing the reference pulse is There is an advantage that the DC component can be regenerated accurately and easily even when variable from positive to negative.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.
Figure 2 is a circuit diagram of the reference voltage generation circuit shown in Figure 1, Figure 3 is a circuit diagram of the positive NAM circuit shown in Figure 1, and Figure 4 is a signal waveform diagram of each part of the circuit in Figure 3. It is. 1... Video signal input terminal, 2... Clamp circuit, 3... Black clip circuit, 4... White clip circuit, 5... Positive NAM circuit,
6...Polarity control circuit, 7...Negative NAM circuit, 8...Clamp circuit, 9...Blanking gate circuit, 10...Synchronization addition circuit, 11...Reference voltage generation circuit, 12...Gate signal input terminal ,1
3...Blanking signal input terminal, 14...Video signal output terminal.

Claims (1)

[Scope of utility model registration request] In a video signal polarity control device that continuously varies the polarity of a television video signal between positive polarity and negative polarity, a first clamp clips and removes a synchronization signal component in blanking of an input video signal. a circuit, a black clip circuit and a white clip circuit that output a video signal whose clip level is a black level and within an amplitude width specified by the black level and a specified white level; A negative NAM circuit generates a reference pulse having an intermediate level between the two and whose level does not change during the polarity control process. A positive NAM circuit is inserted into a video signal to generate a composite video signal, and the polarity of the input composite video signal is controlled using the voltage level of a reference pulse included in the signal as a reference potential, so that the DC component does not fluctuate. A polarity control circuit that obtains a video signal including a signal, and a voltage level of the reference pulse included in the video signal from the polarity control circuit is clamped to an intermediate voltage between a specified white peak level and a black peak level. a second clamp circuit that regenerates the DC component of the video signal; a blanking gate circuit that inserts a regular blanking signal into the video signal after regenerating the DC component and removes the reference pulse; and an output of the blanking gate circuit. A video signal polarity control device comprising: a synchronization addition circuit for inserting a synchronization signal into the video signal polarity control device.