JPS6214776Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a television receiver, and more particularly to a blanking pulse generating circuit that generates pulses corresponding to horizontal and vertical blanking periods of a video signal.

In recent years, for images with insufficient contrast (this occurs because the black appears floating when the video signal does not have a black level), the signal of the part of the video signal closest to the black level is converted to the black level. So-called black level correction is being performed. And in this case,
The peak level on the black level side of the video signal is compared with the black level, and when the aforementioned peak level does not reach the black level, the luminance level is lowered and black level correction is performed. Generally, in order to have a peak level on the black level side of the video signal, a blanking pulse having a peak value on the white level side is added to the blanking period (horizontal/vertical) to shift the level of the blanking period. .

Conventionally, this type of blanking pulse is formed by waveform shaping means to widen the pulse width of the horizontal and vertical synchronizing signals, but the pulse width of the blanking pulse is There was a problem that it could not be expanded.

The present invention was proposed in view of this point, and focused on the fact that the level of horizontal and vertical parabolic waves increases before and after the blanking period, and a blanking pulse is generated based on this parabolic wave. It is something.

The present invention will be explained below with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIG. 2 is a waveform diagram of each part thereof.

In the figure, 1 is a horizontal output circuit connected to a resistor R ₁ and a diode D via a level correction circuit 2. 3 is a vertical output circuit which is grounded via a resistor R ₀ and connected to a diode D. Also, resistor R ₁ is connected to the base of transistor Q ₁ , and the collector of the same transistor is connected to resistor
Grounded through R ₃ and transistor Q ₂
connected to the base of. The emitter of the transistor _Q1 is connected to the power supply + _B1 via a resistor _R2 and is grounded via a variable resistor VR. The emitter of the transistor _Q2 is grounded, and the collector of the transistor is connected to the power supply + _B2 via a resistor _R4 . Note that 4 is an output terminal provided at the collector of the same transistor.

Next, the operation will be explained. From the vertical output circuit 3, as shown in A, a parabolic wave is synchronized with the vertical synchronizing signal and having the same period as the vertical synchronizing signal.
From the horizontal output circuit 1, a parabolic wave is synchronized with the horizontal synchronizing signal and has the same period as the horizontal synchronizing signal, as shown in FIG. The level correction circuit 2 corrects the amplitude and DC level of the parabolic wave B so that the amplitude and DC level of the parabolic wave B are both the same as those of the parabolic wave A.

On the other hand, since parabolic wave A is added to parabolic wave B via diode D, parabolic wave B is amplitude-modulated by parabolic wave A, and the amplitude-modulated parabolic wave shown in C is applied to the base of transistor _Q1 . It will be done. Variable resistor VR is a transistor
It sets the conduction level S of _Q1 , and by adjusting this variable resistor VR, the pulse width of the pulse corresponding to the vertical blanking period is set. A pulse is generated in the transistor _Q1 in response to the input of the parabolic wave C, and this pulse is taken out as a blanking pulse signal D from the output terminal 4 provided at the collector of the transistor _Q2 via the transistor _Q2 . . In addition, since the voltage level of the parabolic wave increases before and after the blanking period, the blanking pulse can have a phase that is temporally more advanced than the actual blanking period, and the pulse that covers the blanking period It will have a width.

As described above, the present invention is effective because it can form a blanking pulse that has a phase that is temporally ahead of the blanking period (horizontal and vertical) and has a pulse width that covers the blanking period.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing one embodiment of the present invention.
The figure is a waveform diagram of each part. 1, 2, 3, D, R ₀ , R ₁ ... waveform shaping means,
Q ₁ , VR...Pulse generation means, A...Vertical period parabolic wave, B...Horizontal period parabolic wave, C...
...amplitude modulated parabolic wave, d...blanking pulse.

Claims (1)

[Claims for Utility Model Registration] Waveform shaping to form an amplitude-modulated parabolic wave by amplitude modulating a horizontally periodic parabolic wave taken out from a horizontal output circuit with a vertically periodic parabolic wave taken out from a vertical output circuit. and pulse generating means for generating blanking pulses corresponding to horizontal and vertical blanking periods in response to the amplitude modulated parabolic wave. generation circuit.