JPS6241492Y2 - - 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 the horizontal or vertical blanking period of a video signal.

The applicant proposed this type of blanking in Japanese Utility Model Application No. 178573 by extracting a predetermined DC voltage in response to a predetermined level of the parabola wave based on a parabola wave synchronized with a vertical (or horizontal) synchronization signal. We proposed a circuit that generates pulses. However, with this type of parabolic wave, although it is possible to maintain a stable DC level, the amplitude tends to fluctuate, so if a predetermined level of the parabolic wave is detected and a blanking pulse is generated due to this amplitude fluctuation, the blanking pulse can be generated. There was a drawback that the pulse width of the ranking pulse varied with the above-mentioned amplitude variation.

The present invention has been proposed in view of these points, and is intended to provide a blanking pulse generation circuit that eliminates the above-mentioned drawbacks.

The present invention will be described 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 vertical (or horizontal) deflection circuit of a television receiver, and the PNP whose collector is grounded via an integrating circuit consisting of a resistor _R1 and a capacitor _C1 .
connected to the base of type transistor _Q1 . The base is grounded via diode _D1 and capacitor _C2 . The connection point between this diode _D1 and capacitor _C2 is an NPN whose emitter is grounded.
connected to the base of type transistor _Q2 . The collector of transistor Q ₂ is connected to DC voltage source +B via resistors R ₄ and R ₂ . The connection point between the resistors R ₄ and R ₂ is connected to the emitter of the PMP transistor Q ₁ . Also, transistor
The collector of Q ₁ forms the output terminal 2.

Next, the operation will be explained. vertical (or horizontal)
When a parabolic wave (close to a triangular wave) whose waveform is synchronized with a vertical (or horizontal) synchronization signal is output from the deflection circuit 1, the waveform is shaped by an integrating circuit consisting of a resistor _R1 and a capacitor _C1 . An ideal parabolic wave is formed and input to the base of PNP transistor _Q1 , and according to the voltage change of the parabolic wave
_Q1 works and the pulse slot is taken out from terminal 2.

On the other hand, a part of this parabolic wave is supplied to capacitor _C2 via diode _D1 , and this capacitor
The voltage between the terminals of _C2 increases according to the peak value of the parabolic wave. On the other hand, the NPN transistor _Q2 is turned on because the voltage across the terminals of the capacitor _C2 increases during the parabolic wave supply period. And when the peak value of the parabolic wave increases, the NPN transistor
The collector current of Q ₂ increases, causing the voltage at the connection point of R ₂ and R ₄ , that is, the emitter voltage of transistor Q ₁ to drop. When the emitter voltage of this transistor _Q1 falls, the voltage level at which the PNP transistor _Q1 responds to turn on falls. That is, as shown in A, when the amplitude level of the parabolic wave is A, the transistor
Q ₁ responds with an ON response at a voltage level of the C value, but when the amplitude level of the parabolic wave increases to B, the voltage level at which the transistor Q ₁ responds with an ON response drops to the D value. Therefore, the blanking pulse generated during the conduction period of transistor _Q1 is controlled to always have a constant pulse width regardless of fluctuations in the amplitude level of the input parabolic wave. The pulse width can be adjusted by selecting the emitter-collector resistance value of the NPN transistor _Q2 and the resistance values of the resistors _R4 and _R5 .

Thus, according to the present invention, vertical (or horizontal)
When a blanking pulse is generated based on a parabola wave of a predetermined DC level synchronized with the synchronization signal of , it is effective because a blanking pulse with a constant pulse width can always be formed even if amplitude fluctuations occur in this parabola wave.

[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. Q ₁ ... Pulse generating means, C ₂ , D ₁ , Q ₂ ... Control means.

Claims (1)

[Claims for Utility Model Registration] In a television receiver, pulse generating means detects that an applied parabolic wave having a first DC level has reached a response level and generates a pulse; a detection means for detecting an input DC voltage indicating a peak value of the parabolic wave; and a detection means for controlling the response level according to the voltage level of the applied DC voltage to keep the pulse width of the pulse generated from the pulse generation means constant. 1. A blanking pulse generation circuit comprising: a control means for controlling a blanking pulse;