JPH0265570A - Gate pulse generating circuit - Google Patents

Abstract

PURPOSE:To obtain a stable gate pulse by inputting a flyback pulse from a flyback transformer to a base of a transistor(TR) via the 1st differentiating circuit, coupling the 2nd differentiating circuit with the output so as to clamp any of positive or negative output waveform. CONSTITUTION:A flyback pulse inputted from an input terminal 1 passes through a resistor R1 and differentiated by the 1st differentiating circuit comprising components C1 and R2 and fed to a base of a TR Q1. The collector potential of the TR Q1 forms a collector waveform of a rectangular wave pulse. The pulse signal formed in this way is outputted from the 2nd differentiating circuit comprising a capacitor C2 and a resistor R4 and a diode D1 cancels a pulse in opposite direction equivalent to a negative pulse and applies peak clamp. Since the output signal waveform is synchronized with the back porch of a composite video signal, the signal is extracted as a gate pulse from an output terminal 4.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a circuit for generating gate pulses for stable DC clamping in a television receiver.

[Conventional technology]

In television receivers, it is necessary to apply a gate pulse to the back porch of the horizontal synchronizing signal in order to maintain the DC (direct current) level of the RGB signals of the RGB interface circuit constant. The synchronization separation circuit 2 extracts the horizontal synchronization signal from the composite video signal input to the input terminal l, and the waveform shaping circuit 37 in the next stage shapes the waveform and shifts the phase to match the timing of the back porch. was generated and output from output terminal 4.

FIG. 4 is a circuit that embodies FIG. 3, and the synchronous separation circuit 2 includes capacitors C1l and C12 and a resistor 1111.1?1.
The waveform shaping circuit 3 was composed of resistors R14, R15, R16, capacitors C13, C14, C15, and coil Lll.

[Problem to be solved by the invention]

However, with the method of obtaining gate pulses using the horizontal synchronization signal as described above, when noise is mixed into the composite video signal due to a weak electric field, or when there is no composite video signal, it is difficult to use for DC clamping. It was not possible to obtain a stable gate pulse.

Furthermore, in television receivers using black-screen picture tubes, there are problems such as forgetting to turn off the power switch because the screen becomes dark when the composite video signal disappears.

Therefore, an object of the present invention is to provide a gate pulse generation circuit that can obtain stable gate pulses regardless of the strength or presence of a composite video signal.

Means for Solving Problem C] The present invention has been made to solve the above problem, and includes inputting a flyback pulse from a flyback transformer to the base of a transistor via a first differentiating circuit, A second differentiating circuit was connected to the output of the transistor, and either the positive or negative output waveform of the differentiating circuit was clamped to form a DC clamp pulse source.

[Effect]

According to the above configuration, the flyback pulse is input to the base of the transistor via the first differentiating circuit, and when the base potential is below a predetermined value, the transistor is turned off and a square wave output pulse is generated. The same pulse is taken out through a second differentiating circuit, and by clamping one of the positive and negative output waveforms that does not match the back porch of the horizontal synchronizing signal in timing with a diode, it can be used as a pulse source for DC clamping. A gate pulse can be generated.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

Figure 1 is a circuit diagram for generating gate pulses, in which gate pulses are generated based on flybank pulses output from a flyback transformer (not shown), for example, by a one-turn coil for voltage extraction. It consists of

To explain the circuit configuration in Fig. 1, 1 is the input terminal of the flyback pulse, the input terminal 1 and the transistor Q
A first differentiating circuit consisting of a capacitor CI connected in series with a resistor R1 and a grounding resistor R2 is interposed between the bases of the first differential circuit.

The collector of the transistor Q1 is grounded via a load resistor R3, and a second differentiating circuit consisting of a capacitor C2 and a grounding resistor R4 is interposed between it and the output terminal 4 of the gate pulse. is connected to the cathode of a diode DI whose anode is grounded.

The emitter of the transistor Ql is at one potential Vee ii
connected to the source.

To explain the circuit operation in conjunction with Figs. 2(a) to 2(e), the flyback pulse input from input terminal l has a chevron-shaped pulse waveform as shown in Fig. 2(b). It is synchronized with the horizontal synchronization signal of the composite video signal in (a).

This flybank pulse passes through the resistor R1, is differentiated by the first differentiating circuit CI, R2, and is applied to the base of the transistor Q1, but the base waveform at that time is shown in Figure 2 (
As shown in C), the charging waveform voltage is charged to the capacitor C1 at the same time as the flyback pulse rises,
At the time of falling (at the rear), the discharge waveform voltage is approximately the same magnitude as the charging waveform voltage, but in the opposite direction.

In addition, when there is no flyback pulse input, the base potential is Ov, and the emitter of the transistor Ql is - potential Ve.
Since it is connected to the e power source, there is a potential difference between the base and emitter, and the collector and emitter are in a conductive state, and the collector potential is held at one potential that is approximately equal to the emitter potential.

By the way, when the base waveform signal voltage is applied to the base and the charging waveform voltage changes to the discharging waveform voltage and the base potential becomes almost equal to the emitter potential, the transistor Q1 is turned off and the collector potential decreases as shown in FIG. 2(d). is Ov
However, when the base potential rises and becomes higher than the emitter potential, the transistor Ql is turned on again, and the collector potential becomes almost equal to the emitter potential, as shown in Figure 2 (d).
Form a collector waveform of rectangular pulses as shown in .

As is clear from FIGS. 2(a) and 2(d), this pulse signal is synchronized with the back porch of the composite video signal.

The pulse signal formed as described above is output from the second differentiating circuit consisting of capacitor C2 and resistor R4.
The output waveform consists of positive and negative signals, and the diode D1 has the role of canceling out the negative pulse in the opposite direction and performing peak clamping.

The output signal waveform generated by canceling the pulse in the opposite direction is synchronized with the back porch of the composite video signal in FIG. 2(a), as shown in FIG. 2(e), so it is output from output terminal 4 as a gate pulse. It can be taken out.

The flyback pulse mentioned above is always output and when there is a composite video signal, it is synchronized with the horizontal synchronization signal of the composite video signal, so the gate pulse generated based on this flybank pulse is The pulse can be constantly synchronized with the back porch of the composite video signal, and stable DC clamping can be performed.

In addition, when there is no composite video signal or when a composite video signal cannot be obtained reliably due to a weak electric field, there is naturally no back porch that is subject to DC clamping, but in reality some kind of noise signal is generated. Since this noise signal can be clamped with the gate pulse generated based on the flyback pulse mentioned above, some kind of signal is also output to the picture tube, making it possible to brighten the picture tube with a black screen to some extent. This is useful as a measure to prevent forgetting to turn off the power switch.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to generate a stable gate pulse for keeping the DC level of the ROB signal constant based on the flyback pulse, regardless of the strength or presence of the composite video signal. In addition to being able to reproduce chromatically stable images, when there is no composite video signal, the noise signal generated within the television receiver is clamped using the gate pulse, making it possible to brighten the picture tube with a black screen to some extent. It is also useful as a measure to prevent forgetting to turn off the power switch, which tends to occur when the composite video signal is lost.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of gate pulse generation showing an embodiment of the present invention, Fig. 2 (a) to (e) are waveform diagrams for explaining the operation of the circuit, and Fig. 3 is a conventional gate pulse generation circuit diagram. circuit diagram,
FIG. 4 is a detailed circuit diagram of FIG. 3. In the figure, 1...input terminal, 4...-output terminal, ql
...-...Transistor, Dl...Diode,
CI, C2--Capacitor, R1-R4...Resistor, Vee--One power supply. Figure 3 Patent applicant Fujitsu General Ltd. Figure 4

Claims (1)

[Claims] The flyback pulse is input to the base of the transistor via the first differentiating circuit, and the second pulse is input to the output of the same transistor.
What is claimed is: 1. A gate pulse generation circuit comprising: a differentiating circuit; and clamping either a positive or negative output waveform of the differentiating circuit to serve as a pulse source for DC clamping.