JPH0728773Y2 - Beam blanking circuit for cathode ray tubes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a beam blanking circuit for a cathode ray tube which is suitable for use in a cathode ray tube for a viewfinder of a video camera device, for example.

[Outline of device]

The present invention, in a beam blanking circuit suitable for a cathode ray tube for a viewfinder of a video camera device, stops a beam within a video blanking period based on a synchronizing signal of a video signal and a blanking pulse.
The beam is surely stopped only during the image blanking period.

[Conventional technology]

Conventionally, a video signal is supplied to a CRT for black and white display used in a viewfinder of a video camera device via a beam blanking circuit as shown in FIG. That is, in FIG. 3, (1) indicates a video signal input terminal,
The image processing circuit (2) outputs the image signal (or the image signal reproduced from the VTR section) obtained by imaging to the input terminal (1).
Is supplied to the beam blanking circuit (3) via the beam blanking circuit (3), and the beam blanking circuit (3) converts the video signal level into a signal having a level sufficiently lower than the normal black level for the horizontal and vertical blanking periods. The video signal output by the ranking circuit (3) is, for example, a cathode ray tube (4).
Supply to the first grid of.

In this case, the input video signal is supplied to the sync separation circuit (5), this sync separation circuit (5) separates the horizontal sync signal from the input video signal, and the separated horizontal sync signal is output to the beam blanking circuit (3) and It is supplied to one input terminal of an automatic frequency control circuit (hereinafter referred to as AFC circuit) (6). this
A flyback pulse drawn from an auxiliary winding (10c) of a flyback transformer (10) described later is supplied to the other input terminal of the AFC circuit (6). Then, the AFC circuit (6) compares the phase difference between the blanking pulse and the horizontal synchronizing signal, and controls the oscillation of the oscillator (7) based on the detected phase difference information. Then, the oscillation signal of the oscillator (7) is supplied to the horizontal drive circuit (8), the output signal of the horizontal drive circuit (8) is supplied to the horizontal output circuit (9), and the output signal of the horizontal output circuit (9) is supplied. An output signal having a horizontal cycle is supplied to the primary winding (10a) of the flyback transformer (10).
Then, the secondary winding of the flyback transformer (10) (10
The high voltage signal obtained in b) is supplied to the horizontal deflection coil (12) via the rectifier (11). Also, the horizontal cycle flyback pulse obtained from the auxiliary winding (10c) of the flyback transformer (10) is supplied to the AFC circuit (6) and the waveform shaping circuit (13). A blanking pulse having a horizontal cycle is created, and this blanking pulse is supplied to the beam blanking circuit (3).

Here, an example of the circuit configuration of the beam blanking circuit (3) is shown in FIG. 4, in which a video signal input terminal (21) to which an output video signal is supplied from the video processing circuit (2) is connected to a resistor ( 22) and connected to the emitter of an npn-type transistor (23). The blanking pulse input terminal (24) from the waveform shaping circuit (13) is connected to the emitter of the transistor (23) through a series circuit of a diode (26) and a resistor (25). Further, the power supply terminal (27) is connected to the collector of the transistor (23) via the resistor (28), and the emitter of the transistor (23) is grounded via the resistor (29). Then, the base of the transistor (23) is grounded via the capacitor (30), and the power supply terminal (27)
Is grounded through a series circuit of resistors (31) and (32), and the midpoint of connection between the resistor (31) and the resistor (32) is connected to the base of the transistor (23).

Then, the collector of the transistor (23) is connected to the base of the npn-type transistor (33), and the power supply terminal (27) is connected to the collector of the transistor (33). The emitter of the transistor (33) is grounded via the resistor (34), and the output terminal (3) is connected via the capacitor (35).
6) Connect to. Furthermore, the horizontal sync signal input terminal (37) from which the horizontal sync signal from the sync separation circuit (5) is obtained,
Via a series circuit of a capacitor (38) and a resistor (39)
It is connected to the base of an npn-type transistor (40), and the collector of this transistor (40) is connected to the output terminal (36). Further, the emitter of this transistor (40) is grounded, and the base is grounded via the resistor (41).

According to the beam blanking circuit having such a configuration, the blanking pulse obtained at the blanking pulse input terminal (24) is added to the video signal obtained at the input terminal (21), and the added video signal is transferred to the transistor ( It is supplied to the output terminal (36) side via a grounded base amplifier composed of 23) and (33). Where the output terminals (36)
Is connected to the collector of the transistor (40), and the horizontal synchronization signal is supplied to the base of the transistor (40) via the capacitor (38) and the resistor (39). The blanking period of the video signal is clamped to a predetermined level lower than the normal black level. Therefore, the video signal supplied from the output terminal (36) to the first grid of the cathode ray tube (4) becomes a signal whose level during the blanking period is lower than the normal black level, and the beam is not output during the blanking period. , Good beam control is performed.

[Problems to be solved by the device]

By the way, the phase control by the AFC circuit (6) has a drawback that the locked state is temporarily released during the vertical blanking period of the video signal, and the synchronization signal output by the oscillator (7) is output during the first horizontal scanning period of the video signal of each field. The phase of is out of phase with the video signal.

When such a phase shift of the synchronization signal occurs, the blanking pulse shifts, the timing of clamping the output video signal by the transistor (40) of the beam blanking circuit (3) shifts, and the first of each field other than the blanking period. Therefore, there is a problem that the upper part of the screen of the image displayed on the cathode ray tube (4) is blackened.

Also, when a video signal reproduced at a variable speed from a video tape reproducing device is obtained at the input terminal (21), the horizontal synchronizing period of the reproduced video signal is often disturbed, and such a video signal is displayed on the cathode ray tube (4). There is a high possibility that the time other than the blanking period will be clamped also when performing, and there is a disadvantage that the displayed image is disturbed during variable speed reproduction.

In view of the above points, the present invention has an object to provide a beam blanking circuit that reliably stops a beam only during a blanking period.

[Means for Solving the Problems]

The beam blanking circuit of the present invention, for example, as shown in FIG. 1, uses a terminal (2) for the video signal obtained at the terminal (21).
4) Addition circuits (25) and (26) for adding the blanking pulse obtained, and horizontal synchronization obtained at the terminal (37) obtained by extracting the output signals of these addition circuits (25) and (26) from the video signal. Clamp circuit (40) designed to clamp with a signal
And the output of this clamp circuit (40) is supplied to the predetermined electrode of the cathode ray tube through the terminal (36) in the beam blanking circuit of the cathode ray tube, which is the clamp signal supplied to the clamp circuit (40). When the synchronizing signal is gated by the blanking pulse obtained at the terminal (24) and the clamped operation is performed by the gated horizontal synchronizing signal, when the blanking pulse and the horizontal synchronizing signal are not supplied at the same timing, the clamp circuit The clamp operation is not performed in.

[Action]

According to such a configuration, the video signal is clamped only during the period when the synchronizing signal of the video signal and the blanking pulse match, so that it is possible to prevent clamping other than the blanking period.

〔Example〕

An embodiment of the beam blanking circuit for a cathode ray tube according to the present invention will be described below with reference to FIGS. 1 and 2.
In FIGS. 1 and 2, parts corresponding to those in FIGS. 3 and 4 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this example, similar to the one described as the conventional example,
A beam blanking circuit used for a CRT for a viewfinder of a video camera device, which is constructed as shown in FIG. That is, the emitter of the clamp npn type transistor (40) is connected to the emitter of the pnp type transistor (42), and the collector of this transistor (42) is grounded. Then, the blanking pulse input terminal (24) is connected to the base of the transistor (42) via the resistor (43).

The other parts are configured similarly to the beam blanking circuit of FIG.

The operation of beam blanking by such a circuit configuration will be described with reference to FIG. 2. First, a normal video signal is supplied to the video signal input terminal (21) as shown in FIG. A blanking pulse as shown in FIG. 2B is added to this video signal by a resistor (25) and a diode (26) which form a circuit. Therefore, a signal having a large difference between the level of the blanking period and the level of the video portion can be obtained as the addition signal. Then, the added signal is clamped to a predetermined level by the transistor (40) by the horizontal synchronizing signal as shown in FIG. 2C. In this example, the transistor (40) is supplied with a blanking pulse. Controlled by (42).
Therefore, the clamp signal is gated by the blanking pulse as shown in FIG. 2B, and the clamp signal is clamped only when the blanking period and the horizontal synchronizing signal supply timing coincide with each other, and only the blanking period is set to the normal black level. An output video signal as shown in FIG. 2D which is clamped at a predetermined lower level is obtained, and this output video signal is supplied to the cathode ray tube (4).

Therefore, according to the circuit of this example, the video signal is clamped only when the blanking pulse and the horizontal synchronizing signal are in phase with each other, and it is not clamped except during the blanking period, and the beam is stopped in the video portion. Is prevented, and the upper side of the image displayed on the cathode ray tube (4) does not sink black.

It should be noted that the present invention is not limited to the above-described embodiments, and it goes without saying that various other configurations can be adopted without departing from the gist of the present invention.

[Effect of device]

According to the present invention, it is possible to reliably clamp only the blanking period of the video signal with a simple structure, and there is an advantage that image display on a cathode ray tube is performed well.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a waveform diagram for explaining the example of the drawing, FIG. 3 is a configuration diagram of the periphery of the beam blanking circuit, and FIG. 4 is a circuit diagram showing an example of a conventional beam blanking circuit. (21) is a video signal input terminal, (24) is a blanking pulse input terminal, (36) is a video signal output terminal, and (37) is a horizontal synchronizing signal input terminal.

Claims (1)

[Scope of utility model registration request] 1. A video signal source, an adder circuit for adding a blanking pulse to the video signal from the video signal source, and an output signal of the adder circuit is clamped by a horizontal synchronizing signal extracted from the video signal. And a beam blanking circuit for a cathode ray tube in which the signal of the clamp circuit is supplied to a predetermined electrode of the cathode ray tube. The horizontal synchronizing signal, which is the clamp signal supplied to the clamp circuit, is supplied to the blanking pulse. And a clamp operation is performed by the gated horizontal synchronizing signal, and when the blanking pulse and the horizontal synchronizing signal are not supplied at the same timing, the clamp circuit does not perform the clamping operation. Beam blanking circuit for cathode ray tubes.