JPH0683412B2 - Brightness adjustment device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a brightness adjusting device suitable for use in a high-definition television receiver, a high-resolution color image display device, and the like.

2. Description of the Related Art Conventional Problems and Their Problems Generally, in a television receiver, an output video signal is supplied to the cathode of a cathode ray tube, and the brightness of the image screen of this cathode ray tube is adjusted as shown in FIG. 2A. This is done by adjusting the DC level of the video signal supplied to the cathode. Therefore, the video output circuit requires the dynamic range of the DC level value b of the brightness variable range in addition to the peak-to-peak value a of the video signal necessary for driving the cathode ray tube.

By the way, in the recently proposed high-definition television receivers, high-resolution color image display devices, etc., the image signal has a wide band, and the image output circuit can increase the power consumption by widening the band, that is, the dynamic range. It is required to be small.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to reduce the dynamic range of a video output circuit to a necessary minimum and to perform brightness adjustment to reduce power consumption.

SUMMARY OF THE INVENTION According to the present invention, a reference voltage is supplied to a cathode ray tube during a predetermined period of a video signal, a beam current during the predetermined period is detected, and a beam current during the predetermined period becomes constant according to the detection signal. A control signal is supplied to the cathode ray tube so that this cathode ray tube operates based on the beam current of this predetermined period, and this reference voltage can be varied.By adjusting this reference voltage, the brightness can be adjusted. According to the present invention, the dynamic range of the video output circuit can be minimized and the brightness can be adjusted, and the power consumption can be reduced.

Embodiment An embodiment of the brightness adjusting device of the present invention will be described below with reference to the drawings.

In FIG. 1, (1) shows a video signal input terminal to which the output signal of the video detection circuit of the television receiver is supplied,
The video signal supplied to this video signal input terminal (1) is used as a reference level during the 16th, 17th, 18th and 19th horizontal periods of the vertical blanking period in this example for a predetermined period. The signal is supplied to one input terminal of the reference level signal insertion circuit (2) for inserting the signal. Further, in FIG. 1, (3) shows a variable resistor for brightness adjustment, one end of this variable resistor (3) is connected to a power supply terminal + B to which a predetermined DC voltage is supplied, and this variable resistor is connected. The other end of the container (3) is grounded. The DC voltage obtained at the mover (3a) of the variable resistor (3) is supplied to the source of the field effect transistor (4) which constitutes the gate circuit. (5) shows the gate signal input terminal, and the gate signal supplied to this gate signal input terminal (5) is the vertical blanking period of the video signal supplied to the video signal input terminal (1) in this example. When the part is as shown in FIG. 3A, as shown in FIG. 3B, the periods corresponding to the four horizontal periods of the 16th, 17th, 18th and 19th vertical blanking periods of the video signal. Is a high voltage signal. The gate signal supplied to the gate signal input terminal (5) is supplied to the gate of the field effect transistor (4), and the variable resistor (during the high voltage period of the gate signal is supplied to the drain of the field effect transistor (4) ( The DC voltage obtained at the mover (3a) of 3) is obtained, and this DC voltage is supplied to the other input terminal of the reference level signal insertion circuit (2) as a reference level signal. In the reference level signal insertion circuit (2), reference level signals are inserted in the 16th, 17th, 18th and 19th horizontal periods of the vertical blanking period of the video signal. In this case, the video signal and the reference level are matched with each other, for example, the pedestal of the video signal is clamped to a predetermined voltage.

The output signal of this reference level signal insertion circuit (2) is connected to the base of a pnp type transistor (7) that constitutes an emitter follower amplifier via the video output amplification circuit (6), and the emitter of this transistor (7) is connected. Cathode ray tube through resistor (8)
Connected to the cathode of (9) and the emitter of this transistor (7) is a pnp type transistor (1
0) collector, and the emitter of this transistor (10) is connected to the power supply terminal + B to which a positive DC voltage is supplied,
The power supply terminal + B is grounded through a series circuit of resistors (11) and (12), and the connection point of the resistors (11) and (12) is connected to the base of the transistor (10). Gate signal input terminal
The gate signal supplied to (5) is supplied to the base of the transistor (10) so that the transistor (10) is turned off when the gate signal is present.

Also, the collector of the transistor (7) is grounded via the resistor (13) for detecting the beam current of the cathode ray tube (9), and the collector of this transistor (7) is connected to the emitter of the pnp type transistor (14). The collector of this transistor (14) is grounded, the base of this transistor (14) is connected to the gate signal input terminal (5), and this transistor (14) is turned off only when this gate signal is present. Only when
This resistor (13) detects the beam current. In this case, the gate signal is present, and at high voltage the transistor
Since (10) and (14) are turned off, respectively, and the signal supplied to the base of the transistor (7) becomes a reference level signal, and this reference level signal is supplied to the cathode of the cathode ray tube (9). The beam current of the cathode ray tube (9) at the time of the level signal can be detected by the resistor (13). The beam current detection signal obtained at both ends of this resistor (13) is supplied to the source of the field effect transistor (16) constituting the gate circuit via the buffer amplifier circuit (15), and the field effect transistor (16) The drain is grounded through a capacitor (17) which constitutes a memory circuit, and the gate of this field effect transistor (16) is connected to a gate signal input terminal (5). In this case, the field effect transistor 16 is turned on only for four horizontal periods in which the gate signal exists. A beam detection signal obtained at both ends of this capacitor (17) is supplied to an inverting input terminal of an operational amplifier circuit (19) forming a comparison circuit via a buffer amplifier circuit (18). A predetermined set voltage is supplied to the non-inverting input terminal of the operational amplifier circuit (19). That is, the non-inverting input terminal of the operational amplifier circuit (19) is connected to the power supply terminal + B to which a positive DC voltage is supplied via the resistor (20), and the non-inverting input terminal is connected via the resistor (21). Ground and connect the non-inverting input terminal to the mover (22a) of the variable resistor (22) for adjusting the set voltage, which is connected between the power supply terminal + B and the ground. The error signal obtained at the output terminal of this operational amplifier circuit (19) is supplied to the voltage conversion circuit (24) via the low-pass filter (23), and the error obtained at the output side of this voltage conversion circuit (24) A control signal corresponding to the signal is supplied to the first grid of the cathode ray tube (9) via the resistor (25). Others are configured similarly to the conventional television receiver.

Since this example is configured as described above, the transistor
The reference level signal is inserted in the 16th, 17th, 18th and 19th horizontal periods of the vertical blanking period of the video signal supplied to the base of (7), and the 16th, 17th and 17th Since the gate signal is present and has a high voltage in the 18th and 19th horizontal periods, the transistor (10) and the transistor (1
4) are turned off respectively, and at this time, since the reference level signal is supplied to the base of the transistor (7), this reference level signal is supplied to the cathode of the cathode ray tube (9), and this cathode ray tube (9) receives this reference level signal. The beam current at the reference level signal flows, and this beam current flows through the resistor (8) and the transistor (7).
Flows through the series circuit of the resistor (13) to this resistor (13)
This beam current can be detected by the voltage across the capacitor and the voltage across the resistor (13) constitutes a memory circuit via the buffer amplifier circuit (15) and the field effect transistor (16) which is on at this time. The beam current detection signal supplied to (17) and obtained in this capacitor (17) is supplied to the comparison circuit (19) via the buffer amplification circuit (18) and is obtained at the output side of this comparison circuit (19). Since the voltage corresponding to the error signal with the set voltage is supplied to the first grid of the cathode ray tube (9) and fed back, a constant beam current determined by the set voltage during the four horizontal periods in which the gate signal exists is a cathode ray. Tube (9)
It works like flowing. Therefore, a signal corresponding to the reference level signal is stored in the capacitor (17) constituting the memory circuit, and a control signal corresponding to this memory signal is supplied to the first grid of the cathode ray tube (9) until the next gate signal comes. To be done.

In the period when the gate signal is not present, the field effect transistors (4) and (16) are off, respectively.
The transistor (10) operates as a constant current circuit and the transistor (1
Since 4) is on, the video signal supplied to the video signal input terminal (1) at this time is the cathode ray tube through the video amplifier circuit (6) and the transistor (7) as in a normal television receiver. A control signal corresponding to the signal supplied to the cathode of (9) and stored in the capacitor (17) constituting the memory circuit is supplied to the first grid of the cathode ray tube (9). In this case, the brightness of the picture screen in the cathode ray tube (9) corresponds to the level V _G of the reference level signal as shown in FIG. 2B. Therefore, the luminance can be relatively changed by changing the level V _G of the reference level signal with respect to the video signal. Therefore, the variable resistor for brightness adjustment of FIG.
The brightness of the image screen of the cathode ray tube (9) can be adjusted by adjusting the mover (3a) of (3). In this brightness adjustment, the level V _G of the reference level signal is adjusted with respect to the video signal to change the brightness relatively. Therefore, the dynamic range of the video output amplifier circuit (6) or the like drives the cathode ray tube (9). Therefore, the dynamic range can be minimized and power consumption can be reduced accordingly.

Furthermore, in this example, since the beam current of the cathode ray tube (9) is operated so as to be constant, the variation of the cutoff voltage of the cathode ray tube (9), the change over time, the variation of the circuit system, the temperature characteristic, etc. The cathode ray tube (9) can always be operated.

Although the above embodiments have been described with respect to the examples in which the present invention is applied to the white and black television receivers, they can be similarly applied to a color television receiver, a high-definition television receiver, a high-resolution color image display device, and the like. Is easy to understand. Further, in the above embodiment, the reference level signal is inserted in the 16th, 17th, 18th and 19th horizontal periods of the vertical blanking period of the video signal, but instead of this, other suitable Of course, this may be inserted in the position. Further, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various other configurations can be adopted without departing from the gist of the present invention.

Advantageous Effects of Invention According to the present invention, there is an advantage that the dynamic range of the video output circuit can be minimized and the brightness can be adjusted, and the power consumption can be reduced. Therefore, it is extremely advantageous to apply the present invention to a high-definition television receiver, a high-resolution color image display device, and the like, which have recently been proposed, in which the image signal has a wide band.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the brightness adjusting device of the present invention,
2 and 3 are diagrams for explaining the present invention. (1) is a video signal input terminal, (2) is a reference level signal insertion circuit, (3) is a brightness adjusting variable resistor, (4) and (16) are field effect transistors respectively, and (5) is a gate signal input. Terminal, (6) video output amplifier circuit, (7), (10) and (14) transistors, (9) cathode ray tube, (13) resistor for beam current detection, (17) memory circuit Is a capacitor, and (19) is a comparison circuit.

Claims (1)

[Claims] 1. A reference pulse generation circuit capable of varying a pulse crest value, and a reference level signal for inserting a reference pulse from the reference pulse generation circuit into a predetermined period of a video signal and supplying this to a cathode of a cathode ray tube. An insertion circuit, a detection circuit for detecting a current corresponding to the cathode ray tube beam current in the predetermined period, a storage circuit for storing the output of the detection circuit, and comparing the output voltage of the storage circuit with a predetermined reference voltage, A comparison circuit that generates an error signal whose amplitude changes according to their magnitude relationship, and a voltage conversion circuit that creates a control signal from the error signal and supplies the control signal to the first grid of the cathode pipe are provided. Then, the control signal is supplied to the first grid of the cathode ray tube so that the beam current of the cathode ray tube becomes constant, and outside the predetermined period, the beam current in the predetermined period is used as a reference. While making the polar tube work,
A brightness adjusting device characterized in that the brightness is adjusted by adjusting the value of the reference pulse.