JPH05336470A - Video signal limiting circuit - Google Patents

Abstract

PURPOSE:To prevent a beam current from exceeding a standardized upper limit value when excessive video signals are inputted and to improve the freedom at the time of setting brightness or the like relating to the video signal limiting circuit suitable for being applied to a television receiver. CONSTITUTION:A clamping circuit 4 is inserted between the luminance signal output terminal 3 of a video signal switching circuit 1 and the inverse amplification circuit 5 of a delay circuit 6 for loss compensation and signals with amplitude more than specified are saturated and limited at an inverse circuit 7. Only the signals with the amplitude less than specified are inputted to a video signal processing circuit 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal limiting circuit in a television receiver.

[0002]

2. Description of the Related Art Conventionally, ABL is a technology in this field.
There is an automatic brightness limiting circuit, and as shown in FIG. 2, a circuit for suppressing the brightness control voltage and the contrast control voltage of the video signal processing circuit by utilizing the voltage drop accompanying the increase of the beam current is provided. The one used was the mainstream.

[0003]

However, in the circuit having the above structure, the beam current is out of the standard due to the limit of the contrast control range, the screen brightness is insufficient due to the overcorrection of the brightness control, or the beam current is detected. AB by time constant
There is a problem that L is oscillated and it is difficult to design efficiently.

[0004]

In order to solve the above problems, the present invention inserts a circuit for limiting the amplitude of a video signal between an input video signal switching circuit and a video signal processing circuit,
It is possible to efficiently set the screen brightness and the beam current limit when a signal within the standard is input.

[0005]

According to the present invention, since the luminance signal output from the input video signal switching circuit is clamped and the pedestal level is adjusted as described above before being input to the amplifier circuit, a signal having a certain amplitude level or more is input. Then, a portion with a certain amplitude or more is saturated in the amplifier circuit and the amplitude level is limited. This causes only a video signal with a certain amplitude or less to be input to the video signal processing circuit. At the same time, the beam current falls within the standard value, and the durability is improved.

[0006]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a video amplitude limiting circuit showing a first embodiment of the present invention. In FIG. 1, 1 is a video signal switching circuit, 2 is a Y / C separation circuit, 3 is a luminance signal output terminal, 4 is a clamp circuit, 5 is an inverting amplifier circuit, 6
Is a delay circuit, and 7 is an inverting circuit.

In FIG. 1, the video signal selected by the video signal switching circuit 1 is the brightness signal output from the brightness signal output terminal 3 as it is in the case of Y / C separation input.
In the case of composite input, the luminance signal separated through the Y / C separation circuit 2 is output from the luminance signal output terminal 3.
The luminance signal output next is fixed to a voltage whose pedestal level is constant by the clamp circuit 4, and the inverting amplifier circuit 5
Entered in. However, since the inverting amplifier circuit 5 sets the values of R2 and R3 to the same value for impedance matching with the delay circuit 6 and sets the parallel resistance values thereof and R1 to the same value, the inverting amplifier circuit 5 operates only by inverting. . Then, in the inverting circuit 7, TR
The signal amplitude is limited on the emitter side of 1 and the polarity of the signal is restored to the original on the collector side for output. D1 is used for temperature characteristic compensation of TR1.

[0009]

As described above in detail, according to the present invention, even if an excessive video signal is input to a television receiver, only a portion having a certain amplitude level or less is displayed on the screen, so that the value is equal to or more than a specified value. Beam current does not flow and the degree of freedom in setting the ABL circuit is increased, so that a brighter screen can be easily created.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a video signal limiting circuit showing a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a conventional circuit.

[Explanation of symbols]

 1 Video signal switching circuit 2 Y / C separation circuit 3 Luminance signal output terminal 4 Clamp circuit 5 Inversion amplification circuit 6 Delay circuit 7 Inversion circuit 8 Video signal input terminal group 9 Synchronization signal 10 Video signal processing circuit 11 Luminance control terminal 12 Contrast control Terminal 13 ABL circuit

Claims (1)

[Claims] 1. An input video signal switching circuit having a luminance signal output terminal, a delay circuit for time synchronization between a Y / C separation signal input and a sync signal when a composite signal is input, and a preceding stage of the delay circuit. And a television provided with an amplifier circuit inserted in the latter stage for performing loss correction in the delay circuit, and a clamp circuit inserted between the input of the former stage amplifier circuit and the luminance signal output terminal of the video signal switching circuit. In John receiver, when the excessive video signal is input, the beam current of CRT does not flow beyond the standard value,
A video signal limiting circuit intended to improve durability and design latitude.