JPH07154649A - Limiter circuit - Google Patents

Abstract

PURPOSE:To obtain a bright white color by limiting a white level peak at a normal contrast so as to prevent blooming and not limiting the white level peak at a contrast of a predetermined value or over. CONSTITUTION:When a contrast voltage is a predetermined value or below, a transistor(TR) Q3 is turned on and a reference voltage is applied to a base of a TR Q2 by a voltage drop across a resistor R2 and a level around a white peak level of a Y signal is limited. On the other hand, when a contrast voltage rises, the TR Q3 is turned off and the TR Q2 is also nonconductive to release the limiter operation and the Y signal is outputted without any modification even in the white peak level state.

Description

Detailed Description of the Invention

[0001]

[0001]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a limiter circuit for clipping a white peak of a video signal to prevent blooming on a cathode ray tube.

[0003]

[0002]

[0004]

2. Description of the Related Art A conventional limiter circuit generally has a structure shown in FIG. In the figure, a video signal is amplified by an amplifier 1 and applied to the base of one differential transistor Q1. The reference voltage E is applied to the base of the other differential transistor Q2, and the output is taken out from the resistor R1 connected to the common emitter.

[0005]

In such a configuration, a video signal (Y signal)
Is near the white level, the transistor Q1 is turned off and the limit is applied, and the reference voltage E is output to prevent blooming on the cathode ray tube and improve the image quality.

[0006]

[0004]

[0007]

In the conventional structure, the white peak is limited regardless of the contrast. Therefore, when a bright white color is required even if the image quality is ignored, the limiter effect prevents brightening. , Especially P
It is disadvantageous for the one in which the maximum brightness is important such as JTV (projection TV).

[0008]

[0005]

[0009]

SUMMARY OF THE INVENTION The present invention, which has been made to solve the above-mentioned problems, is a limiter circuit for clipping a white peak of a video signal to prevent blooming. And a contrast voltage for controlling the contrast are input, the white peak of the video signal is limited and output when the contrast voltage is a voltage corresponding to a predetermined contrast or less, and the voltage is a voltage corresponding to a predetermined contrast or more. A limiter control means for outputting the white peak of the video signal without limiting is provided.

[0010]

[0006]

[0011]

With the limiter control means, the white peak of the video signal is limited within a predetermined contrast to prevent blooming, and when the contrast is higher than the predetermined contrast, the white peak of the video signal is not limited and the image quality is prioritized to obtain a bright white. To be able to reproduce

[0012]

[0007]

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiment of the present invention shown in FIG.
The same parts as those in the figure are denoted by the same reference numerals.

[0014]

In FIG. 1, the differential transistor Q2
Transistor Q3, resistor R2 and capacitor C at the base of
1 parallel circuit is provided. Also, the transistor Q
A contrast control voltage is applied to the base of No. 3.

[0015]

In such a configuration, when the contrast voltage is below a predetermined value, the transistor Q3 is on, and the reference voltage is applied to the base of the differential transistor Q2 due to the voltage drop of the resistor R2, and the circuit configuration similar to that of FIG. Has become. Therefore, a limiter is applied near the white peak of the Y signal, and blooming can be prevented.

[0016]

On the other hand, if the contrast voltage rises and a predetermined value is set near the maximum value (about Vcc), for example, the transistor Q3 turns off when the predetermined value is exceeded, and the transistor Q2 also turns off.

[0017]

Therefore, the limiter operation is canceled and the Y signal is output as it is even at the white peak, and a high-luminance screen is obtained.

[0018]

The capacitor C1 and the capacitor C2 connected between the collector and the base of the transistor Q3.
Are provided to suppress the fluttering of the limiter operation near the on / off operation of the transistor Q3.

[0019]

[0013]

[0020]

As described above, according to the present invention, when the contrast is increased, the brightness becomes high and bright white is obtained, and the white peak is limited within the normal contrast to prevent blooming.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional configuration.

[Explanation of symbols]

 Q1, Q2 differential transistor Q3 transistor

Claims (1)

[Claims] 1. A limiter circuit for preventing blooming by clipping a white peak of a video signal, wherein the video signal and a contrast voltage for controlling contrast are input, and the contrast voltage is a predetermined contrast. When a voltage corresponding to the following, the white peak of the video signal is limited and outputted, and when a voltage corresponding to a predetermined contrast or higher, the white peak of the video signal is outputted without being limited. Characteristic limiter circuit