JPH03211588A - Video input circuit - Google Patents

Abstract

PURPOSE:To assure good images and reliability even if the signal of an excess amplitude is inputted by providing a means for controlling the gain of an amplifying means according to the result of comparison between the amplitude value of an inputted video signal and a reference value when the amplitude value exceeds the reference value. CONSTITUTION:The peak value VSP of the video signal inputted from an input terminal 1 is detected and held by a peak detecting and holding device 2. The peak value VSP is thereafter compared with the reference voltage VSO by a comparator 4. A selector 7 switches to a comparator 4 side and the gain suppression voltage VC of an amplifier 5 is the output voltage VP of the comparator 4 when VSP>VSO is attained. The good images and reliability are assured regardless of the contents of the signal even when the signal of the excess amplitude is inputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video input circuit for a cathode ray tube (hereinafter referred to as CRT) display device.

[Conventional technology]

There are two types of video input signals for a CRT display device: digital signals such as TTL and analog signals. Among these, analog signals are advantageous for gradation display, high speed, etc.
Since the signal waveform is directly transmitted to the CRT drive circuit,
The disadvantage is that the distortion of the input signal is also displayed on the screen. In particular, when an excessive amplitude is input, the amplitude of the CRT drive circuit also becomes excessive, which not only increases screen brightness but also causes screen saturation due to insufficient dynamic range of the circuit (gradation collapse on the high brightness side, trailing of certain colors, etc.). phenomenon), focus deterioration, and other significant image quality deterioration, as well as C due to excessive beam current.
There is a problem of deterioration of RT life.

Conventionally, protection against excessive beam current has been achieved by detecting the average value of the beam current and limiting the gain of the amplifier when it exceeds a certain value.
rast Lim1tter) circuit and the ABL (Automattc B) circuit that controls the DC level of the signal.
There are also methods for detecting the peak value of the beam current and controlling the gain of the amplifier.

These known examples include JP-A-51-118518, JP-A-55-78722, and JP-A-60-2.
There is such a thing as Publication No. 17768.

[Problem to be solved by the invention]

The above conventional technology has the following problems.

That is, in the method of detecting the average beam current, A P L (Average Pictu
It is effective for signals with high reLevel), but when receiving signals with low APL such as characters drawn on a black background, which are normally used in computer equipment (this cannot track excessive amplitude and the image quality deteriorates). There was a problem that could not be avoided.

In addition, with the method of detecting the peak of the beam current, if signals with different amplitudes switch rapidly, for example, an excessive amplitude may occur in an odd field during interlacing.

When a signal with the maximum allowable amplitude is input in an even field, the gain is limited in an odd field and not in an even field, so the difference in signal amplitude ζ will not be able to reproduce the brightness difference that should be displayed, resulting in high brightness. There was a problem in that the gradation display performance of some parts was impaired.

An object of the present invention is to ensure good images and reliability even when a signal with excessive amplitude is input, regardless of the signal content.

[Means to solve the problem]

In order to achieve the above object, the present invention includes an amplifying means for amplifying and outputting a video signal input as an analog signal, and an amplifying means for amplifying and outputting a video signal inputted as an analog signal, and a A video human power circuit is constituted by a control means for controlling the gain of the amplification means according to a comparison result between the amplitude value and a reference value.

[Effect]

The gain of the amplification means is determined by the control means according to the comparison result between the peak value and the reference value when the amplitude value (peak value in %) of the video entertainment signal exceeds a certain reference value. Thus, the amplitude of the output signal of the amplifying means is controlled to be constant.

This prevents the excessive input signal amplitude from affecting the subsequent stages.

〔Example〕

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

In FIG. 1, 1 is a video signal input terminal, and 2 is a peak detector/retainer that detects and holds the amplitude peak (IVsp) of the video signal inputted from the input terminal 1.

5 is a voltage source for the reference 4 voltage Vso 'f: 4 is a comparator that compares the peak value V51F, which is the output of the peak detector/retainer 2, with the reference voltage vso, 5 is the gain control voltage Vc
An amplifier whose gain G is controlled by 6 is a reference control voltage V
The voltage source emitting cm, 7, is controlled by the output of the comparator @I4, and the amplification 1! A switch 8 which switches the gain control voltage Vc of s5 to the voltage source 6 or the output of the comparator 4 is a video signal output terminal.

The peak value VIIP of the video signal inputted from the input terminal 1 is detected and held by the peak detection/holding device 2. After that, VIP is maintained as it is unless a signal with an even larger amplitude is input. Next, the peak value VSF is compared with the reference voltage Vso by the comparator 4,
The 0 switch 7 outputs the voltage Vp according to the comparison result from the comparison s4, and when SP≦VSO, the voltage source 6
1Il is selected, the gain control voltage Vc of the amplifier 5 is set to Veo, and the gain G of the amplifier 5 is set to Go. In this case, the reason why the gain G is kept constant as Go is to prevent the brightness from increasing more than necessary when a signal with a small amplitude is intentionally input. Next, vgp > Vso. In this case, the switch 7 switches over the comparator 4, and the gain control voltage Vc of the amplifier 5 becomes the output voltage Vp of the comparator 4. Therefore, in the comparator 4, as the output voltage Vp, Vp=
If a voltage such as Vco NVsol-SP is output, the gain G of the amplifier 5 will be as shown in FIG. 2(b).

G=□・vC Vc.

Therefore, the output Vo of the amplifier 4 becomes constant as shown in FIG. 2(c).

According to this embodiment, the peak value of an input signal is regarded as the reference width value of that signal, and the gain of the amplifier is set appropriately according to that value, so even if a signal with excessive amplitude is input, the Regardless of the content, it is possible to reproduce a good painting.

〔Effect of the invention〕

According to the present invention, even if a signal with an excessive amplitude is input due to variations on the host device side, it is absorbed at the signal input stage, so it does not affect the amplitude and waveform in the CRT drive circuit.
1, ensuring good performance and reliability at all times. Furthermore, it is possible to expand the number of devices to be connected.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the voltage or gain characteristics of each part in FIG. 1...Video signal input terminal 2...Peak detector/retainer 3...Voltage source 4...Comparator 5...Amplifier 6...Voltage source 7...Switcher 8... Video signal input terminal closed Figure 2 SO ″” Vsp

Claims (1)

[Claims] 1. In a cathode ray tube display device compatible with analog signal input, an amplifying means for amplifying and outputting a video signal input as an analog signal, and an amplifying means for amplifying and outputting a video signal input as an analog signal, and an amplifying means for amplifying and outputting a video signal input as an analog signal, , and control means for controlling the gain of the amplification means according to a comparison result between the amplitude value and a reference value.