| 摘要 |
<p>PURPOSE:To make the level of white noises constant without the effects of external interference noise signals and temperature by performing A/D conversion of a video signal for the stopping period of display, averaging the minimum values of a plurality of periods with a minimum value selecting circuit and an average value circuit, and determining the attenuating amount of an attenuator. CONSTITUTION:A digital signal from an A/D converting circuit 1 becomes large in proportion to a video signal. The maximum value of the video signal is stored in a memory circuit 2. For example, four data are shifted in parallel through a minimum value selecting circuit 3 and a shift register 4. A digitalized signal obtained by averaging the four data in an average value circuit 5 generates a control voltage through a D/C conversion circuit 6 and a circuit 7. The attenuating amount of an attenuator 8 is controlled. When the output value of the average value circuit 5 is stable and the gain of the video signal is increased by the change in temperature, the output value of the average value circuit 5 also becomes large. The output voltage from the D/A converter 6 and a buffer circuit 7 is also increased. The attenuator 8 increases the attenuat ing amount. White noise displayed on a display device 9 is made constant.</p> |
