| 摘要 |
<p>PURPOSE: To attain stable indication of a black level by limiting a video signal input so as not to exceed a prescribed input of the A/D converter thereby preventing a displayed image from being distorted and avoiding fluctuation in its pedestal level. CONSTITUTION: An D/A converter 4 converts a video signal received through a variable gain video amplifier 2 and a pedestal clamp circuit 3 into a digital signal, a latching section 6 latches data denoting a tip of a synchronizing signal, a pedestal level and a video level from the video signal data based on a signal received from a timing signal generating section 12, a comparator section 8 compares relative reference data read out of a reference level setting section 9 to which reference data are set in advance with the latched data and provides the output of a control signal depending on the result of comparison, which is converted into an analog voltage by a D/A converter 10, the voltage is used to control a gain of the variable gain video amplifier 2 and to control the clamp level of the pedestal clamp circuit 3.</p> |
