| 摘要 |
<p>PURPOSE:To make the relative phase between a video signal and a synchronizing signal highly stable while utilizing the accuracy of a D/A converter by adding a compression synchronizing signal at a digital area at the pre-stage of the D/A converter and amplifying the synchronizing signal after D/A conversion. CONSTITUTION:A digital switching circuit 3 switches input signals 21, 22 by using a blanking pulse 23 inputted from an input terminal 2, a PCM composite video signal 24 compressed to, e.g., 1/6 by synchronization only is converted into an analog composite video signal 25 by the D/A converter 5 and inputted to a programmable amplifier 6. The gain is switched at the programmable amplifier 6 by using the blanking pulse 23, the gain is the unity at the outside of blanking, the gain is made to 6 times in the blanking period and the relation between the levels of the picture and synchronization is made normal. A composite video signal 26 being an output of the programmable amplifier 6 is interpolated by a low pass filter 7, power amplification is applied by a video amplifier 8 and the result is sent to an output terminal 9.</p> |
