7-167. Video Circuit7.1 Video Pre-amplifierThe U201 is a video pre-amplifier. It is used to control the following functions.(Fig. 7.1) Video Pre-amplifier7.1.1 Video Signal MixingIn U201, the video signal is mixed with the OSD signal (3, 2, 1 for B, G, R respectively). Then, the resultantsignal is mixed with the horizontal blanking waveform signal. Outputs for B, G, R are generated from Pins 18,19, and 20, respectively.7.1.2 Video ClampThe clamp waveform signal with a polarity is output from the oscillator IC (U501) and is input to U201 Pin 23.7.1.3 Horizontal BlankingThe collector pulses of Q314 are divided by the combination of C331 and C332. The obtained pulses areused as the horizontal blanking pulses and is input to U201 pin 24 with a positive polarity. The potential atPin 24 is HIGH during the horizontal flyback period and the video output voltage of U201 is dropped toperform the blanking operation.U701MPUD-SUBBIAS circuitU202OSDU204OUTPUT-AmpU501OSC IC23161920151118U201Pre-AmpCLAMPCLAMP1371469BGR321BGR765RGB129110SDA SCL2214 161523DACB-Bias DACG-Bias DACR-Bias ABLABL24H-BLKH-BLK
