Patent ID: 7324162

Claim:
A system to improve dynamic range of an analog to digital conversion of a composite video signal, the system comprising: a video signal input for receiving an analog composite video signal; a gain control amplifier coupled to said video signal input and having a gain control amplifier output; a sample and hold circuit having a sample and hold circuit input coupled to said gain control amplifier output and having a sample and hold circuit output; a DC level shift circuit connected to said sample and hold circuit input to DC shift a portion of said gain control amplifier output to reduce the full maximum voltage swing of said sample and hold circuit output to a reduced maximum voltage swing; and an analog to digital converter having an input coupled to said sample and hold circuit output, having a reference voltage related to the reduced maximum voltage swing rather than the full maximum voltage swing and having an analog to digital converter output, wherein said DC level shift circuit shifts a portion of the back porch, the active video and a portion of the front porch of the video signal to a reduced voltage level, and wherein said DC level shift circuit includes: a resistor divider formed by a pullup and a pulldown resistor, the junction of the resistor divided being connected to said sample and hold circuit input; a series combination of a resistor and a switch in parallel with said pulldown resistor; and a DC level shift control circuit coupled to said switch and for receiving timing and clocking signals to properly activate said switch.