Circuit arrangement for clamping black level reference signals contained in a video signal sequence

Claim 1

A circuit arrangement for clamping the black reference signals contained in a video signal sequence of an optical line scanner which comprises a charge coupled device sensor producing an analog output signal, comprising: a timing circuit for producing a sync signal, a black reference timing signal and a charge coupled device transport clock signal each at a respective output, said sync signal output and said charge coupled device transport clock signal connected to the charge coupled device sensor; amplifier means connected to the optical line scanner for amplifying its analog output signal, including a video amplifier; a digital-to-analog converter connected to said video amplifier of said amplifier means and comprising a plurality of outputs; a NOR gate including an output and including a plurality of inputs each connected to a respective output of said analog-to-digital converter; a D flip-flop including an output and including an input connected to said output of said NOR gate, and a clock terminal connected to said black reference timing signal output of said timing circuit for receiving said black reference timing signal; and an integrator including an input and an output, said input connected to said output of said D flip-flop and symmetrically driven with reference to its input voltage, and said output connected to said video amplifier such that its ramp like increasing or decreasing output voltage is added to the sensor signal voltage at the input of said video amplifier.