OPTICAL BLACK LEVEL ADJUSTING CIRCUIT

摘要

PROBLEM TO BE SOLVED: To provide an optical black level adjusting circuit capable of eliminating an external capacitor by constructing the optical black level adjusting circuit with a coarse analog adjusting circuit and a precise digital adjusting circuit, and converging optical black level adjustment with several lines and easily changing a time constant by means of a digital processing. SOLUTION: The optical black level adjusting circuit comprises: a CDS 11 for clamping an analog signal at an optical black level and sampling/holding the analog signal; an A/D converter 12 for converting the analog signal from the CDS into a digital signal; a subtracter 13 for subtracting the digital signal outputted from the A/D converter and an OB pedestal code: a subtracter 31 for subtracting the output of the subtractor 13 and an error value A; a computing element 25 for calculating a new error value A from data outputted from the subtracter 31, a predetermined coefficient and the error value A; a register 23 for storing the error value A; and a D/A converter 15 for supplying an analog voltage corresponding to the error value A as a clamp signal of the CDS 11, and the adjustment of the optical black level is accelerated without using an external capacitor. COPYRIGHT: (C)2006,JPO&NCIPI