Two Techniques to Reduce Gain and Offset Errors in CMOS Image Sensors Using Delta-Sigma Modulation

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A per-column, delta-sigma, analog-to-digital converter for use in CMOS image sensors is reported. Two techniques, subtraction and preconditioning, are proposed to compensate for the column-to-column mismatches and the resulting fixed-pattern noise introduced into the image. Equations governing the operation of the proposed topology are developed. Experimental results verify that even in the presence of very large offsets, such as a 200 mV mismatch in the MOSFETs' threshold voltages, the proposed topology operates as desired.