Automatic responsivity control for a CCD imager

摘要

An automatic responsivity control (ARC) circuit compensates for the nonuniform deviation &Dgr;R in the average responsivity R of a column of photodetectors from a nominal responsivity R.sub.0 which is uniform from column to column. The ARC circuit first establishes a reference level by subtracting two known calibration signals occurring during optical retracing and then multiplies the reference level by each image signal occurring during optical scanning. The resulting product contains undesirable signal components or terms which are algebraic functions of . DELTA.R.sup.2 and other terms which are algebraic functions of &Dgr;R. The terms in &Dgr;R.sup.2 are ignored because &Dgr;R is significantly less than R.sub.0. The terms in &Dgr;R are eliminated by establishing a second reference level, which itself includes terms in &Dgr;R, and then subtracting the foregoing product from the second reference level. If the bias voltages applied to the ARC circuit are adjusted according to a formula discussed in the detailed description, this second subtraction results in a cancellation of all terms in &Dgr;R. The resulting output signal therefore contains only terms in &Dgr;R.sup.2 which are negligible, and thus the output signal is substantially free of distortion due to responsivity deviations.