Correlated double sampling method and apparatus

摘要

A method and apparatus for removing low frequency noise and any offsets common to a plurality of samples of a signal, for calibrating an offset level to be added to the signal to reference the signal to a desired reference level at an output of the apparatus, and for clamping an input voltage level to the apparatus to a desired voltage within an operating range of the apparatus. The apparatus includes a correlated double-sampling circuit which takes a first sample and a second sample of the analog signal, takes a difference between the first sample and the second sample to remove low frequency noise and any offsets common to both sample and which outputs a difference signal. In addition, the apparatus includes a black level correction circuit which adds an offset level to the difference signal to calibrate the offset level to be added to the difference signal so that the difference signal is at a desired reference level at an output of the apparatus. Further, the apparatus includes a clamping circuit which servos a voltage at the output of the correlated double-sampling circuit to a desired voltage level at the input to the correlated double-sampling circuit and within the supply range and operating range of the apparatus.