The present invention provides an improved column readout circuitry and method
of operation which minimizes substrate and other common mode noise during a read
out operation. The circuit improves the consistency of the pixel to pixel output
of the pixel array and increases the dynamic range of the pixel output. This is
accomplished by obtaining a differential readout of the reset signal and integrated
charge signal from a desired pixel along with the reset signal and charge signal
from a reference circuit. In this manner common mode noise can be minimized by
a combination of signals from the desired and reference pixels in the sample and
hold aspect of the column circuitry. In one exemplary embodiment of the invention,
a 3T pixel arrangement is used. In another exemplary embodiment, a 4T arrangement
is used. Additional exemplary embodiments provide differential column readout circuitry
that can be used with any two signal sources.
