Improved column sample-and-hold (CSH) circuitry particularly useful in a
CMOS imager is disclosed. In the improved circuitry layout, the overall
column height of the CSH circuitry is reduced by providing a plurality of
pairs of sampling and reference capacitors in a vertical stack over the
columns that the capacitors service. The number of pairs provided in the
vertical stack is subject to optimization, and for a given set of design
constraints, a certain form factors can prove to be optimal. No
modification needs to be made to the pixel array (such as pixel pitch),
and the sensing circuitry otherwise requires no electrical or process
modifications as the values for the capacitances as well as other design
constraint are preserved. However, the vertical stacking of the plurality
of pairs of capacitors reduces the overall column height (CH), which
conserves layout space on the CMOS imager integrated circuit.