Gain Improvement in 4T Structure Detectors using Cascode Configured Pixels

In this paper, the normal BJT based pixels in the 4T structure detector was replaced with cascode configured pixels and key parameters were compared. Full detectors designs and performance have been published in literature, however generic mathematical methodology research in readout circuitry is lacking for detector development. Two versions of the cascode configured pixels were used (BJT only based and BJT/MOSFET combination based configurations). Y-parameter representation was used to perform the comparison using techniques previously published. It was found in both modified 4T pixel structure detectors that the transresistance gain improved significantly (from MV/A range to GV/A range). Using these modified mathematical models, a designer can easily design a 4T pixel structure detector for a wider set of circumstances previously not possible which results in more optimised detectors. It was found by replacing the normal pixels with cascode configured pixels that the overall gain is improved significantly due to a reduction in input resistance owing to the cascade configured pixels.