Performance Analysis of Cascode Configuration 3T Pixel Structure Detectors Using y-parameter Representation

In this paper, the standard 3T pixel structure detector using BJTs as pixels were replaced with cascode configured BJTs and several key parameters were compared. This work can be used to develop and optimise detectors before it is manufactured saving design time and cost. This was accomplished by inserting the diode-connected BJT in cascode configuration in the place of the normal diode connected BJT in the standard 3T pixel structure. Two different cascode configurations were analysed (the first is the BJT only one and the second one is a BJT MOSFET combined one). Furthermore, the y-parameter representation of the full 3T pixel structure is provided and subsequent mathematical model of both circuits was used to perform the comparison. The modified cascode configuration was found to have increased gain compared to the normal structure. The disadvantage is that the modified cascode configuration was found to be sensitive to ß and Early Voltage where the standard structure is insensitive to these parameters. All three configurations were found to be temperature insensitive. Using this work, the designer can determine mathematically if the cascode configuration would perform better as opposed to standard 3T pixel structure detectors. The designer can also use this to optimise for a specific set of circumstances.