Transfer functions of imaging mosaics utilizing the charge storage phenomena of transistor structures

Silicon phototransistors operating in the integration mode have been used in light detection and imaging systems. A solid-state imaging system employing a monolithic mosaic of 12 800
n-p-n
phototransistors has been developed. An analysis of the integration mode of operation of a silicon phototransistor is presented. The analysis employs a simplified equivalent circuit of a phototransistor. Three different cases are analyzed; each case differs in that the length of the readout cycle is changed. The solution to all three cases gives an output voltage directly proportional to the ratio of light plus leakage generated charge to the base-collector junction depletion layer capacitance. Analysis of phototransistor operation in a mosaic where interactions with the other phototransistors in the array are accounted for is presented. Discussion concerning the parasitic capacitances due to readout switches is given for the particular mosaic design employed.