Crosstalk in Phototransistor Imaging Mosaics at Very High Light Levels

Measurements were made using a 200 X 256 element solid-state imaging system to determine and characterize the behavior of XY interconnected pulse-biased phototransistors in the presence of high light levels such as can occur when the sun or other discrete sources are focused on a part of the mosaic. Wavefom photographs depicting operation under these conditions are presented, along with the conclusions reached from their analysis. Operation was found to agree with previously published results over a wide range of light levels, but at unusually high light levels, a photovoltaic mode becomes significant. Under these conditions desensitization of the mosaic occurs along the affected emitter bus, while parts of the mosaic in which photovoltaic action does not occur are unaffected. At very low image rates, mosaic operation changes from frame integration to line integration. This mode of operation appears applicable to some special imaging conditions of potential interest-most notably, applications in which it is desirable to image very bright scenes with transmission of the signal over very narrow bandwidths.