Hayao Ohzu

Design of bipolar imaging device (BASIS)

The design methodology of a bipolar imaging device, BASIS (base-stored image sensor), with a capacitor-loaded emitter-follower circuitry, is established by analyzing the basic operation of BASIS and the generation mechanism of fixed pattern noise where theoretical results coincide well with experimental results. From this methodology, a wide dynamic range of linearity is assured by optimizing the forward-bias voltage in readout operation, while high sensitivity is realized by making the base-to-collector junction capacitance C/sub bc/ as small as possible and by designing the emitter common current gain h/sub FE/ of a phototransistor in a pixel to be as high as possible. In order to reduce fixed pattern noise, nonuniformities of h/sub FE/ and C/sub bc/ should be made as small as possible by improving fabrication process technology, while the bootstrap factor k/sub f/ defined in this theory should be as small as possible. >

Design of bipolar imaging devices (BASIS): analysis of random noise

A design methodology for a bipolar imaging device, the base-stored image sensor (BASIS), has been established by theoretical analysis and experimental verification for random noise. The random noise in BASIS is dominated by the shot noise in readout and transient reset operation. The theoretical analysis has been carried out by introducing the probability density functions for these operations. The readout noise depends on the base-to-collector junction capacitance C/sub bc/, the emitter common current gain h/sub FE/, the storage capacitor C/sub T/, and the emitter voltage V/sub E/. The reset noise has been confirmed to be given by thermal noise. The theoretical results coincide well with the experimental results obtained by TEG devices. An expression for the S/N ratio has been derived theoretically. It is found that h/sub FE/ should be made as large as possible and (C/sub bc/+C/sub be/) as small as possible to improve the S/N ratio for random noise, where C/sub be/ is the base-to-emitter junction capacitance. >