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Published 1985 | Published
Book Section - Chapter Open

A Sensitive Electronic Photoreceptor


The photoreceptors in biological systems give meaningful outputs over about six orders of magnitude of illumination intensity. If we are to build an electronic vision system that is truly useful, it must have a similar dynamic range. The elements of an electronic receptor with many orders of magnitude dynamic range are described below. Experimental devices were fabricated in p-well cMOS bulk technology through the MOSIS foundry; npn phototransistors with collector connected to substrate are a byproduct of this process. The n-type bulk forms the collector, the p-well is the base, and the n+ diffusion the emitter. In a typical process, a large transistor of this sort has a current gain β of more than a thousand. Smaller transistors have lower current gains, but are still respectable. The key to very sensitive receptors is to use the current gain of this very clean bipolar transistor before subjecting the signal to any noise from subsequent amplification stages.

Additional Information

© 1985 Computer Science Press. Thanks are due David Feinstein for his careful and perceptive review of the manuscript, and to John Tanner and MaryAnn Maher for many helpful discussions. This work was supported by the System Development Foundation.

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