CHARGE STORAGE MODE OPERATION OF PHOTOTRANSISTORS IN A READING AID.
Abstract
Phototransistor performance is considered for the charge storage mode in which the phototransistor is briefly pulsed and then permitted to remain with both junctions reverse-biased while in the presence of illumination. The charge delivered with the next pulse is proportional to the integral of light received since the last pulse. A lumped model of the transistor, amended here to account for photogeneration, is presented; this model employs the relative excess densities of minority carriers as the terminal variables. A complete analysis of phototransistor operation in the charge storage mode is presented, using the model. The equations derived in the analysis are solved on a computer, using the measured values of transistor parameters. The charge storage mode of operating phototransistors is used in the design of the optoelectronic circuit for a reading aid. The reading aid is a device that allows the blind to read directly from the printed page by creating a tactile image on an array of vibrating pins. The design and construction of the first two models of the reading aid are discussed. These models have been used successfully by blind subjects and reading rates of approximately ten words per minute have been achieved. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1968
- Accession Number
- AD0833159
Entities
People
- Richard C. Joy
Organizations
- Stanford University