Browse Prior Art Database

Light Sensor

IP.com Disclosure Number: IPCOM000097104D
Original Publication Date: 1962-May-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Masetti, M: AUTHOR

Abstract

The circuitry senses light variations and produces an output signal. Its rise time does not depend upon the rate of variation of light intensity. The system comprising a photosensitive element serially connected to a tunnel diode switches a transistor every time the light conditions on a photosensitive element pass from dark to light state and vice versa.

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Light Sensor

The circuitry senses light variations and produces an output signal. Its rise time does not depend upon the rate of variation of light intensity. The system comprising a photosensitive element serially connected to a tunnel diode switches a transistor every time the light conditions on a photosensitive element pass from dark to light state and vice versa.

Readout photocell C has the current-voltage characteristics a(1), a(2), a(3), a(4), a(5) as a function of increasing light intensity. The intersections of these characteristics with the tunnel diode characteristic b presents the working point of the solar cell, tunnel diode system.

Point A is the working point in the dark state. Under this condition, transistor T is cut off. By increasing the light intensity, the working point shifts from position A toward point B. When this is reached, the tunnel diode switches along its characteristic b and the operating point of the system becomes B'. This varies the base voltage of T, which rapidly switches into saturation. When the light intensity decreases, a rapid switching of T to cutoff occurs.

The output signal rise does not depend upon the variation speed of light intensity. This is because variation speed is very slow compared to the switching speed of the system. For this reason, it is sufficient that the light intensity reach the characteristic a5 level to obtain a rapid switching of the system.

The dotted line shows the tunnel diode, transistor base c...