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Switching Circuit Employing Photodiodes

IP.com Disclosure Number: IPCOM000098250D
Original Publication Date: 1960-Jun-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Mestre, AF: AUTHOR

Abstract

Photodiodes PD... PDn are employed to control the flow of current to any of a plurality of loads L(1)... L(n) which may be, for example, rows of magnetic cores in a memory matrix.

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Switching Circuit Employing Photodiodes

Photodiodes PD... PDn are employed to control the flow of current to any of a plurality of loads L(1)... L(n) which may be, for example, rows of magnetic cores in a memory matrix.

The left-hand drawing illustrates one form of the circuit. By means of a mask M, a light beam is permitted to fall upon a selected photodiode PD(2), causing the reverse impedance of that element to decrease. This allows current i(1) to flow through capacitor C(2), load L(2) and resistor R to charge capacitor C(2) with its grounded plate positive. When the capacitor is sufficiently charged, the light beam is removed and the photodiode is permitted to recover its unilateral characteristic. Transistor switch 6 is then activated to permit capacitor C(2) to discharge. This sends current i(2) through photodiode PD(2) in the forward direction and through load L(2). No current flows through the other loads L(1)... L(n) since no charge was placed upon their corresponding capacitors.

The right-hand drawing illustrates a second form in which advantage is taken of the minority carrier accumulation characteristics of photodiodes to eliminate the capacitors. in this circuit a selected photodiode PD(2), for example, is saturated and minority carriers accumulated by a light beam directed on it. Thereafter the transistor switch 6 is activated to close a circuit through the diode and its associated load L(2). This permits the stored minority carriers to be withdraw...