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LOGIC COMPATIBLE PULSED PHOTODETECTOR CIRCUIT

IP.com Disclosure Number: IPCOM000023719D
Original Publication Date: 1978-Dec-31
Included in the Prior Art Database: 2004-Mar-31

Publishing Venue

Xerox Disclosure Journal

Abstract

A photodetector concept utilizing a light sensor and infrared LED light source separated by a large distance (18 inches) to detect paper jams or tray position in a xerographic copier. To obtain sufficient light intensity, an infrared LED 2 is pulsed at high currents and low duty cycle directly from a pulse generator 4. A phototransistor 6 receives the radiant energy and generates a signal which is amplified by a logic compatible amplifier 8. The output of amplifier 8 is sampled by a D-type flip-flopwhich is clocked by the trailing edge of the driving pulse via a circuit including amplifier 12 to recover information as to whether the beam from LED 2 is blocked, Amplifier 8 is AC coupled on its input side to pass the short input pulses from LED 2 but reject ambient light or 60 cycle light from room lighting.