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Browse Prior Art Database

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
Document File: 2 page(s) / 225K

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.

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XEROX DISCLOSURE JOURNAL

LOGIC COMPATIBLE PULSED PHOTO~
DETECTOR CIRCUIT
Kent Williams

Proposed Classification
U.S. Cl. 356/201
Int. Cl. G01n 21/06

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.

4

Volume 3 Number 6 November/December 1978 443

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                  XEROX DISCLOSURE JOURNAL
444 Volume 3 Number 6 November/December 1978

[This page contains 1 picture or other non-text object]