Browse Prior Art Database

Optical Sensor Amplifier

IP.com Disclosure Number: IPCOM000052930D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Ackerman, LL: AUTHOR [+3]

Abstract

This circuit provides a down-level true logic signal at output 1 when paper is present in the sensor aperture. Phototransistor 3 is connected to the collector of transistor 5, which operates as a current sink. When current exceeds the sink capacity, the excess flows to the base of transistor 7, driving it strongly on.

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Optical Sensor Amplifier

This circuit provides a down-level true logic signal at output 1 when paper is present in the sensor aperture. Phototransistor 3 is connected to the collector of transistor 5, which operates as a current sink. When current exceeds the sink capacity, the excess flows to the base of transistor 7, driving it strongly on.

The sensor is composed of phototransistor 3, light-emitting diode 9, and focusing optics (not shown) When paper is present in the sensor aperture, phototransistor 3 produces a current flow (I ) into the junction composed of the collector of transistor 5 and resistor 10. This current is approximately proportional to the reflected light into phototransistor 3.

To establish a sharp threshold, a current sink circuit (composed of transistor 5, resistor 11, resistor 13, and resistor 15) is employed which bypasses resistors 10 and 21 until the desired threshold is reached. At that point, current is diverted into resistors 10 and 21 which comprise the base driving circuit for transistor 7.

Resistors 11 and 13 provide a constant voltage at the base of transistor 5. The current in transistor 5 is limited by that which can be produced by phototransistor 3 and that which produces a voltage across resistor 15 in excess of that which can be sustained by the base bias voltage; thus, transistor 5 serves as a current sink.

When current exceeds the sink capacity, the excess flows through resistors 10 and 21, producing base drive to transistor...