Browse Prior Art Database

Optical Closed Loop Analog Amplifier and Detector

IP.com Disclosure Number: IPCOM000082936D
Original Publication Date: 1975-Mar-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Galetto, LV: AUTHOR [+2]

Abstract

A stable and sensitive amplifier/detector system is provided, as shown in the figure, having a long life at a low cost. Infinite gain range is provided to mask parameter and light variations. It has wide-band width and stable operation to DC (has operating point hysteresis to improve noise immunity).

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Optical Closed Loop Analog Amplifier and Detector

A stable and sensitive amplifier/detector system is provided, as shown in the figure, having a long life at a low cost. Infinite gain range is provided to mask parameter and light variations. It has wide-band width and stable operation to DC (has operating point hysteresis to improve noise immunity).

Operational amplifier 1, transistor 2 and resistors 3, 4 and 5 form a transresistance amplifier whose open-loop gain is set by resistor 6, and whose closed-loop input resistance is equal to resistor 5 divided by the open-loop gain. Resistor 7 matches resistor 5 to reduce effects of amplifier 1 input offset current. Capacitor 8 affords a bypass for resistor 7, while capacitors 9 and 10 provide compensation for circuit stability.

When the disk 11 is positioned so that no light is transmitted from light- emitting diode (LED) 12 to phototransistor 13 through the uniformly spaced apertures in the disk, the output voltage of transistor 2 will be nearly zero and more positive than the voltage of divider 16-17. The output of amplifier 18 is positive, transistor 19 is on and the current thru feedback resistor 21 is nearly zero. With transistor 13 darkened, maximum current flows thru LED 12.

As the disk is turned transistor 13 forces more current into node 25 causing voltage 14 to go more negative, so that less current is available from resistors 3 and 4 and the current to LED 12 is reduced also.

As the voltage 14 goes more negative it...