Browse Prior Art Database

Photodetector and Method of Calibrating Same

IP.com Disclosure Number: IPCOM000080544D
Original Publication Date: 1974-Jan-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Palmer, RS: AUTHOR

Abstract

The photodetector shown may be calibrated by a simplified calibration procedure. The photodetector 24 is comprised basically of phototransistor 4, resistors 6, 7 and 8 and operational amplifier 3 connected as shown in the figure. Feedback resistor 7 is chosen high, so the transconductance gain of operation amplifier 3 is always higher than the lowest gain of any phototransistor 4 used. This circuit allows a noninteracting calibrating procedure to be used to calibrate the photodetector, such that all photodetector circuits are interchangeable.

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Photodetector and Method of Calibrating Same

The photodetector shown may be calibrated by a simplified calibration procedure. The photodetector 24 is comprised basically of phototransistor 4, resistors 6, 7 and 8 and operational amplifier 3 connected as shown in the figure. Feedback resistor 7 is chosen high, so the transconductance gain of operation amplifier 3 is always higher than the lowest gain of any phototransistor 4 used. This circuit allows a noninteracting calibrating procedure to be used to calibrate the photodetector, such that all photodetector circuits are interchangeable.

To calibrate the circuit, a current source 1 is provided so as to supply a DC quiescent current to phototransducer 4, to bias that photo-transducer in the middle of its linear range. The output of the current source is also fed into summing node 2 of operational amplifier 3. A light source 5 shines a light beam of average intensity onto the active area 10 of phototransducer 4. Resistor 6 is then varied such that the phototransistor 4's quiescent current is equal to the output current from current source 1. This will be indicated when the output of operational amplifier 3 is at a zero value.

Next, the optical grating 9 to be used with the phototransducer 4 is set in place. The light from the normal light source 5 is alternately varied from light to dark by moving the grating 9 back and forth. During this period of time, resistor 7 is varied so the output signal of operation amplifi...