G - Physics – 01 – J
Patent
G - Physics
01
J
G01J 1/44 (2006.01) H01L 27/144 (2006.01) H03F 3/08 (2006.01) H04B 10/158 (2006.01)
Patent
CA 2142527
Light intensity detecting circuits using reverse biased photodiodes are disclosed. Two photodiodes are fabricated with essentially the same structure in close enough proximity to each other on a single semiconductor substrate so that they both experience the same environment. In one scheme the cathode of the first photodiode is common with the anode of the second photodiode and an inverting terminal of an operational amplifier with negative feedback. A negative voltage is applied to the anode of the first photodiode and a positive voltage of the same magnitude is applied to the cathode of the second photodiode. The output of the operational amplifier is proportional to the incident light provided the intensity on each photodiode are proportional to each other. In another circuit one of either the anodes or cathodes of each diode is common and the other is input into the inverting terminal of a separate operational amplifier. The outputs of each operational amplifier is input into a subtracter circuit to subtract common dark or photocurrent components so the output of the subtracter circuit is proportional to the difference in light incident on the photodiodes. The reverse bias across the photodiodes may be varied and this is of particular use for detectors whose spectral response may be shifted by means of, for instance the Franz-Keldysh or quantum confined Stark effects.
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