My professor gave me a circuit schematics of Balanced photodiode.
This is my first time to study Balanced photodiode.
It is composed of Photodiode pair( picture)
---------------|>|------------------ | | op amp pin 2( - ) g-------- --------------------- n | | d ---------------|
Consider each of the photo diodes to be current sources. Two current sources in parallel just add their outputs together. Turn one around and they subtract from each other.
This difference current (proportional to the difference of the two illuminations) is a current input to the inverting input of the opamp. the feedback path from opamp output to that input must carry away all the resultant current these two sources deliver (since the input can pass no current). The opamp finds what output voltage it takes to force the feedback elements to pass that current by keeping the voltage across the photo diodes (and its two inputs) balanced at zero volts at all times.
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