Photodiode Amplifier

The function of this circuit is to amplify and convert the current of photodiode illuminated by chopped light. The circuit can be used in miscellaneous optical instruments. The photodiode in the circuit is a high impedance device with a 15 V DC back (reverse) bias. The output current of the photodiode is proportional to the amount of light incident on the surface. Because the light incident upon the photodiode is chopped, the AC signal is generated across the 100 kΩ load resistor R₁. This AC signal is amplified by an AC-coupled operational amplifier (IC₁). The amplified AC signal is AC-coupled to a high-gain operational amplifier (IC₂). The AC signal is then rectified and smoothed by a full wave rectifier (IC₃) and integrating amplifier IC₄. The output DC voltage is proportional to the amount of light incident on the surface. The gain of the circuit is adjusted by the feedback resistor (R₂) of the first amplifier.

Useful link: BPW34 datasheet (pdf)