This is a circuit for fiber optic receiver that is based on LH4118 IC. This IC is used as photo diode receiver. This is the figure of the circuit.
The current generated in the PIN diode causes a voltage drop across resistor R1. This voltage is then amplified by the LH4118. It is important to hold the capacitance at the input small. This capacitance consists of the diode, amplifier input and wiring capacitance. Together with the load resistor R1 it determines the frequency roll off at the input. This is also the reason for choosing a small value for R1. A guard around the input node driven from the feedback point helps to reduce the input capacitance. If the PIN diode has a metal case it should also be connected to the driven guard. If this constitutes too much capacitance for the inverting input and therefore causes the gain characteristic to peak, a separate voltage divider from the output can be used to drive the shield. [Circuit’s source: National Semiconductor Notes].
The current generated in the PIN diode causes a voltage drop across resistor R1. This voltage is then amplified by the LH4118. It is important to hold the capacitance at the input small. This capacitance consists of the diode, amplifier input and wiring capacitance. Together with the load resistor R1 it determines the frequency roll off at the input. This is also the reason for choosing a small value for R1. A guard around the input node driven from the feedback point helps to reduce the input capacitance. If the PIN diode has a metal case it should also be connected to the driven guard. If this constitutes too much capacitance for the inverting input and therefore causes the gain characteristic to peak, a separate voltage divider from the output can be used to drive the shield. [Circuit’s source: National Semiconductor Notes].
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