The transimpedance amplifier circuit converts the small photodiode output current in the nA range, into a voltage

signal readable by an ADC following Equation 12:

VOut=Rf.Ipℎotodiode

(12)

The feedback resistance is usually in the MΩ range, in order to get a large enough voltage output range.

However, together with the diode parasitic capacitance, the op-amp input capacitances and the PCB stray

capacitance, this feedback network creates a pole that makes the circuit oscillate. Using a small (few pF)

capacitor in parallel with the feedback resistor is mandatory to stabilize the circuit. The value of this capacitor can

be tuned to optimize the application settling time with a spice simulation using the op-amp macromodel, or by

prototyping.

For more details on tuning this circuit, please read the application note AN4451.

TSV791, TSV792

Photodiode transimpedance amplification

DS13480 - Rev 1

page 26/36