Figure 45. Photodiode transimpedance amplifier circuit

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

signal readable by an ADC following Eq. (13):

VOut=Rf.Ipℎotodiode

(13)

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.

TSV782

Photodiode transimpedance amplification

DS14011 - Rev 3

page 23/32