6.2

Photodiode transimpedance amplification

The TSV7722, with high bandwidth and slew rate, is well suited for photodiode signal conditioning in a

transimpedance amplifier circuit. This application is useful in high performance UV sensors, smoke detectors

or particle sensors.

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

signal readable by an ADC following Eq. (6):VOut=Rf.Ipℎotodiode

(6)

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.

TSV7721, TSV7722, TSV7723

Photodiode transimpedance amplification

DS13614 - Rev 3

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