Photodiode Front-End Design Review Checklist

0 of 24 checked

Device and operating point

Active area and capacitance Junction capacitance at the chosen reverse bias.The input capacitance sets the noise gain peak and the feedback capacitor.
Reverse bias Within the rated maximum, with margin.
Dark current At the highest operating temperature.Dark current rises steeply with temperature; the room-temperature value understates the noise floor in a warm enclosure.
Responsivity At the working wavelength, with its temperature dependence.
Linear range Checked against the highest optical power at the diode.

Transimpedance stage

Feedback resistor From the largest signal current and the output swing.
Feedback capacitor From the input capacitance and the gain-bandwidth product (45° phase margin or Butterworth), checked in simulation.Too small a C_f leaves the loop ringing; too large a C_f gives away bandwidth.
Op amp Input bias current and voltage noise suited to the feedback resistor.
Input capacitance Total listed: diode, op amp common-mode and differential, board.
Bandwidth and rise time Compared with the requirement, from simulation and measurement.

Stability

Phase margin From the open-loop simulation (loop gain), not from the closed-loop curve alone.
Peaking None above the limit in the closed-loop response.
Supply and load Supply decoupling at the op amp pins and the output load, cable included.
Overload Recovery time from saturation measured or simulated.

Noise

Noise budget Resistor Johnson noise, op amp current and voltage noise and diode shot noise added as root sum of squares.
Noise gain Peaking at high frequency checked against the signal bandwidth.The op amp voltage noise is multiplied by 1 + Z_f / Z_in, which rises with frequency as the input capacitance takes over.
Measurement bandwidth Stated for every noise figure.

Layout

Input node Short input trace, guard ring around the summing node, no digital traces under the input.
Feedback parts Placed next to the op amp, on the same layer as the input.
Remote diode Shielding and cable capacitance counted if the diode sits away from the board.
Thermal path For the diode, if dark current matters.

Test and documentation

Test conditions Bias, temperature, wavelength and load stated with every measured value.
Measurement bandwidth Stated for noise and rise time.
Archive Schematic, simulation files and board files archived with the revision.

Notes

Printed with the checklist. Kept in this browser only.

Ticks and notes stay in this browser and in the link you copy; nothing is sent.

See the same quantities worked through on a fictional device in the live photodiode datasheet, where each spec opens to its equation and test condition.

Photodiode front-end design review checklist