Photodiode Sensitivity / TIA Calculator
Calculate photodiode responsivity and transimpedance amplifier gain/bandwidth. Maps optical power to output voltage with shot-noise-limited sensitivity.
How to Use
- Enter photodiode responsivity (A/W, from datasheet) and optical input power.
- Enter TIA feedback resistor Rf and junction capacitance Cj.
- Tool computes output voltage, bandwidth, and shot-noise floor.
Show Work
Formulas
History of the Transimpedance Amplifier
The transimpedance amplifier (TIA) converting photodiode current to voltage became standard in the 1970s with the availability of FET-input op-amps (LF356, 1976; TL071, 1978) and low-capacitance PIN photodiodes for optical communications. Fiber-optic receivers in the 1980s pushed TIA designs to higher bandwidths (100 MHz-10 GHz) using GaAs FETs. Modern lidar, time-of-flight cameras, and FSO systems use avalanche photodiodes with internal gain plus TIA front-end to achieve single-photon sensitivity.
About This Calculator
Enter photodiode responsivity (datasheet A/W), incident optical power (typical for your wavelength source), TIA feedback resistor Rf (typical 1 kΩ to 1 GΩ depending on BW/sensitivity), photodiode junction capacitance Cj, and op-amp GBW. The tool computes photocurrent, output voltage, bandwidth, and shot-noise current floor.
For fast optical links (> 10 MHz), use low-Cj photodiode (1-2 pF) and high-GBW op-amp (100 MHz+). For high sensitivity (NEP < 10⁻¹⁴ W/√Hz), use large Rf (1-100 MΩ) and low-noise FET-input op-amp. Everything runs client-side.
About the Photodiode Sensitivity / TIA Calculator
Whether you are at a desk or on your phone, the Photodiode Sensitivity / TIA Calculator makes electronics and circuit design easy — and it is completely free. Calculate photodiode responsivity and transimpedance amplifier gain/bandwidth. Maps optical power to output voltage with shot-noise-limited sensitivity.
How it works
Type your numbers into the boxes. The answer shows up right away — you do not have to press a button. If you change a number, the answer changes too. So you can try different numbers and watch what happens, or check an answer you worked out yourself. Just make sure each box has the right kind of number in it.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
Responsivity?
A/W — amps of current per watt of incident optical power at a specific wavelength. Silicon: 0.4-0.6 A/W at 850 nm. InGaAs: 0.8-1.0 A/W at 1550 nm. Quantum efficiency η = R · hc/(qλ).
TIA topology?
Transimpedance amplifier: photodiode anode to op-amp inverting input, Rf in feedback. V_out = I_ph · Rf. Bandwidth limited by Cj and op-amp GBW: BW ≈ √(GBW/(2π·Rf·Cj)).
Noise sources?
Shot noise from photocurrent: √(2·q·I_ph) A/√Hz. Resistor thermal noise: √(4kT/Rf) A/√Hz. Op-amp input noise multiplied by (1 + Rf/Rs). Shot noise dominates at high light levels; op-amp noise at low.
How do I use the Photodiode Sensitivity / TIA Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Is it free? Does it work without internet?
Yes to both. It is free with no sign-up, and once the page has loaded it keeps working even with no internet.
Where does my data go?
Nowhere — every calculation runs on your own device. Nothing you enter is uploaded, logged, or stored.
Common Use Cases
Optical Fiber Receiver
InGaAs PD + TIA at 1550 nm for fiber-optic data links. 10 Gbit/s achievable with fast PDs.
Laser Pulse Detector
Si PD + TIA for rangefinder: detect 10 ns optical pulses with shot-noise-limited sensitivity.
Spectrophotometer
Large-area Si PD for lab instrument; low-BW TIA for high-sensitivity absorbance measurement.
Last updated: