Photodiode Transimpedance Calculator

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Estimate photodiode transimpedance amplifier output voltage, dark-current offset, feedback-capacitor bandwidth, and basic noise/stability indicators.

Input Parameters

Photocurrent

µA

Dark Current

Feedback Resistor

kΩ

Feedback Capacitor

Photodiode Capacitance

Op Amp Input Capacitance

Results

Signal Output Voltage

Dark Offset Voltage

Total Input Capacitance

Feedback Pole Bandwidth

Feedback Resistor Noise

Design Note

TIA stability depends on op amp GBW, input capacitance, feedback capacitance, photodiode capacitance, layout leakage, and reverse bias conditions.

Equations Used

Transimpedance output: Vout = Iphoto × Rf

Dark-current offset: Vdark = Idark × Rf

Feedback pole: f ≈ 1 / (2π × Rf × Cf)

Resistor thermal noise: en ≈ √(4kTRfB), using feedback pole as a simple bandwidth estimate.

Frequently Asked Questions (FAQ)

Q1: What does a photodiode transimpedance calculator do?
It estimates the output voltage of a TIA from photodiode current and feedback resistor value.

Q2: How do I choose the feedback resistor?
Choose Rf so the maximum photocurrent produces an output voltage within the op amp and ADC input range.

Q3: Why add a feedback capacitor?
Cf limits bandwidth and helps stabilize the transimpedance amplifier with photodiode and input capacitance.

Q4: Why does photodiode capacitance matter?
Higher capacitance reduces bandwidth and can make the amplifier harder to stabilize.

Q5: Can this predict exact TIA noise?
No. Exact noise requires op amp voltage/current noise, diode shot noise, bandwidth, and layout leakage analysis.

Disclaimer: This tool provides first-pass TIA estimates. Use op amp stability analysis, photodiode datasheets, SPICE simulation, PCB leakage control, and bench measurement for precision optical designs.

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