1. Overview
A transimpedance amplifier converts a small input current into a measurable output voltage.
2. Operating Principle
The input current flows through the feedback network while the amplifier maintains the input summing node near virtual ground.
3. Transimpedance Gain
For an ideal resistive feedback network, the output-voltage magnitude is approximately equal to the input-current magnitude multiplied by the feedback resistance.
BASIC RELATIONSHIP
|Vout| ≈ |Iin| × Transimpedance Gain
4. Detector Equivalent Circuit
A practical photodiode includes photocurrent, junction capacitance, shunt resistance, dark current and parasitic capacitance.
5. Feedback Capacitance and Stability
Feedback capacitance controls closed-loop response and helps prevent excessive ringing or oscillation.
6. Noise Sources
Relevant noise sources include feedback-resistor thermal noise, detector shot noise and amplifier current and voltage noise.
7. Gain and Bandwidth
Higher transimpedance gain generally reduces available bandwidth and increases sensitivity to detector and cable capacitance.
8. Practical Measurement Guidance
High-impedance input connections should be short, clean, shielded and protected from leakage and electromagnetic interference.
9. Product Selection
Product selection must consider expected current, required bandwidth, detector capacitance, noise and amplifier input limits.
ENGINEERING TOOL
Transimpedance Gain Calculator
Estimate output voltage from detector current and transimpedance gain.
Open Calculator