Transimpedance Amplifier Calculator

A transimpedance amplifier is an active current-to-voltage converter that uses an operational amplifier to convert input current into a proportional output voltage. It's commonly used with photodiodes and current-output sensors.

The output voltage is calculated using Vout = -Is × Rf, where Is is the input current and Rf is the feedback resistance. The negative sign indicates phase inversion in the inverting amplifier configuration.

The bandwidth is primarily determined by the feedback resistor and input capacitance. Higher feedback resistance reduces bandwidth, while higher input capacitance also reduces bandwidth due to the RC time constant.

A compensation capacitor (Cf) is placed in parallel with the feedback resistor to ensure stability and prevent oscillation. It's calculated as Cf ≤ 1 / (2π × Rf × fp) where fp is the desired bandwidth.

JFET and CMOS input op-amps are preferred for low bias current to reduce DC errors. JFET inputs offer good performance for most applications, while CMOS provides the lowest bias current for high-impedance sources.

Higher feedback resistance increases the transimpedance gain (voltage output per ampere of input current) but reduces bandwidth. Lower resistance provides wider bandwidth but lower gain. This is the fundamental trade-off in transimpedance design.

The main noise sources include op-amp input voltage noise, op-amp input current noise, thermal noise from the feedback resistor, and shot noise from the photodiode current. Proper design minimizes these effects.

Yes, transimpedance amplifiers work with any current source including photodiodes, phototransistors, current DACs, and current sensors. The design principles remain the same regardless of the current source type.