A photodiode transimpedance amplifier has a load resistor at room temperature

PHYSICS · Multi-part · Fermi University Physics · Scientific Practice & Experimental Methods · Electronics, Instrumentation & Communication · Feedback, operational amplifiers and analogue signal processing

Measurement and Method, Ch Designing the measurement: noise, averaging, null and differential methods

Problem

A photodiode transimpedance amplifier has a load resistor

R = 100\,\mathrm{k\Omega}

at room temperature

T = 293\,\mathrm{K}

, and the amplifier's bandwidth is

\Delta f = 10\,\mathrm{kHz}

. The photodiode's dark current is

I = 2.0\,\mathrm{nA}

. ((a)) Estimate the Johnson noise voltage of the load resistor in this bandwidth, using

v_n = \sqrt{4k_{\rm B}TR\Delta f}

. ((b)) Estimate the shot-noise current of the dark current, using

i_n = \sqrt{2eI\Delta f}

with

e = 1.60\times10^{-19}\,\mathrm{C}

, and convert it to a voltage across the same load. ((c)) Combine the two noise voltages and state which one dominates.

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