An operational amplifier is wired as a non-inverting amplifier: a resistor runs from…

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

Inside the Instrument, Ch Noise sources and amplifier noise

Problem

An operational amplifier is wired as a non-inverting amplifier: a

1.0\,\mathrm{k\Omega}

resistor

R_1

runs from the inverting input to ground, and a

9.0\,\mathrm{k\Omega}

feedback resistor

R_2

runs from the output to the inverting input, giving a closed-loop gain of

10

. The amplifier has

e_n = 10\,\mathrm{nV/\sqrt{Hz}}

and

i_n = 1.0\,\mathrm{pA/\sqrt{Hz}}

; take

T = 300\,\mathrm{K}

, assume the non-inverting input sees no external resistance, and treat every noise source as an uncorrelated white density over the band of interest. ((a)) Find the amplifier's input-referred noise density, including the Johnson noise of

R_1

and

R_2

and the voltage that

i_n

develops across their parallel combination. ((b)) Find the output-referred noise density. ((c)) Find the rms output noise in a

20\,\mathrm{kHz}

noise bandwidth.

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