An operational amplifier has open-loop DC gain and a single dominant open-loop pole…

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 Loop gain in real feedback circuits

Problem

An operational amplifier has open-loop DC gain

A_0 = 4\times10^4

and a single dominant open-loop pole at

f_p = 25\,\mathrm{Hz}

(so its gain-bandwidth product is

A_0f_p = 1\,\mathrm{MHz}

). It is used as a non-inverting amplifier with

\beta = 1/50

; take the amplifier's input resistance as infinite and its output resistance as zero, so the loop gain reduces exactly to

T = A_0\beta

and the direct transmission

d = 0

. ((a)) Find the DC loop gain

T_0

. ((b)) Find the closed-loop DC gain

A_{\rm CL}

from the asymptotic-gain formula. ((c)) Find the frequency of the closed-loop pole, treating the open-loop response as a single pole, and compare it with

GBW/A_{\rm CL}

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