Question

2.152 An op-amp is connected in the inverting config- uration with R2 = 20 ks2 and Ri = 10ks, where R2 is the feedback resistor. The frequency response of the closed-loop amplifier is found to fall off at a frequency of 1.2 MHz (a) What is the op-amp's unity-gain frequency fo? (b) If the open-loop gain is 2 x 10%, what is the open- loop breakpoint frequency fp?

Answer 1

(Arsola Let us consider the open Ao loop op-amp bode plot, with opamp unity gain to fof frequency (fo) & Ao = open loop gain (Ao = 2x109).& breakpoint frequency fp. Then the TF of op-amp = _ Ao = Als) m it einer 10 fo7 Rovelling configuration : Rimi vin Mir I " =10k - Als t vout R2=20k 1 vout= A(s) (Up-VAD Np=0 ; voutRi + Vin R2 l by superposition VN RIHR RitR2 Lg voltage divider out Arsl- voutry _ VinR2 l vous [ + kopi Vout. - ASR2 vin RHR2 17 ACOR

ACS) affer substiting rearanging I vout 2 - ( P232) vin As ett fp. Now closed loop gain = R2 where as closed loop bandwidth Al28) ſcomparing with (R2+1) L 'O I given; | Ao (211fp) - 1.2MHZ X 2T| 2 x 48 x 27 x (p = 1.2 x 48 x 2t t 241 1.2 X 10 X 3 = 36H2 = 23*2; 5) oxfo = Aofp r gain bandisideth product is constant - fo= 2x108 x 36 a onit gain go frequency) so = 7200000 = 702M42