Vout Rc Suppose you have designed the circuit above with Ra-Re-100 , and chosen
ID: 2267298 • Letter: V
Question
Vout Rc Suppose you have designed the circuit above with Ra-Re-100 , and chosen Rb and Rd such that where, Adm is the diference-mode gain, and the common mode gain is zero (i.e. CMRR is infinity) However, the resistors you've used to build the circuit are not precise. Each of them has an x% error (therefore, a resistor with a nominal value of 100 ohms will actually have a resistance of 99 or 101 ohms). Write a MATLAB program to find the worst possible CMRR for a given value of x and Adm. Plot the CMRR (in dB) vs. x for x 1,2,...10. Obtain three graphs (and display in the same window) for Adm = 1, 10 and 100.Explanation / Answer
% Non-inverting amplifier with finite CMRR
%Case-I for Adm=1
%Rd/Rc=Rb/Ra
%Then Adm= Rb/Ra
%For Adm=1
%Rb=Ra=100 Ohm
rb = 100; ra = 100; rr = rb/ra; %rr is our gain
cmrr = logspace(4,9,6); gain = (1+rr)*(1+1./cmrr);
subplot(2,2,1);
semilogx(cmrr,gain,'wo')
xlabel('Common-mode Rejection Ratio')
ylabel('Closed Loop Gain')
title('Gain versus CMRR')
axis([1.0e3,1.0e10,50.998, 51.008])
%For Adm=10
%Rb=10Ra
%So Ra=100 Ohm & Rb= 1000
rb = 1000; ra = 100; rr = rb/ra;
cmrr = logspace(4,9,6); gain = (1+rr)*(1+1./cmrr);
subplot(2,2,2);
semilogx(cmrr,gain,'wo')
xlabel('Common-mode Rejection Ratio')
ylabel('Closed Loop Gain')
title('Gain versus CMRR')
axis([1.0e3,1.0e10,50.998, 51.008])
%For Adm=100
%Rb=100Ra
%So Ra=100 Ohm & Rb= 10000
rb = 10000; ra = 100; rr = rb/ra;
cmrr = logspace(4,9,6); gain = (1+rr)*(1+1./cmrr);
subplot(2,2,3);
semilogx(cmrr,gain,'wo')
xlabel('Common-mode Rejection Ratio')
ylabel('Closed Loop Gain')
title('Gain versus CMRR')
axis([1.0e3,1.0e10,50.998, 51.008])
%subplot is used for plotting all semilog graphs on sigple page
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