An alternative approach to that presented in Example 13.5 for determining the CMRR of

Chapter 13, Problem 13.59

(choose chapter or problem)

An alternative approach to that presented in Example 13.5 for determining the CMRR of the 741 input stage is investigated in this problem. Rather than performing the analysis on the closed loop shown in Fig. 13.23, we observe that the negative feedback increases the resistance at node Y by the amount of negative feedback. Thus, we can break the loop at Y and connect a resistance Rf = (1+A)Ro between the common-base connection of Q3Q4 and ground. We can then determine the current i and Gmcm. Using the fact that the loop gain is approximately equal to P (Exercise 13.17) show that this approach yields an identical result to that found in Example 13.5.