Question

For the difference amplifier as shown in the figure show that if each resistor has a tolerance of ±100 ε % (i.e., for, say, a 5% resistor, ε = 0.05) then the worst-case CMRR is given approximately by (given K = R2/R1 = R4/R3)

(a) 20 log [K+1/4ε].

(b) 20 log [K+1/2ε].

(c) 20 log [K+1/ε].

(d) 20 log [2K+2/ε].

The question was posed to me in an international level competition.

My question is taken from Difference Amplifiers topic in section Operational Amplifiers of Electronic Devices & Circuits

Answer 1

The correct option is (a) 20 log [K+1/4ε].

The best I can explain: None.