Question

An op-amp differential amplifier is built using four identical resistors, each having a tolerance of ±5%. Calculate the worst possible CMRR.

Answer 1

Answer:

80.9 db.

Explanation:

So, in this particular Question/problem we need to determine/calculate for the the worst possible CMRR. The data or information provided by the Question above;

=> ''amp differential amplifier is built using four identical resistors''

Therefore, R1 = R2 = R3 = R4. From the question above, we also know that the tolerance is ±5% for resistor that is;

A1 = A2 = A3 = A4 = A ±5%.

Using the kirchoff formula to each case, we have;

(1). Non Inverting terminal:

[ J - J2 / (A1 = A3) ] + J/ (A2 = A4) = 0.

J = 0.53 J2.

(2). Inverting terminal:

[ J_ - J2 / (A1 = A3) ] + J_ - Jb / (A2 = A4) = 0.

Thus, Jb = 2.11 J_ - 1.11 J2.

Note that J = J_ = 0.53 J2.

Thus, Jb = 1.11 J2 - 1.11 J1.

(Note that we will have that A2 = A4 = A + 0.05 = 1.05A.

Also, A1 = A3 = A - 0.05 = 0.95A).

The voltage is c1 and c2.

Therefore, Jb = 1.11( ccm + cv/2) - 1.11 ( Ccm - cv/2).

= - 10^-4 ccm - 1.11 cv.

Thus, CMMR = 20 log [| 1.11 ÷ (- 10^-4)|] = 80.9 db.