Question

difference amplifier
derived equation for v0 in terms of va and vb: v0 = 10(vb - va)
calculated differential - mode gain with va = 0v: 10
calculated differential - mode gain with vb = 0v: - 10
calculated common - mode gain:
calculated common - mode rejection ratio: i
for vb = 0v
measured va: 0.5 v measured v0: - 5.0 v
measured differential mode gain: - 10
for va = 0v
measured vb: 0.47 v measured v0: 4.8 v

Explanation:

Step1: Recall common - mode gain formula

For a difference amplifier, when $V_A = V_B=V_{cm}$ (common - mode input), the output $V_o$ for an ideal difference amplifier should be 0. In practice, we can use the fact that for a difference amplifier with the output formula $V_o = A_d(V_B - V_A)+A_{cm}V_{cm}$, where $A_d$ is the differential - mode gain and $A_{cm}$ is the common - mode gain. In an ideal case with high CMRR (Common - Mode Rejection Ratio), when $V_A = V_B$, $V_o = 0$. So, the common - mode gain $A_{cm}=0$.

Answer:

0