A differential amplifier with signal terminals $X,Y,Z$ is connected as shown in Fig. (a) below for $CMRR$ measurement where the differential amplifier has an additional constant offset voltage in the output. The observations obtained are: when $V_i=2V, V_0=3mV,$ and when $V_i=3V, V_0=4mV$.
The differential amplifier is connected as shown in Fig. (b) above to a single strain gage bridge. Let the strain gage resistance vary around its no-load resistance $R$ by $\pm 1$%. Assume the input impedance of the amplifier to be high compared to the equivalent source resistance of the bridge, and the common mode characteristic to be as obtained above. The output voltage in $mV$ varies approximately from
- $+128$ to $-128$
- $+128$ to $-122$
- $+122$ to $-122$
- $+99$ to $-101$