Electric Circuits and Networks, Ist Edition by Pearson

These voltages form the two inputs of a single-Opamp subtractor circuit with unity

gain. Therefore, the final output taken across the output of the third Opamp with respect to

the ground node is given by v

o

 v

o1

 v

o2

 (2k  1)(v

1

 v

2

).

It may be verified that v

o1

 v

1

and v

o2

 v

2

when v

1

 v

2

, quite independent of the

resistance values of the resistors in the three-resistor chain. This is so because, when v

1



v

2

, there is no current flow in them at all. Thus, the first stage comprising two Opamps con-

tributes the required differential gain without affecting the common mode gain. The second

stage contributes only unity gain to (v

o1

 v

o2

). The common mode ...