**Differential Input and Differential Output Amplifier:**

In almost all the applications, the op-amp is employed with a single-ended or unbalanced output. However, there are certain applications in which a differential output is desired. The differential input and differential output amplifier is widely employed as a pre-amplifier and in driving push-pull arrangements.

One possible arrangement of a differential input and differential output amplifier is given in Fig. 34.51. This circuit makes use of two identical op-amps.

Using the superposition theorem we have

Similarly

Differential output voltage,

The above equation reveals that the input and output are in phase or are of the same polarity provided that v_{in} = v_{in1} – v_{in2} and v_{out} = v_{out1} – v_{out2}.

The circuit given in Fig 34.51 is very useful in noisy environments, especially if the input signal is comparatively smaller. This is because it rejects the common-mode noise voltages.