What will be the output of a differential amplifier with two identical in-phase signals on the inputs?

In a differential amplifier, the output is determined by the difference between the two input signals. When two identical signals are applied to the inputs of the amplifier and these signals are in phase, the voltage difference between them is zero. This occurs because both inputs experience the same voltage level at all times, leading to:

[ V_{out} = V_{in+} - V_{in-} ]

In this case, since ( V_{in+} ) (the voltage at the non-inverting input) is equal to ( V_{in-} ) (the voltage at the inverting input), the equation resolves to zero. As a result, the output of the differential amplifier will also be zero, indicating that there is no voltage difference to amplify.

Understanding this principle highlights the purpose of boundary conditions for differential amplifiers, as they are designed to amplify the difference between two inputs rather than their absolute values. When the inputs are identical, the amplifier essentially becomes inactive in terms of output voltage.