If a class A differential amplifier is using only one of its two possible inputs, what will the output signal shape be?

The output signal shape of a class A differential amplifier utilizing only one of its two possible inputs will be exactly the same as the input signal. This is due to the fundamental operation of a differential amplifier, which is designed to amplify the difference between two input signals. When only one input is active, the amplifier treats the inactive input as a reference, typically at ground. As a result, any signal applied to the active input will be faithfully reproduced at the output, since there is no other input signal to create a difference.

This characteristic is crucial in applications where signal integrity is important, as it ensures that the output remains a linear representation of the input. The absence of the other input does not introduce distortion or change the waveform shape; instead, the amplifier operates effectively as a single-ended amplifier for that input. Thus, the output directly mirrors the input voltage waveform without alteration, confirming that the shape remains exactly the same.