Hello everybody
Well ! I am always stuck in this question. What is the difference between small signal and large siganl? both of them seems to be ac. Some one told me that an ac with amplitude less than 5 V or 5mV is a small signal. What is the actual amplitude for small siganl. and why we call it small signal..

Thank you

 

A small signal is a relative term, usually a small voltage signal on top of a larger, possibly slower, AC signal.

For example, 5mV @ 3 kHz on top of a 5V @ 120 Hz signal. The 5mV @ 3 kHz would be a small signal component.

 

A "small" signal in the context of "small signal" analysis relates to the linear approximation of a transistor model around it's operating point. In the presence of a "small" signal the output is a replica of the input except for a change in amplitude. In simple terms this means that a sine wave in gives you a sine wave out. That is the hallmark of a linear system.

A large signal will however make the device operate in a non-linear fashion by clipping the output or introducing various kinds of distortion. This is why you cannot turn the volume on an amplifier all the way up to the maximum value because even small input signals will be reduced to unintelligible hash.