Common-Base Amplifier

This circuit is an example of the common-base amplifier configuration which is excellent for high frequency applications since it does not suffer from the miller capacitance of the common emitter amplifier, on the downside the input impedance is very low, in this circuit it is equal to re which at a 500uA quiescent current is 50 ohms at room temperature, the voltage gain is very high being roughly 50, since it essentially buffers the input current to the collector the gain is strongly dependent on source impedance with lower impedance providing more gain, as a result a JFET is preferable as an input stage in RF applications but the common-base does make a good voltage amplification stage, more advanced designs such as the cascode improve this greatly.

published 11 years ago