Bipolar transistors are widely used in both analogue and digital circuits
They can be considered as either voltage-controlled or current-controlled devices
Their characteristics may be described by their gain or by their transconductance
Feedback can be used to overcome problems of variability
The majority of circuits use transistors in a common-emitter configuration where the input is applied to the base and the output is taken from the collector
Common-collector circuits make good buffer amplifiers
Bipolar transistors are used in a wide range of applications