Feedback amplifier configurations

Systematic relations exist between the four basic single-loop feedback amplifier configurations (voltage-gain, current-gain, transfer-admittance and transfer-impedance) and certain newer configurations for which bandwidth is independent of gain. Loop gain provides the link. For a given amplifier without feedback and specified demanded gain, loop gain and hence bandwidth can be maximised by optimum choice of the feedback resistors. For resistors far removed from this optimum, loop gain can remain constant as demanded gain is varied. Clearly defined conditions exist where adding a unity-gain common-collector or common-base stage at the input will increase the loop gain. Shifting the ground point, source or load generates additional feedback amplifier configurations.