An approach to test the open-loop parameters of feedback amplifiers

A novel method for determining open-loop parameters, such as unity-gain frequency and phase margin, in feedback amplifiers is given. It is based on relations between open-loop and closed-loop configurations and is very useful for evaluating the above parameters in a unity-gain amplifier from a simple measure of its closed-loop 3-dB cutoff frequency and the respective phase for a given feedback factor, beta. The approach is validated by simulations of an ideal amplifier and of a real OTA. Moreover, measures carried out for a muA-741 operational amplifier show a percentage error between real and calculated values lower than 2%.