Study of Behaviors of Electronic Amplifiers Using Nichols Chart

This paper explores the use of the Nichols chart to study the operating regions and compute the phase margins in electronic amplifiers. Inspection of the Nichols chart allows the determination of the exact values of the phase margin at unity gain of the self-loop function in a transfer function. Hence, there is no need to use the Nyquist criterion which is an important stability test with applications to adaptive feedback systems. Furthermore, the phase margin allows the prediction of the ringing that drives the system unstable. Several illustrative examples of feedback amplifiers are provided. Experimental results are also presented which confirm the theoretical development of the stability test.