10
CONSTANT M- AND N-CIRCLES AND NICHOLS CHART
10.1 Introduction
The frequency-response techniques discussed in the previous chapters are the open-loop frequency plots that have obtained the information about the closed-loop stability using the open-loop frequency response of the system. In these methods, the frequency response of the loop transfer function 
is plotted and information regarding the closed-loop stability is derived from the plot. In this chapter, constant M-circles (magnitude), constant N-circles (phase) and Nichols chart are discussed, which directly give the information regarding the closed-loop stability of the system.
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