Question

A minimum phase unity feedback system has slope $-20\,dB/decade$ for all frequencies. The value of maximum phase margin is:

• A. $-90^\circ$
• B. $0^\circ$
• C. $90^\circ$
• D. $180^\circ$

Hint:

Slope $-20\,dB/dec$ → phase margin $90^\circ$.

Answer 1

The Correct Option is C

Concept: For a system with slope $-20\,dB/decade$:
• Single pole system
• Phase lag = $90^\circ$

Step 1: Phase margin \[ PM = 180^\circ - 90^\circ = 90^\circ \] \[ \therefore \text{Correct answer is (C)} \]