Gain and Phase Margins Explained!
Why Electrical Engineering Stack Exchange recommends it
Electronics Stack Exchange users link it when asking or answering questions about gain and phase margin, crossover frequencies, and Nyquist-based stability.
Recommended by 1 people across 1 different months, 2016 to 2021.
What it is
A 14-minute control theory explainer by Brian Douglas that defines gain margin and phase margin, shows how to read them from Bode plots and relate them to the Nyquist view, and explains why they matter for feedback system stability.
What people said
Strong rec klamb · 2016-08 · Electrical Engineering Stack Exchange · on “Condition for absolute stability”
This gentleman does an excellent job explaining phase/gain margin and gets into nyquist plots and how they play an imporant role in stability. [this video]
Cites aadil095 · 2018-03 · Electrical Engineering Stack Exchange · on “Why gain crossover frequency must be lower than phase crossover frequency for stable systems?”
As far as I understood from here [this video] , phase margin means the amount of phase that needs to be added in order to coincide with 0 db gain and -180 degrees phase. Likewise for the gain margin it means means the amount of gain that needs to be added in order to coincide with 0 db gain and -180 degrees phase. But i don't understand why do they both necessarily have to be positive for stable systems? Re-stating my question. I want to know: Why gain crossover frequency must be lower than phase crossover frequency for stable systems ? [LINK] Relevant: Can a phase margin become bigger than 180° and is this bad? [LINK]
Cites Unknown123 · 2021-03 · Electrical Engineering Stack Exchange · on “Confused about the gain effect over cutoff frequency”
Assume that everything is ideal LTI ZIC. Try to derive the transfer function first to understand it. Hint: Remember the golden rule of op amp and use nodal analysis at the input terminal of it. [LINK] The result will be like this: [LINK] Ideal second-order LPF LTI ZIC ( such as series RLC [LINK] ) will have prototype transfer function like this: [LINK] The G factor doesn't change the pole frequency (natural frequency). Even though that's true, it still change most of the filter characteristics, which we usually design using known topology (such as Butterworth, Chebyshev, …). It changes asymptotic gain [LINK] (of course), 3dB cut-off frequency, bandwidth, the damping ratio/quality factor [LIN
Cites needbrainscratched · 2021-07 · Electrical Engineering Stack Exchange · on “Please help me clear up this confusion regarding gain margin and phase margin and unity feedback”
I understand the physical significance of gain and phase margin. However, I would like some clarification regarding the mathematical aspects. Videos such as the following: [this video] (time: 6:28) [this video] (time: 7:12) define phase margin and gain margin for unity feedback. Even in Matlab when we plot bode of any transfer function, it assumes unity feedback. What's so special about unity feedback? My next question is, if I want to find gain and phase margin of system with gain G(s) and feedback H(s), whose gain and phase should I plot among the following: G(s)? G(s)/(1+G(s)) ? (unity feedback transfer function) G(s)/(1+G(s)H(s)) ? (closed loop transfer function) G(s)H(s) ? (loop gain) I feel it s