Questions tagged [phase-margin]

A stability metric which is the difference between the phase lag and -180 degrees for a circuit's output relative to its input at unity gain. Positive phase margin indicates stability, negative phase margin indicates that the circuit is not stable. Consider also using related tags such as "stability", "bode-plot", and "transfer-function".

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Confused regarding gain margin and stability

I plotted the bode plots of the transfer function: G(s)= 2.123×10^6 ((0.105s+1.01))/(s^2 (s+12566.37) ) It is as follows: As can be seen, it shows the gain margin as negative infinity, however loop ...
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What will be the values of phase crossover frequency when the gain margin is infinity?

$$G(s) = \frac{s+1}{s^2+2s+100}$$ For the given transfer function I am getting the gain margin equal to infinity in the matlab, but i am not getting the value of phase crossover frequency. What will ...
1 vote
64 views

Gain and phase margin of multiple feedback bandpass filter

I designed a multiple feedback bandpass filter using the Analog filter wizard. The design is purely education therefore I used ideal op-amp. Fc = 50KHz; DC gain = 6dB; Q = 5; I followed the ...
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How can gain and phase margin be used to assess stability of SMPCs as for most of the cases (except buck), they always have a Right Hand Zero?

I was going through this Operational Amplifiers, Theory and Practice by James Roberge. On Page 146, it is mentioned that for systems that have negative feedback at low or mid frequencies and that have ...
100 views

Amplifier Stability - Observing phase margin

I am following a TI lab about opamp stability: "Precision Labs - Op amps: Stability". And I have some trouble to interpret phase margin from bode plot on an example. The transfer function (...
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101 views

Why is the phase margin more important than the gain margin?

I heard from some lecturers that the phase margin is more important than the gain margin. However, after searching online and in some control related textbooks I couldn't find any reference for such ...
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Can a system with more than 180 phase lag ever be stable?

For a system to be stable you must not reach a phase of 180 degrees before gain reaches 1 (for an ideal system). The layman explanation I was offered was that otherwise, your negative feedback becomes ...
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13k views

How to determine the phase margin and transfer function of this bode plot?

I have some struggles to find the transfer function of this plot. We got the hint, that the "breaks" of slope can be assumed to be on vertical and horizontal lines. Also we should pay attention on the ...
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1 vote
193 views

Phase/Gain margin measurements for current mode boost regulator

I'm looking for where to place a sense resistor in the feedback path of a current mode boost regulator with a layout similar to the one in the picture. Should I place in on the FBL or FBH trace?
1 vote
746 views

Why gain crossover frequency must be lower than phase crossover frequency for stable systems?

As far as I understood from here, 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 ...
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79 views

Determining the phase margin of a negative series-shunt feedback circuit

I have been given a transfer function: $H(s)={A_0\over (1+s/w_{p_1})(1+s/w_{p_2})}$ With the condition that $w_{p_1} << w_{p_2}$ It's designed for this feedback circuit ...
4k views

Controller to increase phase or gain margin

I can't find any good sources on this one. The only textbook I have says nothing about it. I've been restricted to the use of some formulas given by our teacher which I don't understand why they ...
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Capacitance on the output of an op amp

I have read a lot about capacitive loads on the output of an op-amp and the possibility of unwanted oscillations and instability. my knowledge on phase margin and frequency domain analysis is a little ...
2k views

Phase margin measured at lowest positive-gain point, rather than 0dB point?

When discussing voltage regulators, one often hears that phase margin should be measured at the 0dB gain crossing. This makes intuitive sense in a simple system where the phase has only a negative ...
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