Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

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".

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 , , and .

85 questions
14
votes
7 answers

Gain margin and Phase Margin Physical Meaning

I have been trying to understand the physical concept of Gain and Phase Margin. What I understand about this is that a relative comparison around the critical point \$(-1,0)\$, which when converted to magnitude and phase form turns out Magnitude =…
Fawaz
  • 354
  • 1
  • 7
  • 17
11
votes
4 answers

What does the "phase margin" parameter of an opamp imply?

I was reading datasheet of MCP6072. I saw a parameter namely "phase margin" (table 1-2, page 4). As far as I know, "phase margin" is a control engineering term, and implies the phase difference between input and output when the gain is unity. I…
hkBattousai
  • 13,913
  • 31
  • 114
  • 190
6
votes
2 answers

How to decrease the voltage spike of a Buck circuit?

I have designed a buck circuit. The Bode plot of my system is as follows: I use a type Ⅲ compensator to control my system. The switching frequency is 100 kHz. The cut-off frequency is 20 kHz and the phase margin is 60°. The transient state of the…
T L
  • 475
  • 1
  • 8
6
votes
1 answer

Interpretation of mathematicial and corresponding physical meaning of gain and phase margin

In my textbook these are the definition of gain and phase margin: The gain margin is defined as the change in open-loop gain required to make the system unstable. The phase margin is defined as the change in open-loop phase shift required to…
Fraïssé
  • 1,507
  • 1
  • 19
  • 38
5
votes
2 answers

What is the phase margin when there are multiple gain crossover frequencies

I am using LTPowerCAD to help design a buck converter circuit using the LT8645S. I would like to add a second stage LC filter at the output to achieve lower output ripple, but when I add the second stage, the bode plot of the loop compensation shows…
imnotarobot
  • 141
  • 9
5
votes
3 answers

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 slope with increasing frequency. However, what about…
user5678
  • 81
  • 3
5
votes
2 answers

I know it has small phase margin.. but why is it oscillating not at rails?

I came across an issue at my workplace with the following circuit. I did a OL response and saw that the gain margin is 21 db and the phase margin is 14 deg. Clearly not so good. Note that the 680nF cap is a populated capacitor on a board!! I…
klamb
  • 312
  • 1
  • 12
4
votes
2 answers

Why is there no frequency compensation required in TI's TL494 example buck regulator design?

This example circuit is given in Texas Instrument's application note SLVA001: "Designing Switching Voltage Regulators With the TL494": They use a 140 μH inductor and a 220 μF electrolytic capacitor for the LC filter (capacitor value not printed on…
Unimportant
  • 4,335
  • 1
  • 18
  • 25
4
votes
1 answer

Can a phase margin become bigger than 180° and is this bad?

I have a wrong mental model about phase margin in control theory. I see that a phase of -180° is bad. If my input is a sine wave and I have negative feedback, which has a -180° phase shift, the feedback will become positive --> oscillation. But why…
Mr.Sh4nnon
  • 340
  • 3
  • 13
4
votes
2 answers

How can I export the frequency response from LTSPICE without phase wrapping?

After I plotted the frequency response of a circuit using LTSpice as shown: I exported the plots data as a .txt file in order to plot them after that using MATLAB, however, after I plotted the data using MATLAB I discovered that the exported data…
Nour
  • 41
  • 2
4
votes
4 answers

Phase margin analysis of a [diy] PMOS LDO [with LTspice]

I'm somewhat familiar with using LTspice to do phase margin analysis for a classic i.e. obvious negative feedback path opamp circuit; in fact I've done that analysis successfully for fixing real opamp circuits. But I'm confused how to do this…
Fizz
  • 14,355
  • 2
  • 43
  • 97
4
votes
4 answers

Can gain and phase margins be obtained from step responses?

We need to comply to specific gain and phase margins requirements whereas the controller has been tuned on-line without knowing the plant transfer function (in order to save time). The response does not exhibit any overshoot, but we need to make…
Mister Mystère
  • 9,477
  • 6
  • 51
  • 82
3
votes
3 answers

Open-loop simulation of a voltage-controlled current source

Short summary: V3 decides the current going through R2. If V3 is 0 V then no current is going through R2. If V3 is 10 V, it will be approximately 50 mA. I want to do an open-loop simulation of this voltage-controlled current source. The…
Tungstein
  • 47
  • 5
3
votes
1 answer

What is the definition of phase margin?

From wiki we could see the definition of Phase Margin: In electronic amplifiers, the phase margin (PM) is the difference between the phase lag φ (< 0) and -180°, for an amplifier's output signal (relative to its input) at zero dB gain - i.e. unity…
T L
  • 475
  • 1
  • 8
3
votes
3 answers

Intuitive understanding of relation between phase margin and peak overshoot and/or damping factor

Second, percent overshoot is reduced by increasing the phase margin, and the speed of the response is increased by increasing the bandwidth. "Control Systems Engineering, Norman S. Nise" The mathematical proof of this statement is available in the…
aviral upadhyay
  • 103
  • 2
  • 7
1
2 3 4 5 6