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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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Design a PID controller for a MG=1.5

Consider the following system: I need to design a PID controller with a gain margin of 1.5 for the disturbance P(s). In order to have a certain gain margin I need to find the critical gain Ku, so ...
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How could we predict the transient response of the multi-loop circuit?

Typically, when analysis the stability of a single loop circuit, we can use the open-loop method, just to break the loop and get the loop gain. Then, using the Bode diagram, we can easily get the PM(...
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What is the phase margin of this inverting amplifier?

I'm having trouble finding the phase margin the telescopic cascode amplifier I'm currently building. This source says that the phase margin for an inverting amplifier is the distance from -360 degrees ...
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AC voltage for phase margin calculation

When using Orcad PSpice to find the phase and gain margin of a circuit, like a linear power supply, what is the best voltage to use for the AC source? Its value affects the phase margin value. Most ...
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How to measure the phase margin of a fully differential ampifier?

How do you measure the phase margin of a fully differential amplifier? We know that the output voltage of a fully differential amplifier is $$V_\text{out} = (V_\text{o+} - V_\text{o-})$$ so how do you ...
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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 ...
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How to determine the phase margin when the Bode plot never crosses 0 dB?

I have a graph that looks like this. I am tasked to measure the phase margin, but the graph doesn't exceed 0 dB. The circuit is this. The input DC level is 0.6 V, which is the problem. When I change ...
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If the phase margin stability test fails at a very high frequency that I will never reach, is this an acceptable design?

If I have a system that fails a phase margin stability test at a very high frequency that I will never reach, can we conclude that my system is stable, given that we will never reach the frequency at ...
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CS amplifier feedback stability

I playing with JFET Common Source amplifier with feedback loop. I am simulating the design showed here. https://www.ti.com/lit/an/slpa018/slpa018.pdf?ts=1669662908797&ref_url=https%253A%252F%...
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LDO phase margin

The recommended phase margin to achieve stability is 45. With a positive phase margin, but less than 45, the system is stable, but the output has some oscillation. For LDOs, we have specifications for ...
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Op-amp phase margin issue

I have designed a PMOS-based 2-stage op-amp. While performing an AC analysis to check the stability of the design, the gain obtained is high and positive. The issue I am facing is the phase margin ...
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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 (...
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How is gain margin defined for this control system?

Lets say there is a system H(s) = 3/s which I want to control with a controller G(s) = Kp·(1+10/s) The Bode diagram of the open loop G(s)H(s) with Kp=1 is: At the transit frequency the phase is ...
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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 ...
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Effect on stability margins when an integrator is introduced in the loop of a closed loop system

I was asked a question in a control system test which is as follows: *Introduction of integral action in the forward path of a unity feedback system results in a a) marginal stability b) system ...
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How to derive phase margin and gain margin from experimental step response?

I have a fabricated closed-loop integrated amplifier circuit. Therefore, I can only conduct transient response experiments. How Do I derive the phase margin and gain margin from the experimental step ...
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Gain and phase margin interpretation in control system

I have a unity feedback system with the open loop transfer function having the following bode plot: As shown on the plot, the gain margin and phase margin are -27.4937dB and 75.0185 degrees. And the ...
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Gain crossover frequency in bode plot for control system

I know that gain crossover frequency (freq at which gain is 0dB) is where the phase margin is calculated. I also know that the gain crossover freq must be lower than phase crossover freq for stable ...
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Checking calculation of phase and gain margin in LtSpice

I am currently studying DCDC stability analysis in LtSpice. Could you please check my phase margin calculation, am I right? And how about the gain margin calculation? Is it equal to infinity in my ...
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Intuitive understanding of relation between phase margin and peak overshoot and/or damping factor [closed]

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" ...
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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 ...
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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 ...
Sambeet Panigrahi's user avatar
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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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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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How to calculate the phase margin from Bode Plot if only the phase angle corresponds to the pole frequencies are given?

I have a Bode plot where only the phase angle corresponds to the two pole frequencies are given. The value of gain crossover frequency where the loop gain is unity is unknown. $$\mathrm{PM} = \phi - (-...
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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 ...
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Why phase margin considers only addition of negative phase?

When the phase margin of \$L(s)\$ is calculated, people calculate how much negative phase (or lag phase) can be added to the system \$L(jw)\$ until \$1+e^{-j\theta}L(jw)=0\$ for some frequency \$w\$. ...
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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: https://www.youtube.com/...
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Phase lower than -180 when reaching unity gain, is it unstable or can we substract 360?

I am getting a phase of -434 degrees when reaching unity gain (0 dB point). The phase curve starts at 0 degrees, thus, can we consider that -434= -434+360= -74 degrees and the phase margin is of 180-...
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How to find gain and phase margin from transfer function without Nyquist or Bode plot

Given transfer function L(s) as a ratio of polynomials of s, I know that we can find gain margin (GM) and phase margin (PM) by using a Nyquist or Bode plot. From a Nyquist plot: Find a point where ...
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Bode plot starting from 180?

This is an NMOS common source amplifier and I'm trying to calculate the Phase Margin, but it's starting from 180 instead of zero? dose it mean I have poles at the origin or it's very stable?
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unstable systems with positive phase/gain margin

Open loop Phase/Gain margins provide information on how much margin the closed loop system have until it becomes unstable. In other words, how much you can increase the effective loop gain and or ...
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20 dB/Decade - Justification

I've read that it is recommended to have 20 dB/Decade slope on the L(jw) magnitude plot of the Bode Diagram at gain crossover. This seems to imply a slope of -1 in dimensionless terms. However, what ...
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Infinite Phase Margin

I have been assigned a control systems problem, where I am supposed to stabilize a system using a controller technique from the frequency domain. When I implemented the system on Matlab and calculated ...
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How to quantify amplitude of oscillations in marginally stable systems?

A transfer function pole on the Imaginary axis indicates that the system is marginally stable which in time domain manifests as a sinusoidal motion with constant amplitude at the frequency of the pole....
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How to find gain and phase crossover from a Nyquist plot?

Note: I need to do this by hand which is why I'm struggling. I'm only using MATLAB here to show the nyquist plot, and I was also using it to try and check my answer. Edit: There are poles at -50, -10 ...
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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 ...
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Optimum phase margin Controller Design

I am designing a PI voltage and current Controller (Cascaded Control for Buck Converter with LC filter) and I am confused about what is the perfect phase margin to choose for the application. I read ...
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About phase margin of inverting amplifiers

Phase margin is usually defined as how far is the phase of the loop gain from -180: $$PM = \angle \text({loop \space gain}) +180^{\circ} $$ Let's suppose that we want to compute the maximum phase ...
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Why do I need phase margin if I know the transfer function?

What is the point of examining the phase margin (or gain margin) for a closed-loop system if I can just solve for the transfer function. The transfer function will give any poles and zeros, which can ...
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Phase margin vs. damping ratio (non-unity feedback)

So there is a well known condition which relates the phase margin with the damping ratio for a unity feedback system: $$\Phi_m = \tan^{-1} \frac{2 \zeta}{\sqrt{-2 \zeta^2 + \sqrt{1+4\zeta^4}}}$$ ...
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Poles from Bode plot

How does one deduct the number of poles from a Bode plot? Is it further possible to decide where the poles are? I have not understood this concept even though there is so much focus on Bode plots in ...
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The Effect of Input and Feedback Capacitors on an Operational Amplifier Open-Loop Gain Response

I have the following circuit that I want to compensate: As shown from the step response, the circuit is unstable because of the high input capacitance (the green plot is without any additional input ...
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Phase margin for a system (design of PD controller)

I have a system with the following transfer function: \$G(s)=\cfrac{20}{s^2+s+20K_f}\$ where \$K_f=1.75\$ I want to use a PD controller and I want obtain a phase margin of 35 degrees. I need to ...
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Phase Crossover Frequency at 0 deg or -180 deg

I've learned in school to calculate gain margin by first finding the phase crossover frequency at -180 deg, but sometimes I see people calculate gain margin by finding the phase crossover frequency at ...
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Estimate the phase margin of a loop gain

The loop gain is \$10^6 /[(s+1)(1+s10^5)]\$. Below I have the Bode plot. How can I derive the unity gain frequency from the Bode Plot? How can I find the phase margin from the phase plot of the Bode?
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Gain margin and phase margin in Nyquist plots

Finding gain and phase margins from Nyquist plots is basically finding the margin of change in gain and phase beyond which the plot encircles -1, respectively, with the assumption that the Nyquist ...
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Convert ringing frequency to phase margin for LDO stability

Based on ROHM document "Simple Test Method for Estimating the Stability of Linear Regulators", it showed that in page 2/4, the phase margin for Fig.5 Phase Margin = 0 deg, Fig.6 Phase Margin = 9.9 deg ...
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