Questions tagged [nyquist-plot]

For questions about Nyquist plots, often used to assess the stability of an electrical circuit which includes feedback. Consider also using the "frequency-response" tag, and "stability" tag if your question is about the stability of an electrical circuit.

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Sampling frequency of ADC and maximum frequency of input signal

As pair the datasheet of LTC2207, maximum input frequency can be 700MHz. whereas the sampling frequency is 105MSPS. Two times 700MHz is way less than 105MSPS. So how is this not contradicting with ...
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Nyquist stability criterion in discrete time domain

I've been transforming systems from the s-domain to the z-domain, and looking at the Nyquist plots I get in the z-domain. So far I've assumed that the Nyquist stability criterion that applies in the s-...
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Allowable process variation for non minimum phase plant

Scenario (plant model subject to process variations) Consider a plant \$P(s)\$ in series with a controller \$D(s)\$ with a negative feedback path around it, where the closed loop is given by the ...
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Control engineering: how to design a system for desired impulse response

I've designed a system to get a desirable step response. However, I think the impulse response of my system is more important. There are many methods for designing a system for transient response ...
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Why is the second red point also considered a clockwise crossing on the Nyquist plot?

From this page: The image below shows the same Nyquist path, but a different line. In this case there are two clockwise crossings (red) and two counterclockwise crossings, for a total of zero ...
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Assign Bode plots to Nyquist diagrams

How do I assign the following Bode plots to their corresponding Nyquist diagram? Can i tell the number of poles of the transfer function of the nyquist plot, by looking at w→infinity (from which of ...
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Deriving a transfer function from Nyquist plot

I am given a half Nyquist plot and exercise as below I know how to plot a Nyquist curve for a given transfer function but I have trouble doing it the other way. I stumbled upon this post Deriving ...
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Instability as seen in time domain

It is my understanding that an unstable closed loop in a minimum-phase system occurs when the loop gain (A*B of the characteristic equation) encircles the -1 point on the Nyquist chart. In https://www....
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Nyquist Plot Stability with Angle

I don't understand the solution done here. The Nyquist criteria I know is Z=N+P and I don't see the relation with this solution. Where do the angles come from?
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Deriving transfer function from nyquist plot

I am given a half Nyquist plot as below The dashed line stands for the asymptote of the locus and the poles are 0 or negative at real parts, besides there is no double root in the transfer function. ...
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How to check for stability for non-constant controller using Nyquist plots?

Let's say I have a unitary feedback system with one unstable (RHP) pole. Now if my \$G_c\$ is a constant, say \$K\$, I know that in order to have stability I should have a single counterclockwise ...
Ahsan Yousaf's user avatar
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Recording aliased tones on purpose

For research purposes, I am trying to transmit a tone and record it using sub-Nyquist sampling. Via the PC microphone, for instance, I would expect to see the aliasing effect somewhere in the ...
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Nyquist Criterion: Encirclement around origin

I am studying the Nyquist stability criterion and I am stuck on the following problem. The open-loop transfer function with unity feedback is \$\small\mathrm{ G(s)=\large\frac{1}{s-3}}\$. Following is ...
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How to determine difference between LHP poles and zeroes by observing Nyquist plot?

I am solving practice problems on Nyquist Plot and I got stuck at a problem having a solution which I do not get at all. Here it is: Which of the following is the transfer function of a system having ...
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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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Nyquist plot mirrored across imaginary axis

I am reading Foundations of Oscillator Design by Guillermo Gonzales. When an amplifier is connected in a positive feedback configuration, the transfer function is \$A_{vf}(s)=\frac{A_v(s)}{1-\beta (s)...
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How to draw a Nyquist plot by hand using standard plotting strategies?

I want to draw by hand the Nyquist plot of an RC filter's transfer function. I do not want to use the "tricks" that help with building it faster (evaluating just some limits points) - I want ...
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ADC Nyquist Zone - Sub Sampling

I am trying to design a system to sample an RF signal using a 10MSPS 12 bit ADC (ADC12010CIVYX/NOPB). During frequency planning I observed that, to get a proper sample with out aliasing the input ...
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Why does Nyquist plot show no encirclement when positive feedback is unstable?

Amended the previous question to be more concise I have the following open-loop plant: $$G(s)=\frac{21.95s^2+224.2s+1906}{s^4+32.7s^3+285.8s^2}$$ These are the poles of the plant, and as you can see, ...
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Meaning of circle passing through -1 (nyquist plotting)

I'm using MATLAB to plot a few functions in nyquist plots. I'm learning nyquist plots and I'm quite new to the concept. I plotted the nyquist plot for (s3 + s2 + 2s + 2)/(s2 - 9) [unstable system] and ...
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Which of the following methods tells Absolute stability & which method tells Relative Stability? Bode Plot, Routh Hurwitz, Root Locus, Nyquist PlotC

Which of the following methods tells Absolute stability & which method tells Relative Stability? I. Bode Plot ii. Routh Hurwitz iii. Root Locus iv. Nyquist Plot What i think is the following ...
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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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S-plane transfer function contour

In Razavi's textbook, the following contour plots for the transfer function \$H(s)=A_0\frac{1+s/ \omega_z}{1+s/\omega_p}\$ are given. It's stated that \$H(\sigma_N) > H(\sigma_M)\$. How is this ...
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Nyquist plot - is my system stable?

I am working on a balance controller for a robot. I have obtained a transfer function between the robots motor voltage and the robot pitch angle. $$G= \frac{ -5.893e05 s^4 - 7.71e08 s^3 - 1.435e11 s^2 ...
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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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Nichols plot confusion

The transfer function is \$F(p)=10/(p^2+2p+1).\$ Using Wolfram Alpha, the Nichols plot shows that the argument \$\to -\pi\$ when \$\omega \to +\infty\$. However, calculating the argument on paper ...
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What would a polar plot or a Nyquist plot of an undamped second order system look like?

I'm relatively new to control systems. I got to know how critically damped system looks like in Nyquist plot (same gain and phase cross over frequencies. PS. correct me if I'm wrong) and Bode plot ...
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Nyquist theory - Control system - Stability

I am trying to understand the Nyquist theory for knowing if a system is stable. Here is what I know : A system is unstable when the open loop transfer function + 1 of the system has one or more right ...
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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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RC circuit not ideal sampling

I have this circuit and I have to find \$x(t)\$, starting from \$ x_c (t) \$ I know that, at \$t=0\$, the switch is closed, so the capacitor is charged and, at the moment \$ x(n)T_c \$ the switch is ...
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Aliased signal has phase shift due to Nyquist

Let's say I have a pure sinusoid at 135MHz and I am sampling at 150MHz (so fin < 2fs). So now in my first Nyquist zone, I will see a 15MHz alised component. From my understanding, the 15MHz signal ...
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Nyquist plot disagreeing with the unity step response of the closed loop

Let us assume that the open loop transfer function of my system is: \$L(s)=\frac{10(s+1)(s+2)}{(s-3)(s-4)}\$ Also, the system has unity feedback, meaning that the closed loop transfer function is \$...
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Nyquist Plot from Bode Plot

How do I know the value at which the Nyquist plot crosses -180 degrees from looking at the Phase plot from 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 ...
Aniket Sharma's user avatar
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What is this functions Phase crossover frequency?

OLTF loop gain My approach What I have done wrong?
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How to find Phase crossover frequency?

I make the imaginary part of \$loop \ gain=0\$ to find phase crossover frequency. But in one video, the person told that this method can only be applied when Polar plot crosses the real axis and ...
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Questions on Bode Plot and Nyquist Plot

Bode Plot 1) Why the gain plot |G(jw)| drops and then increases for conjugate zeroes ? 2) Why the gain plot |G(jw)| increases and then drops for conjugate poles ? Nyqust Plot 3) For Figure 9-18(B),...
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Stability and Positive/Negative feedback

I often read that positive feedback is used to get oscillators (since the output of the circuit is summed up to its input signal and so leads to instability), while negative feedback to get amplifiers ...
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Why "-1 + 0j" is critical point on Nyquist plot?

I am reading about Nyquist plot from this (http://www.cds.caltech.edu/~murray/books/AM08/pdf/fbs-loopanal_11Nov18.pdf) chapter. On page no. 10-2 its mentioned that "-1 + 0j" is critical point on ...
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5 answers
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Is the book wrong about the Nyquist Sampling Criterion?

Is the following statement from a book wrong? I thought sampling with twice the signal's highest frequency component would be adequate to completely recover the signal. But above it says sampling ...
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How does a time delay affect the Gain and Phase Margin?

How does a time delay affect the gain and phase margin. Answers using nyquist plots would be helpful I know that a time delay of t corresponds to gain multiplying by 1 and phase subtracting omega*T . ...
Electronics Wizzter's user avatar
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According to the Nyquist criterion this system is stable but when I apply an impulse I get an unstable response, why?

I have this open loop transfer function and I have to study the stability of the closed loop transfer function using the Nyquist criterion. What I got is that the characteristic equation 1+GH(s)=0 has ...
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Nyquist Stability Criteria

Find the stability where: Find the stability: \$ G(s)= \frac{(s+3)(s+5)}{(s-2)(s-4)}; \$ \$ H(s)= 1; \$ I run this code in matlab: ...
Fazla Rabbi Mashrur's user avatar
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Why isn't Nyquist taught like this?

When I learnt how to do a Nyquist plot I was taught a really long-winded method that I don't understand to this day. I realised by myself that if you are given a system like below where \$s=j\omega\$ $...
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Cole-cole plot curve collapses when trying to alter the valule of horisontal axis

I am a beginner and trying to simulate a cole-cole plot of a simple parallel circuit having two R, one coil and a capacitor. Image attaced, LTspice version is XVII, pc is windows7. I've read this Q-A;...
Chy Farm's user avatar
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Sampling rate understanding for ADC requirement

So I have this voltage plot. These are voltages corresponding to a current changes on a wire. I am trying to understand the rate of transmission for choosing a ADC to read these analog values. The ...
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Is the Nyquist plot useful in actual electrical engineering?

I am currently doing a course on linear control theory, and we are covering Nyquist Plot to study phase and gain margin. I find myself unable to appreciate this concept. One, the proof of the Nyquist ...
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What are the connection between bandwidth, Nyquist criteria and quantization?

I am trying to solve the below problem and I was not able to find the relation between bandwidth, Nyquist criteria and quantization. Can you please provide some hint? Imagine that the possible ...
The Voyager's user avatar
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2 answers
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Why is this system stable?

I was given the system defined by the open-loop transfer function: \$L(s)=\frac{5(s^2+1.4s+1)}{(s-1)^2}\$ I was told to use the Nyquist criterion to determine stability. Examining the Nyquist plot ...
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Nyquist plot Phase Question

The above graph is pulled from the book "Automatic Control Systems" by Kuo. The subject loop transfer function is $$L(s)=\frac{K}{s(1+T_1s)}$$ or $$L(j\omega)=\frac{-jK(1-jT_1\omega)}{\omega(1+T_1^2\...
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