Questions tagged [bode-plot]

Anything related to Bode plots, i.e. a special graphical representation of the frequency response of a linear time-invariant system.

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45 views

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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53 views

Recreate “Voltage gain vs Frequency” graph of Op-Amp in LT Spice

I am trying to recreate the "Voltage gain vs Frequency" graph of the LT1037 Op-Amp in LT Spice. According to the datasheet page 6 the graph looks like this: - Trying to recreate this in LT ...
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2answers
60 views

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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Finding the order of a system

From experiments, I have the step response plot, and input-output plot of a system (at various frequencies). Now, I need to find the transfer function of this system. Is there a way to find the order ...
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1answer
544 views

How can a Bode plot be like that?

Can you do explain how to draw a Bode plot with GH(s)? How do I get the slope and intersection point? This is one of the teacher's examples. He drew it but I don't know what it means. Can you explain ...
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50 views

How would the pole and zero frequency expression look like for this transfer function I derived?

This is a practice problem in deriving the transition frequency function for mos and part of the set of questions is to determine the pole and zero frequency expression but this transfer function i ...
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1answer
46 views

Could somebody clarify the phase angle and gain of this transfer function?

Suppose a circuit with a transfer function of the form \$A(\omega)=\displaystyle\frac{A_0}{1-\frac{j\omega}{\omega_0}}\$ has \$A_0=-10\; V/V\$ and \$\omega_0=100\;rad/sec.\$ We were asked for the gain ...
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54 views

Oscillation frequency / criteria from Bode plot, negative feedback system

Got a question, which is very integral to a project that I am writing a report for (which I am to hand in soon, so in a hurry). Question: What will my oscillation frequency be? How will it be ...
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1answer
32 views

A question about negative phase angles in Bode plots

Looking at the phase Bode plot for the output of a filter as shown below: 1-) Taking the point -460° as an example, can we say that this is equivalent to +100°? 2-) Does that mean the output signal ...
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6answers
1k views

Why is frequency not measured in db in bode's plot?

While drawing bode's graph paper where Y axis is gain given in db while the X axis is frequency given in absolute value but scale used is log. I think the reason for log scale on X axis is to increase ...
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2answers
94 views

How is this pole compensated

I have an amplifier in a closed loop, the diagram looks as follows: The DC gain is simple which \$ -Rf/R1 \$. If I make \$ -Rf=2\cdot R1 \$ the the DC gain is two. This is verified using AC analysis ...
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1answer
88 views

How to find the total phase of this transfer function

I'd always understood that in a transfer function, every pole contributes -90 degrees in phase and every zero contributes +90 degrees in phase. Based on this assumption, I would expect the following ...
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1answer
65 views

2nd order Sallen-Key low pass filter frequency response

I am trying to implement the following circuit in LTspice for studying the frequency response of the 2nd order Sallen-Key low pass filter for a project. Why am I getting a negative peak in the ...
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2answers
55 views

How to understand Bode plot or Bode diagram

I am having difficulty understanding the Bode diagram, which I have understood so far: that depending on the angle of the phase, where the system becomes unstable or stable. I just don't know what the ...
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5answers
704 views

Pole zero plot of band reject filter

Here is a band reject filter with its transfer function and bode plot. I don't understand how the pole frequencies and zero frequencies are drawn on the bode plot. Even with the pole and zero ...
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4answers
360 views

Problem with Bode diagram in LTspice

I am working on a buck converter and I want to obtain the Bode diagrams of the open-loop circuit. The below circuit is what I made. However, the DC-gain is -96 dB while it should be very small around -...
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1answer
61 views

Bode Plot: calculating phase change

I need to plot this transfer function When plotting the phase vs frequency graph, I am having problems to calculate the change in phase between 10 and 10^1.5. To my understanding, at frequency=10 the ...
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30 views

Bode plot acting weird with specific op-amp

Hello why is the behavior of this op-amp so weird (OP177).I simulated another op-amp(uA741) with the same biasing and the bode plot looks fine(still i dont get the 80dB amplification i would like, yea ...
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89 views

What information Bode plot does NOT present?

The classic Bode plot (2D Bode) represent value of the transfer function (a complex number) evaluated at \$j\omega\$ (imaginary axis). It provides information on system closed-loop stability margins ...
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2answers
80 views

Do we analyze real poles the same way you analyze complex conjugate poles?

So I am analyzing a filter and I came up with the following expression for the transfer function in its canonical form: $$\frac{987654 + 4666.67 s + 1. s^2}{2.48519 \times10^8 + 52316.2 s + s^2}$$ ...
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2answers
96 views

What is the bode plot of an inverting op amp if you replace the resistors with caps?

What is the bode plot of an inverting op amp if you replace the resistors with caps? What if you now add a capacitive load to the output? Update: I ran a quick simulation and the bode plot looks as ...
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1answer
53 views

Why bode plot of cascade system is not the sum of subsystems?

I have two subsystems which the transfer functions you could see below as g(s) and h(s). According to some references show below, I found that the bode plot of a cascade system should be the sum of ...
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2answers
78 views

Differentiator cut-off frequency

A practical differentiator has two cut-off frequency but can no longer perform differentiaiton after first cut-off. After first cut-off there is a 20db per decade gain reduction but why does this ...
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1answer
75 views

KHN biquad: why does LTSPICE plot a wrong phase plot for bandpass filter?

I'm studying the KHN biquadratic section and its outputs to obtain a lowpass filter, a highpass filter and a bandpass filter. I simulated the filter using Mathematica and obtained the following plots, ...
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48 views

Having trouble making transfer function from this Bode plot from op Amp datasheet in Mathematica

I am fairly green to control theory. I am trying to reproduce the Open loop transfer function of the LT1X28 op amp in mathematica. I want to get the poles and zeros from the following plots and ...
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76 views

Why is Δt constant in phase shift measurement?

I would like to ask for some help with phase shift plotting. To be precise, with time delay between two waveforms. I am measuring two currents using an oscilloscope. channel A (blue) is my current ...
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3answers
559 views

Transfer function of electrical network

I need help with this problem. The transfer function that I found is ((RCS+1)/(2RCS+1)) , but then I cannot go further because the form of T.S is untypical. The typical form of this question is RC ...
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3answers
138 views

How to do the bode plot for this function without Matlab?

I want to plot the bode diagram without any software for $$G(s)=\frac{(s-2)}{(s^2+4s+15)(s+2)}$$ I do not know how to deal with the factor of \$s-2\$ I will be appreciate if someone can show me your ...
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3answers
205 views

Zeros and poles in the following bode plot

According to the definition, zeros are the frequencies which make transfer function to be zero, and poles are the frequencies which make transfer function to be infinity. The definition can be seen ...
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42 views

Phase margin plot of LDO

For this LDO circuit design at https://github.com/promach/LDO/tree/development , 1) which exact circuit node(s) contributes to the zeroes near 1MHz after removing CL ? 2) If I remove "AC 1" from ...
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1answer
46 views

Bode plot display in matlab

I would like to display a bode plot of a buck-boost converter using Matlab, so I got the figure shown below, If we look closer to the phase plot, we see that it starts from 360°. My wish is to make ...
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1answer
44 views

Determine output filter using the bode approximation

Given that the carrier frequency Fc and modulation input frequency Fm are known, how would I use the bode approximation to determine an output filter, if the carrier frequency component must receive ...
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3answers
78 views

Verification of Sallen Key Design

I have designed this Sallen-Key to give a 2nd order low pass circuit with a cut-off frequency of 150Hz. Another design specification is that R1=R2 and C1=C2. The issue is when simulated on LT-Spice ...
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1answer
183 views

How can I find the drain transfer function of a MOSFET on LTSpice?

I am trying to get the drain transfer function of a MOSFET by setting the drain to source voltage as the input and the gate to source voltage as the output. I created the following circuit in LTSpice: ...
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1answer
27 views

how to plot on the same bode plot a manual function plot() with function bode()?

I have a a transfer function that I plotted manually using Plot(w,abs(f1(w)))(plotted for a digital filer since I dont have signal toolbox) and I have another function that I used directly bode(f2(s))(...
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2answers
122 views

Plotting a bode gain plot with the slope in Excel

I am not an expert in Excel, and therefore, I want to know if there is a way of including the slope (dB/decade) in a bode gain plot in Excel or any free software (that allows to first input the ...
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1answer
54 views

How to visually determine the damping ratio when we know the peak amplitude

I am currently trying to understand this example from the book, where it visually calculates the dampening ratio given the peak amplitude as well as the natural frequency. Here is the graph from which ...
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1answer
50 views

How to choose the transfer function?

Greetings from a physics student. I have to do an activity which aim is to design a filter in frequency. To do so, I need a transfer function (gain, poles and zeros) that must meet the following ...
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145 views

Help deriving the transfer function of an LC circuit?

I have the LC circuit below. I believe (but I'm not certain) that this is a 3rd order filter. Since there are two capacitors and 1 inductor. The circuit is a passive low pass pi filter. The ...
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1answer
67 views

What does 'passband phase' and 'stopband phase' mean?

I've been provided with a Bode plot for an RC filter circuit with a cutoff frequency of 10kHz. Im asked to find the stopband and passband phase from the graph. I'm confused how these can be just a ...
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1answer
62 views

MOSFET Differential Amplifier Bode Plot

I've created a MOSFET Differential Amplifier in PSpice, the schematic of which I've attached. However, when doing an AC sweep and adding a trace to do a Bode plot, the graph is a flat line, and I don'...
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1answer
2k views

What does a Bode plot represent and what is a pole and zero of a Bode plot?

I studied Bode plots and the author of my book is somehow relating zeros of transfer functions to Bode plots. What is the relation between zeros or poles of a Bode plot and transfer function? We ...
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309 views

How to find the cutoff frequency of an underdamped second order lowpass filter

I've learned that for a first order LPF the 3dB frequency is one where the amp's gain is (surprise) -3dB below the DC gain. However, on a second order LPF that is underdamped we get a "peak" at around ...
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1answer
137 views

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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59 views

Octave bode plot looks like a decade plot in LTSpice

When I do a bode plot on a load over a simple LRC filter then compare graphing the frequency in OCT and DEC, I would expect their plot shapes would look different given OCT plots the x-axis in 1Hz,2Hz,...
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2answers
77 views

How to calculate RC (in 2st RC lpf) that satisfies fc in real circuit

I'm designing a two-stage RC LPF (Low-Pass Filter) and I want a cutoff frequency \$f_c=1000\mathrm{Hz}\$. So, I choose \$R_1=3\mathrm{k\Omega}, R_2=33\mathrm{k\Omega}, C_1=4.7\mathrm{nF}, C_2=47\...
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91 views

Bode plot? H(s)= 1 / (s² +1)

I have transfer function $$H(s)=\frac{1}{s^2+1}$$ When I put that in Wolfram Alpha I get that there is peak on Bode plot at 1 and it is 60dB. Why? There is no damping here... Usually in formula ...
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1answer
179 views

Why 180 degrees of phase margin should be considered?

We've had one feedback on the phase difference, with the gain as 1. At 300 to 60 degrees, there's just a phase difference, and 61 to 299 degrees, the output is larger. Shouldn't we consider an angle ...
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42 views

Why the sum of the responses of s and s increase with 20dB per decade or 40dB per decade?

I am not sure by how much will the response of the function H(s) = s^2 increase?
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503 views

Is it possible to sketch a bode plot for a discrete-time transfer function?

For a regular s-domain transfer function, there are simple rules you can use to draw an asymptotic bode graph, basically by taking a slope of +/-20dB per decade and a phase shift of +/-90 degree for ...

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