# 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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99 views

### Negative damping ratio for second order transfer function

For this circuit: We get this transfer function (this is the solution of another student, but I did it by hand and I get the same thing): Where the first damping ratio is negative. I read on another ...
51 views

### 5 th order filter transfer function poles and stability issues

I have 5 th order filter circuit as shown in below. But I am trying to find a mathematical expression to calculate the values of inductances and capacitors. Using Wolfram-Mathematica, I found Iout/Vin ...
63 views

### How do I find gain values between decades on asymptotic Bode plots?

I was doing some past exams for my control theory final and came across a question with the following asymptotic Bode plot given: In order to solve for $\omega_c$, I need to essentially find the ...
121 views

### Why a series resistor on the output of an op amp would add a zero

Capacitance on the output of an op amp I was looking at this post and I totally understand except the answer said that the series resistance at the output of the op amp is creating a pole and a zero. ...
31 views

### 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(...
34 views

### Is there a correlation between conditionally stable systems and non-minimum phase systems?

I know bode plots cannot be used for non-minimum phase systems ( eg: delay, Boost converters). Can we identify the closed loop conditional stability from open-loop bode plot response? Conditional ...
23 views

### Is it correct to use the concept of phase margin for not so 'well-behaved systems'?

The TI document mentions the Phase margin as 60 degree for the given bode plot whereas the lowest PM when Gain >1 is around 45 degree. Wiki says: " Ordinarily, as frequency increases the ...
39 views

### Why do we prefer a cross over slope of -1 (20 dB/decade) for bode plot of power converters?

The video mentions (@12:45), we should ensure the slope at cross over should be around -1 (20 dB/decade). He mentions we can apply phase margin test if this condition is satisfied. As far as I know we ...
38 views

### Frequency response measurement of power converter - Why is the injection point across the resistor?

The standard procedure of measuring the frequency response of a buck converter is to inject a small voltage across a small resistor Rt as shown below. (Ref @4:40) Why do we apply the input voltage ...
46 views

### Boost average current mode control

I have one question about the bode plot of boost average current mode control. Below is my schematic, the circuit is stable. My design is for CCM boost PFC, and the current loop crossover frequency ...
74 views

### 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 ...
35 views

### How to obtain a bode plot for this circuit in Matlab online version

So I've an electrical circuit in matlab as follows: I've already setup the points of linear analysis. But I can't the option for linear analysis in the linearization tab. The problem is that I cannot ...
94 views

### LTspice Bode plot is incorrect or inconsistent (op-amp circuit)

I'm testing the open loop transfer function of an op-amp circuit by following this schematic: This is my LTspice schematic (keep in mind the actual op-amp circuit itself has been thoroughly checked, ...
20 views

### Error during analysis in AWR Microwave Office

How to fix this error, and what does it mean? A port is off grid. All polygon edges with ports attached must be 'snapped' to the grid.
89 views

### Bode plot of second-order system

I was reading about second-order systems in Control systems engineering by Norman Nise and I am confused by the idea that the phase at high frequencies of a second-order system is equal to 180° (check ...
104 views

### Why do we talk about system stability as a whole when Barkhausen criteria is valid only for one specific frequency?

The relationship AB=1 will be applicable only at a specific frequency. For instance, following is the bode plot for a circuit I have and as can be seen, the barkhausen criterion is met only at 6.3MEG ...
167 views

### Frequency response of LC filter with resistance in parallel with the capacitor

The following is the diagram of interest: The impedance of the filter is: $$Z_o=\frac{R_f L_f s}{R_f L_f C_f s^2+L_f s+R_f}$$ and the bode plot with all different components and the total impedance ...
56 views

### Phase response in MATLAB simulation doesn't match the book

I am trying to replicate a result from a textbook that I am using to study input filter design for buck converters. The parameters for the converter and filter are as follows: D = 0.5 L = 100 μH C = ...
53 views

### Reading transfer function values from Bode plot

I am trying to get back into control systems and at the moment I am stuck on how to extract the damping ratio and gain from the Bode plot I generated. Firstly the gain. As far as I can remember the ...
1 vote
120 views

### Meaning behind DC/DC converter frequency response

I am currently reading an article about control methods of DC-DC converters which contains the following diagram: This diagram seems to show the magnitude (gain) and phase of the output signal of the ...
79 views

### LTI system Bode curve

Given an RLC circuit, I needed to find the transfer function, which I did. Now I need to find R and L so that the next two conditions are met: The overshoot is 25% The first peak time is t = 3 The ...
1 vote
83 views

### Optimum design of damping LC filter with parallel (R+C). There is a frequency in which value of R dosn't impact

Apologies for the not so clear title, but I don't know if there is a common phrase that describes the point of concern. I am taking an online course about input filter design interfacing the grid and ...
158 views

### Why do LC filters have 40 dB/decade ripple attenuation at high frequencies?

I am taking an online course on power electronics in which I encountered the following concept which I couldn't understand. The instructor had the following comment about the following grid interface ...
226 views

### 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 ...
224 views

### Why can the Bode plots of transfer functions have negative magnitude values?

I am currently learning about Bode plots and transfer functions. I am confused about what information the "magnitude" values of the transfer function are supposed to contain. I am mainly ...
69 views

### Confusion regarding bode plot?

I am trying to understand bode plot and i came across attached snap especially black solid line in magnitude plot, i captured this snap from wikipedia. Here i am confused,what is cutt off frequency? ...
138 views

### How to design filters with transfer function?

I want to design filters base on transfer function and Bode plots. For example, lets say I want a low pass filter, the limit is 36hz. How should I design a transfer function base on 36 hz limit? (pls ...
37 views

### Double pole, double zero: incorrect plot?

I can't seem to find where I'm going wrong here. Suppose I want a double pole, double zero system that looks like this:  \dfrac{\left(1+\dfrac{s}{\omega_z}\right)\left(1+\dfrac{s}{\omega_z}\right)}{\...
41 views

### Negative loop gain of LDO

I am trying to design an LDO with the following specification: Vout = 1.5V; Vin = 1.7V - 2V; Iload = 75uA to 1200uA. However, while I am simulating its loop gain, its gain is coming negative. Even ...
1 vote
339 views

### Phase shift of an ideal op-amp integrator

I derived the transfer function of an ideal op-amp integrator and calculated the phase response of the Bode plot. My own derivation matches the result of this website. This means for the transfer ...
203 views

### Bode phase plot phase margin

From what I have studied so far, gain margin is defined as how much additional gain the system can be given before it becomes unstable, and this can be measured from the bode magnitude plot ...
449 views

### Finding resonant frequency and cut-off frequency from Bode plot to calculate values for RLC circuit

I am trying to find RLC values from a Bode plot. I have a band-pass filter from a transfer function and have put arbitrary values for the RLC components in Matlab. I am unsure how to mathematically ...
89 views

### Why does the Bode plot in LTspice disagree with my command calculation?

I am trying to use LTspice to plot Bode plot for frequency response. I used command to get the gain at the 1kHz first. In the error log it turns out that it is 47.3dB. When I used small signal AC to ...
1 vote
165 views

### What are the gain and phase margins from this Bode plot?

I thought I had a decent grip on how Bode plots work yet for this model that I am working on, I need to implement a lead or a lag compensator. A lead compensator, which I was thinking about ...
1k views

### Why are there ripples in the passband of some filters, like the Chebyshev filter?

Please see the Bode magnitude plot as we steadily increase the input frequency to the filter. Why does the magnitude oscillate? What physical component(s) in the filter circuit is producing that ...
1 vote
227 views

### 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 ...
114 views

### What does the value projected on the σ axes mean in s plane?

This question is related to my last post. To avoid confusion, I opened another question. From a website that John shared in my last post, this is a plot that is a 3D picture combining the Bode and the ...
96 views

### Frequency response of a cascade opamp circuit using LTSpice

I'm trying to simulate this circuit which consists of multiple stages of op amps, but I couldn't figure out the operating bandwidth of the circuit. Using AC analysis, the Bode plot is a weird shape ...
1 vote
129 views

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### 0 dB Bode plot as a reference in an academic paper

I want to compare the calculated bode plot of an inverting op-amp with the simulated one, on the 1 mHz-200 kHz spectrum. As expected, theoretically there is no stray capacitance on the circuit above, ...
75 views

### Stability in a double-pole system

A simple low-pass RC circuit is a single pole system and it's stable. In a DC-DC buck converter, we have a conjugate double pole due to the LC filter. Yet, we employ several techniques such as D-CAP ...
155 views

### My bode plot does not mach with calculated cut-off frequencies

I have modelled a band-pass filter, but when I calculate the cut off-frequencies and amplitude it does not match with the bode-plot. I am not able to find out what is wrong, hope that someone might ...
150 views

### Bode diagram cutoff frequency in LTspice [closed]

My question is about the cutoff frequency of Bode diagram. In the output of this circuit I got this bode diagram normally. When I read the cutoff frequency on -3 dB. But here I don't have -3 dB. ...
75 views

### 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 ...
204 views

### 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 ...
343 views

### Finding transfer function from Bode plot

While I know how to find the transfer function from the response graph, I don't know how to find it from Bode plot. What I know about the system: The system is a second order system The system has no ...