37
votes
Accepted
What does a Bode plot represent and what is a pole and zero of a Bode plot?
Bode plot
Take a typical 2nd order low pass filter amplitude response bode plot: -
3-D picture introducing pole-zero diagram
Here's the bigger picture of that response when combined with a pole ...
- 436k
30
votes
Gain margin and Phase Margin Physical Meaning
Gain and phase margin are usually applied to systems that are amplifiers of some sort with negative feedback around them. The more negative feedback, the tighter the system is controlled. However, ...
- 311k
13
votes
Accepted
Why are decibels used for Bode plots?
Bode plots show gain and phase. Gain is measured in V/V, A/A, or W/W, and is thus dimensionless. Decibels are ratios, like percentages or parts per million. The question, then, is why we sometimes use ...
- 21.4k
11
votes
Why are decibels used for Bode plots?
A first order filter has a roll-off of 20dB per decade. That is, every time the frequency increases/decreases (for high/low pass filter) by a factor of 10, the signal power drops by a factor of 100.
...
- 946
11
votes
Accepted
Why is frequency not measured in db in bode's plot?
Frequency is not a measure of signal amplitude or power hence, talking about "this or that" frequency in decibels makes no sense. If somebody says "increase the frequency by 3 dB"; ...
- 436k
11
votes
Accepted
How can a Bode plot be like that?
How do I get the slope and intersection point?
Start with a very simple example: -
$$H(s) = \dfrac{1}{s}$$
When \$s = 1\$, the amplitude of the transfer function is clearly 1.
When \$s = 0.1\$, the ...
- 436k
10
votes
Accepted
What does actually the "unravel branch wrap" option do to the phase plot in LTspice?
It adds or subtracts multiples of \$2\pi\$ (360 degrees) to each point in the phase plot so that the phase is plotted continuously rather than having jumps in it.
We know that physically the phase ...
- 159k
10
votes
Is -3dB bandwidth defined for any type of transfer function?
Is -3dB bandwidth defined for any type of transfer function?
Maybe you do not realize what -3dB actually means?
-3 dB means that the amplitude of the voltage (current as well) has dropped by a factor ...
- 80.2k
9
votes
Why are there ripples in the passband of some filters, like the Chebyshev filter?
Please note that this is a quite "normal" expected/desired behaviour.
We have several different methods to approximate the ideal lowpass response (this would be "brickwall" ...
- 24.9k
8
votes
Accepted
Why a low-pass filter applied to a square wave gives a weird wave?
There are many types of low pass filter.
The one that gives your 'weird waveform' is the simplest 1st order RC filter. This passes the fundamental signal. However, it not only passes all the higher ...
- 159k
8
votes
Problem with Bode diagram in LTspice
The AC analysis is a linearized analysis. That means it simulates the small-signal behavior of each element at its operating point.
In the case of the switch, that means it is held in either the on or ...
- 127k
8
votes
Why are there ripples in the passband of some filters, like the Chebyshev filter?
Higher order filters are "made" from building blocks of 2nd order filters and, to get a steeper response in the roll-off area (above \$f_c\$), quite often a 2nd order filter with a low Q ...
- 436k
7
votes
Low Pass Filter Wrong Pole Location
It's just a conversion from radians to degrees. The expression for a capacitor's impedance uses units of radians/sec. for frequency. The simulator is reporting frequencies in Hertz. 10 rad/sec is 1....
- 2,560
7
votes
Accepted
How to sketch the Bode diagram of the output filter of a Buck converter?
Background
Starting with your result and proceeding:
$$\begin{align*}
H\left(s\right)&=\frac{R}{R\,L\,C\,s^2+L\,s+R}\\\\
&=\frac{1}{L\,C\,s^2+\frac LR\,s+1}\\\\
&=\frac{\frac 1 {L\,C}}{s^2+...
- 77.2k
7
votes
Pole zero plot of band reject filter
Perhaps this is where the confusion starts: 's' is complex (re + j*im, or sigma + jw), not just imaginary. Those two terms are often accidentally used interchangeably, and they shouldn't be.
G is ...
- 3,097
7
votes
How to find the Transfer Function of this circuit?
You can easily determine the transfer function of this circuit by considering a simple \$RC\$ low-pass filter followed by a non-inverting structure described in this Wikipedia link. Because the op-amp ...
- 20.5k
6
votes
Accepted
Interpreting bode plot of type 3 compensation network for buck regulator
Calculated values for the poles and zeros look about right, except for the missing integrator pole at the origin. Maybe it would be best to break the loop up into pieces. Write the transfer function ...
- 7,143
6
votes
Why are decibels used for Bode plots?
Do you really think that a "terribly meaningless unit" would be used with enormous success over many decades? Are you not a bit curious if this "meaningless" unit has perhaps some advantages? here are ...
- 24.9k
6
votes
Accepted
What is an "origin pole"?
The "origin pole" is indeed the \$1/s\$ term in the transfer function \$H(s)\$. In the bode plot it results in a first order transfer that does NOT flatten out for low frequencies.
Your Bode plot is ...
- 80.2k
6
votes
What exactly is Pole Frequency in a Filter and how does it affect the frequency response?
1) Why does the magnitude Bode Plot of the response of a filter NOT
approach Infinity at a pole?
Try looking at this picture and recognize that poles may exist as infinities in the bode plot but ...
- 436k
6
votes
Transfer function of electrical network
A quick look at the fast analytical techniques or FACTs gives you the transfer function of this guy in the blink of an eye. First, turn the stimulus off or reduce \$V_{in}\$ to 0 V: replace the source ...
- 20.5k
6
votes
How are the -3dB point and the pole of an op-amp related?
Because a typical op-amp is dominant pole compensated, it has a single pole in the open-loop transfer function at low frequency, and a -20 dB/decade roll off.
This leads to the concept of "gain-...
- 23.1k
6
votes
Accepted
Why are there ripples in the passband of some filters, like the Chebyshev filter?
Filters lie in the domain of rational polynomials, that is, the transfer function is a ratio of the form:
$$ H = \frac{P}{Q} = \frac{p_n \omega^n + p_{n-1} \omega^{n-1} + \ldots + p_1 \omega + p_0}{...
- 23.9k
6
votes
Accepted
LC filter out of the loop if crossover frequency is below resonant frequency?
I am glad you picked up this slide because it can generate confusion with a perfectly-stable converter. Actually, the step response of a switching converter operated in open- or closed-loop, depends ...
- 20.5k
5
votes
Gain margin and Phase Margin Physical Meaning
People tend to make this way too complicated and difficult to understand. Stability margins are only defined for an ideal, linear transfer function model - a model expressed in terms of rational ...
- 864
5
votes
Gain margin and Phase Margin Physical Meaning
May I add a 4th answer in short?
1.) A circuit with feedback is unstable in case the loop gain has a phase shift of 360deg at a frequency where the loop gain magnitude is still larger the 0 dB. Note ...
- 24.9k
5
votes
Accepted
Low Pass Filter Wrong Pole Location
Complex Number Diversion
Complex numbers have both a Cartesian notation as well as two equivalent polar notations. The Cartesian notation, \$a+b\:i\$, is very hard to use in electronics but it is very ...
- 77.2k
5
votes
Accepted
Are phase angles in filter transfer functions primarily for stability?
Different applications are sensitive to phase variation with frequency for different reasons.
It can impact stability margin if the filter is in a closed-loop system.
The total error between a source ...
- 45k
5
votes
Zeros and poles in the following bode plot
How is it possible to make transfer function to become zero or
infinity.
You will only get zeros and poles in the bode plot if those zeros and poles lie on the \$j\omega\$ axis. The bode plot is ...
- 436k
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