# Tag Info

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### 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 ...

### 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, ...
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### 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 ...

### 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. ...
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### 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"; ...
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### 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 ...
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### 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 ...

### 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 ...

### 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" ...
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### 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 ...

### 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 ...

### 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 ...

### 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....
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### 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 ...

### 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 ...

### 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 ...
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### 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 ...
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 ...