butterworth,bessel,Chebyshev

[walters]

Whats the difference between a Sallen Key filter VS a butterworth filter?

Whats the difference between a Sallen Key filter VS Chebyshev filter?

Whats the difference between a Sallen Key filter VS Bessel filter?

 

[audioguru]

Look in Google and you will see that a Sallen-Key filter is just one type of circuit for a filter. It can be Bessel, Butterworth or Chebychev by selecting its Q.
It can be 2-pole (also called 2nd order) or have as many poles or orders as you want for a sharper cutoff.
https://www.beis.de/Elektronik/Filter/Filter.html

 

[walters]

Thanks

Whats the difference between the "Q" VS the Center frequency?
(Q-is the "Ratio" of the center frequency to its bandwidth)


How do i set the Q and Center frequency?

 

[walters]

What changes a filter to have different charterists?

What changes a filter to be like a Chebyshev, bessel, butterworth

The Resistor and Capacitors just set the Center frequency and Q?

What components sets the Chebyshev,bessel,butterworth?

 

[audioguru]

You don't understand filters.
The Q is the amount of positive feedback but some people call 1/Q damping. It is set by the gain of the opamp or by the ratio of the R/C networks.

A highpass or lowpass filter doesn't have a center frequency. It has a cutoff frequency that is determined by its RC values.

 

[walters]

Yes the Q is the negative feedback

Q= resonance

The lowpass filters cutoff frequency with the high pass filter cutoff frequency= a center frequency?


What i don't understand is what makes a filter a Chebyshev, bessel, butterworth ? What components change a filter to be a Chebyshev, bessel, butterworth ?

 

[audioguru]

Yes the Q is the negative feedback

No. It is positive feedback. The opamp has negative feedback to determine its gain.

Q= resonance

The lowpass filters cutoff frequency with the high pass filter cutoff frequency= a center frequency?

You can add a lowpass filter and a highpass filter, but you might as well use a bandpass filter.

What i don't understand is what makes a filter a Chebyshev, bessel, butterworth ? What components change a filter to be a Chebyshev, bessel, butterworth ?

The Q, which is the amount of positive feedback. With a low Q or no positive feedback the cutoff is gradual and droopy because it is Bessel. Add some positive feedback to raise the output to be flat near the cutoff frequency and you have a Butterworth sharp response. Add a little more positive feedback and it is a Chebychev response. Add even more positive feedback and it makes a peak in its response before its cutoff frequency. Add more positive feedback and its peak frequency oscillates.

I told you already and the Google tutorials say which parts determine the Q.

 

[walters]

Thanks for the information

So the Chebyshev, bessel, butterworth filters are just different amounts of Q? and cutoff points?

Positive feedback= Q

 

[audioguru]

So the Chebyshev, bessel, butterworth filters are just different amounts of Q?

Yes.

cutoff points?

The cutoff frequency is determined by the values of the R and the C.

Positive feedback= Q

Yes.

 

[walters]

so how do i have a Variable or a selector switch that has Chebyshev, bessel, butterworth filters all in one filter?

Do i just have a variable positive feedback parameter and that will give me Chebyshev, bessel, butterworth characterists?

How can i make a filter that will have a mode switch that had the opitions Chebyshev, bessel, butterworth characterists?

Mode switch:
1.) Chebyshev characterist
2.) bessel characeterist
3.) butterworth characterist

how can i do this please?

 

[audioguru]

To switch between the amount of Q that is in a filter, the simplest way is to change the gain of the opamp.
First, learn about the Q of a filter and what adjusts it.
Second, learn aboout how opamps work, but please, not here.

 

[walters]

Mode switch:
1.) Chebyshev characterist
2.) bessel characeterist
3.) butterworth characterist

I think its more than just having a variable positive feedback
doesn't it have to have different RC values and cutoff frequencys also ?
or the gain has to be different with the posistive feedback?

 

[audioguru]

Changing the gain of the opamp is the easiest way to switch between the different filter characteristics by changing the Q. You can also change all the RC ratios instead if you want, then keep the gain constant.
The cutoff frequency is changed a little because the Bessel filter begins dropping the levels of frequencies far from the cutoff frequency and the Chebychev maintains the level up to the cutoff frequency of the others.

 

[walters]

Thanks alot for the help

Mode switch:
1.) Chebyshev characterist
2.) bessel characeterist
3.) butterworth characterist

How do i get that overshoot and ripple effects?

I thought all these filter charactist only could have a Pulse waveform or can i have a triangle,squarewave, sinewave to get all these different types of characterists?

 

[audioguru]

These are frequency filters. A lowpass filter passes low frequencies and attenuates high frequencies.
A highpass filter passes high frequencies and attenuates low frequencies.

A Bessel filter has a gradual cutoff.
A Butterworth has a flat frequency response up to the cutoff frequency, then a fairly sharp cutoff.
A Chebychev has ripple in its frequency response up to cutoff then a very sharp cutoff.

You can feed these filters anything:
Music, triangle waves, square waves, or sine waves and their frequencies will be filtered.

Explain what you mean by saying "overshoot and ripple effects".

 

[walters]

Thanks for the help

A Bessel filter has a gradual cutoff.

What makes the Bessel filter have a gradual cutoff?
the RC? the Q?

A Butterworth has a flat frequency response up to the cutoff frequency, then a fairly sharp cutoff.

What makes the Butterworth have a flat frequency response up to cutoff freq? and a sharp cutoff?

Is it the RC values? the Q?


A Chebychev has ripple in its frequency response up to cutoff then a very sharp cutoff.

What makes the Chebychev have Ripple? and a sharp cutoff

is it the RC values? the Q?

 

[audioguru]

A low Q makes a Bessel, a medium Q makes a Butterworth and a higher Q makes a Chebychev.

 

[walters]

Thanks

so it have nothing to do with the gain,cutoff, or RC values?

 

[audioguru]

so it have nothing to do with the gain,cutoff, or RC values?

You don't understand.

 

[walters]

i mean can they be FIXED with the same vaules without changing them to make the different charestics?