Ultimate active filter design tables

[GK]

I just posted up this:

http://www.glensstuff.com/activefilterdesign/activefilterdesign.htm

[GK]

Just corrected half a dozen typos in the meanwhile 

FFS, I really need to proof read before uploading. 4 more typos and grammatical errors fixed... bloody auto spell check corrector...... provenance not providence, etc......

[GK]

OK, so nobody here designs active filters then?

Just made one last correction (technical this time):

"Resistances are initially normalised to one ohm, the frequency of operation to one Hz and....."

Now reads:

"Resistances are initially normalised to one ohm, the frequency of operation to 1 / (2*pi) Hz and....."

[iampoor]

Excellent! Ill be using these soon. 

[G0HZU]

For people that don't like using classic filter design tables, Analog Devices do an online active filter design wizard here although it is a bit odd and annoying to drive and there are only a few basic filter types on offer:

http://www.analog.com/designtools/en/filterwizard/#/type

If you google for active filter design programs there do appear to be a few other basic ones.

However, I can remember using active filter synthesis and simulation tools on a PC 20 years ago that were far more versatile than these programs in terms of the topologies on offer. But these tools weren't free in those dark days of DOS and Win3.

[GK]

And Microchip has their free Filter Lab .exe, which is handy if you need to work-off line.

However none of these calculators are able compute a 3-pole stage with a single op-amp. For example, this is how that AD calculator presents a 5-pole filter:



Three op-amps rather than only two. I make special note of this on my webpage, and is exactly why I still find these tables useful. The electrical engineering mathematicians of yester year appear to be dying out. 

[G0HZU]

The electrical engineering mathematicians of yester year appear to be dying out. 

When it comes to filter synthesis tools I have always been a bit baffled as to why there are so many lame CAD tools available for filter design. I've designed all kinds of filters in the last 25 years (mostly RF) and the only tool that seemed to be any good was Eagleware =FILTER= which I started using in about 1990 along with its linear simulation engine and then they brought out =M/FILTER= for printed filter design and =A/FILTER= in around 1994/5 which was an active filter synthesis tool and I still (but fairly rarely) use the modern version of this active filter design program from Agilent (they bought Eagleware in 2005)

Afilter can design for a 3-pole stage with a single op-amp etc but it certainly isn't a cheap option today. Sadly, it hasn't really changed much in terms of features since its initial release 20 years ago.

Surely there must be a freebie active filter tool out there somewhere that is half decent?

[richiem]

@GK -- nice work. I've bookmarked your page.

[KJDS]

Surely there must be a freebie active filter tool out there somewhere that is half decent?

I've got a spreadsheet that does most of what I want for passive filters without any reference to a look up table, all computed from scratch. It should take too much effort to put something together for active.

[GK]

Excellent! Ill be using these soon. 

@GK -- nice work. I've bookmarked your page.

No worries. 


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It would be relatively trivial, though just time consuming and tedious, to put those tabulated coefficients into a spreadsheet, but I've just never been bothered. I've designed a great many active filter stages over the years, but I don't do it everyday and on the occasions that I do, I've just never considered ten or fifteen minutes with pen, paper and calculator that big a deal.
 

[KJDS]

The coefficients are the outputs from equations.

There's no need to type them into the spreadsheet. It's just a case of getting the equations right.

[GK]

Of course, but show me the equations for a 3-pole VCVS filter. None of the guys that write these on-line and public domain active filter calculators appear to have it.

[nickm]

Thanks for this.  I always get frustrated whenever I need coefficients because you would think they would be somethink easily accesable online.  I usually just end up having to download the Op Amp Applications Handbook and get them from there.  As far as being able to use equations, first order is trivial, 2nd order is doable, anything beyond that I lose the motivation to figure it out and just find a table.