High/Low-Pass filter calculations

Matttcattt · 23rd January 2005, 07:52 PM

Im planning to build some active filters. Searching the web came up with the perfect document - The SLOA093 ap note from TI on active filter design. One simple question. What units do the calculations use? Farads and Ohms right? I dont want to buy components 1,000,000 time too large. :P

12 Cents · 23rd January 2005, 09:01 PM

Quote:

Originally posted by Matttcattt
What units do the calculations use? Farads and Ohms right? I dont want to buy components 1,000,000 time too large. :P

I think it assumes just Farads and Ohms. Of course you can enter Millifarads, but be sure to treat the result as Milliohms

Matttcattt · 23rd January 2005, 10:53 PM

Thanks. I just wanted to get a second opinion.

rpapps · 23rd January 2005, 11:24 PM

Hi Matttcattt
The calculations are intended for basic units ie. ohms, farads and hertz. Just use the appropriate multiplier when entering your component values.
Eg. 100 pF = 100 x 10 to -12 power, 0.1 mF = 0.1 x 10 to -6 power, 1k ohm = 1 x 10 to +3 power, 10 KHz = 10 x 10 to +3 power. You get the idea?
Hope this helps.
Cheers
Rob

Matttcattt · 24th January 2005, 11:55 PM

Thanks.

I dont like standard form (1x10^-6F). I prefer long decimals (0.000001F).

pinkmouse · 25th January 2005, 12:04 AM

You could try the sim on National's website, Webbench, it uses real world values.

Evan Shultz · 25th January 2005, 11:17 PM

TI also has a rather powerful program called FilterPro that will automate much of this for active filters. You can choose topology and choose some components while allow the rest to be auto-selected. I'd check it out.

thomas997 · 26th January 2005, 05:28 AM

Quote:

Originally posted by Evan Shultz
TI also has a rather powerful program called FilterPro that will automate much of this for active filters. You can choose topology and choose some components while allow the rest to be auto-selected. I'd check it out.

I agree, simple and easy to work with.

Here is the link: http://www-s.ti.com/sc/techzip/slvc003.zip

Matttcattt · 26th January 2005, 07:38 PM

I've already calculated the values and ordered the parts now, but I'll have a look anyway.

23rd January 2005, 07:52 PM	#1
Matttcattt diyAudio Member Join Date: Feb 2003 Location: Bristol	High/Low-Pass filter calculations Im planning to build some active filters. Searching the web came up with the perfect document - The SLOA093 ap note from TI on active filter design. One simple question. What units do the calculations use? Farads and Ohms right? I dont want to buy components 1,000,000 time too large. :P __________________ If it aint broke, don't fix it. If it is broke, fix it. If you can't fix it, take it apart and see how it "worked".

23rd January 2005, 10:53 PM	#3
Matttcattt diyAudio Member Join Date: Feb 2003 Location: Bristol	Thanks. I just wanted to get a second opinion. __________________ If it aint broke, don't fix it. If it is broke, fix it. If you can't fix it, take it apart and see how it "worked".

23rd January 2005, 11:24 PM	#4
rpapps diyAudio Member Join Date: Jul 2004 Location: nowhere of interest	Filter Calcs Hi Matttcattt The calculations are intended for basic units ie. ohms, farads and hertz. Just use the appropriate multiplier when entering your component values. Eg. 100 pF = 100 x 10 to -12 power, 0.1 mF = 0.1 x 10 to -6 power, 1k ohm = 1 x 10 to +3 power, 10 KHz = 10 x 10 to +3 power. You get the idea? Hope this helps. Cheers Rob

24th January 2005, 11:55 PM	#5
Matttcattt diyAudio Member Join Date: Feb 2003 Location: Bristol	Thanks. I dont like standard form (1x10^-6F). I prefer long decimals (0.000001F). __________________ If it aint broke, don't fix it. If it is broke, fix it. If you can't fix it, take it apart and see how it "worked".

25th January 2005, 12:04 AM	#6
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	You could try the sim on National's website, Webbench, it uses real world values. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort


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25th January 2005, 11:17 PM	#7
Evan Shultz diyAudio Member Join Date: Jun 2004 Location: California, USA	TI also has a rather powerful program called FilterPro that will automate much of this for active filters. You can choose topology and choose some components while allow the rest to be auto-selected. I'd check it out.

26th January 2005, 07:38 PM	#9
Matttcattt diyAudio Member Join Date: Feb 2003 Location: Bristol	I've already calculated the values and ordered the parts now, but I'll have a look anyway. __________________ If it aint broke, don't fix it. If it is broke, fix it. If you can't fix it, take it apart and see how it "worked".

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