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Christian,

Thanks for trying out FilterPro 3. It sounds like you haven't had a chance to spend much time with it; I'd encourage you to play with it a bit more.

Please see this thread: http://e2e.ti.com/support/development_tools/analog_elab_and_tools/f/399/t/93128.aspx which addresses your component value changing concerns as well as a link to FilterPro 2 on an FTP site. There's also a link in there to the FAQ page for FilterPro, which highlights the differences between FilterPro 2 and 3.

You might also want to check out the Active Filter Designer in WEBENCH. Go to http://www.national.com/ and click on the Filter tab in the WEBENCH window.

Good luck, and let us know if we can help further.

Hi Rick,

I am with Christian. Your new Filter Pro is useless. I have struggled with it , played with it and finally looked elsewhere  for my solutions. Unfortunately, I landed with Max 296 Switched capacitor filter and had yet one more round pf frustration as the device has a pass band floor noise at best giving S:N ratio of just 700 which is no good for most applications. (Max support dis not work, surprisingly)

The reason why I say it is of no use is: that it does not let you choose capacitor values. This I think is important because you will agree, that it is lot easier to tune resistors than to tune capacitors of odd valus thrown up by the software. This took me back , nostalgically to  a Book I had with me 25 years back , by Analog Devices "Analog Design". I do not remember the name of the author but i think it Was " George Brown". Unfortunately I have misplased that book or may be some one flicked it from my lab. so I have started my search for your Filter Pro version 1.0. It was indeed very  useful. It allowed me to tune and select my starting design with selected capacitor values available with me and then deal with odd values of resistors which I can always tune using series parallel combination. I would urge  -beseech - pray Ti "for Gods sake , please give us the version 1 back from the net"

I am sorry for my strong views but I depend on TI for lot many other areas and admire TI for their support.

Mohan Phadnis

Mohan,

Thanks for your feedback. Am I right in reading your post that you want to be able to fix both capacitor values, and deal with the resistors, rather than just the ability to fix one value (because you can do that - see the post I referred to previously)? This is on our list of things to do.

In the meantime, you can still get FilterPro 2 from our FTP site. See  http://e2e.ti.com/support/development_tools/webench_design_center/f/399/t/93128.aspx.

Hi Dick,

You are right. I want the freedom to select capacitors from what is available (E24 ), pick C1 and C2 for every stage, measure their exact value using a good LCR Bridge and then fill these values in the table provided in  Filter Pro V.2. The Filter  Pro then tells me values of R1 and R2 (for each stage). These resistor values , obviously turn out to be odd. Next step, then is to work out a series parallel - combination to fit the value of resistors calculated by Filter Pro and there you are with a design which works. Works , but not really. There is one last problem though! When I test the step response of the filter realized using above procedure, invariably I get about 1% under and over shoot with. ( I am referring to 8th order,  low pass, Bessel, using Sallen-Key unity gain design). One way I can tune the overshoot and undershoot to get smooth ringing free step response is , to play with the gain of the stage with highest Q which invariable is the last stage. Luckily, always I need to attenuate the signal from stage 3 before feeding it to the stage 4 the last stage. While you are at it, I would request you to consider providing "Step Input Response" graph to predict if there is likelihood of under- over shoot  and a procedure of tuning the last stage gain. Having done this I  would  say the new Filter Pro should be the dream tool for all designers.

I think I am putting too many questions to you - this one is hopefully the last one. I hope you won't mind giving me tips on this. Can I port filter pro schematic into TINA to be able to use further analysis features provided by TINA? Thanks

Mohan

Mohan,

OK, I understand what you're doing. As I mentioned, this capability is on our list of things to do. I'm also planning on adding step response capabilities, and eventually true simulation capabilities to our filter design tool. We can't do all that you want today, but we will be able to in the future.

As for your last question, the answer is no, there's no easy way to take a schematic generated by FilterPro and import it into TINA-TI. What you can do is use the example circuits that come with TINA-TI as a starting point (there's several in a folder called Filters - FilterPro) and replace the component values with those generated by FilterPro for your particular filter design. 

Hi Rick

I have to agree with everyone else regarding FilterPro 3 and FilterPro 2. Capacitor choice tends to be limited so I usually specify the caps first & then let the filter tool tell me the resistor values but FilterPro 3 won't let me do this. Good to hear you plan to allow this in the next revision.

Is there a link to FP2 somewhere? If I install it will it conflict with the newer FP3?

regards

Steve