Hi, AnalogBill. I would assume that Microchip has taken non-ideal operations into consideration in the FilterLab software because the program uses Microchip op amps and the company wants engineers to get a good model so they will buy Microchip devices. Good point, though, about watching out for models that do not reflect real-world op-amp characteristics. Thanks for your comments.
Your filter plot highlights a common mistake in filter design. The deviation shown at 5 kHz on the plot may not be due just to the "protoboard" you used. Unless your modeling software contains a comprehensive model of the op-amps used, it may assume they're rather ideal ... especially with regard to gain-bandwidth or GBW. Since most filters, especially "anti-alias" filters, are useful because of their high attenuation beyond their cutoff frequency, this is an especially important consideration. Note that the first capacitor in each section has one end tied to an op-amp output. If the op-amp has infinite GBW, its output impedance will remain very low - even at high frequencies in the "cutoff region" of the filter's response. But if there's not enough GBW, this impedance will allow the first capacitor to feed signal around the stage, causing the "leveling out" of passband attenuation hinted at by the plot.
Texas Instruments has a great filter design program called FilterPro Desktop. Incredibly well done and totally free (you will have to login to download). I've used it many times in the past; not only does it do "theoretical" but also has options for "real world" values. http://www.ti.com/tool/FILTERPRO
If you want something even more advanced and don't mind spending a few dollars ($49 to be exact) there is Filter Wiz Pro from Schematica. It's like the TI program on steroids (http://www.schematica.com/active_filters/fwpro.html). More choices for filter designs than you will ever need.
The Microchip offering is good for what it costs (free) but you will find the other two much more useful as genuine tools.
Jon, thanks for the informative post. By entering our requirements, we will be provided with the filter design along with the schematic, component values, spice. Is this FilterLab software available for free download? If yes, then it will be a great help for self training projects.
Truchard will be presented the award at the 2014 Golden Mousetrap Awards ceremony during the co-located events Pacific Design & Manufacturing, MD&M West, WestPack, PLASTEC West, Electronics West, ATX West, and AeroCon.
In a bid to boost the viability of lithium-based electric car batteries, a team at Lawrence Berkeley National Laboratory has developed a chemistry that could possibly double an EV’s driving range while cutting its battery cost in half.
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This discussion will examine what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.