2015-01-15 – Windoze 10 no longer plays well with TI FilterPro 🙁 The program will run but then lock up toward the results. TI WeBench filter design tool is available on-line but still not as nice as the original.
Want to play with op amp filters? The TI FilterPro Desktop (Version 3.1.0.23446) is a nice tool to quickly design filters with. Note: You will need to register with TI in order to download the executable.
Overview: http://www.ti.com/tool/filterpro&DCMP=hpa_amp_general&HQS=NotApplicable+OT+filterpro
Manual: http://www.ti.com/lit/an/sbfa001c/sbfa001c.pdf
Program: https://focus.ti.com/general/docs/event/accesseventaction.tsp?actionId=896
(Thank you Roy, K1LKY, for sending these updated links)
But below is a “cheat sheet” to quickly calculate values for the CALF. Clicking on the screen shots will show a larger view.
In this example we will make a 4 pole 2.2KHz low pass filter using 2 op amp stages and an overall gain of 1:
From the File menu select New for a new design (by default it will start with a new design)
Select your filter type: Click on Low Pass then click on the Next button.
Enter the following values:
Gain: 1 V/v 0dB (unless you need amplification or attenuation)
Passband: 2200 Hz – This is your cutoff frequency
Ripple: 1dB
Stopband: 5000 Hz
Stopband Attenuation: -45dB
Filter Order (AKA poles):
Check the Set Fixed box
Select 4 in the drop down. This will set the design to a 4th order filter using 2 op amp stages (2 poles / stage).
Click Next
Select the filter type in the list at the bottom. I usually like Bessel low Q type designs. In this case select Bessel with a Q=.81 and click Next.
Select the Feedback type:
Select Multiple Feedback – Inverting (CALF) – my personal preference for designs
Other types for different designs:
Sallen Key – Non-inverting type
Multiple Feedback Fully Differential – Just as the complex name it describes.
Click Finish
You will be presented with a schematic, characteristic curves, BOM, etc.
At this point I will typically play with the standard tolerance values found in the upper right hand corner based on what is in my junk box. Select 5% or 10% in the drop down for resistors and 20% for capacitors to begin with. You can always narrow your results from there.
Adjust the R/C values. For example, maybe I do not have 22nF & 56nF capacitors but plenty of 10nF. Click on the “22nF” and 56nF values of capacitor C1, change it to 10nF, and hit ENTER. The other R/C values in that stage will change as needed.
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Finally from the File menu select Save Design. Just in case you need to go back!
Try out your values on Spice or a breadboard, tweak as needed and enjoy your new filter!
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