Reducing RFI on AD8223

I am using the AD8223 to amplify a low voltage signal (ranges from 0-30 mV) by a factor of 100, up to 0-3V output.  Reading the datasheet, on page 15, it shows how to set up a low-pass RC network to filter RFI.  I don't know what the frequency of any RF noise in my system will be, but the PC board sits right next to a large set of inductors.

My first question is, for the extremely small voltages that I am reading, will using the exact values of resistors and capacitors named in Figure 34 affect my reading?  Should I use those values?

Also, I see that they have a 0.1uF capacitor on the + and - side of the supply, and then a dotted line to a 10 uF capacitor.  What is this for?  Is this recommended regardless of using the RF filter?  And also, the 10 uF symbol has one curved line, is that a special kind of capacitor?


  • You don't need to know frequency of any RF noise in your system. You need to know your signals max deviation frequency (fs) then you can set cut-off frequency of filter to 2fs to 10fs (I prefer 4s for slow signals 2s for fast signals). I think Figure 34 will not effect your signal readings. You can change the R and Cc for common mode or can change R, Cc and Cd for differantial mode using to set cut-off frequency as formula has shown in datasheet. Capacitors at the supply pins are for reducing supply fluctuations or interference effects on supply and different values for different frequencies. You can check with this formula to which frequencies => f = 1/2*pi*C. And if you are using with single supply you can delete the capacitors which are at on negative supply pin.

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    •  Analog Employees 
    on Aug 2, 2018 3:03 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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