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About the RFI input filters design

Category: Datasheet/Specs


In "A Designer’s Guide to Instrumentation Amplifiers" 3rd, p. 5-14, it recommends differential bandwidth of 10 times the signal frequency. And common-mode filter capacitors 10% the value of  C2 or less. So, the common-mode bandwidth should be at least about 20 times the differential bandwidth. But latter, it says:

The common-mode bandwidth should always be less than 10% of the in-amp’s bandwidth at unity gain.

That means the differential bandwidth should be less than 0.5% of the in-amp's bandwidth at unity gain, and the signal bandwidth only 0.05% of the unity gain bandwidth, right? Won't this be too small?


[edited by: diverger at 6:14 AM (GMT -4) on 14 Mar 2024]

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    •  Analog Employees 
    •  Super User 
    +2 verified


    Thank you for reaching out and sharing your questions with the team.

    To be able to understand properly this inquiry, I would like to ask several items:

    • May I know if you are asking these to…
    •  Analog Employees 
    •  Super User 
    in reply to diverger +1 suggested


    Thank you for pointing this out; It's quite misleading on the guideline #2 of the cookbook approach, On page 5-14 of the Designer's guide and the only point here is when choosing an RFI filter…