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CN0292

Hello!

How was engineer calculating the RC networks on the outputs of the ADA4096-4 (47 Ω/47 nF)? How was engineer choosing the cutoff frequency?

Project: http://www.analog.com/media/en/reference-design-documentation/reference-designs/CN0292.pdf 

  • FormerMember
    0 FormerMember

Hi Sir,

Sorry for the delayed response here.  I thought the design engineer had posted their response directly.

Here is the answer that I received from Aine:

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Hi Brandon

Just checked with Rob to find out the reasoning behind the RC combo as well as how it was chosen

The RC was put in place because the mux output capacitance was causing a kick back to the ADA4096 output. The actual values were found through measurement and experiment by testing the THD and INL performance as well as the gain error when switching the mix.

The rule of thumb applied here was to use a capacitance that was 100x larger than the mux capacitance and increase the resistor until the output of the opamp was stable, the resistance was then doubled for margin.  So basically it was trial and error to find the best combination that worked well

Hope this helps …

Rgds

Aine

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Cheers,

Brandon