AD9680 input impedance matching questions

good day

I have several questions regarding the input interface of the AD9680.

I would like to design a matching network using Snp file. Firstly I don't understand why S2p are provided whereas I expect only file having S11 parameter since the purpose is to provide matching impedance. In addition several files are provided, I don't know which one to use. Could you please clarify which context for each file?

In the datasheet page 36 at table 9 parameter values are provided for the components shown in figure 115, I was wondering if these values are still ok whatever differential input impedance value is set (see figure 116 where different resistors can be selected via registers). Is it possible to attach a drawing of an example of matching specifying the context ( frequency range...)

Thank you in advance for your reply

Best regards

Raphael

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    •  Analog Employees 
    on Oct 6, 2016 1:12 AM

    Hello Raphael

    Thank you for contacting engineer zone regarding the AD9680. since the AD9680 inputs are differential, we made 2-port measurements of the analog inputs with port 1 connected to VIN+ and port 2 connected to VIN-. 

    So for a 200ohm termination setup, the simulation setup will look like the one shown below

    Upon simulation, the results will look like the image shown below:

    If you want to create a matching network you can either use a fully differential approach, or use a single ended approach and then generate a differential network. 

    Hope this helps. Please let me know if you have any questions.

    Thanks

    Umesh

  • Hi Umesh,

    What is the recommended input impedance to be used in the evaluation board. I'm using AD-FMCDAQ2-EBZ.

    I believe the two 50Ohm resistors after the second balun, differential 100Ohm along with an internal 400OHm input impedance present a 80Ohm to the Analog input connector.

    Am I correct?

    Regards,

    Vishnu R.

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