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AFE7900: Input/Output impedance matching

benoit PINARD
Prodigy 40 points
Part Number: AFE7900


Hi,

I would like to use AFE7900 for a broadband frequency application : [1 ;5] GHz on TX and RX interfaces.

1. Is it possible to match AFE7900 RX and TX interfaces on this frequency range ?

2. Could you tell me how to calculate the matching network value of the output frequency band we want to use?

Maybe you already have the technical solution ?

Thanks.

B.PINARD

  • 0
    TI__Genius 10895 points

    Hi Pinard,

    Do you want to use frequency band from 1GHz to 5GHz? 

    It will not be possible to match broad-band from 1 to 5GHz without adding some lossy circuit into the matching circuit. 

    Matching networks we used for datasheet plots are given in the secure folder. We also added AFE input/ output return loss S-parameters in secure folder. You can use that to design a matching circuit which probably needs some tweaking based on your board layout and balun used. 

    Regards,

    Vijay

  • 0 in reply to Vijayendra Varma Siddamsetty
    Prodigy 40 points

    Hi Vijay,

    For my application, I need to use 4 TX and 4 RX provided by AFE7900 transceiver. I want to be able to sample the following band frequency, on the same input receiver or output transmitter. 4 RX (or 4 TX) must be matched for these frequencies bands.

    - [1100; 1300] MHz

    - [1560;1630] MHz

    - [2480; 2500] MHz

    - [5000; 5050] MHz

    Have you got schematic example to add some lossy cicuit into matching circuit ? or simulation example to design a matching circuit ?

    I have an access to secure folder and if you have more information about matching circuit, I'm interested.

    Probably, I would have to cut frequency band in two sections: [1000; 2500] MHz and [5000; 5050] MHz.

    Regards,

    B.PINARD

  • 0 in reply to benoit PINARD
    Prodigy 40 points

    Hi Vijay,

    I made a simulation with QucsStudio to evaluate input matching impedance on input RX4.

    With L/S band matching (AFE1900EVM schematics page 3) for RXDIN, input matching, given by simulation, is superior to  -5dB on [1;3] Ghz.

    => Have you got simulation results about matching impedance of AF7900EVM board ?

    => Have you got a compute method to match input/output of AF7900EVM board ?

    Regards,

    B.PINARD

  • 0 in reply to benoit PINARD
    TI__Mastermind 42200 points

    Closing this post, as it was answered via email:

    Hi Benoit,

    Matching the AFE or any HS ADC in the GHz input range is not an easy task.

    ADCs in general have pretty poor return loss, so a simulation will give you a good first order direction what implement.

    But keep in mind, pcb parasitics and layout can also have affects too, and some tweaking will need to be done in order to satisfy your requirements.

     

    There is a full set of sparameter files on the AFE79xx secure folder, which we can give you access to, if you don’t have access already.

    I would urge you to use those in order to get a 1st order simulation per the BW of your application.

    Regards,

    Rob