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CC3200 impedance matching

Serdar Köse
Genius 3360 points
Other Parts Discussed in Thread: CC3200

Here is a schematic from datasheet of CC3200

Here is datasheet of the FL1 filter on http://product.tdk.com/en/catalog/datasheets/rf_bpf_dea202450bt-1294c1-h_en.pdf which I can't find it on stock anywhere. Instead, I am planning to use another RF filter from Johanson technology http://www.farnell.com/datasheets/87155.pdf Do you have any application note that explains how to replace the filter and/or how to decide what values to choose for L1 and C9 pair for a different PCB stack?

I am not much familiar with RF filters, what impedance should be measured on pin 3 of the filter? I will have a 50 ohm antenna at the end of the microstrip, can I select any L1 and C9 values that matches the impedance or what do I need to consider to selecting the L-C values?

  • 0
    Intellectual 545 points

    You don't need to change L1 and C9, if you use a different pcb stack you should calculate S and W in the "Layout Guidelines
    " section 4.1.3 Transmission Line based on your new pcb stack
    http://www.ti.com/lit/ug/swru370a/swru370a.pdf

    There are online calculators for that like this one which gives you 50 Ohm(s) you need
    http://www.microwaves101.com/calculators/864-coplanar-waveguide-calculator

    Thanks,
    Ali

  • 0
    Guru 27285 points

    Hi Serdar, I am new in this forum and still I not analysed in deep transmitter chain of CC3200, the filter you choosed is a low pass filter and you see both Scattering figure by frequency (Schmidt chart on original and linear on alternate) all low frequency are not attenuated so "rf" "if" and "lo" product are routed to aerial, good rejection for LP filter start over 3GHz and too many spurious emission can be radiated, this cannot pass certification FCC or CE for your country nor international rules and can result in law violation too.
    Impedance of both filter are 50Ohms and generally this is a standard.
    Antenna network matching impedance LC is ok till complex radiation impedance is not changed.
    To measure filter impedance you need a network analyser and a good fixture too but if you are not experienced RF a good rule is to stay away from.

  • 0 in reply to Roberto Romano
    Genius 3360 points
    Thank you Roberto for the warning that I did not pay attention on it. I selected a bandpass filter now http://www.farnell.com/datasheets/1640997.pdf I found ADS library of the component that I can simulate for the optimum match.

    Thank you Ali for the links. Just a little correction that I believe L - C values should change when the width,length, and stack height changes in order to get the optimum impedance matching.
  • 0 in reply to Serdar Köse
    Guru 27285 points

    Serdar kose said:
    Thank you Roberto for the warning that I did not pay attention on it. I selected a bandpass filter now http://www.farnell.com/datasheets/1640997.pdf I found ADS library of the component that I can simulate for the optimum match.

     Hi Serdar, I checked data sheet and is a good choice.

    Serdar kose said:
    Thank you Ali for the links. Just a little correction that I believe L - C values should change when the width,length, and stack height changes in order to get the optimum impedance matching

     Stack height change the impedance of transmission lines so you have to match  again to 50 Ohm. LC till antenna doesn't change and impedance at input remain 50Ohm don't change.