Impedance CC2520 transceiver for matching network

Knowns anybody the (complex) impedance of the CC2520 chip? The datasheet only states the following:

"The RF input/output is high impedance and differential. When using an unbalanced antenna such as a monopole, a balun should be used in order to optimize performance. The balun can be implemented using low-cost discrete inductors and capacitors only or in combination with transmission lines replacing the discrete inductors."

Inductance values for transmission lines are not mentioned.

The microstrip balun in DN003, which is listed as application note for the CC2520 on its product page, is not the right one, because the CC2520 has no TXRX pin.

Information in the reference design (http://focus.ti.com/docs/toolsw/folders/print/cc2520em_refdes.html) only contains the layout files, no calculations, formulas or source files from the software it is designed in. This makes it very hard to develop a balun for boards with a different stackup or to choose a chip balun.

Thanks, Johan

  • Johan

    Knowns anybody the (complex) impedance of the CC2520 chip? The datasheet only states the following:

    "The RF input/output is high impedance and differential. When using an unbalanced antenna such as a monopole, a balun should be used in order to optimize performance. The balun can be implemented using low-cost discrete inductors and capacitors only or in combination with transmission lines replacing the discrete inductors."

    Inductance values for transmission lines are not mentioned.

    The microstrip balun in DN003, which is listed as application note for the CC2520 on its product page, is not the right one, because the CC2520 has no TXRX pin.

    Information in the reference design (http://focus.ti.com/docs/toolsw/folders/print/cc2520em_refdes.html) only contains the layout files, no calculations, formulas or source files from the software it is designed in. This makes it very hard to develop a balun for boards with a different stackup or to choose a chip balun.

    Thanks, Johan

    1、cc2420 has no TXRX pin ????

    2、balun on the PCB board,have simple example for datasheet

     

    first time , first idea
  • In reply to yangseababy:

    We're talking about the CC2520, not the CC2420. The balun is therefore not appropriate.

    I also want to implement additional ESD protection, where the protection devices add extra capacitance and inductance. This needs to be compensated for optimum performance.

  • Unfortunately, like many RF transceivers, the CC2520 is highly sensitive to its load impedance - especially at low temperatures. This does not only affect range (sensitivity and output power), but most notably the signal quality (Error Vector Magnitude). Reduced signal quality will make it more difficult to pass regulations (especially FCCs restricted bands and 802.15.5 specs), and can in extreme cases lead to loss of communication (packet loss) at any range. Unfortunately, this is not always easy to detect - it will vary from device to device (though it is almost always worst at low temperatures), and requires extensive testing to evaluate. 

    Due to the difficulty (and risk) involved in finding a suitable matching network for the CC2520, we strongly suggest customers copy the RF section of our reference designs. This is also why we haven't given out more information regarding the complex impedance of the CC2520. Applications that do not need to pass FCC/802.15.4 regulations, and/or will not operate at low temperatures, would probably be able to create their own baluns (or use a chip balun) for the CC2520 without too much trouble. 

  • In reply to arne3009:

    Copying the reference design is not always the best thing: dimensions are not mentioned (or I can't find them) and the DXF and Gerber files don't import correctly in Cadence Allegro PCB Editor (a lot of useless artifarcts appear). In addition, I like to know what the specifications of the balun are:

    • output impedance
    • differential impedance
    • insertion loss
    • return loss
    • phase difference

    And: How does the balun and the CC2520 perform when applying ESD strikes (degradation)?. ESD protection is often implemented by using a BAV99 double diode with an inductor in parallel to correct for the diode capacitance. How will this affect the balun?

    And: Can the circuit be made from lumped components, so the size of the balun can be decreased?

    And: How does the balun perform when components (especially capacitors) have tolerances of 10% (yield analysis)?

    And: How does the balun perform when using a PCB thickness different than the reference design?

  • In reply to Johan3088:

    I would like to know the answers to Johan's las set of questions as well. I have a design that is forcing me to use a layer thickness (signal to ground) that varies from the reference design. 

  • In reply to Johan3088:

    The CC2520 reference design has been extensively tested, and should tolerate normal variations in the components listed (assuming the same make and size is used). More significant changes in the design however, such as going from trace inductors to lumped components, adding diodes or changing the PCB thickness, has not been tested as far as I know.

    The CC2520 is not only sensitive to changes in the impedance at the fundamental frequency but also at its harmonics, which is difficult to measure and accurately simulate. And as I mentioned earlier, the changes in performance can be subtle and requires specialized equipment to evaluate. For this reason we do not give out balun specifications. 

     

  • In reply to arne3009:

    arne
    Due to the difficulty (and risk) involved in finding a suitable matching network for the CC2520, we strongly suggest customers copy the RF section of our reference designs. This is also why we haven't given out more information regarding the complex impedance of the CC2520. Applications that do not need to pass FCC/802.15.4 regulations, and/or will not operate at low temperatures, would probably be able to create their own baluns (or use a chip balun) for the CC2520 without too much trouble.

    For designs that do not require FCC/80.15.4 when selecting the chip balun what is the impedence should I assume on the CC2520 side? Just help me choose a suitable chip baulen.

    I think this is a fair enough question per quoted response.

  • In reply to Arun Krishna:

    Hi Arun Krishna,

    There a few vendors that can support an IC/chip balun for CC2520.

    1. Johanson Technology: http://www.johansontechnology.com/

    2. Anaren: http://www.anaren.com/

    3. Murata: http://www.murata.com/

    4. Würth: http://www.we-online.com/website/emc/eisos/alg/kat_layout.php?id=78

    You should probably contact them directly for insight. I have upload the simulated S-parameters for CC2520 for you that you can use when approaching the vendors.

    The fileis for the CC2520EM 2.1. It is simulated from 1 GHz til 7.5GHz with the following ports:

    Port 1: SMA connector
    Port 2: RF_p
    Port 3: RF_n

     

    Enjoy,

    LPRF Rocks the World

     

    CC2520EM_2_1_SMA_RFp_RFn.txt
  • In reply to LPRF Rocks the World:

    Hi,

    I got the same question on using chip antenna for cc2520. Due the size requirement, I am trying to use an chip antenna for cc2520, but there is no reference design avaiable from TI.

    But I saw a reference design on cc2500 (from EZ430-RF2500 evaluation kit), http://www.ti.com/litv/zip/slac255

     It uses lump components for the matching network. Can I use the same schematic and then tune the capacitors and inductors in ADS to construct matching network for cc2520?

    and if lump components are used, will the thinkness of PCB be critical?

    Thank you

    Adam