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cc1120 lna matching

taeheon kim
Prodigy 30 points
Other Parts Discussed in Thread: CC1120

I'm designing the 430MHz band transceiver based on your reference design guide(420-470MHz).

1. I want to know the impedance of the each point above.

2. How do I measure the  balanced impedance accross the L191 with floating the LNA_N and LNA_P pin ?   I do have  only 2-port Network Analyzer.  It should be 100+j60 from the cc1120 datasheet.

3. I want to know how to decide the values of the L192, L201, C201, C191 and L191?

  Usally LC balun is calculated => L=(SQRT(Rin*Rout))/(2*pi* fc) , C=1/(2*pi* fc* SQRT(Rin*Rout)).

  I don't know how TI deceded the values(L192....).

best regards,

Taeheon Kim

  • 0
    TI__Guru**** 317180 points

    Before going into details:

    The reference design you refer to gives the best known performance for the frequency you are looking at. Why do you want to change the component values?

  • 0 in reply to TER
    Prodigy 30 points

    I'm sorry but there was some misunderstanding.

    I'll follow your reference design guide. I need a tuning method.

    I think, even though I follow the reference design, I would have to tune the circuit.

    If I know how you decided the values of the matching circuit, it will be very helpful.

    Best regards,

    Taeheon Kim 

  • 0 in reply to taeheon kim
    TI__Guru**** 317180 points

    No misunderstanding.

    As I said the reference design is fine tuned to give the best performance possible. If the reference design is followed you will have the best performance. The LNA accept a rather wide range of source impedances and still have the sensitivity stated in the datasheet.

    What we did when developing the design was to simulate the layout in ADS and then measuring with the values found in simulation and based on the results trying one value higher or lower. Trying to measure the differential source impedance with a VNA could easily cause a measurement error and give you worse performance than following the reference design.

  • 0 in reply to TER
    Prodigy 30 points

    Thanks for your reply!

    I have a last question!

    When I test the impedance with VNA, what should be the impedance of each point in RX mode?

    Especially C181-L172 junction point and L174(output) point!

    Best regards,

    Taeheon Kim. 

  • 0 in reply to taeheon kim
    TI__Guru**** 317180 points

    The impedance seen from the PA output (partly into L174) is covered by the datasheet but the numbers are for Tx, not Rx.


    The other impedances has not been measured.