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info about CC1120 TRX_SW line

Nicola
Intellectual 345 points
Other Parts Discussed in Thread: CC1120, CC1120EM-169-RD

Hello,

we are developing a transceiver with a CC1120 chip and an external power amplifier. We would like to get some information about the TRX_SW line, in particular what is its internal configuration (open collector driver?) and what are its maximum ratings.

We would know also if the frequency limits of the crystal oscillator and TCXO inputs found on the datasheet are correct (from 32MHz to 33.6MHz for both)...
SmartRF studio allows frequencies from 32 to 40MHz for this device...

Thank you very much

Nicola

 

  • 0
    TI__Guru**** 317180 points

    TRX_SW: I have to check to find the implementation.

    CC1120 supported frequencies: The datasheet is correct. Unfortunately it is a bug in Smart RF Studio here, in the next version scheduled out in the end of the month it will only be possible to select 32MHz and 33.6MHz.

  • 0 in reply to TER
    Intellectual 345 points

    Ok, thank you very much.

    Do you know also what model of TCXO is planned to be used (the PCB is not actually populated with TCXO) on the CC1120EM-169-RD 169MHz reference board?

    We look forward to get some info on TRX_SW... we need to know the equivalent model of this pin, and possibly also of the other pins involved in RF section (PA, TRX_SW, LNA_P, LNA_N) to optimize our RF amplifier circuit.

    Thank you

    Nicola

     

  • 0 in reply to Nicola
    TI__Guru**** 317180 points

    TCXO: Probably Epson TG-5921CG 33.6MHz. 

    The TRX pin is a open drain configuration. As far as I know we don't have a model for any of the pins in question. If you have access to a network analyzer you can use this to generate a s-parameter file for the pin in TX and RX. For the PA pin you need to find the optimal load. Knowing the input impedance on this pin will not give you any usefull information.

     

  • 0 in reply to TER
    Intellectual 345 points

    Thanks TER,

    We could measure the impedance of all the pins, but it is quite a lot of work to do and it would be much better to have average values taken form a considerable number of ICs. We think that TI should do this.
    The most important data are the input impedance of LNA_P, LNA_N, output impedance of PA, and finally the input impedance of PA when radio is in RX mode. TRX data could also be relevant.
    Let's say that  a document like this would be useful to get a good design:
    http://www.analog.com/static/imported-files/application_notes/AN-859.pdf

    Are you going to produce something like this?

    Thanks

    Nicola

  • 0 in reply to Nicola
    TI__Guru**** 317180 points

    No, no plan exist to produce a document like the one from Analog. We don't use the data you request our self.

    Keep in mind that our PA is not linear and hence you can not use a complex conjugate match approach. If you look at the match that are used on the reference designs filtering both for 2. and 3. harmonics is required. In addition you need to prevent energy leaking into the TX match when in RX to obtain good sensitivity. It is hard to get these requirements in a table.

  • 0 in reply to TER
    Intellectual 345 points

    Thanks for your reply, but I'm sorry for the delay, holidays and other activities were here..

    TER said:
    No, no plan exist to produce a document like the one from Analog. We don't use the data you request our self.

    Are you sure? This would be not a good news.. At least LNA input parameters should be included in an input circuit design.

     

    TER said:
    Keep in mind that our PA is not linear and hence you can not use a complex conjugate match approach.

    We should work with a "power match" rather than impedance match. So I think that TI should publish at least what impedance is needed to get all the possible power from the PA.

     

    TER said:
    In addition you need to prevent energy leaking into the TX match when in RX to obtain good sensitivity. It is hard to get these requirements in a table.

    Of course.

    Anyway the PA pin parameters (when in RX mode) and also the trx_sw pin parameters (in both states) would be serviceable.

  • 0 in reply to Nicola
    TI__Guru**** 317180 points

    - The optimum load impedance for the LNA is given as 30+j*30. This is a simulated value and are not verified by measurements

    - The optimal load seen by the PA is around 30+j*30 for our reference designs

    - I have attached s parameter files measured on the LNA pins in RX>/TX and the TRX_SW pin in RX. These are measured on one EM only. These files have to be used with care and there is no guarantee that using these data will give you an optimal solution. They are included to give an idea on how the impedance look like nothing else.

    http://e2e.ti.com/cfs-file.ashx/__key/CommunityServer-Discussions-Components-Files/155/6457.LNA_5F00_N_5F00_RX.S1P

    http://e2e.ti.com/cfs-file.ashx/__key/CommunityServer-Discussions-Components-Files/155/7220.LNA_5F00_N_5F00_TX.S1P

    http://e2e.ti.com/cfs-file.ashx/__key/CommunityServer-Discussions-Components-Files/155/0243.LNA_5F00_P_5F00_RX.S1P

    http://e2e.ti.com/cfs-file.ashx/__key/CommunityServer-Discussions-Components-Files/155/1018.LNA_5F00_P_5F00_TX.S1P

    http://e2e.ti.com/cfs-file.ashx/__key/CommunityServer-Discussions-Components-Files/155/6747.TRX_5F00_RX_5F00_CC1120_5F00_ref_5F00_plane.s1p