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TX Output Power Limit

Akash Patel
Expert 6245 points
Other Parts Discussed in Thread: WL1801MOD, WL1835MOD, WL1837MOD, WL1837, WL1835

Hi team,

I am looking at page 5 in the WL18xx .INI File Application Report found here: http://www.ti.com/lit/an/swru422a/swru422a.pdf I see that the PwrLimitReference11ABG parameter can be set to 0xFF corresponding to 25.5 dBm and the PerChanPwrLimitArr11ABG can be set up to 0xF corresponding to 15 dBm for each of the 6 modulation types. This would give the final TX output power limit to be 25.5 + 15 = 40.5 dBm (by the way, there is a typo that shows a division sign instead of an addition sign in the PerChanPwrLimitArr11ABG description). The default is 10 + 15 = 25 dBm. What does this TX output power limit mean?

Looking on page 12 for the datasheet for the WL1801MOD, the maximum typical output power is 17.3 dBm (for DSSS and CCK modulations). With MCS12, this is 18.5 dBm typical. How does this relate to the TX output power limit that was set with the above parameters? The default TX output power limit above was set to 25 dBm, does the device ever have a chance of hitting this number?

Regards,

Akash Patel

  • 0
    TI__Mastermind 35795 points
    Akash,
    WL18xxMOD cannot do 40.5 dBm. Values mentioned in the datasheet are typical tx o/p power values and max tx o/p power is around these typical values. In INIs for both WL1835MOD/WL1837MOD PwrLimitReference11ABG is set to 0x55 which is 8.5 dBm. Setting this value to 0xFF would essentially mean that you are not regulating your tx o/p power - this doesn't mean PA will actually transmit at the power values you mentioned above.

    Saurabh
  • 0 in reply to S
    TI__Expert 6245 points
    Saurabh,

    I understand the module cannot do 40.5 dBm but my question is what is the point of having this as an option? Is there a register that we can read to measure the actual TX output power at any given time?

    Also, 0x55 is the default setting for PwrLimitReference11ABG in the C2PC INI for WL1835 and the regular INI for WL1837, however, 0x64 is the default setting for PwrLimitReference11ABG in the regular INI for WL1835. Why are the regular INI for the WL1835 and WL1837 setting these differently? Is there a C2PC INI for WL1837? git.ti.com/.../official_inis

    Regards,
    Akash
  • 0 in reply to Akash Patel
    TI__Mastermind 35795 points
    Akash,
    You may hook a spectrum analyzer to antenna port and measure o/p power. There is no register than can tell you o/p RF power at the antenna. In case the intention is to modify INI for your board , I suggest you run PLT tests on your platform and then compare o/p tx power to set tx power. For TI modules, in case you are using WL1835MOD, use WL1835MOD_INI.ini - in case you are using WL1837MOD use WL1837MOD_INI_FCC_CE.ini/WL1837MOD_INI_FCC_CE_JP.ini .
  • 0 in reply to S
    TI__Expert 6245 points
    Hi Saurabh,

    Thanks for the quick response. Can you clarify what PLT means? I see that it is mentioned all over our TX Testing Wiki: processors.wiki.ti.com/.../WL18xx_TX_Testing

    Can you clarify why PwrLimitReference11ABG is set to 0x64 in WL1835MOD_INI.ini but set to 0x55 in WL1837MOD_INI_FCC_CE.ini and WL1837MOD_INI_FCC_CE_JP.ini? What are the implications of this?

    There are also differences in the PerChanPwrLimitArr11ABG between the WL1835MOD_INI.ini and WL1837MOD_INI_FCC_CE.ini. Most of the entries are 0xF in the former but 0x7 or 0x8 in the latter. Can you help clarify why these differences exist?

    Taking into account these two differences, we are reducing the TX output power limit by a total of 8.5 - 9.5 dBm. The default WL1835 config gives a TX output power limit of 25 dBm while the default WL1837 config gives a TX output power limit of 15.5 dBm

    Regards,
    Akash
  • 0 in reply to Akash Patel
    TI__Mastermind 35795 points

    Akash,
    PLT - Production line testing. Yes, above link is for PLT Tx test. For receive: processors.wiki.ti.com/.../WL18xx_RX_Testing
    Above links have calibrator tool commands. Customer can also use windows based RTTT tool for rx/tx test : www.ti.com/.../WILINK-BT_WIFI-WIRELESS_TOOLS . I am not sure if it makes sense to compare each parameter between different INIs - these parameters are derived after testing on WiLink8 modules for regulatory compliance. Just use the one that goes with your customer product and run PLT tests on it and check tx / rx and then modify any parameter if needed.

    Saurabh