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LMK3H2104: Question regarding FOD

Shunsuke Yamamoto
Genius 10821 points

Part Number: LMK3H2104
Other Parts Discussed in Thread: LMK03328

Hi team,

Does FOD in LMK3H2104 have internal PLL? I would like to know how FOD is consisted of. Please kindly let me share if you have any good materials of FOD.

Best regards,

Shunsuke Yamamoto

  • 0
    TI__Mastermind 23280 points

    Yamamoto-san,

    There is no PLL in this device. Instead, the FOD is a fractional output divider that takes the BAW frequency and divides it down to a frequency between 100MHz and 400MHz. Additional post dividers in the device allow the frequency to be integer divided down further to the outputs.

    Thanks,

    Kadeem

  • 0 in reply to Kadeem Samuel
    TI__Genius 10821 points

    Hi Kadeem,

    Thank you for the reply. I understand that there are no PLLs in this device. I would also like to know how FOD works. May I know if you have good materials? I have read the datasheet, but I don't clearly catch it..

    Best regards,

    Shunsuke Yamamoto

  • +1 in reply to Shunsuke Yamamoto
    TI__Mastermind 23280 points

    Yamamoto-san,

    What I can share about the fractional output divider is this.

    Think of it as similar to the fractional feedback path of a fractional PLL, such as the LMK03328. There is an integer portion of the divider, and a fractional (numerator and denominator) portion of the divider. The denominator is a fixed 2^24, and the numerator is whatever value is needed to generate the frequency in question.

    For BAW devices, the "nominal" BAW frequency of the device is 2467MHz. However, there is some slight variation in BAW frequency from device to device. On every device, we characterize the BAW over temperature to determine (1) the center frequency of the BAW and (2) how the BAW frequency shifts over the entire temperature range. The secondary role of the FOD is to compensate for these variations of the BAW frequency, with a total frequency accuracy out of the FOD of +/-25ppm. The entire compensation is determined for each device, so that users of the device do not have to make any device-specific register reads or writes when using the device.

    Thanks,

    Kadeem