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LMX2694-EP: LMX2694EP

Scott Hardy
Prodigy 20 points
Part Number: LMX2694-EP
Other Parts Discussed in Thread: LMK04828, LMK04832, , LMK1C1102

I have multiple questions.  I have an application where I need the extended temperature range and to output a frequency of either approx. 10.5GHz or 14.5GHz.  Due to a stability specification I was considering using two parts.  The first would be a jitter cleaner part that also has extended temperature range to output 100MHz (or other) to feed to the LMX2694 to output the frequency(s) mentioned above.  I would need approx. -109dBc/Hz max. @ 100kHz offset for 14.5GHz or approx. -112dBc/Hz max at 11GHz.  I believe the noise floor of the jitter cleaners is affecting this.  So, to my questions:

1)  Are you in agreement the 100kHz offset of the jitter cleaner parts (LMK04828 or LMK04832) would prevent meeting the 100kHz offset specification (in PLLatinum it shows a -160dBc/Hz floor).

2)  Do you have any phase noise plots or data over temperature for the LMX2694EP parts?

3)  If the jitter cleaner is indeed affecting the 100kHz offset, do you have any extended range PLL's (OR an output on the LMK series) that doesn't use differential outputs that can supply the reference for the LMX2694.

Thanks!

  • 0
    TI__Mastermind 30920 points

    Hi Scott,

    1. Agreed, neither LMK04828 or LMK04832 have good enough PLL noise to hit these targets. Even LMK04832 with the phase detector at 320MHz (max) is barely pushing -140dBc/Hz @ 100kHz offset with a 400MHz clock; this doesn't feasibly scale to -109dBc/Hz @ 100kHz for your 14.5GHz carrier.
    2. Closed loop variation:

      Open loop (VCO) variation:

      I think a lot of the close-in error at -40 and at 85 during closed loop testing could be a function of inadequate soak time or temperature chamber vibration effects. Note that above 1kHz, the temperature variation is significantly reduced in both cases.
    3. You could use only PLL1 of one of the jitter cleaners with a VCXO, and either drive LMX2694-EP with OSCout or duplicate the VCXO signal with a 1:2 buffer. A good single-ended solution is an LVCMOS style VCXO with an LMK1C1102 buffer on the output - this adds virtually no noise.

    Regards,

    Derek Payne