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LMX2594: Improve Phase Noise Performance

ikon
Genius 5355 points
Part Number: LMX2594
Other Parts Discussed in Thread: LMX2592EVM, LMX2592,

Hi Support,

Tested LMX2594 chip using LMX2592EVM, but the phase noise performance is inferior to LMX2592 chip.

Here are the details about the Ref and output frequency.

Reference to the chip: 50MHz (bliley 50MHz ocxo ,phase noise at 10KHz is -160dBc/Hz) ,used doubler inside the chip so the phase detector frequency is 100MHz. 

Output frequency: 13.275 to 14.5 GHz (only 6 frequencies in this range)

Phase noise requirement: 10KHz@ -90dBc/Hz and 100KHz@-100dBc/Hz

 FYI, Able to achieve the above phase noise LMX2592 chip (6db better since the outfrequency is half of the above mentioned).

In addition, what changes are required to use LMX2594 on LMX2592EVM?

Lastly, please help to advise  the loopfilter values for out above frequency requirement.

Thanks.

  • 0
    TI__Guru** 110880 points
    Hi Ikon,

    I think it is hard to meet the phase noise requirement at 100kHz offset. Datasheet has specified the open loop VCO phase noise at different offsets. At 14.5GHz and 100kHz offset, the phase noise is only -99dBc/Hz. If this is a hard specification, you may consider to use LMX2592 with external frequency doubler.
    Regarding loop filter design, please use our offline tool - PLLatinum Sim, which is avaialble in ti.com.