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lmx2594: LMX2594 SPUR Performance

LMX2594locktime
Prodigy 85 points

Part Number: LMX2594

Hi

I have the following questions and like to get your help, thanks

1.When an automatic ramping is in progress, is the PLL locked? Or this is just sweeping VCO without locking to a reference. Please confirm during this process , PLL is locked

2.On table 17 of your datasheet, “RAMP_THRESH, programing number does not match description, similarly on RAMPX_len,RAMP0_INC.RAMP1_INC, programming value does not match description. Please call or walk through

3.With integer mode at 10.5GHz and other frequencies, we saw spurs between 100Hz to a few kHz. See attached screen shot. These spurs are not related to power supply and moving and changing amplitude with VCO frequency and how the channel divider is programmed. I would like to know whether or not you know the origin of these spurs and how to minimalized it as it is quite high

 

  • 0
    TI__Mastermind 28031 points
    Sheng Chang,
    1. During automatic ramping, the PLL does try to lock to the reference; it is closed loop. Now if the ramp is too fast relative to the loop bandwidth, it will not have time to properly settle.
    2. We are in the process of revising the datasheet. Thank you for your feedback.
    3. I doubt this spur is due to our device and do think it is power supply related. Specifically, the spur looks to be at 180 Hz, which we see all the time and it is very hard to get rid of. We do have internal LDOs on our device, but the output buffer has a pull-up straight to Vcc, so the PSRR is 0 for that.