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LMX2820: Cycle slip on steady state

Andri Haryono
Prodigy 80 points
Part Number: LMX2820

Hi,

What is the possibilities of cycle-slipped occurred in LMX2820 after VCO is locked?

My FPD is 200 MHz and the loop bandwidth is 500kHz.

Best regards,

Andri Haryono

  • +1
    TI__Mastermind 33690 points

    Andri,

    After the VCO is locked to the reference, you should not expect cycle slip unless your reference has a sudden frequency transient that is well outside the range of the loop bandwidth, or you subject the device to some stress it is not rated for (e.g. excessive temperature; insufficient or excessive supply voltage; high dose of radiation; etc) which causes the device circuitry to fail to operate properly.

    Dean Banerjee has a textbook on this subject, and summarizes the equations for cycle slip on page 37: https://www.ti.com/lit/ml/snaa106c/snaa106c.pdf

    You can also estimate the LMX2820 transient response curve using PLLatinum Sim. From this transient response simulation and the cycle slip equations above, you should be able to predict the size of the reference transient needed to cause a cycle slip event. Transient response is loop-filter dependent, and requires more than just the loop bandwidth - the phase margin and sometimes the pole ratios have an effect.

    Regards,

    Derek Payne

  • 0 in reply to Derek Payne
    Prodigy 80 points

    Hi Derek, 

    Thank you for your response.

    we can understood the possibility of cycle slipped in transient. But we can't afford the slip in steady state. so we just need to ensure we can mitigate if the risk is there. thank you for your explanation