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LMX2594: VCO calibration time for small changes in input frequency

Makoto Tsurita
Prodigy 40 points
Part Number: LMX2594

Tool/software:

I want to have a 4.0GHz clock output from RFOUTA.
How long will the VCO Calibration time be when the input signal is varying 100KHz with respect to the desired clock, such as 3.9GHz or 4.1GHz?
Feature 1 of the LMX2594 datasheet states "< 20-µs VCO calibration speed".
In Figure 12, it takes roughly 30us to calibrate from 3.7177GHz to 6.9991GHz, and in Figure 13 it takes 10us to 25us to calibrate from 3.4745GHz to 7.0382GHz.
What I want to know is not the large frequency changes shown in these figures.
I want to know how much calibration time is required for small frequency changes at the 100KHz level.

  • 0
    TI__Mastermind 29272 points

    Hi Makoto, 
    You can use PLLatinumSim to estimate lock time. 

    Regards, 

    Vicente

  • +1 in reply to vicente flores prado
    TI__Guru** 108130 points

    Hi Tsurita-san,

    if your question is, when the input clock frequency changes 100kHz, what is the lock time for the VCO to change its frequency accordingly? To answer this question, we need to know the input clock frequency. Assume input clock is 100MHz. Output clock is 4000MHz, that means VCO is 8000MHz. The ratio of input/VCO is 1:80. So if the input frequency change by 100kHz, then the VCO frequency will change 8MHz. 

    In this situation, the VCO should be able to track the input without a VCO calibration. As such, you don't need to reprogram the device. The lock time will be equal to PLL analog lock time. A rough estimation is, lock time = 4/Loop BW. To get a better estimation, please use PLL Sim (www.ti.com/.../PLLATINUMSIM-SW).