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LMX2594EVM: EVM questions

Marvin Gasis Arcangel
Expert 8990 points
Part Number: LMX2594EVM
Other Parts Discussed in Thread: LMX2594

Hi Team,

I need help with the customer inquiry below:

Can the module distort/stretch the input signal and return an output signal by detuning the VCO? I imagine e.g. a pulse train input with repetition rate 10 MHz. Can I get the same pulse train returned but with, e.g. 10.001 MHz repetition rate? 

Also, What is the resolution of the VCO (clock) detuning? can it go as low as 1E-12, i.e. normalized frequency resolution as small as 1E-6 ppm?

Thanks in advance.

Regards,

Marvin

  • 0
    TI__Guru* 81510 points

    Hi Marvin,

    If you have a stable continuous 10MHz input clock to LMX2594, you can get continuous 10.001MHz clock from the device. Please note the min. output frequency of LMX2594 is 9.765625MHz.

    PLL denominator is 32-bit long, so the min. amount of VCO frequency change is phase detect frequency / 2^32-1.

  • 0 in reply to Noel Fung
    TI__Expert 8990 points

    Hi Noel,

    Noel Fung said:
    If you have a stable continuous 10MHz input clock to LMX2594, you can get continuous 10.001MHz clock from the device. Please note the min. output frequency of LMX2594 is 9.765625MHz.

    Can you send an arbitrary signal (bandwidth >10 MHz) to the LMX2594 (that is no clock) and get it stretched/compressed from the device output? 

    Noel Fung said:
    PLL denominator is 32-bit long, so the min. amount of VCO frequency change is phase detect frequency / 2^32-1.

    Can you please explain what you meant by "phase detect frequency"?

    When the PLL denominator is 32-bit long, I could get a minimum change in frequency of 10 MHz x 2^-32 for a 10 MHz input (as per my example)

    And is there any other similar device with EVM with higher clock res than 32bit?

    Thank you in advance.

    Regards,

    Marvin

  • 0 in reply to Marvin Gasis Arcangel
    TI__Guru* 81510 points

    Hi Marvin,

    The purpose of PLL is to have the VCO tracked with the input clock, if the input clock is not a stable, periodic clock, the output of the VCO is also not stable. 

    in above diagram, fpd = phase detector frequency. In this example, the denominator is set to 1000, so VCO resolution is fpd/1000 = 10M/1000 = 10kHz.

    So if the numerator is incremented by 1, VCO frequency will increase by 10kHz.

    32-bit denominator is the max. in the market.