Translation loop or traditional PLL using a N divider, which to choose?

ADF4401a uses a mixer to down convert the VCO output frequency for a PFD while traditional PLLs use a N divider to divide the VCO output frequency to a relative low frequency for PFD. So which solution is better? What is the difference in the final output phase noise? Looking forward to your reply!



Edited title
[edited by: ggall at 9:59 AM (GMT -4) on 30 Aug 2021]
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  • +1
    •  Analog Employees 
    on Aug 30, 2021 10:14 AM

    The ADF4401A translation loop has the best phase noise performance, as the 20logN phase noise added by the N divider is avoided, but it requires high quality LO and PFD frequency source(s), as the phase noise of the LO & PFD signals will affect the overall system performance.

    This article contains a plot comparing the performance of ADF4401A vs ADF4372 at 6 GHz, shown below:

    The translation loop system is more complicated to implement, and is primarily targeted for instrumentation and other applications that require very low phase noise. For your application, you may find that the phase noise performance of a traditional PLL (such as ADF4372) is acceptable.

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  • +1
    •  Analog Employees 
    on Aug 30, 2021 10:14 AM

    The ADF4401A translation loop has the best phase noise performance, as the 20logN phase noise added by the N divider is avoided, but it requires high quality LO and PFD frequency source(s), as the phase noise of the LO & PFD signals will affect the overall system performance.

    This article contains a plot comparing the performance of ADF4401A vs ADF4372 at 6 GHz, shown below:

    The translation loop system is more complicated to implement, and is primarily targeted for instrumentation and other applications that require very low phase noise. For your application, you may find that the phase noise performance of a traditional PLL (such as ADF4372) is acceptable.

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