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ADF4371 Phase Noise


I have simulated the phase noise of AD4371 to output LO signal between 11-11.5GzHz. ADISIM File attached. 

The LO is applied to ADMV1017 which goes through x2 or x4 LO Multiplier which degrades the phase noise. 

I like to improve the phase noise of the LO coming out of ADF4371. Can someone please advise how can I improve the phase noise? 

Thank you.

  • Hi, could you please try to attach ADIsimPLL file again? Sometimes on EZ you need to compress (zip) the .pll file before it can be attached. In general for improving phase noise it is best to use the highest PFD frequency possible. Is there any particular offset you are trying to get an improvement at, what are your PN targets at each offset?

    What's the step size i.e. is this an integer N use case? FOM improves when in integer N operation and SDM is disabled. We also have a new PLL that will be releasing mid April which has a ~12GHz fundamental VCO and has better FOM than ADF4371. It's integer N only though, in any case the part number will be ADF4377.

  • In the file, I like to specify the reference oscillator (100MHz by Crystek) as used in the ADF4371  EVB. How do I specify this?  Currently, it is specified as custom, but I am not what has been specified in terms of the phase noise of the reference oscillator by the software.

    Step size  is not critical as I want to good phase for the mixer and it is not required to hop.  The Mixer have x2 or x4 which would degrade phase noise.

    The PLL is required to change LO frequency in steps of 200kHz if the IF frequency changes to give a fixed RF output. 

  • Just to clarify, low phase noise is required which I guess fine frequency step is required and keeping high Pfd. Will the fine frequency step allow the LO to step the frequency in steps of 200kHz.  I look forward to hearing from you regarding ways to improve phase noise. 

  • Hi, okay sounds like you will probably need fractional-N operation. You should be using the ref doubler to get 200MHz PFD frequency for best PN performance.

    Here is a forum post which describes how to model the reference component's phase noise in ADIsimPLL.
    RE: ADF5610 - Wenzel 100MHz ref specs

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