AD9545 question

Hello

                 There are two items of AD9545 question as below. 

  1. When DPLL is configured in “close loop” mode, does Free Run Tuning Word (FRTW) will affect the output frequency?

Customer  found ptp4l can track to master clock via setting FRTW when set AD9542 as “close loop” or as “open loop”. But we expect FRTW cannot tune the output frequency in “close loop”. Could you help to advice it?

 

  1. Customer modify .cso file base on “AD9545_20210222_Ch0_RefA_Ch1_FRTW_SCC_AuxDPLL_RefAA_DPLL1_DPLL0.cso”. Please help to check if the configuration is correct or not.  (A) Add 1 Hz in REF B   (B)Add DPLL0 Profile 2. Is it suitable to set the priority of profile 2 as ‘1’? Thank you. 

https://drive.google.com/file/d/1KF8Al2-ri5NBY7PnuRAKS5rt1NZUh38a/view?usp=sharing 

BR

Patrick

  • +1
    •  Analog Employees 
    on Mar 10, 2021 9:30 PM

    Hi,

    I am confused about the closed loop versus open loop question. I can set the DPLL in closed loop mode if I enable a translation profile and the profile becomes active. I can set the DPLL in open loop mode (i.e. freerun or holdover) if I enable a translation profile and the reference associated with this profile becomes (or was from the beginning) invalid. I can also force the freerun or holdover modes.

    In closed loop (meaning I enable a translation profile and the profile becomes active), I cannot modify the tuning word of the DPLL.  Even if I modify the freerun tuning word, it does not matter because the DPLL calculates the active tuning word

    In open loop (meaning the DPLL is in freerun for whatever reason), I can change the freerun tuning word. In holdover, it does not matter if I change the active tuning word because the averaging processor had calculated it based on history settings.

     

    Regarding the question 2: Yes, you can set the profile 0 with priority 0, profile 1 with priority 8 and profile 2 with priority 1.

    I saw that you want to use REFAA (the reference of profile 1) also as a reference to the AuxDPLL of the system clock compensation. This is not good. A reference cannot belong to a profile and then used to compensate the DPLL of that profile. So I suggest you disable the profile 1 of DPLL0 and leave the system clock compensation AuxDPLL settings as they are. If the other two profiles become inactive, the DPLL0 enters holdover and the outputs will be as stable as the REFAA.

    Then you also set DPLL0 to compensate the DPLL1 and TDCs. This is not good. You already set AuxDPLL to compensate DPLL0, DPLL1 and TDCs. It does not make sense to further set DPLL0 to compensate DPLL1 and the TDCs because they are already compensated. You could disable AuxDPLL to compensate DPLL1, so you could use DPLL0 to compensate DPLL1 (not the TDCs because you already set AuxDPLL to do it), but I do not see the point. Once you decided that REFAA is a very stable clock and everything should have its stability, then it does not make too much sense to use one of the DPLLs to compensate something else.

    Petre

  • +1
    •  Analog Employees 
    on Mar 10, 2021 9:58 PM in reply to pminc48

    HI,

    I just realized that your scheme is good if one of the other references (REFA or REFB) are more stable than REFAA. In this case, the stacking of the compensation schemes makes sense. So you are good there.

    Sorry for creating confusion.

    Petre

  • Hello Petre

                   Are you meaning our configuration is correct (A) Add 1 Hz in REF B   (B)Add DPLL0 Profile 2 and it is  suitable to set the priority of profile 2 as ‘1’, am I right for question 2? 

    BR

    Patrick

  • +1
    •  Analog Employees 
    on Mar 15, 2021 1:48 PM in reply to PChen833

    Hi,

    I see you send emails about this applications to EZ and also to my colleague. Please use only one channel of communication.

    Yes, you were right. This happens when you deal with multiple people. I did not know the application when I responded first. Then my colleague explained it to me and we agreed you have a good approach to the system clock compensation.

    Yes, it is suitable to set Profile 2 with priority 1.

    Petre