Lock time reduction in AD9549


My customer used AD9549 in holdover mode.

She wants to reduce the re-locking time of AD9549 when REF_IN was supplied again after that did not been for a while.

1. Could you recommend a method to reduce the re-locking time in AD9549 except for changing internal loop filter bandwidth or Icp ?

2. Please recommend a new device that can set holdover mode and a shorter re-locking time than AD9549.


  • Hi Paul kern,

    Thanks for your reply.

    The Time Threshold Programming Range of AD9548 is shorter than it of AD9549 as the below.

    In this case, my customer guess that the lock time of AD9348 is shorter than AD9549 or it would be able to set shorter.

    Is it right?

    Thanks in advance.

  • 0
    •  Analog Employees 
    on Aug 23, 2016 8:53 PM

    Dear JhShin,

    You can change the lock detect threshold. It's important to remember that there is no universal definition of "lock" on a PLL.The lock detect threshold is for your information only, and you'll need to experimentally determine the most meaningful setting for your application.

    I don't recall the default setting of the AD9549 lock detector, but if it's anything like the AD9548 (which I think is true), then the default lock detect threshold is tight for most applications.

    -Paul Kern

  • 0
    •  Analog Employees 
    on Sep 7, 2016 10:26 PM

    JH - The lock detection section enables the user to tell the device when it should consider itself locked, it should not alter the dynamics of how the device goes about settling; they can increase that speed by altering the damping factor and loop filter bandwidth.  Is the settling time being sought by your customer referring to settling to the phase of the new reference or are they also changing frequency?  How close to the final frequency does the output need to be for them to consider the device is locked?

    They can use the threshold settings to have the device indicate it has reached lock sooner, but that doesn't mean the frequency response is any different.  Referring to the plot below, if you set the threshold to X, you can see that the device considers itself locked much sooner than if you set it to Y, even though the frequency response is unchanged.

    If they just want the device to identify itself as locked sooner, they can widen the threshold, but if their threshold is specific, then it's unlikely the AD9548 will settle any faster than the AD9549.

  • 0
    •  Analog Employees 
    on Aug 2, 2018 3:33 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin