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Glitch on the LMH1983 NO_LOCK indicator

Kikuo Mita
Intellectual 2515 points
Other Parts Discussed in Thread: LMH1983

When LMH1983 gets lock to the reference input, NO_LOCK indicator goes and back
between High and Low state.

Is it expected behavior?
If so, are there any way to remove such glitch?
If not, how long do you need to wait before the indicator gets stable?

Can you expect the minimum pulse width?

  • 0
    TI__Genius 13475 points

    The lock determination on the LMH1983 is a fairly complicated process in which the difference between the reference phase and the VCXO phase is compared, and there is a window of both amplitude and time over which it determines if LOCK has been achieved.   With the default component values in the datasheet, the loop bandwidth is very low, which means that the two phases come into alignment very slowly,  if there is jitter on Hin, it is quite reasonable to expect there to be a period of time during which the lock determination goes on and off.    It is hard for me to determine the time scale on the lower trace, but if it is indeed 10ms/div, then this would say that you are seeing this indeterminate lock state for 15ms, which for something with a loop bandwidth of ~1Hz, would not be surprising.

  • 0 in reply to Mark Sauerwald88474
    TI__Intellectual 2515 points

    Mark-san,

    Thank you for your feedback.