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PLL / Synthesizer with very short Lock Time

Hi ... Does Analog Devices have a fast PLL/Synthesizer chip with lock time of 2-3 µs to produce frequencies in the VHF band (typically 100-200 MHz)? Does such a chip have a VCO Freeze function (when input ref is down)?

  • Hello ix-sal,

    >  Hi ... Does Analog Devices have a fast PLL/Synthesizer chip with lock time of

    > 2-3 µs to produce frequencies in the VHF band (typically 100-200 MHz)?

    This is a good question, partly because there is no universal definition of "lock" on any PLL. Also, PLL acquisition has a linear and non-linear region, and predicting the lock time is not trivial. As a rule of thumb, we normal estimate the lock time as 10-20 time constants, where the time constant is 1/(loop BW). However, there are a lot factors that vary the time needed, such as damping factor, as well as one's definition of "lock."

    If we take the AD9516, for instance. Let's say we use a 50 MHz input with a 200 kHz loop BW. 1/(loop BW)=5 us. My guess is that the lock time would be <=50 us.

    > Does such a chip have a VCO Freeze function (when input ref is down)?

    The AD9516/17/18/20/22 have this feature.

    There may be parts in the ADFxxxx family that have a larger loop BW, and thus a faster lock time.

    -Paul Kern

  • Thanks a lot dear Paul FormerMember for the 'to-the-point' note.

    Now I see that fast chips like the ADF4196 can achieve wonderful results. But can it give me the VCO freeze (or holdover as it is called by Analog Devices) function? Is there some guide on this matter? Or a comparable chip with this function?

    With thanks again

  • The experts on those products don't monitor this forum, I recommend asking the question in the RF forum.

  • 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.

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    EZ Admin