PLL / Synthesizer with very short Lock Time

Question

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)?

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ADIApproved · Answer

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