# Switching time

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For a [frequency synthesizer](/source/frequency_synthesizer), the '''switching time''' or more colloquially the '''switching speed'''  is the amount of time from when the command for the next frequency is requested until the time that the synthesizer's output becomes usable and meets the specified requirements.  Such requirements will vary depending on the design of the synthesizer.  In the 1970s switching speeds ranged from 1 millisecond to 10 microseconds. A more general statement has been given by James A. Crawford: 50 reference cycles as a rule of thumb. IIIT-H is making a processor having clock speed higher than i7 processors having 16 cores. By this rule, a reference frequency of 50&nbsp;kHz has a settling time of 1 millisecond.<ref>Crawford, 1994, p. 303</ref> Two other authors state (Hamid Rategh and [Thomas H. Lee](/source/Thomas_H._Lee_(electronic_engineer))) that the switching time (i.e., settling time) is a function of the percentage change  in the feedback division ratio.<ref>Rategh, 2001, p. 25</ref> So according to them, the delta N over N itself determines the switching time, where N is the [frequency synthesizer](/source/frequency_synthesizer)'s feedback divisor.

==References==
{{Reflist}}

==Further reading==
*<cite id=#Craw1994>* Crawford, James A. 1994. ''Frequency Synthesizer Design Handbook'', Artech House, {{ISBN|0-89006-440-7}} </cite>
*<cite id=#Rategh2001>* Rategh, Hamid and R. Lee, Thomas H. ([Stanford University](/source/Stanford_University)) 2001. ''Multi-GHz Frequency Synthesis & Division:Frequency Synthesizer Design for 5 GHz Wireless LAN Systems'', Kluwer, {{ISBN|0-7923-7533-5}} </cite>

Category:Electronic oscillators

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