Phase difference

What is Plesiochronous

In this short article and your next 2 minutes, you are going to learn “What is Plesiochronous” and (be careful – once you know it you cannot un-know it), you can brag about this concept (and this seemingly-complicated word) to your friends (and foes). So, what is it? What does Plesiochronous really mean and what is it used for?

It is related to TIME (you guessed it right, due to the word “chronos”), but what is so special? If you have been following this website, we have talked in detail about “time and clock synchronization” in a series of articles, however, Plesio+chornous is “slightly” different (pardon me for the pun).

Well, if two or more things (clocks/actions/waves/bits/pendulums) are “almost” synchronized, but not 100% exactly synced, these are Plesiochornous. This is NOT the same as syntonization.  Here is the summary:

Asynchronous: Without any frequency synchronization. (As the frequency itself is not the same, there is no need to talk of phase synchronization as sometimes you will see them match and other times it will be running out)

Asynchronous Pendulum clocks







Syntonize: To only match the frequency, without regards to the phase. Here the phase difference will be seen but that difference will remain constant, as opposed to what we see in asynchronous system. Mesochronous: Same frequency, however, unknown phases.

Phase difference











Synchronous: In exact lock-step with the source. To synchronize is to match the frequency (and phase) with the source. (Note: The term “phase” tends to become over-encompassing though as we start considering longer duration of time. Eg. Seconds should match exactly, Minutes should also match, so should the hours, and day, month, year, etc. To avoid the confusion with the phase/tick the synchronization of other bigger duration is known as ToD (Time of day) synchronization, not just plain phase synchronization). Isochronous: A term used for the events occurring  at equal time intervals.

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Pendulum Clock Synchronous







Plesiochronous: In nominal sync with the source, only slightly different within margin.









So, there you go, now you know what is Synchronous, Mesochronous, Isochronous, Plesiochronous and what it means to Synchronize and Syntonize! Hope it helped you gain bragging rights 🙂

If you liked the article and learnt something new today, share your knowledge with others and help them catch-up with you!


Jagmeet Singh Hanspal 

Jagmeet is a Senior Technical Leader and has worked with various organizations like Ericsson, Juniper Networks, TranSwitch Semiconductors in the field of Telecommunications and Embedded Systems. You can contact him via his Linkedin profile. His interests include Linux, Micro-controllers, Programming, Parallel Processing, Data Visualization, Networks, Synchronization protocols, Statistical analysis etc. You can find more about his profile from Author’s personal page.

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