The issue of jitter and how to deal with it in all its forms – clock, phase, and timing, among others- is a constant in almost any embedded developer’s life. Now, as the world has become increasingly connected, network and packet jitter complicate the developer’s life.
But this is not a problem that is faced only by developers of high performance communications systems. It is occurring in our homes and offices with the growing number of connected devices that often occupy the same confined transmission space.
The problems it causes have recently for me become personal. I now share my home and my home office with a variety of connected devices, both wired and wireless: USB mouse devices, a wirelessly connected printer, a wirelessly connected laptop and desktop computer, a Voice Over IP phone, wireless handsets for my home phone, an ebook device that has content delivered to it wirelessly, an MP3 player with a radio receiver and, oh yes, a mobile phone. And as the Internet of Things phenomenon grows, I am sure there will be still more, whether I need them or not.
As I know from personal experience, the various jitter problems from the interactions of these signals can cause a display on a device to flicker, introduce clicks and other undesired effects into audio signals, and cause loss of transmitted data between network devices. Often the only way to solve the problem without returning the unit is by keeping some physical separation between the devices, often putting the offending systems in separate rooms.
According to the text books, jitter is a measure of the deviation of any communications signal from true periodicity as specified in a design, often in relation to a reference clock source. Jitter manifests itself in many forms, such as in the frequency of successive pulses, the amplitude of the signal, or in the phase of the signal.
Jitter has always been a significant and undesirable characteristic of any design that makes use of high data rate workhorse communications links that embedded developers are familiar with: USB, PCI-e, SATA, and OC-48, among others. But now many other systems – such as mobile phones, wearable medical devices, Zigbee, and other wireless network devices in the home – are increasingly susceptible to a variety of jitter problems.
In a world where many of these connected devices, both wired and wireless, co-exist in the same environment, the problems become even more difficult, with jitter introduced into a previously functioning device by electromagnetic interference (EMI) and crosstalk with carriers of other signals.
And in an increasingly connected Internet of Things world such problems, such problems can be particularly hard to pin down and specify in a design. In this week's Tech Focus Newsletter are a number of design environments in which this is particularly important: M-PHY connectivity in mobile platforms, home automation networks , and wireless multimedia sensor networks .
Fortunately, there are a wide range of techniques and tools available, as noted in the articles and technical papers published on Embedded.com. Of these my Editor's Top Picks are:
Doing jitter timing analysis in the presence of system crosstalk
Jitter has become a significant percentage of a signal's interval, making it increasingly important to fully understand its types and sources. Most high-speed serial designs now use multiple lanes. Thus, crosstalk is nearly unavoidable.
Dealing with PLL clock jitter in advanced processor designs
This three part series examines the sources of clock jitter in designs based on advanced RISC and DSP architectures, how to characterize your system for such problems, and then how to resolve them.
The basics of clock jitter in embedded system designs
With the increasing system data rates, timing jitter has become critical in system design, especially where system performance limit is determined by the system timing margin, making it important to understand the impact of timing jitter.
Much more work remains to be done, both in applying existing tools and techniques to this problem as well as in developing new ones. I look forward to hearing from you about the methods and building blocks you use in your designs.
I also look forward to conferences such as UBM's DesignCon in late January next year, where a whole new set of methods and techniques to deal with signal jitter in all its forms will be discussed. I hope to be there and talk to some of you about this and other design challenges and how you deal with them.
Personally, I hope the new and better tools and techniques arrive quickly. I am adding connected – and noisy – mobile and wireless devices as fast as I am convinced they will be useful to me. But I am running out of rooms and tricks to keep them operating as they should.
Embedded.com Site Editor Bernard Cole is also editor of the twice-a-week Embedded.com newsletters as well as a partner in the TechRite Associates editorial services consultancy. He welcomes your feedback. Send an email to , or call 928-525-9087.