Communications Technology

Connectivity is a key feature of modern embedded products. There’s a wide range of communications modes that can be used, but which is the best for your design? Should you use a wireless technology such as Wi-Fi or Bluetooth and, if so, which one should that be? Or would wired communication, such as Ethernet, be the best way forward?

In this section, New Electronics reviews the latest communications technologies and brings visitors to the website information on how these technologies are being applied.

A matter of protocol

Serial communications: system requirements and design challenges. By Nilam Ruparelia. By the late 1990s, as Moore’s Law continued to deliver semiconductor integration and processing power, high bandwidth chip connectivity had become a significant bottleneck. It quickly became clear that, if the industry did not figure out ways to increase data transfer rates among high performance logic chips (like cpus, wan framers, dsps and network processors), it would end up with many thousands of pins on each multimillion gate device. High speed serial communication surfaced as the obvious solution and cmos technology, at geometries of 0.18um and smaller, enabled integration of high speed plls and I/Os in standard logic chips. Unfortunately, the enthusiasm for high speed serial communication resulted in a plethora of confusing serial protocols. A large number of protocols addressed the ‘sweet spot of 1 to 3.2Gbit/s. To make matters worse, some six other protocols surfaced in the 2.5 to 3.2Gbit/s serial rate range. At first glance, it may seem an abundance of standards would mean a fragmented market, or that a lot of energy was being spent primarily on I/O, but most protocols cater to specific applications. It is useful to understand how system level requirements make one protocol more applicable than another for a particular application. Similarly, we can glean useful information from board design challenges related to signal integrity issues, helping to prepare us for next generation protocols and system designs at 5 to 10Gbit/s.

The eyes have it

High speed serial communications links need to be designed and tested carefully. By Graham Pitcher. It wasn’t long ago that data communications was a relatively simple design task. Today, all that has changed. To meet the demand for higher and higher data rates, designers are moving to serial data links. Along the way, they are having to deal with some fundamental physical issues. Yves Braem is a signal integrity engineer with Tyco Electronics’ circuit and design department (www.tyco.com). He said: “With higher data rates, the problems you encounter become more and more significant. As frequency increases, transition times get smaller and the electrical waveform ‘sees’ the transmission path in ever more detail. This means you have to design carefully.” In Braem’s opinion, high speed data links bring an increasing number of signal integrity problems as data rates move beyond 2.5Gbit/s. “Designers not only have to select reliable and first class components and interconnections, they also have to consider the interfaces between the different ‘building blocks’ in the system.” In his view, these interfaces used to be electrically short because the signal wavelength was much bigger than the component itself. “Now,” he continued, “the interface itself can jeopardise the whole interconnection quality.” He believes three aspects need to be considered when designing high speed backplanes: pcb traces; connector/board interfaces; and board to board connectors. “The throughput of signal traces in pcbs is limited by trace losses, consisting of skin effect and dielectric losses,” he noted. These losses combine to limit the total trace length in the system and, therefore, system size. Dielectric loss can be reduced by specifying low loss pcb materials, whilst skin effect losses are reduced through the use of wider traces. But designers may not be able to specify wider because of space constraints and other factors.

Voice in the wilderness?

As IP networks take on more voice traffic, the rise of IP telephony should have a profound effect on technology developments. By Jim Chalmers.

Picture this

Do you have a digital audio broadcast receiver yet? Would you like one? By Philip Ling.

A tangled web

A web of multi source agreements threaten to engulf 10Gbit transceiver modules. By John Walko.

Let’s get physical

As the communications industry – whether wired or wireless – strives towards ever higher data rates, the role of physical layer (PHY) devices is becoming increasingly important and, in some instances, contentious. It’s not surprising that the range of technologies, architectures and design options being offered is becoming increasingly complex. With Gigabit Ethernet and 10Gbit Ethernet gaining momentum, most competition will be played out in these sectors. PHYs basically provide access to the Media Access Control (MAC) layer through a management interface. If you consider high data rate optical links, such as Gigabit Ethernet, the PHY chip is really a mux/demux combination that acts as a liaison between optics and electronics, such as the framer.

In position

Joel Avey of Trimble explains how system integrators (with or without a background of gps experience) can determine which gps solution is appropriate for their applications.

Moving in

Linux is penetrating further into the network infrastructure, aided by network processors. By Bill Weinberg.

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