Brainstorm - Communication Buses

Thu, 03/20/2008 - 10:26am

As electronic networks become more data-intensive and intelligent subsystems increase in number and complexity, bandwidth limits, signal interference, and device compatibility issues become important concerns. What are some ways that an electronic circuit designer can address these challenges?

Simon Prutton, Akros Silicon Simon Prutton, Akros Silicon

Ethernet offers the highest degree of robustness and interoperability for data-intensive networking. However, Ethernet’s inability to deliver both power and data over the same CAT-5 cable becomes a bigger issue as processing and intelligence moves closer to the edge of the network.
As a solution, the IEEE 802.3af Power over Ethernet (PoE) standard introduced a means for delivering up to 13W to a “powered device,” such as a VOIP phone, from a PoE-enabled Ethernet switch or other “power sourcing equipment.” The upcoming 802.3at standard more than doubles that power level to 30W.
As a result, PoE is seeing rapid adoption in a wide range of markets seeking to add “plug-and-play” power capability to the system. PoE increases system flexibility to significantly reduce support and deployment costs, while eliminating the overhead associated with a separate power infrastructure. Because of IEEE’s standards-driven approach, 802.3 effectively allows engineers to realize these benefits in a way that ensures their systems will continue to work with the today’s applications and in the networked world of the future.
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Chris Ferland, Fairchild Semiconductor Chris Ferland, Fairchild Semiconductor

High resolution displays are becoming a must-have for many consumer electronics. The bandwidth required to support these displays requires...tradeoffs based on data rate, signaling method, acceptable levels of EMI, number or wires, mechanical considerations, power consumption, and on and on. Existing signaling technologies may work up to the data rates necessary for these applications; however the EMI associated with these signals when run at very high speeds is often impractical. Another option is to use parallel signals. In display applications, 24 or more wires are often used to transmit a single image. This will reduce the data rate of any individual wire but may introduce new issues with signal routing or mechanical limitations.
Serializers and deserializers, or SerDes, can be used to solve these issues in high bandwidth applications. In displays, for example, SerDes may be used to serialize the parallel data, transmit the data across a medium using a high speed differential technology, and then deserialize the data back to its original parallel form for the display to use.
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Mark Leinonen, ROHM Electronics USA, LLC Mark Leinonen, ROHM Electronics

Today’s high-end automotive electronic systems typically utilize multiple networks, including CAN, LIN, FlexRay, MOST, Bluetooth and others — all operating in the same vehicle at different data rates. The near future will see cars using LAN interfaces to communicate with the infrastructure and with each other, underscoring the need for circuits designed to prevent interference among automotive frequency bands. Because of their greater efficiency, switching power supplies are seeing rapid growth in automotive applications. However, SMPS operate at frequencies that can couple into adjacent circuitry and thus interfere with other systems. This key design challenge is answered with switch-mode power supply ICs that are user-selectable for operation at different frequencies depending on the application. In this way, interference with other systems is completely eliminated. Another solution, LVDS ICs for video transmission, uses spread spectrum technology to reduce interference with other systems. These ICs also reduce emissions by allowing users to adjust signal swing to lower signal levels. USB interfaces are being introduced for portable device connection in automotive applications owing to the development of single- and dual-channel USB power management ICs that protect against inrush currents or excessive current draw from connected devices.
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Jay Tyzzer, Nordic Semiconductor Jay Tyzzer, Nordic Semiconductor

A Body Area Network (BAN) is a group of wireless sensors carried by a human, such as the Nike + iPod Sport Kit that uses a sneaker-based sensor and iPod Nano to enhance training.
BAN sensors must be light, compact and...inconspicuous. That means coin cells, and that means sensors that boast ultra low power consumption if those tiny batteries are to last nearer a year than a day.
For a one-size-fits all global wireless solution, the 2.4 GHz ISM band means interference. Employ a robust co-existence strategy within the BAN sensors. This isn’t aided by the human body’s 60% water content – a great electromagnetic radiation absorber.
BANs...must “plug and play”...out of the box. A 2.4 GHz RF transceiver for BAN applications should handle around 12 mA peak transmit/receive currents with average operating currents of 2 µA. When combined with an optimized protocol stack, a one-year battery life on a CR2032 coin cell is often achievable.
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Kurt Radtke, ZMDKurt Radtke, ZMD 

In automotive electronics, sensor and actuator and ECU applications do not demand expensive solutions...The data implemented as analog signals, typically in a linear voltage range of 0.5V to 4.5V...due to the MCU on the ECU, which provides several analog inputs with required integrated ADCs. A resolution of 12 bits is almost always sufficient for this situation.  
When SSC-suppliers require a digital signal to adjust sensors, extra steps are taken to make the conversion, resulting in an increased accuracy of 16 bits.
There is PWM-signal processing (which) cannot be defined as a purely digital communication signal since the pulse modulation is still an analog component.
Rather than unnecessarily expensive systems...use digital signal processing for simple stand-alone sensors. When transmitting digital signals, implementation works well when based on communication standards like LIN or PAS.
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