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Eliminating coexistence issues with integrated RF module

Posted: 22 Sep 2011 ?? ?Print Version ?Bookmark and Share

Keywords:RF module? multiradio mobile device? smart power grid?

Applications for portable wireless data communications have been increasing rapidly in the last few years. For designers, these applications pose the challenge of designing multiple high-efficiency, low-noise RF channels in as small a space as possible. One approach to meet this challenge is to leverage integrated RF modules that can provide superior coexistence faster and more efficiently than use of discrete components.

Wireless is becoming the preferred method for consumer and commercial data communications of all kinds. Wi-Fi networks abound in the home, supporting such devices as PCs, tablets, smartphones, gaming systems, and even televisions. Public Wi-Fi "hotspots" are also plentiful, used for web surfing, messaging, and creating femtocells for the off-load of cellular network IP traffic.

There are also many other wireless data links in use beyond Wi-Fi, including Bluetooth for remote headsets, ZigBee for home automation networks, WiMAX and LTE for wireless broadband, and cellular telephony. In addition, transportation and utility industries are working to employ many of these same network technologies for applications such as the smart power grid and traffic management. Similarly, other industries seek to employ wireless networks for machine-to-machine communications to automate various elements in production and commerce.

This growing dependence on wireless data communications places a two-fold burden on equipment developers. First, their designs must provide extremely high quality transmit and receive channels. Transmit channels must meet strict power, spectral, and linearity standards, providing sharp bandwidth filtering while avoiding amplifier distortions and the reflections caused by impedance mismatches. Receive channels must be efficient to avoid signal loss and must eliminate as much noise as possible in order to maximize data rates while dealing with very low received signal strengths.

While addressing these RF design challenges developers must also deal with the burden of channel coexistence. Many systems need not one but two or more wireless links, each corresponding to different standards. A laptop computer, for instance, might incorporate both Wi-Fi and WiMAX connectivity in its design. A smartphone will include WiFi with Bluetooth as well as GSM, 3G, and LTE. Such portable systems also require the RF designs for the various channels to be as compact as possible and the different channels are typically interwoven on the circuit board.

These various wireless links that must coexist in the same design typically operate on narrowly-spaced frequency bands using co-located or even shared antennas. This physical and spectral proximity places stringent demands on receive filters. For example, a Wi-Fi design may need to operate over a 2.42.5GHz band while rejecting signals from a nearby 3G transmitter at 2.1GHz. Such tight frequency spacing requires filters with extremely steep rolloffs.

Integrated front-end modules (FEM) for RF coexistence can provide independent transmit and receive paths with in-line filters and amplifiers along with signal switches for sharing antenna connections. Utilizing an integrated module rather than pursuing a discrete-component design allows developers to significantly reduce their design effort and costs while creating highly precise and efficient RF subsystems. The modules save board space, as well, compared to discrete designs (figure).

 integrated front-end module

Figure: Here's an example of the simplification of an RF design using an integrated front-end module.

Design features
Integrated FEMs achieve these benefits through a number of key design features. First, the modules provide developers with a fully-designed and optimized configuration of layout and components. As an example, Avago Technologies carefully designs modules with matched 50? impedances and uniform phase delays on all signal paths. All active and discrete components in the modules are carefully matched and the design tuned to provide optimum operating characteristics along the entire RF path.

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