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 2.4—2.5GHz 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).

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 50Ω 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.