Ubiquitous coverage, the ability of a mobile device to wirelessly communicate as intended from any location in the world, is not a reality today. Multiple wide-area and local-area wireless systems are now deployed in various places around the world. These mobile systems include cellular, local area networks, personal area networks, and specialized networks. Characteristics of these systems span a broad combination of constant-envelope and envelope-varying signals, time-division (half duplex) and code-division (full duplex) multiplexing, and high (several watts) to very low (microwatts) transmitter output powers. As a result, demands on the RF power amplifier (PA) in a multi-mode application are daunting. Linear RF techniques are unlikely to meet all requirements for near-future mobile terminals - particularly the need to simultaneously realize long mobile-battery life while also providing multi-mode operation using bandwidth-efficient signals. Initial results show that newer polar techniques meet many of the objectives for multi-mode and multi-band mobile terminals, including those for battery life. This is information on the cutting edge of RF progress. This article compares and contrasts advanced architectures and presents encouraging preliminary direct polar modulation results.
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