Reinventing the Transmit Chain for Next-Generation
The need for more integration in multi-mode wireless devices is undisputed. The news media and wireless service providers have done an excellent job of raising consumer expectations, so that subscribers now expect instant access to voice, text, web, location-based, and mobile TV services in their handsets—without sacrificing battery life, form factor, or convenience.
In a traditional design, each service requires its own dedicated signal chain. So, as each feature is added, the pressure to integrate and include chips with small footprints intensifies. In response, the semiconductor industry has leveraged its expertise in design, foundry process improvements, packaging, and manufacturing to shrink radio modems to smaller and smaller form factors. However, high-power device structures, such as those found in RF power amplifiers (PAs), do not benefit from CMOS geometry shrinks as digital and small signal structures do. Instead, GaAs materials are typically used to support the necessary voltage swings that are required for adequate output power and linearity in RF PAs. Unfortunately, the continuing pressure for smaller circuitry raises important concerns, specifically the tradeoffs between efficient use of power and acceptable linearity.