domingo, 21 de marzo de 2010

V. High Efficiency Power Amplifier Design

High Efficiency Power Amplifier Design
Wireless network operators main requests are operational costs reduction and, at the same time, system capabilities increase. In particular, deployment of smaller base stations, featured by higher flexibility, efficiency and lower cost, becomes one of the system suppliers main goals. In this scenario, power amplifiers play a key role, becoming crucial elements of transmitter units in many microwave systems, including mobile phone applications, satellite payloads, microwave transponders, and many others.
Usual PA design approaches seek high power efficiency coupled with suitable gain and output power levels. The former is required to improve battery lifetime and to ease thermal management, thus reducing operating cost, while the latter specifications are needed to reduce the number of amplifier stages together with unit size and weight, thus decreasing manufacturing costs. Such requirements are contrasting ones, therefore demanding a design compromise on achievable performances.
To increase the amplifier efficiency performances, a proper selection of bias point and voltage and/or current waveform shaping become mandatory. For RF application, the best design solutions become the Class E and Class F approaches.
For microwave applications other design strategies have been proposed, in particular for narrow-band applications, based on harmonic tuning design strategies.
In this module, a comprehensive theory of high efficiency power amplifiers design criteria is presented. Starting from simple power balance considerations, extended to encompass the general problem of power amplifier design, traditional Class E and F design strategies are reviewed. Novel harmonic tuning strategies are presented and a comparison is carried out. Useful design criteria are inferred for the design of input and output networks of high efficiency / high frequency power amplifiers.

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