| dc.description.abstract | In RF modules, transmitter consumes considerable amount of DC power. Improving the power efficiency of wireless transmitter would help extend the talk time of mobile devices. Polar transmitter has been proposed as a high-efficiency transmitter architecture. In this thesis, two important circuit components of polar transmitter, namely, envelope amplifier and power amplifier, are investigated.
Due to the ever-increasing data rate in modern communication systems, envelope amplifiers must be able to handle wideband signals while remaining highly efficient. To achieve both high efficiency and wide bandwidth for envelope amplification, one can use linear-assisted envelope amplifiers. In this thesis, the operating principles of linear-assisted envelope amplifiers are introduced. To verify the principles, a hybrid envelope amplifier is designed and implemented. The measurement results show that, with sinusoidal input, the envelope amplifier can operate up to 8 MHz and its peak efficiency is 60%.
High-efficiency switching-mode power amplifiers are often adopted in polar transmitters. Among switching-mode power amplifiers, Class-E power amplifier is widely used for RF power amplification. In this thesis, the theory and operating principles of Class-E amplifier are introduced. Following that, a 1.75-GHz Class-E power amplifier using a GaAs pHEMT transistor is designed, fabricated, and measured. Measurement results show that the saturation output power and the drain efficiency of the amplifier are 21 dBm and 50%, respectively.
For handset power amplifiers, output power of 1 Watt or above is required. In this work, a 1.95-GHz Class-E power amplifier using bondwire inductor is designed in TSMC 0.18-μm CMOS technology. Output power of 1 W is achieved by combining multiple transistors in parallel. The transistors are in cascade configuration in order to withstand the large voltage swing at the drain, which is a characteristic of Class-E power amplifier. Finally, in output matching network, the inductor is realized using bondwire in order to reduce the RF loss and improve the power efficiency of the amplifier. Simulation results show that the saturation output power of the amplifier is greater than 30 dBm and the drain efficiency and PAE at 30 dBm are greater than 50% and 45%, respectively.
In this thesis, the design of high-efficiency linear-assisted envelope amplifier and Class-E power amplifier are investigated. The design concepts are successfully verified by the implemented envelope amplifier and power amplifier.
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