X-band Class-E Power Amplifiers with Dynamic Bias Control

Date The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. Multifunctional RF front ends need to transmit signals with varying peak-to-average ratios requiring high linearity which often implies low efficiency. This thesis studies high-efficiency class-E microwave power amplifiers as a potential candidate for linear amplification. Most part of this work is based on a class-E PA designed at 10 GHz with output power of 20.3 dBm(0.7 dB less than the specified maximum output power) and drain efficiency of 67 %. Generally, a class-E PA is designed to operate in the saturated (nonlinear) regime and does not maintain high efficiency at lower input power levels. To enable class-E amplification of signals with varying envelopes, the idea of dynamic control of the bias supply is brought up. A coupler and detector at the output of the PA provide a feedback signal to the drain bias controller based on an efficient DC-DC converter. The feedback signal is compared with a reference voltage and the drain bias is varied to obtain the desired output power. When compared with a PA with constant drain bias, the average efficiency of the PA with dynamic biasing is improved by a factor of 1.4 over an output power between 15 and 20 dBm. The linear relationship between the drain bias and output signal amplitude of a class-E PA enables linearization using the Envelope Elimination and Restoration (EER) technique. In this thesis, linearity characterization of X-band class-E power amplifiers using different technologies operating in EER mode is discussed. The PA is characterized in terms of its AM-AM, AM-PM conversion and two-tone intermodulation products in the context of EER mode of operation. Measurements of intermodulation distortion are compared with harmonic balance simulations using a TOM model provided by the device iv manufacturer. It is shown experimentally and through simulations that the amplifier in EER mode has improved linearity while maintaining high-efficiency operation. To achieve better linearity, a lookup-table based baseband open-loop digital predistortion is proposed and carried out at two-tone frequency spacing of 20 KHz, 200 KHz, 625 KHz and 1 MHz. The last part of the thesis is investigation of class-E amplifier driven phased array for efficiency and increased functionality. Side lobe control and scanning of the array is accomplished by dynamically biasing the …