Design and Stability Analysis Techniques for Switching-Mode Nonlinear Circuits: Power Amplifiers and Oscillators

Citation

Jeon, Sanggeun (2006) Design and Stability Analysis Techniques for Switching-Mode Nonlinear Circuits: Power Amplifiers and Oscillators. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/V4YT-YM88. https://resolver.caltech.edu/CaltechETD:etd-03242006-132815

Abstract

A design technique for kW level switching mode power amplifiers is presented. Several push pull pairs, independently tuned to Class E/Fodd, are combined by a distributed active transformer. The zero voltage switching (ZVS) condition is investigated and modified for the Class-E/Fodd amplifier with a non-ideal output transformer. All lumped elements including the DAT, the transistor package, and the input power distribution network are modeled and optimized to achieve the ZVS condition and the high drain efficiency. Two power amplifiers are implemented at 29 MHz, following the technique. The amplifier with two push pull pairs combined exhibits 1.5 kW output power with 85 % drain efficiency and 18 dB gain. When four push pull pairs are combined, an output power of 2.7 kW is achieved with 79 % drain efficiency and 18 dB gain.

Nonlinear stability analysis techniques, based on an auxiliary generator and pole zero identification, are introduced to predict and eliminate the instabilities of power amplifiers. The techniques are applied to two switching mode power amplifiers that exhibited different instabilities during the measurements. Self-oscillation, chaos, and hysteresis of a Class E/Fodd amplifier with a distributed active transformer are investigated by the stability and bifurcation analysis tools. An in-depth analysis of the oscillation mechanism is also carried out, which enables an efficient determination of the topology and location of the required global stabilization network. As the other application, the anomalous behavior observed in a Class-E power amplifier is analyzed in detail. It involves hysteresis in the power-transfer curve, self oscillation, harmonic synchronization, and noisy precursors. To correct the amplifier performance, a new technique for elimination of the hysteresis is proposed, based on bifurcation detection through a single simulation on harmonic-balance software. Also, investigated are the circuit characteristics that make the noisy precursors observable in practical circuits and a technique is derived for their elimination from the amplifier output spectrum. All of the stabilization and correction of the amplifiers are experimentally validated.

A simple nonlinear technique for the design of high efficiency and high-power switching-mode oscillators is presented. It combines existing quasi-nonlinear methods and the use of an auxiliary generator in harmonic balance. The auxiliary generator enables the oscillator optimization to achieve high output power and dc to rf conversion efficiency without affecting the oscillation frequency. It also imposes a sufficient drive on the transistor to enable the switching mode operation with high efficiency. The oscillation start-up condition and the steady state stability are analyzed with the pole-zero identification technique. The influence of the gate bias on the output power, efficiency, and stability is also investigated. A Class E oscillator is demonstrated using the proposed technique. The oscillator exhibits 75 W with 67 % efficiency at 410 MHz.

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