Harmonic tuned GaN-based power amplifiers with enhanced efficiency, bandwidth and thermal management

High efficiency broadband power amplifiers (PAs) are increasingly in demand for the novel wireless communication standards to meet the high spectral efficiency and integration requirements in front-end modules (FEMs) and massive multiple input multiple output (MIMO) active antenna systems. Modern PAs are therefore developed to address extended operational bandwidth requirement under increased peak data rates but still suffer from inefficiencies resulting from complicated matching networks and large power dissipation in the active devices. These can degrade the power efficiency and linearity performance and increase the heat density, particularly for high power PAs (HPAs), which in turn affects the overall performance and reliability of transmitters. To address these challenges, a two-pronged approach is taken in this thesis: (i) novel techniques to increase power efficiency and reduce the thermal load over wide bandwidths are proposed and (ii) efficient thermal management techniques are investigated. First, to enhance power efficiency while increasing bandwidth novel harmonic impedance tuning at the device input are developed for two distinct classes of operation: continuous-mode inverse class GF (CCGF−1) and the continuous class GF (CCGF). For the CCGF-1, we propose new closed-form drain current expression to model the PA current waveforms in the time domain. We then use this analytical expression to exploit second source harmonic impedance manipulation in order to expand the design space of the output matching circuit resistively. This approach allows to diminish the complexity of the design of the load matching network at the fundamental and harmonic frequencies and to achieve wider bandwidth while simultaneously improving drain efficiency across the new optimum admittance points. As a proof of concept, a wideband CCGF−1 PA is designed, fabricated and tested. Results show a drain efficiency of more than 70% from 3.05 GHz to 3.85GHz, a gain between 11 and 12.4 dB with a gain flatness of ± 0.7 dB and an output power at 3-dB gain compression between 39.9 and 41.4 dBm over the same frequency band. For the CCGF, the second source harmonic in CCGF is similarly optimized to flatten the power amplifier’s frequency response over a wideband range. Moreover, a new design space is explored by considering the effects of controlling the input nonlinearity of the gate-source capacitance (Cgs) on the drain current waveforms under continuous mode drain voltage waveforms