High-efficiency and broadband PA design considering the impact of device knee voltage (2019)

The new 5G communications system requires the power amplifier (PA) circuits to be operated with high efficiency at both peak and back-off power within a broad RF and video bandwidth. The new 5G signal has an increased complexity for the modulation scheme, resulting into a high signal peak-to-average ratio (PAPR). In consequence, the performances of the PA are limited. This thesis addresses the design analysis for high efficiency and broadband PAs based on harmonic tuned continuous class-F (CCF) mode by including the I-V knee interaction. Most PA modes and waveform engineering techniques to elevate PA performances are ignoring the practical knee voltage. This thesis addresses the new performances of the CCF mode when the I-V knee interaction from the waveforms in considered. The current waveforms are a function of voltage waveforms, that clipped and generates harmonics when voltage waveform is expanded into knee region, as the device is operated with compression. The new performances of the CCF mode does not follow the ideal theoretical performances, instead, changes along the phase of 2nd harmonic impedance termination.
The interaction of the current and voltage (I-V) knee on the waveforms of CCF mode allowing load-pull emulation to be calculated, where the α in CCF mode is the function of 2nd harmonic impedances termination in the actual device’s load-pull technique. In this research, the load-pull emulation is performed only through mathematical calculation in MATLAB by manipulating the equation of drain current and voltage waveforms. Output power and efficiency contours are generated from load-pull emulation for CCF mode, that have almost identical behaviour with the actual device model and measurement, when the non-linear I-V knee interaction is considered. This emulation also investigates the efficiency of the device at the output power back-off (OPBO) range, with the sweep of the α parameter. The investigation of the new CCF mode with I-V knee interaction is used as guide for a PA design with restriction of the phase of 2nd harmonic impedances termination to keep the efficiency high across wide bandwidth.
The video-bandwidth (VBW) performances for the PA can be extended using a baseband termination circuit at the device’s output to shift the resonance frequency coming from the bias network and the device’s output parasitic capacitance. The VBW enhancement is crucial in the 5G communication system where it is expected to operate up to 800 MHz, or even beyond this frequency, for the instantaneous bandwidth. Analyses are made on the components used in the baseband termination circuit in this thesis, where the VBW can be further extended by having the highest value of the shunt capacitor that is placed close to the device, with the lowest equivalent series inductance. This configuration shifted the resonance frequency and reduced the impedances seen by the device output on the matching and bias network. All the methods described in this thesis are adapted to design and investigate the performances of compact PA with integrated matching and baseband termination network. This PA is aimed to operate with high efficiency at the 50 Ω load impedances and at load modulated output power back-off across a wide-bandwidth. A CW simulation tests are used to evaluate the performances of the PA at peak power, while 2 tones signal with sweep frequency spacing is used to evaluate the VBW performances.