Contemporary high-spectral-efficiency communication systems increasingly rely on complex modulation, with high-order constellations and multi-carrier signaling. These formats often have high peak-to-average-power ratios (PAPR). It is difficult to design power amplifiers (PAs) for high PAPR signal with good power efficiency and linearity simultaneously.
Strategies to improve power efficiency fit into established amplifier classes. Some aim to reduce standing current; others reduce supply-voltage overhead. There are also switch-mode classes and load-modulation classes. PA design arts using these classes alone or in combinations achieve good power efficiency for narrowband high-PAPR signals. However, these existing arts lack effective techniques for wideband systems. One of the bottlenecks is the limited-speed supply modulation.
There are several linearization schemes that have been presented to mitigate PA’s nonlinearity. Among these, digital pre-distortion (DPD) is currently the most popular. However, the conventional architecture, ADC-based DPD, requires high speed/resolution ADC, which is high cost and power hungry. It also requires large processor power and memory for time-domain information.
Two techniques are proposed to address the challenges of broadband Class-AB PA’s power efficiency and linearity separately. For efficiency enhancement, we introduce Instantaneous Supply-Switching technique. This technique improves efficiency by high speed current-mode supply-switching in response to instantaneous signal, unlike most prior supply modulation implementations which only responds to the signal envelope. For linearity improvement, we introduce Signal-to-Distortion-Ratio(SDR)-based DPD technique. This methodology only requires the power information of signal- and distortion- channel, which is more data efficient than ADC-based DPD. The hardware for SDR-based DPD therefore potentially has lower cost and power.
The intended application in this dissertation is cable TV upstream power amplifiers.