Broadband Class-AB Power Amplifier Techniques for Cable TV Application

摘要

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.