High Linearity Millimeter Wave Power Amplifiers with Novel Linearizer Techniques

摘要

Millimeter-wave communications have experienced phenomenal growth in recentudyears when limited frequency spectrum is occupied by the ever-developing communicationudservices. The power amplifier, as the key component in the transmitter/receiver moduleudof communication systems, affects performance of the whole system directly and receivesudmuch attention.udFor minimized distortion and optimum system performance, the non-constant en-udvelope modulation schemes used in communication systems have challenging requirementsudon linearity. As linearity is related to communication quality directly, several linearizationudtechniques, such as predistortion and feedforward, are applied to power amplifier design.udPredistortion method has the advantages over other techniques in relatively simple struc-udture and reasonable linearity improvement. But current predistortion circuits have quiteudlimited performance improvement and relatively large insertion loss, which indicate theudneed for further research. In most of millimeter-wave amplifier design, great effort hasudbeen spent on output power or gain, while linearity is often ignored. As almost all theudpredistortion circuits operate at the RF frequencies, the linearized millimeter-wave com-udmunication circuit is still relatively immature and very challenging.udThis project is dedicated to solve the linearity problem faced by millimeter-waveudpower amplifier in communication systems, which lacks of e®ective techniques in this field.udLinearity improvement with the predistortion method will be the key issue in this projectudand some original ideas for predistortion circuit design will be applied to millimeter-waveudamplifiers.ududIn this thesis, several predistortion circuits with novel structure were proposed,udwhich provide a new approach for linearity improvement for millimeter-wave power am-udplifier. A millimeter-wave power ampli¯er for LMDS applications built on GaAs pHEMTudtechnology was developed to a high engineering standard, which works as the test benchudfor linearization. Actual operation and parasitic elements at tens of gigahertz have beenudtaken into consideration during the design.udFirstly, two novel predistorter structures based on the amplifier were proposed, oneudis based on an amplifier with a fixed bias circuit and the other is based on an amplifier withuda nonlinear signal dependant bias circuit. These novel structures can improve the linearityudwhile improving other metrics simultaneously, which can effectively solve the problem ofudinsertion loss faced by the conventional structures. Besides this, an original predistortionudcircuit design methodology derived from frequency to signal amplitude transformation wasudproposed. Based on this methodology, several transfer functions were proposed and relatedudpredistortion circuits were built to linearize the power amplifier. As this methodology isudquite different from the traditional approach, it can improve the linearity signifficantlyudwhile other metrics are affected slightly and has a broad prospect for application.