Theory Based on Device Current Clipping to Explain and Predict Performance Including Distortion of Power Amplifiers for Wireless Communication Systems

摘要

Power amplifiers are critical components in wireless communication systemsudthat need to have high efficiency, in order to conserve battery life and minimise heatudgeneration, and at the same time low distortion, in order to prevent increase of bituderror rate due to constellation errors and adjacent channel interference. This thesis isudaimed at meeting a need for greater understanding of distortion generated by powerudamplifiers of any technology, in order to help designers manage better the trade-offudbetween obtaining high efficiency and low distortion. The theory proposed in thisudthesis to explain and predict the performance of power amplifiers, including distortion,udis based on analysis of clipping of the power amplifier device current, and it is audmajor extension of previous clipping analyses, that introduces many key definitionsudand concepts. Distortion and other power amplifier metrics are determined in the formudof 3-D surfaces that are plotted against PA class, which is determined by bias voltage,udand input signal power level. It is shown that the surface of distortion exhibits veryudhigh levels due to clipping in the region where efficiency is high. This area of highuddistortion is intersected by a valley that is ‘L’-shaped. The 'L'-shaped valley is subjectudto a rotation that depends on the softness of the cut-off of the power amplifier deviceudtransfer characteristic. The distortion surface with rotated 'L'-shaped valley leads toudpredicted curves for distortion versus input signal power that match publishedudmeasured curves for power amplifiers even using very simple device models. Theuddistortion versus input signal power curves have types that are independent ofudtechnology. In class C, there is a single deep null. In the class AB range, that isuddivided into three sub-ranges, there may be two deep nulls (sub-range AB(B)), audledge (sub-range AB(A)) or a shallow null with varying depth (sub-range AB(AB)).