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Unformatted text preview: Self-adaptive biasing technique for microwave bipolar amplifier linearisation K.W. Lau, Q. Xue and C.H. Chan A novel linearised bipolar amplifier topology, integrating both reduc- tion of baseband distortion and self-adaptive biasing techniques, is presented. The linearising circuit suppresses more than 25 dB of the spectral regrowth for the first-order sidelobes and reduces up to 36% DC bias power of the amplifying transistor. Introduction: Microwave power amplifiers are indispensable elements in wireless communications systems and are inherently nonlinear. They are also the critical components that dominate the power consumption of portable devices. The stringent requirement on spectrum emission usually results in their low efficiency. Pre- = post- distorters [1, 2] and active bias networks [3, 4] , which utilise the nonlinearity of microwave diodes, are the highly cost-effective tech- niques for portable devices. However, suppression of the intermodu- lation distortion (IMD) is limited by the rigorous nonlinear characteristic matching between the diode lineariser and the power amplifier. In this Letter, a shunt forward-biased diode linearising circuit is proposed to reduce the baseband distortion (typically called low- frequency even-order IMD products) and perform self-adaptive current biasing. Significant suppression of the spectral regrowth and simple adaptive power management are both successfully demonstrated by the presented experimental results. Circuit description and operation principle: The schematic diagram of the proposed amplifier is shown in Fig. 1 . The linearising circuit mainly consists of an RF choke L D , a decoupling capacitor C D , a forward-biased diode Q D and a current-limited resistor R CL . It integrates both a baseband return path and a self-adaptive bias network. Source and load impedances are the highly desirable objectives for both linearity and efficiency in power amplifier designs....
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This note was uploaded on 05/01/2011 for the course ELECTRICAL EE5602 taught by Professor Xuequan during the Spring '11 term at City University of Hong Kong.
- Spring '11