Direct Conversion Transmitter with Resistance to the Combined Effects of Power Amplifier Distortion and Local Oscillator Pulling

• Main Authors: Chieh-hsun Hsiao, 蕭介勛
• Other Authors: Horng, Tzyy-Sheng
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/84598543272321840733

博士 === 國立中山大學 === 電機工程學系研究所 === 103 === In the wireless communication system, owing to the increasing demands for high data rates and high energy efficiency, several practical implementation-related challenges arise in the design of conventional direct-conversion transmitter (DCT). According to the existing literatures, power amplifier (PA) nonlinear distortions and local oscillator (LO) pulling effects are the most critical factors to deteriorate the RF signal integrity. In this doctoral research, the above two issues have been rigorously investigated, and hence improved, the resultant degradation of DCT output signal quality. Based on the above thought, this dissertation includes two topics. The first topic begins with a theoretical analysis of a LO under directly modulated self-injection, which accounts for the transmitted signal quality deterioration due to pulling effects. Based on the presented theoretical deduction, an integrated approach by incorporating PLL parameters optimization and inner self-injection loop is proposed to mitigate the pulling effect. Furthermore, the next topic of this dissertation is dedicated to elucidate how the combined effects of PA distortion and LO pulling adversely impact a DCT in time-varying envelope modulation systems. To comprehensively enhance the transmitter linearity, an improvement approach for PA linearization and anti-LO pulling is developed by combining an open-loop digital predistortion (DPD) method and the proposed analog feedback compensation mechanism. Experiments are conducted to verify the feasibility of the proposed improvement approaches by implementing a prototype transmitter delivering the cdma2000 1x and WCDMA QPSK-modulated signals. Rigorous theoretical analysis and experimental verification prove that the proposed approaches to improving the DCT signal quality has great potential for application in the future complex modulation and wide bandwidth wireless communication systems.