DSP-Assisted Wireless Transmitter System and Architecture Designs for Power Efficiency Enhancement
Date Issued
2009
Date
2009
Author(s)
Jheng, Kai-Yuan
Abstract
In general, the power amplifier (PA) is one of the most power-hungry devices in a tran-sceiver. Accordingly, the higher the PA efficiency, the longer the mobile handset de-vices can operate. Power efficiency and linearity are two key parameters to determine the performance of wireless transmitters. Linearity and power efficiency must be traded off in the PA. That is, we get more linearity while the power efficiency is decreased. Recent wireless communication systems adopt sophisticated modulation techniques such as 3π/8-shifted 8 PSK for EDGE, HPSK for WCDMA, and OFDM for WiMAX to achieve the increasing demand for spectrum efficiency. Using these complex modula-tions and multiple carriers causes envelope variations that force the PA to work at a large backoff to fulfill the linearity requirements of wireless communication standards. However, the operation under backoff leads to low PA efficiency. In addition, ana-log/RF devices suffer from process variation and often bring non-linearity and distortion into a transmitter system. DSP methods can perform more accurate computation of the signals than analog circuits. Nowadays, DSP is widely available at a relatively low power and cost in CMOS technology.n this dissertation, we study a promising PA linearization technique, LInear am-plifier with Nonlinear Components (LINC), which offers both high PA efficiency and high linearity of wireless transmitters. We focus on the low-cost DSP engine design for a LINC transmitter architecture. Moreover, we propose two multilevel LINC transmitter designs, Envelope-Adjusting Multilevel LINC (EA-MLINC) and Gain-Adjusting Mul-tilevel LINC (GA-MLINC), for power efficiency enhancement. Finally, we utilize the mixed-mode EDA tool ADS to verify these LINC transmitter designs. According to the simulation results, the 3-level EA-MLINC and 3-level GA-MLINC enhance the con-ventional LINC system PAE from 16.5% to 33.4% and 23.6% respectively and both satisfy the linearity requirements of the WCDMA specifications. Instead of the tradi-tional LINC using single-level scaling factor, our proposed MLINC utilize multilevel scaling factors to divide the PDF into several regions. Some research groups have fol-lowed this design concept to develop high-efficiency wireless transmitters. We believe our MLINC designs are valid and effective directions to achieve high-efficiency trans-mitter designs.
Subjects
linear amplifier with nonlinear components
LINC
out-phasing technique
power amplifier linearization
Type
thesis
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