An improved outphasing power amplifier system for wireless communications

Spectrally efficient modulations such as MPSK and MQAM are desired for mobile wireless communications, but they require linear amplification. Limited battery capacity has imposed primary restrictions on the power consumption of mobile handset. In practice it is typically the final power amplifier stage that constitutes these real challenges for the designer. The outphasing power amplifier is one of the promising techniques that can simultaneously achieve high linearity and high power efficiency. With this approach, the amplifier can be operated in a very power-efficient mode, and yet the final output can be highly linear and free of intermodulation.; However, one of the disadvantages of this technique is the extremely tight tolerance on the matching of the two amplifier paths to achieve acceptably small out-of-band rejection. We proposed two novel calibration schemes to correct the path imbalance and compensate the error effects at baseband level. The foreground algorithm simply evaluates the imbalance through a set of calibration signals during a specific time period, while the background algorithm characterizes the imbalance by exchanging the two vector components and managing a downconversion loop. The background scheme has the advantage of being transparent to the regular data transmission. A prototype outphasing system has been constructed to demonstrate the two calibration schemes for CDMA IS-95, and -38 and -35 dBc ACI were achieved, respectively, compared to -28 dBc without calibration.; The efficiency enhancement techniques are investigated in the second part of this dissertation. Conventional hybrid combining provides ideal isolation at the cost of compromised efficiency. Chireix combining boosts power efficiency, however, distortion and intermodulation are created. A power recycling technique is presented to recover the wasted power back to the supply. Numerical calculation predicts 33%–83% improvement on the overall efficiency for various modulations. The experiment achieved a peak recycling efficiency of over 60% for CW, and 50% for CDMA. We also propose a modified Chireix scheme, which combines two class-D amplifiers with a transmission line coupler, to enhance the efficiency and improve amplifier isolation. Analysis and SPICE simulation predicted a significant improvement on the efficiency over hybrid combining. This method is suitable for CMOS on-chip implementation.