Power amplifier linearization for OFDM signal

OFDM (Orthogonal Frequency Division multiplexing) has several properties which make it an attractive modulation scheme for high speed transmission. One marjor difficulty, however, is its high peak-to-average-power ratio (PAPR). If a class A power amplifier is used, a 5 MHz OFDM signal should be back-offed to an unacceptable level which gives an average power efficiency of about 5%. To reduce the PAPR, many baseband techniques have been proposed. However, even these techniques are applied, a linear power amplifier is still required and the power efficiency cannot be improved too much. Instead of attempting to reduce peak-to-average power ratio, a power amplifier linearization technique called Envelope Elimination and Restoration (EER) is adopted in this project to amplify the OFDM signal. System simulation was done on a 5 MHz OFDM radio system to find out the required parameters of the EER PA. A 5 MHz bandwidth switching mode power converter, which is applied to linearize RF power amplifier, has also been designed using delta modulation with 500 MHz sampling frequency. The power converter was fabricated using AMS 0.8μm BiCMOS process. The measured maximum power efficiency is 80% and the maximum harmonic distortion is about -35 dBc. The power converter is used to linearize a nonlinear RF power amplifier which operates in 1.8 GHz to 2 GHz. The measurement results show that the EER power amplifier successfully linearizes the nonlinear power amplifier by reducing the maximum harmonic distortion to less than -30 dBc and raising the efficiency from 15% to 35% at 22 dBm output power