A Polar Transmitter for Multi-mode Wireless Applications

In this paper, a transmitter including a linearassisted switch-mode envelope amplifier (LASEA) and a two-point Sigma - Delta controlled fractional-N phase modulator (TPSDM) is proposed and simulated. The LASEA can amplify wideband envelope signals efficiently and linearly, and its time delay is minimized. The TPSDM can up-convert wideband phase signals to the RF band, and its time response is much more agile than conventional PLL-based phase up-converter. These two modules make it possible to restore the RF signal at the final power amplifier stage with high precision. Simulation results verify these ideas. For EDGE signal, the LASEA has a neglectable impact to the EVM and spectral performance. The TPSDM degrades the EVM to 3.7% and the spectrum is degraded less than 10dB, much lower than the specification mask.