Linearized performance evaluation of polar transmitter for EDGE

Polar transmitters are popular in today´s mobile communications. Envelope and phase information are processed separately and restored at or before the RF power stage depending on the PA configuration. Key components of a typical polar transmitter include an envelope modulator, a phase modulator and a PA. Some technical challenges are described in this paper and some solutions are followed together with simulation results. In order to achieve higher power efficiency, a power supply modulated class-E PA is proposed as the power stage. The variation of the class-E power supply causes AM-AM and AM-PM distortions which must be linearized. Predistortion is a feasible solution to improve both envelope and phase linearization. PLL- based phase modulators potentially offer a higher degree of integration than mixer-based modulators since no SAW filter is required. The modulation bandwidth is expanded by a two- point phase modulator and the modulation accuracy is improved by the phase interpolation technique. This results in a so-called 3-point modulator.