A switch mode resonating H-Bridge polar transmitter using RF ΣΔ modulation

Using saturated power amplifier (PA) as the last stage, polar transmitter has the potential to be the most power efficient architecture to transmit large Peak-to-Average Ratio (PAR) signals. In this work, a polar transmitter using H-Bridge configured Class-D amplifiers is proposed. To fully exploit low voltage resource, maintain linearity and meet the spectrum mask requirements, RF Sigma-Delta Modulation (SDM) is used. An on-chip transformer based filter network is designed to filter out SDM noise and provide load matching. The system verification is carried out by using Matlab passband simulation on a 13dB PAR mobile WiMAX signal. Evaluation of noise shaping and spectral regrowth shows the proposed architecture can achieve -45dBc/10kHz ACPR in a 140MHz bandwidth range. This provides a solid ground for the circuit design work.