A Hybrid Digital Transmitter Architecture for High- Efficiency and High-Speed Applications

Abstract

A Quadrature/Polar hybrid digital transmitter architecture (HB-TX) is proposed in this paper, which consists of a main digital power amplifier (DPA), an auxiliary DPA, and a low-bit phase selector. In the proposed HB-TX, coarse polar modulation is realized by combining the main DPA and a low-bit selector, while a fine quadrature modulation is realized by the asymmetrical quadrature recombination of main and auxiliary DPAs in a small range. Through coarse and fine modulation, the HB-TX realizes fast signal modulation and does not require high-speed and high-resolution phase modulator. With the coarse polar modulation, the HB-TX achieves high efficiency which is close to that of polar transmitter and no longer suffers from 3 dB back-off. Since the asymmetry of two-path DPA arrays improves the isolation between two channels, local oscillators (LOs) with 50% duty cycle is employed to further improve the HB-TX's efficiency. Simulation results show that the HB-TX with a 4-bit selector achieves 23.7-dBm peak output power with 39.2% peak power added efficiency (PAE). When modulating a 64-QAM signal with 80-Msym/s symbol rate and 6.5-dB peak average power rate (PAPR), the HB-TX improves the average drain efficiency from 16.3% (achieved in quadrature transmitter) to 22.2%. The average output power that is delivered by the HB-TX is 17.6-dBm with 17.4% average PAE, while the error vector magnitude (EVM) is -35.87 dB.