A compact dual-band digital doherty power amplifier using parallel-combining transformer for cellular NB-IoT applications

摘要

Narrowband Internet-of-Things (NB-IoT) is a newly developed 3GPP protocol optimized for low-power wide-area IoT applications and is evolving toward the future fifth-generation (5G) mobile communication. It specifies at least 23dBm maximum output power for long-range communication, stringent emission mask compatible with guard-band or in-band scenarios, and it supports multiple operation bands from 699 to 915MHz (LB) and from 1710 to 1980MHz (HB). For cost reduction, longer battery life, and fast time to market, the integration of high-power high-efficiency power amplifiers (PAs) on-chip is greatly demanded. To benefit from advanced CMOS technology, the digital polar transmitter has become a very attractive architecture for NB-IoT applications [1]. To simultaneously support dual bands for user flexibility, the traditional solution is to implement two separately optimized PAs [2], which requires extra design effort and increases die area. An ultra-compact single-transformer-based parallel power combiner proposed in [3] provides optimum load transformation in the two operation bands. Moreover, to support higher throughputs and achieve better spectral efficiency, high peak-to-average-power-ratio (PAPR) multi-subcarrier modulation is adopted in NB-IoT, which requires the PA to be efficient not only at peak power but also at power back-off (PBO) to extend battery life. Efficiency boosting techniques of digital Doherty PAs have been shown in [4-6], but two transformers are needed in the passive network. In this work, a high-power digital Doherty PA for NB-IoT applications is proposed and introduces a parallel-combining-transformer (PCT) power combiner for dual-band coverage, back-off efficiency enhancement, and ultra-compact implementation.