Power amplifier design for next generation WLAN
Date of Issue2017-03-20
School of Electrical and Electronic Engineering
To meet the demand of achieving a multi-Gbps data-rate for the next-generation wireless local area network (WLAN), the 60GHz frequency band is now being explored as a complementary to the existing 2.4GHz and 5GHz frequency bands for WLAN. To take advantages of the high data-rate at 60GHz and the long communication distance at 2.4GHz and 5GHz, transceivers for the next generation WLAN are required to support all of the three frequency bands. As a block which is critical to the communication distance, data-rate and power consumption of a RF system, power amplifiers (PAs) are very important and challenging to design for the next generation of WLAN. For the 2.4GHz and the 5GHz bands which have long been used for WLAN, reported PAs have all been designed separately for each band to optimize the performance. To reduce the circuit area and simplify the RF system for the next generation WLAN, a wideband PA with a bandwidth of 2 to 6GHz is designed in this thesis so that both of these two frequency bands can be supported by one PA. By using a technique to design output matching networks for both the fundamental and 2nd harmonic of Class-AB PAs with bandwidth larger than one octave, the designed PA demonstrates a maximum power-added efficiency (PAE) of 28.4% and an overall PAE above 19% in the entire bandwidth, which is comparable to the PAE of reported WLAN PAs designed separately for the 2.4GHz and the 5GHz bands. When compared to a counterpart without matching for 2nd harmonic, the PA shows a maximum improvement of saturated output power (PSAT) and PAE by 1.9dB and 7.5% respectively. From 2 to 6GHz, the PA is capable of delivering an output power of 11.12-13.24dBm with EVM=-28dB for 11n formatted signals with 64QAM modulation, and 9.31-11.31dBm with EVM=-32dB for 11ac format signal with 256QAM modulation. For the newly introduced 60GHz frequency band, a big challenge of PA design is to maintain good power performance in the large bandwidth of 57 to 66GHz. To address this challenge, it is analyzed in this thesis that both the inter-stage matching network and the output matching network of a mm-wave PA need to be designed with small mismatch in the entire operating bandwidth. For this purpose, the matching equations of transformer-based matching networks (TMNs) are derived, based on which a method to synthesize TMN is proposed and applied to a 60GHz PA designed for the 802.11ad application. Implemented in a 65nm bulk CMOS technology, the PA achieves smaller degradation of power performance even compared to reported works in more advanced CMOS technologies. From 57 to 66GHz, the PA is measured with PSAT of 13.94 to 14.35dBm, P1dB of 10.81 to 11.68dBm, and peak PAE of 18.9% to 21.1%. With an EVM of 8.91%, the PA is capable of delivering 16QAM modulated signal with an output power larger than 10.8dBm and PAE higher than 10.1% in all the 4 channels of 802.11ad.