Reconfigurable high efficiency power amplifier with tunable coupling coefficient based transformer for 5G applications

A frequency reconfigurable high efficiency power amplifier (PA) is presented for 5G applications using on-chip switchable matching networks. To cope with increased gate-drain capacitance (Cgd) in deep submicron CMOS PA design at mm-Wave frequencies, a tunable coupling-coefficient based transformer is proposed. This technique dramatically improves the neutralization of Cgd in a common-source PA while maximizing output power and efficiency. To reconfigure the PA between 24 GHz and 28 GHz, a low-loss reconfigurable matching topology is adopted using a switched substrate-shield inductor. Using the proposed techniques, a single-stage reconfigurable class-AB PA is demonstrated in 65 nm CMOS, achieving 42.6% maximum power added efficiency (PAE_max), 14.7 dBm maximum output power (P_{o, max}) at 24 GHz and 40.1% PAE_max, 14.4 dBm P_{o, max} at 28 GHz. The PA occupies a core area of 0.11 mm² only.

I. Introduction

Frequency reconfigurable transmitter is an attractive choice for next generation mm-Wave communications (e.g., 5G, WiGig, E-band back-haul) for enabling low cost and a high-level of integration while supporting multi-GHz bandwidth. However, little study has been done in mm-Wave frequency reconfigurable power amplifier, which is considered the key building block of a transmitter [1]. The traditional reconfigurable circuits (e.g., voltage control oscillators, VCOs) use varactors for frequency tuning. However, the varactor is not a practical choice for mm-Wave PAs due to poor quality factor (Q), which can severely impact the power efficiency. The Q of a small inductor does not suffer from such dramatic degradation at mm-Waves because of the availability of low loss ultra-thick metal (UTM) layer in moderm CMOS technology. Thus, a tunable inductor without degrading Q is a better choice for mmWave frequency re-configurability [2].