A Transmitter IC with Supply Tuning for Frequency-Reconfigurable Antenna Cluster

Active reconfiguring of the frequency response of an antenna cluster was recently demonstrated involving an integrated transmitter and antenna cluster. The tuning method solely relies on scaling the antenna cluster feed amplitudes and phases, and entirely eliminates the typically required on-chip or off-chip matching networks. This work now advances the prior art by demonstrating and presenting improved solutions for on-chip amplitude and phase scaling blocks. In this paper, we present an optimization for phase resolution, resulting in 5 bit phase tuning architecture. Furthermore, we present an analysis of amplitude tuning on the efficiency and impedance variation for antenna cluster feeds. Two different amplitude scaling alternatives are considered: formerly studied switched capacitor power amplifier (SCPA) topology and a new low-dropout-regulator (LDO) based supply scaling of the class-D power amplifier. The designs are simulated in a 28-nm bulk CMOS technology at 1.5 GHz and 5 GHz respectively. The simulation results indicate that the LDO-based supply tuning method is superior to SCPA in terms of variation on efficiency and output impedance over the amplitude tuning code. The proposed circuit provides 15 dB amplitude tuning range with a 54 Ω impedance interface and 48% drain efficiency at 1.5 GHz whereas it provides an impedance interface of 84 Ω with 23% drain efficiency at 5 GHz.