Frequency Reconfigurable mm-Wave Power Amplifier With Active Impedance Synthesis in an Asymmetrical Non-Isolated Combiner: Analysis and Design

A frequency reconfigurable millimeter-wave (mm-wave) power amplifier (PA), which can be programmed to operate efficiently for a wide swathe of the spectrum, approaching an universal transmitter, can enable a wide range of novel applications in high-speed communication, sensing, and imaging. Classical techniques to allow large operating range either rely on broadband higher order output combining networks or tunable passives, both of which tradeoff directly with output power and efficiency. In this paper, we present an active impedance synthesis methodology that exploits the interaction of multiple unit PA cells in an asymmetrical non-isolated combiner to synthesize complex mm-wave impedances in a programmable fashion. This allows the interacting power cells to see their optimal load-pull impedances for high-efficiency frequency-reconfigurable operation in an efficient combiner network with no lossy variable passives. Compared to a symmetrical combiner, this enables the network to break the strong tradeoffs between output power, efficiency, and frequency reconfigurability, allowing it to achieve N times the Bode-Fano bound compared with an N-way symmetrical architecture. As a proof of concept, an integrated PA, which is in a 0.13-μm SiGe process, is demonstrated to achieve P
_sat
of 23.6 dBm at a power-added efficiency (PAE) of 27.7% at 55 GHz with a frequency reconfigurable P
_sat
,
_-1
dB bandwidth of 25 GHz (40-65 GHz) and a PAE,
_-1
dB bandwidth of 20 GHz (40-60 GHz). Multi-Gbps data rates are demonstrated with non-constant envelope modulations across the frequencies 40-60 GHz.