Large-Scale Power Combining and Mixed-Signal Linearizing Architectures for Watt-Class mmWave CMOS Power Amplifiers

Millimeter wave (mmWave) CMOS power amplifiers (PAs) have traditionally been limited in output power due to the low breakdown voltage of scaled CMOS technologies and poor quality of on-chip passives. Moreover, high data-rates and efficient spectrum utilization demand highly linear PAs with high efficiency under back-off. A novel linearizing architecture which simultaneously employs large-scale power combining, linearization through dynamic load modulation, and improved efficiency under back-off by supply-switching and load modulation is introduced. A quarter-wave combiner that exploits lumped spiral inductor equivalents of quarter-wave transmission lines with higher characteristic impedance enables one-step, low-loss, eight-way combining with a measured efficiency of 75% at 45 GHz. Eight-way combining of stacked SOI CMOS PAs results in a PA array with watt-class (>27 dBm) saturated output power (3x higher than prior art) and ultra-wideband operation (33-46 GHz) in 45 nm SOI CMOS. Another 45 nm SOI CMOS prototype, a three-bit digital to mmWave PA array, utilizing the proposed linearizing architecture achieves 23.3 dBm of saturated output power at 42.5 GHz, PAE(-6dB)/PAE(peak) = 67.7% as well as excellent linearity (DNL < 0.5 LSB} and INL < 1 LSB using end-point fit).