A 44–64-GHz mmWave Broadband Linear Doherty PA in Silicon With Quadrature Hybrid Combiner and Non-Foster Impedance Tuner

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Abstract
The proliferation of millimeter-wave (mmWave) bands across 24–90 GHz and the strict spectral efficiency requirements demand future transmitter front ends to operate across multiple bands with simultaneously back-off efficiency and high linearity—characteristics that typically trade off strongly with each other. In this article, we propose a simultaneously broadband, back-off efficient and linear mmWave Doherty power amplifier (PA) architecture with a quadrature hybrid, and a non-Foster inspired impedance tuner on-chip. The combination of transformer-based hybrid and the quasi-non-Foster tuner allows the architecture to synthesize optimal impedances to the PA across the 2-D variations of power back-off and frequency, enabling high back-off efficiency across a broad frequency range. In addition, the unique location of the tuner at the isolation port of the hybrid allows us to exploit its benefits while shielding the architecture from effects of tuner non-linearity, power losses, and typical stability concerns of traditional non-Foster circuits. For high linearity, we implement an emitter follower-based class-C bias network with boosting effect. The PA is implemented in a 130-nm SiGe BiCMOS process. Across 44–64 GHz, the PA achieves 18.5–21.5-dBm $P_{\text {sat}}$ , the peak collector efficiency of 26%–34.7% and 14%–23.2% at 6-dB back-off, maintaining back-off enhancement ratio of 2.77/2.53/2.37 (1.39/1.27/1.19) at 46/52/62 GHz compared to the class-A (class-B) operation. It supports 6-gigabit-per-second (Gb/s) 64-QAM signal with −26.5-dB/−28.3-dBc error vector magnitude (EVM)/adjacent channel leakage ratio (ACLR) at average $P_{\text {out}}$ /power added efficiency (PAE) of 14.6 dBm/15% at 54 GHz. This work achieves the state-of-the-art bandwidth among silicon-based mmWave PAs where higher than class-B back-off efficiency is achieved.
Funding Information
  • DARPA

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