A 31-45 GHz Wideband Cascode Doubly Neutralized CMOS Power Amplifier for 256-QAM Modulation

Abstract

A 31-45 GHz transformer-based cascode doubly neutralized power amplifier (PA) is implemented in a 90-nm CMOS process. To enhance gain, stability, and linearity at millimeter-wave (mm-wave) frequencies, a cascode double-neutralization technique employing cross-coupled capacitors is utilized demonstrating its effectiveness in broadband mm-wave CMOS PA design, thereby reducing feedback-induced nonlinear distortion. Transformer-based matching networks are used to achieve wideband impedance matching. The presented PA achieves a measured small-signal gain of 20 dB from 31 to 45 GHz, with a peak saturated output power of 17.1 dBm and a peak power-added efficiency (PAE) of 12.1% at 39 GHz. Under a 50-MHz 5G New Radio (NR) 256-QAM signal without digital predistortion (DPD), the PA demonstrates an error vector magnitude (EVM) of -26.7 dB and an adjacent channel power ratio (ACPR) of -32.2 dBc. With DPD, both EVM and ACPR are further improved. The doubly neutralized architecture enables broadband mm-wave CMOS PA operation and supports high-order modulation schemes for emerging wireless applications.