A Compact Ka-Band Bi-Directional PA-LNA with 17.4-dBm Psat Using Three-Stack Power Amplifier in 28-nm CMOS

This paper presents a compact Ka-band bi-directional power amplifier-low-noise amplifier (PA-LNA) employing a three-stack PA in a 28-nm CMOS process. In the proposed PA-LNA, the three-stack PA is cross-coupled with a common-source LNA to neutralize gate-drain capacitance (Cgd) of the LNA, enhancing stability and gain in LNA mode. Simultaneously, the three-stack PA achieves higher output power and gain in PA mode. Furthermore, transformer-based matching networks enable fully bi-directional operation within a compact die area. In PA mode, the proposed PA-LNA demonstrates a peak gain of 20.4 dB with a 3-dB bandwidth of 8.1 GHz (27.3–35.4 GHz), a saturated output power (Psat) of 17.4 dBm with a peak power-added-efficiency (PAE) of 17.2%, and an error vector magnitude (EVM) of -31.5 dB with 256-quadrature amplitude modulation (QAM) and 800-MBaud symbol rate at 7-dBm average output power. In LNA mode, the proposed PA-LNA demonstrates a peak gain of 17.3 dB with a 3-dB bandwidth of 8 GHz (28.0–36.0 GHz), a noise figure (NF) of 5.3 dB, and an input third-order intercept point (IIP3) of 0 dBm. The core area of the PA-LNA is only 0.1 mm².