A Millimeter-Wave Power Amplifier With an Integrated CMOS Isolator/Circulator/Receiver

This article presents a reconfigurable millimeter-wave (mm-wave) fully integrated transceiver (TRX) front end that comprises a power amplifier (PA) and an integrated nonreciprocal ultra-compact isolator/circulator/receiver (RX). The circulator is based on a ring quarter-wave transmission line (QTL) topology with adjusted characteristic impedances, which improves transmitter (TX)-to-antenna insertion loss and TX-to-RX isolation. The circulator’s nonreciprocal gyrator features an and-gate switching-based N-path filter while also acting as a mixer-first RX. By activating the embedded cross-coupled negative resistors, the circulator can be reconfigured as an isolator. This compact N-path filter-based circulator/isolator occupies only 0.38 mm². Over a 27.1–31.1-GHz band, the realized front end offers >20-dB TX-to-RX isolation, with a measured TX-to-antenna insertion loss of $1.7{\sim }2.2$ dB. The RX path tolerates the PA’s blocker signal, achieving 5-dBm in-band and 13-dBm out-of-band (OOB) $B_{\text {1dB}}$ . The PA delivers 15.15-dBm peak output power with 33% drain efficiency. The functionality of the proposed frequency division duplex (FDD) front end is evaluated by simultaneous TX/RX operation with a 400-MHz TX/RX modulation bandwidth and 400-MHz channel spacing. The measured AM–PM of the realized PA with the integrated isolator shows relatively high voltage standing wave ratio (VSWR) resilience at the lower power level and less robustness against VSWR around its peak output power. The front-end prototype occupies only 0.7 mm², including circulator, PA, quadrature hybrid coupler LO generators, and baseband circuits.