A Tunable 5–7 GHz Distributed Active Quasi-Circulator With 18-dBm Output Power in CMOS SOI

Circulators and quasi-circulators (QCs) have a tradeoff between maximum isolation and bandwidth. We present a tunable distributed active circuit to achieve high isolation over a wide frequency range. The reported QC provides more than 40-dB suppression between transmit (TX) output signal at the antenna and TX leakage into the receive (RX) port over a tuning range of 5.3-7.3 GHz in small-signal operation. Large-signal TX-RX suppression is optimized across power level. The TX output achieves peak power of 18 dBm and 12% power-added efficiency at 6.3 GHz. The QC is designed in a high-resistivity 45-nm CMOS silicon-on-insulator process and occupies an area of 1.62 mm × 0.97 mm.