A Wideband Circulator Leakage Canceler for Retro-Directive RF System

This letter presents a wideband circulator leakage canceler (CLC) IC using a negative capacitance (NCAP). It enhances a conventional circulator with a wider bandwidth and high isolation for a full-duplex retro-directive short-range wireless power transfer (WPT) application. The proposed CLC consists of a directional coupler (DC), a hybrid coupler, and a low-pass filter network (LPFN) integrated with NCAP, which shows a considerable capability of suppressing the leakage power signal from transmitter (TX) output to receiver (RX) input. The CLC was fully implemented in the Samsung LR6LP 65-nm RF CMOS process and occupied the size of 2.1 mm
$\times0.89$
mm. The measurement of IC with a commercial circulator shows an average cancelation of 19 dB over the range of 225 MHz from 2.31 to 2.535 GHz. The input P1dB in band was measured at 16 dBm while the noise figure (NF) of antenna-receiver (ANT-RX) path increased by 5.2 dB at 2.5 GHz.