Passive interferometer for wideband and linear transmitter leakage cancellation

This paper presents a new passive approach, interferometer, to cancel transmitter leakage to the receiver with > 600MHz tuneable bandwidth and high linearity (16.9 dBm IP1dB). The interferometer consists of two lumped reflective type phase shifters (RTPS) and a transformer-based current combiner. Facilitated by the two RTPS, the interferometer can provide ±90° phase difference to cover different coupling conditions and process, voltage and temperature (PVT) changes. The interferometer is fabricated in a 65 nm CMOS technology and demonstrates a wide tuneable bandwidth of > 0.6 GHz centred at 10.2 GHz even when the two inputs deviate from differential by +90° with the effective cancellation over 20 dB. The passive approach delivers great linearity, with IP1dB of 16.9 dBm without DC power consumption. The chip size is 0.95×1.05mm2 including all pads.