LAUSR

An active transmitter (TX) cancellation scheme enabling integration of the antenna interface for frequency division duplex systems is presented. A replica of the TX current is synthesized in shunt with the receiver (RX) by a digital-to-analog converter (DAC). The replica DAC virtually shorts out the TX signal at the RX input while having minimal impact on the TX insertion loss. Propagation of the TX phase noise in the RX band is analyzed and shown to be feed-forward cancelled in the proposed system. A prototype chip including integrated TX, measurement RX, and cancellation circuits, operating on a single-shared antenna, is implemented in 65-nm CMOS. The cancellation replica demonstrates > 50 dB cancellation of a +12.6 dBm peak 20-MHz TX signal across a wide range of center frequencies and up to 5:1 voltage standing-wave ratio at the antenna interface. The RX is able to down-convert the RX signal at 40-MHz offset with < 4.3 dB noise figure degradation in the presence of the residual TX signal.