Pre-PA Delay-Line Based FIR Filter for Self-Interference Cancellation in Full Duplex Wireless Systems

In this paper we propose a pre-PA self-interference (SIC) cancellation FIR filter architecture implemented in a quadrature balanced PAs (QBPA) transmitter (TX) for full duplex wireless applications. Pre-PA SIC filter allows for flexible and efficient equalization of the cancellation signal by reusing the TX path, thus eliminating the need to couple TX power and facilitating linearization operations on both the TX and SIC signals. The pre-PA SIC approach is validated in system-level simulation and demonstrated in measurement using 180nm CMOS QBPA transmitter and a single-tap FIR filter SIC stage. The single-tap filter achieves 37 dB and 42 dB of total TX-RX isolation over BWs of 20 MHz and 10 MHz, respectively, at 14 dBm TX power level.