Analysis and Design of Integrated Quadrature Balanced N-Path Transceivers for Frequency Division Duplex Systems

We present a fully integrated and tunable transceiver for frequency-division duplex (FDD) and half duplex (HD) operation based on a quadrature balanced N-path mixer-first receiver (MFRX) architecture. The quadrature balanced N-path transceiver (QBNT) comprises a quadrature hybrid (QH) and two identical MFRXs, presenting a short circuit and a matched impedance at the transmitter (TX) and receiver (RX) bands, respectively. The proposed transceiver achieves low TX to antenna loss while maintaining high RX linearity, and is capable of cancelling both TX noise and reciprocal mixing (RM) at the RX under antenna voltage standing wave ratio (VSWR) variations. Analysis and design equations of the QBNT are shown, and the design considerations of each block are presented. A channel estimation algorithm is proposed to cope with the frequency-dependant antenna reflection QH response. An integrated QBNT prototype was fabricated in TSMC 65nm CMOS process as a proof of concept, occupying an active area of 2.96 <tex-math notation="LaTeX">mm²</tex-math> . The QBNT operates at the frequency range between 0.75-2 GHz with a TX-RX offsets above 200 MHz. It achieves RX noise figure (NF) of 2.8-5.8 dB, RXB1dB of 18 dBm, TX-ANT OIP3 of 27.3 dBm and 29.5 dBm in FDD and HD modes, respectively. The demonstrated FDD operation of the QBNT shows that in our implementation we achieve a simultaneous 6.5 dBm TX output power and an RX EVM of <tex-math notation="LaTeX">$-$</tex-math> 40.8 dB after digital cancellation. The RX and TX (at OP1dB) consume DC power of 82-130 mW and 254 mW, respectively.