A Linear Ratioed Impedance and Driver-Based True Full-Duplex IO with Background Self-Interference Cancellation

In this paper, we propose a high-linearity true full-duplex IO (TFD-IO) cell for space-constrained high-speed interconnects. The proposed TFD-IO cell uses a ratioed impedance and driver-based self-interference (SI) canceler, achieving high linearity with minimal power and area overheads. It can be used for simultaneously transmitting and receiving NRZ (non-return-to-zero) or higher order modulation (such as 4-level pulse amplitude modulation) format signals. A low-power on-chip analog calibration engine, running in the background, takes care of self-interference and echo cancellation even if the modulation format and the baud rate of the signal coming in from the far end are unknown. The high-frequency SI cancellation technique is used to cancel high-frequency components of the SI signal, which further improves the quality of the received signal. Simulation results (R+C extracted) of the TFD-IO cell designed in a low-leakage 65nm CMOS process show a bidirectional throughput of 32 Gbps for PAM-4 signals. A proof-of-concept IC (preliminary version) was successfully tested. The proposed TFD-IO will enable full-duplexing with minimal power and area overhead, to drastically improve bandwidth densities in chip-to-chip high-density interconnects.