Skip to main content
Gigahertz to sub-Terahertz In-Band Full-Duplex Operations in CMOS Based on Wave Frequency and Mode Conversions
In-band full-duplex operations in CMOS are gaining attentions in many diverse applications: from doubling of communication capacity, cryogenic quantum readout, to high performance sensing. Traditional directional/hybrid couplers, while offering the desired TX-to-RX isolation with a shared antenna port, possess an inherent 3dB insertion loss (or 6dB TX-RX round trip loss). Recently, time-variant circuit operations have been innovated to realize circular-like functions without such loss. In this talk, a frequency-conversion based time-variant component is discussed, which achieves broadband isolation by separating the on-chip TX and RX signals onto distant frequencies. A 4GHz prototype, experimentally verified at both 4K and 300K, is presented. For the sub-THz regime, where time-variant circuits through transistor switching are no longer efficient, we demonstrate an electromagnetic-mode conversion scheme, which allows for monostatic FMCW radar sensing without the aforementioned 6dB coupler loss. A 140GHz CMOS radar with 33dB TX-to-RX isolation is presented to showcase this scheme. By mitigating the separation between the TX and RX antennas, the radar exhibits excellent TX and RX needle beam alignment even when pairing with a large aperture lens.