Realization of In-Band Full-Duplex Operation at 300 and 4.2 K Using Bilateral Single-Sideband Frequency Conversion

CMOS-integrated in-band full-duplex (IBFD) operation in wireless links and cryogenic quantum platforms was previously enabled by magnetic-free circulators using the phase non-reciprocity from spatial-temporal modulation. In this article, we present an alternative and simple integrated circuit scheme, which not only realizes non-reciprocal signal flows required for IBFD operations but also improves the isolation performance by completely eliminating any chip-level transmit (TX)-to-receive (RX) coupling. The above functions are enabled by performing a direction/frequency-independent, single-sideband down-conversion to the counter-propagating TX and RX signals, which creates opposite deviations of on-chip TX and RX frequencies with respect to the antenna (ANT) frequency. Such a principle also broadens the isolation bandwidth and enables integrated receiver down-mixing function. As a proof-of-concept, a 3.4-4.6-GHz (30% fractional bandwidth) IBFD interface is implemented using a 65-nm bulk CMOS technology. The measured TX-to-RX isolation of the circuit is 32-51 dB at 300 K, and 14-29 dB at 4.2 K. The measured TX-to-ANT and ANT-to-RX insertion losses are 3.0 and 3.2 dB at 300 K, and 1.9 and 2.0 dB at 4.2 K. At 300 K, the measured TX-to-ANT and ANT-to-RX IIP3 are 29.5 and 27.6 dBm, respectively. The IBFD core of the chip occupies an area of 0.27 mm
²
and has a dc power (nominally consumed in an on-chip modulation clock generator) of 48 mW at 300 K and 42.6 mW at 4.2 K.