Ultra-Wideband Switched-Capacitor Delays and Circulators - Theory and Implementation

Abstract

Recent research has revealed the possibility to achieve non-magnetic non-reciprocity using time variance. However, prior CMOS-based circulators rely on the interference between non-reciprocal switched-capacitor/transmission-line gyrators and reciprocal transmission-line rings, which increases form factor and restricts frequency tunability and bandwidth (BW). On the other hand, our recent work on quasi-electrostatic wave propagation in switched-capacitor networks has proposed a new regime in multipath switched-capacitor network operation that enables an ultra-broadband, ultra-compact reciprocal/non-reciprocal true-time-delay element. In this work, we corroborate these findings by implementing prototype devices of the quasi-electrostatic delay element. Our measurements of the delay element reveal that delays of tens of nanoseconds over hundreds of MHz BW are realizable on-chip in a compact form factor. In addition, we apply synthetic rotation across these switched-capacitor networks to realize an ultra-broadband N-port circulator with ultra-compact form factor. We implemented a wideband three-port circulator showcasing this new architecture in a standard 65-nm CMOS process. The circulator exhibits symmetric performance across all three ports and dc-1-GHz operation for a modulation frequency of 500 MHz. The measured transmission losses of the circulator range between 3.1 and 4.3 dB, matching is-15 dB, isolation is >18 dB, and noise figure (NF) is consistent with the insertion loss. This device occupies an area of 0.19 mm2 (λ center2/1.9× 106), representing about 100-1000 × higher miniaturization compared to the prior art.