Switched-Capacitor Delays Exceeding Delay-Bandwidth Limitations of LTI Circuits
Passive components such as couplers, circulators and isolators are vital in wireless/optical communications. However, conventional linear, time-invariant passive components built from traditional materials are subject to fundamental limitations associated with reciprocity, size, bandwidth and loss. In order to overcome barriers associated with size and aiming for compact implementations, miniaturized couplers based on lumped components and slow-wave coupled microstrip lines were proposed in the past. However, despite all miniaturization efforts, these microwave devices still occupy a significant area, exhibit compromised bandwidth, and lack reconfigurability. Active devices with switchable functionality and tunable operating frequencies suffer from poor linearity and noise, and their performance does not improve when using higher-resolution IC fabrication technology.
As a part of this project, in collaboration with Prof. Alu’s group, we have devoted our efforts to discover new time-modulated non-reciprocal component architectures that achieve infinitesimal size yet extremely broadband non-reciprocal responses varying from gyration and isolation to circulation. As part of this project, we have also shown for the first time the ability to achieve extreme slow-wave propagation in integrated delay lines with reconfigurable delays enabling a new generation of miniaturized reciprocal and non-reciprocal microwave components with extreme reconfigurability. Check out the related publications:
- Mykhailo Tymchenko, Dimitrios Sounas, Aravind Nagulu, Harish Krishnaswamy and Andrea Alu, “Quasielectrostatic Wave Propagation Beyond the Delay-Bandwidth Limit in Switched Networks,” Phys. Rev. X, vol. 9, no. 5, pp. 031015, Jul. 2019. (link)
Ultra-Compact, Ultra-Wideband Circulator
We extended the concept of a 2-port, N-path delays to N-port, N-path circulators. The proposed N-port circulator consists of N identical layers connected in parallel to N ports. Synchronized switching results in a low-loss transmission in one direction and isolation in the reverse direction. Here as well, the usage of just switches and capacitors, and bondwires for matching enabled ultra-compact implementation, leading to prototype with 100-1000 smaller form-factor than the prior integrated circulators. The implemented prototype measures <4dB insertion losses from DC-1GHz in the transmission direction with an isolation 20dB isolation in the reverse direction, representing the first CMOS ultra-wideband circulator with infinitesimal form-factor. This work will be presented at IEEE RFIC 2020 and has been nominated for IEEE RFIC Best Student Paper Award 2020. Check our the related publications:
- Aravind Nagulu, Ahmed Mekkawy, Mykhailo Tymchenko, Dimitrios Sounas, Andrea Alu and Harish Krishnaswamy, “Synthetic Helicoidal Rotation of a Quasi-Electrostatic Ring Resonator: A New Paradigm for Magnet-Free Non-Reciprocity,” in review with Nature Electronics.
- Aravind Nagulu, Mykhailo Tymchenko, Andrea Alu and Harish Krishnaswamy, “Ultra-Compact, Ultra-Wideband, DC-1GHz CMOS Circulator Based on Quasi-Electrostatic Wave Propagation in Commutated Switched-Capacitor Net-works,” accepted and to appear in IEEE Radio Freq. Integ. Circuits Symp. (RFIC), June 2020. (Nominated for Best Student Paper Award) (link)
Swiss-Army-Knife of Microwave Components
Another advantage of such networks is that they can be dynamically reconfigured by changing the commutation direction, capacitance and frequency. We explored this reconfigurable nature of these circuits to their fullest potential by building a first-of-a-kind, highly-reconfigurable device acting as a Swiss Army knife of microwave components. It combines the functionality of a rat-race coupler, a branch-line coupler and a circulator along with tunability of their center frequencies over an octave just by modifying the modulation frequency, clock staggering and the shunt capacitance C . We implemented a prototype device in standard 65nm CMOS process. Related publications:
- Aravind Nagulu, Mykhailo Tymchenko, Andrea Alu, and Harish Krishnaswamy, “Ultra-Compact, Passive, Reconfigurable, CMOS Circulator-Coupler Based on Commutated Multipath Networks,” in 13th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), Sep. 2019.