Integrated Non-Reciprocal Components Based on Spatio-Temporal Conductivity Modulation

Nonreciprocal components, such as gyrators, isolators, and circulators, have numerous applications in the fields of wireless communication, radar, sensing, and quantum information processing. Traditionally, these non-reciprocal components are built using ferrite materials which are incompatible standard CMOS fabrication processes. To circumvent this problem, we modulate conductivity around a delay medium (transmission line) is modulated using synchronized switching, a wide range of nonreciprocal responses can be observed over large-to-infinite bandwidths. Using this concept we presented different types of nonreciprocal functionalities, ranging from non-reciprocal phase shift to ideal isolation, by controlling the modulation depth of conductivity sections (engineered conductance modulation ratios) placed on either side of a transmission line. By using the large ON-to-OFF conductance ratios of the transistor switches, we presented an exhaustive set of nonreciprocal structures, including an arbitrary phase-nonreciprocal element, an ultra-broadband gyrator, a frequency-conversion isolator, an ultra-broadband isolator, and ultra-broadband/high-linearity/high-frequency circulators. Check out the related publications:

  • Tolga Dinc, Mykhailo Tymchenko, Aravind Nagulu, Dimitrios Sounas, Andrea Alu and Harish Krishnaswamy, “Synchronized Conductivity Modulation to Realize Broadband Lossless Magnetic-Free Non-Reciprocity,” Nature Commun., vol .8, p. 795, Oct. 2017. (link) (News)
  • Aravind Nagulu, Tolga Dinc, Zhicheng Xiao, Mykhailo Tymchenko, Dimitrios Sounas, Andrea Alu, and Harish Krishnaswamy, “Non-reciprocal Components Based on Switched Transmission Lines,” IEEE Trans. on Microw. Theory and Techn., vol. 66, p. 4706-4725, Nov. 2018. (link)
  • Aravind Nagulu, Negar Reiskarimian and Harish Krishnaswamy, “Non-reciprocal Electronics Based on TemporalModulation,” Nat. Electron., May 2020. (link) (News)

Multi-Watt CMOS Circulators at RF with In-Built Isolation-Tuning

Leveraging the switched-transmission architecture we reduced the switching frequency which enabled the utilization of transistor switches with larger voltage-breakdown limit, consequently resulting a circulator with higher power handling. In a paper presented in RFIC 2018 we presented a highly linear, high performance 1GHz circulator with >1W TX-ANT P1dB, >+50dBm TX-ANT IIP3 and a novel low loss isolation-tuning technique to achieve high isolation across the entire 1.85 ANT VSWR circle. This work was awarded the IEEE RFIC Symposium Best Student Paper Award (First Place) in 2018. This work achieved a 10-100 enhancement in linearity/power handling over prior CMOS non-reciprocal circulators at that time, demonstrated in-built isolation tuning capability and for the first time has shown to lower the power consumption of a communication link when compared with state-of-the-art links realized using conventional reciprocal hybrids.

In the second generation implementation, we used novel techniques such as switch clock boosting, periodically-loaded inductors and a gyrator with partially-reflecting t-lines to reduce the insertion loss, lower power consumption and shrink the chip area. This prototype measured +34dBm TX-ANT P1dB (2.5x or 4dB better), 40% lower chip area and 80% lower power consumption compared to the 1st generation. We also demonstrated a real-time full-duplex wireless link featuring these CMOS circulators where an OFDM-QPSK modulated data can be transmitted across 100m wireless link with an SNR of 20dB and a system demonstration leveraging the CMOS circulator and code-domain signal processing based SI cancellation. Check out the related publications:

  • Aravind Nagulu and Harish Krishnaswamy, “Non-Magnetic CMOS Switched-Transmission-Line Circulators with High Power Handling and Antenna Balancing: Theory and Implementation,” (invited paper) IEEE J. Solid-State Circuits, vol. 54, no. 5, pp. 1288-1303, Apr. 2019. (link)
  • Aravind Nagulu, Tingjun Chen, Gil Zussman, and Harish Krishnaswamy, ‘Multi-Watt, 1GHz CMOS Circulator Based on Switched-Capacitor Clock Boosting,” (invited paper) IEEE J. Solid-State Circuits 2020 (Early Access). (link)

CMOS Circulator at Millimeter Waves

At millimeter-wave frequencies, switch parasitics leads to increased losses and degraded isolation. In this effort, we recognized that the transmission lines between the switches can be replaced with a low-Q bandpass filters (BPF) with much larger parasitic resiliency, thereby, greatly improving the insertion losses can be greatly reduced. In ISSCC 2019 we demonstrated a 60GHz CMOS circulator based on conductivity modulation across a loss/dispersion-engineered bandpass filter. This new architecture improves the insertion loss, isolation, power consumption and spurious response compared to prior art. We measured 3.6dB/3.1dB insertion loss and isolation >40dB over 1.3GHz, representing the first, fully-integrated, CMOS circulator operating in E band frequencies. Check out the related publications:

  • Aravind Nagulu, Tingjun Chen, Gil Zussman, and Harish Krishnaswamy, “Non-Magnetic 180nm SOI Circulator with Multi-Watt Power Handling Based on Switched-Capacitor Clock Boosting,” accepted and to appear in 2020 IEEE International Solid-State Circuits Conference- (ISSCC), Feb. 2020. (link)