Negar Reiskarimian

Magnetic-free non-reciprocity based on staggered commutation

Lorentz reciprocity is a fundamental characteristic of the vast majority of electronic and photonic structures. However, non-reciprocal components such as isolators, circulators and gyrators enable new applications ranging from radio frequencies to optical frequencies, including full-duplex wireless communication and on-chip all-optical information processing. Such components today dominantly rely on the phenomenon of Faraday rotation in magneto-optic materials. However, they are typically bulky, expensive and not suitable for insertion in a conventional integrated circuit. Here we demonstrate magnetic-free linear passive non-reciprocity based on the concept of staggered commutation. Commutation is a form of parametric modulation with very high modulation ratio. We observe that staggered commutation enables time-reversal symmetry breaking within very small dimensions (λ/1,250 × λ/1,250 in our device), resulting in a miniature radio-frequency circulator that exhibits reduced implementation complexity, very low loss, strong non-reciprocity, significantly enhanced linearity and real-time reconfigurability, and is integrated in a conventional complementary metal–oxide–semiconductor integrated circuit for the first time.

9.8 Receiver with integrated magnetic-free N-path-filter-based non-reciprocal circulator and baseband self-interference cancellation for full-duplex wireless

Full-duplex (FD) is an emergent wireless communication paradigm where the transmitter (TX) and the receiver (RX) operate at the same time and at the same frequency. The fundamental challenge with FD is the tremendous amount of TX self-interference (SI) at the RX. Low-power applications relax FD system requirements [1], but an FD system with -6dBm transmit power, 10MHz signal bandwidth and 12dB NF budget still requires 86dB of SI suppression to reach the -92dBm noise floor. Recent research has focused on techniques for integrated self-interference cancellation (SIC) in FD receivers [1-3]. Open challenges include achieving the challenging levels of SIC through multi-domain cancellation, and low-loss shared-antenna (ANT) interfaces with high TX-to-RX isolation. Sharedantenna interfaces enable compact form factor, translate easily to MIMO, and ease system design through channel reciprocity.

18.2 Highly-linear integrated magnetic-free circulator-receiver for full-duplex wireless

A fundamental challenge of full-duplex (FD) wireless [1] is the implementation of low-cost, small-form-factor, integrated shared-antenna (ANT) interfaces with low loss, low noise, high TX-RX isolation, and large TX power handling. Providing more TX-RX isolation in the ANT interface that is robust to environmental variations lowers the self-interference cancellation (SIC) and dynamic range required in the RF, analog baseband (BB), and digital domains. Reciprocal shared-ANT interfaces, such as electrical-balance duplexers [2], fundamentally feature at least 3dB loss (practically >4dB). A non-reciprocal active shared-ANT duplexing scheme was demonstrated in [3], but such active approaches are limited in their maximum supported TX power (−17.3dBm in [3] limited by RX compression) and noise performance. An integrated FD RX with a magnetic-free non-reciprocal passive circulator was demonstrated in [4]. Despite the circulators low loss and relatively high linearity, the RX could only handle up to −7dBm TX power due to limited circulator isolation and RX LNA linearity. NF under cancellation was also as high as 10.9dB.

A CMOS Passive LPTV Nonmagnetic Circulator and Its Application in a Full-Duplex Receiver

Recently, we demonstrated the first CMOS nonmagnetic nonreciprocal passive circulator based on N-path filters that uses time variance to break reciprocity. Here, the analysis of performance metrics, such as loss, isolation, linearity, and tuning range, is presented in terms of the design parameters. The analysis is verified by the measured performance of a 65-nm CMOS circulator prototype that exhibits 1.7 dB of loss in the transmitter-antenna (TX-ANT) and antenna-receiver (ANT-RX) paths, and has high isolation [TX–RX, up to 50 dB through tuning and 20-dB bandwidth (BW) of 32 MHz] and a tuning range of 610–850 MHz. Through an architectural feature specifically designed to enhance TX linearity, the circulator achieves an in-band TX-ANT input-referred third-order intercept point (IIP3) of +27.5 dBm, nearly two orders of magnitude higher than the ANT-RX IIP3 of +8.7 dBm. The circulator is also integrated with a self-interference-canceling full-duplex (FD) RX featuring an analog baseband (BB) SI canceller. The FD RX achieves 42-dB on-chip SI suppression across the circulator and analog BB domains over a 12-MHz signal BW. In conjunction with digital SI and its input-referred third-order intermodulation (IM3) cancellation, the FD RX demonstrates 85-dB overall SI suppression, enabling an FD link budget of −7-dBm TX average output power and −92-dBm noise floor.

Analysis and Design of Two-Port N-Path Bandpass Filters with Embedded Phase Shifting

N-path switched- RC circuits are a promising solution for realizing tunable high- Q filters on chip. Here, a novel method of embedding phase-shifting functionality into the two-port N- path filter response by shifting the phase of the input and output clock sets relative to each other is introduced. Furthermore, a two-port design allows us to embed variable attenuation that can be useful in applications such as wideband self-interference cancellers and phased-array front ends, where filtering, phase shifting, and variable gain are functionally required. The effect of the embedded phase shift is analyzed with linear periodically time-variant theory and has been verified through simulations and measurement. Measurement results are presented for a two-port N- path filter implemented in a 65-nm CMOS 0.8-1.4-GHz highly reconfigurable self-interference canceling receiver. The two-port filter achieves 13-dB gain control and full 360° phase-shift range for the in-band transfer function.

Integrated Full Duplex Radios

Full duplex wireless has drawn significant interest in the recent past due to the potential for doubling network capacity in the physical layer and offering numerous other benefits at higher layers. However, the implementation of integrated full duplex radios is fraught with several fundamental challenges. Achieving the levels of self-interference cancellation required over the wide bandwidths mandated by emerging wireless standards is challenging in an integrated circuit implementation. The dynamic range limitations of integrated electronics restrict the transmitter power levels and receiver noise floor levels that can be supported in integrated full duplex radios. Advances in compact antenna interfaces for full duplex are also required. Finally, networks employing full duplex nodes will require a complete rethinking of the medium access control layer as well as cross-layer interaction and co-design. This article describes recent research results that address these challenges. Several generations of full duplex transceiver ICs are described that feature novel RF self-interference cancellation circuits, antenna cancellation techniques, and a non-magnetic CMOS circulator. Resource allocation algorithms and rate gain/improvement characterizations are also discussed for full duplex configurations involving IC-based nodes.

Design of all-passive higher-order CMOS N-path filters

In this paper, a methodology for designing all-passive higher-order N-path filters is described. The methodology extends known filter synthesis techniques for LC filters to N-path filters through the use of lumped quarter-wave transmission-line (t-line) equivalents that enable series-LC-like N-path structures. The quarter-wave t-line equivalents also isolate N-path filters from each other, allowing N-path sections to be cascaded to realize filters of arbitrary order. A tunable, nominally 6th-order, high-Q N-path bandpass filter based on this methodology has been implemented in 65nm CMOS. The filter has an insertion loss of 4.7-6.2dB, a tuning range of about 35% from 600MHz to 850MHz, and bandwidth that ranges from 9-15MHz, resulting in a Q that ranges from 40-90. The filter achieves an out-of-band (OOB) rejection of 30-50 dB, input-referred in-band (IB) and OOB 1dB compression point of 0dBm and +14dBm, and input-referred IB and OOB IIP3 of +7 and +17.5dBm respectively. The clock path DC power consumption at 700MHz is 75mW from a 1.2V supply.

Full-duplex in a hand-held device — From fundamental physics to complex integrated circuits, systems and networks: An overview of the Columbia FlexICoN project

Full-duplex wireless is an exciting emerging wireless communication paradigm that also poses tremendous challenges at virtually every layer: from the antenna interface and integrated circuits (ICs) and systems to the network layer. This paper covers recent advances at Columbia University across all these dimensions. Several potential full-duplex system architectures that are appropriate for different application spaces are discussed. Specific research advances include (i) a novel integrated CMOS non-reciprocal circulator that utilizes time-variance to break Lorentz reciprocity, (ii) a polarization-based antenna cancellation technique that achieves very wideband isolation that can be reconfigured as the environment changes, (iii) several generations of RF and analog self-interference cancellation circuits that combat noise, distortion and bandwidth limitations, (iv) higher-layer resource allocation algorithms that evaluate full-duplex rate gains given realistic physical layer models, and (v) demonstrations of full-duplex operation using realistic IC-based nodes.

Fully-integrated non-magnetic non-reciprocal components based on linear periodically-time-varying circuits

Lorentz reciprocity is a fundamental property of passive, linear, time-invariant circuits and systems constructed from conventional materials. Recently, we demonstrated the first CMOS non-magnetic non-reciprocal passive circulator that uses a linear periodically-time-variant (LPTV) phase-shifting N-path filter to break reciprocity. In this paper, we review the concept and present the measured performance of a 65nm CMOS 750MHz prototype that exhibits 1.7dB of loss in the transmitter-antenna (TX-ANT) and antenna-receiver (ANT-RX) paths and has high isolation (up to 50dB through tuning and 20dB bandwidth of 32MHz). Through an architectural feature specifically designed to enhance TX linearity, the circulator achieves an in-band (IB) TX-ANT IIP3 of +27.5dBm, remarkably two orders of magnitude higher than the ANT-RX IIP3 of +8.7dBm.

Linear Periodically Time-Varying (LPTV) Circuits Enable New Radio Architectures for Emerging Wireless Communication Paradigms: Extended Abstract: Invited

The next generation of cellular wireless communication networks (the much hyped “5G”) is targeting a 1000x increase in data capacity. This has sparked an investigation of new and transformative wireless communication paradigms, including massive MIMO, full duplex and millimeter-wave wireless. These new wireless paradigms place requirements on the radio circuitry that are orders of magnitude more challenging than traditional systems, forcing us to rethink conventional radio design. Conventional analog and radio frequency circuit design has relied on linear, time-invariant (LTI) components and circuits. However, LTI components and circuits are restricted in the signal processing functionalities that can be implemented. Recently, there has been significant interest in linear, periodically time varying (LPTV) circuits that can enable new functionalities and components, such as highly-tunable, high quality integrated filters, front-ends with spatio-spectral filtering capability and integrated non-magnetic non-reciprocal components such as circulators and isolators. This paper reviews recent research breakthroughs in LPTV circuits and systems that enable full-duplex and massive MIMO wireless.