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.

Magnetic-free non-reciprocity based on staggered commutation

A fully integrated technique for wideband cancellation of transmitter (TX) self-interference (SI) in the RF domain is proposed for multiband frequency-division duplexing (FDD) and full-duplex (FD) wireless applications. Integrated wideband SI cancellation (SIC) in the RF domain is accomplished through: 1) a bank of tunable, reconfigurable second-order high-Q RF bandpass filters in the canceller that emulate the antenna interface’s isolation (essentially frequency-domain equalization in the RF domain) and 2) a linear $N$ -path $G_m$ - $C$ filter implementation with embedded variable attenuation and phase shifting. A 0.8–1.4 GHz receiver (RX) with the proposed wideband SIC circuits is implemented in a 65 nm CMOS process. In measurement, $>20\;\text{MHz}\;20\;\text{dB}$ cancellation bandwidth (BW) is achieved across frequency-selective antenna interfaces: 1) a custom-designed LTE-like 0.780/0.895 GHz duplexer with TX/RX isolation peak magnitude of 30 dB, peak group delay of 11 ns, and 7 dB magnitude variation across the TX band for FDD and 2) a 1.4 GHz antenna pair for FD wireless with TX/RX isolation peak magnitude of 32 dB, peak group delay of 9 ns, and 3 dB magnitude variation over 1.36–1.38 GHz. For FDD, SIC enhances the effective out-of-band (OOB) IIP3 and IIP2 to $+\text{25}\text{-}27\;\text{dBm}$ and $+90\;\text{dBm}$ , respectively (enhancements of 8–10 and 29 dB, respectively). For FD, SIC eliminates RX gain compression for as high as $-8\;\text{dBm}$ of peak in-band (IB) SI, and enhances effective IB IIP3 and IIP2 by 22 and 58 dB.

/pdf/integrated-wideband-self-interference-cancellation-in-the-rf-gyi9hx3y7e.pdf

Integrated Wideband Self-Interference Cancellation in the RF Domain for FDD and Full-Duplex Wireless

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.

Integrated Full Duplex Radios

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.

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

This paper presents a fully integrated 60 GHz direct-conversion transceiver in 45 nm SOI CMOS for same-channel full-duplex (FD) wireless communication. FD operation is enabled by a novel polarization-based wideband reconfigurable self-interference cancellation (SIC) technique in the antenna domain. The antenna cancellation can be reconfigured from the IC to combat the variable SI scattering from the environment during in-field operation. A second RF cancellation path with $ > 30\;\text{dB}$ gain control and $ > 360^{\circ}$ phase control from the transmitter (TX) output to the LNA output further suppresses the residual SI to achieve the high levels of required SIC. With antenna and RF cancellation together, a total SI suppression of $ > 70\;\text{dB}$ is achieved over a cancellation bandwidth of 1 GHz and can be maintained in the presence of nearby reflectors. In conjunction with digital SIC (DSIC) implemented in MATLAB, a FD link is demonstrated over 0.7 m with a signal-to-interference-noise-and-distortion ratio (SINDR) of 7.2 dB. To the best of our knowledge, this work achieves the highest integration level among FD transceivers irrespective of the operation frequency and demonstrates the first fully integrated mm-wave FD transceiver front-end and link.

A 60 GHz CMOS Full-Duplex Transceiver and Link with Polarization-Based Antenna and RF Cancellation

A fully integrated wideband active duplexing transceiver with baseband noise-cancelling duplexing LNAs is presented. The circuit allows in-band full duplex operation with concurrent reception and transmission in the same band or closely-spaced channels. A passive mixer-first architecture is applied here, sharing a single passive mixer to perform simultaneous up-conversion and down-conversion. The bi-directional transparency of the passive mixer allows the duplexing function to be implemented at baseband instead of RF front end. Under the same condition as required for noise cancellation, the baseband duplexing LNAs buffer the transmitter input signals to the mixer while canceling those signals in receive path. Measurements from the transceiver implemented in 65 nm CMOS show a frequency tuning range of 0.1–1.5 GHz with ${\rm S}_{11} 20 dB, NF as low as 5.5 dB and transmitted power up to ${-}$ 7.1 dBm. A 30 dB linear isolation between receive and transmit is generally maintained across both LO frequency and in-band transmit/receive frequency separation. Significant suppression of transmit-induced noise and nonlinear intermodulation between received and transmitted signals are also achieved.

A Wideband Highly Integrated and Widely Tunable Transceiver for In-Band Full-Duplex Communication

Recent developments in CMOS passive mixers have demonstrated a number of new and useful capabilities, including dynamic RF port impedance control and filter up-conversion, while also allowing low noise figure and high out-of-band linearity, all of which track wide-ranging LO frequencies and tunable baseband bandwidth. However, these circuits also bring a unique set of challenges and requirements. Here we extend a previously derived LTI model for such mixers to the general N-phase case, and discuss basic limits in performance specifications including impedance matching, noise figure and linearity. We then extend this analysis to include high-frequency effects, especially as they relate to transistor properties. We show that essentially all of the key specification of such mixers can be described in terms of an impedance ratio, a characteristic cut-off frequency, the number of phases of the mixer and some process-related parameters. Finally, we discuss how these properties relate to power consumption of LO circuitry.

Optimized Design of N-Phase Passive Mixer-First Receivers in Wideband Operation

In this work we present an architecture for a low power SDR which draws on techniques from both narrowband low power radios and recent work in SDRs. The receiver consists of a wide tuning-range passive mixer, driven with resonant non-overlapping LO drive combined with a noise-power optimized multi-path baseband amplifier. LO generation circuitry drives the mixer with an 8-phase, 12.5% duty cycle LO, but does so directly from complementary LC-tank VCOs in order to resonate out the gate capacitance of the mixer. A capacitor sharing technique on the baseband side of the mixer doubles the RX frequency range of the 8-phase clock at no added cost in power or performance, while achieving a NF as low as 7 dB. The 1.8 mW low noise baseband amplifier reuses the bias current of its four input channels while rejecting the 3rd/5th harmonics by >34 dB. The receiver consumes 10–12 mW (including VCOs, pulse generation and baseband) over a frequency range of 0.7–3.2 GHz with a 1.3 V supply.

A Wideband Receiver With Resonant Multi-Phase LO and Current Reuse Harmonic Rejection Baseband

We present a widely tunable passive mixer first duplexing transceiver which employs baseband noise-canceling, duplexing LNAs. The LNAs buffer transmitted signals to the mixer while canceling those signals in receive path. The transmitted signals are up-converted by the same mixer used for receiver down-conversion. The transceiver operates over a frequency range of 0.1-1.5GHz with -18dBm transmitted power. A 33dB linear isolation between receive and transmit (separated by 135kHz) as well as suppression of transmit-induced noise and nonlinearity are achieved.

A widely tunable active duplexing transceiver with same-channel concurrent RX/TX and 30dB RX/TX isolation

A baseband technique is presented to detect and suppress LO leakage in wideband passive mixer-first receivers. Using a variable shunting resistance on the RF port, the LO leakage signal is modulated, down-converted and detected from baseband outputs. Current DACs injecting to the baseband port are up-converted and can be adjusted to cancel LO leakage. Suppression of LO on the RF port < −80dBm is shown with a fully automated algorithm without the aid of RF spectrum monitoring. Index Terms — Harmonic mixing, local oscillator (LO) leakage, mixer, passive mixer, receiver, software-defined radio (SDR), wideband receiver.

Dong Yang

Papers

A Wideband Highly Integrated and Widely Tunable Transceiver for In-Band Full-Duplex Communication

Optimized Design of N-Phase Passive Mixer-First Receivers in Wideband Operation

A Wideband Receiver With Resonant Multi-Phase LO and Current Reuse Harmonic Rejection Baseband

A widely tunable active duplexing transceiver with same-channel concurrent RX/TX and 30dB RX/TX isolation

A Baseband Technique for Automated LO Leakage Suppression Achieving < −80dBm in Wideband Passive Mixer-First Receivers