Local Oscillator Signal Research Articles

Photonics-based radio frequency self-interference cancellation for radio-over-fiber systems

A photonics-based radio frequency (RF) self-interference cancellation approach for radio-over-fiber (RoF) systems is proposed and demonstrated. An intermediate frequency (IF) signal and a local oscillator (LO) signal are separately modulated to a pair of optical carriers with orthogonal polarization states in the central station. The generated optically carried RF signal is then transmitted to remote base stations over fibers. After performing photodetection at the two outputs of the polarization beam splitter (PBS), a pair of upconverted RF signals with inverse phases are generated. One is used as the transmitted signal, while the other is used as the reference signal for the self-interference cancellation. In this way, the phase inversion between them is realized in the optical domain. In addition, the adjustments with the time delay and the amplitude of the reference signal are both achieved in the optical domain, guaranteeing the self-interference cancellation in a wide bandwidth. Meanwhile, the independent optical system for self-interference cancellation is avoided, simplifying the complex hardware requirements with the base stations. The cancellation depths of 33, 30, and 22 dB over 0.5-, 1-, and 3-GHz bandwidths are experimentally achieved, respectively. The ranging and imaging functions of a frequency modulated continuous wave (FMCW) radar system using the established self-interference cancellation structure are experimentally verified.

A Cryo-CMOS Wideband Quadrature Receiver With Frequency Synthesizer for Scalable Multiplexed Readout of Silicon Spin Qubits

In this article, a cryo-CMOS receiver integrated with a frequency synthesizer for scalable multiplexed readout of qubits is presented, focusing on radio frequency (RF) reflectometry readout of silicon-based semiconductor spin qubits/quantum dots. The proposed spin qubit readout chip consists of a wideband low noise amplifier (LNA), a quadrature mixer, a complex filter, a pair of in-phase/quadrature (I/Q) intermediate frequency (IF) amplifier chains, and a type-II charge-pump phase-locked loop (PLL) with a programmable frequency divider providing local oscillator (LO) signals. Noise optimizations are applied to the LNA design and the quadrature active mixer design to obtain the required performance. A mode-switching complementary voltage-controlled oscillator (VCO) is proposed to achieve low-power and low-phase noise in a wide-frequency tuning range (46.5%). Circuit modifications and design considerations for robust cryogenic temperature operation are presented and discussed. Measurements show that the receiver provides an average gain of 65 dB, a minimum noise figure of 0.5 dB, an IF bandwidth of 0.1–1.5 GHz, and an image rejection ratio of 23 dB at 3.5 K with a power consumption of 108 mW. This cryo-CMOS receiver with frequency synthesizer for spin qubit readout is a first step toward fully-integrated qubit readout and control.

Experimental Realization of 16-Pixel Terahertz Receiver Front-End Based on Bulk Silicon MEMS Power Divider and AlGaN/GaN HEMT Linear Detector Array

A 16-pixel terahertz (THz) receiver front-end working at room temperature was designed, built, and measured in this paper. The designed receiver front-end is based on the antenna-coupled AlGaN/GaN high-electron-mobility transistor (HEMT) THz linear detector array (TeraLDA) and a 16-way THz power divider. The local oscillator (LO) signal is divided by the power divider into 16 ways and transmits to the TeraLDA. Each detector contains a planar unified antenna printed on a 150 μm-thick sapphire substrate and a transistor fabricated on AlGaN/GaN heterostructure. There are 16 silicon hemispheric lenses located on the TeraLDA to increase the responsivity of the TeraLDA. The focus of each lens is aligned in the center of the TeraLDA pixels. Depending on different read out circuits, the receiver front-end could work in homodyne and heterodyne modes. The 16-way power divider is a four-stage power divider that consists of fifteen same 2-way dividers, and was fabricated by bulk silicon microelectromechanical systems (MEMS) technology to achieve low insertion loss (IL). This designed receiver front-end could be a key component of a THz coherent focal plane imaging radar system, that may play a crucial role in nondestructive 3D imaging application.

Coherent EML+TIA Detector for DSP-Free 1 Gb/s/λ Reception Over Extended Budget

The continuing drive towards broadband access necessitates cost-effective optical access and mobile fronthaul solutions. While the fixed-mobile convergence motivates high-speeds for the antenna remoting through broadband digitized radio-over-fiber, the access segment still uses time division multiplexed access equipment. Although the steadily increasing line rates call for 50 Gb/s solutions, the unshared per-user rate remains in the 1-Gb/s range. It is a question whether such data rate can be facilitated without high-speed components, at the same time supporting higher passive splits for the optical distribution networks. We experimentally demonstrate a simplified receiver based on an electro-absorption modulated laser, co-integrated on a die-level with a transimpedance amplifier. We investigate its sensitivity for the phase-agnostic coherent heterodyne downstream detection of data signals in a passive optical network scenario. We will show that despite the omission of a high-performance local oscillator, balanced detection and digital signal processing, the proposed receiver accomplishes reception of 1 Gb/s phase-modulated signals over a link reach of 57 km and an optical budget of 48 dB, thus enabling high passive splits of 1:128. We study the implications raised by this single-ended coherent receiver architecture under multi-channel transmission and investigate the susceptibility of its integrated local oscillator to optical feedback.

Microwave photonics‐based channelized receiving and reconstruction for broadband RF signal

A microwave photonics-based channelized receiver for broadband vector signals is proposed and experimentally demonstrated. A 4-line optical frequency comb (OFC) generated by a dual-parallel Mach-Zehnder modulator (DPMZM) is used as local oscillator (LO) signal in the in-phase/quadrature (I/Q) receiver for coherently down-converting the broadband signal into different channelized bands. By properly setting the frequency difference between the OFC comb line and the broadband signal, either homodyne or heterodyne detection of I/Q receiver is realized. To compensate the amplitude difference and phase difference of adjacent channel signals, an overlap ratio of adjacent slices is introduced for channel equalization and signal reconstruction. The simulated result shows the error vector magnitude of 4-channel channelization for a reconstructed 8 GBaud quadrature phase shift keying (QPSK) signal is very close to the original one. In the experiment, 2-channel channelization for a 2 GBaud QPSK is realized and the whole signal is reconstructed successfully. The experimental result also proves the quality improvement of reconstructed signal with an increase of channel overlap ratio.

RF Self-Interference Cancellation and Frequency Downconversion With Immunity to Power Fading Based on Optoelectronic Oscillation

We report a photonic approach to achieve simultaneous radio frequency (RF) self-interference cancellation (SIC) and frequency downconversion with immunity to power fading based on an optoelectronic oscillator (OEO) for an in-band full-duplex (IBFD) radio-over-fiber (ROF) system. A dual-drive Mach–Zehnder modulator (DDMZM) in a polarization-division multiplexing Mach–Zehnder modulator (PDM-MZM) is used to cancel the RF self-interference (SI) signal and generate optical carrier-suppressed double sidebands (CS-DSBs) of the signal of interest (SOI). Meanwhile, another DDMZM in the PDM-MZM is used to construct an OEO loop to generate optical CS-DSBs of the local oscillation (LO) signal. After detection at a photodetector (PD), a frequency downconverted signal is recovered with the RF self-interference cancellation (SIC). The proposed scheme can directly cancel the RF SI signal in the optical domain, meaning that it can overcome the limitation of SIC in the electrical domain. With the phase compensation introduced by a polarization controller, the desired signal is unaffected by the power fading over fiber transmission, which is significant for IBFD ROF systems. In addition, instead of an external microwave source, an OEO loop is used to generate an LO signal with a high spectral purity, which is very promising for integrated microwave photonics systems.

A Microwave Photonic Converter with High in-Band Spurs Suppression Based on Microwave Pre-Upconversion

A microwave photonic converter based on microwave pre-upconversion is proposed and experimentally demonstrated. Only a single Mach–Zehnder modulator (MZM) is used in the converter system so that the complexity and bandwidth limiting of the link can be reduced. The transmitted and received signals before entering the MZM are firstly upconverted to high frequency (HF) by a microwave upconverter. The HF and local oscillator (LO) signals are combined to drive the MZM. Carrier-suppressed double-sideband (CS-DSB) modulation is introduced to the MZM for effective spectrum utilization. Then, the target signals can be obtained by photoelectric conversion and beating. Experimental results confirm that the mixing spurs including harmonics and intermodulation as well as original signals are all out of system frequency band from 0.8–18 GHz, and the in-band spurious suppression of at least 40 dBc is achieved. In addition, the spurious-free dynamic range (SFDR) reaches 86.23 dB·HZ2/3 for upconversion and 80.95 dB·HZ2/3 for downconversion. The proposed microwave photonic converter provides a wideband and high-purity alternative for the applications of radars and signal processing.

Design of IF-RF-Based Heterodyne Transmitter Using Current Steering DAC with 5.4 GHz Spur-Free Bandwidth

The paper presents an intermediate frequency (IF) radio frequency (RF)-based heterodyne transmitter using current steering DAC. In the proposed design, a single digital AND gate is used as IF mixer and modulator of input data. This IF signal is further mixed with local oscillator signal in the current steering DAC to obtain RF output signal. The AND gate-based IF modulator converts input signal to square wave. This square wave does not contain even harmonics and consists of odd harmonics, which reduces harmonic mixing products. In addition, double differential architecture has been used in current steering DAC to cancel even harmonics. With cancellation of even harmonics in IF and RF signals, the output spectrum consists of only odd multiple of RF output frequency, resulting in spur-free bandwidth of 5.4 GHz for the RF output frequency of 2.4 GHz. The proposed transmitter employs 64-quadrature amplitude modulation which gives an output power of 446 m dBm without a power amplifier. Monte-Carlo simulations have been performed to verify the reliability of the circuit against process and mismatch variations, and it has been found that the circuit parameters are less sensitive to process variations.

W대역 소형 레이다의 주파수 해상도 향상을 위한 위상잡음 분석

FMICW radars detect and track targets using frequency information based on the distance and velocity of the target. Therefore, the phase noise of the received signal and the frequency resolution must be minimized to ensure detection and tracking accuracy of the radars. However, as the signal frequency increases, the phase noise degrades. Therefore, the design requirement of the phase noise is important for radar using high-frequency signals. In this study, the phase noise of the transmission signal (FTX), local oscillation signal (FLO1, FLO2), and reference signal (Fref) are analyzed for application to a W-band compact radar. Additionally, phase-noise requirements are derived to increase the frequency resolution of the radar within a range that can be implemented in a W-band transceiver.

A 24 GHz FMCW/Doppler Dual-Mode Frequency Synthesizer With 68.8 kHz RMS FM Error and 1.25 GHz Chirp Bandwidth

This brief presents a 24 GHz dual-mode frequency synthesizer designed in a 55-nm CMOS technology supporting both Doppler and frequency modulated continuous wave (FMCW) radars. The effects of chirp linearity and delta-sigma modulation (DSM) resolution on the rms FM error is analyzed. A design procedure for the PLL loop bandwidth and time interval of the frequency step to reduce the rms FM error is proposed. A voltage-controlled oscillator (VCO) featuring a four-coil transformer load is developed providing differential local oscillation (LO) signals for the transmitter (TX) and quadrature LO signals for the 2-channel receiver (RX). The prototype is designed with a loop bandwidth of 350 kHz, a frequency step time interval of <inline-formula> <tex-math notation="LaTeX">$2 ~\mu s$ </tex-math></inline-formula>, and a VCO tuning linearity of 26&#x0025;. In the FMCW mode, it achieved an rms FM error of 68.8 kHz over a 1.25 GHz chirp bandwidth. In the Doppler mode, the VCO operates in the free-running mode to save power consumption. An 8-bit digital-to-analog converter (DAC) is used to provide the VCO control voltage compensating process and voltage variations. The free-running VCO operates at a 24.125 GHz and has a frequency error of less than 1 MHz.

28-nm CMOS 공정을 이용한 Ka-Band 수신기 설계

This study presents a Ka-band direct-conversion receiver using a 28-nm CMOS (Complimentary Metal Oxide Semiconductor) process for radar applications. The designed receiver includes a LNA (Low-Noise Amplifier), Mixer, and Baseband amplifier. The LNA adopts a two-stage cascode amplifier structure. Then, the mixer is a single-balanced passive mixer with low flicker noise. At the end, the baseband amplifier is a transimpedance amplifier with fat FET (Field-Effect-transistor) for low flicker noise and current-mode operation of the mixer. The LO (Local Oscillator) signal for driving the mixer is supplied externally. The performance of the receiver is tested using on-wafer probing and an air test is performed by integrating a microstrip antenna. The total conversion gain, noise figure, and 3 dB bandwidth are 28 dB, 6.1 dB, and 6 GHz, respectively. The chip size is 0.320 mm2.

Phase Noise Effects on the Performance of High‐Order Digital Modulation Terahertz Communication System

As the carrier frequency goes into the terahertz band, the phase noise of the signal source has increasing impacts on the performance of the communication system. Considering a 16QAM high-order digital modulation terahertz communication system (DMTCS), by comparing the influence of two kinds of local oscillator signal sources with different phase noise characteristics on the bit error rate (BER) performance of the system based on theoretical analysis and experimental research, it is found that the near-end phase noise of local oscillator signal source has a great influence on the BER performance of the DMTCS. The suppression of phase noise of the local oscillator signal source based on choosing loop bandwidth of the digital phase-locked loop (DPLL) at the receiving end is also discussed. It is found that the negative impacts of phase noise on BER performance of the system can be efficiently decreased by reasonably selecting the loop bandwidth of the DPLL.

40 nm CMOS 공정을 이용한 I/Q 생성이 내재된 D-대역 주파수 체배기

This paper presents a D-band frequency multiplier consisting of a single-ended to differential converter, frequency multiplier-by-nine, 90° hybrid coupler, and D-band amplifier. The designed D-band frequency multiplier was fabricated using the 40 nm CMOS process. A frequency multiplier-by-nine was implemented using a two-stage cascade frequency tripler. A Lange coupler with broadband performance was used to generate an I/Q local oscillator signal with a 90° relative phase difference. The on-wafer measurement showed a peak output power of 3.4 dBm, 3 dB bandwidth of 12 GHz (125～137 GHz), and adjacent harmonic suppression greater than 30 dBc. The power consumption was 170 mW at a supply voltage of 1 V, and an efficiency of 1.28 % was achieved at saturated output power. The chip area, excluding the pads, was 0.235 mm2.

A 28-GHz Phased-Array Relay Transceiver for 5G Network Using Vector-Summing Backscatter With 24-GHz Wireless Power and LO Transfer

This article introduces a wirelessly powered phased-array transceiver for fifth-generation (5G) relay systems. To realize the battery-less relay operation, 24-GHz wireless power transfer (WPT) is employed. This relay transceiver consists of the proposed vector-summing backscatter for Transmitter (Tx) and a passive phase-shifting self-heterodyne Receiver (Rx) with a rectifier for Rx and WPT. The receiver generates dc power from the 24-GHz WPT signal, which is also used as a local oscillator (LO) signal to down-convert the 28-GHz 5G modulated data to a 4-GHz IF. The vector-summing backscatter up-converts the 4-GHz IF signal to 28-GHz using a 24-GHz LO signal while working as a 360° phase shifter with a 7-bit resolution. Both transmitter and receiver operate only using the generated power from the 24-GHz WPT. The chip area of the eight-path transceiver is 1.8 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and the transceiver is mounted on a 32-element phased-array antenna board. This module generates 3.1-mW dc power from 6.7-mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> received power density at 24 GHz. The transmitter achieves a −2.2-dBm measured saturated equivalent isotropically radiated power (EIRP) and supports a −30° to +30° beam range. The measured error vector magnitude (EVM) values are −27.5 dB for Tx mode and −31.3 dB for Rx mode with a 400-MHz 64-QAM orthogonal frequency division multiple access (OFDMA)-mode signal (5G new radio (NR), MCS 19). The power consumption for each path is 0.03 mW in both Tx and Rx modes.

Photonics-Based Adaptive RF Self-Interference Cancellation and Frequency Downconversion

A photonics-based approach for simultaneous adaptive radio-frequency (RF) self-interference cancellation and frequency downconversion is proposed and demonstrated. By introducing photonic polarization-multiplexing, the reference signal and the self-interference signal are separated in the optical domain. Thus, the phase shift, the precise amplitude and the time delay adjustments can be achieved with the reference signal by using optical methods which are program controllable. An intelligent algorithm particle swarm optimization (PSO) algorithm is applied to optimize these parameters for adaptive operation. Meanwhile, the local oscillator (LO) signal is introduced to the two orthogonal polarization states to perform frequency downconversion. Therefore, simultaneous adaptive self-interference cancellation and downconversion are realized. A theoretical model is established for analyses. A proof-of-concept experiment is taken. The simultaneous adaptive self-interference cancellation and downconversion are achieved. The X-band RF signals are downconverted, and the self-interference cancellation depth of 31 dB over a 500-MHz bandwidth and 28 dB over a 1-GHz bandwidth are obtained. The RF signals in the Ku-band are downconverted, with the self-interference cancellation of 28 dB over a 500-MHz bandwidth and 26 dB over a 1-GHz bandwidth. A 16-QAM signal with a 10-Msym/s symbol rate is recovered from the self-interference signals with 500-MHz and 1-GHz bandwidths.

Photonic-enabled radio-frequency self-interference cancellation incorporated into an in-band full-duplex radio-over-fiber system

A photonic approach for radio-frequency (RF) self-interference cancellation (SIC) incorporated in an in-band full-duplex radio-over-fiber system is proposed. A dual-polarization binary phase-shift keying modulator is used for dual-polarization multiplexing at the central office (CO). A local oscillator signal and an intermediate-frequency signal carrying the downlink data are single-sideband modulated on the two polarization directions of the modulator, respectively. The optical signal is then transmitted to the remote unit, where the optical signals in the two polarization directions are split into two parts. One part is detected to generate the up-converted downlink RF signal, and the other part is re-modulated by the uplink RF signal and the self-interference, which is then transmitted back to the CO for the signal down-conversion and SIC via the optical domain signal adjustment and balanced detection. The functions of SIC, frequency up-conversion, down-conversion, and fiber transmission with dispersion immunity are all incorporated in the system. An experiment is performed. Cancellation depths of more than 39 dB for the single-tone signal and more than 20 dB for the 20-MBaud 16 quadrature amplitude modulation signal are achieved in the back-to-back case. The performance of the system does not have a significant decline when a section of 4.1-km optical fiber is incorporated.

Active element pattern measurement in a hybrid antenna array with heterodyne architecture and its application

AbstractA measurement method of an active element antenna pattern in a hybrid antenna array with heterodyne architecture under a real environment is proposed and applied to the design of an ultralow sidelobe level scanning array. To avoid the phase uncertainty caused by the local oscillator signal in the heterodyne architecture, a phase‐normalized active element pattern (PNAEP) is used to characterize the element antenna patterns of both amplitude and phase. The PNAEP has almost taken account of all the practical factors of an array, such as mutual couplings, various types of element antennas, unequal spacing, or diverse environmental effects. The PNAEP is measured with a 16‐element scanning receiving array with a heterodyne architecture to validate the feasibility of the PNAEP. Based on the PNAEP, the scanning array achieve an ultralow sidelobe level of −33 dB. Applying to various receiving array architectures the PNAEP method is a feasible and universal tool for array synthesis and optimization under real environments.

24–40 GHz Gain-Boosted Wideband CMOS Down-Conversion Mixer Employing Body-Effect Control for 5G NR Applications

This brief presents a gain-boosted wideband complementary metal–oxide–semiconductor (CMOS) down-conversion mixer with body-effect control, which operates in a frequency range of 24–40 GHz. In the proposed design, the body voltage of mixer switches is adaptively controlled with respect to an applied local oscillator (LO) signal to enhance the switching capability. This technique improves the conversion gain (CG) and noise figure (NF) of the mixer without increasing LO signal power and current consumption. To validate the concept of the design, conventional and proposed mixers are implemented using a 65-nm CMOS process and their performance is compared. At an identical LO power of 5 dBm, the proposed wideband mixer demonstrates the CGs of 7.2 dB and 4.8 dB and NFs of 12.3 dB and 13.5 dB at 28 GHz and 39 GHz, respectively. Compared with the conventional mixer design, the CG and NF of the proposed mixer are improved by 2.2–3.3 dB and 1.2–2 dB in all operating frequency bands, respectively. The conventional and proposed mixers consume the identical die size of 0.87 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\times }\,\,0.46$ </tex-math></inline-formula> mm and the power of 10.3 mW with the nominal supply of 1.0 V.

A 24‐GHz active up/down bidirectional mixer in 130‐nm RF CMOS

An active bidirectional mixer based on modified Gilbert cell has been proposed to perform the up/down conversion at 24 GHz in a 130-nm RF CMOS. Employing the transconductance gm/load sharing stage, the mixer not only reduces the required power of local oscillator (LO) signal, but also increases the linearity and the conversion gain (CG). With a 2-dBm LO power, the mixer achieves measured CG of −1.7 dB, noise figure (NF) of 14.6 dB, and output 1-dB compression point (OP1dB) of −8.4 dBm at 24 GHz in the up-conversion mode. In the down-conversion mode, the mixer exhibits measured CG of 2.6 dB, NF of 15.9 dB, and input 1-dB compression point (IP1dB) of −0.1 dBm at 24 GHz. From 23 to 25 GHz, the measured LO-to-RF and LO-to-IF isolations (ISOs) are better than 55 dB and 48 dB, respectively. The chip area including all testing pads is 0.75 × 0.8 mm2, which consumes 10.5 mW from a supply of 1.5 V.

High-speed fiber-wireless-fiber system in the 100-GHz band using a photonics-enabled receiver and optical phase modulator.

This Letter describes a high-speed yet simple fiber-wireless-fiber system in the 100-GHz band using a photonics-enabled receiver and optical phase modulator. At the antenna site, a millimeter-wave signal is down-converted to the microwave band using an electronic mixer with a local oscillator signal generated remotely using photonic technology. The down-converted signal is converted to an optical signal using an optical phase modulator. At the receiver, a simple direct detection of the phase-modulated signal is performed using optical filtering technology. To demonstrate the proof-of-concept, we successfully transmitted a 64-quadrature amplitude modulation orthogonal frequency-division multiplexing signal with a record line rate of 80 Gb/s (net data rate of 55 Gb/s) over a system consisting of two radio-over-fiber links and a 5 m wireless link in the 100-GHz band. The proposed system with simple antenna sites and optical transceivers can facilitate the deployment of ultra-dense small cells in high-frequency bands in beyond-5G networks.