RF Bandwidth Research Articles

Frequency Domain Multiplexing for Microwave Kinetic Inductance Detectors: Comparing the Xilinx ZCU111 RFSoC with the New 2x2 RFSoC Board

The Xilinx ZCU111 Radio Frequency System on Chip (RFSoC) is a promising solution for reading out large arrays of microwave kinetic inductance detectors (MKIDs). The board boasts eight on-chip 12-bit / 4.096 GSPS analogue-to-digital converters (ADCs) and eight 14-bit / 6.554 GSPS digital-to-analogue converters (DACs), as well as field programmable gate array (FPGA) resources of 930,000 logic cells and 4,272 digital signal processing (DSP) slices. While this is sufficient data converter bandwidth for the readout of 8,000 MKIDs, with a 2 MHz channel-spacing, and a 1 MHz sampling rate (per channel), additional FPGA resources are needed to perform the DSP needed to process this large number of MKIDs. A solution to this problem is the new Xilinx RFSoC 2x2 board. This board costs only one fifth of the ZCU111 while still providing the same logic resources as the ZCU111, albeit with only a quarter of the data converter resources. Thus, using multiple RFSoC 2x2 boards would provide a better balance between FPGA resources and data converters, allowing the full utilization of the RF bandwidth provided by the data converters, while also lowering the cost per pixel value of the readout system, from approximately EUR2.50 per pixel with the ZCU111, to EUR1 per pixel.

Wideband SiGe down-converter for millimeter-wave radio astronomy applications

A Q-band down-converter module with high conversion gain (CG) is presented for a wideband radio astronomy receiver. This down-converter module is designed on a silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) process (0.13 μm) to realize high CG, low LO power operation, and wideband frequency impedance matching for RF/LO/IF ports. The down-converter consists of a double-balanced Gilbert mixing core with on-chip RF/LO transformer baluns, an IF buffer, and bandpass filter. The performance of the down converter is largely dependent on the passive components and signal line interconnection. The design of all passive structures is analyzed and optimized with FEM simulations for a high-quality factor to minimize losses and parasitic effects. This module achieves 8 dB of CG at a low LO power of −6 dBm over a wide RF bandwidth from 28 to 56 GHz and IF bandwidth from 6 to 18 GHz. It demonstrates LO-to-IF/LO-to-RF/RF-to-IF isolations > dB / 40 dB/35 dB, respectively. The critical FEM simulation is described in the design of this high-density SiGe HBT RF circuit. The measured performance confirms the simulation results. The module meets the original design requirements of the DVA-2 Q-band receiver.

Low Power, Compact Integrated Photonic Sampler Based on a Silicon Ring Modulator

Sampling is the primary functional step of an analogue to digital conversion, required for sensing, measurement, signal processing, metrology, and various data communication applications. Here we present, for the first time, to the best of our knowledge, the optical sampling of different microwave signals with sinc-pulse sequences with a very compact integrated silicon photonics ring modulator. By a simple time interleaving with three branches, the employed ring modulator enables ultra-compact photonic integrated analog to digital converters with a sampling rate of three times the RF bandwidth of itself and of the used photodetector and electronic devices. Therefore, its analogue bandwidth is 50% higher than the RF bandwidth of the incorporated electronics and photonics. Thus, the method might enable high-bandwidth analogue to digital converters with ultra-compact footprint and lower power consumption for future communication systems, sensors, and measurement devices.

Composite acousto-optical modulation.

We propose a composite acousto-optical modulation (AOM) scheme for wide-band, efficient modulation of CW and pulsed lasers. We show that by adjusting the amplitudes and phases of weakly-driven daughter AOMs, diffraction beyond the Bragg condition can be achieved with exceptional efficiencies. Furthermore, by imaging pairs of AOMs with opposite directions of sound-wave propagation, high contrast switching of output orders can be achieved at the driving radio frequency (rf) limit, thereby enabling efficient bidirectional routing of a synchronized mode-locked laser. Here we demonstrate a simplest example of such scheme with a double-AOM setup for efficient diffraction across an octave of rf bandwidth, and for routing a mode-locked pulse train with up to frep = 400 MHz repetition rate. We discuss extension of the composite scheme toward multi-path routing and time-domain multiplexing, so as to individually shape each pulses of ultrafast lasers for novel quantum control applications.

A Dual-Channel High-Linearity Filtering-by-Aliasing Receiver Front-End Supporting Carrier Aggregation

A filtering-by-aliasing (FA) receiver front-end based on a slice-based time-varying architecture was described by Bu and Pamarti (2021). Unlike prior FA architectures, it demonstrated, using a 28-nm CMOS prototype IC, a time-invariant input impedance that enables dual-channel operation with high linearity. Up to 50-dB stopband rejection with a transition bandwidth (BW) of only 3.2 times the RF BW, out-of-band IIP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> of +35 dBm, blocker 1-dB compression point of +12 dBm, and local oscillator (LO) leakage power better than −81 dBm were achieved, using a 0.9-V supply. This article elaborates on the design of this prototype, presents detailed analyses of the slice-based architecture, and shows how it addresses many of the prior FA receivers’ problems.

3D Printed Dual-Band Microwave Imaging Antenna

Microwave imaging utilizes low-power near-field electromagnetic fields at microwave frequencies to detect the internal structure of an object. Sufficient resolution through the thickness is crucial in biomedical applications to detect small objects of concern. Parameters such as the frequency of microwave signals, the design, and the material of the antenna are the most important factors to consider for microwave-based biomedical sensing. The proposed antenna yields merits of: compactness in size, ease of fabrication, wider impedance bandwidth, simple design, and good RF performance. An Asymmetric-fed Coupled Stripline (ACS) antenna is 3D-printed on an FR4 substrate with return loss measurements ranging from 2 GHz to 20 GHz. The impedance bandwidth is obtained between 6 GHz to 8 GHz and 15 GHz to 17 GHz. The proposed microwave antenna was simulated using Ansys HFSS. The parameters are designed to ensure optimum radiation efficiency. The radiation patterns obtained were omnidirectional in H-plane and bidirectional in E-plane.

Optical Versus RF Free-Space Signal Transmission: A Comparison of Optical and RF Receivers Based on Noise Equivalent Power and Signal-to-Noise Ratio

To compare the power efficiency of free-space signal transmission over an optical carrier with that of signal transmission over an RF carrier, we compare the signal to noise ratio and the noise equivalent power of various optical detection schemes with that of simple antenna reception of an RF signal. We point out that for direct optical detection schemes, the noise equivalent power for optical detection is orders of magnitude larger than for RF signal detection with an antenna, with only coherent optical detection requiring similar power levels at the receiver as RF detection with an antenna and mixer, for the same available bandwidth. This is often ignored in articles in which the relative advantages of optical and RF transmission are discussed. Optical transmission mostly has advantages when very high capacity is required and where the available RF bandwidth is small.

Volumetric and multispectral DWI near metallic implants using a non-linear phase Carr-Purcell-Meiboom-Gill diffusion preparation.

DWI near metal implants has not been widely explored due to substantial challenges associated with through-slice and in-plane distortions, the increased encoding requirement of different spectral bins, and limited SNR. There is no widely adopted clinical protocol for DWI near metal since the commonly used EPI trajectory fails completely due to distortion from extreme off-resonance ranging from 2 to 20 kHz. We present a sequence that achieves DWI near metal with moderate b-values (400-500 s/mm2 ) and volumetric coverage in clinically feasible scan times. Multispectral excitation with Cartesian sampling, view angle tilting, and kz phase encoding reduce in-plane and through-plane off-resonance artifacts, and Carr-Purcell-Meiboom-Gill (CPMG) spin-echo refocusing trains counteract T2* effects. The effect of random phase on the refocusing train is eliminated using a stimulated echo diffusion preparation. Root-flipped Shinnar-Le Roux refocusing pulses permits preparation of a high spectral bandwidth, which improves imaging times by reducing the number of excitations required to cover the desired spectral range. B1 sensitivity is reduced by using an excitation that satisfies the CPMG condition in the preparation. A method for ADC quantification insensitive to background gradients is presented. Non-linear phase refocusing pulses reduces the peak B1 by 46% which allows RF bandwidth to be doubled. Simulations and phantom experiments show that a non-linear phase CPMG pulse pair reduces B1 sensitivity. Application in vivo demonstrates complementary contrast to conventional multispectral acquisitions and improved visualization compared to DW-EPI. Volumetric and multispectral DW imaging near metal can be achieved with a 3D encoded sequence.

Novel Unipolar Optical Modulation Techniques for Enhancing Visible Light Communication Systems Performance

Visible Light Communications (VLC) are receiving increased attention in the wireless communications research community. VLC is secured, power efficient, and operates in the visible light range, thus RF communication bandwidth limitation is overcome. In this article, the authors enhance the data rate, system complexity, power efficiency, and spectrum efficiency in VLC systems. An innovative unipolar transceiver system is proposed, mathematically analyzed, and compared with other existing techniques and it demonstrates to have a very high data rate ratio (43.75%) with a good system bit energy to noise ratio (<i>E_b/N_o</i>) compared to other existing techniques. Development for the traditional asymmetrically and symmetrically clipping optical (ASCO-OFDM) system is also proposed, which involves combining a modified receiver with the ASCO-OFDM system traditional transmitter. The proposed receiver reduces the system complexity by O (<i>N</i> log₂ <i>N</i>) with better <i>E_b/N_o</i> than the conventional ASCO-OFDM. Detailed analysis, simulation results, and comparison of the proposed systems with the existing systems are presented beside a brief assessment of existing techniques.

Low-Power High-Linearity Mixer-First Receiver Using Implicit Capacitive Stacking With 3× Voltage Gain

In this article, we present a passive mixer-first receiver front end providing a low-power integrated solution for high interference robustness in radios targeting Internet-of-Things (IoT) applications. The receiver front end employs a novel N-path filter/mixer, a linear baseband amplifier, and a step-up transformer to realize sub-6-dB NF and >20-dBm OB-IIP3 concurrently. The proposed N-path filter/mixer exploits an implicit capacitive stacking principle to achieve passive voltage gain of 3 during down-conversion and high out-of-band linearity simultaneously while using at least 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> less total capacitance for the same RF bandwidth compared to a conventional switch-capacitor N-path filter. Fabricated in 22-nm complementary metal–oxide–semiconductor (CMOS) fully depleted silicon on insulator (FDSOI), the receiver prototype—including a 2:6 transformer—occupies only 0.2 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of active area. Operating in the frequency range of 1.8–2.8 GHz, the front end provides a 45–47-dB conversion gain and a baseband bandwidth of 2 MHz. Due to passive voltage gain in the filter/mixer and transformer, the implemented front end consumes only 1.7–2.5 mW of power to achieve < 6-dB NF, ~24/60/1 dBm out-of-band IIP3/IIP2/B1dB, respectively.

Regenerative terahertz quantum detectors

Because of the ultrafast and photon-driven nature of the transport in their active region, we demonstrate that quantum cascade lasers can be operated as resonantly amplified terahertz detectors with wide RF bandwidth. Tunable responsivities up to 50 V/W and noise equivalent powers down to 100 pW/Hz1/2 are demonstrated at 4.7 THz. Constant peak responsivities with respect to the detector temperature are observed up to 80 K. Thanks to the ≈ps intersub-band lifetime, electrical bandwidths larger than 20 GHz can be obtained, allowing the detection of optical beatnotes from quantum cascade THz frequency combs.

Microwave Photonic Channelizer With Large Instantaneous Bandwidth Based on AOFS

The microwave photonic channelizer can convert the RF signal into the optical domain for transmission and procession, effectively avoiding the limitation of electronic bottleneck, and realizing the instantaneous reception of ultra-wideband signal or multi-frequency signals, which can be perfectly applied to radar system and electronic warfare. In this paper, a microwave photonic channelizer based on dual-output image-reject mixer is proposed, both the signal path and the local oscillator path are divided into three paths by using an optical coupler. An acousto-optic frequency shifter (AOFS) is used by the optical local oscillator to shift the frequency to the left and right and then enters the image rejection mixer with the signal path. Finally, a 6 GHz bandwidth RF signal is divided into six subchannels with a bandwidth of 1 GHz to achieve simultaneous reception. This scheme needs no optical frequency comb and doubles the channelization efficiency, the image rejection ratio of the sub-channels is about 22 dB, and the spurious-free dynamic range of the system can reach 103.2 dB·Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> .

A Wideband Sliding Correlation Channel Sounder in 65 nm CMOS: Evaluation Board Performance

Emerging applications such as wireless sensing, position location, robotics, and many more are driven by the ultra-wide bandwidths available at millimeter-wave (mmWave) and Terahertz (THz) frequencies. The characterization and efficient utilization of wireless channels at these extremely high frequencies require detailed knowledge of the radio propagation characteristics of the channels. Such knowledge is developed through empirical observations of operating conditions using wireless transceivers that measure the impulse response through channel sounding. Today, cutting-edge channel sounders rely on several bulky RF hardware components with complicated interconnections, large parasitics, and sub-GHz RF bandwidth. This paper presents a compact sliding correlation-based channel sounder baseband built on a monolithic integrated circuit (IC) using 65 nm CMOS, implemented as an evaluation board achieving a 2 GHz RF bandwidth. The IC is the worlds first gigabit-per-second channel sounder baseband implemented in low-cost CMOS. The presented single-board system can be employed at both the transmit and receive baseband to study multipath characteristics and path loss. Thus, the singleboard implementation provides an inexpensive and compact solution for sliding correlation-based channel sounding with 1 ns multipath delay resolution.

Ultra-High Bandwidth Radio Frequency and Microwave Photonic Signal Processing Based on Kerr Micro-Combs

Integrated Kerr micro-combs, a powerful source of many wavelengths for photonic RF and microwave signal processing, are particularly useful for transversal filter systems. They have many advantages including a compact footprint, high versatility, large numbers of wavelengths, and wide bandwidths. We review recent progress on photonic RF and microwave high bandwidth temporal signal processing based on Kerr micro-combs with spacings from 49-200GHz. We cover integral and fractional Hilbert transforms, differentiators as well as integrators. The potential of optical micro-combs for RF photonic applications in functionality and ability to realize integrated solutions is also discussed.

Impedance Transparency and Performance Metrics of HBT-Based N-Path Mixers for mmWave Applications

MOS N-path mixer-first receivers are capable of providing instantly-reconfigurable RF impedance and bandwidth while achieving moderate noise figure (NF) and high linearity, but their frequency tuning range is limited by both LO (local oscillator) generation and the RF port input capacitance. State-of-the-art mm-wave MOS N-path receivers often compromise performance to cover the mm-wave range, but this paper presents the theory and design considerations for a new topology of N-path mixer which makes use of high f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> HBTs and breaks this trade-off between performance and tuning range. Here, we borrow from a previously derived LTI model for MOS-based N-path mixers to derive an analogous model for the HBT-based counterpart which provides a meaningful comparison between the performance of the two topologies. We show that the HBT-based implementation is capable of operation beyond the frequency limits of MOS-based implementations while maintaining comparable NF and linearity without consuming exorbitant power. Measurements done on a proof-of-concept chip in GlobalFoundries BiCMOS8HP are consistent with our models and simulations. By organizing process parameters and user-selected design variables into dimensionless ratios, we provide expressions for key performance metrics which enable the designer to make informed decisions about trade-offs and optimizations for both LO generation and the mixer core.

A fully integrated D-band direct-conversion I/Q transmitter and receiver chipset in SiGe BiCMOS technology

This paper presents design and characterization of single-chip 110–170 GHz (D-band) direct conversion in-phase/quadrature-phase (I/Q) transmitter and receiver monolithic microwave integrated circuits (MMICs), realized in a 130 nm SiGe BiCMOS process with ft/fmax of 250 GHz/370 GHz. The chipset is suitable for low power wideband communication and can be used in both homodyne and heterodyne architectures. The Transmitter chip consists of a six-stage power amplifier, an I/Q modulator, and a LO multiplier chain. The LO multiplier chain consists of frequency sixtupler followed by a two-stage amplifier. It exhibits a single sideband conversion gain of 23 dB and saturated output power of 0 dBm. The 3 dB RF bandwidth is 31 GHz from 114 to 145 GHz. The receiver includes a low noise amplifier, I/Q demodulator and ×6 multiplier chain at the LO port. The receiver provides a conversion gain of 27 dB and has a noise figure of 10 dB. It has 3dB RF bandwidth of 28 GHz from 112–140 GHz. The transmitter and receiver have dc power consumption of 240 mW and 280 mW, respectively. The chip area of each transmitter and receiver circuit is 1.4 mm×1.1 mm.

Analytical models of probe dynamics effects on NMR measurements

This paper provides a detailed analysis of three common NMR probe circuits (untuned, tuned, and impedance-matched) and studies their effects on multi-pulse experiments, such as those based on the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence. The magnitude of probe dynamics effects on broadband refocusing pulses are studied as a function of normalized RF bandwidth. Finally, the probe circuit models are integrated with spin dynamics simulations to design hardware-specific RF excitation and refocusing pulses for optimizing user-specified metrics such as signal-to-noise ratio (SNR) in grossly inhomogeneous fields. Preliminary experimental results on untuned probes are also presented.

Hybrid Asymmetrical Load Modulated Balanced Amplifier With Wide Bandwidth and Three-Way-Doherty Efficiency Enhancement

This letter presents a new active-load-modulation power amplifier (PA) architecture, i.e., hybrid asymmetrical load modulated balanced amplifier (H-ALMBA). It is discovered that the control amplifier (CA) of load modulated balanced amplifier (LMBA) can be set as the carrier amplifier and the balanced amplifier (BA) as the peaking amplifier with different threshold settings for two subamplifiers, BA1 and BA2. Through proper amplitude and phase control and cooperative alignment of the turning-on sequence of BA1 and BA2, the entire H-ALMBA can achieve enhanced efficiency overextended power back-off range, similar to a three-way Doherty PA. More importantly, this hybrid load modulation behavior can be replicated over a nearly unlimited frequency span. The theory is well validated by a prototype developed using GaN technology and commercial quadrature couplers, which experimentally demonstrates a 4:1 RF bandwidth from 0.55 to 2.2 GHz and high efficiency, i.e., 55%–82% at peak power, 51%–69% at 5-dB power back-off and 40%–61% at 10-dB power back-off.

Wideband, Circular Polarized Sum and Difference Pattern Coaxial Antenna

We present a compact coaxial flared antenna for communication and tracking applications with a broad instantaneous RF bandwidth greater than alternatives like a circular horn. To solve the free space impedance mismatch due to the small aperture, a flared, impedance transforming outer conductor is proposed. Modal analysis is applied and modal coefficients, as a function of the number of excitations, are assessed; a circular polarized TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> difference mode with the same cutoff frequency as the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> sum mode via impedance matching and specified mode coupling points resulted in a 2.4 to 1 bandwidth. The polarization diverse antenna exhibits linear or circular polarization and is well suited as a direct radiating element or as a feed for low f/D lens or reflector applications.

A Broadband Zero-IF Down-Conversion Mixer in 130 nm SiGe BiCMOS for Beyond 5G Communication Systems in D-Band

This brief presents a broadband D-band down-conversion mixer in a cost efficient 130nm SiGe BiCMOS technology with a f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> /f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 250/370GHz from Infineon Technologies AG. The proposed mixer covers the entire D-band with a 32dB peak conversion gain and a 3dB bandwidth of 35GHz at a measured noise figure between 9.5 and 12dB in the specified band while consuming only 65mW DC power. To achieve large RF and IF bandwidths and a low noise figure, the mixer design is based on a low-biased switching quad, which is loaded with a modified Cherry-Hooper transimpedance amplifier. The results, which are verified by measurements, are based on a detailed analysis of the transistor characteristics, broadband matching networks and an appropriate layout parasitic extraction. All interfaces to the circuit are designed single-ended for a dense chip-to-package transition. For this purpose, high performance Marchand baluns are used at RF- and LO-port, respectively. With a moderate noise figure and a low power consumption, the presented circuit meets the requirements for beyond 5G systems.