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This article presents the X-Hall sensor, a viable sensing architecture for implementing a silicon-integrated, broadband, current/magnetic sensor. The X-Hall sensor overcomes the bandwidth limit of the state-of-the-art Hall sensors by replacing the spinning-current technique with dc-biased-based passive offset compensation. In this way, the X-Hall architecture removes the methodological bandwidth limit due to the spinning-current technique and allows for exploiting the Hall probe up to its practical limit, which is set by the parasitic capacitive effects. Moreover, the X-Hall architecture allows pushing the practical bandwidth limit at higher frequencies due to both the removal of the switches inherent in the spinning-current approach and a specially designed analog front end. To this end, a differential-difference current-feedback amplifier (DDCFA) is proposed as an analog front end in the X-Hall sensor. A prototype of the proposed X-Hall architecture is implemented in bipolar-CMOS–DMOS (BCD) 0.16- $\mu \text{m}$ silicon technology to experimentally assess the performance of the X-Hall architecture. The passive offset compensation implemented into the X-Hall architecture is frequency-independent and preserves an adequate offset reduction performance, though less efficient than the spinning-current technique operated at low frequency. Experimental dynamic tests on the prototype identify the presence of an additive parasitic dynamic perturbation due to the package that prevents from fully exploiting the X-Hall prototype up to its designed bandwidth limit. However, the implementation of a postdeemphasis digital filter allows us to mitigate for the dynamic perturbation and experimentally achieve a sensor bandwidth of 4 MHz, which is the broadest bandwidth ever demonstrated by a purely Hall-effect based sensor.

The Error Vector Magnitude (EVM) is a fundamental metric used in communications to quantify the wideband distortion generated by a non-linear device subject to modulated excitation. While typically adopted for impedance-matched devices, the EVM is here investigated for the performance assessment of mismatched power amplifiers (PAs) across wide modulation bandwidths (BWs). A system-level analysis is developed to characterize the EVM for a non-linear device cascaded with a generic linear network. To study particular operating regimes of interest under wideband load mismatch, the EVM measurement process is here applied together with a novel wideband active load-pull technique, leading to a newly implemented frequency-domain characterization platform based on classical relative measurements from a Vector Network Analyzer (VNA). The experimental results ultimately show that the analyzed EVM measurement method can be consistently and effectively combined with load-pull techniques in realistic application cases, enabling improved wideband radio-frequency (RF) PA design and characterization.

Measuring fruit growth can be useful not only to estimate its final weight but this information, in conjunction with environmental data and weather forecasts, can be used to estimate the water and nutrients requirement of an orchard. This paper describes the design of a very low cost system capable to measure sub-millimeter changes in the size of a fruit during its entire growth cycle. This solution overcomes any need of relocating the measuring unit, a severe limitation of other existing devices, without compromising the measurement resolution. The proposed solution uses low cost, easily available components, while maintaining the ability to measure changes in size higher than 30 um and keeping a measuring range between 1.5 and 12 cm.

In recent years, the demand of efficient and broadband wireless access has escalated, for which Radio over Fiber (RoF) is considered as an appropriate solution. In this paper, we present a Digitized Transmission of 20 MHz LTE signal having 64 quadrature amplitude modulation over 70 Km of Standard Single Mode Fiber (SSMF) for broadband wireless signal transportation and distribution applications. The performance analysis has been evaluated for conventional Analog Radio over Fiber (A-RoF) and proposed Digital Radio over Fiber (D-RoF). The bandpass sampling technique is discussed and employed for digitizing the RF signal. As a figure of merit, the performance evaluation of two architectures is reported by analyzing the Error Vector Magnitude (EVM), Signal to Noise Ratio and Eye-Opening Penalty. It is shown that digital optical links can mitigate the impairments present in A-RoF links and can support the transmission up to 70 Km. Moreover, it is shown that efficient D-RoF links can be obtained with a relatively low amount of analog to digital converter (ADC) resolution bits. An experimental validation of the proposed analytical D-RoF model is done for 30 Km of SSMF, whose experimental results are in line with the analytical ones. The evaluated parameters are within the LTE specifications, proving this is a cost and power effective solution for next generation wireless networks.

In this paper, the use of binary sequences for electrochemical impedance spectroscopy (EIS) of battery cells is experimentally investigated by implementing them on a VLSI 1-bit current digital-to-analog converter. Two types of binary sequences are considered, i.e. sigma-delta modulated multisine sequences and maximum-length binary sequences. Their performance is evaluated using a low-complexity experimental setup. Results prove that the two types of sequences are capable of estimating the complex impedance of a battery in the frequency range of interest 1 Hz-200 Hz with an RMSE smaller than 5% with respect to a reference instrument. Both sequences are suitable for implementing online in-situ EIS monitoring, because they enable fast measurement and simple integration within the battery cell itself.

This work describes an on-wafer measurement architecture tailored to the broadband pulsed characterization of radio-frequency (RF) power field-effect transistors (FETs). Based on a 50- Ω environment and corresponding wave-variable domain representation, the set-up exploits the impedance matching and the broadband feature of its components, together with a full-bandwidth calibration, for the synthesis and measurement of pulsed waveforms with short pulse rise/fall times in the order of a few ns, while guaranteeing a reduced risk of oscillations. These measurement capabilities are particularly suited for experimentally assessing the FET performance reduction due to low-frequency dispersive effects caused by thermal and charge trapping phenomena. The flexibility of the set-up is showcased by discussing experimental examples of different measurement techniques in the kHz-to-GHz range, including single- and double-pulsed I–V characteristics and S -parameters, as well as pulsed continuous-wave (CW) measurements, performed on state-of-the-art gallium nitride (GaN) RF FETs for microwave and millimeter-wave applications.

Innovation of the battery technology is of paramount importance for the development and widespread of electrification in transport modes. In addition to the ongoing evolution and research on novel and better chemistries, the application of sensors and measurement techniques at the battery cell level could foster the electrification process by introducing novel concepts like the Smart Battery. This work presents the Smart Battery paradigm and reviews the state-of-the-art sensor technologies that can be of interest for its development in automotive.

This article presents a compact measurement system for electrochemical impedance spectroscopy (EIS) on lithium-ion battery (LIB). The system is composed of a vector impedance analyzer (VIA) and state parameter estimation. The VIA architecture is based on delta–sigma digital-to-analog and analog-to-digital conversions to achieve the compactness, low-power consumption, and high resolution required to be potentially integrated within a battery cell. The estimation of state parameters is based on equivalent circuit models and the solution of nonlinear optimization problems. The proposed measurement system aims at the integration of complex measurement features directly into the battery cell to allow online and real-time diagnostic of the battery cell. A prototype of the compact measurement system was realized to assess the proposed approach. Experimental results are provided and validated by comparison with a reference laboratory instrument, showing good agreement. The VIA prototype is experimentally tested in both the online monitoring and aging monitoring of a commercial LIR2032 LIB cell. The modeling approach is applied to the experimental data provided by the VIA prototype, showing a good fit of the data. Moreover, parameters of the equivalent circuit models are extracted from the experimental data provided by the VIA prototype and identify trends related to the state of charge of the battery.

This work describes a generalized multitone multiharmonic scattering parameters ( $\mathbf {M^{2}S}$ -parameters) measurement approach suitable for multiport nonlinear network characterization in the wave-variable domain. Based on the incommensurate (or offset) frequency concept, the $\mathbf {M^{2}S}$ -parameters are directly measurable quantities independent of the incident wave phases and display a mild nonlinear dependence on the incident wave amplitudes. They feature a well-defined relationship with the frequency-domain nonlinear transfer functions derived from the Volterra theory, representing a generalization to the multiinput multiharmonic case of the widely used single-input single-frequency describing function approach. The proposed framework allows to capture the nonlinear steady-state behavior from a reduced set of measurements and can be effectively exploited for performance prediction in application-like scenarios. The approach is here applied to RF transistor and power amplifier load-pull measurements, as well as to the case of broadband modulation, showing that the performance assessment of the device can be obtained in a straightforward way from the $\mathbf {M^{2}S}$ -parameters description.

Sigma-delta radio over fiber (ΣΔ-RoF) is an expedient technology for next-generation networks including 5G cloud/centralized radio access networks (C-RAN). In this article, we demonstrate a realistic experimental scenario for ΣΔ-RoF link targeting C-RAN fronthaul applications, by using baseband second-order 1-bit sigma-delta modulation (ΣΔ-M). The experimental set-up validates the LTE 20 MHz signals having modulation order of 256-quadrature amplitude modulation for a carrier frequency of 3 GHz, up to 10 km of standard single mode fiber. A detailed analysis of the ΣΔ-RoF system performance is reported by adjacent channel leakage ratio and error vector magnitude. Furthermore, an experimental study is evaluated where ΣΔ-RoF is compared with its counterparts. It is deduced that ΣΔ-RoF corroborates the present range of C-RAN fronthaul networks and can be a promising candidate for future mobile haul applications.

This work presents the design, experimental characterisation, and digital post-distortion (i.e., digital linearisation) of a MHz-range ADC analogue front-end prototype for a gamma radiation spectrometry system under development at the National Center for Nuclear Research (NCBJ) in Poland. The design accounts for the electrical response of the gamma particle detector in providing signal conditioning and ADC protection against high-voltage spikes due to occasional high-energy cosmic radiation, as well as proper ADC clocking. As the front-end inevitably introduces nonlinear distortion and dynamic effects, a characterisation is performed to quantify the actual performance in terms of Total Harmonic Distortion (THD) and Effective Number of Bits (ENOB). Thus, a digital linearisation based on both static and memory polynomial models is successfully applied by means of post-distortion processing, guaranteeing a substantial improvement in THD and ENOB, and demonstrating the effectiveness of the hardware/software method for gamma radiation spectrometers.

This paper describes a low-cost sensor node prototype for in-field, non-invasive fruit growth measurement, with particular emphasis on the calibration procedures required to obtain a significant improvement in stability when environmental conditions change and, thus, optimized performance. Despite the low-cost components used, the prototype allows to continuously monitor the variations in fruit size during night/day and irrigation/chemical cycles with an effective resolution lower than one millimeter. The full-scale implemented achieves 12 cm, overcoming the need of relocating the sensor during the ripening season, as instead typical of high resolution alternative solutions.

A Ka -band monolithic low-noise amplifier (LNA) with high gain and high dynamic range (DR) has been designed and implemented in a 100-nm gallium nitride (GaN)-on-Si technology. The LNA is designed as the first stage of a high DR receiver in an frequency modulated continuous wave (FMCW) radar for the detection of small drones. The three-stage monolithic microwave integrated circuit (MMIC) LNA has a linear gain of 26 dB and a noise figure (NF) of 2 dB in the frequency band 33–38 GHz. The output 1-dB compression point (P1dB) and output IP3 at 37 GHz are 20 and 28.4 dBm, respectively. To our knowledge, this combination of NF, gain, and DR performance represents the state of art in this frequency band.

Radio over Fiber is a promising technology for the 5G Cloud Radio Access Network. We demonstrate experimentally Sigma Delta Radio over Fiber by means of Sigma Delta Modulator (SDM) subsequently replacing expensive digital to analog converters. A second order SDM is proposed for LTE 20 MHz signal having 256 QAM modulation on a carrier frequency of 3.5 GHz for 10 Km of fiber length. The performance is reported in terms of error vector magnitude, adjacent channel leakage ratio and eye-opening penalty. The results show that the proposed architecture performance is cost and power efficient solution for next-generation wireless networks. Keywords: Radio over fiber, Sigma delta modulation, 5G C-RAN, EVM, ACPR

A new method is proposed for the accurate experimental characterization and fully automated extraction of compact nonlinear models for field-effect transistors (FETs). The approach, which leads to a charge-conservative description, is based on a single large-signal measurement under a two-tone sinusoidal wave excitation. A suitable choice of tone frequencies, amplitudes, and bias allows to adequately characterize the transistor over the whole safe operating region. The voltage-controlled nonlinear functions describing the two-port FET model can be computed over an arbitrarily dense voltage domain by solving an overdetermined system of linear equations. These equations are expressed in terms of a new nonlinear function sampling operator based on a biperiodic Fourier series description of the acquired frequency spectra. The experimental validation is carried out on a 0.25- $\mu \text{m}$ gallium nitride (GaN) on silicon carbide (SiC) high-electron-mobility transistor (HEMT) under continuous-wave (CW) and two-tone excitation (intermodulation distortion test).

A multi-tone multi-harmonic scattering (M2S) parameter measurement approach, suitable for multi-port nonlinear network characterization, is proposed. The M2S parameters, based on the concept of incommensurate excitation frequencies, provide a generalization to the multi-input multi-harmonic case of the well-known single-input describing functions representation using only the fundamental frequency. The M2S parameters are directly measurable quantities featuring a mild nonlinear dependency on the incident wave amplitudes only, with the advantage of a much larger information content with respect to single-tone periodic measurements. The validity of the proposed approach is demonstrated for RF transistor and power amplifier load-pull applications, where good accuracy can be achieved with a smaller number of measurements in comparison with conventional load-pull techniques, since the M2S parameters do not depend on the incident wave phases.

A novel and fast method for the measurement-based identification of an analytical field-effect transistor (FET) compact model from large-signal waveforms is presented. Based on a two-tone two-port experiment, a recently published nonlinear function sampling (NFS) operator providing the samples of the FET state functions in the voltage domain is here exploited, for the first time, to extract an equivalent-circuit model. The approach is demonstrated on a 250-nm gallium nitride (GaN)-on-silicon carbide (SiC) high-electron-mobility transistor (HEMT) at 2.5 and 5 GHz.

Analog Radio-over-Fiber (A-RoF) communication technology constitutes a promising technique for next generation radio access networks thanks to its relatively low bandwidth requirements. Within this context, an efficient predistortion technique is proposed, which can be applied to reduce the impairments of A-RoF systems due to the combined effects of frequency chirp of the laser source and chromatic dispersion of the optical channel. The radio frequency signal is firstly put in digital form through an analog to digital converter, then the predistortion operation is realized, and finally the resulting signal is put again into analog form. A comprehensive analysis on the theoretical basis of the proposed approach is presented, together with the approximations introduced, which makes it practically realizable. The improvements on the quality of the received signal due to the proposed solution are illustrated with reference to scenarios of applicative interest. The performance of proposed technique is evaluated in terms of adjacent channel leakage ratio and error vector magnitude when long term evolution signal is applied at the input.

This paper presents a broadband ([dc--megahertz (MHz)]) current sensor for power applications, which is based only on a Hall-effect probe as the core sensing element. Unlike common solutions for broadband current sensing, the proposed architecture is suitable for integration of the measurement system on the same low-cost CMOS chip used for the power electronics (e.g., Bipolar-CMOS-DMOS), without the need for external transformers and allowing for the realization of ``smart power circuits.'' The Hall-effect probe is biased by implementing the offset compensation-oriented spinning-current technique through a novel front-end, designed to push the operative bandwidth toward the fundamental limit of the probe. Specifically, the proposed front-end employs switches, which are typical of spinning-current techniques, only for biasing the Hall probe, while the readout process is performed by minimum-sized differential amplifiers. In this way, the capacitive load seen by the Hall probe is minimized and the sensor practical bandwidth upper limit is strongly increased. A prototype of the proposed architecture was operated at 8-MHz spinning frequency and characterized by means of standard figures of merit, demonstrating the broadband capability and an adequate overall performance. At the same time, the prototype revealed a new bandwidth limit, masked in conventional architectures by stronger capacitance-induced effects, which is represented by a degradation of the effectiveness of the spinning-current technique. Measured performance is comparable to that of standard, nonintegrated, current sensors, demonstrating the effectiveness of the presented purely Hall approach for broadband current sensing. The architecture was validated by discussing two case studies typical of power applications.

Radio over fiber (RoF) is an empowering technology for the next-generation wireless networks including fifth generation cloud radio access networks. In this paper, we propose a new fronthaul interface which has been demonstrated for a 20-MHz LTE signal having 64-Quadrature amplitude modulation (QAM) modulation over 50 km of standard single-mode fiber. The proposed methodology potentially reduces the overall bandwidth requirement of the link. The performance analysis has been demonstrated for conventional analog RoF (A-RoF) and proposed digital RoF (D-RoF). As a figure of merit, the performance evaluation of the two architectures is reported by analyzing error vector magnitude (EVM), signal-to-noise ratio and eye-opening penalty. It is shown that digital optical links can mitigate the impairments present in A-RoF links and can support the transmission up to 50 km. Moreover, it is shown that efficient D-RoF links can be obtained with a relatively low amount of analog-to–digital-converter resolution bits. For the D-RoF link, the EVM was measured to be less than 2 % at 50 km. This is within the LTE specifications, proving it as a cost and power effective solution for next-generation wireless networks.

A fully automatic procedure for the empirical extraction of field-effect transistors (FETs) parasitic network is proposed. By exploiting a grid search approach combined with linear regression, the identification requires Y-parameter measurements at a very few (even just one) bias points. The method is verified in simulation and applied to measurements of a 250-nm GaN high-electron-mobility transistor (HEMT).