Nonlinearity Of Circuit Research Articles

Performance Degradation Prediction of IF Conversion Circuit Based on DE-GWO-SVM Model

Due to the complex structure, nonlinearity and tolerance of IF conversion circuit, the failure probability of IF conversion circuit is greatly increased. To solve the above problems, a differential evolution adaptive grey wolf algorithm (DE-GWO) was proposed to optimize the parameters of support vector machine model, and the model was applied to the fault diagnosis of IF conversion circuit for the first time. Firstly, the energy feature of the output signal of IF conversion circuit was extracted by wavelet packet decomposition, which effectively reduced the dimension of feature vector. Secondly, the improved grey wolf algorithm was used to optimize the parameters of SVM model and establish DE-GWO-SVM fault diagnosis model; Finally, taking the IF conversion circuit as an example, the fault diagnosis experiment was carried out and compared with other methods. Comparison results show that the fault diagnosis accuracy rate of this method reaches 97.33%. Compared with the traditional methods, this method can better improve the fault diagnosis rate and shorten the diagnosis time.

Analysis of the Partial Demagnetization Process of Magnets in a Line Start Permanent Magnet Synchronous Motor

The paper justifies the validity of analyzing the impact of temperature and the process of partial demagnetization of magnets on the operating parameters of machines. To analyze this impact, a field model of coupled electromagnetic and thermal phenomena in a permanent magnet synchronous motor was proposed. The non-linearity of the magnetic circuit, the effect of temperature on the magnetic, electrical and thermal properties of the materials as well as the developed method of modeling the process of partial demagnetization of the magnet were taken into account. Based on this model, an algorithm and software were developed to analyze the effect of temperature and the process of partial demagnetization of magnets on the work of the line start permanent magnet synchronous motor (LSPMSM). The elaborated software was used to study the effect of temperature during the motor starting phase on the magnetization state of the magnets after the start-up process. The calculation results were compared to the results of experimental studies. The experimental tests were carried out on a specially constructed test stand. The results of the research on the process of partial demagnetization of the magnets are presented and the conclusions resulting therefrom formulated.

Precision Improvement of Power-Efficient Capacitive Senor Readout Circuit Using Multi-Nested Clocks

This paper proposes a clock strategy to improve the precision of power-efficient readout circuit for capacitive sensor. To achieve high power efficiency, capacitive sensor such as MEMS accelerometer is designed with open-loop architecture rather than close-loop one. In the open-loop architecture, the capacitance variation of sensing element is limited to femto-farad level in order to overcome nonlinearity problem. However, due to this limitation, the signal charge from sensing element is weak and the interference charge due to coupling capacitance between clock wires and sensing electrodes becomes a significant issue. Therefore, split clock bus is employed to meet this challenge, but the split clock bus introduces the timing mismatch which causes the charge injection sensitive to fabrication process and circuit operating voltage. As a result, the input offset, the variation of the offset and the nonlinearity of readout circuit will increase, and this will lead to reduction of precision. In this work, a clock scheme named “multi-nested clocks” is proposed to address the charge injection problem. The multi-nested clocks are demonstrated in a readout circuit fabricated using a $0.18-\mu \text{m}$ BCD process. The measurement results show that compared to the readout circuit using traditional clock, the readout circuit using the multi-nested clocks significantly reduces the equivalent input offset from 1.66fF to 0.25fF, the offset variation from 1.4fF to 0.2fF and the nonlinearity from 5.5% to 0.9%.

Hybrid Beamforming Transmitter Modeling for Millimeter-Wave MIMO Applications

Hybrid digital and analog beamforming is an emerging technique for high-data-rate communication at millimeter-wave (mm-wave) frequencies. Experimental evaluation of such techniques is challenging, time-consuming, and costly. This article presents a hardware-oriented modeling method for predicting the performance of an mm-wave hybrid beamforming transmitter. The proposed method considers the effect of active circuit nonlinearity as well as the coupling and mismatch in the antenna array. It also provides a comprehensive prediction of radiation patterns and far-field signal distortions. Furthermore, it predicts the antenna input active impedance, considering the effect of active circuit load-dependent characteristics. The method is experimentally verified by a 29-GHz beamforming subarray module comprising an analog beamforming integrated circuit (IC) and a 2 2 subarray microstrip patch antenna. The measurement results present good agreement with the predicted ones for a wide range of beam-steering angles. As a use case of the model, far-field nonlinear distortions for different antenna array configurations are studied. The demonstration shows that the variation of nonlinear distortion versus steering angle depends significantly on the array configuration and beam direction. Moreover, the results illustrate the importance of considering the joint operation of beamforming ICs, antenna array, and linearization in the design of mm-wave beamforming transmitters.

Open-loop digital clock generator based VLSI architecture for electromagnetic interference reduction

Nowadays, the size of the hearing aid devices are reduced to make them invisible and function rapidly. As a result of these factors, an EMI is generated inside the chips. The general working principle of the hearing aid SoC is disrupted by this internal EMI. Thus, an open loop fractional dividers based all-digital clock generator is introduced in the proposed hearing aid SoC. The jitter is reduced by the use of a high resolution digital-to-time converter with its range and duty cycle calibration in background. Also, the nonlinearity of the analog front-end circuit in the proposed hearing aid SoC is reduced by introducing a switching block based dynamic element matching process. Furthermore, an improved noise reduction algorithm is proposed based on pitch based voice activity detector and multiband complex spectral subtraction to improve the performance of the proposed hearing Aid SoC. The proposed hearing aid SoC is designed in an 180 nm CMOS technology. The simulation results show that, integrated jitter of the proposed structure is reduced to 0.9 psrms and it achieves a signal to noise ratio of 89.24 dB. The total power consumption of this hearing aid is only 996 μW for 1.2 V supply that shows the superiority of the proposed work than existing works.

A Highly Linear CMOS Image Sensor Design Based on an Adaptive Nonlinear Ramp Generator and Fully Differential Pipeline Sampling Quantization with a Double Auto-Zeroing Technique

For a complementary metal-oxide-semiconductor image sensor with highly linear, low noise and high frame rate, the nonlinear correction and frame rate improvement techniques are becoming very important. The in-pixel source follower transistor and the integration capacitor on the floating diffusion node cause linearity degradation. In order to address this problem, this paper proposes an adaptive nonlinear ramp generator circuit based on dummy pixels used in single-slope analog-to-digital converter topology for a complementary metal-oxide-semiconductor (CMOS) image sensor. In the proposed approach, the traditional linear ramp generator circuit is replaced with the new proposed adaptive nonlinear ramp generator circuit that can mitigate the nonlinearity of the pixel unit circuit, especially the gain nonlinearity of the source follower transistor and the integration capacitor nonlinearity of the floating diffusion node. Moreover, in order to enhance the frame rate and address the issue of high column fixed pattern noise, a new readout scheme of fully differential pipeline sampling quantization with a double auto-zeroing technique is proposed. Compared with the conventional readout structure without a fully differential pipeline sampling quantization technique and double auto-zeroing technique, the proposed readout scheme cannot only enhance the frame rate but can also improve the consistency of the offset and delay information of different column comparators and significantly reduce the column fixed pattern noise. The proposed techniques are simulated and verified with a prototype chip fabricated using typical 180 nm CMOS process technology. The obtained measurement results demonstrate that the overall nonlinearity of the CMOS image sensor is reduced from 1.03% to 0.047%, the efficiency of the comparator is improved from 85.3% to 100%, and the column fixed pattern noise is reduced from 0.43% to 0.019%.

Dynamic Power Splitting for SWIPT With Nonlinear Energy Harvesting in Ergodic Fading Channel

We study the dynamic power splitting for simultaneous wireless information and power transfer (SWIPT) in the ergodic fading channel. Considering the nonlinearity of practical energy harvesting circuits, we adopt the realistic nonlinear energy harvesting (EH) model rather than the idealistic linear EH model. To characterize the optimal rate-energy (RE) tradeoff, we consider the problem of maximizing the R-E region, which is nonconvex. We solve this challenging problem for two different cases of the channel state information (CSI): (i) when the CSI is known only at the receiver (the CSIR case) and (ii) when the CSI is known at both the transmitter and the receiver (the CSI case). For these two cases, we develop the corresponding optimal dynamic power splitting schemes. To address the complexity issue, we also propose the suboptimal schemes with low complexities. Comparing the proposed schemes to the existing schemes, we provide various useful and interesting insights into the dynamic power splitting for the nonlinear EH. Furthermore, we extend the analysis to the scenarios of the partial CSI at the transmitter and the harvested energy maximization. Numerical results demonstrate that the proposed schemes significantly outperform the existing schemes and the proposed suboptimal scheme works very close to the optimal scheme at a much lower complexity.

Power Minimization in SWIPT Networks With Coexisting Power-Splitting and Time-Switching Users Under Nonlinear EH Model

This paper investigates the simultaneous wireless information and power transfer (SWIPT) networks with coexisting power-splitting users (PSUs) and time-switching users (TSUs) under the nonlinear energy harvesting (EH) model, where a multiantenna hybrid access point (H-AP) transmits information and power to multiple PSUs and TSUs. For such a network, an optimization problem is formulated to minimize the required transmit power at the H-AP subject to users’ information rate and harvested energy constrains by jointly optimizing the H-AP’s transmit beamforming vectors, PSUs’ power splitting (PS) ratios, and TSUs’ time switching (TS) factors. Due to the interferences among PSUs and TSUs, and the nonlinear EH model, the problem is nonconvex and has no known solution method. Thus, a two-layer algorithm is first presented based on semidefinite relaxation (SDR) and it is theoretically proved that the global optimum is achieved. However, since 1-D search is adopted by the two-layer algorithm, which may be too computationally exhaustive, a successive convex approximate-based (SCA-based) algorithm is then proposed as an alternative, which is able to find the near-optimal solution with low complexity by using the first-order approximation. The numerical results show that with the same EH requirements, TSUs are more likely to enter into the saturation region compared with PSUs, but their EH efficiency is higher than that of PSUs. It is also shown that the minimal required transmit power under the nonlinear EH model is much lower than that under the linear one. Although after the saturation point of the nonlinear EH model, the linear one yields a lower required transmit power, it is a fake result, because the linear EH model mismatches the nonlinearity of practical EH circuits.

Dynamic model of the electromagnetic oscillating system with energy losses

The relevance of the research lies in the need to improve the accuracy of dynamic calculations of electromagnetic oscillating systems used in technical systems for the generation of vibrations with a frequency of up to 100 Hz. The research considers the solution of the problem of creating an accurate dynamic single-mass oscillating system with an electromagnetic drive that characterizes the different operation modes and allows a comprehensive analysis of electromechanical processes by means of structural modeling methods. The distinctive feature of this model is the ability to take into account the nonlinearity of the magnetic circuit, leakage fluxes, properties of elastic linkages, viscous friction and sliding friction, external influence and energy losses of electrical and mechanical nature in an electromagnetic oscillating system. To solve the problem of calculating the magnetic field, the standard finite-element modeling FEMM software was used. To calculate the dynamic part of the problem, the calculation algorithm was developed that was implemented by means of structural modeling method in Matlab Simulink software environment. By the example of calculation of periodic electromechanical processes in the electromagnetic oscillating system, the possibilities of the model for a comprehensive analysis of operation processes are considered. According to the results of the research, recommendations for improving the accuracy of calculations of electromechanical processes were obtained.

A High DR, DC-Coupled, Time-Based Neural-Recording IC With Degeneration R-DAC for Bidirectional Neural Interface

The bidirectional neural interface is essential to realize the closed-loop neuromodulation, which is the core of next-generation neurological devices. For the bidirectional neural interface, a recording circuit with a high dynamic range (DR) is required to record the neural signal while stimulating the neuronal cells simultaneously. This article presents a voltage-controlled oscillator (VCO)-based neural-recording IC, which directly quantizes the input signal and achieves a large DR to process the small-amplitude neural signal in the presence of the large-amplitude stimulation artifact (SA). A feedback-controlled source degeneration is applied to the input transconductor circuit ( $G_{\mathrm {m, in}}$ ) by using a resistor digital-to-analog converter (R-DAC). It mitigates the circuit nonlinearity, resulting in a large signal-to-noise-and-distortion ratio (SNDR) and a high input impedance ( $Z_{\mathrm {in}}$ ). The implemented neural-recording IC achieves 81.3-dB SNDR over 200-Hz signal bandwidth and 200-mVpp maximum allowable input range with consuming 3.9 $\mu \text{W}$ per channel. The in-vitro measurement with prerecorded neural signal demonstrates that the original neural signal is well preserved in the presence of the large-amplitude artifact without any saturation or significant distortion.

The Fault-Tolerant Quad-Channel Brushless Direct Current Motor

In this study, a permanent magnet brushless direct current machine with multi-phase windings is proposed for critical drive systems. We have named the solution, which has four-stator winding, a quad-channel permanent magnet brushless direct current (QCBLDC) motor. The stator windings are supplied by four independent power converters under quad-channel operation (QCO) mode. After a fault in either one, two, or three channels, further operation of the machine can be continued in triple-channel operation (TCO) mode, dual-channel operation (DCO) mode, or single-channel operation (SCO) mode. In this paper, a novel mathematical model is proposed for a QCBLDC machine. This model takes into account the nonlinearity of a magnetic circuit and all of the couplings between the phases within a given channel, as well as between channels. Based on numerical calculations, the static electromagnetic moment and the coupled fluxes were determined for the individual windings of the variants and work modes being analyzed. A normal work condition can be achieved in the QCO or DCO modes. For the DCO mode, an acceptable case uses a balanced magnetic pull (A and C channels supplied). The DCO A and B type work mode is comparable to the DCO A and C mode with regard to its efficiency in processing electrical energy. The vibroacoustic parameters of this mode, however, are much worse. In fault states, TCO, DCO, and SCO work modes are possible. As the number of active channels decreases, the efficiency of energy processing also decreases. In a critical situation, the motor works in overload mode (SCO mode). Laboratory tests conducted for one of the variants demonstrated that the TCO work mode is characterized by worse vibroacoustic parameters than the DCO A and C mode.

SWIPT in mMIMO system with non-linear energy-harvesting terminals: protocol design and performance optimization

In this paper, we design the simultaneous wireless information and power transfer (SWIPT) protocol for massive multi-input multi-output (mMIMO) system with non-linear energy-harvesting (EH) terminals. In this system, the base station (BS) serves a set of uplink fixed half-duplex (HD) terminals with non-linear energy harvester. Considering the non-linearity of practical energy-harvesting circuits, we adopt the realistic non-linear EH model rather than the idealistic linear EH model. The proposed SWIPT protocol can be divided into two phases. The first phase is designed for terminals EH and downlink training. A beam domain energy beamforming method is employed for the wireless power transmission. In the second phase, the BS forms the two-layer receive beamformers for the reception of signals transmitted by terminals. In order to improve the spectral efficiency (SE) of the system, the BS transmit power- and time-switching ratios are optimized. Simulation results show the superiority of the proposed beam-domain SWIPT protocol on SE performance compared with the conventional mMIMO SWIPT protocols.

Beam-Domain SWIPT for mMIMO System With Nonlinear Energy Harvesting Legitimate Terminals and a Non-Cooperative Terminal

In this paper, we design the simultaneous wireless information and power transfer (SWIPT) protocol for massive multi-input multi-output (mMIMO) system in the beam-domain (BD). In this system, the base station (BS) serves a set of fixed uplink half-duplex legitimate terminals with nonlinear energy harvester. Meanwhile, a non-cooperative energy harvesting (EH) terminal, which is not pay for the energy transmission or untrusted, is also within the coverage of the BS. Considering the nonlinearity of practical EH circuits, we adopt the realistic nonlinear EH model rather than the idealistic linear EH model. The entire protocol can be divided into two phases. The first phase is designed for legitimate terminals EH and downlink training. A BD energy beamformer is employed for wireless energy transmission. Meanwhile, the received energy of the non-cooperative EH terminal is minimized. In the second phase, the BS forms the two-layer receive beamformers for the reception of signals transmitted by legitimate terminals. In order to improve the spectral efficiency (SE) and energy efficiency (EE) of the system, the BS transmit power and time switching ratio are optimized. Simulation results show the superiority of the proposed BD SWIPT protocol on SE and EE compared with the conventional mMIMO SWIPT protocols.

Maximum Efficiency Tracking Control Method for WPT System Based on Dynamic Coupling Coefficient Identification and Impedance Matching Network

Transfer efficiency (TE) is an important research topic in the practical application of a wireless power transfer (WPT) system. WPT system is a loosely coupled system; the coupling coefficient changes drastically due to the relative movement of the transmitting and receiving sides. It is difficult to achieve maximum efficiency tracking (MET) only from the research of frequency tracking, impedance matching, and system parameters under a fixed coupling coefficient. This article proposes a novel MET control method of the WPT system with optimized T-type impedance matching network under the real-time identification of a coupling coefficient to realize the MET control. This method synthetically analyzes the nonlinearity of the rectifier circuit, the identification of coupling coefficient, the variation of load resistor, and the controllability of the output voltage, involving the main factors of the MET control. The simulation and experimental results show that the WPT system has a good performance on MET and constant output voltage control; the validity and accuracy of the proposed MET control method are consistently verified.

Design for continuous‐current‐mode operation of inductive‐power‐transfer converters with load‐independent output

The control design of inductive power transfer (IPT) converters can be greatly simplified by exploring the property of load-independent output. However, IPT converters can easily enter a discontinuous current mode (DCM) operation due to the non-linearity of the output diode rectification circuit at some loading conditions. The switching between operations of continuous current mode (CCM) and DCM within a switching cycle is highly non-linear, making the converter behaviour difficult to predict and analyse. The well-known first harmonic approximation (FHA) analysis method and the load-independent output property are no longer applicable when the converter enters DCM operation. This paper presents a simple and yet effective harmonic analysis method to reveal the main reason for the converter to enter DCM operation. Subsequently, the load boundary between CCM and DCM operations is derived in detail as a design criterion. A solution by increasing the input impedances at some higher order harmonic frequencies is also suggested to extend the load range against DCM operation. Finally, IPT prototypes using two higher order compensation circuits, having load-independent voltage output and capacitor filter, are demonstrated to verify the theoretical analysis.

Complex Performance Analysis and Comparative Study of Very High-Speed Switched Reluctance Motors

This paper presents the comparative analysis of the characteristic features of two 4/2 switched reluctance motors (SRMs) designed for a very high-speed drive. The use of two-phase construction of SRM with irregular air-step gap makes it possible to achieve the required parameters of the drive. The analysis presents the comparison of two distinct structures designed for the same very high-speed drive. In this paper, a novel mathematical model that takes into account the nonlinearity of the magnetic circuit is presented. The results of numerical calculations and laboratory tests of the influence of the possible use of an anisotropic magnetic material in the rotor magnetic circuit are presented. The influence of control parameters on the motor properties is specified. Both the structures were compared with the respect to employed electric parameters. It is important for high-speed structures that a maximal speed of the motor should not affect permissible parameters of the rotor in a negative way. The high-speed structures should be properly designed to ensure a safety margin. The selected laboratory test results that show electric parameters are presented following the specification of the first critical speed based on the Campbell diagram, the maximum speed limited by allowable stresses. It was shown that both the structures analyzed fulfill the condition of a safety margin. A number of thermal problems of the structures analyzed are discussed. The design assumptions related to the possibility of using a higher current density in the motor windings were verified under laboratory conditions.

FE analysis of coupled electromagnetic-thermal phenomena in the squirrel cage motor working at high ambient temperature

PurposeThis paper aims to elaborate the method and algorithm for the analysis of the influence of high temperature on electric and thermal properties of the materials, as well as thermal phenomena process.Design/methodology/approachThe paper presents specially author’s software for the transient finite element analysis of coupled electromagnetic-thermal problems in a squirrel cage induction motor. The numerical implementation is based on finite element method and step-by-step algorithm. The nonlinearity of a magnetic circuit, the dependence of electric and thermal parameters on temperature, the movement of a rotor and skewed rotor bars have been taken into account. To verify the developed algorithm and software, the influence of high ambient temperature on selected electromagnetic and thermal parameters of the induction motor was examined.FindingsThe results of simulations compared with measurements confirm the adequacy of this approach to the analysis of coupled electromagnetic-thermal problems.Research limitations/implications3D effects have only been taken into account when using quasi-3D techniques (e.g. the multi-slice for skewed rotor slots).Practical implicationsThe author’s software developed can be useful in the analysis and design of squirrel cage motors, especially motors working in high ambient temperature.Originality/valueThe paper offers appropriate author’s software for the transient and steady-state analysis of coupled electromagnetic and thermal problems in squirrel cage motors with skewed slots.

Nanowire Superinductance Fluxonium Qubit.

We characterize a fluxonium qubit consisting of a Josephson junction inductively shunted with a NbTiN nanowire superinductance. We explain the measured energy spectrum by means of a multimode theory accounting for the distributed nature of the superinductance and the effect of the circuit nonlinearity to all orders in the Josephson potential. Using multiphoton Raman spectroscopy, we address multiple fluxonium transitions, observe multilevel Autler-Townes splitting and measure an excited state lifetime of T_{1}=20 μs. By measuring T_{1} at different magnetic flux values, we find a crossover in the lifetime limiting mechanism from capacitive to inductive losses.

Spectral Leakage-Driven Loopback Scheme for Prediction of Mixed-Signal Circuit Specifications

The rising cost of production testing for a system-on-a-chip (SoC) is one of the crucial matters to chip makers, due to long test time and costly automated-test-equipment. This paper proposes a spectral leakage-driven built-in self-test (BIST) scheme to precisely predict the nonlinearity of mixed-signal circuits in the loopback mode, thereby accomplishing cost-effectiveness (compared to previous BIST-based works). A digitally synthesized single-tone sinusoidal stimulus used for conventional harmonic testing is incoherently sampled by a device under test (DUT). The DUT output signal exhibits the correlation between the DUT harmonics and the spectral leakage introduced by the incoherent sampling. The DUT output signal is then fed to another DUT through a loopback path, so that the harmonics of a pair of DUTs are correlated with the spectral leakage on the loopback response; the magnitude of the spectral leakage is considered as a weighting factor on the harmonic magnitude of those DUTs. The correlation is quantitatively modeled as characteristic equations in (15) , and postprocessing predicts the harmonics of the two individual DUTs, by simultaneously solving the characteristic equations using on-chip DSP core available in an SoC. Simulation and hardware measurements validated that this paper can be practically used for production testing by showing less than 0.3 and 0.6 dB of the prediction errors, respectively.

The Feasibility of Injecting Inaudible Voice Commands to Voice Assistants

Voice assistants (VAs) such as Siri and Google Now have become an increasingly popular human-machine interaction method and have made various systems voice controllable. Prior work on attacking voice assistants shows that the hidden voice commands that are incomprehensible to people can control the VAs. Hidden voice commands, though ‘hidden’, are nonetheless audible. In this work, we design a completely inaudible attack, DolphinAttack , that modulates voice commands on ultrasonic carriers to achieve inaudibility. By leveraging the nonlinearity of the microphone circuits, the modulated low-frequency audio commands can be successfully demodulated, recovered, and more importantly interpreted by the voice assistants. We validate DolphinAttack on popular voice assistants, including Siri, Google Now, S Voice, HiVoice, Cortana, Alexa, etc. By injecting a sequence of inaudible voice commands, we show a few proof-of-concept attacks, which include activating Siri to initiate a FaceTime call on iPhone, activating Google Now to turn on the airplane mode, and even manipulating the navigation system in an Audi automobile. We propose hardware and software defense solutions. We validate that it is feasible to detect DolphinAttack by classifying the audios using supported vector machine (SVM), and suggest to re-design voice assistants to be resilient to inaudible voice command attacks.