Linear Region Of Operation Research Articles

A Modified Algorithm based on the Equal-Areas PWM for the Extend of Linear Operation of a Microprocessor-Controlled PWM-VSI

A modified algorithm based on the Equal-Areas PWM (EAPWM) is being presented in order to extend the linear operation of the inverter in the overmodulation region, while improving the voltage output in terms of fundamental harmonic component amplitude and Total Harmonic Distortion (THD). EAPWM provides an alternative to Regular Sampling (RS) PWM and Space Vector PWM (SVPWM) strategies. EAPWM is a direct digital PWM method that uses the equal areas theorem to determine the pulse widths. This method maintains the commutations through a complete fundamental cycle, in contrast to naturally and regular sampling PWM techniques, where switched pulses progressively disappear for values of modulation index M greater than unity. In addition, this algorithm reveals several linear operating regions of controlling the output fundamental. Simulation and experimental work carried out using a single-phase voltage source inverter (VSI), showing less harmonic content is present for the first harmonic cluster at the switching frequency, compared to (RS) PWM and Space Vector PWM (SVPWM) strategies. This method is suitable for robotic applications where online control through a microcontroller is needed to drive rotating type loads such us ac motor drives and stepper motors.

Detailed characterisation of Si Gate-All-Around Nanowire MOSFETs at cryogenic temperatures

In this work, Gate-All-Around Nanowire MOSFETs have been studied at very low temperatures. DC behaviors have been investigated in the linear operation and saturation regions, giving access to several analog parameters. Static characteristics at 4.2 K and low polarization exhibit step- like variations of the drain current, which can be linked to energy subband scattering. First results on the impact of quantum transport mechanism on the low frequency noise are shown. Finally the low frequency noise spectroscopy has led to the identification of silicon film traps.

Characterization of a signal recording system for accurate velocity estimation using a VISAR

The linearity of a signal recording system (SRS) in time as well as in amplitude are important for the accurate estimation of the free surface velocity history of a moving target during shock loading and unloading when measured using optical interferometers such as a velocity interferometer system for any reflector (VISAR). Signal recording being the first step in a long sequence of signal processes, the incorporation of errors due to nonlinearity, and low signal-to-noise ratio (SNR) affects the overall accuracy and precision of the estimation of velocity history. In shock experiments the small duration (a few µs) of loading/unloading, the reflectivity of moving target surface, and the properties of optical components, control the amount of input of light to the SRS of a VISAR and this in turn affects the linearity and SNR of the overall measurement. These factors make it essential to develop in situ procedures for (i) minimizing the effect of signal induced noise and (ii) determine the linear region of operation for the SRS. Here we report on a procedure for the optimization of SRS parameters such as photodetector gain, optical power, aperture etc, so as to achieve a linear region of operation with a high SNR. The linear region of operation so determined has been utilized successfully to estimate the temporal history of the free surface velocity of the moving target in shock experiments.

Improved compact model for double-gate tunnel field-effect transistors by the rigorous consideration of gate fringing field

In this work, the accuracy of a compact current–voltage (I–V) model for double-gate n-channel tunnel field-effect transistors (TFETs) is improve by considering outer and inner gate fringing field effects. The refined model is benchmarked against technology computer-aided design (TCAD) device simulations and compared against a previously published compact model. The normalized root-mean-square error for current in the linear region of operation (i.e., for 0.05 V drain voltage) is reduced from ∼593 to ∼5%.

Impact of source/drain and bulk engineering on LFN performance of n- and p-MOSFET

In this paper, we present a detailed investigation of the impact of different Lightly Doped Drain (LDD) implants and different well doping on the low frequency noise performance of n- and p-MOS devices from a CMOS technology node. We investigate the impact of three different devices. Two with the same LDD implant but different well doping and one with different LDD implant cocktail. The results demonstrate that the different bulk doping does not affect the low frequency noise performance of the devices. On the other hand there is a serious impact on the noise level of the device with the different LDD implant. In order to further support our results we investigated devices with different lengths in the linear and saturation region of operation.

On The Modeling of Twin Rotor MIMO System Using Chirp Inputs as Test Signals

AbstractThis paper addresses the modeling problem for the twin rotor multi input multi output system. To develop experimental data, this popular commercial laboratory model of a helicopter from Feedback Instruments Ltd is excited with band limited chirp inputs. The conclusions drawn in this paper lead to four significant achievements: 1) derivation of a linear nominal model for Twin Rotor MIMO System, TRMS in short, from its equivalent nonlinear mathematical representation; 2) dynamic modeling of TRMS; 3) determination of non‐minimum phase dynamics; and 4) determination of linear operating region. The work considers systematic study of the system dynamics of TRMS and analytical treatment of its identified data leading to derivation of the RHP zero dynamics followed by pictorial illustrations indicating resonant modes associated with the plant. The method used in the present paper can be essentially used in modeling of 2 × 2 plants exhibiting non‐minimum phase dynamics and model uncertainties.

Abatement of PAPR for ACO-OFDM deployed in VLC systems by frequency modulation of the baseband signal forming a constant envelope

To inhibit the effect of non-linearity of the LEDs leading to a significant increase in the peak to average power ratio (PAPR) of the OFDM signals in the Visible light communication (VLC) we propose a frequency modulated constant envelope OFDM (FM CE-OFDM) technique. The abrupt amplitude variations in the OFDM signal are frequency modulated before being applied to the LED for electro-optical conversion resulting in a constant envelope signal. The LED is maintained in the linear region of operation by this constant envelope signal at sufficient DC bias. The proposed technique reduces the PAPR to the least possible value ≈0dB. We theoretically analyze and perform numerical simulations to assess the enhancement of the proposed system. The optimal modulation index is found to be 0.3. The metrics pertaining to the evaluation of the phase discontinuity is derived and is found to be lesser for the FM CE-OFDM as compared to the phase modulated (PM) CE-OFDM. The receiver sensitivity is improved by 1.6dB for a transmission distance of 2m for the FM CE-OFDM as compared to the PM CE-OFDM at the FEC threshold. We compare the BER performance of the ideal OFDM (without the non linearity of LED), power back-off OFDM, PM CE-OFDM and FM CE-OFDM in an optical wireless channel (OWC) scenario. The FM CE-OFDM has an improvement of 2.1dB SNR at the FEC threshold as compared to the PM CE-OFDM. It also shows an improvement of 11dB when compared with the power back-off technique used in the VLC systems for 10dB power back-off.

Submillimolar Detection of Adenosine Monophosphate Using Graphene-Based Electrochemical Aptasensor

In this paper, we present a successful demonstration of a graphene-based field-effect-transistor-like electrochemical nanobiosensor to accurately detect ultralow concentrations of adenosine monophosphate (AMP). Graphene being a two-dimensional material is a suitable option as a sensing element due to its biocompatibility and large surface area. It has also demonstrated surface binding chemistries as well as its ability to serve as a conducting channel. A short 20-base deoxyribonucleic acid (DNA) aptamer is used as the sensing element to ensure that the interaction between the analyte and the aptamer occurs within the Debye length of the electrolyte. The sensor is found to be nonlinear in nature and sensitive in the picomolar (pM) and nanomolar (nM) concentrations of AMP. The linear region of operation is found to be 1 nM-100 μM and percentage change in drain current in this concentration region is calculated as 1.56%/decade. A minimum concentration of 10 pM of AMP has been detected using this type of sensor.

Seeking maximum linearity of transfer functions.

Linearity is an important and frequently sought property in electronics and instrumentation. Here, we report a method capable of, given a transfer function (theoretical or derived from some real system), identifying the respective most linear region of operation with a fixed width. This methodology, which is based on least squares regression and systematic consideration of all possible regions, has been illustrated with respect to both an analytical (sigmoid transfer function) and a simple situation involving experimental data of a low-power, one-stage class A transistor current amplifier. Such an approach, which has been addressed in terms of transfer functions derived from experimentally obtained characteristic surface, also yielded contributions such as the estimation of local constants of the device, as opposed to typically considered average values. The reported method and results pave the way to several further applications in other types of devices and systems, intelligent control operation, and other areas such as identifying regions of power law behavior.

Innovative approach for electrical characterisation of pseudo‐resistors

Since the use of pseudo-resistors became popular in of bio-amplifiers research, several works have been published, but a lack of knowledge about accurate experimental characterisation and simulation of these non-linear devices remains. An innovative experimental procedure concerning the characterisation of pseudo-resistors is presented. The proposed experimental procedure proves the existence of a linear operation region, where the device can operate like a very high resistance, which is mainly applied on bio-amplifier designs. The main experimental results of the electrical characterisation of pseudo-resistors are described in detail and compared with the SPICE results. The pseudo-resistor experimental curve response including the non-linear operation region is presented. Finally, a new non-linear polynomial resistor model to use in SPICE simulator, replacing with success the electrical representation model based on transistors models is proposed. The presented simulations were performed with Mentor Graphics EldoTM SPICE simulator, using BSIM3V3.1 and PSP103.1 models. The MOSIS Educational Program fabricated the samples used in this work.

An improved analytical and finite element method model of nanoelectromechanical system based micromachined ultrasonic transducers

This paper accurately models the silicon nitride membrane displacement profile of nanoelectromechanical system (NEMS) capacitive micromachined ultrasonic transducer (CMUT). The general analytical model is proposed for the linear and non-linear region of operation with the choice of the appropriate spring constant value. Calculated results are validated with 2-D finite element method (FEM) solver PZFLEX. Full 3-D simulations are carried out to show that for a constant area the circular geometry gives maximum displacement followed by hexagonal and square membranes, respectively. Variation of the membrane displacement with its thicknesses, radii, the electrode separation and voltages are plotted. These demonstrate how a CMUT membrane's displacement can be optimized with a change in structural geometries and biases which is a necessary condition for obtaining the required sensitivity. The model evaluates the collapse voltage very close to experimental and FEM results. The dependency of the resonances on the thickness of the membrane is evaluated. Though this phenomenon is not noticed in the available literature, the FEM results support it. The FEM strain profile also reveals that at the operating biases the structure is working well under its strain limit as predicted by the analytical model.

Hardware implementation of subsampled adaptive subband digital predistortion algorithm

Power amplifiers are key elements for transmission systems that have a high impact on transmission quality and energy consumption. While linearity constraints are set to minimize channel interference, power amplifiers are renowned to have a poor energy efficiency in their linear operation region. And reducing the energy footprint of communication systems is a main challenge for future telecommunication networks. Digital predistortion (DPD) is a technique that aims at linearizing power amplifiers and thus allows energy efficiency improvements. However, this technique usually requires to digitize the distorted signal over its entire bandwidth. Up to now, the distorted signals could be digitized using high-performance analog-to-digital converters (ADC). But, the expected increase in bandwidth for new standards will require even wider bandwidths for the DPD feedback path and larger computational resources. The power consumption caused by the additional parts for the DPD may limit the overall efficiency gain of the linearized system particularly for small-cells base stations. Recently, subband approaches have been proposed to relax the design constraints of the feedback path ADC and the digital processing unit in order to minimize the energy consumption of the DPD. We present in this paper a hardware implementation of a subsampled adaptive subband digital predistortion. We show that running the DPD algorithm on circuits synthesized for lower rate reduces the power consumption by a factor 26.9. This power consumption ratio is approximately five times larger than the subsampling ratio showing the interest of subsampled processing since low rate circuits are more power efficient than their high rate counterparts.

Design and experimental demonstration of electromagnetic actuation utilized on micrograting accelerometers.

This paper presents the design, analysis, and experimental demonstration of electromagnetic actuation utilized on micrograting accelerometers. It mainly consists of a permanent magnet and a driving coil made of three planar printed circuit board coils. A silicon movable platform and the permanent magnet with an axial magnetization of 750×103 A/m form the proof mass. The eight cantilever beams and the movable platform are made by means of the etching process, and the aluminum micrograting is fabricated by the lift-off process. Experimental data show that the electromagnetic force can reach 1.41 mN when the driving voltage is about 2.96 V. The linear operating region of the accelerometer is [-1 g,1 g] under a driving voltage of -2.8 to 2.96 V. A mean sensitivity of 2.82 V/g is obtained by three repeated feedback experiments. In addition, a linear operating region of [-2.2 g,2.2 g] is calculated when the driving voltage is [-7 V,7 V]. There is a linear relation between the driving voltage and the input acceleration.

New sensor and non-contact geometrical survey for the vibrating wire technique

The tolerances for the alignment of the magnets in the girders of the next machine of the Brazilian Synchrotron Light Laboratory (LNLS), Sirius, are as small as 40µm for translations and 0.2mrad for rotations. Therefore, a novel approach to the well-known vibrating wire technique has been developed and tested for the precise fiducialization of magnets. The alignment bench consists of four commercial linear stages, a stretched wire, a commercial lock-in amplifier working with phase-locked loop (PLL), a coordinate measuring machine (CMM) and a vibration sensor for the wire. This novel sensor has been designed for a larger linear region of operation. For the mechanical metrology step of the fiducialization of quadrupoles an innovative technique, using the vision system of the CMM, is presented. While the work with pitch and yaw orientations is still ongoing with promising partial results, the system already presents an uncertainty level below 10µm for translational alignment.

Experiments on a Ku-band gyrotron traveling-wave-tube amplifier with a tapered waveguide

A Ku-band gyrotron traveling-wave-tube (gyro-TWT) amplifier was investigated. To obtain a wide operating bandwidth, we used a two-stage tapered rectangular waveguide interaction circuit. An electron beam of 27 keV and 3.56 A was produced from a double-anode magnetron-injection-gun (MIG). The measured frequency bandwidth over 10 dB gain in the linear operation region was found to be 18%. The gyro-TWT’s saturated output power was 14.9 kW at 14.4 GHz, corresponding to a saturated output power gain of 27.4 dB and an efficiency of 15.5%. The measured experimental results were in agreement with those of non-linear numerical simulations.

Performance and Modeling of a Micro-Grating Accelerometer

We design a packaged micro-optical–electromechanical system (MOEMS) – micro-grating accelerometer – that measures the interference of light resulting from its passage through a diffraction grating and reflection from the proof mass. In the present glass–silicon–glass embodiment, the diffraction optical element made of gold and the sensing proof mass supported by eight aluminum symmetrical cantilevers are fabricated on glass and silicon, respectively. Additional system components include a semiconductor laser, photodiodes, and the necessary electronics. First, we analyze the optical model to achieve high optical sensitivity. Then we optimize the structure parameters using the finite element method. Finally, we successfully fabricated the micro-grating accelerometer and packaged it in a small surface-mount package (12 × 12 × 3.6 mm). Our experiments show that the micro-grating accelerometer has a sensitivity of 5.6 V/G in the linear operating region, a bias stability of 0.94 μG, a resolution of 5.6 μG, and a dynamic range of 82.5 dB. Such a MOEMS accelerometer integrates the micro-grating with the proof mass through an anodic bonding procedure with the advantages of small size and high resolution.

Multi-input intrinsic and extrinsic field effect transistor models beyond cutoff frequency

This work expands the classical theory of operation of FETs beyond cutoff frequency. Using an electron drift transport model, the responsivity of a FET working in the linear region of operation within the semi-classical transport region is derived. Different DC circuit configurations are included in the analysis, as well as multiple AC input signals. Separating the model into intrinsic and extrinsic parts enables better analysis of the effect of multiple input AC signals. A new treatment of the concept of symmetry/asymmetry in FETs beyond the cutoff frequency is presented. The origin of symmetry and factors affecting it are analyzed. The effects of asymmetries from various origins within the FET system are taken into account. The analytical results are used to qualitatively explain published experimental results of symmetry points in FET THz detectors.

Nonlinear Modeling of E-Type Ferrite Inductors Using Finite Element Analysis in 2D.

We present here a modeling procedure for inductors with an E-shaped ferrite core valid for calculating the inductance of an equivalent circuit from the linear operating region to the saturation region. The procedure was developed using Finite Elements in 2D. We demonstrate that using a 2D section of the real core the results obtained are similar to the real ones, which solves the problem of convergence that appeared when E type cores were simulated in 3D, while also saving computational cost. We also discuss the effect of the gap-thickness on the magnetic properties. The data obtained by simulation are compared with experimental results.

A Study of the Linearity Performance of a Stimulated Brillouin Scattering-Based Microwave Photonic Bandpass Filter

The linearity of stimulated Brillouin scattering (SBS) is studied in detail for the first time. A closed-form expression which measures the linearity of an SBS system is derived. This expression allows one to design the region of linear operation, and the amount of Brillouin gain of an SBS system, by altering some basic system parameters. The theory presented is experimentally verified using an SBS-based microwave photonic filter structure. The effect of the length of the Brillouin medium on the linearity of the filter is investigated, and a 9.7 dB extension in the dynamic range is demonstrated by reducing the length of the fibre used as the Brillouin medium, from 25 to 0.57 km, while the filter stopband rejection level remains 30 dB.

Extremum Seeking Control of an Optical Cavity

The frequency locking of optical cavities in the physics community has been traditionally performed using classical controllers. This approach works well as long as the system is not operating far from its linear region of operation. An optical cavity is however a highly nonlinear system and problems arise when it is affected by large disturbances. In this paper, we model the non-linearities arising in such an optical system and propose an extremum seeking controller to frequency lock the optical cavity. Simulation results are presented to validate the proposed scheme.