Charge Control Approach Research Articles

Comprehensive study of charge-based motion control for piezoelectric nanopositioners: Modeling, instrumentation and controller design

High performance motion control of piezoelectric nanopositioners is crucial for a wide range of applications. The primary challenges stem from several aspects, including hysteresis and creep effects, along with the lightly damped mechanical resonance. In view of these issues, this paper proposes a comprehensive charge-based motion control solution, including a generalized electromechanical model, a charge controller with non-resistive DC stabilization and a robust charge control (RCC) strategy. The advantages of charge-based control in system identification and controller design are clearly indicated. Towards this solution, a generalized model of piezoelectric nanopositioner is first proposed, showing the effectiveness of charge control approach in the presence of arbitrarily complicated mechanical dynamics. Furthermore, we present a charge controller with a simple configuration, which eliminates the frequency-dependent performance of classical controller design. This guarantees consistently high control performance over the full operating bandwidth. Finally, to deal with the mechanical resonance and remaining nonlinearities and uncertainties, we propose a control strategy that combines charge control and robust feedback control into a single framework. Superior tracking and damping control performance of the proposed solution is confirmed by extensive experimental validations.

Controllable ion transport by surface-charged graphene oxide membrane

Ion transport is crucial for biological systems and membrane-based technology. Atomic-thick two-dimensional materials, especially graphene oxide (GO), have emerged as ideal building blocks for developing synthetic membranes for ion transport. However, the exclusion of small ions in a pressured filtration process remains a challenge for GO membranes. Here we report manipulation of membrane surface charge to control ion transport through GO membranes. The highly charged GO membrane surface repels high-valent co-ions owing to its high interaction energy barrier while concomitantly restraining permeation of electrostatically attracted low-valent counter-ions based on balancing overall solution charge. The deliberately regulated surface-charged GO membranes demonstrate remarkable enhancement of ion rejection with intrinsically high water permeance that exceeds the performance limits of state-of-the-art nanofiltration membranes. This facile and scalable surface charge control approach opens opportunities in selective ion transport for the fields of water transport, biomimetic ion channels and biosensors, ion batteries and energy conversions.

Design of high stroke electrostatic micropumps: a charge control approach with ring electrodes

A novel design strategy to avoid pull-in occurrence in electrostatic micro electro mechanical systems is proposed. It combines charge control with ring electrodes, on a circular geometry. This idea is introduced here for the design of efficient and reliable high stroke electrostatic diaphragm micropumps, while it has a broad potential applicability. A minimal lumped one degree-of-freedom model is derived and used to introduce and demonstrate the proposed approach for a circular plate geometry. Finite element models are subsequently adopted for a more detailed device modelling. As expected, charge control exhibits a stabilizing effect with respect to voltage drive, but not sufficient to achieve a full-range stability for the considered geometry. When the electrode area is properly defined, stability range can be extended up to gap closure in the central part of the membrane. In this configuration, the increase in voltage required for full-range device drive would be relevant, while in charge control the penalty is considerably lower. Finally, loading conditions and geometrical parameters for an optimized actuation are suggested.

A Charge-Based OTFT Model for Circuit Simulation

In this paper, a mathematical model for the dc/dynamic current of organic thin-film transistors is proposed. The model is based on the variable-range hopping transport theory, i.e., thermally activated tunneling of carriers between localized states, and the mathematical expression of the current is formulated by means of the channel accumulation charge. It accurately accounts for below-threshold, linear, and saturation operating conditions via a single formulation, and does not require the explicit definition of the threshold and saturation voltages. Basing on the charge control approach, the dc model is straightforwardly generalized to dynamic conditions; the resulting mathematical expressions are simple and suitable for CAD applications.

A charge control analytical model for organic thin film transistors

In this paper, a mathematical model for the dc current of organic thin film transistors is proposed. The model is based on the variable range hopping transport theory, while the mathematical expression of the current is formulated by means of the channel accumulation charge. It accurately accounts for below-threshold, linear, and saturation operating conditions via a single formulation and it does not require the explicit definition of the threshold and saturation voltages. Furthermore, thanks to the charge control approach, it is straightforwardly generalizable to dynamic behavior.

Analytical noise model of a high‐electron‐mobility transistor for microwave‐frequency application

AbstractNoise analysis for AlGaAs/GaAs HEMT and AlGaAs/InGaAs/GaAs PHEMT is developed at microwave frequency using an accurate charge control approach. The small‐signal parameters and the drain and gate‐noise sources are calculated to determine the noise coefficients and correlation coefficients. Finally, the minimum noise figure is evaluated by incorporating the extrinsic noise sources and compared with the experimental data, which is in excellent agreement. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 410–417, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11396

A theory of high-frequency distortion in bipolar transistors

High-frequency distortion in bipolar transistors is examined by using the charge-control approach of Poon and Narayanan (H.C. Poon, IEEE Trans. Electron Dev., vol. ED-19, pp. 719-731, 1972; S. Narayanan and H.C. Poon, IEEE Trans. Circuit Theory, vol. CT-20, pp. 341-351, 1973; H.C. Poon, IEEE Trans. Electron Dev., vol. ED-21, pp. 110-112, 1974) to connect the device's distortion behavior to its loaded unity-current-gain frequency (/spl omega//spl circ//sub T/). The resulting expressions for the distortion reveal considerable information on its frequency and bias dependence. Points on the /spl omega//spl circ//sub T/ versus collector current curve yielding optimum distortion performance are identified and interpreted in terms of current cancellation. Both second- and third-order distortion are considered, and the results are validated by both simulation and experiment.

An accurate charge control approach for modeling excess phase shift in the base region of bipolar transistors

The conventional charge control approach is extended to enable the accurate determination of excess phase shift in the ac common-emitter current gain of bipolar transistors arising from distributed stored minority carrier charge in the neutral base. Generalized expressions, valid for transistors with arbitrary impurity profiles and position-dependent transport parameters, are presented from which the excess phase shift can be determined solely from device structure and process data. The ac model parameters which result from the extended charge control approach are used in an existing high-frequency compact nonquasi-static bipolar model which is suitable for SPICE simulation.

A quasi-two-dimensional HEMT model for microwave CAD applications

A new quasi-two-dimensional HEMT model has been developed that solves the physical device equations in a more rigorous fashion than previously reported. The model incorporates a quantum mechanical description of the free electron concentration, self-consistently solving the Schrodinger and Poisson equations. The influence of traps and incomplete donor ionization are also included. The conventional one-dimensional charge-control approach is shown to be inadequate for HEMT's and is replaced by a two-dimensional version that more accurately describes the channel dynamics under normal bias conditions. This allows the simulation to accurately model pinch-off characteristics, which are essential for digital, power and low-noise device characterization. The scheme also includes a detailed energy transport model, avalanche breakdown and gate conduction terms. The highly efficient model is applied to the DC and microwave characterization of AlGaAs-GaAs and pseudomorphic HEMT's. >

Investigations on turn-off effects in fast-recovery power diodes by modelling and simulation

A model describing the transient turnoff behaviour of a fast-recovery power diode is derived and implemented into a simulation program for analysis of electrical networks. The modelling is based on the physical processes in the low-doped middle region of the semiconductor device, using the charge control approach and approximating the excess charge distribution by sinusoidal curves. The transient behaviour of the model is verified by experimental measurements in a chopper circuit with a MOSFET as the switching element.

Current-voltage characteristics of bipolar transistors including quasi-saturation, finite collector lifetime, and high-low junction effects

Abstract A physics-based and compact model is developed to predict the bipolar transistor DC characteristics covering all saturation, quasi-saturation, and active operations. The present model differs from the existing models in that the present model employs a regional approach rather than the charge-control approach used previously and that the present model requires only the physical parameters, such as device make-up, whereas the previous models often require parameters extracted from measurements. Device physics relevant to the base-collector junction, like current-induced base widening and conductivity modulation and electron-hole recombination in the quasi-neutral collector layer, are accounted for in the analysis. We show that the current-voltage characteristics predicted by the present model compare favourably with that obtained from measurements and simulations reported in the literature.

Millimeter-wave performance of ultrasubmicrometer-gate field-effect transistors: A comparison of MODFET, MESFET, and PBT structures

Device structures for the modulation-doped high-electron-mobility transistor (MODFET or HEMT), the metal Schottky-barrier gate transistor (MESFET), and the permeable-base transistor (PBT) With 0.1- to 0.25-µm gate lengths have been examined for their millimeter-wave performance. In particular, their unity-current-gain frequency (f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> ), maximum oscillation frequency (f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> ), and the stability of power gains are Compared. It is shown that in field-effect transistors with gate lengths below 0.25 µm, the high aspect ratio design approach, involving the ratio of the gate length to its associated depletion depth, needs to be extended to include the gate-to-drain separation in an effective gate-length concept. Using the charge-control approach in conjunction with the carrier velocity saturation effect, it is shown that the overall transit time delay across the total effective gate length results in an effective gate capacitance that is significantly larger than that due to the physical size of the gate itself. It is shown with specific examples that a successful design of these ultrasubmicrometer gate structures depends on the choice of the gate-to-drain separation (L <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GD</inf> ) and the separation (d <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> ) between the gate and the channel sheet Charge, with an appropriate choice of doping concentration consistent with the desired drain voltage operation. The designs have been based on practically obtainable values of the gate and source series resistances. When the actual gate length is much smaller than L <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GD</inf> , as in the case of PBT's, it is shown that the stable power gain margin in these devices is determined by the square of the aspect ratio (L <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GD</inf> /d <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> ). The results show that an f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> of approximately 350 GHz can be achieved from a MODFET structure with an effective gate length of 0.14 µm. In a PBT structure an f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> exceeding 500 GHz can be achieved with an effective gate length of 0.15 µm, and in a similar MESFET structure an f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</inf> of approximately 450 GHz can be achieved. The device design approach presented clearly indicates the possibility of achieving FET'S operating beyond 200 GHz with useful power gains.

Studies of turn-off effects in power semiconductor devices

An analytical model has been developed for analyzing current and voltage transients during high power diode recovery. Using the charge control approach and approximating the excess charge distribution by simple geometrical curves a fast and convenient method for computer analysis is obtained. The model is thoroughly physical and makes use of the proper diode design parameters and the differential equations of the electrical network. There is no need for any experimental fitting parameter. All relevant complicating effects as emitter recombination, nonabrupt pn-junction and reverse current influence on the space-charge layer are considered. Comparisons between calculated and measured recovery behavior under several different conditions show good agreement and prove that the model may serve as a useful tool in device and circuit development including RC-snubber design. Furthermore, the calculated charge distribution varies during the recovery in a physically reasonable manner. Starting from measured recovery transients this model may also be used as a new method for determining the excess charge content in the diode at the beginning of the recovery phase.

Pulse generation employing saturation-controlled transistor inverters

An IC compatible variable-frequency pulse generation scheme employing saturation-controlled bipolar transistor inverters is presented. Simple expressions for various time delays figuring in the pulse time period are ohtained using the charge control approach. The experimental performance of the circuit shows good agreement with the theoretical results. The synchronization aspect of the pulse generator is discussed. Various applications of the pulse generator are also outlined.

On the control of saturation in bipolar transistors

A bipolar transistor inverter circuit having a provision of continuous control of saturation time is presented and analysed using charge control approach.

Modeling the dynamic behavior of I/sup 2/L

The validity of the charge control approach is checked for the normal (upward) operation of an I/SUP 2/L gate, leading to the conclusion that deviations are mainly due to the distributed nature of the base resistance. An alternative method is presented to determine the relevant device parameters, starting from experimental data. An equivalent model, incorporating the distributed base resistance, is proposed and verified by simulating the power delay characteristics of ring oscillators.

Description of a technique for the reduction of thyristor turn-off time

A thyristor structure is provided with an anode-gate electrode which is used to speed up the device recovery and reduce its turn-off time. The turn-off process of the anode-gate thyristor is analyzed qualitatively using the charge control approach. Experimental device structures are described and the results of measurements are reported.

Charge-control method of charge-coupled device transfer analysis

An analysis of charge transfer based on the approach has been made for charge-coupled devices (CCD's). A general closed-form equation for the charge transfer efficiency has been obtained that includes the major mechanisms of 1) charge-gradient induced drift, 2) thermal diffusion, 3) an external fringing field, and 4) charge loss due to traps or recombination. When the charge loss and fringing field terms are neglected, the results are in close agreement with the numerical solutions by Strain and Schryer. With the fringing field term included, the closed-form solution compares well with the numerical results by Heller, Chang, and Lo. The effect of charge loss on the transfer efficiency is studied and the temperature dependence of the efficiency, including the temperature dependent surface mobility, is discussed. The effect of a fat zero on the diminution of a digital one is discussed with and without charge loss to surface states. It is believed that the charge-control approach not only simplifies the mathematics involved, but also provides practical charge-coupled device and circuit design guides.

Charge control approach to the small signal theory of field-effect devices

The operation of a field-effect device is described in terms of the total charge in the channel region. The analysis is primarily developed for the small-signal operation for which the charge control equations are linear and have constant coefficients. The complete expressions for the small signal admittance parameters are obtained in both the linear and the pinch-off regions leading directly to equivalent circuits. It is believed that the charge control approach not only simplifies the mathematics involved, but provides new insights into device operation as well.

High injection in epitaxial transistors

An analysis of base widening and the current dependence of the cutoff frequency f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> has been given previously [1]. The analysis is approximate and is based on the location of the edges of transition regions. Definition of transition regions becomes problematic in transistors having nonuniform base doping and for high-current densities. Such difficulties are avoided in this paper by use of the charge control approach. Numerical solutions of delay time ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">= 1/2\pi f_{T}</tex> ) as a function of current density are given for low reverse collector bias. Whereas transition regions can be defined only approximately, the electric field is a well-defined quantity, and changes in the electric field that accompany base widening are shown in detail. At low injection levels, a high-field region exists near the transition between base and epitaxial layer. This high-field region is relocated to the interface between epitaxial layer and substrate under high injection conditions. When this "high-field relocation" has occurred, the epitaxial layer acts as an extension of the base with an attendant increase in the delay time [1].