Nonlinear Cancellation Research Articles

Partitioned block frequency-domain adaptive second-order Volterra filter

Finite-length Volterra filters are known to be able to model a wide range of real world nonlinear systems. In this paper, we present an algorithm that allows for different memory lengths of the linear and quadratic Volterra kernel while preserving the advantages of fast convolution techniques in the frequency domain for a second-order Volterra filter. This is achieved by extending partitioned block methods to second-order Volterra filters. To obtain corresponding adaptive realizations of the proposed approach, we present generalizations of known frequency-domain algorithms for Volterra filters and partitioned block frequency-domain adaptive filters for linear systems, respectively. To exploit the advantages of adaptive frequency-domain algorithms with respect to convergence speed, we provide a frequency bin-wise normalization of the step-size parameters. To evaluate the performance of the proposed approach, simulation results are given for the application to nonlinear acoustic echo cancellation. The results confirm the improved convergence of a second-order partitioned block frequency-domain adaptive Volterra filter (PBFDAVF) compared with time-domain adaptation of the kernel coefficients.

Nonlinear noise cancellation for image with adaptive neuro-fuzzy inference systems

The adaptive neural-fuzzy inference system (ANFIS) algorithm is proposed for nonlinear noise cancellation of images. The quality in terms of mean square error of image restoration using the proposed ANFIS is over 65 times better for Gaussian noise and 500 times better for salt and pepper noise than using conventional filtering systems.

Echo Canceller Algorithm for Adaptive Volterra Filters in Doubletalk States

In an acoustic echo canceller, it is necessary to consider the nonlinearity of an echo path in order to attenuate an echo signal conventionally, and the various methods using adaptive Volterra filters are proposed. Many of those methods have not resulted in the decisive solution about the double talk states in a nonlinear acoustic echo canceller. In this paper, we propose the echo canceller algorithm for adaptive Volterra filters using the idea of the OECLMS (Orthogonal Expanded Correlation Least Mean Squares) algorithm in consideration of the double talk problem. The convergence speed of the proposed method is improved by using Gram-Schmidt orthogonalization for the input signal.

Nonlinear Active Cancellation of the Parametric Resonance in a Magnetically Levitated Body

An active control strategy for the stabilization of parametric resonance in a magnetically levitated body is proposed. The characteristic feature of the strategy is the exploitation of the nonlinear effect of the inertial force associated with the motion of a pendulum-type vibration absorber driven by an appropriate control torque. As a distinguished feature, the proposed control method does not rely on the effective autoparametric energy transfer between the main system and the absorber. Because the main system is not linearly coupled with the absorber, the drawback inherent in the increase of the system degrees of freedom (i.e., the increase of the linear vibrational mode for the main system due to the attachment of the absorber) is overcome. The effective frequency and amplitude of the pure-tone control input—the torque driving the vibration absorber—are designed so that the nonlinear action of the pendulum on the main system counteracts the effect of the resonant parametric excitation. The effectiveness of the theoretically proposed control method is experimentally validated using an apparatus that comprises a phase-lock loop system.

High-frequency characterization and modeling of distortion behavior of MOSFETs for RF IC design

High frequency (HF) distortion of MOSFETs has been characterized at different frequencies and bias conditions with a single tone measurement system. The results show that a MOSFET has much higher "low frequency limit" (LFL) than a bipolar transistor with similar critical dimensions, implying that the HF distortion characteristics of MOSFETs operating at a frequency lower than LFL is dictated by its low-frequency behavior. This discovery is useful for designers and modelers to validate the distortion of a MOSFET model for RF application. It has also been found that the second harmonic P/sub f2/ reaches to its minimum as f/sub T/ peaks, due to a similar nonlinearity cancellation as in bipolar transistors. Furthermore, the measured data shows fairly constant distortion characteristics over a wide range of drain biases as the device operates in the saturation region. Simulation with a BSIM3v3-based sub-circuit model demonstrates that the distortion behavior of MOSFETs can be well predicted by an RF model if it can accurately describe both dc and ac characteristics with proper parameter extraction. Sensitivity of the distortion on various physical effects, such as the mobility degradation, velocity saturation, channel length modulation, and drain-induced barrier lowering, are also studied to provide insights of the key nonlinearity variation contributors from a practical modeling point of view.

Performance analysis of Volterra-based nonlinear adaptive blind multiuser detectors for DS-CDMA systems

The major limitation on the performance and capacity of direct sequence code division multiple access (DS-CDMA) communication systems is the multiple access interference (MAI) due to simultaneous transmission of several users. The linear minimum mean square error (MMSE) detector is a well-known method to suppress MAI adaptively and blindly, however, it is sub-optimal because of the inherent nonlinearity of the system. Therefore, in this paper, two nonlinear blind adaptive interference cancellation algorithms (the exact Newton (EXN) and the approximate Newton (APN)) were proposed and developed based on the 2nd order Volterra expansion. A complete performance analysis of the conventional matched filter (MF) detector, linear adaptive detector (which employs the standard Newton algorithm) and the proposed two nonlinear adaptive (EXN and APN) detectors was carried out in various DS-CDMA systems. Numerical results show that the three Newton type adaptive blind multiuser detectors yield significant bit error ratio (BER) improvement over the conventional MF detector in the presence of strong MAI. Further, the two nonlinear adaptive algorithms always outperformed the linear algorithm. Most attractively, the APN algorithm offers lower computation complexity, higher numerical stability and almost identical BER performance in comparison with the EXN algorithm.

Optimized Link Design for Nonlinearity Cancellation by Optical Phase Conjugation

Nonlinear effects are one of the main causes of pulse degradation in high bit-rate transmission systems and several architectures have been proposed to compensate them by means of optical phase conjugation. In this letter, a new method to exploit an optical phase conjugator for nonlinearity cancellation is disclosed. The proposed method is simpler than those previously described in literature and allows a relevant improvement of systems performances. Link-design rules are analytically studied; moreover, their effectiveness is numerically demonstrated for different applications. This technique can apply to any bit rates and modulation formats.

Simulating nonlinear stator noise for active control

This paper outlines an idea to achieve this type of active control with on-blade actuators. First, a simple analytical example demonstrates how a simple actuator could be used to nonlinearly control sound. Second, results from a realistic geometry demonstrate high amplitude vortical gusts that produce nonlinear harmonics which can destructively interfere with otherwise unattenuating (propagating) acoustical modes. We focus on the 2BPF acoustic response here to simplify the presentation and to show that nonlinear cancellation is effective on realistic blade rows, but similar simulations for higher frequencies have also been successfully completed.

Nonlinear acoustic echo cancellation based on volterra filters

This paper describes a nonlinear acoustic echo cancellation algorithm, mainly focused on loudspeaker distortions. The proposed system is composed of two distinct modules organized in a cascaded structure: a nonlinear module based on polynomial Volterra filters models the loudspeaker, and a second module of standard linear filtering identifies the impulse response of the acoustic path. The tracking of the overall system model is achieved by a modified normalized-least mean square algorithm for which equations are derived. Stability conditions are given, and particular attention is placed on the transient behavior of cascaded filters. Finally, results of real data recorded with Alcatel GSM material are presented.

Robust backstepping control for slew maneuver using nonlinear tracking function

The backstepping control method provides useful control logic, especially for a cascaded system. Because spacecraft dynamics and kinematics form a cascaded system, the spacecraft slew maneuver problem can be solved using the backstepping control method. However, the simple linear backstepping controller may result in poor design: sluggish motion, trivial nonlinear term cancellation, and excessive control input. To overcome these defects, an effective backstepping control method using a nonlinear tracking function is proposed. The proposed backstepping control method is based on the redesign of the Lyapunov function and careful gain selections. To evaluate the effectiveness of the proposed method, numerical simulations including parameter uncertainties are performed. Simulation results demonstrate that the proposed backstepping controller can achieve the slew maneuver with shorter settling time and smaller peak control torque than existing methods.

An Si-SiGe BiCMOS direct-conversion mixer with second-order and third-order nonlinearity cancellation for WCDMA applications

This paper presents a general analysis of the third-order nonlinearity of a differential common-emitter RF amplifier and an improved technique to cancel the third-order nonlinearity. A thorough analysis of the mechanisms leading to the second-order nonlinearity of bipolar double-balanced active mixers is also presented. An SiGe BiCMOS WCDMA direct-conversion mixer is designed based on the third- and the second-order cancellation schemes. The mixer achieves +6-dBm third-order input intercept point, +49-dBm second-order input intercept point, 16-dB gain and 7.2-dB double-sideband noise figure with only 2.2-mA current at 2.1 GHz.

A new perspective on the tracking control of nonlinear structural and mechanical systems

Based on recent results from analytical dynamics, this paper develops a class of tracking controllers for controlling general, nonlinear, structural and mechanical systems. Unlike most control methods that perform some kind of linearization and/or nonlinear cancellation, the methodology developed herein views the nonlinear control problem from a different perspective. This leads to a simple and new control methodology that is capable of ‘exactly’ maintaining the nonlinear system along a certain trajectory, which, in general, may be described by a set of differential equations in the observations/measurements. The approach requires very little computation compared with standard approaches. It is therefore useful for online real–time control of nonlinear systems. The methodology is illustrated with two examples.

Linear Robust Control of Identified Nonlinear Inverse Compensated SI Engine

A technique based on Horowitz’s nonlinear quantitative feedback theory is presented, in which the size of the uncertainty is reduced by cancellation of the plant nonlinearity through nonlinear inverse compensation. Linear identification of the open loop nonlinear inverse compensated plant is used to obtain an unstructured uncertainty representation, however, rather than computing QFT templates based on parametric uncertainty. An increase in achievable robust performance with any linear robust performance control design technique may then be obtained. The method is experimentally validated by application to a SISO automotive SI engine idle speed control problem using an electric dynamometer.

Design of a CMOS opamp input stage immune to EMI

In this paper the behaviour of a complementary nMOS–pMOS differential pair in the presence of RF interference superimposed on the input terminals is analysed. An intrinsic nonlinearity cancellation mechanism in this structure is demonstrated, and proper design criteria are presented to exploit this mechanism in order to achieve a very high immunity to RF interference. A high-immunity complementary differential pair has been employed as an input stage of a folded cascode operational amplifier and its improved behaviour in the presence of RF interference has been verified by computer simulations.

Current-feedback source-degenerated CMOS transconductor with very high linearity

A highly linear current-feedback (CF) transconductor with resistive source-degeneration is developed in CMOS technology. It consists of a differential source follower cascaded with a classical source-degenerated transconductor with its drain current fed back to modulate the bias of the source follower for nonlinearity cancellation, yielding an overall linear transfer function in the circuit. Designed using a 0.35 µm CMOS process for a continuous-time delta-sigma application, the CF transconductor achieves the total harmonic distortion better than −80 dB up to 1 MHz for a 0.8 V input differential voltage while the supply voltage is 2.5 V and the power consumption is 3.4 mW.

Modeling and cancellation of pivot nonlinearity in hard disk drives

This paper considers the issue of modeling the pivot nonlinearity in a typical hard disk drive, taking into account viscous friction, Coulomb friction and hysteresis effects. It presents a nonlinear compensator design, based on a proposed model, to make the compensated system behave like a double integrator regardless of the magnitude of the input current. It describes extensive experiments, carried out in both time domain and frequency domain, to show the effects of pivot nonlinearity and the effectiveness of the compensator.

Continuous Time Universal Filters using Unity Gain Cells

Summary A new circuit configuration for continuous time universal filters using current and voltage followers is proposed. The new configuration employs small number of passive elements. It provides independent control over all filterdesign aspects mainly the natural frequency, ωo, quality factor, Q, and gain. It also allows complete MOS non-linearity cancellation, thus is suitable MOS-C continuous-time fully integrated filters. Analysis ofthe non-idealities associated with the active elements is included. HSpice simulations that confirm theoretical analysis are included.

Multistage Nonlinear Blind Interference Cancellation for DS-CDMA Systems

In this paper we propose a multistage nonlinear blind interference cancellation (MS-NL-BIC) receiver for direct-sequence code-division multiple-access (DS-CDMA) systems. The receiver uses higher order statistics of the received baseband signal. Specifically, we use the second and fourth moments of the received signal to determine a component of the received vector that has significant mean energy and low variability of the energy, both of which are favorable characteristics for application in an interference cancellation scheme that uses hard decisions. The structure of the receiver is multidimensional and can be viewed as a matrix of receivers. Each row in the matrix consists of receivers that perform (hard decisions) cancellation of successive components that have significant mean energy and low variability of the energy. The columns of the matrix essentially resemble multistage receivers that iteratively refine performance from earlier stages. Simulation results show that unlike linear receivers, the MS-NL-BIC is exceptionally efficient in systems with strong and highly correlated interferers, as may be the case in overloaded DS-CDMA systems.

Impact of gamma irradiation on the RF phase noise capability of UHV/CVD SiGe HBTs

This work investigates the effects of gamma irradiation on the residual phase noise performance of SiGe HBTs. The excellent phase noise capability of SiGe HBTs is retained after 1 Mrad(Si) irradiation. The observed radiation hardness is attributed to the minor changes in the low frequency noise and device nonlinearities after irradiations, as well as the nonlinearity cancellation mechanism. The radiation-induced defects do not significantly add to the low frequency noise in these SiGe HBTs, even though they produce a large space-charge-region recombination component in the base current. The inherent excellent linearity of these SiGe HBTs makes the up-conversion from device low frequency noise to phase noise inefficient, and helps to retain the low phase noise after irradiations.

Decision-directed adaptive nonlinear canceller for optical read channels

A simple and yet effective scheme for asymmetry compensation in optical read channels is presented. The simplicity and effectiveness of this scheme make it an excellent candidate for a practical implementation in an optical signal recovery circuit. The performance of this asymmetry compensation scheme is evaluated using bit-error rate (BER) simulation. The results of this simulation show a significant improvement in BER performance when the compensator is included within the read channel circuit.