Feedback Path Research Articles

Efficient Real-Time Acoustic Feedback Cancellation using Adaptive Noise Injection Algorithm.

Acoustic feedback cancellation is a challenging problem in the design of sound reinforcement systems, hearing aids, etc. Acoustic feedback is inevitable when the acoustic signal path forms a loop between the microphone and loudspeaker. An efficient short duration noise injection algorithm is proposed in this paper to estimate the impulse response of the acoustic feedback path model. The algorithm does not require any prior information about the acoustic feedback path. It is capable of optimally estimate the acoustic feedback path for cancellation, and avoid the occurrence of any howling episode, in varying acoustic environments. Presented algorithm is efficiently implemented on smartphone device having close proximity of loudspeaker and microphone to emulate the feedback condition. The algorithm being platform-independent can also be implemented for any set-up or system. The experimental results of the proposed method shows satisfying results and its ability to track and cancel the acoustic feedback in changing characteristics of the acoustic path.

Design-oriented fast response voltage mode buck converter with adaptive ramp control

This paper proposes a new adaptive ramp voltage mode control scheme. Instead of using the conventional slow compensation path of the voltage mode, the proposed scheme adds an extra feedback path to adjust the amplitude and DC-offset of the ramp signal and to directly accelerate the duty cycle according to the output voltage variation. In addition, a design-oriented analytical method is adopted to intuitively analyzes the loop characteristics and provides accurate instructions for the implementation and optimization of the compensator. A 5–1 V buck converter is implemented in the proposed adaptive ramp control scheme with optimized compensation. Simulation and measurement results show that the converter achieves a bandwidth of up to 591 kHz with a 3 MHz switching frequency and a 65° phase margin. In addition, the undershoot voltage and the recovery time are 16 mV and 19 μs with a load change from 0.5 to 1 A. The proposed control scheme shows superior transient response performance while maintaining fixed frequency operations with a simple system structure.

A Single-Stage Natural Power Factor Corrector Based on Dual Active Bridge DC–DC Converter Without Inner Current Tracking Loop

In this article, a single-stage ac-dc based on the dual active bridge with natural power factor correction is proposed. A modulation strategy and a control technique have been given to achieve the unity power factor of the ac side without inner current tracking loops and lookup tables. A notch filter is used in the output voltage feedback path to reduce the influence from the low-frequency output-voltage ripple to the regulator. All of the input-side power devices can achieve zero voltage switching (ZVS) on and all of the output-side power devices can achieve ZVS under certain load conditions with the proposed control strategy. The ZVS conditions and parameter design are given in this article. A 1.4-kW prototype has been fabricated to verify the effectiveness of the proposed converter and control strategy.

Handling-Qualities Perspective on Rotorcraft Load Alleviation Control

The objective of this research effort is to assess the impact of load alleviation control on the quantitative handling-qualities specifications (also known as predicted handling qualities) of both conventional helicopters and compound rotorcraft in forward flight. First, an overview on how the harmonic decomposition methodology is used toward load alleviation control is presented. Next, flight control laws are developed based on an explicit model-following architecture. Parametric studies are performed to provide insights on how both the feedforward and feedback paths of the model-following control laws can be used to alleviate the rotor loads. The impact of load alleviation on predicted handling qualities is studied. It is shown that, for the standard helicopter configuration considered, load alleviation comes at the cost of a degradation in handling qualities. However, for the compound rotorcraft considered, allocation of the control signal to the redundant control surfaces provides load alleviation without degradation in predicted handling qualities. The flight control laws are subsequently optimized using the Control Designer’s Unified Interface to meet a comprehensive set of stability, handling-qualities, and performance specifications for specific mission task elements while minimizing the unsteady rotor loads.

Phase-domain ADC with ∆-modulation frequency tracking loop

The principle of ∆-modulation has been leveraged in time-domain to cancel the nonlinearity of voltage to frequency transfer function in VCO-based ADCs. The proposed modulation technique features frequency-tracking loop (FTL) to compensate for the imperfection of frequency nonlinearities and to eliminate the analog Op-Amp. Injection locking is used to alleviate the mismatch effect between the feedforward and feedback paths. The circuit level design and simulation results validate the functionality. The proposed solution can achieve higher noise shaping orders and better resolutions without compromising the hardware complexity by using fully synthesizable digital accumulators.

A High-Input Voltage Two-Phase Series-Capacitor DC-DC Buck Converter

A high-input voltage 2-phase series-capacitor (2-pscB) DC-DC buck converter is theoretically analyzed, designed, and implemented. A new design approach for an automatic current sharing scheme was presented for a 2-phase series-capacitor synchronous buck converter. The series-capacitor voltage is used to achieve current sharing between phases without a current sensing circuit or external control loop as each phase inductor charges and discharges the series capacitor to maintain its average capacitor voltage constant. A novel isolated gate driver circuit to accommodate an energy storage capacitor is proposed to deliver isolated gate voltages to the switching transistors. An I2 control scheme that uses only one feedback path control for the four gate drivers is proposed to enable higher voltage conversion. An experimental 110-12 V 6 A load prototype converter was designed, and its current sharing characteristics were experimentally verified.

Double-High-Pass-Filter-Based Electrical-Recording Front-Ends and Fluorescence-Recording Front-Ends for Monitoring Multimodal Neural Activity

This brief presents a multimodal neural activity monitoring system consisting of a double-high-pass-filter-based electrical-recording front-end and a fluorescence-recording front-end. The proposed electrical-recording circuit based on double high-pass filters is implemented by placing a narrow-band buffer in the feedback path of the low-noise and programmable-gain amplifiers so that low-frequency artifacts can be sufficiently suppressed during the electrical and fluorescence recording. The implemented system successfully measures the electrical signals and calcium ions in vivo for studying heterogeneous cell populations. For electrical recording, the front-end consumes the power of 2 $\mu \text{W}$ /channel and achieves the input-referred noise of 2.9 $\mu \text{V}_{\mathrm{ rms}}$ . The high-pass cutoff frequency can be programmed from sub-1 Hz to about 300 Hz using the function of double high-pass filtering. For fluorescence recording, the front-end consumes the power of 10.8 $\mu \text{W}$ /block and occupies the area of 0.18 mm2/block.

Multiple model hybrid adaptive vibration control for flexible cantilever beam with varying load

To solve the vibration suppression problem for a piezoelectric flexible cantilever beam with varying load, this study proposes a new type of multiple model hybrid adaptive vibration control method with a new multiple model switching cost index function. It employs a pre-filter consisting of secondary path and positive feedback path model to eliminate the positive feedback between the secondary actuator and reference sensor. By constructing a piezoelectric flexible cantilever beam as the controlled plant, we constructed a real-time control verification experiment platform based on a real-time MATLAB xPC target. We did a real-time control experiment comparison for vibration suppression of single-frequency, narrowband, and broadband disturbances. Experimental results show that the proposed multiple model hybrid adaptive vibration control algorithm is feasible and has good vibration suppression performance with rapid convergence speed.

Direct Torque and Flux Control of PV Connected Permanent Magnet Synchronous Machine

This paper presents a direct torque and flux control (DTFC) method of PV array fed permanent magnet synchronous machine in (d-q) frame. This method retains the traditional DTFC principle of decoupling torque and flux control to compensate the torque and flux errors in a smooth manner with conventional DTFC, while providing greater use of voltage source inverter using optimal switching. Also a feedback path using PI controller is introduces in this system to regulate the speed and to reduce the error. Here, we have presented satisfied results of DTFC method in PMSM with close loop speed controller. All the results are performed in MATLAB Simulink platform.

Developing Teacher Feedback on Written Work Within the Process Approach: One Way Of Improving the Students’ Composition

Issues in EFL and ESL have revealed that students’ performance in writing remain unsatisfactory although the teacher has tried to apply an appropriate technique as maximally as possible. This article discusses about how a teacher can develop feedback technique on Writing by applying the process approach as one way of improving the students’ composition. On the basis of the technique, there are two types techniques the teacher may apply in Writing by using the process approach, namely written comment and student-teacher conference. The use of both forms will simultaneously maximize the amount of feedback and the quality of feedback required for effective revision of the working draft. The appropriateness and accuracy of these techniques as matter of fact depend on several factors: ability, personality, and attitude of the teacher towards a particular technique, and the learners’ need, abilities, and attitude, the number of students in the class, and the time allotment in the actual teaching –learning situation. Consequently, the students need to be encouraged to see Writing as a means of learning rather than demonstrating learning. Furthermore, the teacher feedback activities will be seen as a vehicle to lead the learner towards the path of self feedback in the process of writing.

Reduction of harmonic current distortion for single‐phase grid‐tied inverter operated in discontinuous current mode

AbstractDiscontinuous current mode (DCM) with high‐frequency operation can be an effective way to reduce the volume of inductors for low‐power grid‐tied inverter applications. Unlike the controllers designed for continuous current mode operations, current controllers for DCM are required to address their nonlinear characteristics. A feed‐forward controller can be a good choice for the current control of the grid‐tied inverters operated in DCM. However, distortions in the output current cannot be eliminated, and they can be more severe if devices with large output capacitance are applied. Two harmonic current reduction strategies, namely a partial feedback path and an improved modulation, are proposed to reduce the low‐ and high‐order harmonics for single‐phase grid‐tied inverters operated in DCM. The proposed strategies are discussed and verified by a laboratory prototype in some experiments. It is indicated that the proposed modulation can mitigate the influence of device parasitic capacitance on current distortion and expand the device selections. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Graph Representations for Programmable Photonic Circuits

We propose graph representations for reconfigurable photonic mesh circuits. Waveguide mesh circuits are abstracted into a graph to highlight the connectivity and topology. We model the optical ports as graph nodes. Performance metrics for each connection are incorporated into the edge attributes in categories such as propagation loss, crosstalk penalty, power consumption, phase accumulation, and so on. We use three types of graph representations for tunable couplers to model the flow of light and create a circuit graph representation to an example hexagonal mesh. The representation should respect the physics of waveguide circuits (e.g. directional flow of light). Of the three types, the directed graph with eight artificial nodes performs best for solving light distributions with feedback paths. This graph representation is demonstrated in four distribution cases: a single pair input-output, multi-pair inputs and outputs without collisions, a single input to multiple outputs (distribution), and multiple distributions without collisions. The programming tolerance against malfunctioning tunable elements is also demonstrated. With this circuit representation, we can reduce all these distribution cases to different graph problems and leverage a wealth of existing algorithms developed in graph theory to program the photonic mesh. Thus we provide a systematical strategy to design and program complex reconfigurable photonic circuits, especially in photonic meshes with feedback paths.

Temporal Pyramid Recurrent Neural Network

Learning long-term and multi-scale dependencies in sequential data is a challenging task for recurrent neural networks (RNNs). In this paper, a novel RNN structure called temporal pyramid RNN (TP-RNN) is proposed to achieve these two goals. TP-RNN is a pyramid-like structure and generally has multiple layers. In each layer of the network, there are several sub-pyramids connected by a shortcut path to the output, which can efficiently aggregate historical information from hidden states and provide many gradient feedback short-paths. This avoids back-propagating through many hidden states as in usual RNNs. In particular, in the multi-layer structure of TP-RNN, the input sequence of the higher layer is a large-scale aggregated state sequence produced by the sub-pyramids in the previous layer, instead of the usual sequence of hidden states. In this way, TP-RNN can explicitly learn multi-scale dependencies with multi-scale input sequences of different layers, and shorten the input sequence and gradient feedback paths of each layer. This avoids the vanishing gradient problem in deep RNNs and allows the network to efficiently learn long-term dependencies. We evaluate TP-RNN on several sequence modeling tasks, including the masked addition problem, pixel-by-pixel image classification, signal recognition and speaker identification. Experimental results demonstrate that TP-RNN consistently outperforms existing RNNs for learning long-term and multi-scale dependencies in sequential data.

대역확산 기법을 사용한 단일 채널 중계기 개발

This paper describes the elimination of feedback signals to implement a stable on-channel repeater regardless of input signals in the frequency bandwidth desired by the user. Toward this objective, the spread spectrum technique is applied to an adaptive filter, in which the least mean square algorithm removes the frequency characteristics of input signals. OCRs have been commercialized using adaptive filters based on the LMS algorithm in existing mobile communication services, including in GSM, CDMA, WCDMA, and LTE. However, in current mobile communication networks, various services with different signal characteristics can become mixed in the user’s frequency band, and bands with no signals may also exist. If the integrated bandwidth and the occupied bandwidth do not coincide, a bandpass filter cannot completely suppress other bands. Because the LMS algorithm is affected by the frequency characteristics of input signals as well as the feedback path of the object to be removed, feedback signals cannot be canceled for the entire band. Therefore, in this paper, the SS technique is applied to the existing LMS method to remove the frequency characteristics of input signals, thereby eliminating feedback signals in a more stable manner. The performance of the proposed scheme is verified through simulation and experiments.

A Computationally Efficient Integrated Coupled Opto-Electronic Oscillator Model

Coupled opto-electronic oscillators can generate microwave signals with very low phase noise. Several approaches for modelling these oscillators exist, but none of them include the fast carrier dynamics of the mode-locked laser, due to computational limitations. In this work, we present a new model, that is based on a computationally efficient model for semiconductor mode-locked lasers, which is capable of simulating both the fast laser dynamics and the long term phase stability. We use it to model the phase noise of a hybridly integrated coupled opto-electronic oscillator. The results show that a timing jitter of down to $\mathbf {\sim} \text{0.2}$ $\text{ps}$ in the integration range from $\text{10}$ $\text{kHz}$ to $\text{10}$ $\text{MHz}$ is achievable when using an integrated delay line of $\text{10.2}$ $\text{m}$ in the opto-electronic feedback path. It is also shown that by increasing both gain and bandwidth of the opto-electronic feedback link, the timing jitter is reduced. Together, these results present a path towards low phase noise performance of hybridly integrated coupled opto-electronic oscillators, and the model serves as a new design tool. Such oscillators might increase, for example, the spectral efficiency in future data communication systems and thus enable higher data rates.

Sparse identification of contrast gain control in the fruit fly photoreceptor and amacrine cell layer

The fruit fly’s natural visual environment is often characterized by light intensities ranging across several orders of magnitude and by rapidly varying contrast across space and time. Fruit fly photoreceptors robustly transduce and, in conjunction with amacrine cells, process visual scenes and provide the resulting signal to downstream targets. Here, we model the first step of visual processing in the photoreceptor-amacrine cell layer. We propose a novel divisive normalization processor (DNP) for modeling the computation taking place in the photoreceptor-amacrine cell layer. The DNP explicitly models the photoreceptor feedforward and temporal feedback processing paths and the spatio-temporal feedback path of the amacrine cells. We then formally characterize the contrast gain control of the DNP and provide sparse identification algorithms that can efficiently identify each the feedforward and feedback DNP components. The algorithms presented here are the first demonstration of tractable and robust identification of the components of a divisive normalization processor. The sparse identification algorithms can be readily employed in experimental settings, and their effectiveness is demonstrated with several examples.

Low-Power Built-in Jitter Injection Using Linearized Phase Interpolator

Low-power circuits built in optical transceivers that can be used in characterizing phase interpolators (PIs) and injecting jitter to test the tolerance of clock-data recovery (CDR) are presented. The novelty is in digitally controlling a precompensated PI in the feedback path of a phase lock loop. The latter is driving the sampling clock of the digital-to-analog converter at the transmitter. To improve the accuracy of jitter mask measurements at the receiver, the nonlinearity of used PI is compensated by the mean of a programmable lookup table (LUT), which is populated using a built-in test circuitry. As well, the LUT can serve to allow for generating jitter frequencies that are out of phase-locked loop bandwidth. Both linearization and jitter injection methods are generic and can be applied to any wireline transceivers at both client and modem interface sides.

Reconfigurable control as actuator fault-tolerant control design for power oscillation damping

This paper presents design of an self contained actuators unit in wide area damping control of power system in stabilizing system response for both nominal system condition and during actuator faults. First it is presented that use of multiple actuators in wide area control aid in improving damping in power system. A wide area damping controller feeding multiple actuators to satisfy multiple objectives in wide area damping control of power system is designed. Minimization of infinity norm of closed loop transfer function of power system with wide area controller in feedback path & closed loop poles placement techniques are used in controller synthesis. Second a reconfigurable control on the lines of fault hiding principle is added to the controller design to maintain system damping to pre-fault level in case of actuator faults. A reconfiguration component(RC) is activated on occurrence of actuator fault thereby reconfiguring system dynamics and redistributing wide area control signal among remaining active actuators. RC together with remaining active actuators and under same wide area damping controller maintains system damping to pre-fault level thereby preserving system dynamic response. In the reconfigurable control design presented here no new actuators outside the unit of actuators designed for wide area damping control is required. This makes for an self contained actuators unit in wide area damping control of power system both for nominal system condition and for system affected by actuator faults. A two area power system model is considered here for demonstrating effectiveness of designed robust damping controller with multiple outputs feeding multiple actuators in wide area control and illustrating the idea of self contained actuators unit for maintaining system damping in case of actuator faults.

Adaptive Feedback Cancellation in Hearing Aids Based on Orthonormal Basis Functions With Prediction-Error Method Based Prewhitening

Acoustic feedback is a persistent problem in hearing aids, which limits the achievable amplification and may severely degrade the sound quality by producing howling artifacts. A potential approach to feedback cancellation is to estimate the feedback path utilizing an adaptive filter. However, estimation of the feedback path suffers a large model error, known as the bias, due to the correlation between the loudspeaker and source signals. A prediction-error method (PEM) based prewhitening filter has been widely utilized to reduce the bias. This approach, however, requires a large number of adaptive parameters, thus increasing the computational complexity, reducing the convergence rate, and limiting the added stable gain. We introduce an adaptive feedback cancellation (AFC) algorithm derived based on the orthonormal basis functions (OBFs) for closed-loop identification of the feedback path by minimizing the prediction error. The OBFs are defined by a set of fixed poles and a small number of adaptive tap-output weights. We study two methods for obtaining the fixed poles, an inherently stable least-squares method and a log-scale frequency resolution method. The poles are then embedded as the a priori information into the algorithm. The proposed algorithm is extensively evaluated with speech and music source signals and with sudden changes in the feedback path. The experimental results show that the proposed method significantly increases the added stable gain, accelerates the convergence rate, and enhances the sound quality compared to state-of-the-art, while requiring far fewer adaptive parameters which leads to reduced computational complexity.

A new design of adaptive model following control system for lateral motion of aircraft

In this paper, a new design of an adaptive model following control (AMFC) system is proposed and analysed for a class of multi-input multi-output (MIMO) linear time-varying plants with unknown bounded parameters, and sufficiently slowly varying with time. We then show that the new approach based on combined Lyapunov method and hyper-stability criteria tries to overcome the problems of stability and zero tracking error. The main difficulty of Lyapunov methods is in finding an appropriate Lyapunov control function for the closed-loop system, therefore different choices of Lyapunov functions may result in different control structures and control performance. We show that the design of AMFC for the class of linear time-varying systems could be composed of a stable linear block in the feed forward path which turns out to be easily solvable by Lyapunov equation and a nonlinear time-varying block in the feedback path can be handled with using adaptive control techniques, such that the closed-loop dynamics of the system approaches the reference model. This structure results in greater flexibility in the choice of the adaptive laws. Finally, a typical numerical example to an aircraft control problem is analysed.