Closed-loop Gain Research Articles

On the Bounds of Feedback Rates for Pilot-Assisted MIMO Systems

For pilot-assisted multiple-input-multiple-output (MIMO) systems with imperfect feedback, we investigate the relationship between the feedback transmission rate and the resulting closed-loop capacity gain. Based on this relationship quantified via rate-distortion theory, we investigate the lower and upper bounds of the feedback rate that would effect positive closed-loop capacity gains without overly consuming feedback transmission resources. Extensive simulations are carried out to validate the analytic results and to shed light on the achievable closed-loop MIMO capacity given the system configuration parameterized by the number of antennas, transmit signal-to-noise ratio, pilot power allotment, and finite feedback rate. Such results provide guideline on the feedback channel for meaningful designs of practical pilot-assisted MIMO systems.

Pilot-in-the-Loop Analysis of Aileron Operation and Flight Simulator Experiments

Lateral-directional piloted simulation experiments were conducted in order to analyze pilot responses when the pilot controls an aircraft with only the ailerons after rudder failure. The experiments were carried out using a fixed-base flight simulator and four pilots. Six aircraft configurations, made by changing the stability derivatives, were tested, and pilot models were identified using the least-squares method. An analysis of the closed-loop shows that the closed-loop gain and stabilities correlate with the tracking error of the compensation task. Additionally, from the results of analysis, an evaluation function using pilot-in-the-loop with a fixed pilot model was developed. This function was able to predict the compensational error analytically from the airplane dynamics.

REDUCTION OF AMPLITUDE DEPENDENT GAIN VARIATIONS IN CONTROL OF NON-LINEAR WIENER TYPE SYSTEMS

Amplitude dependent gain variations of the static non-linear block of a Wiener type system is a major source of instability when feedback control is applied. A linearizing feedback can be applied to reduce these variations, using the static non-linearity of an identified Wiener model. The remaining amplitude dependent loop errors are analysed in the paper. A result that quantifies the remaining relative differential loop gain error with a simple formula is given. It is explained why small prediction errors of a model identified in open loop can also be a good indication of small remaining amplitude dependent closed loop gain errors. To illustrate the discussion, linearizing feedback is applied to a highly non-linear pH-control loop.

A fast large dynamic range shaping amplifier for particle detector front-end

The paper describes a fast shaping amplifier with rail-to-rail output swing. The circuit is based on a CMOS operational amplifier with a class AB output stage. A baseline holder, incorporating a closed-loop unity gain buffer with slew rate limitation, performs the AC coupling with the preamplifier and guarantees a baseline shift smaller than 3 mV for unipolar output pulses of 3 V and 10 MHz rate.

Analog AGC Circuitry for a CMOS WLAN Receiver

The IEEE 802.11a standard uses orthogonal frequency division multiplexing (OFDM) to allow high data rates in multipath WLAN environments. The high peak-to-average power ratio (PAPR) of OFDM signals, along with stringent settling-time constraints, make conventional closed-loop automatic gain control (AGC) schemes impractical for WLAN receivers. In a direct conversion receiver, AGC and channel-select filtering are performed by analog baseband circuitry. A baseband signal processor using a new open-loop analog gain-control algorithm for OFDM is described. The new AGC algorithm uses switched coarse gain-setting steps followed by an analog open-loop fine gain-setting step to set the final gain of variable gain amplifiers (VGAs). The AGC was implemented in a 0.18-mum CMOS process using newly designed circuits including linear VGAs, RMS detectors, and current-mode computation circuitry. Simulation and measurement results verify that the new AGC circuit converges with gain error less than 1dB to the desired level within 5.6 mus

An Integrated Design of Structural and Gain Scheduled Control Systems

We deal with an integrated design problem of structural and gain scheduled control systems for LPV systems. The integrated design problem is formulated as an optimization problem of structural design parameters and a gain scheduled controller minimizing L2 gain of the closed-loop system. Even in the simplest case the integrated design problem is represented as a BMI problem which cannot be solved exactly and efficiently. In the present paper we propose an iterative LMI-based method to solve the formulated optimization problem approximately. We can guarantee the local convergence of the closed-loop L2 gain with the proposed design algorithm even if the coefficient matrices of the state-space form of the control object are nonlinear functions on the structural design parameters. We show the effectiveness of the proposed design method through a design example.

Point: The muscle metaboreflex does restore blood flow to contracting muscles

Imposed reductions in oxygen delivery to active skeletal muscle during dynamic exercise in conscious dogs evoke a powerful pressor response, termed the muscle metaboreflex. During submaximal work rates, the major mechanism used by this reflex is to increase cardiac output (CO), which generates a

Estimation of arterial and cardiopulmonary total peripheral resistance baroreflex gain values: validation by chronic arterial baroreceptor denervation

Feedback control of total peripheral resistance (TPR) by the arterial and cardiopulmonary baroreflex systems is an important mechanism for short-term blood pressure regulation. Existing methods for measuring this TPR baroreflex mechanism typically aim to quantify only the gain value of one baroreflex system as it operates in open-loop conditions. As a result, the normal, integrated functioning of the arterial and cardiopulmonary baroreflex control of TPR remains to be fully elucidated. To this end, the laboratory of Mukkamala et al. (Mukkamala R, Toska K, and Cohen RJ. Am J Physiol Heart Circ Physiol 284: H947-H959, 2003) previously proposed a potentially noninvasive technique for estimating the closed-loop (dimensionless) gain values of the arterial TPR baroreflex (GA) and the cardiopulmonary TPR baroreflex (GC) by mathematical analysis of the subtle, beat-to-beat fluctuations in arterial blood pressure, cardiac output, and stroke volume. Here, we review the technique with additional details and describe its experimental evaluation with respect to spontaneous hemodynamic variability measured from seven conscious dogs, before and after chronic arterial baroreceptor denervation. The technique was able to correctly predict the group-average changes in GA and GC that have previously been shown to occur following chronic arterial baroreceptor denervation. That is, reflex control by the arterial TPR baroreflex was virtually abolished (GA = -2.1 +/- 0.6 to 0.3 +/- 0.2; P < 0.05), while reflex control by the cardiopulmonary TPR baroreflex more than doubled (GC = -0.7 +/- 0.4 to -1.8 +/- 0.2; P < 0.05). With further successful experimental testing, the technique may ultimately be employed to advance the basic understanding of TPR baroreflex functioning in both humans and animals in health and disease.

Eigenstructure assignment in a class of second-order descriptor linear systems: A complete parametric approach

In this paper eigenstructure assignment via proportional-plus-derivative feedback is investigated for a class of second-order descriptor linear systems. Under certain conditions, simple, general and complete parametric solutions of both finite closed-loop eigenvector matrices and feedback gain matrices are derived. The parametric approach utilizes directly original system data, involves manipulations only on n-dimensional matrices, and reveals all the design degrees of freedom which can be further utilized to achieve certain additional system specifications. A numerical example shows the effect of the proposed approach.

A 12-bit 80-MSample/s pipelined ADC with bootstrapped digital calibration

This paper presents a prototype analog-to-digital converter (ADC) that uses a calibration algorithm to adaptively overcome constant closed-loop gain errors, closed-loop gain variation, and slew-rate limiting. The prototype consists of an input sample-and-hold amplifier (SHA) that can serve as a calibration queue, a 12-bit 80-MSample/s pipelined ADC, a digital-to-analog converter (DAC) for calibration, and an embedded custom microprocessor, which carries out the calibration algorithm. The calibration is bootstrapped in the sense that the DAC is used to calibrate the ADC, and the ADC is used to calibrate the DAC. With foreground calibration, test results show that the peak differential nonlinearity (DNL) is -0.09 least significant bits (LSB), and the peak integral nonlinearity (INL) is -0.24LSB. Also, the maximum signal-to-noise-and-distortion ratio (SNDR) and spurious-free dynamic range (SFDR) are 71.0 and 79.6dB with a 40-MHz sinusoidal input, respectively. The prototype occupies 22.6 mm/sup 2/ in a 0.25-/spl mu/m CMOS technology and dissipates 755 mW from a 2.5-V supply.

Specific motion processing pathway deficit during eye tracking in schizophrenia: A performance-matched functional magnetic resonance imaging study

The neural mechanisms underlying smooth pursuit eye movement (SPEM) abnormalities in schizophrenia are not well understood. Previous evidence suggests that a deficit in the processing of internal representations of object motion (extraretinal motion) contributes to SPEM deficits in patients. Functional magnetic resonance imaging (fMRI) activation was compared between patients and control subjects to determine whether schizophrenia patients exhibit abnormal cerebral activation in regions associated with extraretinal motion processing during SPEM. Patients and control subjects were selected based on matched performance in the closed-loop gain. Despite similar performance on closed-loop pursuit gain, patients showed consistent deficits in extraretinal motion based on predictive pursuit. In the magnet, subjects were tested using a traditional smooth-pursuit task that elicits closed-loop response. Patients had reduced pursuit-related activation in several known extraretinal motion processing areas including frontal and supplemental eye fields, medial superior temporal cortex, and anterior cingulate. Patients also showed increased activation in medial occipitotemporal cortex. These results provide functional anatomic evidence supporting reduced function in the extraretinal motion processing pathway in schizophrenia. Increased activation in medial occipitotemporal cortex suggests an increased dependence on immediate retinal motion information, which may be used to compensate for reduced extraretinal signaling during sustained visual tracking.

IDENTIFICATION OF THE PNEUMATIC SERVO SYSTEM USING THE SELF-EXCITED OSCILLATIONS

The paper describes the identification of the variable critical gain and natural frequency of the pneumatic cylinder using the self-excited oscillations method. The pneumatic drives are characterized by the low stiffness of the pneumatic cylinder which depends on the piston position and determines the natural frequency of the cylinder. The variety of the stiffness in dependence on the piston position can be obtained using the curve describing the course of the critical gain and natural frequency in dependence on the piston position. This feature is a disadvantage by the closed loop control of the piston position. The low stiffness should be taken into the account by the design of the pneumatic servo system operated in the closed loop, because the natural frequency of the cylinder depends on the stiffness and limits the closed loop gain and quality of the step response of the controlled system. The identified curve can be used for the design of the adaptive controller with variable on the piston position dependent gain. The described approach is presented by the measurements and results realized on the test rig.

Pursuit eye movement deficits in autism

Oculomotor studies provide a novel strategy for evaluating the functional integrity of multiple brain systems and cognitive processes in autism. The current study compared pursuit eye movements of 60 high-functioning individuals with autism and 94 intelligence quotient, age and gender matched healthy individuals using ramp and oscillating target tasks. Individuals with autism had normal pursuit latency, but reduced closed-loop pursuit gain when tracking both oscillating and ramp targets. This closed-loop deficit was similar for leftward and rightward pursuit, but the difference between individuals with autism and their age-matched peers was more apparent after mid-adolescence, suggesting reduced maturational achievement of the pursuit system in autism. Individuals with autism also had lower open-loop pursuit gain (initial 100 ms of pursuit) and less accurate initial catch-up saccades during a foveofugal step-ramp task, but these deficits were only seen when targets moved into the right visual field. Pursuit performance in both open- and closed-loop phases was correlated with manual praxis in individuals with autism. Bilateral disturbances in the ability to use internally generated extraretinal signals for closed-loop pursuit implicate frontostriatal or cerebellar circuitry. The hemifield specific deficit in open-loop pursuit demonstrates a lateralized disturbance in the left extrastriate areas that extract visual motion information, or in the transfer of visual motion information to the sensorimotor areas that transform visual information into appropriate oculomotor commands.

Robust Arm Configuration of Manipulator Mounted on Flexible Base

In this paper, the robustness of a manipulator mounted on a flexible base with a task-space feedback control to a fixed desired point is considered. We define the robust arm configuration (RAC), which is a special configuration where the linearized system is positive real. Lyapunov indirect method and the passivity theory guarantee a local asymptotic stability of the original nonlinear system. A finite but high closed-loop gain can be applied in the neighborhood of the RAC without considering the base flexibility, i.e., an additional sensor or a solution of whole inverse dynamics is not necessary. Considering the positive semidefiniteness of the residue matrices, a measure is proposed that measures the distance from the RAC. This measure represents the controllability of the manipulator itself, and does not depend on the underlying control law. The validity of the proposed approach is confirmed by a numerical example and experiments.

A Collocation-Based Algorithm for Computing the Pull-In Range of a Class of Phase-Locked Loops

The pull-in range (ωp) of a phase-locked loop (PLL) is defined as the maximum value of loop detuning ω0s for which pull-in occurs from anywhere on the PLL's phase plane. That is, pull-in is guaranteed from anywhere on the phase plane if ω0s <ω p. Simple approximation is available for computing ωp for the high gain PLL where saddle-node bifurcation occurs at ω0s = ωp. Unlike the high gain case, a simple approximation for ωp is not available for the low gain case where bifurcation from a separatrix cycle occurs at ω0s = ωp. The vector field model for a class of second-order PLLs is shown to have rotational properties, which imply the existence of a separatrix cycle. The external stability of this separatrix cycle is an indicator of the type of bifurcation (saddle- node or separatrix cycle) which terminates the limit cycle associated with the PLL's stable false lock state and the PLL pulls-in (i.e. achieve phase lock). A formula is given for determining the separatrix cycle's stability, which indicates that the separatrix cycle is externally stable for small values of closed loop gain. A collocation- based algorithm is presented for computing the PLL's separatrix cycle and the value of pull-in range frequency ω0s = ωp at which a stable separatrix cycle exists.

Chopper-stabilized high-pass sigma delta modulator utilizing a resonator structure

A chopper-stabilized high-pass sigma delta modulator (SDM) utilizing a resonator structure for the reduction of low-frequency noise, such as dc offset, thermal drift, and 1/f noise, is presented. The high-pass SDM has a zero of a noise transfer function at half of the sampling frequency and is stabilized by chopper modulation. Since the first integrator of the proposed modulator has a large closed-loop gain, no pre-amplifier is required even when the input signal is small, which is suitable for low-power applications. The signal-to-noise ratios (SNRs) and power dissipations of a high-pass modulator and a conventional modulator have been numerically analyzed.

Smooth pursuit and antisaccade performance evidence trait stability in schizophrenia patients and their relatives

Several forms of eye movement dysfunction (EMD) have been widely regarded as candidate endophenotypes of schizophrenia, ultimately capable of identifying individuals carrying schizophrenia susceptibility genes and elucidating the pathophysiology of schizophrenia. As an indication of their trait-like status, candidate endophenotypes optimally evidence stability over time. However, there have been few published reports of test–retest reliability of several forms of EMD in schizophrenia patients and their relatives. In the current investigation, schizophrenia patients and the first-degree biological relatives of schizophrenia patients ( n=15) were administered by an eye movement battery including smooth pursuit, antisaccade and prosaccade tasks, and re-tested after an average of 1.82 years (range=14–24 months). Adequate test–retest reliabilities of smooth pursuit closed-loop gain (Pearson r=0.72), antisaccade error rate ( r=0.73), saccade reaction time to correct antisaccade responses ( r=0.73), and prosaccade hypometria ( r=0.72) were observed. Lower reliabilities were obtained for smooth pursuit open-loop gain ( r=0.52) and prosaccade reaction time ( r=0.43). The results are supportive of the trait-like characteristics of particular forms of EMD in schizophrenia families and of the candidacy of EMD as an endophenotypic marker of schizophrenia.

An Alternate New Gap Metric for Robustness Measure

Vinnicombe's v-gap metrics is more and more widely used for measuring the distance between two transfer functions. Some alternate new metrics are introduced amplifying the principal frequency domain where the sensitivity equals to one and/or where the closed-loop frequency gain equals to one. Examples are shown, when these metrics are more sensitive to parameter variations.

Dynamic ventilatory response to CO(2) in congestive heart failure patients with and without central sleep apnea.

Nonobstructive (i.e., central) sleep apnea is a major cause of sleep-disordered breathing in patients with stable congestive heart failure (CHF). Although central sleep apnea (CSA) is prevalent in this population, occurring in 40-50% of patients, its pathogenesis is poorly understood. Dynamic loop gain and delay of the chemoreflex response to CO(2) was measured during wakefulness in CHF patients with and without CSA by use of a pseudorandom binary CO(2) stimulus method. Use of a hyperoxic background minimized responses derived from peripheral chemoreceptors. The closed-loop and open-loop gain, estimated from the impulse response, was three times greater in patients with nocturnal CSA (n = 9) than in non-CSA patients (n = 9). Loop dynamics, estimated by the 95% response duration time, did not differ between the two groups of patients. We speculate that an increase in dynamic gain of the central chemoreflex response to CO(2) contributes to the genesis of CSA in patients with CHF.

Some Alternate New Gap Metric

The paper introduces some new alternate gap metrics for measuring the distance between two transfer functions. These metrics amplify the principal frequency domain where the sensitivity equals to one and/or where the closed-loop frequency gain equals to one. Some examples are shown when the new metrics are more sensitive to parameter variations, than the well known v-gap metric