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In this study, a novel optimal anti-windup control scheme is proposed to resolve the input constraint problem for multi-input multi-output (MIMO) systems, without losing the good tracking performance as possible. Avoiding complex numerical calculation, the proposed optimal control scheme can systematically compress a huge control input within the range of the required restriction by adjusting well-designed weighted matrices for linear constrained systems. Combining a conventional linear quadratic analogue tracker (LQAT) with the proposed scheme, the anti-windup-based optimal analogue tracker not only possesses the advantage of the conventional LQAT, good tracking performance, but also effectively resolves the input saturation problem. For practical consideration, the proposed LQAT is implemented by adopting the prediction-based digital redesign technique to design an effective digital control of linear MIMO sampled-data systems under input constraints. [ABSTRACT FROM AUTHOR]

The universal state-space adaptive observer-based fault diagnostics/estimator and the high performance tracker for the sampled-data non-linear slowly time-varying system with unanticipated decay factors in actuators/system states are proposed. The optimal linearisation technique is used to obtain the exact (local) linear model at each operating state for a non-linear system, so that the actuator and state fault detection and performance recovery of a sampled-data non-linear time-varying system can be accomplished. Additionally, an improved Kalman filter-based adaptive observer is proposed to achieve a better estimation-based performance recovery than the conventional one. A residual generation scheme and a mechanism for auto-tuning switched gain is also presented, so that the proposed methodology is applicable for the fault detection and diagnosis (FDD) for actuator and state faults to yield the high tracking performance recovery. For practical implementation, this study also takes advantage of the merit of digital redesign methodology to convert a theoretically well-designed analogue controller/observer with a high-gain property into its corresponding low-gain digital controller/observer without possibly losing the high tracking/estimation as well as FDD performance recovery. Examples are given to illustrate the effectiveness and performances of the provided methodology. [ABSTRACT FROM AUTHOR]

The effect of parameter uncertainties on stability of delayed genetic regulatory networks is investigated. With the presence of parameter uncertainties, the delayed coupled genetic regulatory network is a parameter-dependent non-linear system, in which not only the dynamics are indefinite but also its equilibrium point is unknown. The authors first derive a sufficient condition to guarantee robust stability of uncertain genetic regulatory networks by introducing convergence region. Then, the estimation of convergence region bound is obtained by using Lyapunov stability theory and linear matrix inequality. It is worth noting that these results are derived in the case that the equilibrium point of parameter-dependent non-linear system is unknown. Finally, two examples are given to illustrate the effectiveness of the proposed results. [ABSTRACT FROM AUTHOR]

A fundamental and required property of congestion control algorithms in computer networks is stability. In this study, a class of appropriate Lyapunov functionals is proposed to investigate asymptotic stability in the second-order congestion control systems with heterogeneous communication delays. Novel linear matrix inequality-based delay-dependent stability criteria are given by exploiting free weighting matrices, which can overcome conservativeness of most methods involving a fixed model transformation. Simulation results show that the stability criteria proposed in this study are less conservative in the sense that larger range of control gains and communication delays can be accommodated. [ABSTRACT FROM AUTHOR]

Entropy-based image thresholding has received considerable interest in recent years. Two types of entropy are generally used as thresholding criteria: Shannon's entropy and relative entropy, also known as Kullback–Leibler information distance, where the former measures uncertainty in an information source with an optimal threshold obtained by maximising Shannon's entropy, whereas the latter measures the information discrepancy between two different sources with an optimal threshold obtained by minimising relative entropy. Many thresholding methods have been developed for both criteria and reported in the literature. These two entropy-based thresholding criteria have been investigated and the relationship among entropy and relative entropy thresholding methods has been explored. In particular, a survey and comparative analysis is conducted among several widely used methods that include Pun and Kapur's maximum entropy, Kittler and Illingworth's minimum error thresholding, Pal and Pal's entropy thresholding and Chang et al.'s relative entropy thresholding methods. In order to objectively assess these methods, two measures, uniformity and shape, are used for performance evaluation. [ABSTRACT FROM AUTHOR]

A comparison of RF reliability at 10 GHz on four different undoped AlGaN/GaN HEMT structures with AlGaN bather thickness variation is presented. The output power degradation characteristics during RF stress for each structure are shown, and the results indicate a strong dependence of reliability on AlGaN thickness. A device from the structure with the thinnest AlGaN in the study, with initial output power of 8.8 W/mm at 40 V, showed only a change of 0.55 dB in output power after 185 h of RF stress at 40V. The results demonstrate excellent RF reliability of high-power devices and the potential of stable high-power operation of undoped AlGaN/GaN HEMTs on SiC. [ABSTRACT FROM AUTHOR]

MOCVD-grown 0.25 μm gate-length AlGaN=GaN high electron mobility transistors (HEMTs) have been fabricated on 6H-SiC substrates. These 0.25 μm gate-length devices exhibited maximum drain current density as high as 1.28 A=mm, peak extrinsic transconductance of 310 mS=mm, unity current gain cutoff frequency (f[SUBr]) of 51 GHz, and maximum frequency of oscillation (f[SUBmax]) of 115 GHz. At 18 GHz, a continuous-wave output power density of 6.7 W=mm with power-added efficiency of 26.6% was obtained, yielding the highest reported power performance of AlGaN=GaN HEMTs at 18 GHz. [ABSTRACT FROM AUTHOR]

MOCVD-grown field-plated 0.25 μm gate-length A1GaN/GaN high electron mobility transistors (HEMTs) have been fabricated on 6H-SiC substrates. The devices exhibited maximum drain current density as high as 1.42 A/mm, peak extrinsic transconductance of 437 mS/mm, unity current gain cutoff frequency (fr) of 41 GHz, and maximum frequency of oscillation (fmax) of 63 GHz. At 18 GHz, a continuous-wave output power density of 9.1 W/mm with power-added-efficiency (PAE) of 23.7% was obtained, yielding the highest reported power performance of A1GaN/GaN HEMTs at 18 GHz. [ABSTRACT FROM AUTHOR]

The effects of RF stress on power and pulsed IV characteristics of field-plated AlGaN/GaN HEMTs fabricated on two different epitaxial structures are presented. The power degradation characteristics are shown. The RF stress resulted in different degrees of RF voltage and current swing reduction on the two wafers. The current dispersion became more aggravated after RF stress under high quiescent drain bias conditions in one of the structures. [ABSTRACT FROM AUTHOR]

High-performance, low-noise A1GaN/GaN high electron mobility transistors (HEMTs) with 0.25 µm gate-length have been fabricated on semi-insulating 6H-SiC substrates. The devices exhibited a unity current gain cutoff frequency (f[sub T]) of 52.3 GHz, and maximum frequency of oscillation (f[sub MAX]) of 112 GHz. At 10 GHz, a minimum noise figure (NF[sub min]) of 0.75 dB and an associated gain (G[sub a]) of 10.84 dB was obtained when biased at V[sub DS]= 10 V and I[sub DS]= 40.6 mA/mm. The corresponding values were 1.15 and 7.49 dB at 18 GHz. These results are the first reported microwave noise characteristics obtained from 0.25 µm gate-length GaN HEMTs on 6H-SiC substrates. The use of 6H-SiC substrates provides an alternative solution to the full commercialisation of GaN-based technologies for low-noise and high-power electronics. [ABSTRACT FROM AUTHOR]