On reduced-order filter design for uncertain cascaded 2-1 sigma-delta modulators

[[abstract]]In this paper, we present a new robust matching filter design method for uncertain 2-1 cascaded sigma-delta modulators. This method addresses a well known limitation of H-infinity loop shaping techniques that they yield filters of high order (equal to the sum of the plant order and the order of the weighting function), thus increasing the complexity of circuit implementation. In contrast, the new method yields filters whose order is equal to the plant order, independent of the weighting function. We compare the new method with other existing fixed-order designs, and establish its efficacy.[[conferencetype]]國際[[conferencedate]]20110608~20110610[[iscallforpapers]]Y[[conferencelocation]]Maca

Digital Compensation for MASH Sigma Delta Modulators using H-infinity Approach

[[abstract]]This paper presents a new digital compensation scheme for MASH (cascaded) sigma-delta modulators (SigmaDeltaMs) with 1-bit quantizer. The compensation scheme is designed based on the well-known internal model principle and H-infinity control theory. For numerical illustration, we concentrate on a MASH 2-1 SigmaDeltaM architecture for low and middle frequencies applications. Comparisons between the proposed SigmaDeltaM and the conventional one are made, which reveal that the proposed SigmaDeltaM outperforms the conventional one in several aspects - signal-to-noise ratio (SNR), dynamic range (DR), output swing.[[conferencetype]]åé[[conferencedate]]20081012~20081015[[iscallforpapers]]Y[[conferencelocation]]Singapor

Control of chaos in nonlinear circuits and systems

Nonlinear circuits and systems, such as electronic circuits (Chapter 5), power converters (Chapter 6), human brains (Chapter 7), phase lock loops (Chapter 8), sigma delta modulators (Chapter 9), etc, are found almost everywhere. Understanding nonlinear behaviours as well as control of these circuits and systems are important for real practical engineering applications. Control theories for linear circuits and systems are well developed and almost complete. However, different nonlinear circuits and systems could exhibit very different behaviours. Hence, it is difficult to unify a general control theory for general nonlinear circuits and systems. Up to now, control theories for nonlinear circuits and systems are still very limited. The objective of this book is to review the state of the art chaos control methods for some common nonlinear circuits and systems, such as those listed in the above, and stimulate further research and development in chaos control for nonlinear circuits and systems. This book consists of three parts. The first part of the book consists of reviews on general chaos control methods. In particular, a time-delayed approach written by H. Huang and G. Feng is reviewed in Chapter 1. A master slave synchronization problem for chaotic Lur’e systems is considered. A delay independent and delay dependent synchronization criteria are derived based on the H performance. The design of the time delayed feedback controller can be accomplished by means of the feasibility of linear matrix inequalities. In Chapter 2, a fuzzy model based approach written by H.K. Lam and F.H.F. Leung is reviewed. The synchronization of chaotic systems subject to parameter uncertainties is considered. A chaotic system is first represented by the fuzzy model. A switching controller is then employed to synchronize the systems. The stability conditions in terms of linear matrix inequalities are derived based on the Lyapunov stability theory. The tracking performance and parameter design of the controller are formulated as a generalized eigenvalue minimization problem which is solved numerically via some convex programming techniques. In Chapter 3, a sliding mode control approach written by Y. Feng and X. Yu is reviewed. Three kinds of sliding mode control methods, traditional sliding mode control, terminal sliding mode control and non-singular terminal sliding mode control, are employed for the control of a chaotic system to realize two different control objectives, namely to force the system states to converge to zero or to track desired trajectories. Observer based chaos synchronizations for chaotic systems with single nonlinearity and multi-nonlinearities are also presented. In Chapter 4, an optimal control approach written by C.Z. Wu, C.M. Liu, K.L. Teo and Q.X. Shao is reviewed. Systems with nonparametric regression with jump points are considered. The rough locations of all the possible jump points are identified using existing kernel methods. A smooth spline function is used to approximate each segment of the regression function. A time scaling transformation is derived so as to map the undecided jump points to fixed points. The approximation problem is formulated as an optimization problem and solved via existing optimization tools. The second part of the book consists of reviews on general chaos controls for continuous-time systems. In particular, chaos controls for Chua’s circuits written by L.A.B. Tôrres, L.A. Aguirre, R.M. Palhares and E.M.A.M. Mendes are discussed in Chapter 5. An inductorless Chua’s circuit realization is presented, as well as some practical issues, such as data analysis, mathematical modelling and dynamical characterization, are discussed. The tradeoff among the control objective, the control energy and the model complexity is derived. In Chapter 6, chaos controls for pulse width modulation current mode single phase H-bridge inverters written by B. Robert, M. Feki and H.H.C. Iu are discussed. A time delayed feedback controller is used in conjunction with the proportional controller in its simple form as well as in its extended form to stabilize the desired periodic orbit for larger values of the proportional controller gain. This method is very robust and easy to implement. In Chapter 7, chaos controls for epileptiform bursting in the brain written by M.W. Slutzky, P. Cvitanovic and D.J. Mogul are discussed. Chaos analysis and chaos control algorithms for manipulating the seizure like behaviour in a brain slice model are discussed. The techniques provide a nonlinear control pathway for terminating or potentially preventing epileptic seizures in the whole brain. The third part of the book consists of reviews on general chaos controls for discrete-time systems. In particular, chaos controls for phase lock loops written by A.M. Harb and B.A. Harb are discussed in Chapter 8. A nonlinear controller based on the theory of backstepping is designed so that the phase lock loops will not be out of lock. Also, the phase lock loops will not exhibit Hopf bifurcation and chaotic behaviours. In Chapter 9, chaos controls for sigma delta modulators written by B.W.K. Ling, C.Y.F. Ho and J.D. Reiss are discussed. A fuzzy impulsive control approach is employed for the control of the sigma delta modulators. The local stability criterion and the condition for the occurrence of limit cycle behaviours are derived. Based on the derived conditions, a fuzzy impulsive control law is formulated so that the occurrence of the limit cycle behaviours, the effect of the audio clicks and the distance between the state vectors and an invariant set are minimized supposing that the invariant set is nonempty. The state vectors can be bounded within any arbitrary nonempty region no matter what the input step size, the initial condition and the filter parameters are. The editors are much indebted to the editor of the World Scientific Series on Nonlinear Science, Prof. Leon Chua, and to Senior Editor Miss Lakshmi Narayan for their help and congenial processing of the edition

Signal processing using short word-length

Recently short word-length (normally 1 bit or bits) processing has become a promising technique. However, there are unresolved issues in sigma-delta modulation, which is the basis for 1b/2b systems. These issues hindered the full adoption of single-bit techniues in industry. Among these problems is the stability of high-order modulators and the limit cycle behaviour. More importantly, there is no adaptive LMS structure of any kind in 1b/2b domain. The challenge in this problem is the harsh quantization that prevents straightforward LMS application. In this thesis, the focus has been made on three axes: designing new single-bit DSP applications, proposing novel approaches for stability analysis, and tacking the unresolved problems of 1b/2b adaptive filtering. Two structures for 1b digital comb filtering are proposed. A ternary DC blocker structure is also presented and performanc e is tested. We also proposed a single-bit multiplierless DC-blocking structure. The stability of a single-bit high-order signma-delta modulator is studied under dc inputs. A new approach for stability analysis is proposed based on analogy with PLL analysis. Finally we succeeded in designing 1b/2b Wiener-like filtering and introduced (for the first time) three 1b/2b adaptive schemes

Linear Operation of Switch-Mode Outphasing Power Amplifiers

Radio transceivers are playing an increasingly important role in modern society. The ”connected” lifestyle has been enabled by modern wireless communications. The demand that has been placed on current wireless and cellular infrastructure requires increased spectral efficiency however this has come at the cost of power efficiency. This work investigates methods of improving wireless transceiver efficiency by enabling more efficient power amplifier architectures, specifically examining the role of switch-mode power amplifiers in macro cell scenarios. Our research focuses on the mechanisms within outphasing power amplifiers which prevent linear amplification. From the analysis it was clear that high power non-linear effects are correctable with currently available techniques however non-linear effects around the zero crossing point are not. As a result signal processing techniques for suppressing and avoiding non-linear operation in low power regions are explored. A novel method of digital pre-distortion is presented, and conventional techniques for linearisation are adapted for the particular needs of the outphasing power amplifier. More unconventional signal processing techniques are presented to aid linearisation of the outphasing power amplifier, both zero crossing and bandwidth expansion reduction methods are designed to avoid operation in nonlinear regions of the amplifiers. In combination with digital pre-distortion the techniques will improve linearisation efforts on outphasing systems with dynamic range and bandwidth constraints respectively. Our collaboration with NXP provided access to a digital outphasing power amplifier, enabling empirical analysis of non-linear behaviour and comparative analysis of behavioural modelling and linearisation efforts. The collaboration resulted in a bench mark for linear wideband operation of a digital outphasing power amplifier. The complimentary linearisation techniques, bandwidth expansion reduction and zero crossing reduction have been evaluated in both simulated and practical outphasing test benches. Initial results are promising and indicate that the benefits they provide are not limited to the outphasing amplifier architecture alone. Overall this thesis presents innovative analysis of the distortion mechanisms of the outphasing power amplifier, highlighting the sensitivity of the system to environmental effects. Practical and novel linearisation techniques are presented, with a focus on enabling wide band operation for modern communications standards

Bandpass electromechanical sigma-delta modulator

Ph.DDOCTOR OF PHILOSOPH

Adaptive noise cancellation for second-order delta-sigma A/D converters

Oversampled analog-to-digital (A/D) converter architectures have been receiving increased attention for high-precision A/D converters. These architectures offer the means of exchanging resolution in time for that in amplitude. Among these oversampled A/D converters, delta-sigma modulators are the most popular method used due to their simplicity in the analog circuitry. The analog integrators in delta-sigma modulators suffer from non-idealities such as capacitor mismatches and finite op-amp gain. In the dual quantizer A/D converters, the system relies on the perfect matching of the analog and digital transfer functions to cancel the quantization noise. However, the non-ideality of the analog parameters makes this matching hard to achieve. In this thesis, an off-line adaptive scheme is presented to estimate the non-ideal parameters of the analog section for the second-order delta-sigma modulator. These estimates are then used in the digital part to reduce the quantization noise. The least-mean- square (LMS) algorithm is used to adaptively estimate the analog parameters