Lei Chi-Un
The University of Hong Kong, Electrical and Electronic Engineering, Graduate Student
NULL Conventional Logic (NCL) is a Delay-Insensitive (DI) clockless paradigm and is suitable for implementing asynchronous circuits. Efficient methods of analysis are required to specify and verify such DI systems. Based on Delay... more
NULL Conventional Logic (NCL) is a Delay-Insensitive (DI) clockless paradigm and is suitable for implementing asynchronous circuits. Efficient methods of analysis are required to specify and verify such DI systems. Based on Delay Insensitive sequential Process (DISP) specification, this paper demonstrates the application of formal methods by applying Process Analysis Toolkit (PAT) to model and verify the behavior of NCL circuits. A few useful constructs are successfully modeled and verified by using PAT.
We develop a routing algorithm for fault tolerant 2-D mesh Network-on-Chips (NoCs) with permanent faults. The proposed approach is adaptive and distributed, and does not require extra circuitry or routing tables for fault tolerance... more
We develop a routing algorithm for fault tolerant 2-D mesh Network-on-Chips (NoCs) with permanent faults. The proposed approach is adaptive and distributed, and does not require extra circuitry or routing tables for fault tolerance operation. Deadlock handling and multiple hop links checking are included for a robust system operation. We demonstrate the algorithm mechanism using a mesh example.
Abstract We develop a rational function macromodeling algorithm named warped impulse structure estimation for macromodeling of system responses with time-sampled data. The ideas of digital filter design, Walsh theorem, and complementary... more
Abstract We develop a rational function macromodeling algorithm named warped impulse structure estimation for macromodeling of system responses with time-sampled data. The ideas of digital filter design, Walsh theorem, and complementary signal are introduced to convert the macromodeling problem into a non-pole-based Steiglitz-McBride iteration without initial guess and eigenvalue computation.
A continuous-time system identification technique, Vector Fitting (VF), is extended from symmetric functions, to asymmetrical cases and is used for complex infinite-impulse-response (IIR) continuous-time filter design. VF involves a... more
A continuous-time system identification technique, Vector Fitting (VF), is extended from symmetric functions, to asymmetrical cases and is used for complex infinite-impulse-response (IIR) continuous-time filter design. VF involves a two-step pole refinement process based on a linear least-squares solve and an eigenvalue problem. The proposed algorithm has lower complexity than conventional schemes by designing complex continuous-time filters directly.
The verb zheng in northeast Chinese dialect is a generalized verb which can take various object and complement. Through" meaning component-mode" analyzing toward generalized verb zheng, this thesis focuses on the differences between... more
The verb zheng in northeast Chinese dialect is a generalized verb which can take various object and complement. Through" meaning component-mode" analyzing toward generalized verb zheng, this thesis focuses on the differences between generalized verb and polysemous verb, and then points out that the various" meanings" of verb zheng result from the coercion process of the constructions.
Abstract Data rate traffic and communication capacity demand have been increased continuously. Therefore, a highly advanced 4G wireless system is required to meet a high demand for modern mobile terminals. For getting a further... more
Abstract Data rate traffic and communication capacity demand have been increased continuously. Therefore, a highly advanced 4G wireless system is required to meet a high demand for modern mobile terminals. For getting a further improvement for 4G communication systems, new paradigms of design, analysis tools and applications for 4G communication processors are necessary. In this paper, some of these new paradigms are discussed.
Abstract This paper presents a curriculum design of a course about reliability of circuits and systems. Contents in the learning modules include failure mechanisms of electronics, reliability for electronic components and circuit systems... more
Abstract This paper presents a curriculum design of a course about reliability of circuits and systems. Contents in the learning modules include failure mechanisms of electronics, reliability for electronic components and circuit systems and simulation for circuit reliability. Through learning modules, students can learn concepts about reliability in circuits and systems, as well as develop awareness to design a reliable circuit system.
Abstract A design procedure is proposed. A 2D linear-phase FIR filter prototype is first constructed using semidefinite programming (SDP) and is decomposed into several simpler ID filter design problems via the Schur decomposition method... more
Abstract A design procedure is proposed. A 2D linear-phase FIR filter prototype is first constructed using semidefinite programming (SDP) and is decomposed into several simpler ID filter design problems via the Schur decomposition method (SDM). Each ID filter is then realized by IIR structure using a novel and efficient digital system identification technique called the Discrete-Time Vector Fitting (VFz).
Abstract We present a design methodology for the globally optimal synthesis of multiple loop feedback operational transconductance amplifier-capacitor (OTA-C) filters. Transmission zero realization via input distribution of OTA network is... more
Abstract We present a design methodology for the globally optimal synthesis of multiple loop feedback operational transconductance amplifier-capacitor (OTA-C) filters. Transmission zero realization via input distribution of OTA network is adopted. A generic topology of OTA-C filter is optimized using a two-stage mixed integer nonlinear programming (MINLP), with circuit complexity and circuit sensitivity as the objective functions. A numerical example shows the efficacy of the proposed approach.
In the context of multiple constant multiplications (MCM) design, we propose a novel common subexpression elimination (CSE) algorithm that models synthesis of coefficients into an estimated cost function. Although the proposed algorithm... more
In the context of multiple constant multiplications (MCM) design, we propose a novel common subexpression elimination (CSE) algorithm that models synthesis of coefficients into an estimated cost function. Although the proposed algorithm generally does not guarantee an optimum solution, it is capable of finding the minimum/minima of the function in practically sized problems.
The semiconductor industry has given renewed interest to the asynchronous technology since a number of limiting factors exist in modern synchronous digital systems. NULL Conventional Logic (NCL) is a Delay-Insensitive (DI) clockless... more
The semiconductor industry has given renewed interest to the asynchronous technology since a number of limiting factors exist in modern synchronous digital systems. NULL Conventional Logic (NCL) is a Delay-Insensitive (DI) clockless paradigm convenient for implementing asynchronous circuits but lacks efficient analysis methods and tools for specification and verification.
Abstract: This paper presents a low-voltage, low-power and fault-tolerant implementation of Double Sideband Suppressed Carrier (DSB-SC) amplitude modulator-demodulator circuit for portable communication systems. Through the approximation... more
Abstract: This paper presents a low-voltage, low-power and fault-tolerant implementation of Double Sideband Suppressed Carrier (DSB-SC) amplitude modulator-demodulator circuit for portable communication systems. Through the approximation proposed in this work, a CMOS four quadrant multiplier is used as a (de) modulator circuit to generate DSB-SC (de) modulated signals.
Abstract—We present in this paper a novel parallel binomial algorithm that computes the price of an American option. The algorithm partitions a binomial tree constructed for the pricing into blocks of multiple levels of nodes, and assigns... more
Abstract—We present in this paper a novel parallel binomial algorithm that computes the price of an American option. The algorithm partitions a binomial tree constructed for the pricing into blocks of multiple levels of nodes, and assigns each such block to multiple processors. Each of the processors then computes the option's values at its assigned nodes in two phases. The algorithm is implemented and tested on a heterogeneous system consisting of an Intel multi-core processor and a NVIDIA GPU.
Abstract—We present a scalable image retrieval system based jointly on text annotations and visual content. Previous approaches in content based image retrieval often suffer from the semantic gap problem and long retrieving time. The... more
Abstract—We present a scalable image retrieval system based jointly on text annotations and visual content. Previous approaches in content based image retrieval often suffer from the semantic gap problem and long retrieving time. The solution that we propose aims at resolving these two issues by indexing and retrieving images using both their text descriptions and visual content, such as features in colour, texture and shape. A query in this system consists of keywords, a sample image and relevant parameters.
Abstract—We present a novel model identification technique for designing complex infinite-impulseresponse (IIR) continuous-time filters through generalizing the Vector Fitting (VF) algorithm, which is extensively used for continuous-time... more
Abstract—We present a novel model identification technique for designing complex infinite-impulseresponse (IIR) continuous-time filters through generalizing the Vector Fitting (VF) algorithm, which is extensively used for continuous-time frequencydomain rational approximation to symmetric functions, to asymmetrical cases. VF involves a twostep pole refinement process based on a linear leastsquares solve and an eigenvalue problem.
Abstract—We present a novel parallel binomial algorithm to compute prices of American options. The algorithm partitions a binomial tree into blocks of multiple levels of nodes, and assigns each such block to multiple processors. Each... more
Abstract—We present a novel parallel binomial algorithm to compute prices of American options. The algorithm partitions a binomial tree into blocks of multiple levels of nodes, and assigns each such block to multiple processors. Each processor in parallel with the others computes the option's values at nodes assigned to it. The computation consists of two phases, where the second phase can not start until the valuation in the first phase has been completed.
Abstract—As modern processors and semiconductor circuits move into 32 nm technologies and below, designers face the major problem of process variations. This problem makes designing VLSI circuits harder and harder, affects the circuit... more
Abstract—As modern processors and semiconductor circuits move into 32 nm technologies and below, designers face the major problem of process variations. This problem makes designing VLSI circuits harder and harder, affects the circuit performance and introduces faults that can cause critical failures. Therefore, fault-tolerant design is required to obtain the necessary level of reliability and availability especially for safety-critical systems.
Abstract In the context of multiple constant multiplication (MCM) design, we propose a novel common subexpression elimination (CSE) algorithm that models the optimal synthesis of coefficients into a 0-1 mixed-integer linear programming... more
Abstract In the context of multiple constant multiplication (MCM) design, we propose a novel common subexpression elimination (CSE) algorithm that models the optimal synthesis of coefficients into a 0-1 mixed-integer linear programming (MILP) problem. A time delay constraint is included for synthesis. We also propose coefficient decompositions that combine all minimal signed digit (MSD) representations and the shifted sum (difference) of coefficients.
DATICS Workshops were initially created by a network of researchers and engineers both from academia and industry in the areas of Design, Analysis and Tools for Integrated Circuits and Systems. Recently, DATICS has been extended to the... more
DATICS Workshops were initially created by a network of researchers and engineers both from academia and industry in the areas of Design, Analysis and Tools for Integrated Circuits and Systems. Recently, DATICS has been extended to the fields of Communication, Computer Science, Software Engineering and Information Technology.
Abstract—Deep sub-micron technology enables a high inte-gration of (non-linear) circuit systems for electronic products. In order to design non-linear circuits with guaranteed reliability, a sophisticated simulation procedure is required.... more
Abstract—Deep sub-micron technology enables a high inte-gration of (non-linear) circuit systems for electronic products. In order to design non-linear circuits with guaranteed reliability, a sophisticated simulation procedure is required. However, in existing GPU-enhanced circuit simulation methodologies, numerous data transfers between cores hamper the benefits of GPU computations. In this project, we focus on the parallelization of computations for nonlinear analog/mixed-signal circuit transient simulation.
Abstract We present a least-squares (LS) algorithm for rational function macromodeling of port-to-port responses with discrete-time sampled data. The core routine involves over-determined equations and filtering operation, and avoids... more
Abstract We present a least-squares (LS) algorithm for rational function macromodeling of port-to-port responses with discrete-time sampled data. The core routine involves over-determined equations and filtering operation, and avoids numerical-sensitive calculation and initial pole assignment. We demonstrate the fast computation and excellent accuracy and robustness, even with noisy data, in stable response approximation.© 2008 IEEE.
Abstract We present a discrete-time time-domain vector fitting algorithm, called TD-VFz, for rational function macromodeling of port-to-port responses with discrete time-sampled data. The core routine involves a two-step pole refinement... more
Abstract We present a discrete-time time-domain vector fitting algorithm, called TD-VFz, for rational function macromodeling of port-to-port responses with discrete time-sampled data. The core routine involves a two-step pole refinement process based on a linear least-squares solve and an eigenvalue problem. Applications in the macromodeling of practical circuits demonstrate that TD-VFz exhibits fast computation, excellent accuracy, and robustness against noisy data.
Compared to the traditional teaching method, the PBL approach should help students to build a more solid digital IC design foundation. Students should also develop confidence and transferable skills to handle new design challenges at... more
Compared to the traditional teaching method, the PBL approach should help students to build a more solid digital IC design foundation. Students should also develop confidence and transferable skills to handle new design challenges at present and in the future. Keywords: Problem-based learning (PBL), engineering education, electrical engineering
Abstract Wireless sensor networks (WSNs) have been widely used for monitoring applications. However, due to the rigorous deployment environment, reliable operation of WSNs is difficult to guarantee. Thus, the assurance of WSN reliability... more
Abstract Wireless sensor networks (WSNs) have been widely used for monitoring applications. However, due to the rigorous deployment environment, reliable operation of WSNs is difficult to guarantee. Thus, the assurance of WSN reliability should be concerned in order to measure physical quantities correctly and effectively, as well as to maximize the lifetime of the system. In this paper, concerns of WSN reliability and assurance measures have been discussed via a systematic reliability checking flow.
Abstract We present a least-squares (LS) algorithm for rational function macromodeling of port-to-port responses with discrete-time sampled data. The core routine involves over-determined equations and Altering operation, and avoids... more
Abstract We present a least-squares (LS) algorithm for rational function macromodeling of port-to-port responses with discrete-time sampled data. The core routine involves over-determined equations and Altering operation, and avoids numerical-sensitive calculation and initial pole assignment. We demonstrate the fast computation and excellent accuracy and robustness, even with noisy data, in stable response approximation.
Abstract A recent digital system identification technique, called discrete-time vector fitting (VFz), is extended to two communication system filter design problems. The first one is the complex infinite-impulse-response (IIR) filter... more
Abstract A recent digital system identification technique, called discrete-time vector fitting (VFz), is extended to two communication system filter design problems. The first one is the complex infinite-impulse-response (IIR) filter design. The second one is the common-denominator MIMO filter design. In the second problem, a combination of VFz and QR decomposition is proposed to reduce the computational complexity. Robustness in finite-precision arithmetic is imposed in both problems via a pole radius constraint.
Abstract We present a novel way of approximating FIR filters by IIR structures through generalizing the vector fitting (VF) algorithm, popularly used in continuous-time frequency-domain rational approximation, to its discrete-time... more
Abstract We present a novel way of approximating FIR filters by IIR structures through generalizing the vector fitting (VF) algorithm, popularly used in continuous-time frequency-domain rational approximation, to its discrete-time counterpart called VFz. VFz progressively refines the filter poles for improved approximation. Linear equation and eigenvalue solves are used in each iteration, with real-arithmetic formulation to accommodate complex poles.
Abstract—Pedagogy with Web 2.0 technologies is shown to facilitate the teaching-learning process through content sharing and idea collaboration. In this paper, we explore the possibility of using social networking tools, to support... more
Abstract—Pedagogy with Web 2.0 technologies is shown to facilitate the teaching-learning process through content sharing and idea collaboration. In this paper, we explore the possibility of using social networking tools, to support teaching practice in technological courses.
Abstract—This paper presents an integration of a loosely defined design project in an introductory electrical engineering course. The proposed project aims to introduce first-year engineering students to the world of electrical... more
Abstract—This paper presents an integration of a loosely defined design project in an introductory electrical engineering course. The proposed project aims to introduce first-year engineering students to the world of electrical engineering and develop their general engineering skills. Because of its innovative and unconventional nature, a Rube Goldberg Machine has been used as the project vehicle. In the project, students have been asked to design the machine with electrical sensors and actuators.
Abstract A generalized Hamiltonian method (GHM) is proposed for passivity test of descriptor systems (DSs) which describe impedance or admittance input-output responses. GHM can test passivity of DSs with any system index without minimal... more
Abstract A generalized Hamiltonian method (GHM) is proposed for passivity test of descriptor systems (DSs) which describe impedance or admittance input-output responses. GHM can test passivity of DSs with any system index without minimal realization. This frequency-independent method can avoid the time-consuming system decomposition as required in many existing DS passivity test approaches.
Abstract Recent attention has been drawn to the hybrid Delta-Sigma (ΔΣ) structure featuring the integration of continuous-time (CT) and discrete-time (DT) structures in the loop filter. It combines the accurate loop filter characteristic... more
Abstract Recent attention has been drawn to the hybrid Delta-Sigma (ΔΣ) structure featuring the integration of continuous-time (CT) and discrete-time (DT) structures in the loop filter. It combines the accurate loop filter characteristic of a DT ΔΣ modulator and the inherent anti-aliasing of a CT ΔΣ modulator. We present a design methodology for building a CT-DT ΔΣ modulator via the transformation from a DT ΔΣ modulator prototype.
Abstract—Battery management system (BMS) emerges a decisive system component in battery-powered applications, such as (hybrid) electric vehicles and portable devices. However, due to the inaccurate parameter estimation of aged battery... more
Abstract—Battery management system (BMS) emerges a decisive system component in battery-powered applications, such as (hybrid) electric vehicles and portable devices. However, due to the inaccurate parameter estimation of aged battery cells and multi-cell batteries, current BMSs cannot control batteries optimally, and therefore affect the usability of products.
Commission (FCC) of a bandwidth of 7.5 GHz (from 3.1 GHz to 10.6 GHz) for ultra wideband (UWB) wireless communications, UWB is rapidly advancing as a high data rate wireless communication technology. As is the case in conventional... more
Commission (FCC) of a bandwidth of 7.5 GHz (from 3.1 GHz to 10.6 GHz) for ultra wideband (UWB) wireless communications, UWB is rapidly advancing as a high data rate wireless communication technology. As is the case in conventional wireless communication systems, an antenna also plays a very crucial role in UWB systems. However, there are more challenges in designing a UWB antenna than a narrow band one. A suitable UWB antenna should be capable of operating over an ultra wide bandwidth as allocated by the FCC.
Abstract—Linear macromodeling has been applied to high-frequency circuit simulations to accelerate the global interconnect system simulation process. By approximating tabulated structure response data, reduced macromodels can be... more
Abstract—Linear macromodeling has been applied to high-frequency circuit simulations to accelerate the global interconnect system simulation process. By approximating tabulated structure response data, reduced macromodels can be generated. However, conventional macromodeling approaches suffer from numerical robustness and convergence problems. This paper aims to apply digital signal processing techniques to facilitate the macromodeling process.
Vector Fitting (VF) has been introduced as a partial‐fraction basis response fitting methodology for over a decade. Because of its reliability and versatility, VF has been applied and extended to a number of areas. In this book chapter,... more
Vector Fitting (VF) has been introduced as a partial‐fraction basis response fitting methodology for over a decade. Because of its reliability and versatility, VF has been applied and extended to a number of areas. In this book chapter, we will discuss the applications of VF in the context of macromodeling of linear structures in signal∕ power integrity analyses. We will also discuss main features of VF along three directions: data, algorithms and models. Two practical examples are given to demonstrate the merits of VF.
Abstract Numerous algorithms to macromodel a linear time-invariant (LTI) system from its frequency-domain sampling data have been proposed in recent years [1, 2, 3, 4, 5, 6, 7, 8], among which Loewner matrix-based tangential interpolation... more
Abstract Numerous algorithms to macromodel a linear time-invariant (LTI) system from its frequency-domain sampling data have been proposed in recent years [1, 2, 3, 4, 5, 6, 7, 8], among which Loewner matrix-based tangential interpolation proves to be especially suitable for modeling massive-port systems [6, 7, 8]. However, the existing Loewner matrix-based method follows vector-format tangential interpolation (VFTI), which fails to explore all the information contained in the frequency samples.
We present an efficient and novel procedure to design two-dimensional (2D) linearphase IIR filters with less hardware resource. A 2D linear-phase FIR filter prototype is first designed using semidefinite programming (SDP). The prototype... more
We present an efficient and novel procedure to design two-dimensional (2D) linearphase IIR filters with less hardware resource. A 2D linear-phase FIR filter prototype is first designed using semidefinite programming (SDP). The prototype filter is then decomposed into modular structures via Schur decomposition method (SDM). Each section is reduced into IIR structures using a novel digital system identification technique called the discrete-time vector fitting (VFz).
We present a discrete-time hybrid-domain vector fitting algorithm, called HD-VFz, for the IIR approximation of FIR filters with an arbitrary combination of time-and frequency-sampled responses. The core routine involves a two-step pole... more
We present a discrete-time hybrid-domain vector fitting algorithm, called HD-VFz, for the IIR approximation of FIR filters with an arbitrary combination of time-and frequency-sampled responses. The core routine involves a two-step pole refinement process based on a linear least-squares solve and an eigenvalue problem. Through hybrid-domain data approximation and digital partial fraction basis with relative stability consideration, HD-VFz exhibits fast computation and remarkable fitting accuracy in both time and frequency domains.
We present a novel technique for approximating finite-impulse-response (FIR) filters with infinite-impulse-response (IIR) structures through extending the vector fitting (VF) algorithm, used extensively for continuous-time... more
We present a novel technique for approximating finite-impulse-response (FIR) filters with infinite-impulse-response (IIR) structures through extending the vector fitting (VF) algorithm, used extensively for continuous-time frequency-domain rational approximation, to its discrete-time counterpart called VFz. VFz directly computes the candidate filter poles and iteratively relocates them for progressively better approximation. Each VFz iteration consists of the solutions of an overdetermined linear equation and an eigenvalue problem, with real-domain arithmetic to accommodate complex poles. Pole flipping and maximum pole radius constraint guarantee stability and robustness against finite-precision implementation. Comparison against existing algorithms confirms that VFz generally exhibits fast convergence and produces highly accurate IIR approximants.