George S. Moschytz

Autonomous cellular neural networks: a unified paradigm for pattern formation and active wave propagation

This tutorial paper proposes a subclass of cellular neural networks (CNN) having no inputs (i.e., autonomous) as a universal active substrate or medium for modeling and generating many pattern formation and nonlinear wave phenomena from numerous disciplines, including biology, chemistry, ecology, engineering, and physics. Each CNN is defined mathematically by its cell dynamics (e.g., state equations) and synaptic law, which specifies each cells interaction with its neighbors. We focus on reaction-diffusion CNNs having a linear synaptic law that approximates a spatial Laplacian operator. Such a synaptic law can be realized by one or more layers of linear resistor couplings. An autonomous CNN made of third-order universal cells and coupled to each other by only one layer of linear resistors provides a unified active medium for generating trigger (autowave) waves, target (concentric) waves, spiral waves, and scroll waves. When a second layer of linear resistors is added to couple a second capacitor voltage in each cell to its neighboring cells, the resulting CNN can be used to generate various turing patterns. >

Nodal analysis of switched-capacitor networks

Switched-capacitor (SC) networks comprise capacitors interconnected by an array of periodically operated switches. Such networks are particularly attractive in light of the high circuit density possible with MOS integrated circuit technology and hybrid integrated circuits using thin-film and silicon technology. The paper describes the analysis of SC networks by using nodal charge equations. It is shown that SC networks are time-variant sampled-data networks, which can be viewed as tandem connected four-ports in the z -domain. One pair of ports is viewed as a signal path corresponding to the even time slots, the other pair of ports as a path corresponding to the odd time slots of the periodically operated switches. In a subsequent publication the authors will show how four-port equivalent circuits in the z-domain of six basic building blocks can be used for the description of any SC network. This method allows the direct use of traditional network analysis tools like the transmission matrix for deriving transfer functions. The method ultimately leads to a two-port analysis of SC networks in which conventional two-port theory can be applied.

A software package for the decomposition of long-term multichannel EMG signals using wavelet coefficients

This paper presents a method to decompose multichannel long-term intramuscular electromyogram (EMG) signals. In contrast to existing decomposition methods which only support short registration periods or single-channel recordings of signals of constant muscle effort, the decomposition software EMG-LODEC (ElectroMyoGram LOng-term DEComposition) is especially designed for multichannel long-term recordings of signals of slight muscle movements. A wavelet-based, hierarchical cluster analysis algorithm estimates the number of classes [motor units (MUs)], distinguishes single MUAPs from superpositions, and sets up the shape of the template for each class. Using three channels and a weighted averaging method to track action potential (AP) shape changes improve the analysis. In the last step, nonclassified segments, i.e., segments containing superimposed APs, are decomposed into their units using class-mean signals. Based on experiments on simulated and long-term recorded EMG signals, our software is capable of providing reliable decompositions with satisfying accuracy. EMG-LODEC is suitable for the study of MU discharge patterns and recruitment order in healthy subjects and patients during long-term measurements.

An integrated CMOS switched-capacitor bandpass filter based on N-path and frequency-sampling principles

A new combined switched-capacitor (SC) frequency-sampling N-path filter is presented, which allows the implementation of very narrow bandpass filters. The included frequency-sampling (FS) filter suppresses undesirable passbands of the SC N-path filter. The center frequency f/SUB m/ of the bandpass filter is identical to the circuit clock frequency f/SUB c/. Experimental results are presented for a CMOS SC frequency-sampling four-path filter with second-order filter cells, a center frequency of 1 kHz, and -3-dB passband bandwidth of 11.5 Hz.

Nullators and norators in voltage to current mode transformations

In this circuit transformation, the short-circuit transfer function of the resulting circuit is then exactly the same as the open-circuit voltage transfer function of the original circuit

Two-port analysis of switched-capacitor networks using four-port equivalent circuits in the z-domain

In a previous publication by the authors it was shown how switched-capacitor (SC) networks can be analyzed by using nodal charge equations. The result was a description of SC networks as time-variant sampled-data networks which led to a four-port equivalent circuit representation in the z-domain. In this paper, the four-port representation is expanded by considering six basic building blocks for the design of any general active or passive SC network. With the four-port equivalent circuit representation, traditional two-port analysis tools, such as the transmission matrix and two-port transfer functions, can be used conveniently. An SC-filter design example is given and the measured response is shown to coincide with the response predicted by the theory.

High-precision EMG signal decomposition using communication techniques

This paper presents a new approach to the decomposition of electromyographic (EMG) signals. EMG signals consist of a superposition of delayed finite-duration waveforms that carry the information about the firing of different muscle fiber groups. The new approach is based on a communication technical interpretation of the EMG signal. The source is modeled as a signaling system with intersymbol-interference, which encodes a well defined sparse information sequence. This point of view allows a maximum-likelihood (ML) as well as a maximum a posteriori (MAP) estimation of the underlying firing pattern to be made. The high accuracy attainable with the proposed method is illustrated both with measured and artificially generated EMG signals.

An exact and direct analytical method for the design of optimally robust CNN templates

In this paper, we present an analytical design approach for the class of bipolar cellular neural networks (CNNs) which yields optimally robust template parameters. We give a rigorous definition of absolute and relative robustness and show that all well-defined CNN tasks are characterized by a finite set of linear and homogeneous inequalities. This system of inequalities can be analytically solved for the most robust template by simple matrix algebra. For the relative robustness of a task, a theoretical upper bound exists and is easily derived, whereas the absolute robustness can be arbitrarily increased by template scaling. A series of examples demonstrates the simplicity and broad applicability of the proposed method.

A New Framework and Computer Program for Quantitative EMG Signal Analysis

Techniques for analyzing electromyographic signals, which estimate and detect potentials caused by active motor units in human striated muscles, are described. A framework within which these techniques are incorporated into a computer program for the quantitative analysis of EMG signals is then proposed. The resulting program allows the diagnosis of neurogenic and myogenic diseases by analyzing the waveforms of the motor unit potentials (MUPs). It also permits the research of the healthy and disturbed neuromuscular control loop by analyzing the point processes given by the activation of the single motor units.

Gain-sensitivity product-a figure of merit for hybrid-integrated filters using single operational amplifiers

It is shown that a different measure of performance must be used to evaluate hybrid-integrated active filters from that used to evaluate active filters in discrete form. Where sensitivity was previously found to be an adequate and useful measure for Q stability of discrete active filters, the gain-sensitivity product gives an accurate measure of Q stability for hybrid-integrated circuits. Where negative feedback filter schemes were found to be preferable with respect to Q stability when realized in discrete form, positive feedback schemes with their very much lower gain- sensitivity product may be preferable in hybrid-integrated filter circuits. In addition, they require low-gain amplifiers than can be used up to higher frequencies. Q-stability measurements of hybrid- integrated positive feedback, or Sallen-Key-type circuits, which were realized with tantalum thin-film resistors and capacitors combined with beam-leaded operational amplifier chips agree very accurately with the predictions derived from gain-sensitivity calculations.