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After summarizing the commutativity results for analogue linear time-varying systems, the commutativity of cascade connected discrete-time linear time-varying systems is introduced. Some general open questions on the subject are stated and new results are presented, intended to answer some of them. Two examples are given to reinforce the concept and to show up its possible benefits in engineering to reduce noise effects and design robust systems.

In this article, a general all-pole current transfer function synthesis procedure using current backward transconductance amplifiers (CBTAs) is proposed. The proposed configuration uses n current backward transconductance amplifiers and n grounded capacitors as the only type of passive elements. The circuit is eligible to realize any all-pole transfer characteristics with a given strictly Hurwitz (stable) denominator polynomial. Further, it is straightforward to find the values of the passive elements from the coefficients of this polynomial by using the Routh–Hurwitz algorithm as in the realization of a two-element kind passive network synthesis. In this sense and as far as the author's knowledge, it is the only active structure that can be synthesized like a passive two-element kind Cauer circuit. The simulations that are performed using PSPICE exhibit satisfactory results coherent with the theory. Copyright © 2011 John Wiley & Sons, Ltd.

WOS: 000300771700002, A novel circuit for the realization of the mutually coupled circuit using three current-controlled current backward transconductance amplifiers (CC-CBTAs) as active components is proposed. The active mutually coupled circuit structures are also called the synthetic transformers. The circuit is derived by using three floating simulated inductors that are connected as the T-type transformer model. The circuit has the following attractive advantages: (i) The values of a primary self-inductance, a secondary self-inductance and a mutual inductance can be independently tuned by the transconductance gain of the CC-CBTAs; (ii) The circuit uses three grounded capacitors that are suitable from the point of integrated circuit implementation; (iii) It uses only three active components; (iv) It has a good sensitivity performance with respect to the tracking errors; (v) Both positive and negative couplings are achieved and the coupling coefficient is not limited by 1 in magnitude; (vi) Symmetrical coupling is achieved without necessitating any matching condition; (vii) The proposed circuit has a floating structure.

In this paper, a simple and effective stabilization method for integrating time delay systems using fractional order PD controllers C(s)=k"p+k"ds^@m is proposed. The presented method is based on finding the stability regions according to the fractional orders of the derivative element in the range of (0, 2). These regions are computed by using three stability boundaries: Real Root Boundary (RRB), Complex Root Boundary (CRB) and Infinite Root Boundary (IRB). The method gives the explicit formulae corresponding to these boundaries in terms of fractional order PD controller (PD^@m controller) parameters. Thus, the complete set of stabilizing controllers for an arbitrary integrating time delay system can be obtained. In order to demonstrate the effectiveness in solution accuracy and the simplicity of this method, two simulation studies are given. The simulation results indicate that the PD^@m controllers can provide larger stability regions than the integer order PD controllers.

In the present paper, the use of three-step difference schemes generated by Taylor's decomposition on four points for the numerical solutions of third-order time-varying linear dynamical systems is presented. The method is illustrated for the numerical analysis of an up-converter used in communication systems.

This paper presents a new approach based on Feed-Forward multilayered Neural Networks (FNNs) for the transient and steady-state analysis of piecewise-linear circuits. Nonlinear circuits are changed by linear circuits containing switches together with some state matrices and control inequalities by using piecewise linearization approach. One of the two problems arising in the analysis of these circuits is that control inequalities belonging to piecewise linearized components and control times for internally or externally controlled components is needed to determine switching times. Another is that the analysis time is very long. The proposed approach is considered as the solution to the problems. FNNs are used for modeling the piecewise linear circuits. By using the obtained model networks, the switching sequence and switching times from one state to another for transient and steady states are determined. The transient and steady-state solutions are fast accomplished through this knowledge. As an example, a nonlinear circuit is used for demonstrating the utility of the proposed approach, and the results are compared with that of the model constructed at Matlab/Simulink. Example circuit is analyzed in the time of 1 h 42 min by using the proposed approach but the time of 2 h 27 min by Matlab/Simulink. Moreover, simulation results demonstrate that the proposed approach yields more accurate approximation for the switched nonlinear circuits.

A general synthesis procedure is given for a versatile signal flow graph realization of a general current transfer function by using multi-output second generation current controlled current conveyors (MO-CCCIIs). The proposed configuration uses n + 1 multi-output second generation current conveyors (MO-CCIIs), n capacitors and at most 2 ( n + 1 ) resistors. This number of resistors can be reduced to n for special cases. Using MO-CCCIIs instead of MO-CCIIs, the resistors can be removed completely for the n th-order universal structure. The general transfer function having any numerator dynamics can be derived from the universal structure by using a single MO-CCCII and at most n + 1 resistors. It is very easy to find the values of the passive elements from the coefficients of the transfer function to be realized. The validity of the proposed synthesis is verified through PSpice simulations.

A general synthesis procedure is given for a versatile signal flow graph realization of a general transfer function by using current differencing buffered amplifier (CDBA). The proposed configuration uses n + 1 CDBAs, n capacitors and at most 2 n + 4 resistors. This number of resistors can be reduced to n + 1 for special cases. The circuit is eligible to obtain a variety of transfer characteristics with the same common denominator polynomial, and it is easily converted to different modes of operations. It is straightforward to find the values of the passive elements from the coefficients of the transfer function to be realized. Simulations results are obtained by using commercially available active component AD844 and CMOS technology as well. All of these make the proposed circuit attractive.

In this work, a novel voltage-mode (VM) single-input four-output universal filter topology is presented. The proposed structure uses two resistors, two capacitors and only one voltage differencing current conveyor (VDCC) and generates all biquadratic filtering functions namely: low-pass (LP), band-pass (BP), high-pass (HP) and band-reject (BR). The quality factor and natural frequency of the filter can be adjusted electronically without changing the values of the passive components. Moreover, the circuit does not require any condition of component matching and has a good sensitivity performance with respect to tracking errors of passive components and the active parameter. PSpice simulation results confirm the results of the theoretical analysis.

Coefficient Diagram Method (CDM) is a new method proposed for the analysis and design of linear time-invariant control systems. The control system design by this method results with satisfactory stability, time response and robustness properties compatible with, and in most cases better than, the ones obtained by the other present design methods. In this study, the design procedure described in the literature for CDM is improved so that a systematic and easy tool with understandable sufficient detail is presented. A visual toolbox, which can be used efficiently both for education and research, is obtained based on the procedure presented by using MATLAB. 2004 Wiley Periodicals, Inc. Comput Appl Eng Educ 12: 165� 174, 2004; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20011

A proportional integral derivative (PID) controller employing only a single commercially available active component, two resistors and two capacitors is presented. The PID controller circuit has low impedance voltage output which can be easily cascaded with other voltage-mode (VM) structures. The effects caused by the non-ideality of the current feedback operational amplifier (CFOA) are analyzed. The performance of the proposed circuit is demonstrated by using PSPICE simulations.

WOS: 000305249000013, In this paper, a general electronically tunable resistorless biquad, which realizes current ratio transfer function using current backward transconductance amplifiers is proposed. The biquad contains only two active components and two grounded capacitors, which make it convenient for production by the integrated circuit technology. The proposed biquad realizes all of the basic second order filter characteristics: low pass, high pass, band pass, band reject, and finally all pass. It is convenient for cascading with other similar biquads as well as with any two-port circuit with low impedance input to achieve higher order filter characteristics. The simulations that are performed using PSPICE simulator exhibit satisfactory results coherent with the theory.

Necessary and sufficient conditions for the commutativity of linear time-varying systems are derived in the case of nonzero initial conditions. It is shown that some commutative class of linear time-varying systems may not commute with arbitrary initial conditions. In this respect, commutativity of Euler differential systems is investigated. Explicit commutativity conditions for the fifth-order systems are solved. New results about the effects of commutativity on system sensitivity and disturbance properties are presented, which is very important for network design and industrial applications where many of the systems are composed of subsystems cooperating one after another in a chain. The results are supported by examples treated either analytically or numerically.

In this paper, a distributed-parameter state variable approach is used to calculate transients on transmission lines based on the concept of travelling waves. The method of characteristics for lossless line is used and the state equations are derived for the system. These equations are converted to a set of difference equations using the trapezoidal rule of integration and solved in time domain using LU decomposition. Single- and multi-phase transmission lines with various linear and non-linear terminations are considered in the illustrative examples. State-space modeling of transposed lines using modal decomposition is introduced and the effects caused by lumped parameter approximation of line losses are described. Comparisons with the results obtained by EMTP and conventional methods based on s-domain are given.

WOS: 000262504400004, A new floating immittance function simulator circuit is proposed using two different active elements, a dual-output second generation current conveyor (DO-CCII) and an operational transconductance amplifier (OTA). The presented circuit can realize a positive and negative floating inductor, capacitor and resistor depending on the passive component selection. Since the passive elements are all grounded, this circuit is suitable for fully integrated circuit design. The circuit does not require any component matching conditions, and it has a good sensitivity performance with respect to tracking errors. Moreover, the proposed positive and negative inductance, capacitor and resistor simulator can be tuned electronically by changing the biasing current of the OTA or can be controlled through the grounded resistor or capacitor. The proposed floating inductor simulator circuit is demonstrated by using a SPICE simulation for 0.35 mu m TSMC CMOS technology. The proposed circuit consumes an average power of 1 mW using +/- 1.5 V supply voltages.

European Conference on Circuit Theory Design -- AUG 23-27, 2009 -- Antalya, TURKEY, WOS: 000276473700173, A new second-order multi-mode multifunction filter configuration is introduced. This configuration uses a single current differencing buffered amplifier (CDBA) and, depending on topology, a total of four/five passive elements (two/three capacitors and two/three resistors). Current-mode (CM), voltage-mode (VM), transimpedance-mode (TIM) and transadmittance-mode (TAM) topologies are presented for realizing BP, LP and HP filter responses. The validity of the proposed filters is verified through PSpice simulations and experiments.

WOS: 000254240200009, A flexible synthesis procedure for electronically tunable nth-order current-mode (CM) universal filter using state variable-method is given. The proposed configuration uses n+1 multi-output second generation current conveyors (MO-CCIIs), n capacitors and n resistors. These resistors can be removed by using multi-output second generation current controlled conveyors (MO-CCCIIs) instead of MO-CCIIs. It is straightforward to find the values of the passive elements from the coefficients of the transfer function to be realized. The validity of the proposed filter is verified through PSpice simulations.

WOS: 000264490800009, A novel resistorless oscillator is presented. The proposed structure enjoys electronic tunability property with minimum number of active and passive components. This oscillator uses a current-mode (CM) active device and has properties of current mode circuits. The validity of the proposed circuit is verified by experimental results.

WOS: 000258183700003, Six new second order band-pass filter configurations using only a single cuffent-controlled current differencing buffered amplifier (CC-CDBA) are proposed. Further, the proposed filters also have a minimum number of external electronic components. They realize current-mode, voltage-mode and transadmittance-mode filter characteristics. The quality factor and natural frequency can be adjusted electronically without changing the values of the passive components. The proposed filters use a minimum number of passive elements (two or three). There is no second order active filter structure which uses two passive components and one active component in the literature. The validity of the proposed filters is verified through PSpice simulations.

A new multi-mode multifunction filter using CDBA is proposed. The original filter has a single current input and three voltage outputs and operates in transimpedance-mode. It can generate all biquadratic filter functions of low-pass, high-pass and band-pass, and also band-reject and all-pass filter responses by selecting different output signal combinations. This filter can be converted into voltage-mode by an additional input resistor. It can also be used in current-mode at the output by using one extra load resistor at each output. With these additional resistors at the input and outputs the filter operates in transadmittance-mode. The structure of the new filter proposed contains two capacitors, three resistors and three CDBAs.

Three new electronically tunable filter configurations which employ only one current controlled differencing buffered amplifier (CDBA) are proposed. The proposed filters operate in voltage-mode (VM) and use three passive elements. Each proposed filter can realize one of the band-pass, low-pass or high-pass responses. The parameters /spl omega//sub 0/ and /spl omega//sub 0//Q enjoy independent electronic tunability. Effect of the non-idealities and the sensitivity analysis of the proposed filter are also examined. The validities of the proposed filters are verified through PSPICE simulations.

In this paper, coefficient diagram method (CDM) is used to design controller for two-input two-output (TITO) processes. The interactions between the loops are minimized by using the conventional decoupler design method; then, decentralized CDM controllers are designed for the process and decoupler blocks. Several examples are presented to illustrate the effectiveness of the proposed method and compared it with existing ones. It is shown that CDM design is more stable and robust whilst giving the desired time domain performance.