Brent Maundy

Field programmable analogue array implementation of fractional step filters

In this study, the authors propose the use of field programmable analogue array hardware to implement an approximated fractional step transfer function of order (n+α) where n is an integer and 0 < α < 1. The authors show how these filters can be designed using an integer order transfer function approximation of the fractional order Laplacian operator sα. First and fourth-order low- and high-pass filters with fractional steps from 0.1 to 0.9, that is of order 1.1–1.9 and 4.1–4.9, respectively, are given as examples. MATLAB simulations and experimental results of the filters verify the implementation and operation of the fractional step filters.

Measurement of Supercapacitor Fractional-Order Model Parameters From Voltage-Excited Step Response

In this paper, we propose using a numerically solved least squares fitting process to estimate the impedance parameters of a fractional order model of supercapacitors from their voltage excited step response, without requiring direct measurement of the impedance or frequency response. Experimentally estimated parameters from low capacity supercapacitors of 0.33, 1, and 1.5 F in the time range 0.2-30 s and high capacity supercapacitors of 1500 and 3000 F in the time range 0.2-90 s verify the proposed time domain method showing less than 3% relative error between the simulated response (using the extracted fractional parameters) and the experimental step response in these time ranges. An application of employing supercapacitors in a multivibrator circuit is presented to highlight their fractional time-domain behavior.

A novel current-mode instrumentation amplifier based on operational floating current conveyor

This paper presents a novel current-mode instrumentation amplifier (CMIA) that utilizes an operational floating current conveyor (OFCC) as a basic building block. The OFCC, as a current-mode device, shows flexible properties with respect to other current- or voltage-mode circuits. The advantages of the proposed CMIA are threefold. First, it offers a higher differential gain and a bandwidth that is independent of gain, unlike a traditional voltage-mode instrumentation amplifier. Second, it maintains a high common-mode rejection ratio (CMRR) without requiring matched resistors, and finally, the proposed CMIA circuit offers a significant improvement in accuracy compared to other current-mode instrumentation amplifiers based on the current conveyor. The proposed CMIA has been analyzed, simulated, and experimentally tested. The experimental results verify that the proposed CMIA outperforms existing CMIAs in terms of the number of basic building blocks used, differential gain, and CMRR.

On the practical realization of higher-order filters with fractional stepping

We propose the use of a compact integer-order transfer function approximation of the fractional-order Laplacian operator s^@a to realize fractional-step filters. Lowpass and bandpass filters of orders (n+@a) and 2(n+@a), where n is an integer and 0 5.9) is given as an example with its characteristics compared to 5th- and 6th-order Butterworth filters. Spice simulations and experimental results are shown.

High-quality factor asymmetric-slope band-pass filters: A fractional-order capacitor approach

This study presents new techniques for implementing continuous-time second-order band-pass filters with high-quality factors and asymmetric slopes. The techniques are centred around the realisation of two non-conventional transfer functions which include the non-integer-order Laplacian operator sα; 0<α<1. Four main possible circuit realisations; one based on a frequency-dependent negative resistor (FDNR), another based on an inductor and two based on multiple amplifier biquads (MABs) are given and verified using Spice and experimentally for both transfer functions. In addition, a field programmable analogue array (FPAA) realisation is tested and verified. Last but not least, a possible realisation using current conveyors is also given, tested and verified.

Fractional-order models of supercapacitors, batteries and fuel cells: a survey

This paper surveys fractional-order electric circuit models that have been reported in the literature to best fit experimentally collected impedance data from energy storage and generation elements, including super-capacitors, batteries, and fuel cells. In all surveyed models, the employment of fractional-order capacitors, also known as constant phase elements, is imperative not only to the accuracy of the model but to reflect the physical electrochemical properties of the device.

A new design topology for low-voltage CMOS current feedback amplifiers

A new topology for designing low-voltage current feedback amplifiers (CFAs) is presented. By employing a second-generation positive current conveyor followed by an operational amplifier in an unconventional manner, the design circumvents the problem of trying to achieve large transimpedance in a low-voltage environment. It is shown that this CFA configuration also results in near gain independent closed-loop bandwidth defined by a single feedback resistor. The proposed amplifier was verified experimentally by a chip designed using Taiwan Semiconductor Manufacturing Companys 0.18-mum digital CMOS process of a single-ended power supply of 1.8 V

Versatile Precision Full-Wave Rectifiers for Instrumentation and Measurements

This paper analyzes the performance of a family of high-quality precision full-wave rectifiers that utilize operational conveyors. The circuits have high precision, wide bandwidth, and high accuracy and are superior to the corresponding operational-amplifier (op amp)-based circuits. Using the LF351 op amp, they are able to rectify signals up to 100 kHz and beyond with little or no distortion. PSPICE results for the circuits are presented.

Improving the bandwidth gain-independence and accuracy of the current feedback amplifier

A high-performance current feedback amplifier circuit referred to as an operational current feedback amplifier is described in this paper. The technique employed involves the incorporation of the input circuit of the current feedback amplifier in the feedback loop of an operational amplifier to reduce the input impedance at the inverting terminal of the current feedback amplifier. The new circuit possesses the gain accuracy and bandwidth of the current feedback amplifier but realizes significant improvement in bandwidth accuracy and bandwidth gain-independence. Experimentally, using AD844s, an order of magnitude reduction in bandwidth variation with changing gain was achieved in the noninverting configuration and almost complete bandwidth invariance was realized in the inverting configuration.

Approximated Fractional Order Chebyshev Lowpass Filters

We propose the use of nonlinear least squares optimization to approximate the passband ripple characteristics of traditional Chebyshev lowpass filters with fractional order steps in the stopband. MATLAB simulations of , , and order lowpass filters with fractional steps from  = 0.1 to  = 0.9 are given as examples. SPICE simulations of 1.2, 1.5, and 1.8 order lowpass filters using approximated fractional order capacitors in a Tow-Thomas biquad circuit validate the implementation of these filter circuits.