Current‐mode wave field programmable analogue arrays

A new configurable analogue block (CAB), the key element in the design of field programmable analogue arrays (FPAAs), is introduced in this paper. This CAB is based on wave equivalents of the passive elements and it is easily reconfigurable resulting in very simple and versatile FPAA structures. The proposed topology employs a minimum number of switches in the signal path due to the absence of the interconnection network required in other FPAA structures, and thus an improved performance is achieved in comparison with the already introduced corresponding programmable configurations. Copyright © 2008 John Wiley & Sons, Ltd.     

On the transposition of Gm–C filters to DC stabilized log‐domain filters

High‐order log‐domain filters could be designed by transposing the already known linear‐domain G_m–C filter topologies to the corresponding topologies in the log‐domain. This is achieved by using a non‐linear transconductor configuration, where the output current is exponentially related to its input and output voltages. A drawback of the non‐linear transconductor configuration already introduced in the literature is that a number of the transposed log‐domain filter topologies suffer from DC instability, while in some others a DC offset current appears at their output. In order to eliminate the aforementioned problems a modified non‐linear transconductor configuration for transposing G_m–C filter topologies to log‐domain filter topologies is introduced in this paper. The achieved improvements are demonstrated through a number of log‐domain filter configurations derived using the already introduced and the proposed transposition schemes. Copyright © 2006 John Wiley & Sons, Ltd.     

Square‐root domain wave filters

In this paper the wave method is used for designing high‐order square‐root domain filters, which emulate the topology of the corresponding LC ladder prototypes. This is achieved by transposing the signal flow graph that corresponds to the wave equivalent of the elementary two‐port subnetwork in the linear domain to the corresponding one in the square‐root domain, by employing an appropriate set of complementary operators. As the equivalents of the other reactive elements are derived from the wave equivalent of the elementary subnetwork, by interchanging the terminals of the appropriate wave signals and/or using inverters, an advantage offered by the proposed technique is the modularity of the derived filter configurations. As an example, a fifth‐order lowpass square‐root domain wave filter was designed and its behaviour was studied through simulation results in order to demonstrate the validity of the proposed design technique. Copyright © 2006 John Wiley & Sons, Ltd.     

Design of current‐mode MOSFET‐C filters using OTRAs

In this paper, third‐order current‐mode MOSFET‐C filters that use operational transresistance amplifiers (OTRAs) with little parasitic capacitance effects are presented. On the basis of the proposed systematic method and design procedure, we can efficiently synthesize third‐order active filters with OTRAs along with simplified MOSFET resistor circuits, and all virtually grounded capacitors. Third‐order current‐mode Chebychev low‐pass and high‐pass filters are realized to verify the validity of the theoretical analysis. Experimental results employing commercially available current feedback amplifiers are also given. Copyright © 2008 John Wiley & Sons, Ltd.     

Realization of log‐domain high‐order transfer functions using first‐order building blocks and complementary operators

High‐order log‐domain filters could be easily designed by using the functional block diagram (FBD) representation of the corresponding linear prototype and a set of complementary operators. For this purpose, lossy and lossless integrator blocks have been already introduced in the literature. Novel first‐order log‐domain highpass and allpass filter configurations, which are fully compatible with the already published integrator blocks, are introduced in this paper. These are realized using integration and subtraction blocks or a novel differentiation configuration. As a result, a complete set of first‐order building blocks would be available for synthesizing any arbitrary high‐order transfer function. In order to verify the correct operation of the proposed structures, the performance of the introduced highpass filters was evaluated through simulation results. In addition, a fifth‐order log‐domain bandpass filter was designed and simulated using one of the introduced first‐order highpass filter configurations. Copyright © 2006 John Wiley & Sons, Ltd.     

Voltage mode and current mode Tow Thomas bi‐quadratic filters using inverting CCII

A voltage mode Tow Thomas bi‐quadratic filter using the inverting second‐generation current conveyor (ICCII) is given. The filter has high input impedance, employs two grounded capacitors, and has independent control on Q, independent control on the band‐pass and low‐pass response gain. Three alternative current mode filters are generated from the voltage mode circuit. The three circuits have zero input impedance, employ grounded capacitors and have independent control on Q. Two of the circuits have also all resistors grounded and the other uses only ICCII?and has only one floating resistor. Copyright © 2007 John Wiley & Sons, Ltd.     

Design of square‐root domain filters by substituting the passive elements of the prototype filter by their equivalents

A novel technique for designing square‐root domain (SRD) filters is introduced in this paper. The concept of the proposed method is based on the substitution of the passive elements of the corresponding prototype filter by their SRD equivalents. The signal processing performed by the proposed SRD equivalents achieves that the voltage at each terminal of the SRD equivalent is the compressed version of the voltage at the corresponding terminal of the passive element, and that the current that flows through the SRD equivalent is the same as that flows through the passive element. The main attractive characteristic of the proposed method is that a quick procedure for designing SRD filters is offered. The validity of the proposed technique was verified by studying the behaviour of a 5th‐order SRD low‐pass filter. In order to demonstrate the benefits offered by the proposed technique, a SRD leapfrog filter was also designed and its performance is compared with that of the active filter that topologically simulates the same prototype filter. Copyright © 2007 John Wiley & Sons, Ltd.     

A current‐mode automatic frequency tuning system for filters with current mirrors

A new current‐mode automatic frequency tuning system is proposed in this paper. The system is based on the master–slave technique and is suitable for integrated current‐mode filters based on current mirrors. Automatic control is accomplished by controlling the bias current of the current mirrors employed in the master and slave filters. The proposed scheme has been applied in the leapfrog and wave filters and the corresponding simulation results confirm its validity. Copyright © 2009 John Wiley & Sons, Ltd.     

Square‐root domain linear transformation filters

A new systematic method for designing square‐root domain (SRD) linear transformation (LT) filter is introduced in this paper. For this purpose, a substitution table containing the SRD LT equivalent of each passive element has been introduced. The proposed equivalents have been realized by employing appropriate SRD building blocks with low‐voltage operation capability. As a design example, a 3rd‐order SRD LT filter has been realized and its performance has been evaluated through simulation results. In addition, the most important performance factors of the SRD filter have been compared with those achieved by the SRD filters derived according to the leapfrog, wave, and topological emulation methods. Copyright © 2010 John Wiley & Sons, Ltd.     

Current‐mode programmable piecewise‐linear neural synapses

Cellular Neural Networks with piecewise linear connection have been proposed by several authors as a generalization of the basic paradigm, which allows for more complex functionality. None of the prototypes realized to date, however, provides for such kind of synapses. As a feasibility study, a current‐mode subthreshold CMOS piecewise‐linear synapse circuit is developed in this paper. Copyright © 2003 John Wiley & Sons, Ltd.     

Log‐domain linear transformation filters revised: improved building blocks and comparison results

A method for designing high‐order log‐domain filters has already been proposed in the literature based on the concept of the classical linear transformation (LT) filters. For this purpose, a substitution table containing the log‐domain LT equivalent of each passive element has been introduced. Drawbacks of the log‐domain filter topologies derived according to this table are the following: (a) a dc offset current appears at the output of all pole filters and (b) dc instability is observed in the case of the substitution of LC resonators. In addition, an alternative technique already proposed for simulating filters with LC resonators is valid only under small‐signal conditions. In order to overcome the aforementioned problems, new log‐domain LT equivalents of a number of passive elements are introduced in this paper. The correct operation of the novel blocks has been verified through simulation results. Also, a comparison concerning the behaviour of the log‐domain LT filters and that of the filters derived according to the leapfrog and the wave methods has also been performed. Copyright © 2007 John Wiley & Sons, Ltd.     

Low power switched‐current circuits with low sensitivity to the rise/fall time of the clock

The switched‐current (SI) technique permits realizing analog discrete‐time circuits in standard digital CMOS technology. A very important property of the analog part of a system on a chip is the possibility it offers for realizing some functions of a digital circuit, but with reduced power consumption. In this paper, a low power SI integrator is presented. It is shown that an integrator consuming a fraction of a milliwatt can be designed in 0.35µm CMOS technology with the use of narrow transistor channels, and with the channel length as a design parameter. The impact of the rise/fall time of the clock signal on the integrator operation is observed. It is shown that this effect can be reduced when the proper switch dimensions are taken for the integrator. Analysis and measurements of the integrator noise are presented. The integrator was built with equal size transistors, yielding less sensitivity to variations in production parameters. An experimental chip in 0.35µm CMOS technology was fabricated, and measurements are compared with results obtained during analysis and simulations. In order to verify the properties of the designed integrator experimentally, a first‐order filter is built with the use of elementary cells on the chip. Copyright © 2008 John Wiley & Sons, Ltd.     

Ultra‐low voltage fractional‐order circuits using current mirrors

Fractional‐order blocks, including differentiators, lossy and lossless integrators as well as filters of order 1 + a (0 < a < 1), are presented in this paper. The proposed topologies offer the benefit of ultra low‐voltage operation; in addition, reduced circuit complexity is achieved compared to the corresponding companding schemes, which have been already introduced in the literature. The ultra‐low voltage operation is performed through the employment of metal oxide semiconductor transistors biased in the subthreshold region. The reduction of circuit complexity is achieved through the utilization of current mirrors as active elements for realizing the required building blocks. The performance of the proposed fractional‐order circuits has been evaluated through the Analog Design Environment of the Cadence software and the design kit provided by the Taiwan Semiconductor Manufacturing Company (TSMC) 180 nm complementary metal oxide semiconductor process. Copyright © 2015 John Wiley & Sons, Ltd.     

Fractional‐order electronically controlled generalized filters

Novel topologies of fractional‐order generalized filters are introduced in this paper. These offer the following benefits: (1) realization of lowpass, highpass, bandpass, allpass, or bandstop filter functions by the same topology; (2) resistorless realizations; (3) electronic adjustment of their frequency characteristics as well as their order; and (4) employment of only grounded capacitors. All the above have been achieved using Operational Transconductance Amplifiers as active elements and appropriate multi‐feedback topologies. The behavior of the proposed designs is verified through simulation results using the Cadence IC design suite and the Design Kit provided by the Austrian Micro Systems 0.35‐µm complementary metal–oxide–semiconductor process. Copyright © 2016 John Wiley & Sons, Ltd.     

Electronically controlled multiphase sinusoidal oscillators using current amplifiers

A novel current‐mode multiphase oscillator topology is introduced in this letter. This is realized by employing current amplifiers and only grounded capacitors. Attractive characteristics offered by the new topology are the electronic adjustment of the oscillation frequency, the absence of passive resistors, and the requirement of only grounded capacitors. Comparison with the corresponding already published current follower based structure shows that the proposed topology has better performance in terms of the number of required active elements, the employment of passive resistors, and the ability for electronic adjustment of the oscillation frequency. Copyright © 2008 John Wiley & Sons, Ltd.     

Harmonic oscillators realized using current amplifiers and grounded capacitors

New configurations of harmonic oscillators, realized using current amplifier blocks and only grounded capacitors, are introduced in this article. The proposed configurations are based on a grounded inductor simulator scheme and on a loop constructed from first‐order sections, respectively. Comparison with the already published topologies shows that the new configurations have attractive characteristics concerning their implementation in integrated form. Copyright © 2006 John Wiley & Sons, Ltd.     

A DC stabilized log‐domain nth‐order multifunction filter based on the decomposition of nth‐order HP filter function to FLF topology

The design of high‐order log‐domain filters can be easily accomplished by transposing already known linear‐domain G_m‐C filter topologies to their counterparts in the log‐domain through the employment of a set of complementary operators. To achieve the G_m‐C filter topologies, the multiple feedback approach is widely used due to its accrued advantages. In this paper a synthesis approach for the development of an nth‐order multifunction log‐domain filter comprising lowpass (LP), highpass (HP) and bandpass (BP) filter functions is proposed. The approach is based on the decomposition of nth‐order HP filter function to follow‐the‐leader‐feedback (FLF) topology. The design is simple and simultaneously achieves nearly all of the chief advantages. The design offers superior performance factors vis‐à‐vis the ones recently reported. To verify the high‐order behavior of the topology, a 5th‐order multifunction filter was designed and the achieved simulated results verify the theory. Copyright © 2008 John Wiley & Sons, Ltd.     

Sinusoidal oscillators with explicit current output employing current‐feedback op‐amps

Employing a state‐variable synthesis, a number of new current‐mode oscillators with explicit current output have been derived, which can be practically implemented from commercially available current‐feedback op‐amps (CFOA). The workability of the proposed structures has been confirmed by experimental results using AD844‐type CFOAs and some sample results have been presented. Copyright © 2008 John Wiley & Sons, Ltd.