Analytical synthesis of odd/even‐nth‐order elliptic Cauer filter structures using OTRAs

The operational transresistance amplifier (OTRA), the dual of the well‐known operational transconductance amplifier, is an attractive element for use in circuit design. One odd‐nth‐order and two even‐nth‐order OTRA‐R‐C or OTRA‐MOS‐C elliptic Cauer filter structures are presented using new analytical synthesis methods (ASMs). Because it is assumed in the synthesis procedure that the transresistance R_m → ∞, but in view of the fact that R_m is finite in practice, the more the number of OTRAs employed, the worse the precision of the output signals. By studying the sensitivity of the output to component variations, more precise output may be obtained by selecting one or two appropriate capacitance(s)/resistance(s) and adjusting their values suitably. H‐spice simulations are given to validate and demonstrate the theoretical predictions. Copyright © 2012 John Wiley & Sons, Ltd.     

Current‐mode filters based on current mirror arrays

A technique is proposed for obtaining current‐mode filters based on current mirror arrays that operate as unity gain current amplifiers. These amplifiers by properly driving capacitors realize active lossless integrators which are the basic active elements for the derivation of filters according to the leapfrog method. Due to the fact that both the structure of the amplifiers and the adapted method for filter design are simple, the proposed technique is attractive for filter design and implementation. A design and the implementation of two third‐order low‐pass filters are presented. The array of the amplifiers has been implemented in a 0.8 µm CMOS technology. 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.     

Explicit design formulas for current‐mode leap‐frog OTA‐C filters and 300 MHz CMOS seventh‐order linear phase filter

The leap‐frog (LF) configuration is an important structure in analogue filter design. Voltage‐mode LF OTA‐C filters have recently been studied in the literature; however, general explicit formulas do not exist for current‐mode LF OTA‐C filters and there is also need for current‐mode LF‐based OTA‐C structures for realization of arbitrary transmission zeros. Three current‐mode OTA‐C structures are presented, including the basic LF structure and LF filters with an input distributor or an output summer. They can realize all‐pole characteristics and functions with arbitrary transmission zeros. Explicit design formulas are derived directly from these structures for the synthesis of, respectively, all‐pole and arbitrary zero filter characteristics of up to the sixth order. The filter structures are regular and the design formulas are straightforward to use. As an illustrative example, a 300 MHz seventh‐order linear phase low‐pass filter with zeros is presented. The filter is implemented using a fully differential linear operational transconductance amplifier (OTA) based on a source degeneration topology. Simulations in a standard TSMC 0.18µm CMOS process with 2.5 V power supply have shown that the cutoff frequency of the filter ranges from 260 to 320 MHz, group delay ripple is about 4.5% over the whole tuning range, noise of the filter is 420nA/√Hz, dynamic range is 66 dB and power consumption is 200 mW. Copyright © 2008 John Wiley & Sons, Ltd.     

All‐pass filters using DDCC‐ and MOSFET‐based electronic resistor

The main motivation in this paper is to draw attention to the tunability and input‐signal amplitude limitations when a nonlinear device is used as a resistor. For this purpose, two first‐order all‐pass filters are proposed using differential difference current conveyor (DDCC), a capacitor and a resistor without element‐matching restriction. These all‐pass filter circuits can be made electronically tunable with electronic resistors. Tunability and input‐signal amplitude limitations of the proposed circuits due to the operational restrictions of the electronic resistors are examined. PSPICE simulations confirm the validity and the practical utility of the proposed circuits. Copyright © 2010 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.     

Micropower high current‐drive class AB CMOS current‐feedback operational amplifier

A novel CMOS current‐feedback operational amplifier (CFOA) aimed to low‐power applications is proposed. The use of a compact class AB implementation allows high current‐drive capability and simultaneously very low quiescent power consumption. Measurement results of a fabricated prototype show for an inverting configuration a closed‐loop bandwidth of 1 MHz independent of gain setting, and a slew rate of 2V/µs for a load capacitance of 30 pF and a quiescent power consumption of 264µW. Copyright © 2010 John Wiley & Sons, Ltd.     

Balanced Gm‐C filters with improved linearity and power efficiency

A novel G_m‐C filter design technique is presented. It is based on floating‐gate metal oxide semiconductor (FGMOS) transistors and consists in a topological rearrangement of conventional fully differential G_m‐C structures without modifying the employed transconductors at transistor level. The proposed method allows decreasing the number of active elements (transconductors) of the filter. Moreover, high linearity is obtained at low and medium frequencies of the pass band. Drawbacks inherent to the use of FGMOS transistors are analyzed, such as large occupied area, high sensitivity to mismatch, or parasitic zeros in transfer functions. The features of the proposed technique are fully exploited in all‐pole G_m‐C filter design, specially implementing unity gain Butterworth transfer functions. Thus, two low‐power second‐order Butterworth G_m‐C filters have been designed and fabricated to compare the proposed FGMOS technique with their equivalent topologies obtained by a conventional design method. Measurement results for a test chip prototype in a 0.5‐µm standard complementary MOS process are presented, confirming the advantages of the proposed FGMOS design technique. Copyright © 2014 John Wiley & Sons, Ltd.     

Universal current‐mode filters and parasitic impedance effects on the filter performances

In this letter, two universal current‐mode (CM) filters for simultaneously realizing low‐pass, band‐pass and high‐pass characteristics are proposed. Both of the presented filters can also realize notch and all‐pass responses with interconnection of the relevant output currents. They employ second‐generation current‐controlled conveyors (CCCIIs) and only grounded capacitors. They also have low active and passive element sensitivities along with electronically adjustable angular resonance frequency (ω₀) and quality factor (Q). Based on the first developed filter, the parasitic impedance effects of the conveyors on the filter performances are investigated in detail. Simulation results using SPICE simulation program are included to verify the theory. Copyright © 2007 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.     

On the input common‐mode voltage range of CMOS bulk‐driven input stages

In this paper the response of a bulk‐driven MOS Metal‐Oxide‐Semiconductor input stage over the input common‐mode voltage range is discussed and experimentally evaluated. In particular, the behavior of the effective input transconductance and the input current is studied for different gate bias voltages of the input transistors. A comparison between simulated and measured results, in standard 0.35‐µm CMOS Complementary Metal‐Oxide‐Semiconductor technology, demonstrates that the model of the MOS transistors is not sufficiently accurate for devices operating under forward bias conditions of their source‐bulk pn junction. Therefore, the fabrication and the experimental evaluation of any solution based on this approach are highly recommended. A technique to automatically control the gate bias voltage of a bulk‐driven differential pair is proposed to optimize the design tradeoff between the effective input transconductance and the input current. The proposed input stage was integrated as a standalone block and was also included in a 1.5‐V second‐order operational transconductance amplifier (OTA)‐C lowpass filter. Experimental results validate the effectiveness of the approach. Copyright © 2010 John Wiley & Sons, Ltd.     

Analytical synthesis and comparison of voltage‐mode Nth‐order OTA‐C universal filter structures

Complementary single‐ended‐input operational transconductance amplifier (OTA)‐based filter structures are introduced in this paper. Through two analytical synthesis methods and two transformations, one of which is to convert a differential‐input OTA to two complementary single‐ended‐input OTAs, and the other to convert a single‐ended‐input OTA and grounded capacitor‐based one to a fully differential OTA‐based one, four distinct kinds of voltage‐mode nth‐order OTA‐C universal filter structures are proposed. TSMC H‐Spice simulations with 0.35µm process validate that the new complementary single‐ended‐input OTA‐based one holds the superiority in output precision, dynamic and linear ranges than other kinds of filter structures. Moreover, the new voltage‐mode band‐pass, band‐reject and all‐pass (except the fully differential one) biquad structures, all enjoy very low sensitivities. Both direct sixth‐order universal filter structures and their equivalent three biquad stage ones are also simulated and validated that the former is not absolutely larger in sensitivity than the latter. Finally, a very sharp increment of the transconductance of an OTA is discovered as the operating frequency is very high and leads to a modified frequency‐dependent transconductance. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

0.5‐V bulk‐driven OTA and its applications

A new 0.5‐V bulk‐driven operational transconductance amplifier (OTA), designed in 50 nm CMOS technology, is presented in the paper. The circuit is characterized by improved linearity and dynamic range obtained for MOS devices operating in moderate inversion region. Some basic applications of the OTA such as a voltage integrator and a second‐order low‐pass filter have also been described. The filter is compared to other low‐voltage filters presented in the literature. Copyright © 2013 John Wiley & Sons, Ltd.     

Bandwidth extension,linearity enhancement,and cost reduction techniques for continuous‐time channel‐select filters

Achieving a wide bandwidth in a conventional active‐RC filter requires large power consumption and is often accompanied by significant performance degradation. In this paper, a new structure to implement active‐RC continuous‐time filters and also a new frequency compensation scheme for the operational amplifiers that are the main building blocks of active‐RC filters are proposed. Exploiting these techniques increases the maximum possible bandwidth with lower power consumption in comparison with the conventional architectures, reduces die area, and enhances the dynamic range. The effectiveness of these methods has been verified by analysis and simulation of the conventional and proposed filters under identical conditions. Both the analytical investigations and extensive simulation results prove that the adopted techniques improve the performance of continuous‐time filters considerably in terms of bandwidth and linearity while reducing the die area. Simulations have been carried out in a standard 90‐nm CMOS process by using Advanced Design System (ADS), and the proposed filter features 11.08‐dB spurious‐free dynamic range improvement and 5.9 times bandwidth enhancement. Also, the total on‐chip capacitance is made 2.4 times smaller by using the new biquad structure. Copyright © 2016 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.     

IC‐constrained optimization of continuous‐time Gm–C filters

This paper presents an automated synthesis procedure for integrated continuous‐time fully‐differential G_m?C filters. Such procedure builds up on a general extended state‐space system representation which provides simple matrix algebra mechanisms to evaluate the noise and distortion performances of filters, as well as, the effect of amplitude and impedance scaling operations. The proposed technique not only addresses the dynamic range optimization under power dissipation constraints, but also accounts for other relevant integrated circuit related features, such as transconductor decomposition in unitary instances, spread of capacitances and estimated area occupation, among other characteristics. The proposed approach, implemented in the MATLAB^® framework, can be also used as an exploratory tool to compare different circuit implementations for a given set of filter specifications. Copyright © 2010 John Wiley & Sons, Ltd.     

Current mode filters using two output inverting CCII

Current mode Tow Thomas filter using two‐output inverting second‐generation current conveyor is given, the circuit has low input impedance, employs two grounded capacitors and three grounded resistors and has independent control on Q. A universal current mode filter capable of realizing the five filter functions is also given. Both circuits have low sensitivities to all circuit components. Spice simulation results are included. Copyright © 2007 John Wiley & Sons, Ltd.     

Low-noise and low-sensitivity filters using current-mode coupled biquads

In this paper, it is shown that by adding coupling to biquad pairs to obtain a fourth-order band-pass filter, the output thermal noise is reduced. It is shown analytically that minimum output thermal noise is obtained when the biquads are identical and the negative-feedback factor used for coupling is the same as for the minimum sensitivity to component tolerances and ambient changes. Furthermore, by optimizing the coupled biquads for maximum dynamic range, the output noise is further decreased.