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The architecture, design and implementation of a low power complementary metal‐oxide semiconductor (CMOS) class‐G audio amplifier with gradual power‐supply switching (GPSS) are presented. The proposed class‐G amplifier output stage strategically uses the parallel connection of a class‐AB output stage operating from smaller supplies (VDDL/VSSL), and a class‐C output stage (with crossover from VSSL to VDDL) operating from higher supplies (VDDH/VSSH). GPSS is achieved using an efficient biasing scheme with level shifters. Moreover, the proposed biasing scheme in conjunction with negative feedback enables low distortion during the power‐supply transition. Experimentally, the class‐G amplifier prototype achieves a −82.5 dB THD + N, a peak load power of 50 mW and a quiescent power consumption of 350 μW. The proposed class‐G amplifier was implemented in a standard CMOS 90 nm technology and occupies an active silicon area of 0.08 mm2. [ABSTRACT FROM AUTHOR]

Summary Scattering of light by disordered structures is a common phenomenon in our daily life. For many scientific applications, scattering is often treated as a detrimental effect. However, recent development in the field of nanophotonics shows that scattering in disordered nanostructures can enable new functionalities, including the unexpected property of random lasing. A random laser is different from a traditional laser in that the feedback amplification is not provided by a cavity formed by reflection components, but by disorder-induced scattering. Depending on the nature of disordered nanostructures, which can range from a few nanometers to several hundreds of nanometers in size, disorder-induced scattering can provide intensity feedback or amplitude feedback. Thus random lasers are classified into two categories: incoherent random lasers and coherent lasers. During the past two decades, many disordered nanostructures, including laser dye in colloidal systems, photonic crystals, polymeric matrices, rare earth doped nanopowders, quantum dots, semiconductors, and biological tissues have been proposed and demonstrated to form high-performance random lasers. Excitation mechanisms have included optical and electrical pumping. In the former, besides single photon excitation, multiphoton pumped upconversion random lasing has also been demonstrated. In this review, we describe the physics that explains the optical properties of disordered nanostructures and scattering used to develop the random lasers, particularly discussing the role of modes in random lasers. We then present the current state-of-art of fabrication and processing of various disordered nanostructures for the development of random lasers, including techniques to manipulate characteristics such as tunability and directionality. In this context, random fiber lasers will be discussed, as they play an important role in applications of random lasers. It will also be pointed out that random lasers keep the spatial and the temporal coherence characteristic behavior of conventional lasers, as well as the Poissonian statistics well above the threshold. Recent achievements in upconversion lasing, Raman lasing and SPASER lasing in a random medium will also be covered. Then we discuss the impact of random lasers in cross-disciplinary areas such as astrophysics. A major emphasis of this review is to cover the various applications that have already emerged. The review concludes with the author's views on future perspectives, including some envisioned futuristic applications. [ABSTRACT FROM AUTHOR]

A CMOS variable gain amplifier (VGA) based on a novel linear and tunable triode transconductor is presented. The proposed transconductor employs local negative feedback for linearisation controlling the drain voltage of the input transistors biased in the triode region. The new design is able to operate at low supply voltage and the stability is guaranteed. The transconductor features a 47.75 dB dc gain and a 4.23 MHz unity gain frequency with a power consumption of only 91 µA. To show the feasibility of the proposed transconductor, a VGA has been fabricated. Measurement results for a 0.13 µm CMOS design show a −3 dB bandwidth above 2.8 MHz and a third‐order harmonic distortion at 500 kHz below −46 dB over the whole gain range. The VGA exhibits a maximum power consumption of only 395 µW from a single 1.2 V supply. [ABSTRACT FROM AUTHOR]

The invention of the negative feedback amplifier by Harold S. Black (1898-1983) in 1928 is considered one of the great achievements in electronics. In fact, it is listed among the IEEE Milestones, where it is credited to Bell Labs. Black was hired by Western Electric in 1921 and assigned to work on the Type C system, a newly introduced three-channel telephone network whose push-pull, vacuum-tube, repeater amplifiers produce too much harmonic distortion when connected in tandem [1]. At that time, telephone networks were spreading, and Bell Labs emerged quickly as the major research company in the telephone industry. The extension of lines over long distances required counteracting signal attenuation, which occurred, though at a reduced level, even in lines provided with Pupin's loading coils, which discretely increased the line longitudinal inductance L so as to match the Heaviside condition L/R=C/G for distortionless transmission (R being the longitudinal resistance and C and G the transverse capacitance and conductance, respectively). [ABSTRACT FROM PUBLISHER]

A low‐noise, wide‐bandwidth DNA readout instrument for nanopore applications is presented. Owing to hardware simplicity and reliability, a resistive‐feedback transimpedance amplifier (rf‐TIA) is adopted as the headstage for the readout instrument. However, to achieve a high gain and low input noise, its high feedback resistance induces a high parasitic capacitance, thus significantly limiting the 3 dB bandwidth. To drastically reduce the parasitic capacitance and widen the bandwidth, a novel rf‐TIA architecture is fabricated that utilises a split‐resistor technique for the high feedback resistor. This is demonstrated in a benchtop test employing an α‐haemolysin nanopore. [ABSTRACT FROM AUTHOR]

A class AB differential difference amplifier for continuous‐time common‐mode feedback (CMFB) is presented. It employs local CMFB to improve gain‐bandwidth product and dynamic performance of the CMFB loop, without increasing static power consumption or supply voltage requirements. Measurement results for a 0.5 μm CMOS test chip prototype validate the proposal. [ABSTRACT FROM AUTHOR]

The use of positive feedback as a solution to intrinsic gain degradation in scaled CMOS technologies, such as 65 nm and below, is discussed in detail. Criteria for increasing gain while keeping the system stable are derived using a positive feedback amplifier model. These criteria are shown to provide significant gain enhancement in silicon. This work extends the previously reported DC gain analysis to include evaluation of additional effects of positive feedback as well an investigation of the frequency behavior using S-parameter measurements in silicon. These S-parameter measurements of fully differential positive feedback amplifiers designed in TSMC's 65 nm technology show gain enhancements of up to 26.7 dB at frequencies up to 8.5 GHz. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The influence of external circuit designs on ASET shapes in a high speed current feedback amplifier (CFA) (AD844) is investigated by means of the pulsed laser single event effect (PLSEE) simulation technique. Changes of the feedback resistors modify circuit’s electrical parameters such as closed-loop gain and bandwidth, affecting amplifier stability and so ASET shapes. Qualitative explanations based on general electronic rules and feedback theories enable the understanding of a CFA operation establishing a correlation between the evolution of external feedback resistor values and ASET parameters. TID effects on the ASET sensitivity in AD844 CFA are also investigated in this work highlighting different behaviors according to the impacted bipolar transistor in the integrated circuit. [ABSTRACT FROM PUBLISHER]

ABSTRACT This paper introduces novel four-phase oscillator employing two Dual-Output Controlled Gain Current Follower Buffered Amplifiers (DO-CG-CFBAs), single Current Amplifier, three resistors, and two grounded capacitors suitable for differential quadrature signal production (floating outputs). To control the frequency of oscillation (FO) and condition of oscillation (CO), only the current gain adjustment of active elements is used. The circuit was designed by well-known state variable approach. The oscillator employs three active elements for linear control of FO and to adjust CO and provides low-impedance voltage outputs. Furthermore, two straightforward ways of automatic amplitude gain control were used and compared. Active elements with very good performance are implemented to fulfill required features. Suitable CMOS implementation of introduced DO-CG-CFBA was shown. Important characteristics of the designed oscillator were verified experimentally and by PSpice simulations to confirm theoretical and expected presumptions. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We introduce a new class of feedback amplifiers, called switched-mode operational amplifiers (SMOAs) that address voltage-swing limitations of classical feedback amplifiers in scaled CMOS technologies. By exploiting the increased timing resolution available in scaled CMOS, SMOAs encode analog signal information in the time domain and provide near-rail-to-rail output-signal swing, high output-stage efficiency and better linearity. A 4th-order, 70 MHz continuous-time active-RC Butterworth filter is presented in 65 nm CMOS to demonstrate the advantages of SMOAs. The filter consumes 25.4 mW from a 0.6 V supply and achieves 55.8 dB peak SNDR while operating at a full-scale of 873 mV ppd. Thanks to SMOAs, the full-scale (73% of the 0.6 V supply voltage) and the bandwidth are respectively, a 2.5\times and 6.2\times improvement over other state-of-the-art low-voltage filters. [ABSTRACT FROM AUTHOR]

This study presents a three‐mode controllable master‐slave monostable multivibrator based on current‐feedback operational amplifiers (CFOAs) for analogue signal‐processing applications. The circuit is operated using a positive‐edge triggering signal to generate the output pulses. The pulse width of the output signals can be adjusted by controlling the voltage, current or resistance to yield various circuit operating modes. This study also presents a three‐mode controllable inverting and non‐inverting operation master‐slave monostable multivibrator to extend the application of the proposed circuit. In addition, the circuit operations, related governing equations, non‐ideality analyses and experimental examples and results for the proposed monostable multivibrators are described. Commercially available CFOA integrated circuits (AD844ANs) and discrete passive components are used to construct the prototype circuits. The experimental results verified the validity of the proposed circuits. [ABSTRACT FROM AUTHOR]

In this study the authors present a novel technique for control of signal power transients caused by signal add/drops in optical communication networks with erbium‐doped fibre amplifiers (EDFAs). The approach utilises the electronic automatic gain control that combines both feedback and feedforward control of EDFA. Feedback control is non‐linear integral control and feedforward control is a steady‐state gain scheduling technique. The feedback non‐linear control requires information about the average inversion level that is obtained via a simple linearised first‐order observer. The scheduling variable used is the nominal pump power needed to keep the average inversion level at the desired value at steady state and the input signal powers given at particular wavelengths. In the simplified gain scheduling version, the scheduling variable is the total input signal power. Simulation examples indicate that the proposed controller completely eliminates at steady state the photon power transients caused by signal add/drops with the steady state being reached within a few milliseconds. [ABSTRACT FROM AUTHOR]

This paper presents a bandwidth enhancement technique for broadband Darlington amplifiers. A detailed analysis of the high-frequency performance of the Darlington amplifier and the effect of bandwidth enhancement is provided. A design procedure is also given for broadband feedback Darlington amplifiers with bandwidth enhancement and gain flattening. A single- and a three-stage feedback amplifier with the proposed improvements are designed and implemented in a 0.25-\mu\ m AlGaAs–InGaAs pHEMT technology. The single-stage amplifier provides \ 6\pm \ 0.4~\ dB of small-signal gain in the frequency band of 1–30 GHz. The three-stage amplifier features \ 17.8\pm \ 0.8~\ dB of small-signal gain in the frequency band of 2–29 GHz. It provides a gain-bandwidth product of 217 GHz, which is 3.3 times larger than the unity gain frequency (f T) of the process. [ABSTRACT FROM AUTHOR]

This study investigates the closed-loop performance of the basic current feedback operational amplifier (CFOA), with particular emphasis on its dynamic response. It also focuses on the design, performance and advantages of the CFOA in its ability to provide a substantially constant closed-loop bandwidth for closed-loop voltage gain. Furthermore, an improved CFOA with wide bandwidth and common-mode-rejection ratio (CMRR) performance is also presented. The design presented in this article uses a bootstrapping technique with Quasi-Darlington in the input stage to reduce the influence of the Early effect which results in improved performance. Another advantage of this design is that the inverting input impedance is reduced significantly, which leads to further improvement in bandwidth and CMRR. [ABSTRACT FROM PUBLISHER]

The realization of electronically tunable allpass phase-selective filters using the new Multiplication Mode Current Conveyor (MMCC) device is proposed; both first and second order implementations are presented. Electronic tunability is obtained by applying the control voltage directly to the control terminal of the device without necessitating any elaborate current sensing circuitry. The second order function is designed by using a high quality shunt-LC resonator based on a new synthetic lossless-L derived from a Differential Voltage Current Conveyor Transconductance Amplifier (DVCCTA) device wherein both capacitors are grounded. Both these active devices were implemented for the proposed work by readily available current feedback amplifier (CFA) elements. The configurations have been thoroughly analyzed with respect to device imperfections and it has been shown that the active sensitivities arc quite low. Experimental results had been verified satisfactorily using hardware test and by PSPICE simulation; desired electronic tunability of the output-phase were obtained upto 300KHz whereby the unity-transmission gain remained unaltered. [ABSTRACT FROM AUTHOR]

This paper presents new realizations of Controlled Sources using current feedback operational amplifier (CFOA). All proposed realizations are canonic in the number of passive components and do not require any critical component matching condition. The inverting, non-inverting and differential behavior is discussed and studied. The workability of the circuits and result is verified on the basis of simulation done using ICAP software. [ABSTRACT FROM AUTHOR]

This paper deals with an extension of the Rosenstark's linear model of an amplifier to a nonlinear one for the purpose of performing nonlinear distortion analysis. Contrary to an approach using phasors, our method uses the Volterra series. Relying upon the linear model mentioned above, we define first a set of the so-called amplifier's constitutive equations in an operator form. Then, we expand operators using the Volterra series truncated to the first three components. This leads to getting two representations in the time domain, called in-network and inputoutput type descriptions of an amplifier. Afterwards, both of these representations are transferred into the multi-frequency domains. Their usefulness in calculations of any nonlinear distortion measure as, for example, harmonic, intermodulation, and/or cross-modulation distortion is demonstrated. Moreover, we show that they allow a simple calculation of the so-called nonlinear transfer functions in any topology as, for example, of cascade and feedback structures and their combinations occurring in single-, two-, and three-stage amplifiers. Examples of such calculations are given. Finally in this paper, we comment on usage of such notions as nonlinear signals, intermodulation nonlinearity, and on identification of transfer function poles and zeros lying on the frequency axis with related real-valued frequencies. [ABSTRACT FROM AUTHOR]

In this paper, a novel grid multiscroll chaotic electronic oscillator with simple circuit design is proposed. The proposed grid multiscroll chaotic circuit only needs two current feedback operational amplifiers (CFOAs) as current integrators, passive RC, and nonlinear elements in the form of current stair nonlinear function series (SNFS) realized with CFOAs. Compared with existing grid multiscroll circuits such as Chua's circuit and Jerk circuit, etc., its component count is reduced. Mathematical models of the proposed generators are derived. Theoretical analysis and numerical simulations of the derived models are included. Moreover, the experimental results are verified that the proposed simpler chaotic electronic oscillator can generate grid multiscroll chaotic attractors with higher frequency. [ABSTRACT FROM AUTHOR]

A fully integrated near-infrared spectroscopy photoreceiver including two new silicon avalanche photodiodes (SiAPDs) and a new transimpedance amplifier (TIA) is proposed in this paper. SiAPDs are designed in p+/n-well structure with guard-rings realized in different shapes. The TIA front-end has been designed using distributed-gain concept combined with resistive-feedback and common-gate topology to reach low-noise, low-power consumption, high gain-bandwidth product characteristics and it is robust against power-supply variation (1-3 V). This circuit is developed using 0.35 μm CMOS technology and the measurement results are compared with other results from the literature. The designed rectangular and octagonal SiAPDs have the avalanche gain of 100 and 45 with the breakdown voltage of 9 and 6 V and the photon absorption efficiency of 45% and 25% at 800 nm. Fabricated TIA offers high-transimpedance gain (up to 250 MV/A), tunable BW (1 kHz-1 GHz), extremely low input and output noises (100 fA/√Hz, 1.8 μV/√Hz), and low-power consumption (0.8 mW). The impact and effects of on-chip integration of SiAPD and TIA front-end have been also measured and evaluated. [ABSTRACT FROM PUBLISHER]

Constant input and output mismatch circles in the output load plane are introduced as the basis for low-noise amplifier design methodology. Optimum tradeoff between input and output matching levels results as the application of a design chart providing, at the same time, the corresponding stage transducer gain. The role of degenerative series feedback is studied and systematically embedded in the design procedure, thus providing a direct way to evaluate its optimum level. [ABSTRACT FROM AUTHOR]

A new low-voltage low-power CMOS current feedback amplifier (CFA) is presented in this paper. This is used to realize a novel digitally programmable CFA (DPCFA) using transistor arrays and MOS switches. The proposed realizations nearly allow rail-to-rail swing capability at all the ports. Class-AB output stage ensures low power dissipation and high current drive capability. The proposed CFA/ DPCFA operate at supply voltage of ±0.75 V and exhibit bandwidth better than 95 MHz. An application of the DPCFA to realize a novel voltage mode high-Q digitally programmable universal filter (UF) is given. Performances of all the proposed circuits are verified by PSPICE simulation using TSMC 0.25/µm technology parameters. [ABSTRACT FROM AUTHOR]

In this work, the package influence on a feedback low-noise amplifier has been studied.The electromagnetic simulator of ADS was used to obtain the QFN16 package model and the bonding model. The influence of the package and the pad on the supply node was negligible when it was studied separately. However, the circuit performance is reduced when the inductance introduced by the bonding of the supply node is combined with the parasitic capacities associated to the pad with electrostatic discharge protection. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1435-1440, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27601 [ABSTRACT FROM AUTHOR]

ABSTRACT We present an adaptive frequency compensation technique providing maximum bandwidth closed-loop amplifiers. The approach exploits an auxiliary variable gain amplifier to implement an electrically tunable compensation capacitor proportional to the feedback factor. In this manner, the closed-loop bandwidth is kept ideally constant irrespective of the closed-loop gain. The proposed method can be applied to any amplifier adopting dominant-pole compensation. As an example, we designed a CMOS amplifier providing 66-dB direct current gain and 310-MHz gain-bandwidth product. For closed-loop gains ranging from 1 to 10, the closed-loop bandwidth was found never lower than 401 MHz (noinverting configuration) and 229 MHz (inverting configuration). A similar amplifier with equal gain-bandwidth product, but adopting the traditional fixed compensation approach, would exhibit a closed-loop bandwidth reduced to 33 MHz (noninverting) and 30 MHz (inverting) when the gain magnitude is set to 10. The enhanced frequency performance is obtained with a 48% increase in current consumption, whereas the other main operational amplifier performance parameters remain almost unchanged compared with the standard solution. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper we describe the design of a low noise amplifier (LNA) using two feedback loops, one with a transformer, and the other with a resistor. We determine first the double loop feedback (DLF) topologies that are suitable for LNA design. One of these is analyzed in detail, first assuming an ideal amplifying block, and then with a nonideal block (to determine the gain required for the amplifying block to be considered as ideal). Simulation results show that it is possible to obtain wideband DLF LNAs with very low noise figure. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a current-steering approach to implement a fast transient response low-dropout regulator (LDO) based on a current feedback amplifier (CFA) topology. The circuit does not require any internal compensation capacitor, being stable for a wide range of output load currents [0–100mA] and a 1μF output capacitor. The CFA consists of an open-loop voltage follower with output local current–current feedback based on a level-shifted flipped voltage follower (LSFVF) which is instrumental to achieve high regulation and fast transient response. The inverting output buffer stage of the CFA together with current-mirror-based driving of the power pass transistor results in high PSRR. Post-layout simulation results for a 0.35μm CMOS process design reveal that the proposed LDO requires 59μA quiescent current at no-load condition and at full-load condition has a current efficiency of 99.8%. For a 1μF output capacitor, the maximum output voltage variation to a 0–100mA load transient with rise and fall times of 10 and 100ns is only 3mV, and the PSRR is smaller than −56dB over the entire load current range. [Copyright &y& Elsevier]

This paper proposes a multistage transformer-feedback-based design approach for a high fractional-bandwidth (fBW) IF stage in a 60-GHz heterodyne receiver. An in-depth analysis of source-to-gate transformer-feedback amplifiers, including the design of the matching network, is presented. Analytic expressions for the input resistance, quality factor, and noise figure (NF) as a function of the transformer turns-ratio (n) and magnetic coupling factor (k) are derived. To validate the proposed analysis, a wideband IF amplifier and mixer were designed in a 40-nm CMOS process. From measured results, this device achieves a 16% -3-dB fBW, a peak power gain of 27.6 dB, an NF of 5.3 dB while consuming 28.8 mW from a 0.9-V supply. [ABSTRACT FROM AUTHOR]

This paper presents a CMOS inverter-based class-AB pseudo-differential amplifier comprising current-mode common-mode feedback (CMFB). The circuit employs two CMOS inverters and the complementary CMFB consisting of current-mode common-mode (CM) detector and transimpedance amplifier. The circuit has been designed using 0.18 μm CMOS technology and operates at 1 V supply. The simulation results demonstrate rail-to-rail operation with low CM gain (−15 dB). The power dissipation of the circuit is 102.5 μW. [ABSTRACT FROM AUTHOR]

We successfully fabricated a large-area flexible strain-sensing system based on a 2-D array of organic self-bias-feedback amplifier with a signal gain of 400. The amplifier system consists of three layers: a self-assembled monolayer (SAM) capacitor matrix, a 2-D array of organic pseudo-CMOS inverters with a floating-gate structure using SAM gate dielectric, and an active matrix of organic thin-film transistors. The amplifier sheet comprises 8 \times 8 amplifier cells, with an effective size of \7 \times \7\ \cm^2. The organic transistors exhibit a mobility of 1.7 \cm^2/\V\cdot \s in the saturation regime at an operation voltage of 2 V. A strain sensor is made of a polymeric piezoelectric [polyvinylidene difluoride (PVDF)] sheet. When a cell of the PVDF sheet is touched (that is, when mechanical pressure is applied), a small signal is generated by intermolecular polarization in the PVDF. These signals are amplified by the organic amplifier circuits from 10 to 150 mV. [ABSTRACT FROM AUTHOR]

This paper describes a GaN monolithic microwave integrated circuit (MMIC) cascode feedback amplifier design which achieves up to 8 W of output power and greater than +51 dBm OIP3 across a 250–3000-MHz decade bandwidth. The LNA also achieves 20 dB of flat-gain across the band. The design was fabricated with a 0.25-µm GaN HEMT technology with an fT ∼ 50 GHz and a BVgd > 60 V. A 40-V 750-mA high-bias LNA design achieves an OIP3 of 51.9 dBm, P1dB of 38.5 dBm, and NF ∼ 3 dB at 2 GHz . A 40-V 500-mA medium-bias LNA design achieves a lower NF ∼ 2.5 dB , an OIP3 of 48.4 dBm, and a P1dB of 36.8 dBm at the same frequency. At an optimum low-noise bias of 20 V and 300 mA, a NF ∼ 0.96 dB, an OIP3 of 43.4 dBm, and a linear P1dB of ∼32.2 dBm was also obtained. The combination of high OIP3 and low NF from these GaN MMIC LNA designs exceed that achieved by many state-of-the-art PHEMT, HBT, and HFET technologies for decade-BW MMIC amplifiers operating in the popular wireless and wire-line S- and C-band frequency ranges. The linear GaN LNA performance demonstrated here can enable new generations of software-defined and reconfigurable radios which require ultra-linearity over multiple octaves of bandwidth. [ABSTRACT FROM AUTHOR]

The goal of internal frequency compensation of a low dropout voltage regulator (LDO) is the selection of a small-value, ESR-independent output capacitor. Cascode compensation formed by a common-gate transistor acting as a current buffer, an optional series resistor, and a compensation capacitor creates a dominant pole and a left-half-plane (LHP) zero, allowing adequate phase margin and stable LDO design. To this end, a 1.21 V output, 100 mA, 0.1-10 μF output capacitor, ESR-independent, low voltage LDO using cascode compensation with replica bias is designed and fabricated in a 0.5 μm CMOS process with an area of 0.22 mm. A line regulation of 0.05% V/V, load regulation of 0.001% V/mA and dropout voltage of 220 mV were measured. LDO-specific pole-zero analysis is detailed. In addition to this design, two improved transient response LDO architectures using cascode compensation with split-length transistors are also explored. A Power Good feature is discussed, which enables direct interface between the LDO and a micro-processor. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a novel second order universal filter using current-feedback amplifier, commercially available active component, is presented. The signal-flow graph method is used to synthesize the filter. The proposed filter has three high impedance input and one output, (multiple input single output (MISO) configuration). It can generate all biquadratic filtering functions namely: low-pass (LP), band-pass (BP), high-pass (HP), band-reject (BR) and all-pass (AP) at the output terminal by selecting different input signal combinations. The validity of the proposed circuits is demonstrated by simulations. [Copyright &y& Elsevier]

Loop gain is an important variable in communications theory. Here, we derive its exact distribution. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various papers within the issue on topics including digital phase-locked loop (DPLL), circuit techniques to enhance efficiency of high current light-emitting-diode (LED) drivers and current-feedback instrumentation amplifier (CFIA).

A prosthetic swing-phase control mechanism simulates the action of leg musculature, aiding gait function by controlling the duration of swing, extent of heel rise, and by allowing the shank to smoothly decelerate into full knee extension without excessive impact. Nonfluid-based (NBF) mechanisms have the potential to provide a durable and affordable solution as required in many parts of the world, but the design variables that lead to improved performance of NBF swing-phase control technologies are not well established. Seven transfemoral amputees were fitted with a prosthetic knee joint and different NBF swing-phase setups were systematically assessed. Clinical testing included walk tests utilizing a potentiometer (to measure knee flexion angles) and accelerometer (to measure terminal impact decelerations) mounted on the prosthetic limb. As hypothesized, the friction and spring systems improved gait function. This includes an increased walking speed that closely matched high-end hydraulic prosthetic knee joints, decreased and more normal maximum prosthetic knee flexion, decreased flexion duration, and lower terminal impact. Further improvements were obtained using a dual-spring system, two springs in series, over the more conventional single spring system. NBF swing-phase control mechanisms are simple and significantly improve the performance of prostheses. Their application is ideal where size, weight, and cost may be constrained. [ABSTRACT FROM PUBLISHER]

Novel high-order filter topologies realised by employing current feedback operational amplifiers as active elements are introduced in this article. These are constructed from multiple-loop feedback paths and could be utilised for the realisation of filters of arbitrary order and type. An offered benefit is the requirement for employing only grounded capacitors and resistors. Two design examples are provided and the correct operation of the corresponding topologies has been evaluated through experimental results. [ABSTRACT FROM AUTHOR]

The paper presents a systematic approach of synthesizing sinusoidal linear VCOs (i.e., an oscillator providing linear tuning law of the type f0 ∝ VC between the oscillation frequency f0 and an external control voltage VC). In view of recent interest on current feedback operational amplifier (CFOA)-based oscillators, the proposed methodology has been demonstrated by deriving a class of linear VCOs employing CFOAs and analog multipliers (AM). The workability of the new VCOs has been established by experimental results of the circuits implemented with commercially available AD844 type CFOAs and AD534 type AMs. [ABSTRACT FROM AUTHOR]

The Cryogenic Dark Matter Search (CDMS) employs DC Superconducting Quantum Interference Device (SQUID) Series Array Amplifiers (SSAAs) in its phonon readout system. These amplifiers are in a transresistance topology utilizing feedback from room-temperature electronics. The input coil of each SSAA is in series with a phonon sensor composed of many parallel transition edge sensors (TES's). The SSAA consists of 100 individual SQUIDs, each surrounded by planar input and feedback coils with an electrically isolated flux-focusing washer, which increases the inductive coupling between the SQUID and each coil. A room-temperature gain stage completes the feedback loop between the SSAA output voltage and the feedback coil current. We report on a significant mutual inductance that exists directly between the feedback and input coils, on its impact on the feedback network of the amplifier, and on the resulting transfer function. The consequent effects include a partial nulling of the input coil's self-inductance, as well as resonant peaking in the closed-loop response that depends on the impedance of the input coil circuit. [ABSTRACT FROM AUTHOR]

The paper presents new realizations of grounded negative capacitance, using current feedback operational amplifiers (CFOAs), two resistors and one capacitor. All the proposed realizations are canonic in the number of passive components and do not require any critical component matching condition. Application examples in capacitive cancellation schemes and resistance-controlled low-frequency quadrature sinusoidal oscillator design are provided. The workability of the circuits has been verified by PSPICE simulations. [ABSTRACT FROM AUTHOR]

The output of the linear feedback amplifier is modelled as the superposition of a series of succeeding feedback components. The loop circuit is interpreted as a distributed delaying circuit that spreads an instantaneously applied impulse signal into many infinitesimal components of various delay times. This interpretation is used to explain that the instantaneous feedback component is infinitesimal regardless of how large the loop gain is. Since the instantaneous loop gain between succeeding feedback components is infinitesimal, convergence of the series can be achieved. The relationship between the input and output of the overall system is then derived. We hope that our point of view can provide more insight into the operating mechanism of the feedback circuit and serve as a bridge between introductory textbooks and Nyquist's theory. [ABSTRACT FROM AUTHOR]

The design and analysis of some new voltage controlled oscillators with sinewave output are proposed. The configurations are based on the implementation of double-integrator loop (DIL) using the Current Feedback Amplifier (CFA) device. For voltage control of the time constants of the DIL, the ICL-8013 multiplier element has been appropriately utilized in a feedforward/feedback connection within the loop. The oscillation frequency (ωo) is tunable by the d.c. control voltage (Vc) of the multiplier. The active ωo-sensitivity relative to the CFA port errors (ε) is quite low. The VCO practical performance had been tested both with hardware implementation and with PSPICE macromodel simulation, in a typical frequency range of 50 KHz–1.5 MHz. [ABSTRACT FROM AUTHOR]

This paper presents a dual-active capacitance in reversed nested Miller compensation (DACRNMC) technique for low-voltage and large capacitive load amplifiers. The frequency bandwidth of the DACRNMC amplifier has been improved due to the usage of active compensation capacitors. The amplifier's die area is reduced in compare to the existing techniques in the RNMC scheme. The architecture also generates two left half plane zeros to increase the phase margin. The simulation for the proposed DACRNMC amplifier with a 0.18μm standard CMOS process reveals a unity gain bandwidth of 17.4MHz and phase margin of 64 degrees , while 500 pF load is driven from a single 1.5 V power supply. [ABSTRACT FROM AUTHOR]

A pipelined analog-to-digital converter (ADC) uses switched-capacitor stages that settle in two steps that occur sequentially in time. The first step of settling places charge onto the load capacitance using charge pumps, and the second fulfills the settling requirements using typical negative feedback around an operational amplifier. Hence, the design combines the efficiency of a fast charge-transfer phase with the gain and noise-immunity advantages of amplifier-driven settling. Improved conversion efficiency results from a higher ratio of current delivered to the load to that consumed in static biasing. Additional circuitry constrains critical amplifier node voltages during the charge transfer, facilitating a graceful transition to amplifier-driven settling. The two-step settling technique is demonstrated in a 2.5 bit/stage 10-bit pipelined ADC that consumes 11.1 mW while sampling a 21.3 MHz input signal at 42 MS/s. The resulting SNDR is 55.6 dB (ENOB = 8.94) and the SFDR is 67.5 dB. [ABSTRACT FROM AUTHOR]