Current Feedback Op-amps Research Articles

Single-resistance-tunable oscillators using a single CFOA and two grounded capacitors

An exhaustive literature survey on current feedback op-amps (CFOA)-based oscillators circuits indicates that till date, no canonic single-CFOA-based single resistance controlled oscillators (SRCO) employing two grounded capacitors (GC) has ever been discovered so far. The main object of this communication is to present eight new single resistance tunable oscillators (SRTO) each of which uses only one CFOA, six resistors and two grounded capacitors. The workability of the presented SRTOs has been demonstrated by the experimental results using commercially available AD844-type integrated circuit CFOA.

Design Of High-Speed Low Voltage Operational Amplifier

Background: The Operational amplifier (op-amp) is the building block of linear integrated electronics, therefore proposing newer design models with improved parameters is an essential landmark in the electronics industry in the hunt for a faster and more efficient design. Objective: To attain high speed and low power supply, the authors designed an op-amp using three different techniques. Initially compensating network was designed and simulated but the resultant output voltage saturates in inverting and non-inverting modes. Methods: Voltage feedback op-amp (VFOA) and current feedback op-amp (CFOA) were proposed to achieve the target. The authors have successfully designed the circuit, but the power dissipated is less and Common Mode Rejection Ratio (CMRR) is high in CFOA in comparison to VFOA. Results: The results are simulated for three different configurations and inverting configuration results in remarkable results in comparison to a non-inverting and differential amplifier. Inverting configuration using VFOA results in 91.22dB, and 0.0131W CMRR and power dissipation, respectively, while that of CFOA results in 97.34dB, and 0.0129W CMRR, and power dissipation, respectively. Conclusion: 1.6% improvement in CMRR and a 26.8% improvement in power dissipated for the proposed CMOS CFOA in comparison to the proposed VFOA. All the validations are done by plotting the bode plot and Nyquist plot.

CFOA‐based simple mixed‐mode first‐order universal filter configurations

AbstractThis brief communication presents two current feedback op‐amp (CFOA)‐based simple first‐order mixed‐mode universal filter topologies—one of them providing first‐order low‐pass (LP), high pass (HP), and all pass (AP)—all the three filters in voltage‐mode (VM)/trans‐admittance‐mode (TAM) while the other one realizing the quoted three functions in current‐mode (CM)/trans‐impedance‐mode (TIM). Except the all pass filter realization from the first configuration which needs a second CFOA also as gain‐of‐two amplifier, in all the remaining cases of both the configurations, only a single CFOA is needed. The other notable features of the circuits are employment of only three resistors and a grounded capacitor (as preferred for IC implementation) and the availability of independent tunability of the gain (H0) and cut‐off frequency/pole frequency (ω0) of all the three filters, in both the cases. In spite of not offering ideally infinite input impedance in VM/TAM mode and ideally zero input impedance in CM/TIM mode, the circuits still possess easy cascadability due to providing a voltage output from a low‐output impedance terminal W while the current output from the high output impedance terminal Z. Non‐ideal and sensitivity analyses have also been carried out. The workability of the proposed circuits has been demonstrated through PSPICE simulations and experimental results using the commercially available AD844‐type IC CFOA.

CMOS voltage and current feedback opamps: a comparison between two similar topologies

ABSTRACT The voltage feedback operational amplifier (VFOA) and the current feedback operational amplifier (CFOA) are the main voltage type output opamps currently used in electronics. The VFOA is a combination of an operational transconductance amplifier (OTA) used as an input stage and an output voltage buffer (VB). In this paper, the CFOA is described as a combination of an operational transconductance conveyor (OTC) used as an input stage and with an output voltage buffer. Two similar CMOS architectures are then defined, analysed and simulated in order to provide some elements of comparison. Results, from a typical CMOS 0.35μm transistor parameters, show the role of compensation capacitances in boosting the frequency performances of the non-inverting amplifier.

A New Current Conveyor Full-Wave Rectifier for Low Frequency/Small Signal Medical Applications

This paper presents a new current conveyor (CCII+) full-wave rectifier for low frequency/small signal medical applications. The proposed rectifier is based on the current conveyor full-wave rectifier proposed previously, but the proposed rectifier is better in view of no need diodes to rectify, and no need bias sources to overcome the zero crossing error. It needs only two CCII+s, two resistors, and three simple current mirrors, which is easy for IC implementation and for building in many countries. The PSPICE simulation with the current conveyor CCII+ in the current feedback opamp AD844 IC and the 2N2222 bipolar current mirror shows the good low frequency/small signal rectification, the operation voltage of down to 6 .

Current feedback op-amp based linear voltage-controlled oscillator using analog multipliers and minimum passive components

This paper reports a new realization of linear Voltage-Controlled Oscillator (VCO) using three Current-Feedback Op-Amps (CFOAs), three analog multipliers, and only four passive components. Thus, minimum numbers of passive components are used to devise a canonic sinusoidal oscillator. The circuit provides non-interactive electronic tuning of both the Condition of Oscillation (CO) and the Frequency of Oscillation (FO) via the gains of two di erent analog multipliers. The impedance at output node exhibits low impedance which is easy to directly connect to load without any additional voltage bu er. The proposed circuit has been simulated in SPICE using macro-model of AD844 CFOA ICs and AD633 multiplier ICs.

Design of Self-tracking High-pass Filter

A novel self-tracking high-pass filter by using analog multiplier and current feedback op-Amp (CFA) is proposed in this paper. The frequency-voltage (F/V) converter transforms the input pulse signal into the voltage, and then the output of F/V converter controls the cut-off frequency of voltage controlled high-pass filter. Thus, the cut-off frequency of designed filter is linear with the frequency of input signal in case that resistors and capacitors are reasonable adjusted. The experiment and simulation results show that the cut-off frequency of designed filter is 1 kHz-100 kHz..

Synthetic Floating Inductors realized with only two Current Feedback Op-amps

Two floating inductance (FI) circuits are presented which employ a canonical number of passive components (namely, only two resistors and a capacitor) as well as canonical number of active elements (only two CFOAs) and realize single-resistance-tunable inductance value, without requiring any component-matching or cancellation constraints. The workability of the proposed circuits and their applications has been confirmed by hardware implementation and SPICE simulations based on AD844-type CFOAs.

Novel Single-CFOA-based Sinusoidal Oscillator Capable of Absorbing All Parasitic Impedances

Although a large number of single current feedback op-amp (CFOA)-based sinusoidal oscillator circuits have been proposed in the literature, to the best knowledge of the authors, no single-CFOA oscillator configuration has been reported earlier which can absorb all the parasitic impedances of the CFOA in the various external passive elements employed. The major intention of this paper is to report such a circuit. The workability of the proposed circuit has been confirmed by experimental results employing an AD844-type CFOA.

Improved designs for current feedback op-amps

The performance of the current feedback op-amps (CFOAs) is very much determined by the input stage of CFOAs, including common-mode rejection ratio (CMRR). Two new CFOAs topologies are presented in this article: one topology uses a cascoding technique, and the second one uses a bootstrapping technique, both of which provide a much better CMRR and lower DC offset voltage than the conventional CFOAs. Moreover, the new CFOAs design exhibits an extended high frequency bandwidth, with a gain accuracy improvement. Applications requiring constant bandwidth with variable (closed loop) gain will benefit from the proposed topologies.

Linear Tunable Analog Front-End Electronics for Silicon Charged-Particle Detectors

A linear front-end electronic system based on a high-speed charge sensitive amplifier and a tunable shaping amplifier suitable for silicon detectors has been presented. The designed charge sensitive amplifier features simplicity and compactness. It is based on the combination of a low-noise field-effect transistor input device and a current feedback opamp ensuring high frequency and small rise time. The circuit provides both an energy signal and a timing signal. The shaping amplifier is a fifth-order complex filter based on an opamp- RC topology providing a nearly Gaussian response. The shaper also includes a pole-zero cancellation circuit and a base line restorer to preclude the pileup of subsequent input signals. A control system has been developed to adjust the main parameters of the channel. The designed readout channel has been optimized for a medium energy range up to 50 MeV coupled to silicon detectors up to 100 pF. Its feasibility for nuclear physics applications has been experimentally validated.

Parameter Matching Using Adaptive Synchronization of Two Chua's Oscillators

In this paper, we develop a parameter matching technique using adaptive synchronization with a chaotic attractor. Two Chua's oscillators, identical in every parameter except for one, are set-up in a master/slave configuration where the slave's mismatched parameter is adaptable. Using Lyapunov functions and incorporating the presence of chaotic signals, adaptive control laws are designed to ensure exact parameter matching. One of the derived adaptive controllers is experimentally validated by using an adaptive inductor-gyrator composed of current feedback op-amps (CFOAs). The experimental results are compared to high-fidelity SPICE simulations, and performance of adaptive controllers are compared over a wide range of parameter values using MATLAB.

A Novel Memristor Chaotic Circuit Based on CFOA

In this work, we propose a novel memristor chaotic circuit, which is composed of a current feedback op amp (CFOA) and a piecewise-linear memristor. The dynamic properties of the new circuit are demonstrated, such as system dissipation、equilibrium stability、phase portrait、Lyapunov exponent spectrum and bifurcation analysis. Numerical simulation results show that the circuit produces a class of special chaotic attractors. By adjusting the system parameter, the proposed circuit performs chaotic and hyper-chaotic behaviors from inverse doubling-periodic .

Design of the Voltage-Controlled Bandpass Filter Based on Current Feedback Op Amp

This paper puts forward structure and realization method of the voltage-controlled band-pass filter based on the current feedback operational amplifier (CFA) which uses bi-quad loop filter circuit model to design the new filter circuit. Input voltage signal is input to voltage-controlled band-pass filter circuit composed by an analog multiplier AD835 and a current feedback operational amplifier AD8001 which are the core. Using the voltage signal to adjust the center frequency of the filter, the filter has wide frequency band and good high-frequency performance. This paper describes the design principles, infers the design formulas and designs the circuit of the voltage-controlled first-order and second-order band-pass filter.Through the simulation, the filter can realize the scope of the center frequency from 200KHz to 10MHz.

Design and simulation of a memristor chaotic circuit based on current feedback op amp

In this work, we propose a novel memristor chaotic circuit, which combines current feedback op amp with four basic electronic components, such as capacitance, inductance, resistance and memristor. The dynamic properties of the new circuit are demonstrated, such as system dissipation, equilibrium stability, phase portrait, Lyapunov exponent spectrum, and parameter influence. Numerical simulation results show that the circuit produces a kind of special chaotic attractor and exhibits complicated chaotic behaviour with the evolution of the system parameters. In order to confirm the correctness of the system, a realizing circuit is designed, Pspice simulation results verify the correctness of theoretical analysis.

DVCC based Readout Circuitry for Water Quality Monitoring System

new configuration realizing water quality monitoring device using ISFET involving CMOS differential voltage current conveyor (DVCC) based low pass filter free from trans-conductance variation using Low-voltage PMOS bulk- driven cascade current mirror (P MOS BDCCM) current mirrors is proposed. The circuit uses four DVCCs as active elements and together with two capacitors and five resistors as passive elements, only one current mirror. The use of this active component makes the implementation simple and attractive. The functionality of the circuit is tested using Tanner simulator version 15 for a 70nm CMOS process model also the transfer function realization is done on MATLAB R2011a version, the Very high speed integrated circuit Hardware description language(VHDL) code for the same scheme is simulated on Xilinx ISE 10.1 and various simulation results are obtained. Simulation results are included to demonstrate the results. OTA's. These applications are suffer from low band widths (BW's) arising due to stray and circuit capacitances. Also the need for low voltage, low power circuits makes these circuits not suitable for water quality monitoring as these circuits required the minimum bias voltage depends on the threshold voltage of the MOSFETs. However, with the advancement in the analog VLSI new analog devices are based on currents are developed called current mode circuits (CMC's). These circuits have a significant advantage of low power, low voltages and can operate over wide dynamic range. These circuits, CMC can offer to the designer large bandwidths, greater linearity, wider dynamic range, simple circuitry and low power consumption. Current feedback op-amps (CFOAs), operational floating conveyors (OFCs) and current conveyors (CCs) etc. are popular CMC configuration and most widely used structure among them is DVCC, extension of the second- generation current conveyor (CCII). Hence, we decided to use the DVCC in the proposed scheme.

New analogue inverse filters realised with current feedback op-amps

This article presents new configurations for realising analogue inverse lowpass, inverse bandpass, inverse highpass and inverse bandreject filters using commercially available current feedback op-amps (CFOA) with an accessible z-terminal (such as AD844). The workability of the proposed circuits has been confirmed by experimental results by employing AD844-type CFOAs.

Current feedback operational amplifiers as fast charge sensitive preamplifiers for photomultiplier read out

Fast charge sensitive preamplifiers were built using commercial current feedback operational amplifiers for fast read out of charge pulses from a photomultiplier tube. Current feedback opamps prove to be particularly well suited for this application where the charge from the detector is large, of the order of one million electrons, and high timing resolution is required. A proper circuit arrangement allows very fast signals, with rise times down to one nanosecond, while keeping the amplifier stable. After a review of current feedback circuit topology and stability constraints, we provide a "recipe" to build stable and very fast charge sensitive preamplifiers from any current feedback opamp by adding just a few external components. The noise performance of the circuit topology has been evaluated and is reported in terms of equivalent noise charge.

Linear sinusoidal VCOs: new configurations using current-feedback-op-amps

It is shown how sinusoidal voltage-controlled oscillators (VCO) providing linear tuning laws can be realised with current feedback op-amps (CFOA) in conjunction with analogue multipliers (AM) and eight such new VCO configurations are presented. The new VCOs offer several advantages compared to previously known VCOs realised with traditional voltage-mode op-amps in conjunction with FETs or AMs. The workability of the new propositions is demonstrated by experimental results based upon AD844 type CFOAs and AD534 type AMs.

10.1007/s11180-008-1007-0

The behavior is investigated of a current-feedback opamp exposed to pulsed ionizing radiation sufficiently intense to produce voltage surges in the opamp. For a system using such opamps, the possibilities of maintaining normal operation under the stated conditions are explored.