Current Feedback Operational Amplifier Research Articles

Design and Implementation of Electronically Controllable Sinusoidal Oscillators Using Commercially Available Current-Feedback Operational Amplifiers with Externally Accessible Compensation Node z

This paper presents the structure and operational principles of high-frequency electronically controllable sinusoidal oscillators employing current-feedback operational amplifiers (CFOAs) with externally accessible compensation node [Formula: see text] as active components. The resonant circuits in the oscillators are connected to the terminal [Formula: see text], and for them in the selective network varactor diodes or varicaps as the variable capacitances are utilized, which are controlled by external DC voltage. Based on an analysis of the proposed circuit configurations, analytical expressions for the characteristic equation in a steady-state mode of operation and formulas for the basic electrical parameters have been obtained. In order to verify the functionality of the proposed electronic circuits and the effectiveness of the derived analytical expressions, an experimental and simulation study of sample electronic circuits with commercially available integrated circuit CFOAs AD844 in the frequency range up to about 10[Formula: see text]MHz is performed. The obtained results for the studied electronic circuits confirm the theoretical studies and hypotheses, and the comparative analysis shows that the maximum value for the relative error does not exceed 10%, which is acceptable considering the tolerances of the technological parameters of the used passive and active elements.

Design of Fractional-order Transitional Filters of the Butterworth-Sync-Tuned, Butterworth-Chebyshev, and Chebyshev-Sync-Tuned Types: Optimization, Simulation, and Experimental Verification

This paper presents the optimal and generalized design of three different fractional-order (FO) transitional filters for the first time in the literature. The transitional filters considered are of the FO Butterworth-sync-tuned, the FO Butterworth-Chebyshev, and the FO Chebyshev-sync-tuned types. A metaheuristic swarm intelligence optimizer, namely the Crow Search Algorithm (CSA), helps to achieve the optimal FO filter model that minimizes the magnitude error with the theoretical function. The accuracy of the proposed approximants is examined for 19 different combinations of orders of the constituent filters for each of the three types of FO transitional filters. Comparisons with the modified stability boundary locus-based second-, third-, and fourth-order filter approximants demonstrate the compactness and superior accuracy of the proposed models. The average performance regarding the approximation accuracy, computational time, and convergence of CSA for solving the proposed filter design problems is investigated. Circuit simulations conducted on the OrCAD PSPICE platform for the proposed filter using the current feedback operational amplifier as an active element highlight good matching between the proposed model and theoretical filter function. Experimental validation is also carried out to justify the practical feasibility of the proposed filter with printed circuit board fabricated FO capacitor emulators.

Design of Lossless Negative Capacitance Multiplier Employing a Single Active Element

In this paper, a new negative lossless grounded capacitance multiplier (GCM) circuit based on a Current Feedback Operational Amplifier (CFOA) is presented. The proposed circuit includes a single CFOA, four resistors, and a grounded capacitor. In order to reduce the power consumption, the internal structure of the CFOA is realized with dynamic threshold-voltage MOSFET (DTMOS) transistors. The effects of parasitic components on the operating frequency range of the proposed circuit are investigated. The simulation results were obtained with the SPICE program using 0.13 µm IBM CMOS technology parameters. The total power consumption of the circuit was 1.6 mW. The functionality of the circuit is provided by the capacitance cancellation circuit. PVT (Process, Voltage, Temperature) analyses were performed to verify the robustness of the proposed circuit. An experimental study is provided to verify the operability of the proposed negative lossless GCM using commercially available integrated circuits (ICs).

Voltage-Mode Multifunction and Universal Biquads with Two CFOAs

In this paper, a new voltage-mode (VM) multifunction filter including only two grounded capacitors, three resistors, and two current feedback operational amplifiers is introduced. This filter with one high input impedance and two low output impedances can simultaneously provide band-pass filter (BPF) and low-pass filter (LPF) responses with an adjustable gain. A universal VM filter topology with three inputs and one output generating high-pass filter (HPF), BPF, LPF, notch filter, and all-pass filter (APF) responses is obtained from the multifunction one. It has the same number of active and passive elements as the multifunction and a low output impedance. Sensitivities of both introduced filters are low enough. However, the APF of the introduced universal filter has a passive element-matching problem. As an example, parasitic impedance effects are considered for the LPF of the universal filter, while non-ideal gain analyses are given for the HPF. To see how the introduced universal filter works, countless simulations are performed through the SPICE (Simulation Program with Integrated Circuit Emphasis) program in which 0.13 [Formula: see text]m IBM CMOS technology parameters are utilized. DC supply voltages are selected as ± 0.9 V. Also, several experiments using commercially available AD844s with ± 10 V supply voltages are carried out to see the performance.

Current feedback operational amplifier‐based fully orthogonal universal and multifunction filters

SummaryThis paper introduces a second‐order voltage‐mode (VM) multiple‐input single‐output (MISO) universal filter and a second‐order current‐mode (CM) single‐input multiple‐output (SIMO) multifunction filter. The introduced VM MISO universal filter includes a single current feedback operational amplifier (CFOA) and a single voltage follower as active elements, while the introduced CM SIMO multifunction filter contains two CFOAs. Both introduced circuits are orthogonally controllable. In other words, the quality factors can be controlled through a single resistor without affecting the resonance frequencies. Both circuits have low sensitivities and no passive element‐matching conditions. The introduced VM MISO universal filter has a low output impedance. Moreover, to extract the output currents of the proposed CM SIMO from high impedance terminals, second‐generation current conveyor‐based version of the circuit is introduced. Simulations are made through the PSPICE program, where 0.13‐μm IBM CMOS technology parameters are utilized. DC supply voltages are selected as ±0.9 V. In the experiments, AD844s are used, and DC supply voltages are chosen as ±7.5 V.

Lossless Grounded Capacitance Multiplier Based On Two CFOAs

A new lossless grounded capacitance multiplier (GCM) based on two current-feedback operational amplifiers (CFOAs) is proposed. The proposed circuit is built with a least number of passive elements. The capacitor is selected as grounded in the proposed circuit, while one resistor is grounded and the other is floating. The proposed GCM has low power consumption and a very large multiplying factor. The passive element matching conditions are not necessary for the designed GCM. The SPICE program is used for the simulations, and all the simulations are performed with 0.18µm CMOS technology parameters. The simulation results verify the ideal results from 10Hz to 15MHz. Further, the designed GCM is tested in the application circuit, which is a second-order passive filter. The experiments of the desgined GCM are achieved by using AD844s instead of CFOAs.

Current-mode PID controllers employing commercially available active components

This work describes two current-mode (CM) PID controllers using only two commercially active components, namely, current feedback operational amplifier (CFOA), and four passive components, i.e. two capacitors and two resistors. They have appropriate output and input impedance values, allowing them to be utilized in cascade connections without requiring a buffer circuit. Since all capacitors are grounded, it is suitable for integrated circuit (IC) technology. Moreover, the controllers can be easily modified to operate in voltage-mode (VM), transimpedance-mode (TIM), and transadmittance-mode (TAM) PID controllers. Using 0.18 µm CMOS parameters and the PSPICE program, the proposed circuits are simulated to verify the theoretical behavior. To demonstrate the viability of the circuits, experimental tests using commercially available AD844 integrated circuits are performed. The suggested PID circuits are alsoexperimental tested in a closed-loop system as an example.

New Approach of deriving Third-Order Quadrature Sinusoidal Oscillators

Numerous approaches/methods have been employed in the past to derive various third-order sinusoidal oscillators (TOSOs). In this communication, a new simple approach for realizing TOQSO is presented, utilizing a second order inverse high-pass active filter with a cascade connection of traditional lossless integrator. The proposed approach can provide quadrature voltage outputs by leveraging the availability of lossless integrator. It is demonstrated that the proposed approach has the potential to generate various TOQSOs, as exemplified by the voltage-mode TOQSO based on current feedback operational amplifiers (CFOAs). The oscillation condition (CO) and frequency (FO) of the derived oscillator can be independently controlled. Experimental results utilizing AD844 CFOA ICs have been included to validate the theoretical propositions.

Low-noise fast-response readout circuit to improve coincidence time resolution

Time-of-flight (TOF) PET detectors with fast-rise-time scintillators and fast-single photon time resolution silicon photomultiplier (SiPM) have been developed to improve the coincidence timing resolution (CTR) to sub-100 ps. The CTR can be further improved with an optimal bandwidth and minimized electronic noise in the readout circuit and this helps reduce the distortion of the fast signals generated from the TOF-PET detector. The purpose of this study was to develop an ultra-high frequency and fully-differential (UF-FD) readout circuit that minimizes distortion in the fast signals produced using TOF-PET detectors, and suppresses the impact of the electronic noise generated from the detector and front-end readout circuits. The proposed UF-FD readout circuit is composed of two differential amplifiers (time) and a current feedback operational amplifier (energy). The ultra-high frequency differential (7 GHz) amplifiers can reduce the common ground noise in the fully-differential mode and minimize the distortion in the fast signal. The CTR and energy resolution were measured to evaluate the performance of the UF-FD readout circuit. These results were compared with those obtained from a high-frequency and single ended readout circuit. The experiment results indicated that the UF-FD readout circuit proposed in this study could substantially improve the best achievable CTR of TOF-PET detectors.

Single-input multiple-output inverse filters designs with cascade capability

Enhancing a topology of the literature, single-input multiple-output first-order inverse filter topologies are presented in this work. They offer the features of minimized circuit complexity, grounded capacitors requirement and, the most important, the capability of cascade connection with other stages without extra buffers needed. This is achieved thanks to the properties of the Current Feedback Operational Amplifier terminals. The behavior of the structures with regards to the effect of parasitics is evaluated for establishing the suitable frequency range of their operation. The performance of the filters is evaluated using the OrCAD PSpice suite, as well as through experimental results.

Two inverting CFOA-Based lossless floating immittance simulator

Inverting current feedback operational amplifier (ICFOA)-based lossless floating immittance simulator (FIS) is introduced in this manuscript. In the proposed FIS, floating capacitance multiplier (FCM), simulated floating inductor (SFI), and floating frequency-dependent negative resistor (FFDNR) can be obtained with selections of the passive elements. The proposed FIS is realized with a minimum number of passive elements. The proposed FIS is not suffered from any resistor and/or capacitor matching conditions; nevertheless, all the passive elements are chosen as floating. All the simulations of the FCM, SFI, and FFDNR are made by using the SPICE program in which 0.18 µm CMOS technology parameters are utilized. As an application example, the second-order passive band-pass filter is given for the FCM and SFI. Simulation results confirm the ideal results between about 5 Hz and 2 MHz for the FCM, between approximately 200 Hz and 5 MHz for the SFI, and between about 50 kHz and 13 MHz for the FFDNR. The proposed circuit has 1.49 mW power dissipation. In addition, the experiments of the proposed circuit and application are achieved by using AD844s instead of the ICFOAs.

Design and Verification of a New Universal Active Filter Based on the Current Feedback Operational Amplifier and Commercial AD844 Integrated Circuit.

This paper presents a triple-input and four-output type voltage-mode universal active filter based on three current-feedback operational amplifiers (CFOAs). The filter employs three CFOAs, two grounded capacitors, and six resistors. The filter structure has three high-input and three low-output impedances that simultaneously provide band-reject, high-pass, low-pass, and band-pass filtering functions with single-input and four-output type and also implements an all-pass filtering function by connecting three input signals to one input without the use of voltage inverters or switches. The same circuit configuration enables two unique filtering functions: low-pass notch and high-pass notch. Three CFOAs with three high-input and low-output impedance terminals enable cascading without voltage buffers. The circuit is implemented using three commercial off-the-shelf AD844 integrated circuits, two grounded capacitors, and six resistors and further implemented as a CFOA-based chip using three CFOAs, two grounded capacitors, and six resistors. The CFOA-based chip has lower power consumption and higher integration than the AD844-based filter. The circuit was simulated using OrCAD PSpice to verify the AD844-based filter and Synopsys HSpice for post-layout simulation of the CFOA-based chip. The theoretical analysis is validated and confirmed by measurements on an AD844-based filter and a CFOA-based chip.

Floating parallel lossy inductance, parallel lossy capacitance, parallel C‐D, and lossless capacitance multiplier circuits using current feedback operational amplifiers

SummaryA new synthetic floating simulator topology is proposed which realizes lossy parallel inductance (R‐L), lossy parallel capacitance (R‐C), lossy parallel C‐D, and lossless floating capacitance multiplier (FCM) circuits using only three current feedback operational amplifiers (CFOA) as active elements and three impedances. In all the presented circuits, the value of L, C, and D is independently controllable through a single resistance without requiring any matching condition for passive elements. A novel feature of the proposed circuit involves a straightforward adjustment in the CFOA connections, allowing the circuit to function as either a floating lossless immittance simulator or a floating series‐type lossy immittance simulator. Various application examples of the presented circuits such as lead compensator, lag compensator, first‐order high‐pass filter, and fourth‐order Butterworth filter are also given to justify the theoretical analysis. To validate the workability of the proposed circuits, several analyses are conducted, including frequency analysis, transient analysis, Monte‐Carlo analysis, and temperature analysis, using the macro‐model of AD844 in the SPICE simulation tool. Experimental results of the parallel R‐L simulator and application examples are also provided using commercially available IC AD844‐type integrated CFOAs.

Design and Implementation of Self-Limiting Two-Stage LC Oscillators Using Cascade Structure of Monolithic CCIIs as Active Elements

This paper presents the structure and principle of operation of two circuit configurations of self-limiting LC oscillators using monolithic positive second-generation current conveyors (CCII+s), that are implemented using Current-Feedback Operational Amplifiers (CFOAs) with an available compensation pin (Z). The proposed LC oscillators are synthesized using a systematic approach in the design of analog electronic circuits and can be considered as variants of the basic three-point oscillators, implemented using transistors (BJTs or FETs). Based on the analysis of the structure and electrical parameters of the CFOAs with a compensation pin (Z), electronic circuits of oscillators with two-stage amplifier blocks are synthesized. The characteristic equations and self-oscillation conditions are derived for the obtained analog circuits, and recommendations for designing circuits with arbitrary frequencies are defined. To verify the efficiency of the proposed LC oscillators, an experimental study is performed in the frequency range from 100 kHz to 10 MHz. The CFOAs AD844A with an external terminal z of the internal current conveyor are used as active elements. The obtained experimental results well match the results of the simulation modelling and the parameters based on the derived analytical expressions. The developed LC oscillators are intended to be used in schematic configurations of gas sensors based on surface acoustic wave (SAW) resonators.

Voltage-controlled oscillators using CFOAs with correction terminal Z

ABSTRACT In this work, a realization of a voltage-controlled LC oscillator (VCO), using monolithic current-feedback operational amplifiers (CFOAs) with accessible correction terminal Z, is proposed. The frequency variation for the developed oscillator is obtained by replacing the capacitor in the resonant LC circuit with pairs of varactor diodes that use a common cathode. The barrier capacitance of the varactor diodes is controlled by a DC voltage obtained from an external voltage source. The proposed circuit configurations include single active element, a small number of discrete components, an operating frequency range of up to about 10 MHz and a relatively high value of the equivalent quality factor. To verify the effectiveness of the realised oscillators, results of computer simulations and experimental studies of sample electronic circuits using commercially available monolithic CFOAs with correction terminal Z are presented. Moreover, the obtained experimental results confirm the theoretical analyses of the circuits and the obtained mathematical expressions for the basic parameters, and the differences between them are within 10% and are mainly due to tolerances in the technological parameters of the used electronic components.

A Novel Chaotic System with Exponential Nonlinearity and its Adaptive Self-Synchronization: From Numerical Simulations to Circuit Implementation

In this paper, a new three-dimensional chaotic system with two exponential nonlinearities is presented. The analysis of fixed points of the proposed system suggests existence of one hyperbolic index-2 spiral saddle-type fixed point. The proposed system fulfils Shilnikov criterion and nature of the chaos is found to be dissipative. Bifurcation diagrams, maximum Lyapunov exponents and Kaplan–Yorke dimension are examined through numerical simulations to investigate dynamics of proposed system. The hardware feasibility of the proposed system is illustrated through current feedback operational amplifier (CFOA)-based circuit implementation. The proposed circuit uses six CFOAs, two diodes to establish nonlinearity, eleven resistors and three capacitors. The absence of analog multiplier in the proposed circuit makes it superior to the existing counterpart in the sense that it does not require area and power-consuming active building block. To confirm the chaotic nature of the proposed circuit, LTspice simulations are done to obtain phase portraits which are found to be strange attractors and are topologically different from the shape of the existing attractors. Moreover, we have investigated the synchronization of the proposed chaotic system using adaptive control scheme and proposed CFOA-based complete circuit design of the adaptively synchronized system. Also, the effect of the tolerance of passive components and temperature on the behavior of the proposed chaotic circuit and the complete synchronization circuit has also been studied. It is found that the circuit is sensitive to the value of resistors and temperature to an extent and can work properly within their limits.

Very‐low frequency capacitively coupled AC amplifier with a current feedback operational amplifier

SummaryIn this paper, we propose the idea of using transimpedance amplifiers, in lieu of operational amplifiers (OAs) or transconductance amplifiers (OTAs) to design capacitively coupled AC amplifiers. The idea is demonstrated with a current feedback operational amplifier (CFOA) as an active element, which is actually an architecture consisting of voltage buffers and current copiers (mirrors). This last characteristic is further exploited to make the corner frequency of the AC amplifier tunable by means of bootstrapping low‐valued resistors with the output buffer. It is particularly suited to achieve very‐low corner frequencies as needed in applications such as bio‐ or seismic signals. The idea is demonstrated with simulations and experimental results with a discrete implementation.

Exact Inductorless Realization of Chua Circuit Using Two Active Elements

In this brief, we present two inductorless realizations of Chua’s circuit in an exact form while using only two active elements, namely a current feedback operational amplifier (CFOA) for the precise implementation of the Chua circuit equations, and an op-amp for the realization of the active nonlinear resistor. First, we analyze the widely used Wien bridge based modified Chua circuit and apply a variable transformation and reveal the difference of its mathematical model from the original Chua circuit in a precise form. Second, we present an exact inductorless implementation of the Chua circuit employing the Wien bridge structure, using two active elements only. Third, we introduce another simple yet exact inductorless implementation of the Chua circuit with a featured property where the state variable corresponding to the inductor current of the original Chua circuit can be accessed as a capacitor voltage. Chaotic attractors obtained by experimental realizations match well with the result of numerical simulations, demonstrating the success of the proposed designs.

Current-mode fractional-order shelving filters using MCFOA for acoustic applications

In this study, low-pass and high-pass current-mode fractional-order shelving filters were designed for use in acoustic applications. The filter’s architecture has two main components, Modified Current Feedback Operational Amplifier (MCFOA) active block structure based on Bipolar Junction Transistors (BJTs) and a minimum number of only grounded passive elements. These components enable the filter to operate in current-mode and low voltage/power applications. The grounded capacitor design uses a 5th-order Oustaloup approximation and a properly configured Foster type-I RC network. The main advantage of the fractional-order shelving filters is that they provide an extra order of freedom in the transition slope from the passband to the stopband, improving the listening experience. In this paper, a new approach of using an MCFOA structure to design the fractional-order filters that operate in current-mode is presented. The filters provide current-mode circuit advantages such as wide dynamic range, low noise, low THD and are suitable for low voltage/power applications. The results from theoretical calculations, along with simulations of the filters were compared and verified. From the obtained data, it was observed that the cut-off frequency of 2 kHz is suitable to be used in acoustic applications.

Third‐order quadrature sinusoidal oscillators with fully uncoupled tuning laws using only two CFOAs and grounded capacitors

SummaryRecently, three current feedback operational amplifiers (CFOA)‐based third‐order quadrature sinusoidal oscillators (TOQSO) have been presented whose condition of oscillation (CO) and frequency of oscillation (FO) can be regulated independently. In this communication, we present two new TOQSO circuits, which require only two CFOAs and yet achieve as significant features as the quoted circuits, namely, the availability of fully uncoupled control of CO and FO, availability of both outputs from ideally zero output impedance nodes (which is beneficial for easy cascadability in VM operations) and employment of all (three) grounded capacitors as preferred for IC implementation. The verification of the workability of proposed circuits has been carried out experimentally using commercially available off‐the‐shelf ICs AD844‐type CFOAs, and some experimental results have been appended.