Standard Operational Amplifiers Research Articles

EoG based Biopotential Instrumentation Amplifier

To examine the biomedical signals from the human body is of a challenging task. Signal acquisition of the biosignal needs proper design methodology with the estimation of consequences further. In this paper we discuss about the signal acquisition of EoG using the surface electrodes and to amplify the weak biopotential signal an amplifier is proposed with the additive noise reduction filter. The biopotential instrumentation amplifier is designed using standard operational amplifier that posses the high voltage swing. However the major artifacts present in the EoG signal acquisition is because of power line interference can be eliminated by notch filter.

High-voltage synthetic inductor for vibration damping in resonant piezoelectric shunt

Resonant piezoelectric shunts are a well-established way to reduce vibrations of mechanical systems suffering from resonant condition. The vibration energy is transferred to the electrical domain through the bonded piezoelectric material where it is dissipated in the shunt. Typically, electrical and mechanical resonance frequencies are several orders apart. As such, finding a suitable high inductance component for the resonant shunt is not feasible. Therefore, these high inductance values are mimicked through synthetic impedances, consisting of operational amplifiers and passive components. A downside of these synthetic impedances is that standard operational amplifiers can only handle up to 30 V peak to peak and the state-of-the-art amplifiers up to 100 Vpp. However, as mechanical structures tend to become lighter and more flexible, the order induced voltages over the piezoelectric material electrode voltages increase above these limitations. In this research, a high-voltage synthetic inductor is proposed and built by combining the bridge amplifier configuration and the output voltage boost configuration around a single operational amplifier gyrator circuit, effectively quadrupling the range of the synthetic inductor to 400 Vpp. The impedance of the circuit over a frequency range is numerically and experimentally investigated. The synthetic inductor is then connected to a piezoelectric material bonded to a cantilever beam. Numerical and experimental investigation confirms the high-voltage operation of the implemented circuit and its suitability as a vibration damping circuit.

A Two-Wired Ultra-High Input Impedance Active Electrode.

This paper presents a novel two-wired active electrode that achieves ultrahigh input impedance using power supply bootstrapping. The proposed circuit reduces the input capacitance of a buffer amplifier while enabling measurements using leads with only two wires, providing a low-complexity and low-cost solution for interference rejection and artifact reduction in dc-coupled dry-contact biopotential measurements. An implemented prototype shows that, even using standard operational amplifiers, an input capacitance as low as 71 fF can be obtained, maintaining a high impedance in a 0-1 kHz bandwidth, sufficient for ECG, EEG, and EMG measurements. The circuit has a simple and easily replicable implementation that requires no individual adjustment. A common mode rejection ratio (CMRR) above 103 dB at 50Hz was achieved and the increased rejection to interference due to the potential divider effect was experimentally tested maintaining a 92-dB CMRR at 50Hz with a 1.2-M source impedance unbalance. ECG measurements were conducted to validate the active electrode against a traditional alternative, and a test with dry-contact EEG electrodes was successfully conducted. Although the proposed circuit is intended to acquire superficial electrophysiological signals using dry electrodes, it can be used for measurement from other high-impedance sources, such as micropipette electrodes.

Increasing the performance of negative capacitance shunts by enlarging the output voltage to the requirements of piezoelectric transducers

Piezoelectric shunt damping is investigated as one possible solution for improving the vibroacoustic behavior of noise-prone lightweight structures. The negative capacitance shunt circuit appears to be the best choice due to its broadband damping effect. Usually it is built from analog electronic components, such as operational amplifiers, resistors and capacitors. Laboratory tests are possible with this setup, but it is limited to low vibrational excitation levels, because the known circuits are not capable of accessing a sufficient voltage amplitude at the piezoelectric transducers, which is required for high vibration amplitudes. Therefore an improved approach is presented in this paper, which addresses the specific voltage requirements of a common piezoelectric transducer. It comprises a tailored power source and an appropriate concept for the negative capacitance shunt hardware. There only standard operational amplifiers together with an external high-voltage power amplifier circuit are used to cover the whole operating range of a piezoelectric transducer. A demonstrator board is developed and experimentally investigated at a test structure. Finally, the results are compared with a conventional setup. It can be shown that using the full voltage range of the piezoelectric transducer allows higher damping of structures without any saturation effects.

A <inline-formula><tex-math notation="LaTeX">$0.7\;\text{V}\;24\;\upmu\text{A}$</tex-math></inline-formula> Hybrid OTA Driving 15 nF Capacitive Load With 1.46 MHz GBW

A cascade structure of six proposed signal-current enhancers is applied to a standard operational transconductance amplifier (OTA) to improve its gain-bandwidth (GBW) product, slew rate (SR), and voltage gain through significant enhancements of the small-signal and transient output currents from the proposed enhancers. The proposed hybrid OTA is implemented in a standard $\text{0.13}\;\upmu\text{m}$ CMOS technology, with an active chip area of $\text{0.0027}\;\text{mm}^{2}$ . Working under a 0.7 V supply and as proven by the measurement results, the resultant OTA when driving an output capacitor of 15 nF attained ${\sim}\text{100}\;\text{dB}$ gain, a GBW of 1.46 MHz, and an SR of $\text{0.47}\;\text{V}/\upmu\text{s}$ , consuming only $\text{24}\;\upmu\text{A}$ of current and requiring no compensation capacitor.

High input impedance DC servo loop circuit

DC suppression is a common instrumentation signal processing technique, used to reject spurious DC components and thus allow centring of the signal between the power supply rails and exploitation of all the available voltage range. A generic DC servo loop that presents high input impedance and can work as a front-end is proposed. It is designed to be implemented with standard operational amplifiers, to offer solutions for ‘board level’ analogue instrumentation design. The main features of the circuit are analysed, and analytical expressions are provided for its adaptation for solving different instrumentation problems.

Analysis of Dynamic Performance of Half-Wave Rectifiers and its Improvements

This paper deals with the analysis of dynamic behaviour of half-wave rectifiers and compares circuit solutions using standard operational amplifiers and current conveyors as active elements. The voltage and current sourcing principle and their influence to dynamic limits of diodes are given. Using the voltage or current biasing scheme, improvements in the dynamic performance of the diodes and rectifier are shown and discussed. The theoretical conclusions are supported by experimental results. DOI: http://dx.doi.org/10.5755/j01.eee.20.2.6382

Operational Transresistance Amplifier Using Submicron Technology

Operational Transresistance Amplifier is important active element in Analog integrated circuits and system. The OTRA is receiving increasing attention as a basic building block in analog circuit design. It is relatively a new building block operating from low voltage supplies and overcomes the finite gain bandwidth product associated with traditional op-amp. The basic principle behind the design of OTRA is to provide amplification of high frequency signals with the using standard operational amplifier. In this work effort is made to study the role of OTRA as an active building block in analog circuits. Various CMOS realization of OTRA present in the literature are studied and these circuits are used to realize various signal processing and generating circuits. Based upon component sensitivity tendency and variation amount, just properly adjusting one or two resistances by a small difference, or giving approximate component values for achieving precise output responses is investigated and developed different OTRA realization. In many applications high speed and efficient power consumption is required is desired. For this purpose conventional transistor technique are usually chosen, but this results in lower power efficiency. So, the different sub- micron technologies are used. A sub-micron system integrates millions and millions of Electronic components in a small area .The main objective behind the use of this technology is to make the analog and digital system as compact as possible and more power efficient with the required functionality of OTRA and VLSI. The Low Power is the key contribution of the main processing blocks in OTRA system.

Development of capacitance measurement system for human serum albumin detection

The use of interdigitated electrodes and binding with Cibacron blue F3GA by self-assembly technology, which has high affinity for human serum albumin (HSA), and serves as a receptor for HSA detection, is reported. In preliminary tests, the interdigitated chip measured the impedance of HSA by electrochemical impedance spectroscopy and this result indicated the characteristic frequency of impedance change below 1.1 kHz. However, a portable capacitance measurement system made using a standard operational amplifier circuit and AC excitation was applied at 1 kHz. The detection result showed a significant linear correlation between HSA concentration (0.1 to 1 mg/ml) and output voltage. The regression equation was Y=17.91+323.72X with R2=0.999. This reported study has successfully demonstrated that the capacitive sensor has great potential for applications in HSA detection.

Oscillator circuit based on a single organic transistor

We design and demonstrate an oscillator circuit based on feedback and controlled by a single organic transistor. Oscillations are assisted by standard operational amplifiers. The oscillator frequency f partly depends on the parameters of the circuit, but also on the transistor’s channel length and charge carrier mobility. Monitoring f provides a fast and simple tool in following the change in semiconductor mobility under changing environmental conditions. We demonstrate the application of the circuit for cheap, portable organic transistor-based odor sensors.

Room-temperature tunnel current amplifier and experimental setup for high resolution electronic spectroscopy in millikelvin scanning tunneling microscope experiments

The spectroscopic resolution of tunneling measurements performed with a scanning tunneling microscope is ultimately limited by the temperature at which the experiment is performed. To take advantage of the potential high spectroscopic resolution associated with operating a scanning tunneling microscope in a dilution refrigerator we have designed a room-temperature tunnel current amplifier having very small back action on the tunnel contact and allowing to nearly reach the predicted energy resolution. This design is a modification of the standard operational amplifier based tip-biasing current-voltage converter which implements differential voltage sensing and whose back action on the tip voltage is only ∼2μV rms for a 14MV∕A transimpedance and 22kHz bandwidth.

MPPT of photovoltaic systems using extremum - seeking control

A stability analysis for a maximum power point tracking (MPPT) scheme based on extremum-seeking control is developed for a photovoltaic (PV) array supplying a dc-to-dc switching converter. The global stability of the extremum-seeking algorithm is demonstrated by means of Lyapunov's approach. Subsequently, the algorithm is applied to an MPPT system based on the perturb and observe method. The steady-state behavior of the PV system with MPPT control is characterized by a stable oscillation around the maximum power point. The tracking algorithm leads the array coordinates to the maximum power point by increasing or decreasing linearly with time the array voltage. Off-line measurements are not required by the control law, which is implemented by means of an analog multiplier, standard operational amplifiers, a flip-flop circuit and a pulsewidth modulator. The effectiveness of the proposed MPPT scheme is demonstrated experimentally under different operating conditions.

Design and applications of the operational floating amplifier (OFA): The most universal operational amplifier

The operational floating amplifier (OFA) is the most universal type of operational amplifier. Both input and output ports are floating ports, i.e., free from restrictive ground connections. The floating input port enables the OFA to accurately equate two voltages between the two input terminals, like a standard operational amplifier, but in addition to that the OFA is able to accurately equate two currents through the two terminals of the floating output port. Specific applications are given, such as current amplifiers, voltage-to-current converters, gyrators, hybrids, and filters. The concept of the OFA allows these analog transfer functions to be realized with the absolute minimum number of accurate internal and external elements necessary to accurately determine the transfer. The OFA does not need accurate internal matched elements, except for offset, to obtain accurate overall transfer functions. This is in contrast to other current-output devices, such as the current conveyer, which transfer depends on the accuracy of internal current mirrors. Several designs of class A and class AB OFAs based on different topologies are presented and compared. This paper gives an overview of the application, the specification, and the design.

Voltage-mode and current-mode Sallen-Key implementations based on translinear conveyors

The simulation results of two Sallen-Key bandpass implementations with standard operational amplifiers are compared and discussed. The implementation using a voltage follower as a controlled source compares favourably with the one using equal valued passive components. Voltage-mode and current-mode Sallen-Key implementations from translinear conveyors with unity gain are described. The filters use five passive components so that the quality factor Q can be adjustable from one of them, without varying ω0. Simulation results are given and discussed.

Large-signal feedback control of a bidirectional coupled-inductor Cuk converter

Under conditions of order reduction, a nonlinear control of a bidirectional coupled-inductor Cuk converter suitable for large-signal applications is presented. The converter is accurately modeled as a second-order bilinear system, and the conditions for local controllability are established. The integration of converter state equations and the subsequent introduction of a linear recurrence between the output variable and an external reference signal lead to a nonlinear control law that is implemented by means of an analog divider, standard operational amplifiers, and a pulsewidth modulator. As a result, the output variable proportionally follows the reference signal, thus allowing different types of power waveforms in the converter output to be obtained. Experimental results verify the theoretical predictions. >

A differential-input, differential-output current mode operational amplifier

Abstract A current operational amplifier with differential input and differential output is described. The amplifier is based on the parallel connection of a CCII+ current conveyor and a CCII− current conveyor followed by a differential output transconductance gain stage. The performance of the amplifier is analysed and experimental results obtained from an implementation using standard operational amplifiers and current mirrors realized using transistor arrays are presented and compared to the theoretical analysis. It is concluded that the static small signal open loop gain and the frequency response matches the performance of conventional voltage operational amplifiers. The input offset and bias errors and the common mode rejection are shown to be strongly dependent on the matching accuracy of the current mirrors used in the conveyors. The proposed configuration can easily be integrated into a monolithic amplifier in either CMOS or bipolar technology.

Performance of transfer resistance amplifiers with capacitive sources in optical applications

Transfer resistance amplifiers using standard operational amplifiers are often employed when moderate bandwidths and low noise are required from capacitive current sources, such as photodetectors for optical imaging and the samples which are used in the OBIC and EBIC techniques of semiconductor microscopy. Analytic design equations are derived that predict bandwidth and noise performance as a function of source capacitance and allow the selection of the most suitable amplifier for specified conditions. Both the noise performance and frequency response will change if the source capacitance departs from its design value, as it will when the reverse bias on a photodiode is altered, and the significance of these changes is calculated. Results from specific design examples, based on standard low-noise operational amplifiers, are discussed.

Operational floating amplifier

The operational floating amplifier (OFA) is the most general 'nullor' implementation, which is a basic active two-port network element. The definition, applications, and design of OFAs are described. The OFA accurately equates two voltages connected to the terminals of the input port, like a standard operational amplifier, but in addition, an OFA accurately equates two currents connected to the terminals of the output port. Specific applications are given, e.g.: current amplifiers, voltage-to-current convertors, and gyrators. The design of class-A and class-AB OFAs based on several topologies is covered.

A trapezoidal function voltage generator for electrochemical applications

An analog circuit based on standard operational amplifiers is described, which generates a trapezoidal voltage signal with rise and fall times as well as holding times variable over a wide range. Application of the circuit in spectroelectrochemistry is described, its properties are compared to currently available electrochemical instrumentation providing similar voltage functions.

Analog Functions Implemented on Digital CMOS Gate Arrays---Merits and Problems

Standard digital CMOS gate arrays, originally developed for digital circuits only, also allow the implementation of analog functions on the chip. Knowing the problems and limitations, the designer can achieve a very compact solution. At first, the basic analog elements, like current mirror and difference amplifier, will be introduced. With these elements, more complex circuits can be built. Possible problems are discussed. Simulation of the circuit will demonstrate how it is an extremely useful design tool. The results of simulation and measured values are compared with a standard operational CMOS amplifier. Several industrial applications demonstrate that analog and digital functions can be combined.