High Gain Operational Amplifier Research Articles

Fast-settling, high-gain GaAs operational amplifiers for switched-capacitor applications

The authors are concerned with fast-settling, high-gain GaAs operational amplifiers for high-frequency, switched-capacitor circuit applications. A previous amplifier with a gain of 60 dB is critically assessed from the point of view of settling time, and the device geometries altered to reduce settling time from 450 ps to a minimum of 360 ps. General circuit techniques for obtaining faster settling are developed, and this leads to two designs which have gains still exceeding 60 dB but with minimum settling times now approaching 200 ps. >

Data acquisition system for chemical kineticstudies

A microcomputer-interfaced data acquisition system for chemical kinetics (interfacing with laboratory analogue instruments) has been developed. Analogue signals from instruments used in kinetics experiments are amplifed by a wide-range adjustable high-gain operational amplifier and smoothed by an op-based filter, and then digitized at rates of up to 104 samples per channel by an ADC 0816 digitizer. The ADC data transfer and manipulation routine was written in Assembler code and in high-level language; the graphics package and data treatment package is in Basic. For the various sampling speeds, all of the program can be written using Basic-Assembler or completely in Assembler if a high sampling rate is needed. Several numerical treatment methods for chemical kinetics have been utilized to smooth the data from experiments. The computer-interfaced system for second-order chemical kinetic studies was applied to the determination of the rate constant of the saponification of ethyl acetate at 35°C. For this specific problem, an averaging treatment was used which can be called an interval method. The use of this method avoids the diffcully of measuring the starting time of the reaction. Two groups of experimental data and results were used to evaluate the systems performance. All of the results obtained are in agreement with the reference value.

A linear NMOS depletion resistor and its application in an integrated amplifier

A linear resistor has been realized by using NMOS depletion transistors operated in the triode region. While such a resistor is mainly intended for single-ended and first quadrant mode of conduction, where it achieves a nonlinearity of .03% full scale in the 0-10 V voltage range, it can also be used as a floating element and operated in the first as well as third quadrant mode of conduction (i.e. with V and I both either positive or negative) with some degradation in linearity and voltage range. A linear noninverting amplifier with an accurately controlled gain of 16 has been realized by using a high open-loop gain (90 dB) operational amplifier and dimensioning the simulated resistors to set the closed-loop gain.

A resonant-type amorphous ribbon magnetometer driven by an operational amplifier

The resonant-type magnetometer presented here is composed of a high gain operational amplifier and a resonant circuit with an amorphous core connected to the input terminals of the operational amplifier. In this circuit, the operational amplifier with high input impedance operates a voltage switching element to invert the polarity of the driving voltage. Therefore, under the current source excitation, the duty ratio of the driving voltage is sensitive to a very weak dc magnetic field applied to the core. It is shown that the absolute value and the polarity of the mean value of the driving voltage can be converted into corresponding strength and direction of the de magnetic field. The maximum sensitivity of the magnetometer was around 12.4 V/Oe and the resolution was around 1.3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> Oe.

Active sensitivity minimization in SAB's with active compensation and optimization

In this paper, a new high-gain three-port operational amplifier (OA) circuit is used to replace the single OA in single amplifier biquads (SAB's). The resultant biquads will have the first-order effect of the OA's finite gain-bandwidth products (GB) completely eliminated from their dominant pole frequencies. Then, the widely used bandpass filter will be considered, where the remaining dominant second-order effects of the OA's GB products will be minimized by choosing appropriate element spreads satisfying the technology. This results in a bandpass filter which has better performance than any other actively compensated filters. The comparison of the results and experimental results follow to prove some of the conclusions made in this paper.

A prototype switched-capacitor voltage-wave filter realized in NMOS technology

Presents a novel approach to the realization of monolithic filters. The method is based on using sampled analog signals and is related to the wave digital filter in its design techniques. The eventual monolithic realization in NMOS technology is in the form of a switched-capacitor structure. The design is exact and there is no requirement for a high relative clock frequency. Only unity-gain buffers are required, as opposed to high-gain differential-input operational amplifiers, and so the technique is well suited to CMOS technology. Performance is determined by capacitance ratios and the design is optimally insensitive to parameter variations. Capacitance ratios are moderate relative to those encountered in existing switched-capacitor filters. Results are presented for a prototype integrated circuit design containing fifth- and seventh-order low-pass Chebyshev filters with a designed cutoff at one-eighth clock frequency. The responses achieved for the prototype design show excellent agreement with the theory.

Regulated DC Power Supply Employs Digital Control for Firing its SCRs

A regulated DC power supply using full-wave rectification by SCRs’, with digitally-variable firing angle, is described. The output voltage is sampled by a high-gain operational amplifier which controls the frequency of a voltage-controlled oscillator (VCO). The firing angle of the SCRs' is varied to stabilize the output voltage by counting a fixed number of variable-frequency pulses from the VCO, from each zero crossing of the mains sinusoidal voltage. The merit of the circuit is the inherent stability achieved through the digital negative feedback loop. The load regul-tion, line regulation, ripple factor and temperature stability of the circuit are measured. In particular, the circuit has an excellent temperature stability from 12°C to about 45°C.

Preliminary Study of a Nonbridge Method for Precision Measurement of Capacitors at Low Frequencies Using Operational Amplifiers and Resistance Standards

High-precision measurements of capacitance and dissipation factor can be made without capacitor standards using active circuits known as gyrators, which are constructed with high-gain operational amplifiers and precision resistors. A theoretical analysis of the technique is carried out here using one particular gyrator circuit. A preliminary experimental study yielded values of dissipation factor, which agreed with measurements made by the manufacturer of the precision capacitors tested to within four parts per million. The theory suggests that with a more carefully engineered instrument, capacitors of 0.01-1 ??F in the 10-1000 Hz range may be measured with an accuracy of the order of 1-2 ppm. The accuracy appears to be determined primarily by the precision of two critical resistors in the gyrator.

On inductor simulation using a unity-gain amplifier

The authors deal with two recently reported active circuits for realization of a grounded inductor using a single unity-gain amplifier and RC networks. It is shown that the inductance parameters are very sensitive to amplifier gain; this can be remedied by using a high-gain differential-input operational amplifier. Amplifier imperfection in respect of nonzero output impedance is found to make both circuits behave similarly. Sensitivity of tuned circuits using the active inductances is analyzed and conditions for minimum sensitivity are derived.

Operational Amplifier Differentiator for Photoemission Studies: Origin and Control of Errors

Errors encountered in time differentiating a voltage signal with a simple high gain operational amplifier differentiator are studied. Numerical and electronic means of correcting these generally small errors are suggested. The circuit, including a linear sweep voltage source, used for photoemission studies in this laboratory is presented. The coefficient of the error terms for this particular circuit are calculated numerically. Presently achieved sensitivity and resolution are discussed.

Realization of the ideal transformer using operational amplifiers

A means of representing the ideal transformer by an admittance matrix is given, in contrast to the more usual representation by the transmission matrix. Several possible admittance matrices are developed, together with derived circuits using high gain operational amplifiers. An apparent anomaly in the Reciprocity Principle when applied to these matrices is explained in a manner which may be of interest in related fields of activity.

Fast Recovery, Low Noise Transistorized Voltage Regulator for Tungsten Lamps

A solid-state voltage regulator was developed to supply 12 V at up to 5 A to a fixed load (two tungsten lamps) of approximately 4 Ω. The circuit employs a high gain operational amplifier in the feedback loop and the reference potential is supplied by a temperature-compensated Zener diode in an impedance cancelling bridge. The complete system has a line regulation of 4.5×10−4% for line variations from 100 to 130 V. The dc output impedance for the regulator is 0.003 Ω and the ripple is less than 5μV peak-to-peak at full load. Transient recovery is 120 μsec no load to full load.

An improved Hi-Q bandpass filter for electroencephalography

This paper has dascribed an extremely stable low frequency bandpass filter which is very useful in electroencephalographic signal analysis. The use of filters in EEG signal analysis has been discussed in the literature so only bibliographic references have been mentioned in this paper. The frequency and selectivity dapend only on a few capacitors and resistors because of the use of high gain operational amplifiers. Thus, the stability and calibration dapend only on a few passive circuit elements which can be precision components, rather than on the characteristics of the tubes or transistors. For values of Q in the ordar of 100 or less, the dasign is rather straight forward. The filter characteristics are the same as those of a parallel resonant circuit with the same Q as that of the filter. In the dasign, the bandwidth is constant and the Q of the filter changes as the frequency is adjusted. Filters of this dasign have been satisfactorily used in EEG signal analysis at The University of Texas for about 2 years.

An Amplitude Distribution Analyzer for Studying Brain Waves

An amplitude-distribution analyzer which estimates the probability-density and probability-distribution functions of brain wave forms is described. The circuit uses high-gain dc operational amplifiers as its basic component and is simple in design. The theoretical probability-density and probability-distribution functions for a sine wave, a triangle wave and a random signal are discussed and compared with the experimental results of the analyzer.

Portable dynamic electronic speed-torque indicator

The concept of instantaneous observation of the complete speed-torque characteristic of a motor while it accelerates from standstill to full speed is based on the assumption that a large percentage of the torque is utilized in acceleration of the inertia if the motor is otherwise unloaded. The basic instrument needed is an accelerometer with dynamic response capable of indicating the true starting torque and the transient cusps of the torque curve. This paper discusses the application of a 2-phase a-c instrument tachometer and active high-gain operational amplifiers to the design of a portable speed-acceleration instrument. The tachometer utilizes a drag-cup rotor and produces a constant frequency carrier output that has a minimum of ripple with frequency proportional to speed, thus eliminating the problem at low speeds of ripple amplification by differentiation encountered when using conventional tachometers. The constant frequency carrier output simplifies the problem of amplification and noise found with the homopolar-type generator. The use of stabilized operational amplifiers for differentiation and amplification after demodulation both provide the necessary dynamic response for the torque signal and virtually eliminates the problem of drift in the d-c stages. Operational applications of the instrument including torque versus speed, acceleration versus time, and speed versus time are included from the engineering laboratories of Robbins and Myers, Inc., Springfield, Ohio.