Precision Operational Amplifier Research Articles

Offset Voltage Reduction in Two-Stage Folded-Cascode Operational Amplifier Using High-Precision Source Degeneration

The demand for CMOS precision operational amplifiers for critical applications has continuously increased over time due to higher accuracy and sensitivity requirements. Trimming or chopper architectures are advanced solutions that reduce the offset voltage and improve the circuit’s parameters, but the complexity and the increased chip die size are serious downsides. An efficient solution is a source degeneration configuration to control the transistor’s current-mirror transconductance, which impacts the offset voltage, with cost savings and a die area reduction also obtained. This paper focuses on designing and implementing such an approach in a two-stage folded-cascode operational amplifier. State-of-the-art thin-film resistors that use silicon–chromium as the metallic alloy were implemented to reduce mismatch variations between these passive components. Distinct methods that control the offset voltage parameter are also discussed and established. A comparison between the offset voltage standard deviation obtained using different types of resistors and that achieved with the innovative high-precision resistors was also carried out. The source degeneration’s impact on the common-mode rejection ratio, power supply rejection ratio, bandwidth and phase margin was also analyzed, and a comparison between the proposed design and the classical one was performed. The process variation’s influence on the circuit functionality was studied. A pre-layout ±1.273 mV maximum offset voltage at T = 27 °C was achieved using vector/array notations for the amplifier with the best overall performance. Post-layout simulations that included parasitic effects were performed, with a ±1.254 mV maximum offset voltage reached at room temperature.

Circuit Design Modernization of Operational Amplifiers for Increasing Slew Rate of Output Voltage

To meet the existing needs of the domestic market of radio electronic equipment in high-speed wideband operational amplifiers, it was previously proposed to use the MH2XA031 master slice array containing complementary bipolar transistors, together with the developed circuits of the OAmp9 high-speed operational amplifier and the OAmp10 precision operational amplifier with unified cascades and the ability to program parameters such as current consumption, maximum output current, bandwidth, slew rate. The article discusses the increase in the performance of these operational amplifiers by reducing the parasitic collector capacitance of transistors by applying a reverse bias voltage to OAmp9 and using correction circuits in OAmp10, which made it possible to increase the output voltage slew rate by 29 % in the first case and 3.1 times in the second. The electrical circuits and the results of circuit simulation of the upgraded amplifiers, called OAmp9M, OAmp10M, are presented, which are respectively characterized by a zero offset voltage of 0.35 and 0.03 mV, a voltage gain of 2.7 · 103 and 3 · 105, the gain bandwidth product 161 and 68 MHz, output voltage slew rate 708 and 64.5 V/µs.

Integrated biosensing system of electrochemistry and electrophysiology for cortisol and skin conductance analysis on smartphone

High level of mental stress will lead to negative psychological and health consequences, such as insomnia, depression, and cardiovascular disease, which will increase the suicide rate and affect social stability. Mental stress has been proved to be related to biomarkers cortisol and skin conductance, and reflects the complementary advantages of stress monitoring. Based on electrochemistry and electrophysiology analysis technology, combined with microelectronic design and biosensors, this paper constructed an integrated physiological and biochemical sensing system, and an intelligent user interaction system. Firstly, a molecularly imprinted biosensor with gold nanoparticles (AuNPs), prussian blue (PB), and polypyrrole (PPy), achieved highly sensitive detection of cortisol in the range of 1–10000 ng/mL and demonstrating good specificity. The cortisol detection unit used differential pulse voltammetry (DPV) method by dual power amplifier chip AD8674, which was a precision operational amplifier with low noise, low input bias current, and unit gain stability. Then, the skin conductance detection unit was mainly composed of a pulse width modulation (PWM) drive circuit, which was designed to achieve a 100 Hz voltage output. The integrated system was designed with microcontroller module, transimpedance amplifier (TIA) module, power management module, signal transmission module, cortisol and skin conductance detection module, which was suitable for constructing precision voltage control and weak current signal conditioning. Finally, based on the software and hardware platform of smartphones, an intelligent analysis system was developed to improve the portability and user interaction convenience. Our system achieved the physiological and biochemical joint detection for the first time, showing enormous application potential in future multimode sensing monitoring.

High-speed amplifier development for the heat flow sensor

This article describes characteristics of preamplifiers for Atomic Layer Thermopile (ALTP) sensor based on precision operational amplifiers AD8597, ADA4004, ADA4075, ADA4896 and ADA4528. Transfer functions and total output noise values of these preamplifiers were obtained experimentally using an Agilent InfiniiVision 3000 series X oscilloscope. Results of experimental verification of preamplifier characteristics using a high-speed heat source are presented and discussed; the best operational amplifier for the application is determined.

Device for Automated Measurement of Volt-Ampere Characteristics

The device, which allows automated measurement of volt-ampere characteristics of semiconductor devices, is developed. The device is implemented using the microcontroller of STM32F4 series, DAC, voltage–current transform circuit, voltage and current sensor and a laptop with LabVIEW programming environment. A wide range of current measurement is possible - from 25 μA to 800 mA with current control up to 0,4 μA. The digital voltage value from the microcontroller is transmitted to the AD5624R DAC via the SPI interface. AD5624R is a 12 bit four channel DAC with built-in voltage reference of 2,5 Volts. Using two DAC channels allowed to increase the resolution of voltage control to up to 12 μV. The voltage-current transform circuit consists of two precision operational amplifiers AD8510 and OP97 with low offset voltage, n-channel and p-channel field-effect transistors with low leakage current and voltage. In the device it is important to control the offset voltage in order to provide a minimum initial current through the sample tested. The schematic is discussed for expanding the measurement range and compensating for the error of the zero code from the DAC. In the circuit, coarse control of the output voltage is implemented with a step of 1,2 mV, and fine control - with a step of 12 uV. Two channels of the DAC channel C and D were used for this purpose. The device circuit also provides compensation for the error of the zero DAC code. Among the resistive current sensors, we chose the INA226 chip, which can be purchased on the so-called breakout board. This sensor is one of the most accurate among analogues, containing a 16-bit ADC and providing digitized values of current and voltage at the output. The developed device has a linear dependence of the code to current. The linearity of current control is confirmed to have the correlation coefficient 99,9%. The approach to calibrate the device is described, which will minimize the error and expand the range of measurements. In order to correct the INA226 readings, correction coefficients are used, so that the approximated line equation for the precise voltmeter readings and the INA226 readings match. It is possible to use the approximated values of the current for obtaining the volt-ampere characteristic in the subthreshold region when the voltage on the sample is less than the voltage and current values are low (less than 1 mA), and the correted values from INA226 for building the volt-ampere characteristic in the upper threshold region, when the voltage on the sample exceeds the and current values are higher. Ref. 12, fig. 8.

Experimental Investigation of Measurement Error in Networked Resistors Arrays Based on Zero Potential Method

This paper provides a comprehensive study on the zero potential method for restriction of the crosstalk-based measurement error in network resistor arrays. We introduce four circuits with different architectures based on the zero potential method to comparatively study the effect of the switches on-resistance on the measurement error. Moreover, the effect of the operational amplifiers with different specifications on the measurement error will be investigated. The results show that the measurement error introduced by the onresistance of the switches can be effectively suppressed by inserting a buffer between the sensing elements and the switches on each driven electrode, and utilizing the virtual ground of the trans-impedance amplifier on each scanned electrode. We will show that, the efficiency of the circuits on elimination of the measurement error may be improved by employing high precision operational amplifiers.

Crosstalk Error Analysis in IIDFC Readout Circuit for Use in Piezoresistive Composite

Resistive sensor arrays (RSAs) have been developed for a variety of applications depending on resolution requirements, active sensor area, and cost. Composite-based piezoresistive sensors are commonly found in RSAs. However, they present an intrinsic problem related to the parasitic current paths that flow through the whole composite, which cause a crosstalk effect. Various circuits have been proposed to reduce the crosstalk effect in sensor arrays. In this paper, we compare a number of readout circuits with PSpice models, mainly those including voltage feedback (VF) circuits and zero potential (ZP) circuits. To develop an array with 3600 sensors using a piezoresistive composite, we selected the improved isolated drive feedback circuit ( IIDFC ). Using nodal analysis, we were able to develop an alternative mathematical circuit model, which allowed us to identify its unique characteristics, including the influence of array size on the crosstalk effect and the restriction on minimal impedance that the array elements must attain to maintain a minimum error. In a resistive array with 3600 sensors and a sensor range of 10–100 $\text{k}\Omega $ , we obtained an absolute error of less than 3.56%. In addition, the proposed mathematical circuit model obtained a maximum absolute error difference of 0.03% when compared with the PSpice model with the precision operational amplifier OPA37. Thus, using the IIDFC circuit and considering the minimal allowable impedance, it is possible to maintain a reduced error in an RSA with a large number of sensors.

Evaluation and optimization of quartz resonant-frequency retuned fork force sensors with high Q factors, and the associated electric circuits, for non-contact atomic force microscopy.

High-Q factor retuned fork (RTF) force sensors made from quartz tuning forks, and the electric circuits for the sensors, were evaluated and optimized to improve the performance of non-contact atomic force microscopy (nc-AFM) performed under ultrahigh vacuum (UHV) conditions. To exploit the high Q factor of the RTF sensor, the oscillation of the RTF sensor was excited at its resonant frequency, using a stray capacitance compensation circuit to cancel the excitation signal leaked through the stray capacitor of the sensor. To improve the signal-to-noise (S/N) ratio in the detected signal, a small capacitor was inserted before the input of an operational (OP) amplifier placed in an UHV chamber, which reduced the output noise from the amplifier. A low-noise, wideband OP amplifier produced a superior S/N ratio, compared with a precision OP amplifier. The thermal vibrational density spectra of the RTF sensors were evaluated using the circuit. The RTF sensor with an effective spring constant value as low as 1000 N/m provided a lower minimum detection limit for force differentiation. A nc-AFM image of a Si(111)-7 × 7 surface was produced with atomic resolution using the RTF sensor in a constant frequency shift mode; tunneling current and energy dissipation images with atomic resolution were also simultaneously produced. The high-Q factor RTF sensor showed potential for the high sensitivity of energy dissipation as small as 1 meV/cycle and the high-resolution analysis of non-conservative force interactions.

A 32 ppm/°C temperature-compensated operational amplifier for application in medical device tracking

This paper presents a low-power, low-noise and high precision operational amplifier for a tracking system containing the intelligent medical device, and is an extended version of paper previously published by Nenadovic et al. in proc. of ICECS 2014. The accuracy of the tracking system strongly depends on the accurate amplitude acquisition of the received signal. Therefore, an operational amplifier with precise gain control and effective temperature compensation has been designed and fabricated. The operational amplifier provides linear and temperature independent signal amplification at frequencies between 0.2 and 20 kHz at a body temperature. The amplifier shows measured gain over temperature sensitivity as low as 32 ppm/°C in temperature range from 20 to 40 °C and consumes 300 μA from a supply voltage of 2.5 V. Furthermore, the measured gain over temperature sensitivity in the range from ?40 to 130 °C is only 60 ppm/°C. Simulated linearity for signal amplitudes up to 10 mV is 0.4 % and the input-referred noise at 1 kHz is 32 nV/?Hz. An open-loop gain of 46 dB at 1 kHz and bandwidth-gain product of 4.8 MHz is measured. The operational amplifier was designed in IHPs 250 nm SiGe BiCMOS technology and occupies an area of 0.2 mm2.

Research on Multi-Functional Weak Current Real-Time Detection of Gas Corrosion Sensor

At present, the detection of weak corrosion current is not perfect and automated, to solve the problem, this paper put forward and designed a kind of weak and wide-range corrosion current real-time detection circuit with functions of automatic switching range . By choosing low bias current and high precision operational amplifier, using I - V conversion technology transform the weak current into voltage, then do voltage signal acquisition, using the SD card module and electronic analog switch combined with single chip microcomputer to realize real-time and auto-switching detection of the corrosion current. This circuit has good real-time performance and accuracy, and can achieve the corrosion current value that was outputted by gas corrosion sensor well.

Design of a Portable Formaldehyde Meter

This paper describes the design of a portable formaldehyde detector instrumentation which is based on the C8051F021 microcontroller. Using the Dart sensors for detection of formaldehyde and AD8571 precision operational amplifier for signal amplification, this meter will achieve real-time detection of formaldehyde in the air. The instrument's low power consumption, intelligent and portable features are suitable for the rapid detection of formaldehyde in indoor air.

A Laser-Trimmed Rail-to-Rail Precision CMOS Operational Amplifier

This brief presents a rail-to-rail input-output precision operational amplifier with integrated laser-trimmable polysilicon resistors for reducing the input offset voltage. The amplifier is fabricated in a standard Taiwan Semiconductor Manufacturing Company 0.18-μm complementary-metal-oxide-semiconductor process technology. The resistors' trimming sequence allows for minimizing the offset voltage over the complete input common mode voltage range (ICMR) extending from the ground to the supply. Experimental results are presented to demonstrate the steps involved in offset-voltage trimming. The prototype amplifier drives a 400-pF capacitive load and operates from a 3.3-V supply. The amplifier is unity-gain stable with a phase margin of 58° and has an open-loop direct-current gain greater than 130 dB with a unity-gain bandwidth of 0.5 MHz. Experimental results show that an untrimmed input offset voltage ranging from +0.1 to +0.5 mV over the ICMR was reduced to -30 to + 30 μV.

Design and Study on Power Supply for Giant Magnetostrictive Accurate-Motion Actuator

The architecture and operation theory of Giant Magnetostrictive Accurate-motion Actuator have been introduced. After analysing the driving characteristic of giant magnetostrictive material and requirement of driving power, a design method of wide range and high precision NC constant-current source has been put out. The output circuit is composed of serial 12-bit DACs Max531, low-noise high-speed precision operational amplifiers OP27 and driving circuit. It provides current from 0 to 2.048A with 0.5mA step value. Two fully differential input channels 16-bit, sigma-delta ADCs AD7705 collects output current in feedback loop. Current ripple is controlled under 0.25mA through using homemade high-performance linear power. The result shows that the driving power with characteristic of high stability and fast response meets the needs of driving of Giant Magnetostrictive Accurate-motion.

Long-term behavior of operational amplifiers

The voltage and current offsets of two typical precision operational amplifiers (OPAs) with BJT and FET input, respectively, were continuously measured for two years. The paper presents the experiment, explains the method of data analysis, and discusses the results. The long-term stability turns out to be limited mainly by random walk processes.

A micro-power precision amplifier for converting the output of light sensors to a voltage readable by miniature data loggers.

To record photosynthetically active radiation (PAR) simultaneously at a number of points throughout a forest canopy, we developed a simple, inexpensive (< $10 US) current-to-voltage converter that processes the current generated by a photodiode radiation sensor to a voltage range that is recordable with a miniature data logger. The converter, which weighs less than 75 g and has a volume of only 100 cm(3), is built around an ultra-low power OP-90 precision operational amplifier, which consumes less than 0.5 mA at 9 V when converting the output of a Li-Cor LI-190SA quantum sensor exposed to photosynthetically active radiation (PAR) of 2500 &mgr;mol m(-2) s(-1) or only 5 &mgr;A in low light. A small 9-V battery thus powers the amplifier for more than 1000 h of continuous operation. Correlations between photometer readings and voltage output from the current-to-voltage converter were high and linear at both high and low PAR. Sixteen Li-Cor LI-190SA quantum sensors each equipped with current-to-voltage converters and connected to a miniature data logger were deployed in the upper branches of a Panamanian tropical rainforest canopy. Each unit performed reliably during a one- or two-week evaluation.

A high temperature precision amplifier

A precision operational amplifier has been developed for instrumentation applications in which the circuitry must operate in ambient temperatures as high as 200/spl deg/C. At 200/spl deg/C the amplifier maintains an input offset voltage and current of less than 200 /spl mu/V and 1 nA respectively, a gain bandwidth product of 2.2 MHz, and a slew rate of 5.4 V//spl mu/S. The amplifier is fabricated in a standard CMOS process and consumes 5.5 mW of power at a supply voltage of 5 V. A continuous time auto-zeroed amplifier topology is used to achieve the low offset voltage levels. At high temperatures the leakage currents of the sample and hold switches used to achieve auto-zeroing, degrading the offset correction voltages stored on the hold capacitors. This degradation is reduced by using large external hold capacitors and by minimizing the diffusion area of the switches through the use of a doughnut shaped layout. The effect of the voltage degradation is reduced by sensing the offset correction voltage with a low sensitivity differential auxiliary input stage. A new input switch topology is used to reduce the amplifier's input offset current at high temperatures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A 20-μW precision operational amplifier

A precision operational amplifier is described which draws 12 /spl mu/A of quiescent current and can operate from a 1.6-V supply while requiring no external components such as the usual biasing resistor. The amplifier has DC characteristics comparable to the industry standard OP-07 and AC characteristics as good as currently available micropower devices. The circuit has an input voltage range and an output swing which include the negative supply to facilitate its use in battery-powered and other single-supply applications.

The Effects of Nitride Passivation on the Total Dose Radiation Resistance of a Precision Operational Amplifier

This study investigated the effect of different processing steps on the total dose radiation resistance of a precision operational amplifier, the OP-108A. A unique bipolar process that uses a high temperature deposited silicon nitride as a surface passivation layer was modified to determine the role of the silicon nitride in circuit hardening. Process lots with and without nitride layers showed that the nitride layer is the dominant step in assuring radiation resistant circuits. Further experiments showed that the increase in epi inversion threshold voltage resulting from the nitride layer and its associated interface charges cannot be used to explain this hardening effect. The epi inversion voltage is the voltage that it takes to turn on a parasitic p-channel MOS device degrading circuit performance.

A precision trim technique for monolithic analog circuits

A technique for permanent adjustment of precision analog circuits at wafer test by selective shorting of Zener diodes is presented. Analytical details of the trimming procedure and a physical description of diode short-circuiting are given. The method is applied to a precision operational amplifier with input offset voltage reduced to 10 /spl mu/V. The necessity of optimizing other related parameters is demonstrated. Practical considerations limiting wafer test accuracy are discussed. Circuit performance is summarized.