Programmable, very low noise current source

Flicker Noise in Resistive Gas Sensors-Measurement Setups and Applications for Enhanced Gas Sensing

We discuss the implementation challenges of gas sensing systems based on low-frequency noise measurements on chemoresistive sensors. Resistance fluctuations in various gas sensing materials, in a frequency range typically up to a few kHz, can enhance gas sensing by considering its intensity and the slope of power spectral density. The issues of low-frequency noise measurements in resistive gas sensors, specifically in two-dimensional materials exhibiting gas-sensing properties, are considered. We present measurement setups and noise-processing methods for gas detection. The chemoresistive sensors show various DC resistances requiring different flicker noise measurement approaches. Separate noise measurement setups are used for resistances up to a few hundred kΩ and for resistances with much higher values. Noise measurements in highly resistive materials (e.g., MoS2, WS2, and ZrS3) are prone to external interferences but can be modulated using temperature or light irradiation for enhanced sensing. Therefore, such materials are of considerable interest for gas sensing.

Ultra-low noise, bi-polar, programmable current sources

We present the design process and implementation of fully open-source, ultra-low noise programmable current source systems in two configurations. Although originally designed as coil drivers for Optically Pumped Magnetometers (OPMs), the device specifications make them potentially useful in a range of applications. The devices feature a bi-directional current range of ±10 and ±250 mA on three independent channels with 16-bit resolution. Both devices feature a narrow 1/f noise bandwidth of 1 Hz, enabling magnetic field manipulation for high-performance OPMs. They exhibit a low noise of 146 pA/Hz and 4.1 nA/Hz, which translates to 15 and 16 ppb/Hz noise relative to full scale.

An ultrahigh performance laser driver based on novel composite topology enhanced Howland current Source

Laser diodes (LDs) are used in a wide range of applications, such as optical wireless communications and LIDAR. To meet the demanding requirements of LDs for high accuracy and stability of the injection current, a high-precision, high stability LD driver with overvoltage protection is proposed. A novel structure based on enhanced Howland current source is described: composite topology enhanced Howland current source (CTEHCS), which has the advantages of high precision, high stability, and extensive regulation range. A 20-bit DAC and high-precision reference source are used to form a front-stage DAC circuit for precise and stable voltage reference. A closed-loop feedback calibration loop is applied to eliminate significantly the absolute errors and auxiliary calibrating of the effect of power operational amplifier on the temperature rise of critical devices. An innovative overvoltage protection circuit is designed for the load side of the CTEHCS, and the protection range can be flexibly set to 4/5/6 V to avoid damage to loads such as LDs. The noise performance, accuracy and stability, modulation bandwidth, nonlinear error, overvoltage protection performance, and turn-on and turn-off time of the experimental prototype are described in detail.

A review of design approaches for the implementation of low-frequency noise measurement systems

Electronic noise has its roots in the fundamental physical interactions between matter and charged particles, carrying information about the phenomena that occur at the microscopic level. Therefore, Low-Frequency Noise Measurements (LFNM) are a well-established technique for the characterization of electron devices and materials and, compared to other techniques, they offer the advantage of being non-destructive and of providing a more detailed view of what happens in the matter during the manifestation of physical or chemical phenomena. For this reason, LFNM acquire particular importance in the modern technological era in which the introduction of new advanced materials requires in-depth and thorough characterization of the conduction phenomena. LFNM also find application in the field of sensors, as they allow to obtain more selective sensing systems even starting from conventional sensors. Performing meaningful noise measurements, however, requires that the background noise introduced by the measurement chain be much smaller than the noise to be detected and the instrumentation available on the market does not always meet the specifications required for reaching the ultimate sensitivity. Researchers willing to perform LFNM must often resort to the design of dedicated instrumentation in their own laboratories, but their cultural background does not necessarily include the ability to design, build, and test dedicated low noise instrumentation. In this review, we have tried to provide as much theoretical and practical guidelines as possible, so that even researchers with a limited background in electronic engineering can find useful information in developing or customizing low noise instrumentation.

Dual feedback based bipolar current source with high stability for driving voice coil motors in wide temperature ranges

Bipolar current sources with a stability better than 0.1% in the temperature range of -30 to +70 °C are demanded for driving voice coil motors applied in a new ultra-quiet satellite platform, but almost none of the existing designs satisfy the harsh requirements. This paper presents a possible solution, which is essentially a floating-load, bipolar current source circuit with a dual feedback path. The key circuit is a composite amplifier (co-amp) composed of a high precision amplifier for error correction and a high power amplifier for load driving. The first feedback path comprises a specially designed four-wire current-sense resistor for current-to-voltage conversion and a discrete instrumentation amplifier for amplifying the converted voltage and closing the loop. The second feedback path is a proposed compensation network for loop stability. Error budgets for evaluating current stability and choosing key components of the circuit are comprehensively studied based on a derived rigorous current equation. Loop-stability problems attributable to the inductive load and the high open-loop gain of the co-amp are analyzed, and the proposed dual feedback compensation method is verified by theory, simulation, and measurement. All these contributions are demonstrated by three implemented prototypes with an output of up to ±2 A. The measured results agree well with theoretical predictions. The best and the worst stability performances of the three prototypes at +2 and -2 A are, respectively, 394 and 986 ppm in the temperature range of -30 to +70 °C, which are close to the theoretical value of 776 ppm.

Single JFET Front-End Amplifier for Low Frequency Noise Measurements with Cross Correlation-Based Gain Calibration

We propose an open loop voltage amplifier topology based on a single JFET front-end for the realization of very low noise voltage amplifiers to be used in the field of low frequency noise measurements. With respect to amplifiers based on differential input stages, a single transistor stage has, among others, the advantage of a lower background noise. Unfortunately, an open loop approach, while simplifying the realization, has the disadvantage that because of the dispersions in the characteristics of the active device, it cannot ensure that a well-defined gain be obtained by design. To address this issue, we propose to add two simple operational amplifier-based auxiliary amplifiers with known gain as part of the measurement chain and employ cross correlation for the calibration of the gain of the main amplifier. With proper data elaboration, gain calibration and actual measurements can be carried out at the same time. By using the approach we propose, we have been able to design a low noise amplifier relying on a simplified hardware and with background noise as low as 6 nV/√Hz at 200 mHz, 1.7 nV/√Hz at 1 Hz, 0.7 nV/√Hz at 10 Hz, and less than 0.6 nV/√Hz at frequencies above 100 Hz.

Ultra-low noise and high bandwidth bipolar current driver for precise magnetic field control

Current sources with extremely low noise are significant for many branches of scientific research, such as experiments of ultra-cold atoms, superconducting quantum computing, and precision measurements. Here we construct and characterize an analog-controlled bipolar current source with high bandwidth and ultra-low noise. A precise and stable resistor is connected in series with the output for current sensing. After being amplified with an instrumentation amplifier, the current sensing signal is compared with an ultra-low noise reference, and proportional-integral (PI) calculations are performed via a zero-drift low-noise operational amplifier. The result of the PI calculation is sent to the output power operational amplifier for closed-loop control of the output current. In this way, a current of up to 16 A can be sourced to or sunk from a load with a compliance voltage of greater than ±12 V. The broadband current noise of our bipolar current source is about 0.5 μA/Hz and 1/f corner frequency is less than 1 Hz. Applications of this current source in a cold atom interferometer, as well as active compensation of a stray magnetic field, are presented. A method for measuring high-frequency current noise in a 10 A DC current with a sensitivity down to a level of 10 μA is also described.

A low noise modular current source for stable magnetic field control

A low cost, stable, programmable, unipolar current source is described. The circuit is designed in view of a modular arrangement, suitable for applications where several DC sources must be controlled at once. A hybrid switching/linear design helps in improving the stability and in reducing the power dissipation and cross-talking. Multiple units can be supplied by a single DC power supply, while allowing for a variety of maximal current values and compliance voltages at the outputs. The circuit is analogically controlled by a unipolar voltage, enabling current programmability and control through commercial digital-to-analogue conversion cards.