Programmable Current Source Research Articles

A 1.5 mm2 4-Channel EEG/BIOZ Acquisition ASIC With 15.2-Bit 3-Step ADC Based on a Signal-Dependent Low-Power Strategy.

This article presents a multichannel EEG/BIOZ acquisition application specific integrated circuit (ASIC) with 4 EEG channels and a BIOZ channel, a switch resistor low-pass filter (SR-LPF). Each EEG channel includes a frontend, and a 4-channel multiplexed analog-to-digital converter (ADC), while the BIOZ channel features a pseudo sine current generator and a pair of readout paths with multiplexed SR-LPF and ADC. The ASIC is designed for size and power minimization, utilizing a 3-step ADC with a novel signal-dependent low power strategy. The proposed ADC operates at a sampling rate of 1600 S/s with a resolution of 15.2 bits, occupying only 0.093 mm2. With the help of the proposed signal-dependent low-power strategy, the ADC's power dissipation drops from 32.2 μW to 26.4 μW, resulting in an 18% efficiency improvement without performance degradation. Moreover, the EEG channels deliver excellent noise performance with a NEF of 7.56 and 27.8 nV/√Hz at the expense of 0.16 mm2 per channel. In BIOZ measurement, a 5-bit programmable current source is used to generate pseudo sine injection current ranging from 0 to 22 μApp, and the detection sensitivity reaches 2.4 mΩ/√Hz. Finally, the presented multichannel EEG/BIOZ acquisition ASIC has a compact active area of 1.5 mm2 in an 180nm CMOS technology.

An lpGBT subsystem for environmental monitoring of experiments

In this paper, the Low Power Giga Bit Transceiver (lpGBT) built-in system for environmental monitoring of the LHC experiments is presented. Eight external analogue inputs and eight internal voltages are multiplexed into an instrumentation amplifier with selectable gain, whose output is digitised by a 10-bit SAR ADC. A programmable current source can be enabled for each external input to implement resistance measurements. Internal channels are used to monitor power supplies and the output of the temperature sensor. The environmental monitoring system includes a precise 1 V reference voltage source and a 10-bit voltage DAC. All blocks were designed and fabricated in 65 nm CMOS technology, fully characterised, and the pre- and post-irradiation measurement results are presented in this work.

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 1Hz, 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.

A Model-Based Approach Digital Pre-Distortion Method for Current-Steering Digital-to-Analog Converters

This paper presents a novel static digital pre-distortion (DPD) method for a current-steering digital-to-analog converter (CS-DAC). The proposed method utilizes the knowledge of the current cell array architecture to calculate the static mismatch currents of the cells. The mismatch values are stored in memory and added to the original input code to generate the new pre-distorted input word. The converter corrects the static error with its own current cells without incorporating an additional calibration DAC (CALDAC) or programmable current sources. This results in a reduction in area, power and simulation run times because of the simpler circuit design. An Overflow-Cell-Selection (OCS) is introduced as a novel solution to further enhance the static linearity of the converter. It also can be implemented as a software solution for already existing DAC designs which do not have an integrated DPD and lab/measurement equipment (e.g., arbitrary wave generator (AWG)). This poses as a strong differentiation factor compared to other state-of-the-art static DPD methods. The evaluation of the proposed DPD is done via simulations in MATLAB and on- chip measurements with a 14-bit CS-DAC in 16 nm. Single tone measurements show a performance gain of the total harmonic distortion (THD) of 12 dB.

Implementation of radial basis function network-based maximum power point tracking for a PV-fed high step-up converter

This research offers a maximum power point tracking (MPPT) algorithm for photovoltaic (PV) systems based on neural networks (NNs) and a rapid step-up converter configuration. An improved variable step size-radial basis function network (RBFN) in the NN algorithm is accomplished in the proposed system to track the maximum power point (MPP) with high convergence speed and obtain maximum power with reduced oscillations. Under various irradiance and temperature conditions, the performance of the recommended algorithm was compared to that of particle swarm optimization (PSO), modified perturb and observe (P&O) MPPT technique, artificial neural network (ANN), and multilayer perceptron feed-forward (MPF) NN-based MPPT method. In this system, a new interleaved non-isolated large step-up converter with the coupled inductor technique is suggested to compensate for the discord in PV devices to enable a continuous and independent power flow. The proposed PV-fed converter system is validated under partial shading conditions (PSCs) and uniform solar PV, and the results are experimentally verified with the use of a programmable direct current (DC) source. The obtained results indicate that the proposed converter produces output with high gain, continuous input current, low voltage stress on switches, minimal ripple, high power density, and extensive input and output operations. Finally, a prototype has been implemented to verify the functionality of the presented converter in continuous conduction mode operation with an input voltage range of 20 V and an output voltage of 200 V.

Study on a method of prolonging the life of catalytic combustion sensor

The catalytic combustion combustible gas sensor is restricted by the principle, process, environment and other factors. When it is used in the actual working environment, the output value will drift and the measurement error will increase with the passage of time. The longer the service time is, the more serious the problem of sensitivity degradation will be, until it completely fails. In general, the effective service life of the sensor is only 1-2 years. Based on the conventional detection technology, this paper proposes the constant temperature bridge method based on the programmable constant current source. By reducing the use frequency of the catalytic sensitive element, it can avoid the problem that the sensitivity of the element drops too fast under frequent use, and can effectively extend the service life of the sensor to about one time.

Development of dual-mode precision current source for macro-microcomposite actuator based on field programmable gate array.

To meet the requirements of variable input current forms, microstep adjustment, low error coefficient, high output linearity, and the low ripple of macro-microcomposite actuators developed by combining voice coil motors and a giant magnetostrictive actuator, in this study, a design scheme of dual-mode precise programmable current sources based on a field programmable gate array (FPGA) was proposed. First, according to the working principle and control characteristics of macro-microcomposite drivers, an overall circuit system model of a driving power supply was established. Second, based on the circuit operational amplifier principle, an output current equation of the power supply was obtained, and a current switching circuit and a dual-mode current sampling circuit were designed. Finally, an FPGA was used as the current control core, and an incremental PI algorithm was introduced to compensate for the current feedback. The experimental results showed that the precision current source can output two current modes (positive current 0-5A and positive and negative current -5 to 5A) under the FPGA control. The average current error coefficient of the output in the two current output modes was ε ≦ 0.006, the maximum nonlinearity was ηmax ≦ 0.005, and the error between the current adjusting step value and the preset value was less than 1%.

Design of programmable current source for MOSFET based gamma dosimetry system

In this paper, a programmable current source based simple, compact and low cost MOSFET dosimetry system is developed and characterized for the measurement of cumulative gamma radiation doses. The proposed readout system is microcontroller based which can be used to set-up different zero temperature coefficient currents (IZTC) (range: 200μA – 400μA) using digital rheostat and subsequently measuring changes in the threshold voltages of irradiated sensors. The proposed current source characterized by interfacing with six indigenously developed MOSFET sensors under gamma environments up to 1000 cGy with an average sensitivity of 5 mV/cGy and its performance is compared with commercially available Keithley’s source measurement unit, albeit at much lower cost and size. The comparison shows that the threshold voltage measured from both the systems differ less than 1%.

Design of a high speed 14‐bit digital to analog converter circuit

AbstractA 14‐bit current domain digital to analog converter (DAC) is presented, which employs 4 + 4 + 6 segmented current‐steering architecture. The high 4‐bit and intermediate 4‐bit adopted thermometer code control, and the low‐6 bit used direct control of binary weighted current source, so the dynamic performance of DAC is improved. The detailed design of the core modules of DAC is also given, including high‐precision programmable reference current source, DAC encoding and decoding circuit, and the current source array. The DAC is fabricated in SMIC 0.18 μm 1P6M CMOS technology. The simulation results of Hspice show that the spurious free dynamic range for 80 MHz output signal at 400 MHz sampling clock rate is 72.47 dB, and the design has met the requirements.

CAAC-IGZO FET/Si-FET hybrid structured analog multiplier and vector-by-matrix multiplier for neural network

An analog multiplier with a hybrid structure where crystalline oxide semiconductor (OS), specifically c-axis-aligned crystalline In-Ga-Zn oxide, based FETs (OS-FETs) are stacked on Si-FETs is fabricated. The analog multiplier demonstrates favorable multiplier characteristics such as high linearity, long data retention, and small device-to-device variation. An analog vector-by-matrix multiplier composed of the analog multiplier and an offset circuit formed of a programmable current source and a programmable current sink with the hybrid structure is proposed. The validity of the proposed analog vector-by-matrix multiplier is verified by employing it in a neural network trained to recognize handwritten digits. According to the circuit simulation results, the analog vector-by-matrix multiplier allows the network to achieve adequately high recognition accuracy, suggesting the suitability of the multiplier for running neural networks.

Scheme design and experimental verification of programmable current source for giant magnetostrictive actuator based on field programmable gate array

In order to meet the requirements of a giant magnetostrictive actuator for a microstep, high precision, and wide range of input power supply, a design scheme of the high performance programmable current source based on a field programmable gate array processor and the OPA549 amplifier is proposed. Based on the circuit principle of the microstepping continuous adjustment current source, the microstepping control circuit and the constant current source control circuit are designed and the feasibility of the design scheme is verified by circuit simulation and experimental test. The results show that the current output range of the programmable current source is 0 A–6.99 A and the minimum step value is 1.7 mA. The output current precision can reach 1.10% in circuit simulation and 4.38% in experimental test. The research results show that the proposed design scheme of the programmable current source satisfies the requirements of the giant magnetostrictive actuator.

Design and Validation of a New Programmable Current Source for Electrical Impedance Tomography Applications

This paper proposed an advanced digital voltage-controlled multi-frequency based constant current source, which is a wide range of loads and high SNR ratio for Electrical Impedance Tomography (EIT) application. In EIT a constant current source is required for injecting a sinusoidal current pulse to the phantom boundary. The boundary potentials are measured by inserting content current from the phantom boundary according to the variation in frequency and current levels. For studying the wide range of tissue conductivity among different type of subjects (the multi-frequency scanning) is desired in medical Electrical impedance tomography. The proposed Current source, which shows that the simulation has good performance at multi-frequency range with accuracy and stability. In proteus simulation software, the results show that the proposed circuit presents a more stable impedance output and the obtained boundary data at multi-frequency for the validation of the obtained data has been shown using suitable image reconstruction algorithm and is found suitable for image reconstruction much easier.

Reference Ultralow DC Current Source Between 1 fA and 100 pA at TÜBİTAK UME

In this paper, we present a programmable Ultra Low DC Current Source (ULCS) developed at T\"UB\.ITAK UME. The output current range is from 1 fA up to 100 pA with 100 aA resolution and is directly traceable to DC voltage, capacitance and time units. The principle of the device is based on applying a linear ramp voltage on standard capacitors with values between 1 pF and 1000 pF. These standard capacitors are commercial standard capacitors which are kept in a temperature controlled insulated box. Linear ramp voltage is generated using a commercial DAQ card. Current source device is fully automated with computer control and can be used to generate any currents with 100 aA resolution in its full range. The uncertainty is 2.5 mA/A at 1 fA current.

A Programmable Single-Phase Multilevel Current Source Inverter

The conventional single-phase multilevel current source inverters suffer from the high count of switches for increasing the levels. Therefore, how to generate more levels with reduced-count of switches is attractive. In this paper, a programmable single-phase current source inverter is presented. It can achieve the programmable level output with only five switches. Different from the existing single-phase reduced-count multilevel inverters, it has the advantages of a simple structure and programmable level output. Finally, the simulation and experimental tests are carried out. And, the experimental results verify the effectiveness of the proposed programmable multilevel inverter.

Component technology development of thermal absolute humidity sensor for high humidity and condensation environments

AbstractThe author presents a thermal conductivity absolute humidity sensor whose substrate and its channel can be heated. Water droplets getting into the channel due to condensation can be removed by the substrate heater and the bridge heater setting in the channel. Thus this sensor is expected to be applied in condensation environment, such as a humidity sensor for medical ventilator. The output voltage from the prototype platinum hot wire sensor is stably obtained by using the pulse current waveform from the programmable current source under the conditions of 100%RH and 33℃.

High-Precision Electrical Impedance Tomography Data Acquisition System for Brain Imaging

In electrical impedance tomography (EIT), it is difficult to obtain the intracranial impedance due to the highly resistive skull enclosing the brain. Therefore, a high-precision data acquisition system is required for brain EIT. In this paper, we used a high-precision digital synthesis method and a digital demodulation technique with high noise immunity to eliminate random errors. Moreover, we focused on two problems encountered during EIT data acquisition: 1) the shunt effect on the excitation current due to the distributed capacitance between electrodes and ground and 2) high common-mode voltages in the boundary measurements. We designed a new electrode interface to reduce the influence of the distributed capacitance and a programmable current source to accurately compensate for the excited current. We also proposed a new voltmeter circuit with improved CMRR. Overall, this EIT data acquisition system can produce a programmable current with SNR greater than 89 dB. It can also measure the voltage difference precisely with CMRR higher than 75 dB with a 1- $\text{k}\Omega $ impedance imbalance. The results on a calibration model show that this system has a high SNR of 83 dB and a low reciprocity error of 0.125%. In addition, EIT imaging results were acquired using a brain physical phantom. The system can detect small disturbances of 0.35% in volume (1.99% of the cross-sectional area) and 17% in resistivity. Experiments on healthy volunteers also suggest that small intracranial impedance variations due to temporary occlusion and reperfusion of the unilateral carotid artery may be monitored by the system.

A 0.079 mm2 2.1-to-4.2 GHz ring-VCO employing programmable current topology

PurposeThe purpose of this work in designing a wideband ring voltage-controlled oscillator (VCO) based on programmable current topology. It occupies a very tiny area yet achieving a good phase noise performance, which is suitable to be implemented in cost-effective and wideband frequency synthesizers.Design/methodology/approachThe tuning range and gain are improved by dividing the VCO tuning curve into multiple curves controlled by programmable current sources without introducing additional parasitic capacitance.FindingsFabricated in 130-nm standard complementary metal oxide semiconductor technology and occupying an area of 0.079 mm2, the VCO is tunable from 2.05 to 4.19 GHz, with a tuning percentage of 68.5 per cent. The VCO measures a phase noise performance of −96.7 dBc/Hz at an offset of 1 MHz from a 4.19 GHz carrier while consuming an average current of 6.5 mA, achieving figure of merit (FoM) and FoMT of −158.9 and −175.6 dBc/Hz, respectively.Originality/valueThe proposed design uses programmable current topology without introducing parasitic capacitance, hence achieving wideband operation. It also occupies a tiny area and achieves a good phase noise performance.

A 15-V Bidirectional Current Clamp Circuit for Integrated Patch Clamp Electrophysiology

This brief presents a high-voltage low-noise current clamp circuit for patch clamp electrophysiology systems. The circuit includes a novel programmable bidirectional current source spanning a pA to nA range, while supporting an 11.1-V input voltage range and being insensitive to opamp offset voltage. The measured output current noise floor is $8.0\,\,\text{fA}/\boldsymbol {\sqrt {\mathrm {Hz}}}$ while sourcing 100 pA. For a measurement bandwidth of 1 kHz, the corresponding integrated noise current is 588 fARMS. The system occupies an area of 0.2 mm2 in 180-nm CMOS and consumes 4 mA from a 15-V supply.

Design of current source for multi-frequency simultaneous electrical impedance tomography.

Multi-frequency electrical impedance tomography has been evolving from the frequency-sweep approach to the multi-frequency simultaneous measurement technique which can reduce measuring time and will be increasingly attractive for time-varying biological applications. The accuracy and stability of the current source are the key factors determining the quality of the image reconstruction. This article presents a field programmable gate array-based current source for a multi-frequency simultaneous electrical impedance tomography system. A novel current source circuit was realized by combining the classic current mirror based on the feedback amplifier AD844 with a differential topology. The optimal phase offsets of harmonic sinusoids were obtained through the crest factor analysis. The output characteristics of this current source were evaluated by simulation and actual measurement. The results include the following: (1) the output impedance was compared with one of the Howland pump circuit in simulation, showing comparable performance at low frequencies. However, the proposed current source makes lower demands for resistor tolerance but performs even better at high frequencies. (2) The output impedance in actual measurement below 200 kHz is above 1.3 MΩ and can reach 250 KΩ up to 1 MHz. (3) An experiment based on a biological RC model has been implemented. The mean error for the demodulated impedance amplitude and phase are 0.192% and 0.139°, respectively. Therefore, the proposed current source is wideband, biocompatible, and high precision, which demonstrates great potential to work as a sub-system in the multi-frequency electrical impedance tomography system.

Investigation of severity of voltage flicker caused by second harmonic

Second harmonic produces asymmetrical waveform which leads to fluctuation of root-means-square (rms) value with certain frequency. Meanwhile, function of weighting filter in flickermeter is designed for sixth-order low-pass filtering function with frequency to be limited to 35 Hz, signal with frequency ranging from 35 to 100 Hz, at certain gain, still can pass through. Since the second harmonic produces fluctuation of rms value with 50 Hz, there is high possibility that it can be passed by this filter and thus resulting in flicker detection. Therefore, this study points out a worthwhile research gap to justify that the presence of the second harmonic can directly increase severity of voltage flicker. In addition, further simulation work using semi-converter has been carried out, as one of main even harmonic sources, in order to justify the concept. To practically validate the concept, Fluke power analyser 435 series II and programmable alternative current source are utilised in the experimental setup. In the main finding, it is confirmed that severity of the voltage flicker increases directly with the presence of the second harmonic and it also formed a clear relationship between short-term perceptibility (Pst) and percentage of the second harmonic component.