Digital Amplifier Research Articles

Development of a digital amplifier system for cut-open oocyte electrophysiology

The cut-open oocyte Vaseline gap (COVG) technique is a powerful electrophysiological method for the characterization of ion channels. However, traditional amplifiers for COVG are labor-intensive and require significant user expertise. We introduce an innovative, open-source digital amplifier system with high-speed digitization and software-controlled electronics for computer-driven automation. This system compares well to existing commercial systems in terms of conventional specifications of step response (current peak at 25°μs and decay of 36°μstime constant), current noise (1.0 nA at 3 kHz bandwidth), and dynamic range (96.9 dB). Additionally, it unlocks new methods through close integration of the amplifier and software, including machine learning techniques for tuning capacitive compensation waveforms, achieving a 100-fold suppression of mean-squared transient current, and impedance measurement methods to identify system components such as membrane capacitance and electrode resistances. For future extensions, the design has unique attributes such as real-time digital signal processing for feedback; multiple-input and multiple-output; and allows for user customization. By providing open-source access to the circuit board designs, control software, and FPGA code on GitHub, this approach aims to foster cross-disciplinary collaboration and facilitate instrument customization enabling previously inaccessible electrophysiology experiments.

A handheld rapid detector of soil total nitrogen based on phase-locked amplification technology

Soil total nitrogen (STN) serves as a critical indicator for agricultural productivity. Rapid STN detection is crucial for nutrient monitoring in farmland and for guiding precision fertilization. Traditional near-infrared spectroscopy-based STN detectors necessitate darkrooms or subterranean settings to negate ambient light interference, restricting their practical use. This study develops a handheld rapid STN detector employing phase-locked amplification technology to address this issue. The device comprises optical, circuit, and control units. The optical unit features a ring-shaped split fiber structure to mitigate soil surface irregularities’ effects on the signal, with a central InGaAs photodiode for signal reception. Eight wavelengths (970 nm, 1050 nm, 1085 nm, 1200 nm, 1300 nm, 1450 nm, 1550 nm, and 1600 nm) are selected for the light sources through an information theory optimized genetic algorithm. The circuit unit employs direct digital synthesis and operational amplifiers for light signal generation and modulation. Reflected soil light signals are demodulated using an InGaAs photodiode and a phase-locked amplifier, effectively filtering ambient light noise. The control unit integrates an STM32F103C8T6 microcontroller and a Raspberry Pi 4B. The STM32 microcontroller manages signal generation, channel selection, frequency control, A/D conversion, and display, while the Raspberry Pi handles data processing, uploading, and transmission. A BP neural network model optimized by genetic algorithms is embedded for real-time STN data acquisition. Cloud-based data storage and visualization are facilitated through the Alibaba Cloud IoT platform. Performance testing reveals the device’s stability and interference resistance, with a standard deviation of electrical signal under varying light conditions below 3 mV. Compared to commercial spectrometers, the correlation coefficient (r) for reflectance data at eight wavebands exceeds 0.9. Accuracy testing shows an R2 above 0.8 and an RMSE of 0.30 g/kg when comparing detector-obtained STN values with standard chemical methods. These results demonstrate the detector’s efficacy in ambient light isolation, stability, and accuracy in agricultural settings, offering technical support for variable fertilization in precision farming.

Исследование точности определения места повреждения воздушных линий по данным от устройств синхронизированных векторных измерений различных классов и производителей

The technology of synchronized phasor measurements has been widely used in the Russian power system to analyze the parameters of steady-state electrical power modes and to record electro-mechanical transient processes. Issues on fault location based on synchronized phasor measurements have mainly been discussed in foreign publications. A significant drawback of most research papers on this issue is simplified modeling of both overhead lines and current and voltage measurement channel as well as digital filters of phasor measurement units (PMUs). The goal of this research is to develop a fault location algorithm based on synchrophasor measurements and to study its accuracy by using specialized equipment including a real-time digital simulator (RTDS), PONOVO current and voltage amplifiers and production-grade PMUs. A PMU-based double-ended fault location algorithm is developed using long-line equations and well-known electromagnetic transient theory concepts. Currents and voltage oscillograms of both overhead transmission line ends are modelled in the MATLAB/Simulink software package. These oscillograms are saved as COMTRADE files and played back using the RTDS hardware and all-in-one software package RSCAD. In addition, the study uses two production-grade PMUs, the first one is TPA-02, and the second one is a merging unit ENMU acting as a PMU, thus imitating PMUs at the line terminals. To time-align all the measurements and to aggregate PMU data frames, various auxiliary software such as PMU Connection Tester, and hardware is used. A double-ended fault location (FL) method utilizing synchrophasors under a fault has been developed. The method is based on an overdetermined system of nonlinear equations that describes physical processes in an overhead power line and can be applied under various fault types. An integrated study of the efficiency of the developed FL method has been conducted. FL errors have been computed using production-grade PMUs ENMU and TPA-02, along with the RTDS and other equipment. The authors have considered the case of configuring PMUs of different classes at the overhead line terminals, and different phasor reporting rates as well. The conducted experiments make it possible to reveal that the fault location errors do not exceed the thresholds imposed by the standard STO 56947007-29.120.70.241-2017 in 88 % of all the analyzed fault scenarios. The developed FL method makes it possible to achieve the accuracy required by regulatory guide in calculating the distance to the short circuit point in most of the cases examined. Based on the results of numerical experiments for various types of fault cases, it can be concluded that the PMU class and phasor reporting rate do not have a significant impact on the FL accuracy, provided that the fault duration is enough for the PMU filter to approach a steady output.

A Full-Duplex 60 GHz Transceiver with Digital Self-Interference Cancellation

This paper presents the design and measurement of an IEEE 802.11ad standard compatible RF transceiver for 60 GHz wireless communication systems. In addition to the traditional half-duplex (HD) mode, this work supports full-duplex (FD) operations to deliver better channel utilization and faster response times for the system. The isolation between the transmitter and receiver from the architecture design to system integration for FD operations has been fully considered. A digital self-interference cancellation (DSIC) is implemented in MATLAB to verify the FD performance. The super-heterodyne architecture with an intermediate frequency (IF) of 12 GHz is designed to suppress the image frequencies without using extra filters. A flexible phase-locked loop (PLL) synthesizer provides a local oscillator (LO) frequency with a 2 kHz resolution. Other than the time division duplex (TDD) mode used in the conventional 60 GHz system, a wide-bandwidth baseband digital variable-gain amplifier (DVGA) with a 3 dB bandwidth of more than 4 GHz also supports frequency division duplex (FDD) operations. The transceiver chip is fabricated using the Tower Jazz 0.18 µm SiGe BiCMOS process. With an on-board antenna, the transceiver covers all four channels in the 802.11ad standard, with MCS-12 (7.04 Gbps under 1.76 GSym/s and 16-QAM) under 1.5 m. In the proposed system design, the RF frontend-based self-interference (SI) suppression from the local transmitter to receiver LNA is around 54 dB. To achieve a practical FD application, the SI is further suppressed with the help of a digital SI compensation. The measured power consumption for the transmitter and receiver configurations are 194 mW and 231 mW, respectively, in HD mode and 398 mW for the FDD or FD operation mode.

An All-Digital Spread Spectrum Method with Distortion Correction for Filterless Digital Class-D Amplifiers

An All-Digital Spread Spectrum Method with Distortion Correction for Filterless Digital Class-D Amplifiers

Design of displacement detection system for differential inductance sensor

To improve the resolution of displacement detection of the differential inductance sensor and meet the requirement of real-time, that is, high output bandwidth of displacement detection system, a displacement detection system of differential inductance sensor was designed based on the Zynq-7020 platform. The PL terminal (FPGA) of Zynq 7020 is used to generate the sensor excitation signal, collect the sensor probe displacement signal, digital phase-lock amplification and demodulation of the sensor, and transmit the original shift signal and the displacement signal after demodulation at the PS terminal (ARM). The measurement error can be reduced by using the band-pass filter to pretreat the signal before the digital phase-locked amplifier. According to the experimental results, the resolution of the demodulated displacement signal can reach more than 0.0028%FS, and the nonlinear error can reach 0.0278%FS after smooth approximation fitting.

Research progress of lock-in amplifiers

The lock-in amplifier can perform high-precision measurement in both time and amplitude dimensions, so that it becomes a key component of instrumental system for precision measurement and control. This article overviews the concept, technology, and application of phase-locked amplifiers as a guide. It first explains the development and evolution of phase-locked amplifiers of analog, digital, and virtual phase-locked amplifiers, demonstrating their relationship and differences. Then, it classifies phase-locked amplifiers from a mathematical perspective based on the order and type of phase-locked loops. Subsequently, the testing process and metrological calibration progress of the main performance of phase-locked amplifiers, such as amplitude, frequency, and phase noise, are introduced. The conversion relationship between key indicators such as phase noise, time-domain jitter, Allan variance, and the coupling relationship with amplitude noise are discussed. Finally, the application forms and effects of phase-locked amplifiers in the fields of spectral enhancement, impedance analysis, magnetic measurement, microscopic imaging, and space exploration are listed. Through some new applications, the prospects of their transition from scientific instruments to industrial and even civilian products through intelligent computing, precise IoT, and other means are briefly given.

Switch-Mode MOSFETs for Class A Radio Frequency Amplification

Vertical double diffused MOSFETs (“VDMOSFETs”) developed for switching power supplies were successfully used in high voltage, high frequency linear amplifier circuits. These high voltage power switches are surprisingly useful for linear RF power amplifiers and transmitters. In most of their intended applications such as in switching power supplies or switched digital amplifiers, VDMOSFETs are pulsed by a high voltage and the pulsed output is heavily filtered. This avoids the linear region of the VDMOSFET, which normally limits the efficiency to a theoretical maximum of 25%. However, in a search of MOSFETs for high voltage linear amplification using Class A bias without heavy use of filtering, these low-cost switching MOSFETs were found to work best, if limited to radio frequencies above 1.5 MHz. Conditions, and in particular, very low impedance driving of the MOSFET gate, were discovered that gave efficiencies of 70%, rivaling that of non-linear pulse techniques such as Class C or Class D operation. The beneficial effect of linear operation combined with high efficiency at a high voltage is suggested to arise from Miller capacitance. This was only seen at radio frequencies and with the larger current, higher gate capacitance devices. Switching MOSFETs as described here should be considered alongside dedicated RF MOSFETs such as the more expensive LD (lateral diffused) MOSFET when working with RF power.

THE UTILIZATION OF PHOTODIODE IN MAKING AN ENHANCED OCULUS CANE FOR VISUALLY IMPAIRED PEOPLE

Vision impairment is a worldwide problem which significantly impacts quality of life of all ages. For this reason, this study aims to create an enhanced oculus cane which uses a photodiode to help the visually impaired people detect objects, and mobilize freely and safely. To assess its effectiveness, a PN photodiode was utilized which detects objects with programmed barcodes in various distances and sizes. Response time in identifying objects was tested together with the loudness of audio volume measured in decibel. The cane is used mainly in the household, wherein barcodes are scanned by a photodiode connected to a Bluetooth module and transmitter. The Bluetooth module and transmitter are linked to a digital amplifier audio board and double diaphragm speaker, which are used to verbally transmit the name of the object with barcode. The results proved the capabilities of the Oculus cane with 1.60 seconds response time, and scanning range in distances of 4 cm. (minimum) and 22 cm. (maximum), and the sizes of the barcodes 3 cm. and 5 cm. The loudness of the audio volume from the speaker of the Oculus cane was 82.7 dB, the safe level which will not cause damage to the ears. It is therefore recommended to use the enhanced oculus cane with photodiode as an alternative to existing smart canes which is more affordable and offers features which will greatly help visually impaired people live an independent and safe life.

The Class D Audio Power Amplifier: A Review

Class D power amplifiers, one of the most critical devices for application in sound systems, face severe challenges due to the increasing requirement of smartphones, digital television, digital sound, and other terminals. The audio power amplifier has developed from a transistor amplifier to a field-effect tube amplifier, and digital amplifiers have made significant progress in circuit technology, components, and ideological understanding. The stumbling blocks for a successful power amplifier are low power efficiency and a high distortion rate. Therefore, Class D audio amplifiers are becoming necessary for smartphones and terminals due to their power efficiency. However, the switching nature and intrinsic worst linearity of Class D amplifiers compared to linear amplifiers make it hard to dominate the market for high-quality speakers. The breakthrough arrived with the GaN device, which is appropriate for fast-switching and high-power-density power electronics switching elements compared with traditional Si devices, thus, reducing power electronic systems’ weight, power consumption, and cost. GaN devices allow Class D audio amplifiers to have high fidelity and efficiency. This paper analyzes and discusses the topological structure and characteristics and makes a judgment that Class D amplifiers based on GaN amplifiers are the future development direction of audio amplifiers.

Whole-process visualization and in-situ monitoring of tunable diode laser absorption spectroscopy for optical gas sensing

Optical gas sensing based on tunable diode laser absorption spectroscopy (TDLAS) has characteristics of high sensitivity and real-time response, but interferences and distortions may result in fluctuations and errors in the precious and stable measurement of gas concentration. Therefore, it is required to monitor and analyze parameters and waveforms throughout the TDLAS process. We propose and establish a visualized architecture with real-time interfaces and modules for the complete TDLAS process. It basically includes several functional modules, i.e., multiple frequency laser driving, operating temperature control, harmonic processing, and curve fitting, allowing elaborately in-situ monitoring the overall working status. The digital error amplifier based on type II compensation network for the proportional-integral-differential feedback controller was developed. Generated first and second harmonics and dual channel digital phase-locking algorithms were also developed in the TDLAS system. In the gas sensing experiment, the driving signal of the laser includes a 5-Hz triangular wave and a 1-kHz sine wave, and results show the favorable laser operating temperature variation of below ±0.02 ° C and the concentration calibration. The overall estimated measurement errors in the experiment are about 4.55% for the 300-ppmv gas. This visualization and in-situ monitoring system are helpful and universal for the optimization, calibration, and improvement of the TDLAS-related optical gas sensing.

Filterless, Digital Class-BD Audio Amplifiers with Constant Common Mode Output Voltage

This paper presents new and original architectures and implementations of two filterless, open-loop digital Class-BD audio amplifiers with constant common mode (CM) output voltage. The first, low-power amplifier consists of four ultrahigh-current EL7158 pin drivers, the OUT pins of which form the H bridge. The drivers are controlled from the extended LBDD PWM modulator and have appropriately set voltage levels on the VL and VH pins. The second proposed amplifier consists of two cooperating H-bridge power stages (HBS) implemented on complementary MOSFET pairs and powered by two different voltages. Both HBSs are driven by four EL7158 pin drivers having appropriately adjusted voltage levels on the VL and VH pins and controlled by an extended LBDD PWM modulator. The hybrid 9 bit DPWM modulator uses a linearized Class-BD double-sided modulation scheme with pre-compensation, enabling the most faithful emulation of natural NBDD PWM and, thus, providing attractive spectral characteristics at the DM output. Basic SPICE simulations and experimental results of the proposed digital Class-BD amplifiers were compared with the conventional digital Class-BD amplifiers. The elimination of CM signals significantly contributes to the reduction in electromagnetic interference (EMI), particularly those produced on the cables connecting the loudspeaker to the HBS terminal. Proposed Class-BD amplifiers with original and new topologies, due to their simple design and easy control (no galvanic isolation of control signals and no floating bias power supplies), which generate no CM voltage and feature excellent DM performance, similar to conventional Class-BD amplifiers, are very attractive solutions for filterless Class-BD amplifiers.

First application of a digital mirror Langmuir probe for real-time plasma diagnosis.

For the first time, a digital Mirror Langmuir Probe (MLP) has successfully sampled plasma temperature, ion saturation current, and floating potential together on a single probe tip in real time in a radio-frequency driven helicon linear plasma device. This is accomplished by feedback control of the bias sweep to ensure a good fit to I-V characteristics with a high frequency, high power digital amplifier, and field-programmable gate array controller. Measurements taken by the MLP were validated by a low speed I-V characteristic manually collected during static plasma conditions. Plasma fluctuations, induced by varying the axial magnetic field (f̃ = 10Hz), were also successfully monitored with the MLP. Further refinement of the digital MLP pushes it toward a turn-key system that minimizes the time to deployment and lessens the learning curve, positioning the digital MLP as a capable diagnostic for the study of low radio-frequency plasma physics. These demonstrations bolster confidence in fielding such digital MLP diagnostics in magnetic confinement experiments with high spatial and adequate temporal resolution, such as edge plasma, scrape-off layer, and divertor probes.

Study of Early Onset Schizophrenia: Associations of GRIN2A and GRIN2B Polymorphisms.

Background: Schizophrenia is a complex mental disorder with a high heritability. Dysfunction of the N-methyl-D-aspartate (NMDA)-type glutamate receptors may be involved in the pathogenesis of schizophrenia. In this study, we examined the contribution of GRIN2A and GRIN2B (Glutamate Ionotropic Receptor NMDA Type Subunit 2A/2B) polymorphisms to the clinical features of schizophrenia, such as the leading symptoms, the type of course, and the age of onset. Methods: A population of 402 Russian patients with schizophrenia from the Siberian region was investigated. Genotyping of seventeen single-nucleotide polymorphisms (SNPs) in GRIN2A and GRIN2B was performed using QuantStudio™ 3D Digital PCR System Life Technologies amplifier using TaqMan Validated SNP Genotyping Assay kits (Applied Biosystems). The results were analyzed using Chi-square and the Fisher’s exact tests. Results: We found an association of GRIN2A rs7206256 and rs11644461 and GRIN2B rs7313149 with the early onset (before the age of 18 years old) schizophrenia. We did not reveal any associations of GRIN2A and GRIN2B polymorphisms with leading (positive vs. negative) symptoms or type of course (continuous vs. episodic) of schizophrenia. Conclusions: In the study, we confirmed the involvement of the GRIN2A and GRIN2B genes in the early onset of schizophrenia in a Russian population of the Siberian region.

Workshops (WS) Workshop 1: Electroencephalogram (EEG) WS1.1. The origin of EEG, recording techniques and quality

EEG records the electrical activity of the cerebral cortex, mainly from large pyramidal neurons close to the surface, and this activity is influenced by subcortical structures. At least 6 cm 2 of synchronised cortical activity is required to be recorded by scalp EEG. Surface electrodes are placed equidistantly over the scalp according to an international convention (10–20 System), ensuring good electrical contact, with electrode impedances <5000 ohms. Each electrode is influenced by both physiologically relevant activity and high amplitude environmental electrical noise, so pairs of electrodes are connected to differential (common-mode rejection) amplifiers to hopefully cancel out the environmental noise and record any differences between the two electrodes. Digital EEG amplifiers then use analogue-to-digital converters to translate the recorded voltage differences into numerical values, requiring an amplitude resolution of at least 12 bits (usually ≥16 bits), and with the number of measurements per second (sampling rate) at least three times the highest frequency being recorded (≥256 Hz). Filtering highlights activity that is biologically relevant, using a bandpass of 0.5–70 Hz for routine diagnostic EEG, but filtering distorts raw data and is no substitute for good technique. Digital EEG recording uses a system reference electrode separate from the 10–20 recording electrodes and stores the voltage measurements for each recording electrode relative to this system reference electrode. This allows reformatting of EEG channels and montages after the recording simply by combining any electrode pair to create the channel. At least longitudinal bipolar, transverse bipolar and referential montages should be used to read EEG. Unfortunately, EEG is commonly misinterpreted, leading to misdiagnosis. Age and state dependency dramatically influence the normal EEG, and there are many variations of normal, especially during drowsiness and sleep. ECG, careful clinical observation and video recording (routine if possible) are required throughout the recording to recognise artefacts and other important changes. For EEG to be useful, comprehensive knowledge, training and experience are required under the supervision of a skilled mentor. When in doubt, it is best to assume that background slowing is related to drowsiness/sleep, and every sharply contoured wave is an artefact or normal variant until proven otherwise.

Design and performance analysis of low power LNA with variable gain current reuse technique

This paper presents a CMOS low power Variable Gain Low Noise Amplifier for 26–34 GHz in 45 nm process technology, which composes of cascaded complimentary common gate (CCG) stage and digital current steering amplifier. First stage is CCG stage, which helps in achieving the low power consumption and less area. Second stage is variable gain amplifier, uses current reuse technique as well as gm-boost technique and has constant dc current to make the input impedance stable. Source degeneration technique cancel out MOS parasitic capacitance help in achieving linearity. Simulated maximum peak gain is 13.139 dB at 30.57 GHz and lowest peak gain is 7.75 dB at 26 GHz i.e. approximately flat over the entire band. Lowest NF is 3.08 dB at 32.6 GHz. Process corner simulation has been done for all four corners (S–S, S–F, F–S, F–F) showing robustness of LNA. Input return loss has value less than − 9.58 dB while output return loss has less than − 2.6 dB showing good matching; power consumption is 16 mW for dc current of 16 mA at 1 V. MOS active chip area is 76.727 µm2.

Triple-sensitivity X-ray computed tomography using analog and digital amplifiers

Triple-sensitivity X-ray computed tomography using analog and digital amplifiers

Design of low power single-stage bias current control technique- based DVGA for LTE receivers

In this study, a novel single-stage Digital Variable Gain Amplifier architecture (DVGA) was presented for Long Time Evolution (LTE) receivers. The proposed DVGA combines two transimpedance amplifiers, a transconductance amplifier and a novel digitally controlled current. Using a digital control block, an auxiliary pair to retain a constant current density enabled changing the gain. The Heuristic Method was used to optimize the proposed circuit performance for a high gain, low noise and low power consumption. This circuit was simulated using device-level description of TSMC 0.18 µm CMOS process. The VGA achieved 59 dB gain control range, 171 MHz bandwidth, 11.5 dBm third-order input-intercept point as a minimum gain and below 19 dB noise figure as a maximum gain which makes it convenient for LTE receivers. For maximum gain, The Total Harmonic Distortion (THD) is less than -62 dB. The fully differential VGA has a low THD which it represents a key performance satisfying the LTE system application requirements. The overall power consumption of the circuit is 0.35 mW for ± 0.9 V power supply. This paper also dealt with the prediction of optimized DVGA performances for the upcoming CMOS nanoprocess using the robust Bisquare Weights (BW) method for 16 to 10 nm process nodes. The behavior of the optimized DVGA performances with process scaling was detailed.

Pendulum Accelerometer with Digital Control and New Functionality

In this paper, we consider a compensation-type quartz pendulum accelerometer, a feature of which is the use of a digital feedback amplifier in the control loop (for the implementation of a discrete controller and algorithmic compensation for errors from the pendulum unbalance and temperature dependences of the zero offset and scale factor). The problem is related to the construction of a digital control system for the considered accelerometer, which provides a high-precision measurement of the projection onto the sensitivity axis of the actual apparent acceleration of the object on which the accelerometer is installed. A solution to this problem, which allows finding digital control algorithms using various methods of synthesis of discrete controllers of the control loop, is provided. The obtained solutions in the time and frequency domains are analyzed, confirming the high quality of regulation. The results of experimental studies are presented.

Static and dynamic bridge amplifier calibration according to ISO 4965-2

Dynamic measurements to correctly adjust the magnitude in fatigue testing require a dynamic calibration of force transducers and conditioning electronics if the dynamic loads are to be measured correctly. International standard ISO 4965 describes a calibration method for these components. At PTB, such a calibration of bridge amplifiers has now been performed for the first time. The calibration includes tests with static and dynamic signals. The reference for the calibration is the dynamic bridge standard of PTB. It is particularly suitable for this application as it can generate static and dynamic signals, and thus all investigations can be performed with one reference and in a reasonably short time. The signal creation and the data analysis were carried out using the open source program GNU Octave. For the data analysis, a semi-automatic procedure was developed to simplify the process. Calibrations of two digital bridge amplifiers were carried out.