Analog Signal Processing Techniques Research Articles

Effect of Filters in Photoplethysmography Analog Signals Using Open-Source LTspice Software

Analog signal processing plays a crucial role in the realm of biomedical signal analysis. This study investigates the application of analog signal processing techniques in the domain of biomedical signals, focusing on enhancing the quality and reliability of recorded physiological data. The primary emphasis is on the implementation of analog filters and amplifiers to address challenges such as noise reduction, signal conditioning, and overall signal improvement. The processing of physiological signals, such as photoplethysmography (PPG), necessitates the use of amplifiers and filters within a range of 0.4 to 5Hz. Signal noise can stem from various sources, including the test subject’s muscle movement, respiration, humming, power line interference, or even from the device itself. The research methodology involves a comparison of 3 different order of Butterworth filter circuits and their impact on the signal. The test input signal is derived from an SpO$_2$ simulator, read by a standard PPG sensor, and processed by the internal 12-bit ADC of Nucleo-F429ZI. The resulting data is stored in CSV format for subsequent use in filter design simulations with SPICE. For analog circuit designers, the utilization of SPICE in the form of LTspice proves invaluable. This open software, LTspice, boasts a simple yet powerful interface, facilitating a focus on the conceptualization and performance of the design

A 2.2 nW Analog Electrocardiogram Processor based on Stochastic Resonance Achieving a 99.94% QRS Complex Detection Sensitivity.

This paper presents an ultra-low power electrocardiogram (ECG) processor that can detect QRS-waves in real time as the data streams in. The processor performs out-of-band noise suppression via a linear filter, and in-band noise suppression via a nonlinear filter. The nonlinear filter also enhances the QRS-waves by facilitating stochastic resonance. The processor identifies the QRS-waves on noise-suppressed and enhanced recordings using a constant threshold detector. For energy-efficiency and compactness, the processor exploits current-mode analog signal processing techniques, which significantly reduces the design complexity when implementing the second-order dynamics of the nonlinear filter. The processor is designed and implemented in TSMC 65 nm CMOS technology. In terms of detection performance, the processor achieves an average F1 = 99.88% over the MIT-BIH Arrhythmia database and outperforms all previous ultra-low power ECG processors. The processor is the first that is validated against noisy ECG recordings of MIT-BIH NST and TELE databases, where it achieves better detection performances than most digital algorithms run on digital platforms. The design has a footprint of 0.08 mm2 and dissipates 2.2 nW when supplied by a single 1V supply, making it the first ultra-low power and real-time processor that facilitates stochastic resonance.

Study on analog-based ex-core neutron flux monitoring systems of Korean nuclear power plants for digitization

The analog-based Ex-core Neutron Flux Monitoring System (ENFMS) in Korean Nuclear Power Plants (NPPs) has been performing its intended functions successfully for a long time. On the other hand, the primary concern with the extended use of analog systems is the aging effect, such as mechanical failures, environmental degradation, and obsolescence. The transition to a digital-based Man-Machine Interface Systems (MMIS) in Korea and other countries has been accelerating, but some systems are still analog-based IC systems, such as the ENFMS in APR1400 NPPs. Digitalized ENFMS can become a reality using computers and microprocessors owing to the progress in digital electronics and information technology. This paper presents the result of the first phase of the research on the digitalization of the ENFMS signal processing electronics for NPPs operated or produced in Korea. It has two main parts: (1) review engineering bases of ex-core neutron flux monitoring system, including nuclear engineering, instrumentation techniques, and analog and digital signal processing techniques, and (2) analysis of analog signal processing electronics of ENFMS for OPR1000 and APR1400 power plants. They are prerequisite to the second phase of the research which is the detailed implementation of the digitalization.

Time reversal of a high frequency signal based on time-varying guided wave system

A full-electronic method to realize time reversal of electromagnetic (EM) signal by using analog signal processing (ASP) technique is reported in this paper. A time-varying guided wave system, based on a transmission line with periodically loaded microwave switches, is described and discussed theoretically, analytically and experimentally. Examinations on a prototype demonstrator show that an amplitude-modulated pulse signal can be time reversed effectively, where the pulse has a time duration of 7 ns and the amplitude-modulated carrier is 3.5 GHz.

High-Level Modeling of Analog Computational Elements for Signal Processing Applications

Large-scale field-programmable analog array ICs have made analog and analog-digital signal processing techniques accessible to a much wider community. Given this opportunity, we present a framework for considering analog signal processing (ASP) techniques for low-power systems. The core of this paper is the definition of an analog abstraction methodology and the creation of a library of high-level analog computation blocks. By abstracting the analog design, we ensure that users have a similar experience to what they would expect with digital design, thus empowering system-level engineers to take advantage of ASP concepts. The result of this paper is to pull analog computation toward system-level development, comparable with the trend in digital system design over the last 30 years.

Signal Processing Techniques to Improve an Acoustic Emissions Sensor


 
 
 Acoustic Emissions (AE) are stress waves produced by the sudden internal stress redistribution of material caused by changes in the internal structure of the material. Possible causes of these changes are crack initiation and growth, crack opening/closure, or pitting in monolithic materials (gear/ bearing material). Where as vibration can measure the effect of damage, AE is a direct measure of damage. Unfortunately, AE methodologies suffer from the need of high sample rates (4 to 10 Msps) and relatively immature algorithms for condition indictors (CI). This paper hypothesizes that the AE signature is the result of some forcing function (e.g. periodic motion in the case of rotating machinery). By using analog signal processing to demodulating the AE signature, one can reconstruct the information carried (e.g. modulation) by the AE signature and provide improved diagnostics. As most on-line condition monitoring systems are embedded system, analog signal processing techniques where used which reduce the effective sample rate needed to operate on the AE signal to those similarly found in traditional vibration processing systems. Further, by implementing another signal processing technique, time synchronous averaging, the AE signal is further enhanced. This allowed, for the first time, an AE signal to be used to identify a specific component within gearbox. This processing is tested on a split torque gearbox and results are presented.
 
 

Depth Resolution Enhancement Technique for CMOS Time-of-Flight 3-D Image Sensors

Introducing Time-of-Flight 3-D image sensors to actual engineering applications, such as pattern recognition, is constrained not only by their limited depth and lateral resolution, but also by how similar the precision of depth measurement throughout the whole pixel-matrix is. In real operating environment, an observed 3-D-scene hardly exhibits a homogeneous reflectance factor. Moreover, the light-beam (laser source) presents a nonuniform optical power distribution in space. Thus, the amount of the incident light on the sensor surface varies drastically from one pixel to another, and so does the signal-to-noise ratio. To address this problem, this paper investigates the impact of both scene and light-source non-ideal characteristics on the sensor performance. An adaptive on-pixel analog signal processing technique is also presented and applied to the design of a 32 × 32 complementary metal oxide semiconductor (CMOS) range camera, featuring an interesting cost-efficient solution.

All-digital TX frequency synthesizer and discrete-time receiver for Bluetooth radio in 130-nm CMOS

We present a single-chip fully compliant Bluetooth radio fabricated in a digital 130-nm CMOS process. The transceiver is architectured from the ground up to be compatible with digital deep-submicron CMOS processes and be readily integrated with a digital baseband and application processor. The conventional RF frequency synthesizer architecture, based on the voltage-controlled oscillator and the phase/frequency detector and charge-pump combination, has been replaced with a digitally controlled oscillator and a time-to-digital converter, respectively. The transmitter architecture takes advantage of the wideband frequency modulation capability of the all-digital phase-locked loop with built-in automatic compensation to ensure modulation accuracy. The receiver employs a discrete-time architecture in which the RF signal is directly sampled and processed using analog and digital signal processing techniques. The complete chip also integrates power management functions and a digital baseband processor. Application of the presented ideas has resulted in significant area and power savings while producing structures that are amenable to migration to more advanced deep-submicron processes, as they become available. The entire IC occupies 10 mm/sup 2/ and consumes 28 mA during transmit and 41 mA during receive at 1.5-V supply.

Recent improvements to a transportable neutron spectrometer (TNS)

This paper reviews the design, operation and future development of a transportable neutron spectrometer (TNS). Analogue signal processing techniques are used to condition the signals from an array of radiation sensors, comprising five gas-filled sensors and a hydrogenous oil-filled scintillator. This high reliance on analogue signal processing techniques is because of the nano-second rise time of the pulses produced from the sensor array. The analogue circuitry requires a high degree of expertise from the operator and frequent instrument calibration. An overview of the present instrument will be given together with a description of how the raw data from the individual sensor channels are combined to give a continuous neutron energy spectrum. Digital processing techniques are now being applied to the TNS to handle some of the more complex analogue functions, particularly neutron/γ-ray pulse-shape discrimination for the photo-scintillator column. Potential advantages of this approach are on qualities such as usability, reliability, testability, repeatability and portability of the instrument. The paper will report on the progress to date and give the latest results from experiments using a mixed neutron/γ-ray radiation source.

An instrument for measurement of induction motor drives based on phasor and modelling techniques

This paper describes a practical instrument for realtime visualization of the necessary quantities for analysis, diagnosis and investigations of AC machine drives on an oscillographic display. The instrument needs no shaft position or speed sensor, it uses exclusively the acquired stator currents and voltages and provides information, in electrical and visual form, of: stator and rotor flux; torque; reactive power; torque current; flux current; torque angle; and slip frequency. In the present version, the instrument circuitry is based on analogue signal processing techniques. The theoretical basis is a continuous-time machine model defined by a pair of simultaneous complex-coefficient differential equations. A formalization of the various calculation methods for the signal estimation is presented as well as one interpretative computer simulation for the stator current pattern. Practical results obtained with the device when applied to test and measure a real motor drive are presented and some conclusions are drawn. Main fields of application of the calculator include: monitoring systems, control units, research tools for induction motor drives, and test shops.

Sampled baseband correlators for in-air ultrasonic rangefinders

Conventional in-air ultrasonic rangefinders for robotic applications employ inexpensive analog signal processing techniques, based on threshold methods, to perform range measurements. Digital signal processing techniques using correlation methods can provide more accurate measurements, at the expense of greater system complexity and cost. The authors propose using a modified second-order bandwidth sampling technique for making data acquisition concomitant with frequency shift of the sampled narrow-band signals from in-air ultrasonic transducers to their equivalent baseband representations. The reduction of the frequency-analyzing interval allows one to conceive sampled baseband correlators for multiple receiving transducers with a complexity comparable to that of analog receivers. They develop a procedure of sensor calibration that is based on a stochastic model of time-of-flight noise; the effect of the receiver noise on the ranging accuracy is, thus, evaluated separately from the effect, due to environmental changes of the speed of sound. The simulation study and the experimental results obtained with their demonstration system offer promise for multichannel sampled baseband correlators, the time-of-flight estimation accuracy of which is close to the theoretical Cramer-Rao (CR) lower bound for signals in additive white Gaussian noise.

Signal processing for improving gas sensor response time

In this paper, we describe a system for reducing the response time of gas sensor arrays. The system uses analog signal processing techniques to analyze the transient response of sensory inputs sufficiently to discriminate among chemicals of interest before steady state is reached. The signal processing thresholds the sensory inputs at periodic intervals during the transient response, thereby producing a binary wavefront that is stored and retained for discrimination tasks. Experimental results described in this paper effectively reduce the response time of an array of discrete tin-oxide gas sensors from 10 to 2 s; experimental data are consistent across a range of concentrations for a variety of reducing gases. We expect that equivalent improvements in response time will also be possible for integrated microsensor systems using the same techniques described in this work.

AN ADAPTIVE NOISE CANCELER IMPLEMENTED WITH CMOS ANALOG TECHNOLOGY

A fully analog implementation of an adaptive noise canceler is presented, including design, simulation, and test results of the fabricated chip. The prototype chip was fabricated using 2-µ CMOS P-Well technology on a 4.0 mm2 die and uses ±5 V power supplies. The static power dissipation is 276 milliwatts. Analog signal processing techniques are used to realize an adaptive system based upon a finite impulse response (FIR) filter and least mean squares (LMS) adaptive algorithm. The circuit is tested as an adaptive noise canceler, where a signal corrupted by noise is the input. The circuit adaptively converges to cancel the noise to produce an output that is the best LMS estimate of the signal. The circuit could be used for other real-time adaptive filter applications or for realizing an on-chip learning algorithm. The implementation illustrates the advantages of an analog system with no requirements for A/D and D/A converters, reduced size of circuit subsystems (e.g. multipliers), and the relatively fast convergence.

Measurement and compensation of fictitious power under nonsinusoidal voltage and current conditions

The definitions of power are reviewed to establish a method for fictitious power measurement and to derive fictitious power compensation criteria in power systems with nonsinusoidal currents and voltages. A time-domain definition of power, using correlation techniques, is proposed. This leads to the proposal of a network parameter. A combination of digital and analog signal-processing techniques is proposed in the measurement and analysis of the components of power. The results of simulated and practical power measurements, the latter on an experimental electronic pulsewidth-modulated power converter, used for fictitious power compensation are given. >

Developing a CMOS Single-Chip Stereo Decoder and Audio Processor for Dual-Channel TV

Advanced analog design techniques using switched- capacitor filters allow full integration of audio signal processing. Developing a software-controlled stereo decoder and audio processor IC using analog signal processing techniques, will lead to easy design of compact dual-channel TV-sound receiving systems where analog-processing parameters are controlled by an external microprocessor.

Analog signal processing of eye movements for on-line digital computer analysis

An analog signal processing circuit is described which allows accurate measurement of the amplitude, velocity, and interval of both fast and slow components of eye movements. This system, in conjunction with an on-line minicomputer, can measure amplitudes up to 32° and velocity to 640° per sec. The analog signal processing methods and technique for achieving a reliable output signal are discussed. Data obtained from human and animal subjects are portrayed.

Digital signal processing concepts

Within the last few years, digital techniques have been extensively applied to the solution of signal processing problems. This paper briefly examines the relative merits of analog and digital signal processing techniques and then considers the conceptual issues involved in formulating the solution to a signal processing problem as a digital signal processor. Issues considered are the representation of a digital processor by a difference equation, formal solution of the difference equation, the system function corresponding to the processor, as well as the frequency response of the system.