A Single-Chip CMOS Pulse Oximeter with On-Chip Lock-In Detection

Pulse oximeter bench tests under different simulated skin tones

Pulse oximeters' (POs) varying performance based on skin tones has been highly publicised. Compared to arterial blood gas analysis, POs tend to overestimate oxygen saturation (SpO2) values for people with darker skin (occult hypoxemia). The objective is to develop a test bench for assessing commercial home and hospital-based POs in controlled laboratory conditions. A laboratory simulator was used to mimic different SpO2 values (~ 70 to 100%). Different neutral density and synthetic melanin filters were used to reproduce low signal and varying melanin attenuation levels. Six devices consisting of commercial home (Biolight, N = 13; ChoiceMMed, N = 18; MedLinket, N = 9) and hospital-based (Masimo Radical 7 with Neo L, N = 1; GE B450 Masimo SET with LNCS Neo L, N = 1; Nonin 9550 Onyx II™, N = 1) POs were reviewed and their response documented. Significant variations were observed in the recorded SpO2 values among different POs when exposed to identical simulated signals. Differences were greatest for lower SpO2 (< 80%) where empirical data is limited. All PO responses under low signal and melanin attenuation did not change across various simulated SpO2 values. The bench tests do not provide conclusive evidence that melanin does not affect in vivo SpO2 measurements. Research in the areas of instrument calibration, theory and design needs to be further developed.

System anti-jamming technology in the design of intelligent single chip computer constant current source of field strength machine

With the development of the electric power industry, the technical level of automatic testing equipment for the reliability of electrical component circuit breakers in the transmission and distribution network is getting higher and higher. The stability and accuracy of the test power supply are the basis for ensuring the pass rate of the test product. Most of the electrical testing and testing equipment has defects such as inaccurate power supply current regulation, low power, and low level of intelligence, which are difficult to meet the testing requirements. Based on the theory of a closed-loop control system, this paper adopts embedded system design technology to realize a high-current, high-power, high-stability digital constant current source system for line detection. This paper studies the rule-based intelligent anti-jamming decision engine design and system anti-jamming performance analysis of NC-OFDM system. We give the design of an intelligent anti-jamming decision engine based on rule-based decision-making, and focus on two intelligent anti-jamming decision-making algorithms: Adaptive Modulation and Coding (AMC) algorithm based on signal-to-noise ratio difference and packet error rate and Adaptive Sub-Band Selection (ASBS) algorithm. Experimental test results show that the output current range is 200 mA to 2000 mA, the system has realized a microstep adjustment of±5 mA, and the absolute error of current measurement is less than 0.3%+4 mA. The system is stable and reliable, and has high practical value in the field of high precision and low power.

A Textile Sleeve for Monitoring Oxygen Saturation Using Multichannel Optical Fibre Photoplethysmography

Textile-based systems are an attractive prospect for wearable technology as they can provide monitoring of key physiological parameters in a comfortable and unobtrusive form. A novel system based on multichannel optical fibre sensor probes integrated into a textile sleeve is described. The system measures the photoplethysmogram (PPG) at two wavelengths (660 and 830 nm), which is then used to calculate oxygen saturation (SpO₂). In order to achieve reliable measurement without adjusting the position of the garment, four plastic optical fibre (POF) probes are utilised to increase the likelihood that a high-quality PPG is obtained due to at least one of the probes being positioned over a blood vessel. Each probe transmits and receives light into the skin to measure the PPG and SpO₂. All POFs are integrated in a stretchable textile sleeve with a circumference of 15 cm to keep the sensor in contact with the subject’s wrist and to minimise motion artefacts. Tests on healthy volunteers show that the multichannel PPG sensor faithfully provides an SpO₂ reading in at least one of the four sensor channels in all cases with no need for adjusting the position of the sleeve. This could not be achieved using a single sensor alone. The multichannel sensor is used to monitor the SpO₂ of 10 participants with an average wrist circumference of 16.0 ± 0.6 cm. Comparing the developed sensor’s SpO₂ readings to a reference commercial oximeter (reflectance Masimo Radical-7) illustrates that the mean difference between the two sensors’ readings is −0.03%, the upper limit of agreement (LOA) is 0.52% and the lower LOA is −0.58%. This multichannel sensor has the potential to achieve reliable, unobtrusive and comfortable textile-based monitoring of both heart rate and SpO₂ during everyday life.

Source-Detector Spectral Pairing-Related Inaccuracies in Pulse Oximetry: Evaluation of the Wavelength Shift

Pulse oximetry enables oxygen saturation estimation (SpO2) non-invasively in real time with few components and modest processing power. With the advent of affordable development kits dedicated to the monitoring of biosignals, capabilities once reserved to hospitals and high-end research laboratories are becoming accessible for rapid prototyping. While one may think that medical-grade equipment differs greatly in quality, surprisingly, we found that the performance requirements are not widely different from available consumer-grade components, especially regarding the photodetection module in pulse oximetry. This study investigates how the use of candidate light sources and photodetectors for the development of a custom SpO2 monitoring system can lead to inaccuracies when using the standard computational model for oxygen saturation without calibration. Following the optical characterization of selected light sources, we compare the extracted parameters to the key features in their respective datasheet. We then quantify the wavelength shift caused by spectral pairing of light sources in association with photodetectors. Finally, using the widely used approximation, we report the resulting absolute error in SpO2 estimation and show that it can lead up to 8% of the critical 90–100% saturation window.

A 2.6 μW Monolithic CMOS Photoplethysmographic (PPG) Sensor Operating With 2 μW LED Power for Continuous Health Monitoring

Photoplethysmography (PPG) enables wearable vitals monitoring. Nevertheless, it is still limited by the few mA of the LEDs driving current. We present a PPG sensor integrating an array of dedicated pinned-photodiodes (PPD) with a full readout chain integrated in a 0.18 μm CMOS Image Sensor (CIS) process. The sensor features a total input referred noise of 0.68 e-rms per PPD, independently of the input light, and achieves a 4.6 μW total power consumption, including the 2 μW LED power, at 1.38 bpm heart rate average error.

Local Pulse Wave Velocity: Theory, Methods, Advancements, and Clinical Applications

Local pulse wave velocity (PWV) is evolving as one of the important determinants of arterial hemodynamics, localized vessel stiffening associated with several pathologies, and a host of other cardiovascular events. Although PWV was introduced over a century ago, only in recent decades, due to various technological advancements, has emphasis been directed toward its measurement from a single arterial section or from piecewise segments of a target arterial section. This emerging worldwide trend in the exploration of instrumental solutions for local PWV measurement has produced several invasive and noninvasive methods. As of yet, however, a univocal opinion on the ideal measurement method has not emerged. Neither have there been extensive comparative studies on the accuracy of the available methods. Recognizing this reality, makes apparent the need to establish guideline-recommended standards for the measurement methods and reference values, without which clinical application cannot be pursued. This paper enumerates all major local PWV measurement methods while pinpointing their salient methodological considerations and emphasizing the necessity of global standardization. Further, a summary of the advancements in measuring modalities and clinical applications is provided. Additionally, a detailed discussion on the minimally explored concept of incremental local PWV is presented along with suggestions of future research questions.

Optical Fibre-Based Pulse Oximetry Sensor with Contact Force Detection

A novel optical sensor probe combining monitoring of blood oxygen saturation (SpO₂) with contact pressure is presented. This is beneficial as contact pressure is known to affect SpO₂ measurement. The sensor consists of three plastic optical fibres (POF) used to deliver and collect light for pulse oximetry, and a fibre Bragg grating (FBG) sensor to measure contact pressure. All optical fibres are housed in a biocompatible epoxy patch which serves two purposes: (i) to reduce motion artefacts in the photoplethysmogram (PPG), and (ii) to transduce transverse loading into an axial strain in the FBG. Test results show that using a combination of pressure measuring FBG with a reference FBG, reliable results are possible with low hysteresis which are relatively immune to the effects of temperature. The sensor is used to measure the SpO₂ of ten volunteers under different contact pressures with perfusion and skewness indices applied to assess the quality of the PPG. The study revealed that the contact force ranging from 5 to 15 kPa provides errors of <2%. The combined probe has the potential to improve the reliability of reflectance oximeters. In particular, in wearable technology, the probe should find use in optimising the fitting of garments incorporating this technology.

A CMOS Self-Contained Quadrature Signal Generator for SoC Impedance Spectroscopy

This paper presents a low-power fully integrated quadrature signal generator for system-on-chip (SoC) impedance spectroscopy applications. It has been designed in a 0.18 μm-1.8 V CMOS technology as a self-contained oscillator, without the need for an external reference clock. The frequency can be digitally tuned from 10 to 345 kHz with 12-bit accuracy and a relative mean error below 1.7%, thus supporting a wide range of impedance sensing applications. The proposal is experimentally validated in two impedance spectrometry examples, achieving good magnitude and phase recovery results compared to the results obtained using a commercial LCR-meter. Besides the wide frequency tuning range, the proposed programmable oscillator features a total power consumption lower than 0.77 mW and an active area of 0.129 mm², thus constituting a highly suitable choice as stimulation module for instrument-on-a-chip devices.

Low-Power Photoplethysmogram Acquisition Integrated Circuit with Robust Light Interference Compensation

To overcome light interference, including a large DC offset and ambient light variation, a robust photoplethysmogram (PPG) readout chip is fabricated using a 0.13-μm complementary metal–oxide–semiconductor (CMOS) process. Against the large DC offset, a saturation detection and current feedback circuit is proposed to compensate for an offset current of up to 30 μA. For robustness against optical path variation, an automatic emitted light compensation method is adopted. To prevent ambient light interference, an alternating sampling and charge redistribution technique is also proposed. In the proposed technique, no additional power is consumed, and only three differential switches and one capacitor are required. The PPG readout channel consumes 26.4 μW and has an input referred current noise of 260 pArms.