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

He D, Morgan SP, Trachanis D, van Hese J, Drogoudis D, Fummi F, Stefanni F, Guarnieri V, Hayes-Gill BR - Sensors (Basel) (2015)

Bottom Line: The experimentally measured AC and DC characteristics of individual circuits including the DC output voltage of the transimpedance amplifier, transimpedance gain of the transimpedance amplifier, and the central frequency and bandwidth of the analogue band-pass filters, show a good match (within 1%) with the circuit simulations.With modulated light source and integrated lock-in detection the sensor effectively suppresses the interference from ambient light and 1/f noise.The single-chip sensor enables a compact and robust design solution that offers a route towards wearable devices for health monitoring.

View Article: PubMed Central - PubMed

Affiliation: Electrical System and Optics Research Division, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK. diwei.he@nottingham.ac.uk.

ABSTRACT
Pulse oximetry is a noninvasive and continuous method for monitoring the blood oxygen saturation level. This paper presents the design and testing of a single-chip pulse oximeter fabricated in a 0.35 µm CMOS process. The chip includes photodiode, transimpedance amplifier, analogue band-pass filters, analogue-to-digital converters, digital signal processor and LED timing control. The experimentally measured AC and DC characteristics of individual circuits including the DC output voltage of the transimpedance amplifier, transimpedance gain of the transimpedance amplifier, and the central frequency and bandwidth of the analogue band-pass filters, show a good match (within 1%) with the circuit simulations. With modulated light source and integrated lock-in detection the sensor effectively suppresses the interference from ambient light and 1/f noise. In a breath hold and release experiment the single chip sensor demonstrates consistent and comparable performance to commercial pulse oximetry devices with a mean of 1.2% difference. The single-chip sensor enables a compact and robust design solution that offers a route towards wearable devices for health monitoring.

No MeSH data available.


Optical setup for laboratory characterization of the I/V converter and band-pass filters. The ac and dc light levels of the λ = 640 nm red LED (KINGBRIGHT—L-7104SRC-J4) is controlled by a signal generator (Tektronix AGF3252). The reference photodiode (PDA520) has a known transimpedance gain and is used to calculate the light falling on the CMOS sensor.
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sensors-15-17076-f003: Optical setup for laboratory characterization of the I/V converter and band-pass filters. The ac and dc light levels of the λ = 640 nm red LED (KINGBRIGHT—L-7104SRC-J4) is controlled by a signal generator (Tektronix AGF3252). The reference photodiode (PDA520) has a known transimpedance gain and is used to calculate the light falling on the CMOS sensor.

Mentions: AC and DC laboratory test characterization of the I/V converter and band-pass filters were carried out. The experimental setup shown in Figure 3 uses a λ = 640 nm LED (KINGBRIGHT—L-7104SRC-J4) to produce the optical test signal. The intensity and modulation depth of the light are controlled by a signal generator (Tektronix AGF3252). The light is collimated by a 30 mm focal length bi-convex lens and passes through a beam-splitter which enables illumination of both the pulse oximetry sensor and a reference photodiode (PDA520, Thorlabs). The on chip 1 mm × 2.5 mm photodiode is an n-well-p-substrate type whose responsivity is approximately 0.3 A/W at a wavelength of 667 nm [15]. Table 1 shows the light power incident on the photodiode, the corresponding generated photocurrent and the voltage output of the transimpedance amplifier. It should be noted that the dark current output is 1.65 V representing the effective analogue ground in the circuit. The reference photodetector has known transimpedance gain of 106 V/A and is used to calculate the amount of light falling onto the sensor.


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

He D, Morgan SP, Trachanis D, van Hese J, Drogoudis D, Fummi F, Stefanni F, Guarnieri V, Hayes-Gill BR - Sensors (Basel) (2015)

Optical setup for laboratory characterization of the I/V converter and band-pass filters. The ac and dc light levels of the λ = 640 nm red LED (KINGBRIGHT—L-7104SRC-J4) is controlled by a signal generator (Tektronix AGF3252). The reference photodiode (PDA520) has a known transimpedance gain and is used to calculate the light falling on the CMOS sensor.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4541923&req=5

sensors-15-17076-f003: Optical setup for laboratory characterization of the I/V converter and band-pass filters. The ac and dc light levels of the λ = 640 nm red LED (KINGBRIGHT—L-7104SRC-J4) is controlled by a signal generator (Tektronix AGF3252). The reference photodiode (PDA520) has a known transimpedance gain and is used to calculate the light falling on the CMOS sensor.
Mentions: AC and DC laboratory test characterization of the I/V converter and band-pass filters were carried out. The experimental setup shown in Figure 3 uses a λ = 640 nm LED (KINGBRIGHT—L-7104SRC-J4) to produce the optical test signal. The intensity and modulation depth of the light are controlled by a signal generator (Tektronix AGF3252). The light is collimated by a 30 mm focal length bi-convex lens and passes through a beam-splitter which enables illumination of both the pulse oximetry sensor and a reference photodiode (PDA520, Thorlabs). The on chip 1 mm × 2.5 mm photodiode is an n-well-p-substrate type whose responsivity is approximately 0.3 A/W at a wavelength of 667 nm [15]. Table 1 shows the light power incident on the photodiode, the corresponding generated photocurrent and the voltage output of the transimpedance amplifier. It should be noted that the dark current output is 1.65 V representing the effective analogue ground in the circuit. The reference photodetector has known transimpedance gain of 106 V/A and is used to calculate the amount of light falling onto the sensor.

Bottom Line: The experimentally measured AC and DC characteristics of individual circuits including the DC output voltage of the transimpedance amplifier, transimpedance gain of the transimpedance amplifier, and the central frequency and bandwidth of the analogue band-pass filters, show a good match (within 1%) with the circuit simulations.With modulated light source and integrated lock-in detection the sensor effectively suppresses the interference from ambient light and 1/f noise.The single-chip sensor enables a compact and robust design solution that offers a route towards wearable devices for health monitoring.

View Article: PubMed Central - PubMed

Affiliation: Electrical System and Optics Research Division, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK. diwei.he@nottingham.ac.uk.

ABSTRACT
Pulse oximetry is a noninvasive and continuous method for monitoring the blood oxygen saturation level. This paper presents the design and testing of a single-chip pulse oximeter fabricated in a 0.35 µm CMOS process. The chip includes photodiode, transimpedance amplifier, analogue band-pass filters, analogue-to-digital converters, digital signal processor and LED timing control. The experimentally measured AC and DC characteristics of individual circuits including the DC output voltage of the transimpedance amplifier, transimpedance gain of the transimpedance amplifier, and the central frequency and bandwidth of the analogue band-pass filters, show a good match (within 1%) with the circuit simulations. With modulated light source and integrated lock-in detection the sensor effectively suppresses the interference from ambient light and 1/f noise. In a breath hold and release experiment the single chip sensor demonstrates consistent and comparable performance to commercial pulse oximetry devices with a mean of 1.2% difference. The single-chip sensor enables a compact and robust design solution that offers a route towards wearable devices for health monitoring.

No MeSH data available.