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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.


Experimental and simulated chip characterization results (a) DC response of the I/V converter; (b) Frequency response of the I/V converter; (c) Frequency response of the two band-pass filters.
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sensors-15-17076-f004: Experimental and simulated chip characterization results (a) DC response of the I/V converter; (b) Frequency response of the I/V converter; (c) Frequency response of the two band-pass filters.

Mentions: Figure 4a shows the measured DC output voltage of the op-amp I/V converter as the DC photocurrent is varied. As expected the output voltage increases linearly as the dc photocurrent increased until the output saturates at 3.1 V. Figure 4b shows the measured frequency response of the I/V converter at a typical current generated in the in vivo experiments (240 nA DC photocurrent). At low frequencies the transimpedance gain is 8 MΩ due to the 8 MΩ feedback resistor and the circuit has a −3 dB cut-off frequency at 30 KHz. By observing the ac amplitudes of the I/V converter and the two band-pass filters, the voltage gains of the band-pass filters are calculated and shown in Figure 4c. The band-pass filters have centre frequencies at 10 KHz and 19.9 KHz with −3 dB bandwidth of 2 KHz and 4 KHz respectively. The measured results including Vdc output of the transimpedance amplifier, transimpedance gain of the transimpedance amplifier, and the central frequency and bandwidth of the analogue band-pass filters are also illustrated by way of comparison in Figure 4 with Cadence simulation. It was found that the measured results, indicate <1% difference to the original design specification (as simulated).


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)

Experimental and simulated chip characterization results (a) DC response of the I/V converter; (b) Frequency response of the I/V converter; (c) Frequency response of the two band-pass filters.
© Copyright Policy
Related In: Results  -  Collection

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

sensors-15-17076-f004: Experimental and simulated chip characterization results (a) DC response of the I/V converter; (b) Frequency response of the I/V converter; (c) Frequency response of the two band-pass filters.
Mentions: Figure 4a shows the measured DC output voltage of the op-amp I/V converter as the DC photocurrent is varied. As expected the output voltage increases linearly as the dc photocurrent increased until the output saturates at 3.1 V. Figure 4b shows the measured frequency response of the I/V converter at a typical current generated in the in vivo experiments (240 nA DC photocurrent). At low frequencies the transimpedance gain is 8 MΩ due to the 8 MΩ feedback resistor and the circuit has a −3 dB cut-off frequency at 30 KHz. By observing the ac amplitudes of the I/V converter and the two band-pass filters, the voltage gains of the band-pass filters are calculated and shown in Figure 4c. The band-pass filters have centre frequencies at 10 KHz and 19.9 KHz with −3 dB bandwidth of 2 KHz and 4 KHz respectively. The measured results including Vdc output of the transimpedance amplifier, transimpedance gain of the transimpedance amplifier, and the central frequency and bandwidth of the analogue band-pass filters are also illustrated by way of comparison in Figure 4 with Cadence simulation. It was found that the measured results, indicate <1% difference to the original design specification (as simulated).

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.