A Sub-mW Fully-Integrated Pulse Oximeter Front-End

Abstract

This paper presents the implementation of the first fully integrated pulse oximeter front-end with a power consumption lower than 1 mW. This is enabled by system- and block-level noise optimisation, also detailed in the manuscript. The proposed design features an analogue feedback loop that enables fast and accurate regulation of the detected photocurrent level and a serial-to-parallel interface allowing for extensive programmability of several operation parameters. The front-end was fabricated in the AMS 0.35 μm technology and occupies an area of 1.35 mm(2). Extensive measured results, both electrical and physiological from human subjects are reported, demonstrating an estimated SNR of 39 dB and ability to detect 2% changes in SpO2, similar to commercial pulse oximeters. This is despite the constrained power consumption which amounts to 0.31 mW for the LEDs and 0.53 mW for the rest of the front-end from a 3.3 V supply. Statistical results from 20 chips verify good matching across the Red and Infrared channels of the front-end and the accurate operation of the proposed analogue feedback loop.

Comprehensive noise analysis in PPG read-out chains

“…ZTIA and CTIA, in terms of SNR, targeting a minimum SNR of 28.5 dB for an accuracy within 2 % of the S p O 2 (oxygensaturation) corresponding signal [5]. The SNR at the output of the ADC can be expressed as SN R = 10 log 10 S 2 N 2 = 10 log 10…”

“…Note that I ph is roughly linearly proportional to the LED current, i.e. LED power, through a constant representing the tissue attenuation, whose values range from 10 −3 to 10 −4 [5]. For a generic noise source, having a Power-Spectral Density (PSD) S n (f ), its corresponding noise variance, accounting for the effect of CDS, is equal to…”

“…The proposed analysis clarifies, by the means of analytical equations, the impact of the input photocurrent, the photodiode parasitic capacitance, the feedback impedance and the system bandwidth (BW) on the SNR of the two proposed front-end topologies. This allows to directly determine the minimum LED power for a targeted minimum SNR (28.5 dB) [5] and a set of design parameters.…”

A 172 $\mu$W Compressively Sampled Photoplethysmographic (PPG) Readout ASIC With Heart Rate Estimation Directly From Compressively Sampled Data

“…SI stage, apart from providing additional gain, also acts as a noise limiting filter [13]. This is particularly important in pulsed PPG acquisition systems, where the thermal noise originating from the OTA of the TIA exhibits noise peaking at high frequencies.…”

Design and simulation of an integrated optical CMOS heart rate sensor

“…A fully integrated CMOS sensor for blood flow imaging was reported recently [4]. However the published works [5][6][7][8][9] on the chip level designs of 978-1-4799-5475-9/14/$31.00 ©2014 IEEE Photoplethysmography and pulse oximeter are focused on individual low power circuits, and the systems were operated in transmission mode. This paper presents a single-chip reflectance PPG sensor using green light for heart rate monitoring.…”