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Photodiode and analog front end integrated SpO2 sensor for wearables

Date: 17/09/2020
ams launched a transducer and analog front-end integrated sensor device to measure blood oxygen level packing highly sensitive photo-diode, four LED drivers, an analog front end, and a sequencer. The new AS7038RB SpO2 sensor targets both consumer wearables such as earbuds, smart watches and wristbands and exclusive medical devices including patches and oximeters.

AS7038RB SpO2 sensor is also suggested for remote diagnostic equipment, such as disposable patches used for SpO2 and electro-cardiogram (ECG) measurement in hospital emergency rooms.

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The devices made out of this sensor detects symptom of the COVID-19 disease and any such lung-infection related diseases before the onset of breathing difficulty in some at-risk patients and help in the treatment of people infected with the SARS-CoV-2 virus.

Wim Renirie, Vice President and General Manager for the Accessory and Wearable Solutions Business Line at ams, said "The introduction of the AS7038RB marks another ams breakthrough in technology for remote diagnostics. Ams is working actively with a range of partners to develop innovative solutions for the testing and diagnosis of COVID-19. The AS7038RB offers an additional diagnostic tool, enabling the creation of wearable and disposable equipment for monitoring blood oxygen saturation accurately and safely, without requiring the presence of a medical practitioner."

The physical dimensions of AS7038RB sensor makes it a choice where space is an issue. AS7038RB housed in a package with a footprint of 3.70mm x 3.10mm and is 0.65mm thin. Ams provides application software for SpO2 and heart rate measurement. The analog front end also supports concurrent ECG measurement complying with the requirements of the IEC 6060-2-47 medical standard.

Ams claims the accuracy of the AS7038RB's SpO2 measurements, very closely matching the outputs from medical-grade pulse oximeters used in hospital testing facilities, is in part due to the unique on-wafer interference filter technology developed by ams. The filter enables the AS7038RB to capture optical signals in the 590nm-710nm and near infrared (800nm-1050nm) wavelength bands of inter-est for SpO2 measurement, while blocking interference from ambient light at other wavelengths.

Ams suggests when AS7038RB combined with ams high-sensitivity photodiode, which has a large light-sensitive area of 2.5mm2, this produces a very high optical signal-to-noise ratio and eases implementation in optically challenging applications such as disposable chest patches, wristbands, and smart watches.

By having built-in drivers to support four external LEDs, AS7038RB allows OEM product developers to place these external LEDs in optimal positions of the patient's body such as wrist, chest, forehead and finger depending on the skin thickness and bone structure.

High sensitivity and high signal ratio of the sensor enable it to work with low optical power output from the LEDs.

The drive current of integrated LED drivers can be adjusted to balance system power consumption and measurement performance to reduce the power consumption particularly in application such as earbuds with tiny batteries having extremely low amphour rating.

AS7038RB is sampling now and mass production in October.

Ams has also announced the AS7038GB, a version of the sensor with peak sensitivity at the 525nm (green) wavelength for use in heart rate (HRM) and heart rate variability (HRV) measurement. A modular version, the AS7030B HRM/HRV sensor, integrates two 535nm LEDs in a single package measuring 3.55mm x 6.2mm x 1mm.