heart rate variability, oxygen levels,
cardiac health, blood pressure, hemo-
globin, glucose, and body temperature.
Here, more sophisticated algorithms
combined with sleek new sensors
ensure that these health-care wearables
are far more accurate for many medical
use cases.
These types of medical wearables
are not only a growing market; their
focus on higher accuracy and greater
performance also makes them less
prone to price pressures that designers
commonly face in consumer wearables.
However, these medical designs face
the challenge of long qualification
periods. Here, validated and certified
sensor modules come into play.
Take the case of a reference design
for wearable devices providing 24/
cuffless blood pressure measure-
ment launched by the Premstaetten,
Austria-based sensor supplier ams.
It’s built around the AS7024 sen-
sor chip and software that conducts
blood pressure measurement, heart
rate measurement (HRM), heart rate
variability (HRV) monitoring, and
electrocardiograms (ECG).
The AS7024 sensor chip includes
three LEDs, photodiodes, an optical
front end and sequencer for HRM, and
an analog front end for ECG, a stan-
dard method for measuring the electri-
cal pulses generated by the sinoatrial
node. The sensor chip’s HRM opera-
tion is based on photoplethysmography
(PPG), a technique that uses sampling
light to measure the pulse rate in blood
vessels, which expand and contract as
blood pulses through them.
The accompanying software in this
reference design analyzes the synchro-
nized HRM and ECG measurements
to calculate blood pressure. According
to ams, the AS7024’s blood pressure
measurements have been validated in a
clinical trial at the Medical University
of Graz in Austria as per IEEE standard
for cuffless wearable devices.
Wearables’ power crunch
Power consumption, a crucial issue
in portable electronics, becomes even
more critical in wearable devices that
mostly offer always-on detection
and measurement functions. More-
over, wearable devices usually feature
smaller-capacity batteries due to size
constraints. Consequently, for sensing
designs in wearable devices, engineers
must choose between low power and
high performance.
Therefore, sensor makers are nowemploying innovating new techniques
to further lower the power draw from
always-on sensors without perfor-
mance and accuracy trade-offs. A new
crop of solutions combines MEMS
sensors with algorithms and firmware
that intelligently process, synthesize,
and calibrate the output of sensors.
A new position tracking sensorMEMS & Sensors for Wearables FEATURE 9
ELECTRONIC PRODUCTS • electronicproducts.com • JANUARY 2019