Continuous Medical Monitoring Is Now a Reality With Sophisticated Smartwatch Circuitry

July 09, 2020 by Nicholas St. John

Smartwatches are increasingly used as medical devices. What's going on at the circuit level for these bio-metric wearables?

Recently, Qualcomm released the new Snapdragon Wear 4100 platform for next-generation smartwatch technology. According to the press release, the low-power hybrid architecture includes a super-fast system-on-chip (SoC), always-on co-processor, and platform power improvements from the original Snapdragon Wear 3100 platform (built in the 12nm technology node).


Mobvol smartwatches plan to integrate the new platform

Mobvol smartwatches plan to integrate the new platform. Screenshot used courtesy of Qualcomm

While this platform can be utilized in a myriad of applications, one of the stated purposes of smartwatches outfitted with this technology is health monitoring. This use case is but one example of how designers are building in medical diagnostic tools in wearables. For instance, smartwatches have the capability to monitor and detect parameters within the body, such as temperature and heart rate.

But how exactly does a smartwatch measure these variables on the circuit level? 


How Smartwatches Measure Biometrics

According to researchers at the University of Central Florida, there are some basic and innovative circuits to perform these tasks.


Heart Rate

First, to measure heart-rate, one can use an infrared emitter and receiver. The emitter will transfer light into the wrist, and the blood will reflect the light back at a magnitude directly proportional to the amount of blood flowing at that time.

That means that when the receiver detects the reflected light, it will see spikes during times of higher blood flow. These spikes can then be filtered into pulses via signal-shaping circuitry. The period of the pulse train produced from this is then used to determine heart rate.


Body Temperature

Another important measurement in smartwatches is body temperature—a metric employers are especially interested in as employees return to work post-COVID-19.


Simplified diagram of a temperature sensor used in an integrated circuit.

Simplified diagram of a temperature sensor used in an integrated circuit. Image used courtesy of Omega and the University of Central Florida

For this biometric, designers simply implement a temperature sensor via a thermistor. A thermistor is a resistor whose resistance changes based on the temperature. Through a current or voltage sensing circuit, the resistance can be measured accurately and interpreted into body temperature.


Movement Monitoring

Smartwatch circuitry can be customized based on specific health conditions as well.


Capacitors for position measurement.

Capacitors for position measurement. Image used courtesy of MIT

For example, to monitor a person with Parkinson’s disease, a customized smartwatch would include an accelerometer to sense spontaneous resting discharge, monitor the speed of muscle contractions, and alert the user of tremors.


ECGs and Blood-Oxygen Levels 

Smartwatches can also monitor ECG signals and blood-oxygen levels in wearers. IDTechEx explains how Apple has innovated ways for smartwatches to monitor ECG signals via an electrode measuring potential on the skin, as well as measuring oxygen saturation of the blood using a photonic sensing system similar to the heart-rate circuitry.


Blood Pressure

Omron has been able to utilize the same technology as heart-rate circuitry to measure blood pressure itself through the smartwatch. The capabilities of Omron and Apple’s monitoring algorithms are so robust that they have received FDA Class II clearance.

Overall, the sensor combinations available for body monitoring are only limited to what can be detected at skin level with smartwatch technology.


What Does a Health-Focused Smartwatch Include?

In order for a smartwatch to continuously monitor parameters such as heart rate—as well as support features like GPS tracking, wireless connectivity, and clock functions—you need hardware that’s up to the task. As an example of what this hardware stack might look like, we might consider the new Snapdragon Wear 4100 platform

  • SoC comprised of a quad-core A53 processor
  • LPDDR3 memory with 750 MHz capability
  • Extended discontinuous reception (eDRX) for low power
  • Qualcomm Adreno 504 class graphic processing
  • Support for CAT 4/3/1
  • Single/dual-antenna support
  • Always-on (AON) coprocessor
  • Up to 64K colors for image and video capture
  • Continuous heart-rate and sleep monitoring
  • Dynamic clock and voltage scaling
  • Low-power tracking support
  • Bluetooth 5.0


Block diagram of the Snapdragon Wear 4100+

Block diagram of the Snapdragon Wear 4100+. Image used courtesy of Qualcomm


Qualcomm has partnered with many companies, including imoo, the leading brand for kids smartwatches; Mobvol Inc.; am AI company; and Suunto. Each of these companies will create smartwatches centered around the Snapdragon Wear 4100 platform.


For COVID-19 and Beyond

Qualcomm is joining companies like Apple, Fitbit, Garmin, and Omron in the race to develop smartwatches that can be utilized as full-blown medical devices. Perhaps the trend for bio-measuring smartwatches is a manifestation of a more health-conscious society—one in which wearables may promote public safety.