Proving the Business Case for the Internet of Things

Maxim combines PPG and ECG into mobile device

Steve Rogerson
January 22, 2019



Designers have been given an easier way to deliver photoplethysmogram (PPG) and electrocardiogram (ECG) measurements for health monitoring from a mobile, battery-powered device. A biosensor module from California-based Maxim Integrated is comprised of internal LEDs, photodetectors and an ECG analogue front-end.
 
This provides highly accurate, FDA-certifiable PPG and ECG performance in compact, power-saving designs, including mobile phones, laptops, tablets and smart speakers.
 
Delivering synchronised PPG and ECG measurements has been difficult because designers have had to use two separate biosensors that together consume more board space and power than a mobile device can typically afford. In addition, achieving high accuracy in the measurements has also been challenging, particularly in cases where sensor sensitivity might be impacted by low perfusion levels or dry skin.
 
The MAX86150 biosensor module overcomes these problems, sampling both PPG and ECG simultaneously to provide high sensitivity of pulse transit time. To reduce battery drain, the module can be shut down through software with near-zero standby current, allowing the power rails to remain powered at all times. The device is available in a 3.3 by 6.6 by 1.3mm, 22-pin optical module.
 
Accurate: at 136dB, the module’s common mode rejection ratio (CMRR), a measurement of noise rejection, is said to be the highest on the market. Its 100mA-capable, high-dynamic-range LED driver enables higher sensitivity on an array of skin types. A low-impedance contact for the ECG sensor enables more accurate measurements, even in cases of dry skin.
 
Battery drain is reduced with a shutdown current of 0.7µA typical. Low power consumption extends battery life.
 
Its dry electrode operation eliminates the need for gels, fluids and sticky or wet pads on other parts of the body to obtain accurate readings.
 
The same size as a stand-alone ECG sensor, integrating an ECG sensor with an optical PPG sensor saves space and provides more functionality without requiring a third electrode.
 
“The MAX86150 is another important breakthrough at Maxim, continuing the company’s push to enable a healthier world,” said Mohammad Zarghami, executive business manager at Maxim Integrated. “With highly accurate heart-rate measurements from a compact, low-power device, consumers will be empowered to be more proactive about their healthcare.
 
Designers of always-on wearable and IoT devices have an easier way to extend battery runtime while shrinking form factor with a power-management IC (PMIC) from Maxim Integrated. The MAX20345 integrates a lithium charger and debuts an architecture that optimises the sensitivity of optical measurements for wearable fitness and health applications.
 

 
In wearables, optical-sensing accuracy is impacted by a variety of biological factors unique to the user. Designers have been striving to increase the sensitivity of optical systems, in particular the signal-to-noise ratio (SNR), to cover a broader spectrum of use cases. Traditional low-quiescent-current regulators favoured in wearable applications come with trade-offs that degrade SNR on the wrist, such as high-amplitude ripple, low-frequency ripple and long-settling times. Some designers have even turned to high-quiescent-current alternatives to overcome these drawbacks, but they must deal with increased power consumption, which reduces battery runtime or requires a larger battery.
 
The MAX20345 has a buck-boost regulator based on an architecture that’s optimised for highly accurate heart-rate, blood-oxygen (SpO2) and other optical measurements. The regulator delivers low-quiescent-current performance without the drawbacks that degrade SNR and, as a result, can increase performance by up to 7dB depending on measurement conditions.
 
“With sales of fitness and wellness wearable electronics expected to rise to over 114 million units by 2020, there is increasing demand for better, more precise sensing technology for measuring health vitals including heart rate and blood-oxygen levels,” said Kevin Anderson, senior analyst for power semiconductors at IHS Markit.
 
Frank Dowling, director of business management at Maxim Integrated, added: “Maxim is continuing to deliver precedent-setting innovations in the wearable healthcare arena. Our new MAX20345 extends our portfolio of ultra-low-power PMICs for wearable and always-on applications, bringing to the market a solution that enables the highest sensitivity optical sensing in wrist-worn form factors for more accurate vital-sign measurements.”