Ams Osram Releases Low-Noise AFE Sensor for Vital Sign Monitoring

The holy grail of health monitoring technology is a design that integrates multiple vital sign measurements into a single device. This week, Ams Osram announced an integrated multi-vital sign monitoring device that may make such a solution possible in low-power wearables. The new chip, called the AS7058, includes functionality for photoplethysmogram (PPG), electrocardiogram (ECG), body impedance (BioZ), and electrodermal activity (EDA) measurements.

 

The AS7058 is an analog front end (AFE) designed to measure vital signs while extending battery run-time in smart watches, smart rings, and other wearables. Image (modified) used courtesy of Ams Osram

How does the AS7058 achieve these measurements, and what sets it apart in terms of integration and performance?

 

An AFE for Health-Monitoring Wearables

The AS7058 (datasheet linked) monitors various vital signs in a compact and efficient design, coming in a small 42-ball wafer-level chip scale package and measuring 2.82 mm × 2.55 mm.

 

Block diagram of the AS7058. Image used courtesy of Ams Osram

 

Below is a breakdown of each of the health monitoring measurements and how they are integrated into a wearable-friendly form factor.

 

Photoplethysmogram (PPG)

PPG is a non-invasive method used to detect blood volume changes inside human tissue. The process works by emitting light into the skin and measuring the amount of light either absorbed or reflected by the blood vessels, which varies with each heartbeat.

 

Working principles of PPG. Image used courtesy of MDPI

 

The AS7058’s PPG acquisition system is equipped with up to eight LEDs and eight photodiode inputs, powered by high-current programmable LED drivers. This system includes an advanced automatic offset control (AAOC) for ambient light suppression, enhancing measurement accuracy in various lighting conditions.

 

Electrocardiogram (ECG)

ECG leverages skin-mounted electrodes to measure the electrical activity generated by the heart as it contracts and relaxes. The resulting data can be vital for assessing heart health and detecting anomalies.

For ECG measurements, the AS7058 features a high input impedance, low noise, and high common-mode rejection ratio (CMRR) with programmable gain. It complies with IEC 60601-2-47 standards for ambulatory ECG systems, ensuring reliable and accurate heart monitoring.

 

Body Impedance (BioZ)

BioZ measures the impedance of body tissues to an applied electric current. It’s used to determine body composition, such as fat and muscle mass, and can also assess fluid status and cardiac output.

The BioZ channel in the AS7058, used for measuring body composition, is similarly advanced. It includes a low-pass filter, high input impedance, and a range of excitation currents and frequencies. This makes the device suitable for various applications, including fitness tracking and medical diagnostics.

 

Electrodermal Activity (EDA)

EDA measures the electrical conductance of the skin as an indicator of psychological or physiological arousal. The conductance, which varies with its moisture level, is influenced by the sweat glands, which are controlled by the sympathetic nervous system.

 

Advanced Integration for Better Wearables

The AS7058 from Ams Osram exemplifies the advanced integration prevalent in modern health monitoring technologies. By combining PPG, ECG, BioZ, and EDA measurements into a single, compact device, the AS7058 may be a comprehensive solution for both consumer and medical applications. Its design, including the advanced automatic offset control and high-resolution ADCs, enhances its reliability and accuracy in various environmental conditions. 

As the demand for integrated health monitoring solutions grows, devices like the AS7058 may play a crucial role in both enhancing individual wellness and advancing medical diagnostics.