Ultra-low noise AFE sensor technology targets wearables

2 mins read

ams OSRAM, a developer of intelligent sensors and emitters, has launched the AS7058, an analogue front end (AFE).

The device will enable manufacturers of smart watches, smart rings and other wearable devices to improve the accuracy and reliability of vital signs measurements derived from photoplethysmographic (PPG) or electrical signals while extending battery runtime.

The AS7058 also provides a new means for differentiating wearable products, introducing the capability to perform body impedance measurement, for analysis of body composition.

The AS7058’s ultra-low noise characteristics produce a very high optical signal-to-noise ratio of 120dB, which enables substantial improvements, compared to competing products, in PPG measurement performance in the parameters of heart rate, respiration rate, blood oxygen saturation (SpO2), and blood pressure.

The improved optical noise performance of the AS7058 has been achieved through a number of new developments including the integration of two low-noise, 20-bit analogue-to-digital converters (ADCs), the provision of integrated low-noise LED drivers, and the introduction of new automatic ambient light offset correction technology.

The signal-to-noise ratio of the AS7058 also enables wearable device manufacturers to reduce power consumption by driving the device’s LEDs at lower current while maintaining high signal integrity.

Commenting Florian Lex, Product Marketing Manager of ams OSRAM, said, “If the health monitoring outputs of smart watches can change from an approximate indicator of lifestyle factors to medically actionable data, the value of the product to the consumer will be dramatically enhanced. This is what the AS7058 helps to enable, by lowering the optical noise floor of the PPG measurements on which smart watches, smart rings and other wearable devices depend for high-quality vital signs data.”

The AS7058 incorporates a comprehensive set of capabilities for optical and electrical measurement of vital signs. It includes:

  • Two current sinks for driving eight LED emitters (four LEDs/current sink)
  • Eight photodiode inputs
  • Two 20-bit ADCs for PPG measurement
  • A 20-bit digital-to-analogue converter (DAC) for electrical measurements – electrocardiogram (ECG), body impedance measurement (BIO-Z), or electrodermal activity (EDA).

The device’s medical-grade ECG measurements conform to the specifications of the IEC 60601-2-47 standard.

The two PPG ADCs can also perform simultaneous photodiode data acquisition. Measurements of PPG and ECG signals can be synchronised to enable measurement of blood pressure.

This set of features has been integrated into a compact WLCSP chip which has dimensions of 2.8 mm x 2.5 mm x 0.5 mm.

Ams has a broad portfolio of optical and electrical products that provide a unified source of components and system know-how for every aspect of vital signs monitoring in consumer devices. Products for vital signs monitoring include: LEDs, photodiodes and temperature sensors as well as the AS705x series of AFEs.

The hardware products are supported by algorithms for measurement functions such as heart rate, respiration rate and SpO2.

ams OSRAM also supplies a complete hardware demonstration system for vital signs monitoring in a smart watch form factor.