Optical sensor for heart rate measurement in smart devices

February 22, 2016 // By Graham Prophet
GoerTek and Infineon have produced optical sensors for precise, ultra-low power heart rate monitoring for smart devices.

The high-resolution, highly integrated optical sensors are designed to deliver the precise measurement, small size and ultra-low power consumption demanded by ambient light sensing, proximity detection, heart rate and pulse oximetry monitoring applications such as headphones, fitness bands, smart watches and phones. They integrate three LED outputs, a photodetector, a low-noise analogue front-end, a digital interface and a state machine into a single die. For best application results the bare die is either packaged with an infrared or a green LED or can drive up to three external LEDs.

The sensors offer a fully integrated solution for optical heart rate measurement featuring an I²C interface for a programmable sample rate of up to 256 per second. This allows a significantly better signal-to-noise ratio (SNR) than discrete alternatives. Additionally, monitoring algorithms can filter out motion artifacts and deliver precise heart rate and pulse oximetry measurements during exercise. High optical sensor resolution enables accurate measurement across the widest possible variety of skin types, while high optical sensitivity reduces photo diode area and drives down LED power consumption with a typical 300 μA LED current on fair skin. A standby current of 0.3 μA further reduces power consumption.

Infineon and GoerTek sensor solutions are available either as bare die or as packaged products with application algorithms from Infineon’s partner GoerTek. Packages measure 3.94 x 2.36 x 1.35 mm. In addition to the bare die chips from Infineon, GoerTek is offering starter kits and demonstration boards for designers looking to rapidly evaluate and test the technology for use in their smart applications.

Infineon; www.infineon.com