Photodiode improves accuracy in medical wearables

Ams Osram has introduced the TOPLED D5140, SFH 2202 photodiode for wearable health trackers and medical diagnostics devices. The new photodiode offers improved performance compared to existing standard photodiodes, including higher sensitivity to visible light in the green part of the spectrum and higher linearity. 

(Source: ams Osram)

The TOPLED D5140, SFH 2202 achieves 30 times higher linearity in the infrared (IR) spectrum than standard photodiodes, according to ams OSRAM internal benchmarking. In addition, laboratory characterization shows increased sensitivity at the green wavelength used for heart rate measurement in photoplethysmography (PPG), which is a technique that tracks the peaks and troughs of light absorption by blood vessels, said the company.

Thanks to these improved features, wearable devices such as smart watches and activity trackers will be able to measure heart rate and blood oxygen saturation (SpO2) more accurately. This is achieved “by reducing the effect of interference from ambient light and improving the quality of the received optical signal,” said ams Osram.

(Source: ams Osram)

In addition, the photodiode will enable higher accuracy in SpO2 measurements in environments with strong or fast-changing ambient light intensity when used in PPG systems. An example cited is when a user runs or cycles through a dense urban area and moves in and out of shady areas.

The higher sensitivity to green wavelengths improves heart rate measurement by enabling the system to operate with lower LED light intensity, which saves power and helps to extend battery run-time, while maintaining high-accuracy measurements, according to the company.

The TOPLED D5140, SFH 2202, housed in a specially-designed package with black sidewalls, minimizes internal crosstalk, which further decreases errors in optical measurements and increases the stability of heart rate measurements, said ams Osram. The photodiode is in volume production now.