A new photodiode offering superior performance for wearable vital sign monitoring applications

     Ams Osram introduces a new photodiode TOPLED D5140 SFH 2202. Compared with existing standard photodiodes, this photodiode has superior performance, higher sensitivity to visible light in the green part of the spectrum, and higher linearity.

     These improved features significantly reduce the impact of ambient light interference, resulting in higher quality light signals received, allowing smartwatches, activity trackers, and other wearables to more accurately measure heart rate and blood oxygen saturation (SpO2).

     Internal benchmarks by AMS Osram show that the TOPLED D5140 SFH 2202 is 30 times more linear in the infrared spectrum than a standard photodiode thanks to the optimization of the photodiode chip manufacturing process technology. In addition, the experimental data show that the sensitivity of photoplethysmography (PPG) is significantly higher at the wavelength of green light used for heart rate measurement. PPG technology measures heart rate by tracking the peaks and valleys of light absorption in blood vessels.

     By using the highly linear TOPLED D5140 SFH 2202 in PPG systems, wearable device manufacturers can enable their products to achieve higher SpO2 measurement accuracy under conditions of strong ambient light or rapid changes. For example, a typical example would be a user running or cycling through the shadows cast by tall buildings in a densely built urban area.

     Because the TOPLED D5140 SFH 2202 is more sensitive to green light wavelengths, the system is able to operate at lower LED light intensity, saving power and helping to extend battery life, while maintaining highly accurate measurements that provide superior heart rate measurement performance. The TOPLED D5140 SFH 2202 comes in a specially designed package with black sidewalls to minimize internal crosstalk, further reducing optical measurement errors and improving the stability of heart rate measurements.

     Florian Lex, Product Marketing Manager at AMS OSram, said: "In the wearable device market, high-end products provide users with reliable vital signs measurement capabilities, creating greater value for users. "By eliminating the high nonlinearity of photodiodes, which can affect the performance of SpO2 measurement circuits, AMS OSram can help wearables manufacturers differentiate their products in the highly competitive lifestyle technology market and stay ahead of the curve."