New Photodiode Improves Performance in Visible and IR Light Applications

These improved features enable smart watches, activity trackers and other wearable devices to measure heart rate and blood oxygen saturation (SpO2) more accurately, by substantially reducing the effect of interference from ambient light, and improving the quality of the received optical signal.

Benefiting from various optimizations of the process technology with which the photodiode die is fabricated, the TOPLED® D5140, SFH 2202 achieves 30 times higher linearity in the infrared spectrum than standard photodiodes, according to ams OSRAM internal benchmarking. Laboratory characterization also shows substantially increased sensitivity at the green wavelength used for heart rate measurement in photoplethysmography (PPG) – a technique that tracks the peaks and troughs of light absorption by blood vessels.

When used in PPG systems, the highly linear TOPLED® D5140, SFH 2202 will enable manufacturers of wearable devices to achieve much higher accuracy in SpO2 measurements in conditions exposed to strong or fast-changing ambient light intensity. A typical example of such conditions occurs when the user runs or cycles through a dense urban area and moves in and out of the shade thrown by tall buildings.

The TOPLED® D5140, SFH 2202’s higher sensitivity to green wavelengths improves heart rate measurement by enabling the system to operate with lower LED light intensity, saving power and helping to extend battery run-time, while maintaining highly accurate measurements. The TOPLED® D5140, SFH 2202’s specially designed package with black sidewalls minimizes internalcross-talk, further decreasing error in optical measurements and increasing the stability of heart rate measurements.

Florian Lex, Product Marketing Manager at ams OSRAM, said: ‘Premium products in the wearable device market add value by providing vital signs measurements that the user can trust. By designing out the photodiode’s high non-linearity, which impairs the operation of SpO2 measurement circuits, ams OSRAM is enabling wearable device manufacturers to differentiate their products and secure a higher premium positioning in the competitive market for active lifestyle technology products.’