Create the finest wearable electronics utilizing the most sensitive photodiode
Heart rate measurement is one of the key features in health and fitness devices. Both high accuracy and long battery lifetime are needed to differentiate in competition. A trade-off between accuracy and low power consumption is a challenge which development engineers face time after time.
Photodiode is the source of the raw signal in the system. ElFys offers the most sensitive photodiodes available on the market. It achieves nearly 100% Quantum Efficiency in green light and beyond. More sensitive photodiode offers better measurement data accuracy with given LED driving current. On the other hand, the more sensitive the photodiode is, the less current is needed to drive the LEDs. Another system design factor is that footprint of the photodiode can be optimized which allows designers to create wonderful smart watches and smart jewelries.
Health monitoring or physical condition tracking is commercialized in various application scenarios, and it will thrive more rapidly in everyday life in the future. PPG is the fundamental approach to enable the measurement of heart rate and blood oxygen level by using optical sensors.
Green light has been used to measure heart rate. The volume of blood in skin varies along the cardiac cycle, hence the absorption of the green light and therefore reflection of the green light from the skin changes periodically. The frequency of optical signal variation of the green light represents the heart rate. Similarly, the absorption of the light varies according to the oxygen level bonded with haemoglobin in the blood. Since red light and NIR are more sensitive to the oxygen level, their reflection signals are mostly used to calculate that.
ElFys offers the most sensitive photodiodes with black silicon induced junction technology compared to the other state of the art technology as shown in the picture below. As high as 50% improvement of photosensitivity in Green light is achieved, and additional 15% improvement of photosensitivity in Red light is achieved. Another benefit of the high sensitivity of the photodiode is that it enables less light to achieve equivalent precision, which means less power consumption. This extends battery lifetime at given measurement frequency.
In wearable devices like smartwatches, chest straps, wristband, smart rings, etc. both high accuracy measurement and long battery lifetime are needed to satisfy the end customers. Among all other components, photodiode is the key sensor to catch the light signal reflected from the skin. Therefore, the performance of the photodiode determines the quality of raw data regardless of the software AI algorithm used afterwards. One of the most important parameters of photodiode is sensitivity. Higher sensitivity with given noise means higher SNR (signal noise ratio) resulting in more accurate measurement capability to detect smaller signals which were invisible before.