Power Electronics
The photodiode works by shining light into the skin Different amounts of this light are absorbed by blood and the surrounding tissue The light that is not absorbed is reflected to the detector which determines pulse rates and oxygen saturation Image courtesy of Osram Opto

The photodiode works by shining light into the skin. Different amounts of this light are absorbed by blood and the surrounding tissue. The light that is not absorbed is reflected to the detector, which determines pulse rates and oxygen saturation. (Image courtesy of Osram Opto).

Optical Sensor Measures Pulse Rate and Blood Oxygen Level

The new SFH 7060 sensor from Osram Opto Semiconductors is designed to measure pulse rates and the oxygen saturation level of blood. It offers excellent signal quality and low energy consumption. The main market segment for this component includes mobile devices such as smart watches and fitness armbands for continuously monitoring fitness levels. This integrated optical sensor contains five light emitting diodes with three different wavelengths and one high-sensitivity photodiode.

The SFH 7060 is a further development of optical sensor SFH 7050, which Osram introduced in the fall of 2014. It performs the same functions as its predecessor but with improved power consumption and signal quality. The SFH 7060 consists of three green LEDs, one red LED, one infrared LED and one large-format photodiode, which is optically separated from the emitters by an opaque barrier. It works by shining light into the skin. Different amounts of this light are absorbed by blood and the surrounding tissue. The light that is not absorbed is reflected to the detector. Absorption measurements with different wavelengths are used to determine the pulse rate and the saturation level of oxygen in the blood.

Green light is best for measuring the pulse at the wrist. The SFH 7060 is equipped with three green LEDs with a wavelength of 530 nanometers (nm) based on the latest high-efficiency UX:3 chip technology from Osram. At their optimum operating point at a current of 20 mA, they are particularly efficient and typically deliver an optical output of 3.4 mW at a voltage of 3.2 V per chip. The higher light output, compared with the SFH 7050, results in better signal quality and more stable pulse measurements. The lower power consumption also means longer battery life in the device. 

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