News: LEDs
4 December 2023
ams OSRAM launches multi-LED package that boosts heart rate and blood oxygen measurements for wearables
ams OSRAM GmbH of Premstätten, Austria and Munich, Germany has launched a new multi-LED package that offers more than 40% higher radiant intensity than the previous-generation product, resulting in higher-accuracy PPG (photoplethysmography) measurements in smart watches, wristbands and other wearable devices.
The SFH 7018 features a highly reflective QFN (quad flat no leads) package for significantly increased light output. In addition, an improved two-cavity design separates the green LED from the red LED and infrared (IR) LED: the spacing and optical isolation ensure that the light sources are optimally placed relative to their photodiodes and reduce interference between the green light (for heart-rate measurements) and the red light and IR source (for blood oxygen saturation, or SpO2, measurements). Furthermore, the green chip does not cause the red and IR chips to fluoresce due to cross-excitation from the shorter wavelength.
The optimized form factor of the surface-mount QFN package – just 0.6mm high – makes it easy to integrate the module into any type of wearable device. Despite its compact size, the SFH 7018 provides dual driving capability with optimized forward voltage headroom and reduced overall power consumption.
“By using the new SFH 7018, manufacturers of wearable devices can dramatically improve the quality of the optical signals on which heart rate and blood oxygen measurements are based, making them more accurate and reliable in all operating conditions,” says senior staff system architect Dr Sergey Kudaev. “The SFH 7018 can help to transform vital signs measurements into accurate and absolute determinations of heart rate, blood oxygen levels and even more advanced parameters, such as blood pressure.”
Higher radiant intensity increases signal-to-noise ratio
The SFH 7018’s improvement in radiant intensity is said to be dramatic: the red and IR LEDs are more than 40% brighter than in the existing SFH 7016, and the green LED in the SFH 7018A version of the product is 80% brighter, while in the SFH 7018B version the green LED is more than twice as bright. The brightness of the SFH 7018 at each of the red, green and IR wavelengths also greatly exceeds that of today’s best-performing competing product, it is claimed.
Since all vital signs monitoring devices face the challenge of detecting small modulations in already small light signals, the result of scattering and absorption in tissue (depending on various factors), the amount of light emitted by the LEDs strongly affects system performance. When more light is modulated by the blood flow and subsequently reaches the photodiode, signal quality improves, yielding higher accuracy and better repeatability of measurements. The SFH 7018 enables this superior performance by emitting more light into the body.
The SFH 7018 is available in two versions: SFH 7018A is optimized for low forward voltage at high currents, allowing for operation without a costly voltage booster. SFH 7018B is optimized for maximum radiant intensity. Both variants are in volume production now.
