According to market research firm IDC, smartwatches, wristbands, and other wearable devices will continue to lead the wearable market in the coming years. IDC predicts that shipments of wearable devices will reach 40.7 million units in 2015, accounting for 90% of all wearable device shipments. Because wearable devices help people analyze their daily activities and significantly improve our lifestyles, related wearable technologies are receiving increasing attention.
We know that a typical wearable device integrates user data and external data analysis through an external device to display user information. The structure of a wearable device includes one or more sensors, storage devices, connectivity devices (RF controllers), a display screen, and a battery. Currently, the most well-known wearable electronic devices on the market are smartwatches, fitness trackers, and activity detectors. These devices measure and capture user information through one or more sensors. Therefore, wearable products have a high demand for sensors, driving the rapid growth of the entire sensor industry. According to Luo Guangchuan, product manager at Worldway, "Wearable devices have attracted widespread attention globally, and this trend is particularly evident in China. As a crucial component of wearable devices, sensors have become extremely sought after."
He stated that some newer wearable devices currently utilize optical sensors to track vital signs. Silicon Labs offers high-performance, low-power sensor products, such as UV sensors and infrared/ambient light sensors, capable of detecting UV index, ambient light, heart rate/pulse oxygen saturation, and 2D or 3D gestures. Worldway's broad target customer base has enabled significant growth in its sensor business. Luo Guangchuan explained, "For wearable devices, Silicon Labs' Si1132/4X series of biosensors are primarily used to measure heart rate, blood pressure, and track sunlight UV intensity, and these sensors are designed for miniaturization to address the challenges of the wearable field."
Figure 1: Si1132/4X proximity/ambient light/UV detector
The Si1132 is Silicon Labs' world's first single-chip digital UV index sensor, supporting UV index detection and making it a top choice for smart wearables and healthcare applications. Thanks to its integrated light sensor, the Si1132 automatically adjusts the display to optimize power consumption and improve eye comfort, and can be used with an accelerometer for sleep tracking. Moderate exposure to ultraviolet radiation is beneficial, but excessive exposure can cause deadly skin cancer. Luo Guangchuan stated, "In UV detection applications, the Si1132 provides real-time cumulative UV index irradiation, helping people reduce their risk of skin cancer and easily enjoy a healthy outdoor life. Therefore, the Si1132 has been successfully applied to health bracelets and health rings. In proximity/ambient light detection applications, the Si1132 has powerful long-distance proximity detection, reaching up to 2 meters indoors. Worldway is optimistic about the Si1132's display interface applications in IoT, industrial, and consumer electronics. The proximity function can be used to wake up devices. For example, IoT control panels detect human wake-up, remote controls detect human wake-up, video doorbells detect human wake-up, and contactless hand dryers, etc. Furthermore, the ambient light sensor automatically adjusts the display brightness, thereby improving readability, reducing eye strain, and lowering power consumption."
Figure 2: UV detection function of Si1132
In terms of specific product technology, the Si1132 boasts an exceptionally long battery life, consuming only 1.2uA at a 1Hz sampling frequency. It utilizes a 2×2×0.65mm QFN package and undergoes pre-shipment calibration to improve product consistency. The Si1132 is equipped with an I2C interface. Furthermore, its robust sensing architecture incorporates a photosensitive sensor with a sensitivity of up to 128klux, ensuring consistent performance even under wide dynamic range lighting conditions. Luo Guangchuan points out that the Si1132 single-chip solution integrates a photodiode, ADC, and signal processing functions, simplifying product design and providing high sensitivity, enabling operation under various materials, including dark glass.
In addition, Silicon Labs' Si114X series UV and IR proximity/ambient light sensors are identical to the Si1132 in terms of UV and ambient light functionality. The difference lies in the fact that the Si114X offers single, dual, and triple LED driver integration options depending on the model, and provides 15 selectable drive levels for gesture recognition. According to Luo Guangchuan, "The Si114X series can be applied to heart rate and blood oxygen measurement and biometrics, long-distance proximity detection up to 1.5m, and advanced 2D and 3D gesture detection. For example, LG's heart rate earphones use the Si114X." It's worth noting that the Si114X is also an innovative ultra-low power single-pulse sensor, minimizing the IR LED conduction time to 25.6µs. Luo Guangchuan particularly emphasized that the Si114X features multi-LED non-touch 2D and 3D gesture sensing, and has a very high dynamic range even under sunlight.
Figure 3: The Si114X integrates three LED drivers.
As shown in the diagram above, the Si114X can integrate up to three LED drivers. The LED drivers enable health and fitness trackers to measure heart rate and blood saturation via reflective methods, and the contactless interface allows for remote control by end users. The Si114X series internally includes one or more infrared LED drivers. The drive current can be set via a register. The driver drives an external infrared emitting diode to emit infrared light (wavelength range typically between 750 and 950 nm, with 850 nm being optimal). When a person or other object approaches, the emitted infrared light is reflected back to the proximity sensor's infrared receiving window. After internal ADC conversion, the light is sent to the MCU via I2C interface circuitry. The MCU can then determine the approach of a person or object based on the calculated light intensity. The Si1146 and Si1147 support advanced motion and gesture sensing. The Si1146 can achieve Z-axis and X-axis motion sensing and contactless control, while the Si1147 adds a third axis, enabling three-dimensional motion sensing. The reflective measurements provided by the two sensors can be post-processed for further gesture recognition.
Figure 4: Advantages of Si114x in gesture applications
In wearable product systems, a large number of discrete components not only increases the complexity of electrical compatibility and testing, but also increases power consumption, BOM cost, and PCB size. Silicon Labs' UV index sensor IC single-chip solution specifically addresses these issues. Luo Guangchuan stated that the solution's advantage lies in integrating a UV index sensor and digital processing circuitry into a single-chip IC within a 2mm×2mm package. In other words, 655 UV index sensor ICs can be housed within an 8.5-inch wide page. Due to its ultra-low power architecture, users of Silicon Labs UV index sensors can achieve thin, wearable designs with small batteries, while the average circuit power consumption is as low as 1.2 uA at a UV measurement rate of once per second, thus extending battery life. Luo Guangchuan stated, "Worldway not only provides a wide range of feature-rich sensor products, but we will also continuously deepen our cooperation with original equipment manufacturers (OEMs), leveraging Worldway's extensive distribution network to provide better service to our customers, while also offering timely field application support."
