Many electronic devices must be able to detect the world around them in order to function properly. A zoom cannot autofocus, an automatic faucet cannot start or stop, a robot cannot avoid obstacles if they can’t quickly detect their surroundings. There are many ways for smart products to sense their environment, but one tried-and-tested method is to use a Time-of-Flight (ToF) sensor.
STMicro broke the record for the world’s smallest ToF package at just 4.4 mm x 2.4 mm x 1.0 mm with its VL53L0X. On top of its amazing size, the chip offers great performance with an absolute range of two meters, the ability to detect objects independent of their reflectance, and measurement times of only 30 ms.
VL53L0X : Smaller, but More Powerful
VL53L0X Time-of-Flight Sensors
A ToF sensor emits a tiny laser beam burst, waits for it to bounce off an object, then determines its distance based on the time the light took to return. Despite a remarkably small size, what is even more fascinating is that ST is the only manufacturer at the moment able to integrate a 940-nm VCSEL laser inside such a package. A Vertical-Cavity Surface-Emitting Laser uses a series of mirrors to emit a light perpendicular to the substrate. VCSEL lasers offer many advantages over more traditional in-plane lasers, such as the ability to better focus on a particular wavelength, and the possibility of testing them at various stages of production, instead of waiting for the end of the manufacturing process.
The previous generation of ToF sensors used an 850-nm laser. By improving the design of its component, while still shrinking the packaging, ST was able to install a 940-nm laser. The greater wavelength massively improves performance and detects objects regardless of their surface’s reflectance. The reason is that this wavelength is completely invisible and thus is not affected by bright ambient light, meaning the VL53L0X will continue to offer precise measurements down to a few millimeters over a range of two meters whether it is used in a dark room or outside on a bright sunny day. It explains why the chip has found its way inside drones or robots that use the system for obstacles, walls, or cliff detection.
Inside the VL53L0X
Despite being able to pass through the eye of a needle, the packaging not only contains the laser, but the logic needed to process the information received, which means it can internally compute the object’s distance. Not only does it save resources by reducing the demands on the host controller, the whole system becomes more responsive, and measurements can take as little as 30 ms. The VL53L0X also uses a common I2C interface to simplify designs. This explains why the component is very popular in smartphones with camera autofocus as well as detection of the approach of the users ear to disable the screen touch detection. These devices must not only perform well no matter the light condition, they must also be easy to design-in and have fast performance to capture brief moments perfectly.
Finally, the new ToF sensor has a power consumption of only 20 mW in active ranging mode and only needs 5 µA in standby, which has enabled the VL53L0X to be integrated in small, low-power devices to add important features to connected objects and home appliances. It also means that engineers can easily use more than one VL53L0X without dramatically adding to the power envelope of their device.
Using multiple ToF can allow a system to detect the distance of objects coming from different directions, but also provides more accurate gesture detection, and enhances the environmental perception of robots. To aid creators, ST provides documentation to quickly help them determine which GPIO pins are available in each configuration and to give them the information they need to implement and manage this kind of design.