LED-based time-of-flight IC for object detection and distance measurement

Although Intersil’s ISL29501 time-of-flight (ToF) signal processing IC doesn’t have anything to do with the lighting applications I normally cover, I felt compelled to bring it to your attention because it’s one of the most innovative LED applications I’ve seen this year. The device requires little more than an external emitter (LED or laser) and a photodiode to implement a complete object detection and distance measurement solution that provides precision long-range accuracy up to 2m in both dark and bright ambient light conditions.

According to Intersil, the ISL29501 overcomes the shortcomings of traditional amplitude-based proximity sensors and other ToF solutions, most of which perform poorly in lighting conditions above 2,000 lux, or cannot provide distance information unless the object is perpendicular to the sensor. Alternative solutions do exist but, until recently, most of them have been be too expensive, bulky, or power hungry for use in small form factor, battery-powered applications. Unlike competitive solutions, the ISL29501 allows customers to select the emitter and photodiode of their choice and configure a low power ToF sensing system customized for their application.

In order to perform accurate, low-power proximity detection and distance measurement at up to 2m, Intersil integrates several innovative design features within the ISL29501. This includes an on-chip DSP that calculates ToF and an active ambient light rejection circuit to minimize the influence of ambient light during distance measurement. To prevent interference with other consumer products such as IR TV remote controls that operate at 40kHz, the IC’s emitter DAC uses a modulation frequency of 4.5 MHz. Achieving high accuracy is simplified thanks to the ISL29501’s programmable distance zones, which allow the user to define three ToF distance zones for determining interrupt alerts. The ToF system also performs system calibration to accommodate performance variations of the external components across temperature and ambient light conditions.

The ISL29501 includes several power-saving innovations that can greatly extend battery life in handheld applications. The TX emitter driver output is programmable (up to 255 mA), allowing system designers to select the desired current level for driving the external infrared (IR) LED or laser. This feature enables designers to strike an optimal balance between distance measurement, object detection, and power budget for their particular application. The device’s single shot mode provides additional power savings by allowing designers to define the sampling period for initial object detection and approximate distance, while continuous mode more accurately measures distance. The ISL29501 can also be combined with the ISL9120 buck-boost regulator to further reduce power consumption and extend battery life.

Intersil’s solution offers a compact form factor, low-power consumption, and superior performance, which make it well-suited for connected devices that make up the Internet of Things (IoT), as well as consumer mobile devices. Intersil also sees many potential applications for the device in the emerging commercial drone market. Speaking of drones, I’m sorely tempted to order up one of Intersil’s eval kits to experiment with an idea I’ve had for an auto-land system for quadcopter-style drones. And if Intersil could cut the price significantly (more about this shortly) I’ll also bet that the ISL29501 could become very popular for distance and proximity sensing in robotic applications.

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