Proximity sensor to control RF exposure from smartphones/tablets

November 12, 2015 // By Graham Prophet
With the aim of enabling phone and tablet makers to minimise radio frequency exposure in next generation handheld products, Semtech has developed a sensor that distinguishes human body from other objects and controls RF radiation for targeted SAR reduction.

SX9306 is a proximity sensors that allows selective reduction of radio-frequency power in mobile phones and tablets. It is an ultra-low power, capacitive proximity sensor with an on-chip smart engine for human body detection and advanced SAR (Specific Absorption Rate) control.

The on-chip smart engine can detect the permittivity of different surfaces, giving it the ability to accurately discriminate between inanimate objects or human body. Smart Phone manufacturers use this capability to program their devices to reduce RF emission power when a device is near a human body part. With higher RF-power devices and more extensive device usage, the SX9306 allows these manufacturers to proactively reduce SAR without affecting RF strength during normal usage.

SAR is the measure of the amount of RF power that is radiated into the human body when in a close proximity to a mobile device. In the U.S., SAR standards are set by the Federal Communications Commission (FCC) and these limits are often followed by other countries around the world. In Europe, the standard is set by CENELEC. In China, the standard is set by TENAA.

SX9306 is part of Semtech's SX9300 smart proximity sensing platform. The part has four high-resolution capacitive sensor inputs with sensing resolution of 0.08 femto-farad (fF). Each sensor also features a capacitance-offset compensation of up to 30 pF. With its integrated RF shield, the device provides very robust noise immunity and eliminates false triggers that commonly occur in these applications.

"The pervasiveness of smart devices and their usage has triggered an incredible revolution in the habit of human population world-wide. All manufacturers are looking at ways to reduce SAR without impacting the consumer's experience, which makes proximity sensors an ideal alternative," said David Wong, Product Line Director of Semtech Consumer Sensing Product Groups. "The SX9306 is our new flagship SAR proximity sensor because it offers the resolution and power draw required to seamlessly control RF performance without the user being