Gesture/touch sensor and controller achieves 15cm detection distance

January 19, 2017 // By Graham Prophet
ON Semiconductor’s high-integration capacitance-digital converter is an eight-channel device capable of sensitivity up to 150 mm away, and claims superior gesture sensing and enhanced touch performance for automotive and industrial systems

This touch/proximity sensing device, the LC717A30UJ high dynamic range capacitance-to-digital converter, uses mutual capacitance to detect changes in capacitance down to femtofarad (fF) levels. Parasitic capacitance cancellation raises the detector sensitivity, while its built-in noise rejection mechanism combats the effects of electromagnetic interference (EMI). The eight capacitance-sensing input channels optimise the LC717A30UJ for use in systems where an array of switches is required. The device includes an integrated multiplexer for input channel selection, analogue-to-digital converter, dual-stage amplifier that determines capacitance changes plus outputs analogue amplitude values, system clock, power-on reset circuit, and all the necessary control logic to create a total solution. Both I ²C and SPI interfaces are selectable based on the system application needs.

 

Range of 150 mm is, ON says, greater than any competing device and the higher sensitivity enables gesture motions as well as offering conventional touch functionality, enhancing control options to address a wide range of application scenarios. It is capable of operating with an airgap between the sensor/PCB and the protective cover - so engineers can eliminate the inclusion of a light guide from the assembly and reduce overall complexity. This device also includes an integrated automatic calibration function which optimises and self-calibrates total capacitance according to electrode, line capacitance, and surrounding environment, thus significantly accelerating system development cycle time as well as robustness in the field.

 

The LC717A30UJ delivers rapid responsiveness, with a measurement time of 16 msec for its eight sensing channels and runs off a +2.6 to +5.5V supply with a low-power standby mode of 1 µA. The high degree of integration means that minimal external components are required, thereby further reducing the bill of materials. To support the needs of automotive applications such as vehicle entry systems and dashboard controls, the device is AEC-Q100 compliant. With its high integration level and wide dynamic range, it can also be employed in a range of touch or gesture human