Proximity capacitive sensing is a technology that enables touch detection by measuring capacitance, exhibiting a change in capacitance in response to a change in surrounding materials. Certain sensors gauge the change by generating an electric field (e-field) and measuring the attenuations suffered by this field. Unlike inductive sensors, a proximity capacitive sensor can detect anything that is either conductive or has different dielectric properties than the sensor’s electrodes’ surroundings. They are excellent touchpad enablers because we, humans, being mostly water, have a high dielectric constant, and we contain ionic matter, which makes us good electric conductors.

Freescale uses multiple technologies in its proximity capacitive sensors. The portfolio of MC33794, MC33941 and MC34940 products contains oscillator circuitry in the sensor integrated circuit (IC) to generate a high purity, low frequency 5V sine wave, tunable by an external 39k ohms load resistor. This AC signal is fed to a multiplexer, which directs the signal to a selected electrode or reference pin or to an internal measurement node. The IC automatically connects the unselected nodes to the circuit ground, and these act as the return path needed to create the e-field current.

Read more: Proximity Capacitive Sensor Technology for Touch Sensing Applications