Technology Overview

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Technology Overview

STMicroelectronics offers capacitive sensing technology. This technology is based on:



The projected acquisition principle with STM8TL5x microcontrollers.

An overview of how it works: a capacitor is modified when the finger gets close to a sensor.

The finger changes the dielectric properties.

The sensor consists of two electrodes:



Tx driven by a port in output mode,



Rx in the return path to a dedicated port in read mode.

There is a sampling capacitor which stores the charges coming from the electrodes which

form a coupling capacitor with less capacitance than the sample one. When a finger

approaches, the dielectric (between the two electrodes) is modified and so the capacitance

decreases. As a consequence, the time taken to load the sample capacitor will increase and

this difference is used to detect if a finger is present or not.