In many applications, it is necessary to shield the touch sensors to prevent incorrect activation by the Electromagnetic Interference (EMI), or by touch contact at a location that is not intended to be touch-sensitive such as the PCB tracks leading to the sensor.
A variety of shield types may be used with self-capacitance sensors depending on the measurement technology.
These may be generally classed into ‘passive’ shield, where a shielding electrode is driven to a DC level, and ‘active’ shield, where the shield is driven with the same signal as the electrode being acquired.