3.3 Lumped Sensor

A Lumped sensor is implemented as a combination of multiple sense lines (self-capacitance measurement) or multiple drive and sense lines (mutual capacitance measurement) to act as one single sensor. This provides the application developer with greater flexibility in the touch sensor implementation.

• Improve the touch sensor responsiveness by reducing the number of measurements and therefore, the time required for initial touch detection
• Fast position resolution by binary search
• Improved moisture rejection through ‘All but one’ key lumping in a touch button application
• Provide wake-on-touch functionality on any key (up to maximum capacitance limits) with significantly lower power consumption as only one sensor measurement is required for all keys
• Dual-purpose sensor electrodes – e.g., individual keys may be lumped together to form a proximity sensor

Touch detection on a lumped sensor is implemented in the same way as a single node touch button. The capacitance of the lump sensor is equal to or more than the sum of the individual sensors’ capacitance. Lumping too many sensor may result in saturation. In general, the capacitance of the self-capacitance sensor is higher than the mutual capacitance sensor. The number of sensor electrodes that can be lumped is relatively less for self-capacitance designs.