AN-1103 Self-referencing Capacitive Touch Sensor

In a previous application note, AN-1077 Capacitive Touch Button Sensor, the GreenPAK algorithm involved comparing the RC oscillation frequency with a reference RC. The issue with that design lies with guaranteeing performance over temperature, voltage, and part to part variation. In this improved design, the GreenPAK compares the RC oscillation frequency with itself, not a reference RC. Using a differential instead of absolute measurement eliminates the need for a reference RC. Not only are fewer external components needed, we get more robust performance with less variables to account for. The improved algorithm can be implemented with any chip in the GPAK4 family. We are using a SLG46140 in this example.

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