TSI Methods
KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016
NXP Semiconductors
3
Self-capacitive mode
The figure describes the touch sensor structure of the self-capacitive mode:
•
Cs: Intrinsic self-capacitance. 10pF ~ 50pF as usual.
•
ΔCs: Touch generated self-capacitance. 0.3pF ~ 2pF as usual.
•
Sensitivity of sensor: ΔCs/Cs. 1% 10% as usual.
Inside the TSI IP module, the charge transfer is operated by non-overlapping clock ph1/ph2 and trans-
conductance amplifier. The averaging current (icx) generates on Analog Front End and charges the
integration cap then the voltage ramp generates on vci as figure shown which is used to trigger the
comparator.
Block diagram of TSI self-capacitive mode
The following figure shows the timing of TSI measurement for the self-capacitive mode.
