Where
S_CTRIM: is internal trim capacitance which can be configured by S_CTRIM <2:0>.
S_XDN: is parameter of analog front end which can be configured by S_XDN<2:0>.
S_CTRIM, S_XDN, S_XCH can be used to adjust the sensitivity. The intrinsic sensitivity
of sensor is given by ∆Cs/Cs. With this option, sensitivity can be improved to ∆Cs/(Cs-
S_CTRIM*(S_XDN/S_XCH)).
If touch sensor encounters strong low frequency noise, noise cancellation can be
activated by setting S_NOISE. The formula is given by
Where
Vddlv: is internal power supply voltage. Typical 1.2V.
During noise cancellation mode, vdd3v and vddlv are dual sample voltages. Analog front
end samples twice which includes charging phase (sampling vdd3v) and discharging
phase (sampling vddlv). At the end of each second phase, low frequency noise will be
subtracted. In a long integration period, the noise induced error can be cancelled.
Example
In one typical case, Ci=90 pF, Cx=25 pF, vdd3v=3.3 V, DVOLT=1 V, S_XIN=1/8,
S_XCH=1/8; Dec=8, Order=2.
Then,
NSTEP=69; TSICNT=4416; SCANTIME = 1.117 ms.
NOTE
Do not set S_SEN and S_NOISE at the same time.
48.5.4 Mutual-cap sensing mode
Chapter 48 Touch Sensing Input (TSI)
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
NXP Semiconductors
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Summary of Contents for Kinetis KE1xZ256
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