AT42QT1012_10 ATMEL [ATMEL Corporation], AT42QT1012_10 Datasheet - Page 9

• Manufacturer Part Number: AT42QT1012_10
• Description: One-channel Toggle-mode Touch Sensor IC with Power Management Functions
• Manufacturer: ATMEL [ATMEL Corporation]

3.7
3.8
9543D–AT42–08/10
Response Time
Spread Spectrum
Figure 3-3.
The QT1012's drift compensation is asymmetric; the reference level drift-compensates in one
direction faster than it does in the other. Specifically, it compensates faster for decreasing
signals than for increasing signals. Increasing signals should not be compensated for quickly,
since an approaching finger could be compensated for partially or entirely before even
approaching the sense electrode. However, an obstruction over the sense pad, for which the
sensor has already made full allowance, could suddenly be removed leaving the sensor with an
artificially elevated reference level and thus become insensitive to touch. In this latter case, the
sensor will compensate for the object's removal very quickly.
With large values of Cs and small values of Cx, drift compensation will appear to operate more
slowly than with the converse. Note that the positive and negative drift compensation rates are
different.
The QT1012's response time is highly dependent on the run mode and burst length, which in
turn is dependent on Cs and Cx. With increasing Cs, response time slows, while increasing
levels of Cx reduce response time.
The QT1012 modulates its internal oscillator by ±7.5 percent during the measurement burst.
This spreads the generated noise over a wider band, reducing emission levels. This also
reduces susceptibility since there is no longer a single fundamental burst frequency.
Threshold
Output
Drift Compensation
S ignal
R eference
H ysteresis
AT42QT1012
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