at42qt2100 ATMEL Corporation, at42qt2100 Datasheet - Page 15

• Manufacturer Part Number: at42qt2100
• Description: Qtouch Touch Sensor Ic
• Manufacturer: ATMEL Corporation

4.3.3
4.3.4
4.3.5
4.3.6
9554CX–AT42–11/11
Detection Integrator Filter
Adjacent Key Suppression (AKS)
Autorecalibration (MOD)
Proximity Sensor
Detect Integrator (DI) filter confirmation reduces the effects of noise on key states. The DI
mechanism requires a specified number of measurements that qualify as detections (and
these must occur in a row) or the detection will not be reported.
In a similar manner, the end of a touch (loss of signal) also has to be confirmed over several
measurements.
The QT2100 provides a choice of either two or six DI measurements.
This patented feature works to prevent multiple keys from incorrectly responding to a single
touch. This can happen with closely spaced keys, or a scroll wheel that has buttons very near
it.
Adjacent Key Suppression
group of keys to suppress touch detections from those that have a weaker signal change than
the dominant one.
When enabled globally on the QT2100, AKS allows only one key or the scroll section to
indicate a touch at a time. The QT2100 has a range of preset AKS groupings, where only one
key in an AKS group can indicate a touch at any time while keys in different groups can
indicate touch in any combination.
AKS can also be disabled.
The device can time out and recalibrate all sensors after a continuous touch detection that
lasts for the chosen “Maximum on-duration” (MOD). This ensures that a key can never
become ‘stuck on’ due to foreign objects or other external influences. After recalibration the
key will resume normal functionality.
The nominal delay is selectable to be 10s, 20s, 60s, or infinite (disabled) though the actual
delay is different in Sleep mode, as timing is entirely driven by host communications.
The device also automatically recalibrates a key when its associated signal reflects a sufficient
decrease in capacitance from the reference level (signal error). In this case, unlike “MOD”
recalibration, only the key that shows a signal error is recalibrated.
This recalibration is triggered when the decrease in capacitance is seen on the key signal for
more than 1.5 seconds.
Usually, any key can be optimized for operation as a hand proximity sensor. The sensitivity
can be increased by a higher value of Cs.
However, If using AKS only channel seven can be used as a proximity sensor and the AKS
bits should be set to 101, to ensure that the proximity key does not lock out other keys or the
slider/wheel (see
Design of proximity electrodes requires care, so as to ensure that the electrode area is
maximized whilst ensuring adequate and easy coupling to a hand as it approaches the
equipment.
Table 5-2 on page
®
(AKS
®
) operates by comparing signal strengths from keys within a
21).
AT42QT2100
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