AT42QT1110-AZ Ver la hoja de datos (PDF) - Atmel Corporation
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AT42QT1110-AZ Datasheet PDF : 50 Pages
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4.11 Signal Processing
4.11.1 Detection Integrator
The device features a detection integration mechanism, which acts to confirm a detection in a robust fashion. A per-
key counter is incremented each time the key has exceeded its threshold. When this counter reaches a preset limit
the key is finally declared to be touched. For example, if the DI limit is set to 10, then a key signal must fall by more
than the key threshold, and remain below that level for 10 acquisitions, before the key is declared to be touched.
Similarly, the DI is applied to a key that is going out of detect: it must take 10 acquisitions where the signal has not
exceeded its detect threshold before it is declared to leave touch.
4.11.2 Burst Length Limitations
The maximum burst length is 2048 pulses. The recommended design is to use a capacitor that gives a signal of
<1000 pulses.
The number of pulses in the burst can be obtained by reading the key signal (that is, the number of pulses to
complete measurement of the key signal) over the SPI interface (see Section 6.8 on page 27). Alternatively, a scope
can be used to measure the entire burst, and then the burst length divided by the time for a single pulse.
Note that the keys are independent of each other. It is therefore possible, for example, to have a signal of 100 on one
key and a signal of 1000 on another.
4.11.3 Adjacent Key Suppression Technology
The device includes the Atmel patented Adjacent Key Suppression (AKS) technology to allow the use of tightly
spaced keys on a keypad with no loss of selectability by the user.
AKS is enabled or disabled for each key individually; only one key out of those enabled for AKS may be reported as
touched at any one time. The first key touched dominates and stays in detect until it is released, even if another
stronger key is reported. Once it is released, the next strongest key is reported. If two keys are simultaneously
detected, the strongest key is reported, allowing a user to slide a finger across multiple keys with only the dominant
key reporting touch.
Each key can be enabled for AKS processing via the AKS mask (see Section 7.11 on page 34). Keys outside the
group of enabled keys may be in detect simultaneously.
AT42QT1110-MZ / AT42QT1110-AZ [DATASHEET]
21
9570J–AT42–05/2013
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