at42qt1481 ATMEL Corporation, at42qt1481 Datasheet - Page 44

• Manufacturer Part Number: at42qt1481
• Description: 48-key Qmatrix Ic
• Manufacturer: ATMEL Corporation

5.9
5.10
44
Burst Length – BL
Adjacent Key Suppression Technology – AKS
AT42QT1481
Then, when the condition causing the negative swing ceases to exist (the object is removed) the
signal can suddenly swing back positive to near its normal reference.
It is almost always desirable in these cases to cause the key to recalibrate quickly so as to
restore normal touch operation. The time required to do this is governed by PRD. In order for
this to work, the signal must rise through the positive threshold level PTHR continuously for the
PRD period.
After the PRD interval has expired and the autorecalibration has taken place, the affected key
once again functions normally. PRD is set on a per-key basis.
The functioning of the PRD setting is determined by an offset to a lookup table, found on
page
feature.
PRD Typical values:
PRD Default value:
PRD Range:
The signal gain for each key is controlled by circuit parameters as well as the burst length.
The burst length is simply the number of times the charge-transfer (QT) process is performed on
a given X line. Each QT process is simply the pulsing of an X line once, with corresponding Y
lines enabled to capture the resulting charge passed through the keys capacitance Cx.
QT1481 uses a fixed number of QT cycles which are executed in burst mode. There can be up
to 64 QT cycles in a burst, in accordance with the list of permitted values shown in
page
Increasing burst length directly affects key sensitivity. This occurs because the accumulation of
charge in the charge integrator is directly linked to the burst length. The burst length can be set
on each X line individually; charge is captured on all Y lines simultaneously during the burst on
each X line.
Apparent touch sensitivity is also controlled by the Negative Threshold level (NTHR). Burst
length and NTHR interact. Normally burst lengths should be kept as short as possible to limit RF
emissions, but NTHR should be kept above 6 to reduce false detections due to external noise.
The detection integrator mechanism also helps to prevent false detections.
BL Typical values:
BL Default value:
BL Possible values:
This QT1481 incorporates Adjacent Key Suppression (AKS) technology that can be selected on
a per-key basis. AKS technology permits the suppression of multiple key presses based on
relative signal strength. This feature assists in solving the problem of surface moisture which can
bridge a key touch to an adjacent key, causing multiple key presses. This feature is also useful
for panels with tightly spaced keys, where a fingertip might inadvertently activate an adjacent
key.
57. The values of time can range from 0.1s to 25s. Setting the parameter to 0 disables the
57.
2, 3 (48, 64 pulses / burst)
2 (48 pulses / burst)
0, 1, 2, 3 (16, 32, 48, 64 pulses)
5 to 8 (0.7s to 2.0s)
6 (1 second)
0 – 15 (, 0.1 – 25s)
9621B–AT42–06/11
Table 5-7 on