©Quantum Research Group Ltd.
Drift compensation should usually be set to compensate
2.7 Positive Recalibration Delay
See also command ^K, page 23
faster for increasing signals than for decreasing signals.
Decreasing signals should not be compensated quickly, since
an approaching finger could be compensated for partially or
entirely before even touching the touch pad. However, an
obstruction over the sense pad, for which the sensor has
already made full allowance for, could suddenly be removed
leaving the sensor with an artificially suppressed reference
level and thus become insensitive to touch. In this case, the
sensor should compensate for the object's removal by raising
the reference level quickly.
A recalibration can occur automatically if the signal swings
more positive than the positive threshold level. This condition
can occur if there is positive drift but insufficient positive drift
compensation, or if the reference moved negative due to a
recalibration, and thereafter the signal returned to normal.
As an example of the latter, if a foreign object or a finger
contacts a key for period longer than the Negative Recal
Delay, the key is recalibrated to a new lower reference level.
Then, when the condition causing the negative swing ceases
to exist (e.g. the object is removed) the signal can suddenly
swing back positive to near its normal reference.
The drift compensation rate can be set for each key
individually, and can also be disabled completely if desired on
a per-key basis.
It is almost always desirable in these cases to cause the key
to recalibrate to the new signal level so as to restore normal
touch operation. The device accomplishes this by simply
setting Reference = Signal.
Drift compensation and the detection time-outs (Section 2.5)
work together to provide for robust, adaptive sensing. The
time-outs provide abrupt changes in reference location
depending on the duration of the signal 'event'.
The time required to detect this condition before recalibrating
is governed by the Positive Recalibration Delay command. In
order for this feature to operate, the signal must rise through
the positive threshold level (Section 2.2) for the proscribed
interval determined by Setup ^K.
2.5 Negative Recalibration Delay
See also command ^L, page 23
If a foreign object contacts a key the key's signal may change
enough in the negative direction, the same as a normal
touch, to create an unintended detection. When this happens
it is usually desirable to cause the key to be recalibrated in
order to restore its function after a time delay of some
seconds.
After the Positive Recal Delay interval has expired and the
fast-recalibration has taken place, the affected key will once
again function normally. This interval can be set on a per-key
basis; it can also be disabled by setting ^K to zero.
The Negative Recal Delay timer monitors this detection
duration; if a detection event exceeds the timer's setting, the
key will be recalibrated so that it can function thereafter. The
^L function can be altered on a key by key basis. It can be
disabled if desired by setting the ^L parameter to zero, so that
it will never recalibrate automatically.
2.8 Reference Guardbanding
See also commands ^N, ^O, page 23; ‘L’, page 24
The QT60161B provides for a method of self-checking that
allows the host to ascertain whether one or more key
reference levels are 'out of spec'. This feature can be used to
determine if an X or Y line has broken, the matrix panel has
delaminated from the control panel, or there is a circuit fault.
2.6 Detection Integrator
See also command ^J, page 22
Reference guardbanding alerts the host when the reference
level of a key falls outside of user-defined levels. The
reference guardband is determined as a percent deviation
from the 'locked' reference level for each individual key.
These reference levels can be stored into internal eeprom via
the Lock command 'L' during production; deviations in
reference levels that fall outside the guardbands centered on
these locked reference levels are then reported as key errors.
To suppress false detections caused by spurious events like
electrical noise, the QT60161B incorporates a 'detection
integrator' counter that increments with each detection
sample until a user-defined limit is reached, at which point a
detection is confirmed. If no detection is sensed on any of the
samples prior to the final count, the counter is reset
immediately to zero, forcing the process to restart.
The amount of guardbanding can be set differently for each
signal direction relative to the stored and locked levels. The
possible settings are from 0.1% to 25.5% of signal reference
in steps of 0.1% as set by commands ^N (positive swings)
and ^O (negative swings). A setting of 0 (zero) disables the
corresponding guardband direction.
When an active key is released, the counter must count down
to zero before the key state is set to 'off'. Setting a key’s
detection integrator target value to zero disables that key
although the bursts for that key continue normally.
The detection integrator is extremely effective at reducing
false detections at the expense of slower reaction times. In
some applications a slow reaction time is desirable; the
detection integrator can be used to intentionally slow down
touch response in order to require the user to touch longer to
operate the key.
Once the L command has recorded all values of signal
reference into eeprom, and if guardbanding is enabled, the
part will compare the actual reference level of each key to its
corresponding guardbands to see if it falls outside of these
limits. If so, either of bits 2 and 3 of command 'e' will be set
for that key. The error will also appear in a bitfield reported
via command 'E'.
There are 16 possible values for this function.
2.9 Adjacent Key Suppression (‘AKS’)
See also command ^P, page 24
The QT60161B incorporates adjacent key suppression
(‘AKS’) that can be enabled on a per-key basis. AKS permits
lQ
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