QT320-D View Datasheet(PDF) - Quantum Research Group
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QT320-D Datasheet PDF : 18 Pages
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If SC > 0, then PDC+1 sets the number of burst spacings,
Tbs, that determines the interval of drift compensation, where:
Tbs = SC x Ti
(Section 1.5.1)
Example:
then
PDC = 9,
Tbs = 100ms
(user setting)
Tpdc = (9+1) x 100ms = 1 sec.
If SC = 0, the result is multplied by 16, and Tbd becomes the
time basis for the compensation rate, where:
Tbd = Tbd1 + Tbd2 (Section 1.5.2)
Example:
then
PDC = 5,
Tbd = 31ms
(user setting)
Tpdc = (5+1) x 31ms x 16 = 2.98 sec
NDC operates in exactly the same way as PDC.
2.3 THRESHOLDS (THR1, THR2)
Range: 1..16; Default: 6
Affects sensitivity.
The detection threshold is set independently for each channel
via the cloning process. Threshold is measured in terms of
counts of signal deviation with respect to the reference level.
Higher threshold counts equate to less sensitivity since the
signal must travel further in order to cross the detection point.
If the signal equals or exceeds the threshold value, a
detection can occur. The detection will end only when the
signal become less than the hysteresis level.
2.4 HYSTERESIS (HYS1, HYS2)
Range: 0...16; Default: 2
Affects detection stability.
2.2.1 POSITIVE DRIFT COMPENSATION (PDC)
Range: 0..255; Default: 100; 255 disables
Ability to compensate for drift with increasing signals.
PDC corrects the reference when the signal is drifting up.
Every interval of time the device checks each channel for the
need to move its reference level in the positive direction in
accordance with signal drift. The resulting timing interval for
this adjustment is Tpdc.
This value should not be set too fast, since an approaching
finger could be compensated for partially or entirely before
even touching the sense electrode. Tpdc is common to both
sensing channels and cannot be independently adjusted.
2.2.2 NEGATIVE DRIFT COMPENSATION (NDC)
Range: 0...255 Default: 2; 255 disables
Aability to compensate for drift with decreasing signals.
The hysteresis levels are set independently for each channel
via the cloning process. Hysteresis is measured in terms of
counts of signal deviation below the threshold level. Higher
values equate to more hysteresis. The channel will become
inactive after a detection when the signal level falls below
THRn-HYSn. Hysteresis prevents chattering of the OUT pin
when there is noise present.
If HYS1 or HYS2 are set to a value equal or greater than
THR1 or THR2 respectively, the channel may malfunction.
Hysteresis should be set to between 10% and 40% of the
threshold value for best results.
If THR1 = 10 and HYS1 = 2, the hysteresis zone will represent
20% of the threshold level. In this example the ‘hysteresis
zone’ is the region from 8 to 10 counts of signal level. Only
when the signal falls back to 7 will the OUT pin become
inactive.
This corrects the reference level when the signal is
decreasing due to signal drift. This should normally be faster
than positive drift compensation in order to compensate
quickly for the removal of a touch or obstruction from the
electrode after a MOD
recalibration (Section 1.5.3).
This parameter is common to
both channels. The resulting
timing interval for this
adjustment is Tndc.
lQ
Figure 2-2 Detect Integrator Filter Operation
8
QT320/R1.03 08/02
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