QT60161B 查看數據表（PDF） - Quantum Research Group
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QT60161B Datasheet PDF : 36 Pages
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©Quantum Research Group Ltd.
Figure 1-5 Circuit Block Diagram
The threshold is user-programmed using the setup process
described in Section 5 on a per-key basis.
Vcc
Opt A Opt B
QT60161
LED
X0
Scope X1
Sync
X2
Reset X3
Wake /
Sync
CS0A
CS0B
SPI
to Host CS1A
UART
to Host CS1B
CS2A
CS2B
Sample caps
CS0
CS1
CS2
CS3A
CS3
CS3B
VREF
Sample
Y0 Y1 Y2 Y3
X0
X1
X2
X3
2.3 Hysteresis
See also command ^C and ^D, page 21
Refer to Figure 1-6. The QT60161B employs programmable
hysteresis levels of 12.5%, 25%, or 50% of the delta between
the reference and threshold levels. There are different
hysteresis settings for positive and negative thresholds which
can be set by the user. The percentage refers to the distance
between the reference level and the threshold at which the
detection will drop out. A percentage of 12.5% is less
hysteresis than 25%, and the 12.5% hysteresis point is closer
to the threshold level than to the reference level.
The hysteresis levels are set for all keys only; it is not
possible to set the hysteresis differently from key to key on
either the positive or negative hysteresis levels.
2.4 Drift Compensation
See also commands ^H, ^I, page 22
Signal levels can drift because of changes in Cx and Cs over
time. It is crucial that such drift be compensated, else false
detections, non- detections, and sensitivity shifts will follow.
The QT60161B can compensate for drift using two setups, ^H
and ^I.
2 Signal Processing
The device calibrates and processes signals using a number
of algorithms specifically designed to provide for high
survivability in the face of adverse environmental challenges.
The QT60161B provides a large number of processing
options which can be user-selected to implement very
flexible, robust keypanel solutions.
2.1 Negative Threshold
See also command ^A, page 21
The negative threshold value is established relative to a key’s
signal reference value. The threshold is used to determine
key touch when crossed by a negative-going signal swing
after having been filtered by the detection integrator (Section
2.6). Larger absolute values of threshold desensitize keys
since the signal must travel farther in order to cross the
threshold level. Conversely, lower thresholds make keys
more sensitive.
As Cx and Cs drift, the reference point drift-compensates for
these changes at a user-settable rate (Section 2.4); the
threshold level is recomputed whenever the
reference point moves, and thus it also is drift
compensated.
Drift compensation is performed by making the reference
level track the raw signal at a slow rate, but only while there is
no detection in effect. The rate of adjustment must be
performed slowly, otherwise legitimate detections could be
ignored. The devices drift compensate using a slew-rate
limited change to the reference level; the threshold and
hysteresis values are slaved to this reference.
When a finger is sensed, the signal falls since the human
body acts to absorb charge from the cross-coupling between
X and Y lines. An isolated, untouched foreign object (a coin,
or a water film) will cause the signal to rise very slightly due to
the enhanced coupling thus created. These effects are
contrary to the way most capacitive sensors operate.
Once a finger is sensed, the drift compensation mechanism
ceases since the signal is legitimately detecting an object.
Drift compensation only works when the key signal in
question has not crossed the negative threshold level
(Section 2.1).
The drift compensation mechanism can be made asymmetric
if desired; the drift-compensation can be made to occur in
one direction faster than it does in the other simply by setting
^H and ^I to different settings.
Figure 1-6 Detection and Drift Compensation
The threshold is user-programmed on a per-key
basis using the setup process (Section 5).
Reference
2.2 Positive Threshold
See also command ^B, page 21
The positive threshold is used to provide a
mechanism for recalibration of the reference point
when a key's signal moves abruptly to the positive.
These transitions are described more fully in
Section 2.7.
Hysteresis
Threshold
Output
Signal
lQ
5
www.qprox.com QT60161B / R1.03
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