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PDF QT60161B Datasheet ( Hoja de datos )

Número de pieza QT60161B
Descripción 16 KEY QMATRIX KEYPANEL SENSOR IC
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QT60161B datasheet

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QT60161B pdf
©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
Scope
Sync
Reset
X0
X1
X2
X3
Wake /
Sync
CS0A
CS0B
SPI
to Host CS1A
UART
to Host CS1B
CS2A
CS2B
Sample caps
CS0
CS1
CS2
CS3A
CS3B
CS3
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 keys
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

5 Page

QT60161B arduino
©Quantum Research Group Ltd.
the burst during which the key is being sensed, i.e. with a
very low duty cycle. Each additional key being detected will
also create a low pulse for that keys burst. During all other
times, the LED pin will be off (high).
This pin can be used to alert the host that there is key activity,
in order to further limit the amount of communication between
the device and the host. The LED / Alert line should ideally be
connected to an interrupt pin on the host that can detect a
negative edge, following which the host can proceed to poll
the device for keys.
3.18 ESD / Noise Considerations
In general the QT60161B will be well protected from static
discharge during use by the overlying panel. However, even
with a dielectric panel transients currents can still flow into
scan lines via induction or in extreme cases, dielectric
breakdown. Porous or cracked materials may allow a spark to
tunnel through the panel. In all cases, testing is required to
reveal any potential problems. The IC has diode protected
pins which can absorb and protect the device from most
induced discharges, up to 5mA.
This line also pulls low if there is a key error of any kind.
Note that in sleep mode if the LED was on prior to sleep, it
will remain on during sleep.
3.16 Oscilloscope Sync
See also Command ^R, page 26
The SOpin can output an oscilloscope sync signal which is
a positive pulse that brackets the burst of a selected key. This
feature is controlled by the ^R command. More than one burst
can output a sync pulse, for example if the scope of the
command when set is a row or column, or is all keys. The ^R
command is volatile and does not survive a reset or power
down.
This feature is invaluable for diagnostics; without it, observing
signals clearly on an oscilloscope for a particular burst is
nearly impossible.
This function is supported in QmBtn PC software via a
checkbox.
The X lines are not usually at risk during operation, since they
are low-resistance output drives. Diode clamps can be used
on the X and Y matrix lines if desired. The diodes should be
high speed / high current types such as BAV99 dual diodes,
connected from Vdd to Vss with the diode junction connected
to the matrix pin. Diode arrays can also be used.
Capacitors placed on the X and Y matrix lines can also help
to a limited degree by absorbing ESD transients and lowering
induced voltages. Values up to 100pF on the X lines and
22pF on the Y lines can be used.
The circuit can be further protected by inserting series
resistors into the X and/or Y lines to limit peak transient
current. RC networks as shown in Figures 4-6 and 4-7 can
provide enhanced protection against ESD while also limiting
the effects of external EMI should this be a problem.
External field interference can occur in some cases; these
problems are highly dependent on the interfering frequency
and the manner of coupling into the circuit. PCB layout
(Section 3.17) and external wiring should be carefully
designed to reduce the probability of these effects occurring.
3.17 Power Supply & PCB Layout
Vdd should be 5.0 volts +/- 5%. This can be provided by a
common 78L05 3-terminal regulator. LDO type regulators are
often fine but can suffer from poor transient load response
which may cause erratic signal behavior.
If the power supply is shared with another electronic system,
care should be taken to assure that the supply is free of
low-level spikes, sags, and surges which can adversely affect
the circuit. The devices can track slow changes in Vcc
depending on the settings of drift compensation, but signals
can be adversely affected by rapid voltage steps and impulse
noise on the supply rail.
Supply bypass capacitors of 0.1uF to a ground plane should
be used near every supply pin of every active component in
the circuit.
PCB layout: The PCB layout should incorporate a ground
plane under the entire circuit; this is easily possible with a
2-layer design. The ground plane should be broken up as
little as possible. Internal nodes of the circuit can be quite
sensitive to external noise and the circuit should be kept
away from stray magnetic and electric fields, for example
those emanating from mains power components such as
transformers and power capacitors. If proximity to such
components is unavoidable, an electrostatic shield may be
required.
The use of the Sync feature (Section 3.14) can be invaluable
in reducing these types of noise sources, but only up to a
point.
SPI / UART data noise: In some applications it is necessary
to have the host MCU at a distance from the sensor, perhaps
with the interface coupled via ribbon cable. The SPI link is
particularly vulnerable to noise injection on these lines;
corrupted or false commands can be induced from transients
on the power supply or ground wiring. Bypass capacitors and
series resistors can be used to prevent these effects as
shown in Figures 4-6 and 4-7.
4 Communications Interfaces
The QT60161B uses parallel, UART, and SPI interfaces to
communicate with a host MCU. The serial interfaces use a
protocol described in Section 5. Only one interface can be
used at a time; the interface type is selected by
resistor-coupled jumpers connected to pins X0OPA (pin 13)
and X0OPB (pin 14) shown in Table 4-1. See also Figure 3-2.
Further specific information on each interface type is
contained in the following sections:
SPI Slave-Only Mode:
SPI Master-Slave Mode:
UART Interface:
Parallel Interface:
Section 4.3
Section 4.4
Section 4.5
Section 4.7
4.1 Serial Protocol Overview
The SPI and UART interface protocols are based entirely on
polled data transmission, that is, the part will not send data to
the host of its own volition but will do so only in response to
specific commands from a host.
lQ
11 www.qprox.com QT60161B / R1.03

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