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Электронный компонент: QT60161B

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L
Q
QT60161B
16 K
EY
QMatrix
TM
K
EYPANEL
S
ENSOR
IC
Advanced second generation QMatrix controller
16 touch keys through any dielectric
100% autocal for life - no adjustments required
SPI Slave or Master/Slave interface to a host controller
Parallel scan interface for electromechanical compatibility
Keys individually adjustable for sensitivity, response time,
and many other critical parameters
Sleep mode with wake pin
Synchronous noise suppression
Mix and match key sizes & shapes in one panel
Adjacent key suppression feature
Panel thicknesses to 5 cm or more
Low overhead communications protocol
44-pin TQFP package
APPLICATIONS -
Automotive panels
Machine tools
ATM machines
Touch-screens
Appliance controls
Outdoor keypads
Security keypanels
Industrial keyboards
The QT60161B digital charge-transfer ("QT") QMatrixTM IC is designed to detect human touch on up 16 keys when used in
conjunction with a scanned, passive X-Y matrix. It will project the keys through almost any dielectric, e.g. glass, plastic, stone,
ceramic, and even wood, up to thicknesses of 5 cm or more. The touch areas are defined as simple 2-part interdigitated
electrodes of conductive material, like copper or screened silver or carbon deposited on the rear of a control panel. Key sizes,
shapes and placement are almost entirely arbitrary; sizes and shapes of keys can be mixed within a single panel of keys and can
vary by a factor of 20:1 in surface area. The sensitivity of each key can be set individually via simple functions over the SPI or
UART port, for example via Quantum's QmBtn program, or from a host microcontroller. Key setups are stored in an onboard
eeprom and do not need to be reloaded with each powerup.
The device is designed specifically for appliances, electronic kiosks, security panels, portable instruments, machine tools, or
similar products that are subject to environmental influences or even vandalism. It can permit the construction of 100% sealed,
watertight control panels that are immune to humidity, temperature, dirt accumulation, or the physical deterioration of the panel
surface from abrasion, chemicals, or abuse. To this end the device contains Quantum-pioneered adaptive auto self-calibration,
drift compensation, and digital filtering algorithms that make the sensing function robust and survivable.
The part can scan matrix touch keys over LCD panels or other displays when used with clear ITO electrodes arranged in a matrix.
It does not require 'chip on glass' or other exotic fabrication techniques, thus allowing the OEM to source the matrix from multiple
vendors. Materials such as such common PCB materials or flex circuits can be used.
External circuitry consists of a resonator and a few capacitors and resistors, all of which can fit into a footprint of less than 6 sq. cm
(1 sq. in). Control and data transfer is via either a SPI or UART port; a parallel scan port provides backwards compatibility with
scanned electromechanical keys.
The QT60161B makes use of an important new variant of charge-transfer sensing, transverse charge-transfer, in a matrix format
that minimizes the number of required scan lines. Unlike some older technologies it does not require one sensing IC per key.
The QT60161B is identical to earlier QT60161 in all respects except that the device exhibits lower signal noise. This
device replaces QT60161 parts directly. After December 2003 the QT60161 will no longer be sold.
lQ
Copyright 2001 Quantum Research Group Ltd
Pat Pend. R1.03/04.03
QT60161B-AS
-40
0
C to +105
0
C
TQFP Part Number
T
A
AVAILABLE OPTIONS
SS
SO
VRE
F
DR
DY
LE
D
Vs
s
Vd
d
CS
0
A
CS
0
B
CS
1
A
CS
1
B
SM
P
X0
O
P
A
X1
O
P
B
X2
X3
Vd
d
Vs
s
XS
0
XS
1
XS
2
XS
3
MOSI
MISO
SCK
RST
Vdd
Vss
XTO
XTI
RX
TX
WS
YS0
YS1
YS2
YS3
AVdd
AGnd
Aref
CS3B
CS3A
CS2B
CS2A
1
2
3
4
5
6
7
8
9
10
11
23
24
25
26
27
28
29
30
31
32
33
44 43 42 41 40 39 38 37 36
34
35
12 13 14
22
21
19 20
18
17
16
15
QT60161B
TQFP-44
18
y 0x79 - Column Keys Scope
. . . . . . . . . . . . . . . . . . . . . . . . . . .
18
x 0x78 - Row Keys Scope
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
S 0x53 - All Keys Scope
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
s 0x73 - Specific Key Scope
. . . . . . . . . . . . . . . . . . . . . . . . . . .
18
5.2 Scope Commands
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
p 0x70 - Put Command
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
g 0x67 - Get Command
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
5.1 Put / Get Direction Commands
. . . . . . . . . . . . . . . . . . . . .
17
5 Commands & Functions
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
4.8 Eeprom Corruption
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
4.7 Parallel Scan Port
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
4.6 Sensor Echo and Data Response
. . . . . . . . . . . . . . . . . .
14
4.5 UART Interface
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
4.4 SPI Master-Slave Mode
. . . . . . . . . . . . . . . . . . . . . . . . . .
12
4.3 SPI Slave-Only Mode
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
4.2 SPI Port Specifications
. . . . . . . . . . . . . . . . . . . . . . . . . . .
11
4.1 Serial Protocol Overview
. . . . . . . . . . . . . . . . . . . . . . . . . .
11
4 Communications Interfaces
. . . . . . . . . . . . . . . . . . . . . . . . . .
11
3.18 ESD / Noise Considerations
. . . . . . . . . . . . . . . . . . . . . .
11
3.17 Power Supply & PCB Layout
. . . . . . . . . . . . . . . . . . . . .
11
3.16 Oscilloscope Sync
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
3.15 LED / Alert Output
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.14 Sleep_Wake / Noise Sync Pin (WS)
. . . . . . . . . . . . . . . . .
9
3.13 Startup / Calibration Times
. . . . . . . . . . . . . . . . . . . . . . . . .
9
3.12 Oscillator
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.11 Reset Input
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.10 Water Film Suppression
. . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.9 Sample Capacitors
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.8 Burst Spacing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.7 Intra-Burst Spacing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
3.6 Burst Acquisition Duration
. . . . . . . . . . . . . . . . . . . . . . . . . .
8
3.5 Burst Length & Sensitivity
. . . . . . . . . . . . . . . . . . . . . . . . . . .
8
3.4.2 Noise Coupling Into Y Lines
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
3.4.1 RFI From Y Lines
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
3.4 'Y' Gate Drives
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
3.3.2 Noise Coupling Into X lines
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
3.3.1 RFI From X Lines
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
3.3 'X' Electrode Drives
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
3.2 Signal Path
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
3.1 Matrix Scan Sequence
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
3 Circuit Operation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
2.11 Device Status & Reporting
. . . . . . . . . . . . . . . . . . . . . . . . .
7
2.10 Full Recalibration
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
2.9 Adjacent Key Suppression (`AKS')
. . . . . . . . . . . . . . . . . . . .
6
2.8 Reference Guardbanding
. . . . . . . . . . . . . . . . . . . . . . . . . . .
6
2.7 Positive Recalibration Delay
. . . . . . . . . . . . . . . . . . . . . . . . .
6
2.6 Detection Integrator
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
2.5 Negative Recalibration Delay
. . . . . . . . . . . . . . . . . . . . . . . .
5
2.4 Drift Compensation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
2.3 Hysteresis
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
2.2 Positive Threshold
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
2.1 Negative Threshold
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
2 Signal Processing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
1.3 Communications
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
1.2 Circuit Overview
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
1.1 Field Flows
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
1 Overview
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
8 Index
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33
7.2 Marking
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33
7.1 Dimensions
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33
7 Mechanical
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
6.5 Maximum Drdy Response Delays
. . . . . . . . . . . . . . . . . .
31
6.4 Protocol Timing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
6.3 DC Specifications
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
6.2 Recommended operating conditions
. . . . . . . . . . . . . . . .
31
6.1 Absolute Maximum Specifications
. . . . . . . . . . . . . . . . . .
31
6 Electrical Specifications
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
30
5.8 Erratta / Notes
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
30
5.7 Timing Limitations
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27
5.6 Function Summary Table
. . . . . . . . . . . . . . . . . . . . . . . . .
26
^W 0x17 - Noise Sync
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26
^R 0x12 - Oscilloscope Sync
. . . . . . . . . . . . . . . . . . . . . . . . . . .
25
^Q 0x11 - Data Rate Selection
. . . . . . . . . . . . . . . . . . . . . . . . . .
25
Z 0x5A - Enter Sleep
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
W 0x57 - Return Part Signature
. . . . . . . . . . . . . . . . . . . . . . . . .
25
V 0x56 - Return Part Version
. . . . . . . . . . . . . . . . . . . . . . . . . . .
25
r 0x72 - Reset Device
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
l 0x6C - Return Last Command Character
. . . . . . . . . . . . . . . . . . .
24
b 0x62 - Recalibrate Keys
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
L 0x4C - Lock Reference Levels
. . . . . . . . . . . . . . . . . . . . . . . . .
24
6 0x36 - Eeprom Checksum
. . . . . . . . . . . . . . . . . . . . . . . . . . .
24
5.5 Supervisory / System Functions
. . . . . . . . . . . . . . . . . . . .
24
^P 0x10 - Adjacent Key Suppression (`AKS')
. . . . . . . . . . . . . . . . . .
23
^O 0x0F - Negative Reference Error Band
. . . . . . . . . . . . . . . . . . .
23
^N 0x0E - Positive Reference Error Band
. . . . . . . . . . . . . . . . . . . .
23
^M 0x0D - Intra-Burst Pulse Spacing
. . . . . . . . . . . . . . . . . . . . . . .
23
^L 0x0C - Negative Recalibration Delay
. . . . . . . . . . . . . . . . . . . . .
23
^K 0x0B - Positive Recalibration Delay
. . . . . . . . . . . . . . . . . . . . .
22
^J 0x0A - Negative Detect Integrator Limit
. . . . . . . . . . . . . . . . . . .
22
^I 0x09 - Positive Drift Compensation Rate
. . . . . . . . . . . . . . . . . .
22
^H 0x08 - Negative Drift Compensation Rate5
. . . . . . . . . . . . . . . . .
22
^G 0x07 - Burst Spacing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
^F 0x06 - Burst Length
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
^D 0x04 - Positive Threshold Hysteresis
. . . . . . . . . . . . . . . . . . . . .
21
^C 0x03 - Negative Threshold Hysteresis
. . . . . . . . . . . . . . . . . . . .
21
^B 0x02 - Positive Detect Threshold
. . . . . . . . . . . . . . . . . . . . . . .
21
^A 0x01 - Negative Detect Threshold
. . . . . . . . . . . . . . . . . . . . . . .
21
5.4 Setup Commands
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
k 0x6B - Reporting of First Touched Key
. . . . . . . . . . . . . . . . . . . .
20
E 0x45 - Error Codes for Group
. . . . . . . . . . . . . . . . . . . . . . . . .
19
e 0x65 - Error Code for Selected Key
. . . . . . . . . . . . . . . . . . . . . .
19
% 0x25 - Detect Integrator Counts for Group
. . . . . . . . . . . . . . . . .
19
" 0x22 - Reference Levels for Group
. . . . . . . . . . . . . . . . . . . . . .
19
! 0x21 - Delta Signals for Group
. . . . . . . . . . . . . . . . . . . . . . . . .
19
<sp> 0x20 - Signal Levels for Group
. . . . . . . . . . . . . . . . . . . . . . .
19
7 0x37 - General Device Status
. . . . . . . . . . . . . . . . . . . . . . . . . .
18
6 0x36 - Eeprom Checksum
. . . . . . . . . . . . . . . . . . . . . . . . . . .
18
5 0x35 - Detection Integrator Counts
. . . . . . . . . . . . . . . . . . . . . .
18
2 0x32 - Reference Value
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
1 0x31 - Delta Signal for Single Key
. . . . . . . . . . . . . . . . . . . . . . .
18
0 0x30 - Signal for Single Key
. . . . . . . . . . . . . . . . . . . . . . . . . .
18
5.3 Status Commands
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Quantum Research Group Ltd.
lQ
ii
www.qprox.com QT60161B / R1.03
Contents
Table 1.1 Device Pin List
Slave select for SPI direction control; active low
I/O OD
SS
44
Oscilloscope sync output
O PP
SO
43
Vref input for conversion reference
I
Vref
42
Data ready output for Slave SPI mode; active low
O OD
DRDY
41
Active low LED status drive / Activity indicator
O PP
LED
40
Ground
Pwr
Vss
39
+5 supply
Pwr
Vdd
38
Cs0 control A
I/O PP
CS0A
37
Cs0 control B
I/O PP
CS0B
36
Cs1 control A
I/O PP
CS1A
35
Cs1 control B
I/O PP
CS1B
34
Cs2 control A
I/O PP
CS2A
33
Cs2 control B
I/O PP
CS2B
32
Cs3 control A
I/O PP
CS3A
31
Cs3 control B
I/O PP
CS3B
30
+5 supply for analog sections
Pwr
Aref
29
Analog ground
Pwr
AGnd
28
+5 supply for analog sections
Pwr
AVdd
27
YS3 Scan output line
O PP
YS3
26
YS2 Scan output line
O PP
YS2
25
YS1 Scan output line
O PP
YS1
24
YS0 Scan output line
O PP
YS0
23
XS3 Scan input line
I
XS3
22
XS2 Scan input line
I
XS2
21
XS1 Scan input line
I
XS1
20
XS0 Scan input line
I
XS0
19
Ground
Pwr
Vss
18
+5V supply
Pwr
Vdd
17
X3 Drive matrix scan
O PP
X3
16
X2 Drive matrix scan
O PP
X2
15
X1 Drive matrix scan / Communications option B input
I/O PP
X1OPB
14
X0 Drive matrix scan / Communications option A input
I/O PP
X0OPA
13
Sample output control
O PP
SMP
12
Wake from Sleep / Sync to noise source
I
WS
11
UART transmit output
O PP
TX
10
UART receive input
I
RX
9
Oscillator drive input. Connect to resonator or crystal, or external clock source.
I
XTI
8
Oscillator drive output. Connect to resonator or crystal.ply
O PP
XTO
7
Ground
Pwr
Vss
6
+5V supply
Pwr
Vdd
5
Reset input, active low reset
I
RST
4
SPI Clock. In Master mode is an output; in Slave mode is an input
I/O PP
SCK
3
Master-In / Slave Out SPI line. Not used in Master/Slave SPI mode.
In Slave mode outputs data to host (out only).
I/O PP
MISO
2
Master-Out / Slave In SPI line. In Master/Slave SPI mode is used for both communication directions.
In Slave SPI mode is the data input (in only).
I/O PP
MOSI
1
Description
Type
Name
Pin
I/O: I = Input
O = Output
Pwr = Power pin
I/O = Bidirectional line
PP = Push Pull output drive
OD = Open drain output drive
Quantum Research Group Ltd.
lQ
iii
www.qprox.com QT60161B / R1.03
1 Overview
QMatrix devices are digital burst mode charge-transfer (QT)
sensors designed specifically for matrix geometry touch
controls; they include all signal processing functions
necessary to provide stable sensing under a wide variety of
changing conditions. Only a few low cost external parts are
required for operation. The entire circuit can be built in under
6 square centimeters of PCB area.
The device has a wide dynamic range that allows for a wide
variety of key sizes and shapes to be mixed together in a
single touch panel. These features permit new types of
keypad features such as touch-sliders, back-illuminated keys,
and complex warped panels.
The devices use an SPI interface running at up to 3MHz rates
to allow key data to be extracted and to permit individual key
parameter setup, or, a UART port which can run at rates to
57.6 Kbaud. The serial interface protocol uses simple
commands; the command structure is designed to minimize
the amount of data traffic while maximizing the amount of
information conveyed.
In addition to normal operating and
setup functions the device can also
report back actual signal strengths
and error codes over the serial
interfaces.
QmBtn software for the PC can be
used to program the IC as well as
read back key status and signal
levels in real time.
A parallel scan port is also provided
that can be used to directly replace
membrane type keypads.
QMatrix technology employs
transverse charge-transfer ('QT')
sensing, a new technology that
senses the changes in an electrical
charge forced across an electrode
set.
1.1 Field Flows
Figure 1-1 shows how charge is
transferred across an electrode set
to permeate the overlying panel
material; this charge flow exhibits a
high dQ/dt during the edge
transitions of the X drive pulse. The
charge driven by the X electrode is partly received onto the
corresponding Y electrode which is then processed. The part
uses 4 'X' edge-driven rows and 4 'Y' sense columns to sense
up to 16 keys.
The charge flows are absorbed by the touch of a human
finger (Figure 1-1) resulting in a decrease in coupling from X
to Y. Thus, received signals decrease or go negative with
respect to the reference level during a touch.
As shown in Figure 1-3, water films cause the coupled fields
to increase slightly, making them easy to distinguish from
touch.
1.2 Circuit Overview
A basic circuit diagram is shown in Figure 1-5. The `X' drives
are sequentially pulsed in groupings of bursts. At the
intersection of each `X' and `Y' line in the matrix itself, where
a key is desired, should be an interdigitated electrode set
similar to those shown in Figure 1-4. See Quantum App Note
AN-KD01, or consult Quantum for application assistance.
The device uses fixed external capacitors to acquire charge
from the matrix during a burst of charge-transfer cycles; the
burst length can be varied to permit digitally variable key
signal gains. The charge is converted to digital using a
single-slope conversion process.
Burst mode operation permits the
use of a passive matrix, reduces RF
emissions, and provides excellent
response times.
Refer to Section 3 for more details
on circuit operation.
1.3 Communications
The device uses two variants of SPI
communications, Slave-only and
Master-Slave, a UART interface,
plus a parallel scan interface. Over
the serial interfaces are used a
command and data transfer
structure designed for high levels of
flexibility using minimal numbers of
bytes. For more information see
Sections 4 and 5.
The parallel scan port permits the
replacement of electromechanical
keypads that would be scanned by
a microcontroller; the scan interface
mimics an electromechanical
keyboard's response.
Quantum Research Group Ltd.
l
Q
4
www.qprox.com QT60161B / R1.03
Figure 1-2 Field Flows When Touched
Figure 1-3 Fields With a Conductive Film
ov e rly in g pan el
X
element
Y
elem ent
Figure 1-4 Sample Electrode Geometries
PARALLEL LINES
SERPENTINE
SPIRAL
Figure 1-1 Field flow between X and Y elements
overly ing panel
X
element
Y
elem ent
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.
The threshold is user-programmed on a per-key
basis using the setup process (Section 5).
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.
The threshold is user-programmed using the setup process
described in Section 5 on a per-key basis.
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.
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.
Quantum Research Group Ltd.
l
Q
5
www.qprox.com QT60161B / R1.03
Figure 1-5 Circuit Block Diagram
X0
X1
X2
X3
Y0 Y1 Y2 Y3
KE
YM
A
T
RI
X
QT60161
SPI
to Host
X0
X1
X2
X3
CS0A
CS0B
Sample
CS0
Sample caps
CS1A
CS1B
CS2A
CS2B
CS3A
CS3B
CS1
CS2
CS3
UART
to Host
Sc
an I
n
p
u
t
Sca
n
O
u
t
p
ut
VREF
Reset
Wake /
Sync
Vcc
Opt A
Opt B
LED
Scope
Sync
Figure 1-6 Detection and Drift Compensation
Threshold
Signal
Hysteresis
Reference
Output