ChipFind - Datasheet

Part Number QT60645

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L
Q
QT60325, QT60485, QT60645
P
RELIMINARY
32, 48, 64 K
EY
QMatrix
TM
K
EYPANEL
S
ENSOR
IC
S
Advanced second generation QMatrix controllers
Up to 32, 48 or 64 touch keys through any dielectric
Panel thicknesses to 5 cm or more
100% autocal for life - no adjustments required
Keys individually adjustable for sensitivity, response time,
and many other critical parameters
Mix and match key sizes & shapes in one panel
Passive matrix - no components at the keys
Moisture suppression capable
AKSTM - Adjacent Key Suppression feature
Synchronous noise suppression
Sleep mode with wake pin
SPI Slave or Master/Slave interface to a host controller
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 QT60325, QT60485, and QT60645 digital charge-transfer ("QT") QMatrixTM ICs are designed to detect human touch on up to
32, 48, or 64 keys respectively using 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 port, for example via Quantum's QmBtn program. Key setups are stored in an onboard eeprom and do not need to be
reloaded with each power-up.
These ICs are designed specifically for appliances, electronic kiosks, security panels, portable instruments, machine tools, or
similar products that are subject to environmental influences or even vandalism. They 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 devices contain Quantum-pioneered adaptive self-calibration, drift
compensation, and digital filtering algorithms that make the sensing function robust and survivable. The devices use short dwell
times and Quantum's patent-pending AKSTM feature to permit operation in wet environments.
The parts use a passive key matrix, dramatically reducing cost over older technologies that require an ASIC for every key. The
key-matrix can be made of standard flex material (e.g. Silver on PET plastic) or ordinary PCB material to save cost.
External circuitry consists of an opamp, R2R ladder-DAC network, a common PLD, a FET switch, and a small number of resistors
and capacitors which can fit into a footprint of roughly 8 sq. cm (1.5 sq. in). Control and data transfer is via a SPI port which can
be configured in either a Slave or Master/Slave mode.
QT60xx5 ICs make 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 to provide a high economy of scale.
l
Q
Copyright © 2001 Quantum Research Group Ltd
Pat Pend. R1.05/0802
SS
YG
X7
DR
DY
LE
D
Vs
s
Vd
d
MS
AIN
CS
R
CZ
1
X3
X4
X5
X6
XS
Vd
d
Vs
s
YC0
YC1
YC2
YC3
MOSI
MISO
SCLK
RST
Vdd
Vss
XTO
XTI
X0
X1
X2WS
YC4
YC5
YC6
YC7
AVdd
AGnd
Aref
YS2
YS1
YS0
CZ2
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
QT60325
QT60485
QT60645
TQFP-44
QT60645-AS
-40
0
C to +105
0
C
QT60485-AS
-40
0
C to +105
0
C
QT60325-AS
-40
0
C to +105
0
C
QT60645-S
0
0
C to +70
0
C
QT60485-S
0
0
C to +70
0
C
QT60325-S
0
0
C to +70
0
C
TQFP
T
A
AVAILABLE OPTIONS
21
1 0x31 - Delta Signal for Single Key
. . . . . . . . . . . . . . . . . . . . . . .
21
0 0x30 - Signal for Single Key
. . . . . . . . . . . . . . . . . . . . . . . . . .
21
5.3 Status Commands
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
y 0x79 - Column Keys Scope
. . . . . . . . . . . . . . . . . . . . . . . . . . .
21
x 0x78 - Row Keys Scope
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
S 0x53 - All Keys Scope
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
s 0x73 - Specific Key Scope
. . . . . . . . . . . . . . . . . . . . . . . . . . .
21
5.2 Scope Commands
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
p 0x70 - Put Command
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
g 0x67 - Get Command
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
5.1 Direction Commands
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
5 Commands & Functions
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
4.6 Eeprom Corruption
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
4.5 Sensor Echo and Data Response
. . . . . . . . . . . . . . . . . . . . . . .
18
4.4 SPI Master-Slave Mode
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
4.3 SPI Slave-Only Mode
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
4.2 Protocol Overview
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
4.1 Serial Port specifications
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
4 Serial Interface
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
3.22 ESD / Noise Considerations
. . . . . . . . . . . . . . . . . . . . . . . . . .
15
3.21 Power Supply and PCB Layout
. . . . . . . . . . . . . . . . . . . . . . . .
15
3.20 Oscilloscope Sync
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
3.19 CSR Drive Polarity
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
3.18 LED / Alert Output
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
3.17 Sleep_Wake / Noise Sync
. . . . . . . . . . . . . . . . . . . . . . . . . . .
14
3.16 Startup / Calibration Times
. . . . . . . . . . . . . . . . . . . . . . . . . .
14
3.15 Oscillator
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
3.14 Reset Input
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
3.13 Water Film Suppression
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
3.12 R2R Resistor Ladder
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
3.11 Sample Capacitors
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
3.10 Opamps
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
3.9 PLD Circuit and Charge Sampler
. . . . . . . . . . . . . . . . . . . . . . .
12
3.8 Burst Spacing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
3.7 Intra-Burst Spacing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
3.6 Burst Length & Sensitivity
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
3.5.2 Noise Coupling Into Y Lines
. . . . . . . . . . . . . . . . . . . . . . . . . .
12
3.5.1 RFI From Y Lines
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
3.5 'Y' Gate Drives
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
3.4.2 Noise Coupling Into X lines
. . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.4.1 RFI From X Lines
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.4 'X' Electrode Drives
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.3 Signal Path
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.2 Matrix Scan Sequence
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.1 Part Differences
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3 Circuit Operation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
2.12 Device Status & Reporting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
2.11 Boundary Error Reporting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
2.10 Full Recalibration
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
2.9 Adjacent Key Suppression (AKSTM)
. . . . . . . . . . . . . . . . . . . . . . .
7
2.8 Reference Guardbanding
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
2.7 Positive Recalibration Delay
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
2.6 Detect Integrator (`DI')
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
2.5 Detection Recalibration Delay
. . . . . . . . . . . . . . . . . . . . . . . . . . .
6
2.4 Drift Compensation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
2.3 Hysteresis
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
2.2 Positive Threshold
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
2.1 Negative Threshold
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
2 Signal Processing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
1.4 Communications
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
1.3 Matrix Configuration
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
1.2 Circuit Model
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
1.1 Field Flows
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
1 Overview
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
39
9 Index
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
38
8.2 Marking
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
38
8.1 Dimensions
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
38
8 Mechanical
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
7.5 Maximum Drdy Response Delays
. . . . . . . . . . . . . . . . . . . . . . .
36
7.4 Timing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
36
7.3 DC Specifications
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
36
7.2 Recommended operating conditions
. . . . . . . . . . . . . . . . . . . . .
36
7.1 Absolute Maximum Specifications
. . . . . . . . . . . . . . . . . . . . . .
36
7 Electrical Specifications
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
35
6 PLD Source Listing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
5.7 Timing Limitations
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
5.6 Function Summary Table
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
30
^W 0x17 - Noise Sync
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
30
^V 0x16 - Boundary Equation Constant C2
. . . . . . . . . . . . . . . . . . .
30
^U 0x15 - Boundary Eqn Constant C1, LSB
. . . . . . . . . . . . . . . . . .
30
^T 0x14 - Boundary Eqn Constant C1, MSB
. . . . . . . . . . . . . . . . . .
29
^S 0x13 - Cs Clamp Polarity
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
^R 0x12 - Oscilloscope Sync
. . . . . . . . . . . . . . . . . . . . . . . . . . .
29
^Q 0x11 - Data Rate Selection
. . . . . . . . . . . . . . . . . . . . . . . . . .
29
Z 0x5A - Enter Sleep
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
W 0x57 - Return Part Signature
. . . . . . . . . . . . . . . . . . . . . . . . .
29
V 0x56 - Return Part Version
. . . . . . . . . . . . . . . . . . . . . . . . . . .
28
r 0x72 - Reset Device
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
l 0x6C - Return Last Command Character
. . . . . . . . . . . . . . . . . . .
28
b 0x62 - Recalibrate Keys
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
L 0x4C - Lock Reference Levels
. . . . . . . . . . . . . . . . . . . . . . . . .
28
D 0x44 - DAC Test
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
6 0x36 - Eeprom Checksum
. . . . . . . . . . . . . . . . . . . . . . . . . . .
28
5.5 Supervisory / System Functions
. . . . . . . . . . . . . . . . . . . . . . . .
27
^P 0x10 - Adjacent Key Suppression (`AKS')
. . . . . . . . . . . . . . . . . .
27
^O 0x0F - Negative Reference Error Band
. . . . . . . . . . . . . . . . . . .
27
^N 0x0E - Positive Reference Error Band
. . . . . . . . . . . . . . . . . . . .
27
^M 0x0D - Intra-Burst Pulse Spacing
. . . . . . . . . . . . . . . . . . . . . . .
26
^L 0x0C - Negative Recalibration Delay
. . . . . . . . . . . . . . . . . . . . .
26
^K 0x0B - Positive Recalibration Delay
. . . . . . . . . . . . . . . . . . . . .
26
^J 0x0A - Detect Integrator Limit
. . . . . . . . . . . . . . . . . . . . . . . . .
26
^I 0x09 - Positive Drift Compensation Rate
. . . . . . . . . . . . . . . . . . .
26
^H 0x08 - Negative Drift Compensation Rate
. . . . . . . . . . . . . . . . . .
25
^G 0x07 - Burst Spacing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
^E 0x05 - Dwell Time in Machine Cycles
. . . . . . . . . . . . . . . . . . . . .
25
^D 0x04 - Positive Threshold Hysteresis
. . . . . . . . . . . . . . . . . . . . .
25
^C 0x03 - Negative Threshold Hysteresis
. . . . . . . . . . . . . . . . . . . .
24
^B 0x02 - Positive Detect Threshold
. . . . . . . . . . . . . . . . . . . . . . .
24
^A 0x01 - Negative Detect Threshold
. . . . . . . . . . . . . . . . . . . . . . .
24
5.4 Setup Commands
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
K 0x4B - Key Touch Reporting for Group
. . . . . . . . . . . . . . . . . . .
23
k 0x6B - Reporting of First Touched Key
. . . . . . . . . . . . . . . . . . . .
23
e 0x65 - Error Code for Selected Key
. . . . . . . . . . . . . . . . . . . . .
22
% 0x25 - Detect Integrator Counts for Group
. . . . . . . . . . . . . . . . .
22
$ 0x24 - Charge Cancellation for Group
. . . . . . . . . . . . . . . . . . . .
22
# 0x23 - R2R Offset for Group
. . . . . . . . . . . . . . . . . . . . . . . . . .
22
" 0x22 - Reference Levels for Group
. . . . . . . . . . . . . . . . . . . . . .
22
! 0x21 - Delta Signals for Group
. . . . . . . . . . . . . . . . . . . . . . . . .
22
<sp> 0x20 - Signal Levels for Group
. . . . . . . . . . . . . . . . . . . . . . .
22
7 0x37 - General Device Status
. . . . . . . . . . . . . . . . . . . . . . . . .
22
6 0x36 - Eeprom Checksum
. . . . . . . . . . . . . . . . . . . . . . . . . . .
22
5 0x35 - Detection Integrator Counts
. . . . . . . . . . . . . . . . . . . . . .
21
4 0x34 - Cz State
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
3 0x33 - R2R Offset
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
2 0x32 - Reference Value
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
© Quantum Research Group Ltd.
l
Q
ii
www.qprox.com
QT60xx5 / R1.05
Contents
Table 1.1 Device Pin List
Slave select for SPI direction control; active low
IO OD
SS
44
Y gate control to drive Y dwell timing circuit
O
YG
43
X7 Drive matrix scan
O
X7
42
Data ready output for Slave SPI mode; active low
O OD
DRDY
41
Active low LED status drive / Activity indicator
O
LED
40
Ground
Pwr
Vss
39
+5 supply
Pwr
Vdd
38
SPI Mode / Sync out. Connect via 10k resistor to Vcc or Gnd for mode. Scope sync yields Pulse.
I/O OD
MS
37
Analog input from amplifier
I
Ain
36
Charge integrator reset line. Active high or active low (select polarity via Setups)
O
CSR
35
Charge cancellation drive for CZ1 capacitor
O
CZ1
34
Charge cancellation drive for CZ2 capacitor
O
CZ2
33
Transfer switch control bit 0
O
YS0
32
Transfer switch control bit 1
O
YS1
31
Transfer switch control bit 2
O
YS2
30
Analog reference, connect to Vcc
Pwr
Aref
29
Analog ground
Pwr
AGnd
28
+5 supply for analog sections
Pwr
AVdd
27
Y 7 Line clamp control
O
YC7
26
Y 6 Line clamp control
O
YC6
25
Y 5 Line clamp control
O
YC5
24
Y 4 Line clamp control
O
YC4
23
Y 3 Line clamp control
O
YC3
22
Y 2 Line clamp control
O
YC2
21
Y 1 Line clamp control
O
YC1
20
Y 0 Line clamp control
O
YC0
19
Ground
Pwr
Vss
18
+5 supply
Pwr
Vdd
17
X summation / R2R DAC Ladder drive
O
XS
16
X6 Drive matrix scan / R2R DAC Ladder drive
O
X6
15
X5 Drive matrix scan / R2R DAC Ladder drive
O
X5
14
X4 Drive matrix scan / R2R DAC Ladder drive
O
X4
13
X3 Drive matrix scan / R2R DAC Ladder drive
O
X3
12
X2 Drive matrix scan / R2R DAC Ladder drive / Wake from Sleep / Sync to noise source
O
X2WS
11
X1 Drive matrix scan / R2R DAC Ladder drive
O
X1
10
X0 Drive matrix scan / R2R DAC Ladder drive
O
X0
9
Oscillator drive input. Connect to resonator or crystal, or external clock source.
I
XTI
8
Oscillator drive output. Connect to resonator or crystal. Can drive a charge pump circuit for Vee
supply
O
XTO
7
Ground
Pwr
Vss
6
+5 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 = Bi-directional line
PP = Push Pull output drive
OD = Open drain output drive
©Quantum Research Group Ltd.
l
Q
iii
www.qprox.com
QT60xx5 / R1.05
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 external parts are required
for operation. The entire circuit can be built within 8 square
centimeters of PCB area.
QMatrix devices include charge cancellation methods which
allow for a wide range of key sizes and shapes to be mixed
together in a single touch panel. These features permit the
construction of entirely new classes of keypads never before
contemplated, such as touch-sliders, back-illuminated keys,
and complex warped panel shapes, all at very low cost.
The devices use an SPI interface running at up to 1.5MHz to
allow key data to be extracted and to permit individual key
parameter setup. The interface protocol uses simple single
byte commands and responds with single byte responses in
most cases. 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.
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.
QMatrix parts employ transverse
charge-transfer ('QT') sensing, a
new technology that senses
changes in the charge forced
across an electrode by a digital
edge.
The parts are electrically
identical with the exception of the
number of keys which may be
sensed.
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 emitted by
the X electrode is partly received onto the corresponding Y
electrode which is then processed. The parts use 8 'X'
edge-driven rows and 8 'Y' sense columns to permit up to 64
keys. Keys are typically formed from interleaved conductive
traces on a substrate like a flex circuit or PCB (Figure 1-2).
The charge flows are absorbed by the touch of a human
finger (Figure 1-3) 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.
Water films cause the coupled fields to increase slightly,
making water films easy to distinguish from touch.
1.2 Circuit Model
An electrical circuit model is shown in Figure 1-5. The
coupling capacitance between X and Y electrodes is
represented by Cx. While the reset switch is open, a sample
switch is gated so that it transfers charge flows only from the
rising edge of X into a charge integrator. On the falling edge
of X, the switch connects the Y line to ground to allow the
charge across Cx to neutralize to zero. The voltage change
on the output of the charge integrator after each X edge is
quite small, on the order of a few tens of millivolts. Changes
due to touch are typically under 0.1% of total integrator
voltage. The X pulse can be
repeated in a burst of up to 64
pulses to increase the change in
integrator output voltage due to
touch during an acquire (Section
3.6) to increase gain.
The charge detector is an opamp
configured as an integrator with a
reset switch; this creates a virtual
ground input, making the Y lines
appear low impedance when the
sample switch is closed. This
configuration effectively
eliminates cross-coupling among
Y lines while greatly lowering
susceptibility to EMI. The circuit
is also highly immune to
capacitive loading on the Y lines,
since stray C from Y to ground
appears merely as a small
parallel capacitance across a
virtual ground.
The circuit uses an 8-bit ADC,
with a subranging structure to
effectively deliver a 14-bit total
conversion 'space' (see Figure
1-6 and Section 3.3). In this way
the circuit can tolerate very large
© Quantum Research Group Ltd.
l
Q
4
www.qprox.com
QT60xx5 / R1.05
Figure 1-3 Field Flows When Touched
Figure 1-4 Fields With a Conductive Film
ov e rly in g pan el
X
element
Y
elem ent
Figure 1-2 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
absolute signals yet still respond to very small signal
changes. Subranging is provided by two offset mechanisms
which can be thought of as 'coarse' and 'fine' offsets.
The 'coarse' method uses one or two switched Cz capacitors
to subtract charge from the charge integrator to create up to
two step offsets, to bring the analog signal back to a more
reasonable level. This action occurs during the course of the
burst.
The 'fine' method of offset uses an 8-bit R2R ladder DAC
driven by the X drive lines to create an offset in the amplifier
stage. The DAC is driven after the burst has ceased and the
charge accumulated, so there is no conflict in this dual-use of
the X lines.
Short sample gate dwell times after the X
edges will limit the effect of moisture
spreading from key to key by taking
advantage of the RC filter-like nature of
continuous films; a short dwell time will limit
the time that the charge has to travel
through the impedance of the film (Section
3.13). This effect is independent of the
frequency of burst repetition, intra-burst
pulse spacing, or X drive pulse width.
Burst mode operation permits reduced
power consumption and reduces RF
emissions, while permitting excellent
response time.
1.3 Matrix Configuration
The matrix scanning configuration is shown
in Figure 1-5. The `X' drives are sequentially
pulsed in groupings of bursts; an 8:1 analog
mux acts as the sample switch for all `Y'
lines. 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 1-2. The outermost electrode or the
key border should always be connected to an `X' drive;
flooding the area around keys with X fill to a width of up to
10mm can help in suppressing moisture films further.
Although it is referred to as a `matrix', there is no restriction
on where individual keys can be located. The term `matrix'
refers to the electrical configuration of keys, not the physical
arrangement. Consult Quantum for application assistance on
key design.
1.4 Communications
The device uses two variants of SPI communications,
Slave-only and Master-Slave. Over this interface is 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.
Device variations: Refer to Section 3.1 for
differences between the parts covered by
this datasheet.
2 Signal Processing
The devices calibrate and process all
signals using a number of algorithms
specifically designed to provide for high
survivability in the face of adverse
environmental challenges. They provide 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 24
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
© Quantum Research Group Ltd.
l
Q
5
www.qprox.com
QT60xx5 / R1.05
Figure 1-5 QT60xx5 Basic Circuit Model
0
0
1
1
+
X drive
(1 of 8)
Y line
(1 of 8)
X
electrod e
Y
e lectrod e
Sample
switch (1 o f 8)
Cx
C s
Reset sw itch
Cz2
Cancellatio n
switches
8-bit
Offset DAC
Xn
+
Cz1
Am p
C ha rge
In te grator
To 60 xxx AD C
From 60xxx
O ffset Control
ou t
V
0
Reset
switch
Sample
sw itch
Amp
out
Xn
C a
0
0
1
1
+
X drive
(1 of 8)
Y line
(1 of 8)
X
electrode
Y
electrode
Sample
switch (1 of 8)
Cx
Cs
Reset sw itch
Cz2
Cancellation
switches
8-bit
Offset DAC
Xn
+
Cz1
A mp
C ha rge
In te grator
To 60xxx ADC
From 60xxx
Offset Control
ou t
V
0
R eset
switch
Sample
sw itch
Amp
out
Xn
Ca
Figure 1-6 Circuit Block Diagram (8x8 Matrix Shown)
C harge
Integrator
Transfer
M ux
G ain
A mp
X 0
X 1
X 2
X 3
X 4
X 5
X 6
X 7
Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7
Integrator R eset
"
Signal Offset
R 2R
DA C
C harge C ancellation 1
Transfer S elect
+
-
K
E
YMA
TR
IX
C harge C ancellation 2
Transfer S trobe
Timin g &
Ch arge
N eutralizin g
C ontrol
(PL D)
QT60xx5
SP I
to
Host
X
{1..7}
X 7
X0
X1
X2
X3
X4
X5
X6
X7
YC0 .
YC1 .
YC2 .
YC3 .
YC4 .
YC5 .
YC6 .
YC7 .
X0 .
X1 .
X2 .
X3 .
X4 .
X5 .
X6 .
XS .
XS
YS0..YS2
C
Z1
C
Z2
Cz1
Cz2
CSR
AIN
C harge
Integrator
Transfer
M ux
G ain
A mp
X 0
X 1
X 2
X 3
X 4
X 5
X 6
X 7
Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7
Integrator R eset
"
Signal Offset
R 2R
DA C
C harge C ancellation 1
Transfer S elect
+
-
K
E
YMA
TR
IX
C harge C ancellation 2
Transfer S trobe
Timin g &
Ch arge
N eutralizin g
C ontrol
(PL D)
QT60xx5
SP I
to
Host
X
{1..7}
X 7
X0
X1
X2
X3
X4
X5
X6
X7
YC0 .
YC1 .
YC2 .
YC3 .
YC4 .
YC5 .
YC6 .
YC7 .
X0 .
X1 .
X2 .
X3 .
X4 .
X5 .
X6 .
XS .
XS
YS0..YS2
C
Z1
C
Z2
Cz1
Cz2
CSR
AIN