lQ
Advanced second generation QMatrix™ controller
Keys individually adjustable for sensitivity, response
time, and many other critical parameters
Panel thicknesses to 50mm through any dielectric
32 and 48 key versions
100% autocal for life - no in-field adjustments
SPI Slave and UART interfaces
Sleep mode with wake pin
Adjacent key suppression feature
Synchronous noise suppression pin
Spread-spectrum modulation: high noise immunity
Mix and match key sizes & shapes in one panel
Low overhead communications protocol
FMEA compliant design features
Negligible external component count
Extremely low cost per key
44-pin Pb-free TQFP package
QT60326, QT60486
32 & 48 K
EY
QM
ATRIX
™ IC
s
S_SYNC
/SS
DRDY
VREF
Y5A
Y5B
Vdd
LED
Y4A
Y4B
Vss
MOSI
MISO
SCK
/RST
Vdd
Vss
XT2
XT1
RX
TX
WS
1
2
3
4
5
6
7
8
9
44 43 42 41 40 39 38 37 36 35 34
33
32
31
30
29
28
27
26
25
Y3B
Y2B
Y1B
Y0B
Vdd
Vss
Vdd
X7
X6
X5
X4
QT60326
QT60486
TQFP-44
10
24
11
23
12 13 14 15 16 17 18 19 20 21 22
SMP
Y1A
Y2A
Y3A
Y0A
Vdd
X1
X0
Vss
X3
X2
APPLICATIONS -
Security keypanels
Industrial keyboards
Appliance controls
Outdoor keypads
ATM machines
Touch-screens
Automotive panels
Machine tools
These digital charge-transfer (“QT”) QMatrix™ ICs are designed to detect human touch on up 48 keys when used with a scanned,
passive X-Y matrix. They will project touch 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.
These devices 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. 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 parts can scan matrix touch keys over LCD panels or other displays when used with clear ITO electrodes arranged in a matrix.
They do 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 passive parts, all of which can fit into a 6.5 sq cm footprint (1 sq inch). Control and
data transfer is via either an SPI or UART port.
These devices 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. Unlike older methods, it does not require one IC per key.
AVAILABLE OPTIONS
T
A
-40
0
C to +105
0
C
-40
0
C to +105
0
C
# Keys
32
48
Part Number
QT60326-AS-G
QT60486-AS-G
LQ
Copyright © 2003-2005 QRG Ltd
QT60486-AS R8.01/0105
Contents
..............................
1.1 Part differences
. . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Enabling / Disabling Keys
. . . . . . . . . . . . . . . . . . . .
2 Hardware & Functional
. . . . . . . . . . . . . . . . . . . . .
2.1 Matrix Scan Sequence
. . . . . . . . . . . . . . . . . . . . . .
2.2 Burst Paring
. . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 Response Time
. . . . . . . . . . . . . . . . . . . . . . . . .
2.4 Oscillator
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5 Sample Capacitors; Saturation Effects
. . . . . . . . . . . . . .
2.6 Sample Resistors
. . . . . . . . . . . . . . . . . . . . . . . .
2.7 Signal Levels
. . . . . . . . . . . . . . . . . . . . . . . . . .
2.8 Matrix Series Resistors
. . . . . . . . . . . . . . . . . . . . .
2.9 Key Design
. . . . . . . . . . . . . . . . . . . . . . . . . . .
2.10 PCB Layout, Construction
. . . . . . . . . . . . . . . . . . .
2.10.1 LED Traces and Other Switching Signals
............
2.10.2 PCB Cleanliness
.......................
2.11 Power Supply Considerations
.................
2.12 Startup / Calibration Times
. . . . . . . . . . . . . . . . . . .
Table 2-1 Calibration Timings
....................
2.13 Reset Input
..........................
2.14 Spread Spectrum Acquisitions
. . . . . . . . . . . . . . . . .
2.15 Detection Integrators
. . . . . . . . . . . . . . . . . . . . . .
2.16 FMEA Tests
. . . . . . . . . . . . . . . . . . . . . . . . . .
2.17 Wiring
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Table 2.2 - Pin Listing
.......................
Figure 2.7 Wiring Diagram
......................
3 Serial Communications
. . . . . . . . . . . . . . . . . . . . .
3.1 DRDY Pin
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 SPI Communications
......................
3.3 UART Communications
. . . . . . . . . . . . . . . . . . . . .
4 Control Commands
. . . . . . . . . . . . . . . . . . . . . . .
4.1 Null Command - 0x00
. . . . . . . . . . . . . . . . . . . . . .
4.2 Enter Setups Mode - 0x01
. . . . . . . . . . . . . . . . . . . .
4.3 Cal All - 0x03
. . . . . . . . . . . . . . . . . . . . . . . . . .
4.4 Force Reset - 0x04
. . . . . . . . . . . . . . . . . . . . . . .
4.5 General Status - 0x05
. . . . . . . . . . . . . . . . . . . . . .
4.6 Report 1st Key - 0x06
. . . . . . . . . . . . . . . . . . . . . .
4.7 Report Detections for All Keys - 0x07
..............
Table 4.1 Bit fields for multiple key reporting and key
numbering
............................
4.8 Report Signals for All Keys - 0x08
. . . . . . . . . . . . . . . .
4.9 Report References for All Keys - 0x09
. . . . . . . . . . . . . .
4.10 Report Deltas for All Keys - 0x0a
. . . . . . . . . . . . . . . .
4.11 Report Error Flags for All Keys - 0x0b
.............
4.12 Report FMEA Status - 0x0c
..................
4.13 Dump Setups Block - 0x0d
. . . . . . . . . . . . . . . . . . .
4.14 Eeprom CRC - 0x0e
. . . . . . . . . . . . . . . . . . . . . .
1 Overview
3
3
3
3
3
3
4
4
4
4
5
5
6
6
6
6
6
6
7
7
7
7
7
9
9
10
11
11
11
12
13
13
14
14
14
14
15
15
15
15
15
15
15
15
15
15
..................
......................
4.17 Internal Code - 0x11
. . . . . . . . . . . . . . . . . . . . . .
4.18 Internal Code - 0x12
. . . . . . . . . . . . . . . . . . . . . .
4.19 Sleep - 0x16
. . . . . . . . . . . . . . . . . . . . . . . . . .
4.20 Data Set for One Key - 0x4k
. . . . . . . . . . . . . . . . . .
4.21 Status for Key ‘k’ - 0x8k
....................
4.22 Cal Key ‘k’ - 0xck
. . . . . . . . . . . . . . . . . . . . . . . .
4.23 Command Sequencing
. . . . . . . . . . . . . . . . . . . . .
Table 4.2 Command Summary
...................
5 Setups
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.1 Negative Threshold - NTHR
. . . . . . . . . . . . . . . . . . .
5.2 Positive Threshold - PTHR
...................
5.3 Drift Compensation - NDRIFT, PDRIFT
. . . . . . . . . . . . .
5.4 Detect Integrators - NDIL, FDIL
. . . . . . . . . . . . . . . . .
5.5 Negative Recal Delay - NRD
. . . . . . . . . . . . . . . . . . .
5.6 Positive Recalibration Delay - PRD
...............
5.7 Burst Length - BL
. . . . . . . . . . . . . . . . . . . . . . . .
5.8 Adjacent Key Suppression - AKS
................
5.9 Oscilloscope Sync - SSYNC
. . . . . . . . . . . . . . . . . . .
5.10 Negative Hysteresis - NHYST
.................
5.11 Dwell Time - DWELL
. . . . . . . . . . . . . . . . . . . . . .
5.12 Mains Sync - MSYNC
.....................
5.13 Burst Spacing - BS
. . . . . . . . . . . . . . . . . . . . . . .
5.14 Serial Rate - SR
. . . . . . . . . . . . . . . . . . . . . . . .
5.15 Lower Signal Limit - LSL
. . . . . . . . . . . . . . . . . . . .
5.16 LED / Alert Output - LED
. . . . . . . . . . . . . . . . . . . .
5.17 Host CRC - HCRC
. . . . . . . . . . . . . . . . . . . . . . .
Table 5.1 Setups Block
.......................
Table 5.2 LED Function Control Byte Bits
...............
Table 5.3 Key Mapping
.......................
Table 5.4 Setups Block Summary
..................
6 Specifications
..........................
6.1 Absolute Maximum Electrical Specifications
. . . . . . . . . . .
6.2 Recommended operating conditions
. . . . . . . . . . . . . . .
6.3 DC Specifications
. . . . . . . . . . . . . . . . . . . . . . . .
6.4 Timing Specifications
. . . . . . . . . . . . . . . . . . . . . .
6.5 Mechanical Dimensions
. . . . . . . . . . . . . . . . . . . . .
6.6 Marking
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 Appendix
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.1 8-Bit CRC Software C Algorithm
. . . . . . . . . . . . . . . . .
7.2 16-Bit CRC Software C Algorithm
. . . . . . . . . . . . . . . .
7.3 1-Sided Key Layout
. . . . . . . . . . . . . . . . . . . . . . .
7.4 PCB Layout
. . . . . . . . . . . . . . . . . . . . . . . . . . .
4.15 Return Last Command - 0x0f
4.16 Internal Code - 0x10
16
16
16
16
16
16
16
16
16
18
20
20
20
20
21
21
21
22
22
22
22
22
22
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27
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30
30
lQ
2
QT60486-AS R8.01/0105
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 a few square centimeters of
single-sided PCB area. CEM-1 and FR1 punched, single-sided
materials can be used for possible lowest cost. The PCB’s rear
can be mounted flush on the back of a glass or plastic panel
using a conventional adhesive, such as 3M VHB 2-sided
adhesive acrylic film.
QMatrix parts employ transverse charge-transfer ('QT') sensing,
a technology that senses changes in electrical charge forced
across an electrode by a pulse edge (Figure 1-1).
QmBtn software for the PC can be used to program the
operation of the IC as well as read back key status and signal
levels in real time.
The parts are electrically identical with the exception of the
number of keys which may be sensed.
1.1 Part differences
Versions of the device are capable of a maximum of 32 or 48
keys (QT60326, QT60486 respectively).
These devices are identical in all respects, except that each is
capable of only the number of keys specified. These keys can
be located anywhere within the electrical grid of 8 X and 6 Y
scan lines.
Unused keys are always pared from the burst sequence in
order to optimize speed. Similarly, in a given part a lesser
number of enabled keys will cause any unused acquisition burst
timeslots to be pared from the sampling sequence to optimize
acquire speed. Thus, if only 40 keys are actually enabled, only
40 timeslots are used for scanning.
Figure 1-1 Field flow between X and Y elements
overlying panel
1.2 Enabling / Disabling Keys
The NDIL parameter is used to enable and disable keys in the
matrix. Setting NDIL = 0 for a key disables it (Section 5.4). At
no time can the number of enabled keys exceed the maximum
specified for the device in the case of the QT60326.
On the QT60326, only the first 4 Y lines (Y0..Y3) are
operational by default. On the QT60326, to use keys located on
lines Y4 and Y5, one or more of the pre-enabled keys must be
disabled simultaneously while enabling the desired new keys.
This can be done in one Setups block load operation.
X
element
cmos
driver
Y
element
QMatrix devices allow for a wide range of key sizes and shapes
to be mixed together in a single touch panel. The approximate
design rules for these keys can be seen in Figure 2-6.
The actual internal pattern style is not as important as is the
need to achieve regular X and Y widths and spacings of
sufficient size to cover the desired graphical key area or a little
bit more; 2mm overhand is acceptable in most cases, since the
fields drop off near the edges anyway. The overall key size can
range from 10mm x 10mm up to 100mm x 100mm. The keys
can be any shape including round, rectangular, square, etc.
The internal pattern can be as simple as a single bar of Y or as
complex as the interleaved structure shown in Figure 2-6.
For better surface moisture suppression, the outer perimeter of
X should be as wide as possible, and there should be no
ground planes near the keys. The variable ‘T’ in this drawing
represents the total thickness of all materials that the keys must
penetrate.
A picture of an actual board made using similar key geometries
is shown on page 30.
The devices use both UART and SPI interfaces 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.
2 Hardware & Functional
2.1 Matrix Scan Sequence
The circuit operates by scanning each key sequentially, key by
key. Key scanning begins with location X=0 / Y=0 (key #0). X
axis keys are known as rows while Y axis keys are referred to
as columns. Keys are scanned sequentially by row, for example
the sequence X0Y0 X1Y0 .... X7Y0, X0Y1, X1Y1... etc. Keys are
also numbered from 0..47. Key 0 is located at X0Y0. A table of
key numbering is located on page 25.
Each key is sampled in a burst of acquisition pulses whose
length is determined by the Setups parameter BL (page 22),
which can be set on a per-key basis. A burst is completed
entirely before the next key is sampled; at the end of each burst
the resulting signal is converted to digital form and processed.
The burst length directly impacts key gain; each key can have a
unique burst length in order to allow tailoring of key sensitivity
on a key by key basis.
2.2 Burst Paring
Keys that are disabled by setting NDIL =0 (page 21) have their
bursts pared from the scan sequence to save time. This has the
consequence of affecting the scan rate of the entire matrix as
well as the time required for initial matrix calibration. It does not
affect the time required to calibrate an individual key once the
matrix is initially calibrated after power-up or reset.
lQ
3
QT60486-AS R8.01/0105
2.3 Response Time
The response time of the device depends on the scan rate of
the keys (Section 5.13), the number of keys enabled (Section
5.4), the detect integrator settings (Section 5.4), and the serial
polling rate by the host microcontroller (or the use of the LED
pin as an interrupt to the host; Sections 5.16, and Table 5.2 on
page 25). An example timing:
Keys enabled (KE) = 20
Burst spacing (BS) = 1ms
NDIL = 3
FDIL = 5
Host polling rate (PR) = 10ms
The worst case response time is computed as:
((KE + FDIL) x NDIL x BS) + PR = Worst case response
((20 + 5) x 3 x 1ms) + 10ms = 85ms
The use of the LED pin to trigger host sampling can reduce this
to ~75ms by saving the majority of the host polling time; see
Section 5.16.
increasing BL to a high count and watching what the waveform
does as it descends towards and below -0.25V. The waveform
will appear deceptively straight, but it will start to flatten even
before the -0.25V level is reached.
A correct waveform is shown in Figure 2-3. Note that the
bottom edge of the bottom trace is substantially straight
(ignoring the downward spikes).
Unlike other QT circuits, the Cs capacitor values on QT60xx6
devices have no effect on conversion gain. However they do
affect conversion time.
Unused Y lines should be left open.
2.6 Sample Resistors
There are 6 sample resistors (Rs) used to perform single-slope
ADC conversion of the acquired charge on each Cs capacitor.
These resistors directly control acquisition gain: larger values of
Rs will proportionately increase signal gain. Values of Rs can
range from 220K✡ to 1M✡. 220K✡ is a reasonable value for
most purposes.
Larger values for Rs will also increase conversion time and may
reduce the fastest possible key sampling rate, which can impact
response time especially with larger numbers of enabled keys.
Unused Y lines do not require an Rs resistor.
2.4 Oscillator
The oscillator can use either a quartz crystal or a ceramic
resonator. In either case, the XT1 and XT2 must both be loaded
with 22pF capacitors to ground. 3-terminal resonators having
onboard ceramic capacitors are commonly available and are
recommended. An external TTL-compatible frequency source
can also be connected to XT1 in which case, XT2 should be left
unconnected.
The frequency of oscillation should be 16MHz +/-1% for
accurate UART transmission timing.
Figure 2-1 VCs - Non-Linear During Burst
(Burst too long, or Cs too small, or X-Y capacitance too large)
2.5 Sample Capacitors; Saturation Effects
The charge sampler capacitors on the Y pins should be the
values shown. They should be X7R or NP0 ceramics or PPS
film. The value of these capacitors is not critical but 4.7nF is
recommended for most cases.
Cs voltage saturation is shown in Figure 2-1. This nonlinearity
is caused by excessively negative voltage on Cs inducing
conduction in the pin protection diodes. This badly saturated
signal destroys key gain and introduces a strong thermal
coefficient which can cause 'phantom' detection. The cause of
this is usually from the burst length being too long, the Cs value
being too small, or the X-Y coupling being too large. Solutions
include loosening up the interdigitation of key structures,
separating X and Y lines on the PCB more, increasing Cs, and
decreasing the burst length.
Increasing Cs will make the part slower; decreasing burst
length will make it less sensitive. A better PCB layout and a
looser key structure (up to a point) have no negative effects.
Cs voltages should be observed on an oscilloscope with the
matrix layer bonded to the panel material; if the Rs side of any
Cs ramps more negative than -0.25 volts during any burst (not
counting overshoot spikes which are probe artifacts), there is a
potential saturation problem.
Figure 2-2 shows a defective waveform similar to that of 2-1,
but in this case the distortion is caused by excessive stray
capacitance coupling from the Y line to AC ground, for example
from running too near and too far alongside a ground trace,
ground plane, or other traces. The excess coupling causes the
charge-transfer effect to dissipate a significant portion of the
received charge from a key into the stray capacitance. This
phenomenon is more subtle; it can be best detected by
Figure 2-2 VCs - Poor Gain, Non-Linear During Burst
(Excess capacitance from Y line to Gnd)
Figure 2-3 Vcs - Correct
lQ
4
QT60486-AS R8.01/0105
Figure 2-4 X-Drive Pulse Roll-off and Dwell Time
Figure 2-6 Recommended Key Structure
‘T’ should ideally be similar to the complete thickness the fields need to
penetrate to the touch surface. Smaller dimensions will also work but will give
less signal strength. If in doubt, make the pattern coarser.
X drive
Lost charge due to
inadequate settling
before end of dwell time
Dwell time
Y gate
Figure 2-5 Probing X-Drive Waveforms with a Coin
2.8 Matrix Series Resistors
The X and Y matrix scan lines should use series resistors
(referred to as Rx and Ry respectively) for improved EMI
performance.
X drive lines require them in most cases to reduce edge rates
and thus reduce RF emissions. Typical values range from 1K to
20K✡.
Y lines need them to reduce EMC susceptibility problems and in
some extreme cases, ESD. Typical Y values range around
1K✡. Y resistors act to reduce susceptibility problems by
forming a natural low-pass filter with the Cs capacitors.
It is essential that the Rx and Ry resistors and Cs capacitors be
placed very close to the chip. Placing these parts more than a
few millimeters away opens the circuit up for high frequency
interference problems (above 20MHz) as the trace lengths
between the components and the chip start to act as RF
antennae.
The upper limits of Rx and Ry are reached when the signal
level and hence key sensitivity are clearly reduced. The limits of
Rx and Ry will depending on key geometry and stray
capacitance, and thus an oscilloscope is required to determine
optimum values of both.
The upper limit of Rx can vary depending on key geometry and
stray capacitance, and some experimentation and an
oscilloscope are required to determine optimum values.
Dwell time (page 22) affects the duration in which charge
coupled from X to Y can be captured. Increasing the dwell will
increase the signal levels lost to higher values of Rx and Ry, as
shown in Figure 2-4. Too short a dwell time will cause charge to
be 'lost', if there is too much rising edge roll-off. Lengthening
the dwell time will cause this lost charge to be recaptured,
thereby restoring key sensitivity. In these devices, dwell time is
adjustable (see Section 5.11) to one of 3 values.
Dwell time problems can also be solved by either reducing the
stray capacitance on the X line(s) (by a layout change, for
example by reducing X line exposure to nearby ground planes
or traces), or, the Rx resistor needs to be reduced in value (or a
combination of both approaches).
One way to determine X settling time is to monitor the fields
using a patch of metal foil or a small coin over the key (Figure
2.7 Signal Levels
Using Quantum’s QmBtn™ software it is easy to observe the
absolute level of signal received by the sensor on each key.
The signal values should normally be in the range from 250 to
750 counts with properly designed key shapes (see appropriate
Quantum app note on matrix key design). However, long
adjacent runs of X and Y lines can also artificially boost the
signal values, and induce signal saturation: this is to be
avoided. The X-to-Y coupling should come mostly from
intra-key electrode coupling, not from stray X-to-Y trace
coupling.
QmBtn software is available free of charge on Quantum’s web
site.
The signal swing from the smallest finger touch should
preferably exceed 10 counts, with 15 being a reasonable target.
The signal threshold setting (NTHR) should be set to a value
guaranteed to be less than the signal swing caused by the
smallest touch.
Increasing the burst length (BL) parameter will increase the
signal strengths as will increasing the sampling resistor (Rs)
values.
lQ
5
QT60486-AS R8.01/0105
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