QPROX QT60161B-AS Datasheet

LQ QT60161B

16 KEY QMatrix™ K

 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

MOSI

MISO

SCK

RST

Vdd

Vss

XTO

XTI

RX

TX

WS

EYPANEL SENSOR

DRDY

VREF

SO

SS

43 42

44

2

3

4

5

6

7

8

9

10

11 23

12

41 40393837363435

QT60161B

TQFP-44

13

1615

14 22

SMP

X0OPA

X1OPBX2X3

CS0A

CS1A

CS0B

LED

Vdd

Vss

17

Vdd

Vss

CS1B

21192018

XS0

XS1

XS2

XS3

IC

CS2A1

33

CS2B

32

CS3A

31

CS3B

30

Aref

29

AGnd

28

AVd d

27

YS3

26

YS2

25

YS1

24

YS0

 44-pin TQFP package

APPLICATIONS -

 Security keypanels



Industrial keyboards



Appliance controls



Outdoor keypads



ATM machines



Touch-screens

The QT60161B digital charge-transfer (“QT”) QMatrix™ 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.



Automotive panels



Machine tools

lQ

AVAILABLE OPTIONS

A

TQFP Part NumberT

QT60161B-AS-400C to +1050C

Copyright © 2001 Quantum Research Group Ltd

Pat Pend. R1.03/04.03

Contents

1 Overview

2 Signal Processing

3 Circuit Operation

4 Communications Interfaces

5 Commands & Functions

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3.3.1 RFI From X Lines

3.3.2 Noise Coupling Into X lines

3.4.1 RFI From Y Lines

3.4.2 Noise Coupling Into Y Lines

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g 0x67 - Get Command

p 0x70 - Put Command

s 0x73 - Specific Key Scope

S 0x53 - All Keys Scope

x 0x78 - Row Keys Scope

y 0x79 - Column Keys Scope

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©Quantum Research Group Ltd.

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4

41.1 Field Flows

41.2 Circuit Overview

41.3 Communications
5

52.1 Negative Threshold

52.2 Positive Threshold

52.3 Hysteresis

52.4 Drift Compensation

62.5 Negative Recalibration Delay

62.6 Detection Integrator

62.7 Positive Recalibration Delay

62.8 Reference Guardbanding

62.9 Adjacent Key Suppression (‘AKS’)

72.10 Full Recalibration

72.11 Device Status & Reporting
7

73.1 Matrix Scan Sequence

73.2 Signal Path

83.3 'X' Electrode Drives
8
8

83.4 'Y' Gate Drives
8
8

83.5 Burst Length & Sensitivity

83.6 Burst Acquisition Duration

93.7 Intra-Burst Spacing

93.8 Burst Spacing

93.9 Sample Capacitors

93.10 Water Film Suppression

93.11 Reset Input

93.12 Oscillator

93.13 Startup / Calibration Times

93.14 Sleep_Wake / Noise Sync Pin (WS)

103.15 LED / Alert Output

113.16 Oscilloscope Sync

113.17 Power Supply & PCB Layout

113.18 ESD / Noise Considerations
11

114.1 Serial Protocol Overview

124.2 SPI Port Specifications

124.3 SPI Slave-Only Mode

134.4 SPI Master-Slave Mode

144.5 UART Interface

154.6 Sensor Echo and Data Response

154.7 Parallel Scan Port

164.8 Eeprom Corruption
17

175.1 Put / Get Direction Commands
17
17

185.2 Scope Commands
18
18
18
18

0 0x30 - Signal for Single Key

1 0x31 - Delta Signal for Single Key

2 0x32 - Reference Value

5 0x35 - Detection Integrator Counts

6 0x36 - Eeprom Checksum

7 0x37 - General Device Status

<sp> 0x20 - Signal Levels for Group

! 0x21 - Delta Signals for Group

" 0x22 - Reference Levels for Group

% 0x25 - Detect Integrator Counts for Group

e 0x65 - Error Code for Selected Key

E 0x45 - Error Codes for Group

k 0x6B - Reporting of First Touched Key

^A 0x01 - Negative Detect Threshold

^B 0x02 - Positive Detect Threshold

^C 0x03 - Negative Threshold Hysteresis

^D 0x04 - Positive Threshold Hysteresis

^F 0x06 - Burst Length

^G 0x07 - Burst Spacing

^H 0x08 - Negative Drift Compensation Rate5

^I 0x09 - Positive Drift Compensation Rate

^J 0x0A - Negative Detect Integrator Limit

^K 0x0B - Positive Recalibration Delay

^L 0x0C - Negative Recalibration Delay

^M 0x0D - Intra-Burst Pulse Spacing

^N 0x0E - Positive Reference Error Band

^O 0x0F - Negative Reference Error Band

^P 0x10 - Adjacent Key Suppression (‘AKS’)

6 0x36 - Eeprom Checksum

L 0x4C - Lock Reference Levels

b 0x62 - Recalibrate Keys

l 0x6C - Return Last Command Character

r 0x72 - Reset Device

V 0x56 - Return Part Version

W 0x57 - Return Part Signature

Z 0x5A - Enter Sleep

^Q 0x11 - Data Rate Selection

^R 0x12 - Oscilloscope Sync

^W 0x17 - Noise Sync

6 Electrical Specifications

7 Mechanical

8 Index

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185.3 Status Commands
18
18
18
18
18
19
19
19
19
19
19
20
20

215.4 Setup Commands
21
21
21
21
21
22
22
22
22
23
23
23
23
23
24

245.5 Supervisory / System Functions
24
24
24
25
25
25
25
25
25
26
26

275.6 Function Summary Table

305.7 Timing Limitations

305.8 Erratta / Notes
31

316.1 Absolute Maximum Specifications

316.2 Recommended operating conditions

316.3 DC Specifications

316.4 Protocol Timing

326.5 Maximum Drdy Response Delays
33

337.1 Dimensions

337.2 Marking
34

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ii

www.qprox.com QT60161B / R1.03

Table 1.1 Device Pin Lis

t

I/O PPMOSI1

I/O PPMISO2

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.

DescriptionTypeNamePin

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).
Master-In / Slave Out SPI line. Not used in Master/Slave SPI mode.
In Slave mode outputs data to host (out only).
SPI Clock. In Master mode is an output; in Slave mode is an inputI/O PPSCK3
Reset input, active low resetIRST4
+5V supplyPwrVdd5
GroundPwrVss6
Oscillator drive output. Connect to resonator or crystal.plyO PPXTO7
Oscillator drive input. Connect to resonator or crystal, or external clock source.IXTI8
UART receive inputIRX9
UART transmit outputO PPTX10
Wake from Sleep / Sync to noise sourceIWS11
Sample output controlO PPSMP12
X0 Drive matrix scan / Communications option A inputI/O PPX0OPA13
X1 Drive matrix scan / Communications option B inputI/O PPX1OPB14
X2 Drive matrix scanO PPX215
X3 Drive matrix scanO PPX316
+5V supplyPwrVdd17
GroundPwrVss18
XS0 Scan input lineIXS019
XS1 Scan input lineIXS120
XS2 Scan input lineIXS221
XS3 Scan input lineIXS322
YS0 Scan output lineO PPYS023
YS1 Scan output lineO PPYS124
YS2 Scan output lineO PPYS225
YS3 Scan output lineO PPYS326
+5 supply for analog sectionsPwrAVdd27
Analog groundPwrAGnd28
+5 supply for analog sectionsPwrAref29
Cs3 control BI/O PPCS3B30
Cs3 control AI/O PPCS3A31
Cs2 control BI/O PPCS2B32
Cs2 control AI/O PPCS2A33
Cs1 control BI/O PPCS1B34
Cs1 control AI/O PPCS1A35
Cs0 control BI/O PPCS0B36
Cs0 control AI/O PPCS0A37
+5 supplyPwrVdd38
GroundPwrVss39
Active low LED status drive / Activity indicatorO PPLED40
Data ready output for Slave SPI mode; active lowO ODDRDY41
Vref input for conversion referenceIVref42
Oscilloscope sync outputO PPSO43
Slave select for SPI direction control; active lowI/O ODSS44

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©Quantum Research Group Ltd.

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.

Figure 1-1 Field flow between X and Y elements

overlying panel

X

element

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.

Figure 1-3 Fields With a Conductive Film

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

Y

elem ent

Figure 1-2 Field Flows When Touched

X

element

Figure 1-4 Sample Electrode Geometries

PARALLEL LINES SERPENTINE SPIRAL

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

overlying panel

Y

element

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.

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4

www.qprox.com QT60161B / R1.03

©Quantum Research Group Ltd.

V

Figure 1-5 Circuit Block Diagram

cc

Opt B

Opt A

QT60161

LED

Scope
Sync

Reset

Wake /
Sync

CS0A

CS0B

SPI
to Host

CS1A

UART

CS1B

to Host

CS2A

CS2B

CS3A

CS3B

Scan Output

VREF

Scan Input

Sample

X0

X1

X2

X3

Sample caps

CS0

CS1

CS2

CS3

Y0 Y1 Y2 Y3

X0

X1

X2

X3

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).

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

KEYMATRIX

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.

Figure 1-6 Detection and Drift Compensation

Reference

2.2 Positive Threshold

See also command ^B, page 21

Hysteresis

Threshold

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.

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Output

5

Signal

www.qprox.com QT60161B / R1.03

©Quantum Research Group Ltd.

Drift compensation should usually be set to compensate
faster for increasing signals than for decreasing signals.
Decreasing signals should not be compensated quickly, since
an approaching finger could be compensated for partially or
entirely before even touching the touch pad. However, an
obstruction over the sense pad, for which the sensor has
already made full allowance for, could suddenly be removed
leaving the sensor with an artificially suppressed reference
level and thus become insensitive to touch. In this case, the
sensor should compensate for the object's removal by raising
the reference level quickly.

The drift compensation rate can be set for each key
individually, and can also be disabled completely if desired on
a per-key basis.

Drift compensation and the detection time-outs (Section 2.5)
work together to provide for robust, adaptive sensing. The
time-outs provide abrupt changes in reference location
depending on the duration of the signal 'event'.

2.5 Negative Recalibration Delay

See also command ^L, page 23

If a foreign object contacts a key the key's signal may change
enough in the negative direction, the same as a normal
touch, to create an unintended detection. When this happens
it is usually desirable to cause the key to be recalibrated in
order to restore its function after a time delay of some
seconds.

The Negative Recal Delay timer monitors this detection
duration; if a detection event exceeds the timer's setting, the
key will be recalibrated so that it can function thereafter. The
^L function can be altered on a key by key basis. It can be
disabled if desired by setting the ^L parameter to zero, so that
it will never recalibrate automatically.

2.6 Detection Integrator

See also command ^J, page 22

To suppress false detections caused by spurious events like
electrical noise, the QT60161B incorporates a 'detection
integrator' counter that increments with each detection
sample until a user-defined limit is reached, at which point a
detection is confirmed. If no detection is sensed on any of the
samples prior to the final count, the counter is reset
immediately to zero, forcing the process to restart.

When an active key is released, the counter must count down
to zero before the key state is set to 'off'. Setting a key’s
detection integrator target value to zero disables that key
although the bursts for that key continue normally.

The detection integrator is extremely effective at reducing
false detections at the expense of slower reaction times. In
some applications a slow reaction time is desirable; the
detection integrator can be used to intentionally slow down
touch response in order to require the user to touch longer to
operate the key.

There are 16 possible values for this function.

2.7 Positive Recalibration Delay

See also command ^K, page 23

A recalibration can occur automatically if the signal swings
more positive than the positive threshold level. This condition
can occur if there is positive drift but insufficient positive drift
compensation, or if the reference moved negative due to a
recalibration, and thereafter the signal returned to normal.

As an example of the latter, if a foreign object or a finger
contacts a key for period longer than the Negative Recal
Delay, the key is recalibrated to a new lower reference level.
Then, when the condition causing the negative swing ceases
to exist (e.g. the object is removed) the signal can suddenly
swing back positive to near its normal reference.

It is almost always desirable in these cases to cause the key
to recalibrate to the new signal level so as to restore normal
touch operation. The device accomplishes this by simply
setting Reference = Signal.

The time required to detect this condition before recalibrating
is governed by the Positive Recalibration Delay command. In
order for this feature to operate, the signal must rise through
the positive threshold level (Section 2.2) for the proscribed
interval determined by Setup ^K.

After the Positive Recal Delay interval has expired and the
fast-recalibration has taken place, the affected key will once
again function normally. This interval can be set on a per-key
basis; it can also be disabled by setting ^K to zero.

2.8 Reference Guardbanding

See also commands ^N, ^O, page 23; ‘L’, page 24

The QT60161B provides for a method of self-checking that
allows the host to ascertain whether one or more key
reference levels are 'out of spec'. This feature can be used to
determine if an X or Y line has broken, the matrix panel has
delaminated from the control panel, or there is a circuit fault.

Reference guardbanding alerts the host when the reference
level of a key falls outside of user-defined levels. The
reference guardband is determined as a percent deviation
from the 'locked' reference level for each individual key.
These reference levels can be stored into internal eeprom via
the Lock command 'L' during production; deviations in
reference levels that fall outside the guardbands centered on
these locked reference levels are then reported as key errors.

The amount of guardbanding can be set differently for each
signal direction relative to the stored and locked levels. The
possible settings are from 0.1% to 25.5% of signal reference
in steps of 0.1% as set by commands ^N (positive swings)
and ^O (negative swings). A setting of 0 (zero) disables the
corresponding guardband direction.

Once the L command has recorded all values of signal
reference into eeprom, and if guardbanding is enabled, the
part will compare the actual reference level of each key to its
corresponding guardbands to see if it falls outside of these
limits. If so, either of bits 2 and 3 of command 'e' will be set
for that key. The error will also appear in a bitfield reported
via command 'E'.

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2.9 Adjacent Key Suppression (‘AKS’)

See also command ^P, page 24

The QT60161B incorporates adjacent key suppression
(‘AKS’) that can be enabled on a per-key basis. AKS permits

6

www.qprox.com QT60161B / R1.03

©Quantum Research Group Ltd.

the suppression of multiple key presses based on relative
signal strengths. AKS assists in solving the problem of
surface water which can bridge a key touch to an adjacent
key, causing multiple key presses, causing multiple key
presses even though only one key was touched. This feature
is also useful for panels with tightly spaced keys, where a
fingertip can partially overlap an adjacent key.

AKS works for keys that are AKS-enabled anywhere in the
matrix and is not restricted to physically adjacent keys; the
device has no knowledge of which keys are physically
adjacent. When enabled for a key, adjacent key suppression
causes detections on that key to be suppressed if any other
AKS-enabled key in the panel has a more negative signal
deviation from its reference.

This feature does not account for varying key gains (burst
length) but ignores the actual negative detection threshold
setting for the key. If AKS-enabled keys in a panel have
different sizes, it may be necessary to reduce the gains of
larger keys relative to smaller ones to equalize the effects of
AKS. The signal threshold of the larger keys can be altered to
compensate for this without causing problems with key
suppression.

AKS works to augment the natural moisture suppression
capabilities of the device (Section 3.10), creating a more
robust touch panel.

2.10 Full Recalibration

See also command ‘b’, page 24

The part fully recalibrates one or more keys after the ‘b’
command has been issued to it, depending on the current
scope of the ‘b’ command. The device recalibrates all keys on
powerup, after a hard reset via the RST pin or on power up,
or via a reset using the ‘r’ command. Since the circuit
tolerates a very wide dynamic signal range, it is capable of
adapting to a wide mix of key sizes and shapes having widely
varying Cx coupling capacitances.

If a false calibration occurs due to a key touch or foreign
object on the keys during powerup, the affected key will
recalibrate again when the object is removed depending on
the settings of Positive Threshold and Positive Recal Delay
(Sections 2.2 and 2.7).

Calibration requires 9 full burst cycles to complete, and so the
time it takes is dependent on the burst spacing parameter
(Section 3.8 also, ^G, page 22.

2.11 Device Status & Reporting

See also commands ‘7’, page 19; ‘e’, page 19; ‘E’, page 20;

‘k’, page 20, ‘K’, page 20

The device can report on the general device status or specific
key states including touches and error conditions, depending
on the command used.

Usually it is most efficient to periodically request the general
device status using command ‘7’ first, as the response to this
command is a single byte which reports back on behalf of all
keys. ‘7’ indicates if there are any keys detecting, calibrating,
or in error.

If command ‘7’ reports a condition requiring further
investigation, the host device can then use commands ‘e’, ‘E’,
‘k’ or ‘K’ to provide further details of the event(s) in progress.
This hierarchical approach provides for a concise information

flow using minimal data transfers and low host software
overhead.

3 Circuit Operation

A QT60161B reference circuit is shown in Figure 2-1.

3.1 Matrix Scan Sequence

The circuit operates by scanning each key sequentially, key
by key. Key scanning begins with location X=0 / Y=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 Y0X0 Y0X1 Y0X2 Y0X3 Y1X0 etc.

Each key is sampled from 1 to 64 times in a burst whose
length is determined by Setup ^F. A burst is completed
entirely before the next key is sampled; at the end of each
burst the resulting analog signal is converted to digital using a
single-slope conversion process. The length of the burst
directly impacts on the gain of the key; each key can have a
unique burst length in order to allow tailoring of key sensitivity
on a key by key basis.

3.2 Signal Path

Refer to Figures 1-5, 3-1, and 3-2.

X-Drives. The X drives are push-pull CMOS lines which drive
charge through the matrix keys on the positive and negative
edges of X. Only the positive edge of X is used for signal
purposes, however the negative edge must cause the charge
across the keys to neutralize prior to the next positive edge,
else the sampling mechanism will cease after one pulse. The
part accomplishes this by holding all Y lines to ground during
the falling edge of X.

Charge gate. Only one X row is pulsed during a burst.
Charge is coupled across a key's Cx capacitance from the X
row to all Y columns. A particular key is chosen by gating the
charge from a single Y column into a single one of four
possible sampler capacitors. The other three X and three Y
lines are clamped to ground during this process.

Dwell time. The dwell time is determined internally and is
the same as one oscillator period, i.e. 83.3ns with a 12MHz
resonator. The dwell time is set via internal switching action

Figure 3-1 QT60161B Circuit Model

X drive

Start

Result

(1 of 4)

X

electrode

CSA

14 bit ADC

CSB

Done

Single-slope

SMP

Burst

Control

Cx

X

Y line (1 of 4)

Cs (1 of 4)

Rs (1 of 4)

Y
electrode

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which limits the interval during which charge can be accepted
by a Cs capacitor after the rise of an X drive line.

Dwell time has a dramatic effect on the suppression of
moisture films as described in Section 3.10.

Cs Charge Integrator capacitor. The Cs capacitors
integrate charge arriving through the matrix keys' Cx
capacitances, correspondent with the rise of X; to do this a
switching arrangement on the Cs control pins permits the
charge to accumulate so that the B side of the Cs capacitors
becomes negative when the A side is clamped to ground.

Charge conversion. At the end of each burst the voltage on
Cs is converted to digital by means of a single-slope
conversion process, using one of the external resistors to
ramp up the capacitor towards a reference voltage. The
elapsed time required to reach the comparison voltage is the
digital result. The time required to perform the conversion
depends on Cs, Cx, Rs, Aref, and the burst length.

3.3 'X' Electrode Drives

The 'X' lines are directly connected to the matrix without
buffering. The positive edges of these signals are used to
create the transient field flows used to scan the keys. Only
one X line is actively driving the matrix for scanning purposes
at a time, and it will pulse repetitively for a ‘burst length’ for
each key as determined by the 'Burst Length' Setups
parameter (see command ^F, page 21 and Section 3.5).

3.3.1 RFI F

X drive lines will radiate a small amount of RFI. This can be
attenuated if required by using series resistor in-line with
each X trace; the resistor should be placed near to the
QT60161B. Typical values can range from 100 to 500 ohms.
Excessive amounts of R will cause a counterproductive drop
in signal strength. RC networks can also be used as shown in
Figure 4-6.

Resistance in the X lines also have the positive effect of
limiting ESD discharge currents (Section 3.18).

3.3.2 N

External noise, sometimes caused by ground bounce due to
injected line noise, can couple into the X lines and cause
signal interference in extreme cases. Such noise can be
readily suppressed by the use of series resistors as
described above. Adding a small capacitor to the matrix line
on the QT60161B side of the R, for example 100pF to ground
near the QT60161B, will greatly help to reduce such effects.

ROM

X L

INES

OISE COUPLING INTO

X

LINES

3.4 'Y' Gate Drives

There are 4 'Y' gate drive pairs (CS0A,B..CS3A,B); only one
pair of these lines is used during a burst for a particular key.
The magnitude of the voltages accumulated on the Cs
capacitors should never exceed 0.25V.

3.4.1 RFI F

Y lines are nearly 'virtual grounds' and are negligible radiators
of RFI; in fact, they act as ‘sinks’ for RFI emitted by the X
lines. Resistors are not required in the Y lines for RFI
suppression, and in fact can introduce cross-talk among keys
if large enough. However, small resistance values can be
beneficial to limit ESD transients and make the circuit more
resistant to external RF fields (Section 3.18).

3.4.2 N

External noise, sometimes caused by ground bounce due to
power line noise, can couple into the Y lines and cause signal

ROM

Y L

INES

OISE COUPLING INTO

Y L

INES

interference in extreme cases. Such noise can be readily
suppressed by adding a 22pF capacitor from each Y line to
ground near the QT60161B.

3.5 Burst Length & Sensitivity

See also Command ^F, page 21

The signal gain in volts / pF of Cx for each key is controlled
by circuit parameters as well as the burst length.

The burst length is simply the number of times the
charge-transfer (‘QT’) process is performed on a given key.
Each QT process is simply the pulsing of an X line once, with
a corresponding Y line gated so as to capture the resulting
charge passed through the key’s capacitance Cx.

QT60161B devices use a finite number of QT cycles which
are executed in a short burst. There can be from 1 to 64 QT
cycles in a burst, in accordance with the list of permissible
values shown on page 21. If a key's burst length is set to
zero, that burst is disabled but its time slot in the scanning
sequence of all keys is preserved so as to maintain scan
timing.

Increasing burst length directly affects key sensitivity. This
occurs because the accumulation of charge on Cs is directly
linked to the burst length. The burst length of each key can be
set individually, allowing for direct digital control over the
signal gains of each key, indivudally.

Apparent touch sensitivity is also controlled by the Negative
Threshold setting (Section 2.1). Burst length and negative
threshold interact; normally burst lengths should be kept as
short as possible to limit RF emissions, but the threshold
setting should normally be kept above a setting of 6 to limit
false detections. The detection integrator can also prevent
false detections at the expense of slower reaction times
(Section 2.6).

The value of Rs also affects sensitivity. Higher values of Rs
will lead to larger values of ADC result and higher conversion
gains. The side effect of this is that the conversion will take
longer and timing conflicts can occur (Section 3.6).

Cs does not significantly affect gain. Smaller values of Cs will
have higher delta signal voltages but this gain increase is
offset by the decrease in gain caused by a steeper ADC
conversion slope. However smaller values of Cs lead to faster
conversion times for a given value of Rs, which in turn allows
for more relaxed burst timings. Smaller values of Cs also
reduce the dynamic range of the system, meaning that the
acquisition becomes less tolerant of high values of Cx, due to
earlier saturation of the voltage across Cs.

3.6 Burst Acquisition Duration

The total time required to acquire a key's signal depends on
the burst length for that key plus the time required to convert
the voltage on the corresponding Cs capacitor to digital. The
conversion is performed via a single-slope ADC process
using one of the external Rs resistors.

If the total time required for the acquisition, i.e. the burst
length plus ADC times plus the signal processing and serial
interface command handler times exceed the burst spacing
setup parameter (Section 3.8), significant timing errors and
communications problems can occur.

The time taken by the burst itself is straightforward to
quantify, but the time required to do the ADC step is not. The
ADC step depends on the value of Vref (pin 42), Cs, Rs, and

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Cx. Therefore it is vital that the circuit be checked with an
oscilloscope to make sure that burst spacings are unaffected
during normal operation.

3.7 Intra-Burst Spacing

See also Command ^M, page 23

The time between X drive pulses during a burst is the
intra-burst pulse QT spacing. This timing has no noticeable
effect on performance of the circuit, but can have an impact
on the nature of RF spectral emissions from the matrix panel.
The setting of this function can be from 1µs to 10µs, loosely
corresponding to fundamental emission frequencies of from
1MHz to 100kHz respectively.

Longer spacings require more time to execute and can limit
the operational settings of burst length and/or burst spacing
(Section 5.7).

The intra-burst QT spacing has no effect on sensitivity or
water film suppression and is not particularly important to the
sensing function other than described above.

3.8 Burst Spacing

See also Command ^G, page 22

The interval of time from the start of one burst to the start of
the next is known as the burst spacing. This is an alterable
parameter which affects all keys.

Shorter spacings result in faster response time, but due to
increasing timing restrictions at shorter spacings burst
lengths or the conversion resolution may be restricted,
limiting the amount of gain that can be obtained; see Sections

3.6 and 5.7. Conversely longer spacings permit higher burst
lengths but slow down response time.

Three settings of burst spacing are possible: 500µs, 1ms, and
2ms.

3.9 Sample Capacitors

Charge sampler capacitors Cs should be either ceramic NPO,
X7R 5%, or PPS film for stability reasons.

The values of capacitance should not be altered from that
shown in the schematic of Figure 3-2 without good reason.

Changes in Cs have only a limited effect on signal gain.

3.10 Water Film Suppression

Water films on the user surface can cause problems with
false detection under certain conditions. Water films on their
own will not normally cause false detections. The most
common problem occurs when surface water bridges over 2
or more keys, and a user touches one of the keys and the
water film causing an adjacent key to also trigger. Essentially,
the water film transports the touch contact to adjacent keys.

The circuit suppresses water coupling by having a short dwell
time, equal to one oscillator period or 83ns. A short dwell time
reduces the amount of charge collected via resistive water
films, i.e. it suppresses charge from areas adjacent to the
scanned key. This effect has nothing to do with the frequency
of the burst itself.

Very short dwell times can cause excess suppression of
human touch as well. If series resistors are used in line with
the X and Y matrix lines for noise and ESD suppression

(Section 3.18), a short dwell time can seriously affect signal
gain.

Mechanical measures can also be used to suppress key
cross-coupling, for example one can use raised plastic
barriers between keys, or placing keys in shallow wells to
lengthen the electrical path from key to key.

3.11 Reset Input

The RST’ pin can be used to reset the device to simulate a
power down cycle, in order to bring the part up into a known
state should communications with the part be lost. The pin is
active low, and a low pulse lasting at least 10µs must be
applied to this pin to cause a reset.

To provide for proper operation during power transitions the
devices have an internal brown-out detector set to 4 volts.

A reset command, ‘r’, is also provided which generates an
equivalent hardware reset (page 25).

3.12 Oscillator

The oscillator can use either a quartz crystal or a ceramic
resonator. In either case, the XTI and XTO 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 XTI; XTO should
be left unconnected.

The frequency of oscillation should be 12MHz +/-2%.

3.13 Startup / Calibration Times

The QT60161B requires initialization times as follows:

1. From very first powerup to ability to communicate:
2,000ms (One time event to initialize all of eeprom)

2. Normal cold start to ability to communicate:
70ms (Normal initialization from any reset)

3. Calibration time per key vs. burst spacings:
spacing = 500µs: 100ms
spacing = 1ms: 150ms
spacing = 2ms: 300ms

To the above, add 2,000ms or 70ms from (1) or (2) for
the total elapsed time from reset to ability to report key
detections.

Keys that cannot calibrate for some reason require 5
calibration cycles before they report as errors. However, the
device can report back during this interval that the key(s)
affected are still in calibration via status function bits.

3.14 Sleep_Wake / Noise Sync Pin (WS)

The Sleep_wake and Noise sync features use input pin WS.
The Sleep and Sync features can be used simultaneously;
the part can be put into Sleep mode, but awakened by a
noise sync signal which is gated in at the time desired.

Sleep mode: See also command ‘Z’, page 25. The device
can be put into an ultra low-power sleep mode using the ‘Z’
command. When this command is received, the WS pin must
be placed immediately thereafter into a logic-high state. The
part will complete an ongoing burst before entering Sleep.
The part can be awakened by a low transition on the WS pin
lasting at least 5µs. One convenient way to wake the part is
to connect WS to MOSI, and have the host send a null

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Figure 3-2 Recommended Circuit Diagram

command to the device. The part will wake and the null
command will not be processed. The MOSI line in turn
requires a pullup resistor to prevent the line from floating low
and causing an unintentional wake from sleep.

During Sleep the oscillator is shut down, and the part
hibernates with microamp levels of current drain. When the
part wakes, the part resumes normal functionality from the
point where it left off. It will not recalibrate keys or engage in
other unwarranted behavior.

Just before going to sleep the part will respond with a
response of 'Z'. In slave-only SPI mode (see Section 4.3), the
SS line must be floated high by the host as soon as it
receives this response; if SS does not float high, sleep will fail
and the device will instead completely reset after about 2
seconds. Upon waking the part will issue another 'Z' byte
back to the host.

Noise sync: See also command ^W,
page 26. External fields can cause

interference leading to false
detections or sensitivity shifts. The
strongest external fields usually
come from AC power. RF noise
sources are heavily suppressed by
the low impedance nature of the QT
circuitry itself.

External noise only becomes a
problem if the noise is uncorrelated
with signal sampling; uncorrelated
noise can cause aliasing and beat
effects in the key signals. To
suppress this problem the devices
feature a noise sync input which
allows bursts to synchronize to the
noise source. This same input can
also be used to wake the part from a
low-power Sleep state.

The device’s bursts can be
synchronized to an external source
of repetitive electrical signal, such as
50Hz or 60Hz, or possibly a video
display vertical sync line, using the
Sleep_wake / Noise sync line. The
noise sync operating mode is set by
command ^W. This feature allows
dominant external noise signals to
be heavily suppressed, since the
system and the noise become
synchronized and no longer beat or
alias with respect to each other. The
sync occurs only at the burst for key
0 (X0Y0); the device waits for the
sync signal for up to 100ms after the
end of a preceding full matrix scan
(after key #15), then when a negative
sync edge is received, the matrix is
scanned in its entirety again.

The sync signal drive should be a
buffered logic signal, or perhaps a
diode-clamped signal, but never a
raw AC signal from the mains.

Since Noise sync is highly effective
yet simple and inexpensive to implement, it is strongly
advised to take advantage of it anywhere there is a possibility
of encountering electric fields. Quantum’s QmBtn software
can show signal noise caused by nearby AC electric fields
and will hence assist in determining the need to make use of
this feature.

If the sync feature is enabled but no sync signal exists, the
sensor will continue to operate but with a delay of 100ms
from the end of one scan to the start of the next, and hence
will have a slow response time.

3.15 LED / Alert Output

Pin 40 is designed to drive a low-current LED, 5mA
maximum, in an active-low configuration. Higher currents can
cause significant level shifts on the die and are not advised.
The LED will glow brightly (i.e. pin 40 will be solid low) during
calibration of one or more keys, for example at startup. When
a key is detected, the LED will pulse low for the duration of

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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 key’s 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.

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 ‘SO’ pin 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.

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.

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.

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.

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: Section 4.3
SPI Master-Slave Mode: Section 4.4
UART Interface: Section 4.5
Parallel Interface: 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.

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