QProxTM QT140 / QT150

AND

5 K

OUCH

TM S

ENSOR

APPLICATIONS

Instrument panels
Gaming machines

Access systems
Pointing devices

Appliance controls
Security systems

PC Peripherals
Backlighted buttons

QT140 / QT150 charge-transfer ("QT'") QTouch ICs are self-contained digital controllers capable of detecting near-proximity or
touch on 4 or 5 electrodes. They allow electrodes to project independent sense fields through any dielectric like glass, plastic,
stone, ceramic, and wood. They can also turn metal-bearing objects into intrinsic sensors, making them responsive to proximity
or touch. This capability coupled with their continuous self-calibration feature can lead to entirely new product concepts, adding
high value to product designs.

Each of the channels operates independently of the others, and each can be tuned for a unique sensitivity level by simply
changing its sample capacitor value.

The devices are designed specifically for human interfaces, like control panels, appliances, gaming devices, lighting controls,
or anywhere a mechanical switch or button may be found; they may also be used for some material sensing and control
applications.

These devices require only a common inexpensive capacitor per sensing channel in order to function. They also offer patent
pending AKSTM Adjacent Key Suppression which suppresses touch from weaker responding keys and allows only a dominant
key to detect, for example to solve the problem of large fingers on tightly spaced keys.

These devices also have a SYNC I/O pin which allows for synchronization with additional similar parts and/or to an external to
suppress interference.

The RISC core of these devices use signal processing techniques pioneered by Quantum which are designed to survive
numerous real-world challenges, such as `stuck sensor' conditions, component ageing, moisture films, and signal drift.

By using the charge transfer principle, these devices deliver a level of performance clearly superior to older technologies yet
are highly cost-effective.

QT140/150 1.01/1102

/RST

OSC_I

OSC_O

OPT2

OPT1

SYNC

OUT5

OUT4

OUT3

OUT1

AKS

SNS5B

Vss

Vdd

SNS1A

SNS1B

SNS2A

SNS2B

Vss

OUT2

SNS3A

SNS3B

SNS4A

SNS4B

SNS5A

Vss

SSOP

/RST

OSC_I

OSC_O

OPT2

OPT1

SYNC

OUT5

OUT4

OUT3

OUT1

AKS

SNS5B

Vdd

Vss

SNS1A

SNS1B

SNS2A

Vdd

OUT2

SNS2B

SNS3A

SNS3B

SNS4A

SNS4B

SNS5A

DIP

Completely independent QT touch circuits

Individual logic outputs per channel (open drain)

Projects prox fields through any dielectric

Only one external capacitor required per channel

Sensitivity easily adjusted on a per-channel basis

100% autocal for life - no adjustments required

3~5.5V, 5mA single supply operation

Toggle mode for on/off control (strap option)

10s, 60s, infinite auto-recal timeout (strap options)

AKSTM Adjacent Key Suppression (pin option)

Sync pin for multi-chip sync or line sync

Less expensive per key than many mechanical switches

Eval board with backlighting - p/n E160

QT150-AS

-40

C to +105

QT150-D

C to +70

QT140-AS

-40

C to +105

QT140-D

C to +70

DIP-28

SSOP-28

AVAILABLE OPTIONS

QT150 shown - NOTE: Pinouts are not the same!

1 - OVERVIEW

QT140/150 devices are burst mode digital charge-transfer
(QT) sensor ICs designed specifically for touch controls; they
include all hardware and signal processing functions
necessary to provide stable sensing under a wide variety of
conditions. Only a single low cost capacitor per channel is
required for operation.

Figures 1-6 and 1-7 show basic circuits for these devices.
See Table 1-1 for device pin listings.

The DIP and SOIC pinouts are not the same and serious
damage can occur if a part is miswired.

1.1 BASIC OPERATION

The devices employ bursts of charge-transfer cycles to
acquire signals. Burst mode permits low power operation,
dramatically reduces RF emissions, lowers susceptibility to
RF fields, and yet permits excellent speed. Internally, signals
are digitally processed to reject impulse noise using a
'consensus' filter that requires three consecutive
confirmations of detection. Each channel is measured in
sequence starting with Channel 1.

The QT switches and charge measurement hardware
functions are all internal to the device. A single-slope
switched capacitor ADC includes the QT charge and transfer
switches in a configuration that provides direct ADC
conversion; an external Cs capacitor accumulates the charge
from sense-plate Cx, which is then measured.

Larger values of Cx cause the charge transferred into Cs to
rise more rapidly, reducing available resolution; as a
minimum resolution is required for proper operation, this can
result in dramatically reduced gain. Conversely, larger values
of Cs reduce the rise of differential voltage across it,
increasing available resolution by permitting longer QT
bursts. The value of Cs can thus be increased to allow larger
values of Cx to be tolerated. The IC is responsive to both Cx
and Cs, and changes in Cs can result in substantial changes
in sensor gain.

QT140/150 1.01/1102

/RST

OSC_I

OSC_O

OPT2

OPT1

SYNC

OUT4

OUT3

OUT1

AKS

Vss

Vdd

SNS1A

SNS1B

SNS2A

SNS2B

Vss

OUT2

SNS3A

SNS3B

SNS4A

SNS4B

Vss

SSOP

/RST

OSC_I

OSC_O

OPT2

OPT1

SYNC

OUT4

OUT3

OUT1

AKS

Vdd

Vss

SNS1A

SNS1B

SNS2A

Vdd

OUT2

SNS2B

SNS3A

SNS3B

SNS4A

SNS4B

DIP

Reset pin (active low input)

/RST

Reset pin (active low input)

/RST

Oscillator input

OSC_I

Oscillator input

OSC_I

Oscillator output

OSC_O

Oscillator output

OSC_O

Option Mode (Input pin - see Table 2-1)

OPT2

Option Mode (Input pin - see Table 2-1)

OPT2

Option Mode (Input pin - see Table 2-1)

OPT1

Option Mode (Input pin - see Table 2-1)

OPT1

Synchronization pin (I/O pin - pull high with 10K)

SYNC

Synchronization pin (I/O pin - pull high with 10K)

SYNC

Channel 5 output, o-d or p-p (n/c on QT140)

NC/OUT5

Channel 5 output, o-d or p-p (n/c on QT140)

NC/OUT5

Channel 4 output, o-d or p-p

OUT4

Channel 4 output, o-d or p-p

OUT4

Channel 3 output, o-d or p-p

OUT3

Channel 3 output, o-d or p-p

OUT3

Channel 2 output, o-d or p-p

OUT2

Channel 2 output, o-d or p-p

OUT2

Channel 1 output, o-d or p-p

OUT1

Channel 1 output, o-d or p-p

OUT1

Adjacent Key Suppression Opt. (input ; 1=AKS)

AKS

Adjacent Key Suppression Opt. (input; 1=AKS)

AKS

Output Option (input pin; 1= open drain)

Sense pin (to Cs5) n/c on QT140

NC/SNS5B

Sense pin (to Cs5) n/c on QT140

NC/SNS5B

Sense pin (to Cs5, electrode) n/c on QT140

NC/SNS5A

Supply negative rail (ground)

Vss

Sense pin (to Cs4)

SNS4B

Sense pin (to Cs5, electrode) n/c on QT140

NC/SNS5A

Sense pin (to Cs4, electrode)

SNS4A

Sense pin (to Cs4)

SNS4B

Sense pin (to Cs3)

SNS3B

Sense pin (to Cs4, electrode)

SNS4A

Sense pin (to Cs3, electrode)

SNS3A

Sense pin (to Cs3)

SNS3B

Sense pin (to Cs2)

SNS2B

Sense pin (to Cs3, electrode)

SNS3A

Sense pin (to Cs2, electrode)

SNS2A

Sense pin (to Cs2)

SNS2B

Sense pin (to Cs1)

SNS1B

Sense pin (to Cs2, electrode)

SNS2A

Sense pin (to Cs1, electrode)

SNS1A

Sense pin (to Cs1)

SNS1B

Negative power (Ground)

Vss

Sense pin (to Cs1, electrode)

SNS1A

Negative power (Ground)

Vss

Positive power

Vdd

Negative power (Ground)

Vss

Positive power

Vdd

Positive power

Vdd

Negative power (Ground)

Vss

Positive power

Vdd

Negative power (Ground)

Vss

Description

Name

Description

Name

QT140 / QT150 DIP-28

QT140 / QT150 SSOP-28

Table 1-1 Pin Listing

Fig 1-1 QT140 Pinouts

NOTE: SSOP / DIP Pinouts are not the same!

Unused channels: If a channel is not used, a dummy sense
capacitor (nominal value: 1nF) of any type must be
connected between the unused SNSnA / SNSnB pins ensure
correct operation.

Unused pins: Unused device pins labeled NC should
remain unconnected.

1.2 ELECTRODE DRIVE

These devices have completely independent sensing
channels. The internal ADC treats Cs on each channel as a
floating transfer capacitor; as a direct result, sense
electrodes can be connected to either SNSnA or SNSnB and
the sensitivity and basic function will be the same; however
there is an advantage in connecting electrodes to SNSnA
lines to reduce EMI susceptibility.

The PCB traces, wiring, and any components associated
with or in contact with SNSnA and SNSnB will become touch
sensitive and should be treated with caution to limit the touch
area to the desired location.

Multiple touch electrodes connected to SNSnA can be used,
for example to create control surfaces on both sides of an
object.

It is important to limit the amount of stray capacitance on the
SNSnA and SNSnB terminals, for example by minimizing
trace lengths and widths to allow for higher gains and lower
values of Cs.

1.3 KEY DESIGN

1.3.1 K

IRCHOFF

URRENT

Like all capacitance sensors, these parts rely on Kirchoff's
Current Law (Figure 1-2) to detect the change in capacitance
of the electrode. This law as applied to capacitive sensing
requires that the sensor's field current must complete a loop,
returning back to its source in order for capacitance to be
sensed. Although most designers relate to Kirchoff's law with
regard to hardwired circuits, it applies equally to capacitive
field flows. By implication it requires that the signal ground
and the target object must both be coupled together in some
manner for a capacitive sensor to operate properly. Note that
there is no need to provide actual galvanic ground
connections; capacitive coupling to ground (Cx1) is always

sufficient, even if the coupling might seem very tenuous. For
example, powering the sensor via an isolated transformer will
provide ample ground coupling, since there is capacitance
between the windings and/or the transformer core, and from
the power wiring itself directly to 'local earth'. Even when
battery powered, just the physical size of the PCB and the
object into which the electronics is embedded will generally
be enough to couple a few picofarads back to local earth.

1.3.2 K

EOMETRY

, S

IZE

AND

OCATION

There is no restriction on the shape of the key electrode; in
most cases common sense and a little experimentation can
result in a good electrode design. The devices will operate
with long thin electrodes, round or square ones, or keys with
odd shapes. Electrodes can also be on 3-dimensional
surfaces. Sensitivity is related to the amount of electrode
surface area, overlying panel material and thickness, and the
ground return coupling quality of the circuit.

If a relatively large touch area is desired, and if tests show
that the electrode has more capacitance than the part can
tolerate, the electrode can be made into a sparse mesh
(Figure 1-3) having lower Cx than a solid plane.

Since the channels acquire their signals in time-sequence,
any of the electrodes can be placed in direct proximity to
each other if desired without cross-interference.

1.3.3 B

ACKLIGHTING

EYS

Touch pads can be back-illuminated quite readily using
electrodes with a sparse mesh (Figure 1-3) or a hole in the
middle (Figure 1-4). The holes can be as large as 4 cm in
diameter provided that the ring of metal is at least twice as
wide as the thickness of the overlying panel, and the panel is
greater than 1/8 as thick as the diameter of the hole. Thin
panels do not work well with this method as they do not
propagate fields laterally very well, and will have poor
sensitivity in the middle. Experimentation is required.

A good example of backlighting can be found in the E160
evaluation board.

1.3.4 V

IRTUAL

APACITIVE

ROUNDS

When detecting human contact (e.g. a fingertip), grounding
of the person is never required. The human body naturally
has several hundred picofarads of `free space' capacitance
to the local environment (Cx3 in Figure 1-2), which is more
than two orders of magnitude greater than that required to
create a detection. The sensor's PCB however may be
physically small, so there may be little `free space' coupling
(Cx1 in Figure 1-2) between it and the environment to

QT140/150 1.01/1102

Figure 1-2 Kirchoff's Current Law

S e nse E le ctro de

S u rro u n d in g e n v iro n m e n t

SENSO R

Figure 1-3 Mesh Electrode Geometry

complete the return path. If the circuit ground cannot be
earth grounded by wire, for example via the supply
connections, then a `virtual capacitive ground' may be
required to increase return coupling.

A `virtual capacitive ground' can be created by connecting
the IC's circuit ground to:

(1) A nearby piece of metal or metallized housing;
(2) A floating conductive ground plane;
(3) A larger electronic device (to which its output might be

connected anyway).

Free-floating ground planes such as metal foils should
maximize exposed surface area in a flat plane if possible. A
square of metal foil will have little effect if it is rolled up or
crumpled into a ball. Virtual ground planes are more effective
and can be made smaller if they are physically bonded to
other surfaces, for example a wall or floor.

1.3.5 F

IELD

HAPING

The electrode can be prevented from sensing in undesired
directions with the assistance of metal shielding connected
to circuit ground (Figure 1-5). For example, on flat surfaces,
the field can spread laterally and create a larger touch area
than desired. To stop field spreading, it is only necessary to
surround the touch electrode on all sides with a ring of metal
connected to circuit ground. The ring will stop field spreading
from that point outwards.

If one side of the panel to which the electrode is fixed has
moving traffic near it, these objects can cause inadvertent
detections. This is called `walk-by' and is caused by the fact
that the fields radiate from either surface of the electrode
equally well. Again, shielding in the form of a metal sheet or
foil connected to circuit ground will prevent walk-by; putting
an air gap between the grounded shield and the electrode
will help to keep the value of Cx low.

1.3.6 S

ENSITIVITY

Sensitivity can be altered to suit various applications and
situations on a channel-by-channel basis. The easiest and

most direct way to impact sensitivity is to alter the value of
Cs; more Cs yields higher sensitivity.

1.3.6.1 Alternative Ways to Increase Sensitivity
Sensitivity can also be increased by using bigger electrodes,
reducing panel thickness, or altering panel composition.

Increasing electrode size can have diminishing returns, as
high values of Cx counteract sensor gain; however, Cs can
be increased to combat this up to the rated device limit. Also,
increasing the electrode's surface area will not substantially
increase touch sensitivity if its diameter is already much
larger in surface area than fingertip contact area.

The panel or other intervening material can be made thinner,
but again there are diminishing rewards for doing so. Panel
material can also be changed to one having a higher
dielectric constant, which will help propagate the field
through to the front. Locally adding some conductive material
to the panel (conductive materials essentially have an infinite
dielectric constant) will also help; for example, adding carbon
or metal fibers to a plastic panel will greatly increase frontal
field strength, even if the fiber density is too low to make the
plastic bulk-conductive.

1.3.6.2 Decreasing Sensitivity
In some cases the circuit may be too sensitive. Gain can be
lowered further by a number of strategies: a) making the
electrode smaller, b) making the electrode into a sparse
mesh using a high space-to-conductor ratio (Figure 1-3), or
c) by decreasing the Cs capacitors.

QT140/150 1.01/1102

Figure 1-4 Open Electrode for Back-Illumination

Figure 1-5 Shielding Against Fringe Fields

Sense

wire

Sense

wire

Part Number QT150