QT60040-D Atmel, QT60040-D Datasheet - Page 2

• Manufacturer Part Number: QT60040-D
• Description: SENSOR IC MATRIX TOUCH 4CH 14DIP
• Manufacturer: Atmel
• Series: QMatrix™r
• Type: Capacitiver

Specifications of QT60040-D

• Rohs Status: RoHS non-compliant
• Number Of Inputs/keys: 4 Key
• Resolution (bits): 12 b
• Data Rate/sampling Rate (sps, Bps): 106k
• Voltage Reference: Internal
• Voltage - Supply: 4.5 V ~ 5.25 V
• Current - Supply: 650µA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Through Hole
• Package / Case: 14-DIP (0.300", 7.62mm)
• Output Type: *
• Interface: *
• Input Type: *
• Other names: 427-1032

©Quantum Research Group Ltd.
1 - OVERVIEW
The QT60040 is a CMOS charge-transfer (QT) sensor designed
specifically for matrix touch controls; it includes all signal
processing functions necessary to provide stable sensing under a
wide variety of changing conditions. Only one low cost external
capacitor is required for operation.
The QT60040 uses burst-mode charge transfer methods
pioneered and patented by Quantum. This revolutionary new
technology allows the construction of entirely new forms of
keypanels which can include back-illumination, arbitrary shapes
of keys, 'morphed' keys wrapped onto complex surfaces, and
keys having unique textures and feel, all at very low cost.
The QT60040 uses a 4x1 matrix, having 4 'X' drive lines and 1 'Y'
receive
requirements and also lowers the external component count to
one charge sampling capacitor which is sequentially shared by
the four keys.
The QT60040 has four simple active-high CMOS outputs that go
high when the corresponding key is touched. Up to 2 keys can be
touched at the same time; three or more keys touched will limit to
the first two touch outputs. An option pin allows this to be
restricted to only one key if desired.
The device operates on a 2.5 to 5.5 regulated power supply
which can be from a common 78L05-type IC regulator or a simple
2-stage zener regulator supply.
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 rapid dQ/dt during the edge transitions of the X drive
pulse. The charge emitted by the X electrode is partly received
onto the Y electrode which is then captured by the Cs capacitor
and processed.
The QT60040 matrix uses 4 'X' edge-driven rows and 1 'Y' sense
column to detect 4 keys. The X drive occurs as a burst of pulses
on each key.
The charge flows set into motion by the X drive signals are
partially absorbed by the touch of a human finger (Figure 1-2)
resulting in a decrease in coupling from X to Y; coupled charge
increases in the presence of a conductive film like water (Figure
1-3) which acts to bridge the two elements. Increasing signals
due to water films are quite easy to discern and are not detected
by the QT60040.
lQ
Figure 1-1 Field flow between X and Y elements
driver
cmos
line.
This
element
configuration
X
reduces
overlying panel
element
interconnect
Y
- 2 -
1.2 CIRCUIT MODEL
An electrical circuit model is shown in Figure 1-4. The coupling
capacitance across the X and Y electrodes and from each to a
finger is represented by Cx1, Cx2a, and Cx2b. The sampling
capacitor Cs is used to accumulate charge during the course of a
burst.
ground, Cx3, is also shown.
QT switch timing action is shown in Figure 1-5.
Initially, switch S3 is closed to reset Cs then re-opened. After S3
is opened, S1 is closed to charge the capacitances associated
with the Y-line, including all Y-to-X capacitances. After S1 is
closed, one of the four X lines is raised high, so that there is then
a zero differential potential from the selected X line to the Y line.
Then, S1 is opened and S2 is closed, causing charge to flow
from the Cx capacitances into Cs; Cs charges up slightly with the
polarity shown. Then the selected X line is driven low, causing a
step-function decrease in charge on Cs whose magnitude is
proportionate to the amount of coupling from X to Y.
The final charge accumulated on Cs per QT cycle is thus a direct
function of Cx3 minus the small amount of charge subtracted via
the Cx1 / Cx2a / Cx2b / Cfinger network. Since the charge from
the Cx2a / Cx2b network is highly dependent on Cfinger, which
effectively forms a capacitive divider, the total charge absorbed
by Cs is dependent on touch: a touch nets more charge
transferred into Cs per QT cycle because less charge is
transferred out of Cs per QT cycle.
The acquisition process is controlled by a state machine which
continues the acquisition cycle as a burst, which finally
terminates when the voltage across Cs reaches the predefined
level Vref. This burst takes hundreds or even thousands of cycles
Water film
Figure 1-3 Fields With a Conductive Film
Figure 1-2 Field Flows When Touched
An important parasitic capacitance from the Y line to
driver
cm os
element
X
QT60040 / R1.04 / 0303
ove rly in g p an e l
elem ent
Y