AT42QT1040-MMH Atmel, AT42QT1040-MMH Datasheet - Page 9

• Manufacturer Part Number: AT42QT1040-MMH
• Description: IC TOUCH SENSOR 4KEY 20-VQFN
• Manufacturer: Atmel
• Series: QTouch™r
• Type: Resistiver

Specifications of AT42QT1040-MMH

• Touch Panel Interface: 4, 2-Wire
• Number Of Inputs/keys: 4 Key
• Data Interface: I²C, Serial
• Data Rate/sampling Rate (sps, Bps): 200k
• Voltage Reference: Internal
• Voltage - Supply: 1.8 V ~ 5.5 V
• Current - Supply: 10mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-VQFN Exposed Pad, 20-HVQFN, 20-SQFN, 20-DHVQFN
• Output Type: Logic
• Input Type: Logic
• Supply Voltage: 1.8 V to 5.5 V
• Dimensions: 3 mm L x 3 mm W x 0.8 mm H
• Output Voltage: 0.7 V to 0.8 V
• Temperature Range: - 40 C to + 85 C
• Termination Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Interface: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: AT42QT1040-MMH; AT42QT1040-MMHTR

Touch Sensors Design Guide
Capacitance (C) is defined in
Equation 1-1. Capacitance
It should therefore be clear that thinner panels and higher dielectric constant materials yield higher
capacitance change during touch and hence a higher gain and a better SNR.
Materials” on page 2-5
Figure 1-2.
In the context of capacitive sensors, SNR is defined as in
of the touch signal levels.
Equation 1-2. SNR
1. Note that this definition uses the RMS noise present during touch, as this is the worst case.
T
Touchscreen Panel
Touch Area (A)
SNR(dB) = 20Log( TouchStrength / NoiseTouched
TouchStrength = SignalTouched
NoiseTouched
where:


C
AVG100 means the simple numeric average of 100 data points, typically taken evenly
spaced over a period of 2 seconds.
RMS100 means the root-mean-square of 100 data points, typically taken evenly
spaced over a period of 2 seconds, using the AVG100 figure as a baseline.
=

------------------------- -
0
discusses the thickness of the panel and its effect on the SNR.
Overlying Panel ( )

T

r

A
Equation
RMS100
=
e
1-1.
r
n
--------------------------------------------------------------------------------------------------------------------- -
n

=
=
99
0

Signal n   SignalTouched
AVG100
- SignalUntouched
–
Equation
100
RMS100
1-2.
Introduction To Sensor Design
(1)
)
AVG100
AVG100
See
Section 2.3.3 “Front Panel
Figure 1-3

2
Sensor
Behind
Panel
10620D–AT42–04/09
for definitions
1-3