QT115A-ISG Atmel, QT115A-ISG Datasheet - Page 35

• Manufacturer Part Number: QT115A-ISG
• Description: IC TOUCH SENSOR PROX 8SOIC
• Manufacturer: Atmel

Specifications of QT115A-ISG

• Input Type: *
• Output Type: *
• Interface: *
• Current - Supply: *
• Mounting Type: Surface Mount
• Operating Supply Voltage: 3 V to 5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: SO-8
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Package / Case: -
• Lead Free Status / Rohs Status: Details

4.2.2.5
4.2.2.6
4.2.2.7
Touch Sensors Design Guide
Coupling Length
Calculations for the X Electrode
Example Calculation
The goal with this interdigitated design is to optimize SNR by maximizing the coupling length
the X and Y electrodes within the confines of the space allocated for the key. The coupling length is
determined by a combination of the number of X and Y fingers, their individual widths, and the spacing
between them; several thin fingers means a longer coupling length than a few wide ones, which results
in a better SNR.
Given the widths of the Y and X traces, you will need to calculate the number of X fingers (X
will fit in the digitated electrode, allowing for a border at least T wide. Note that any unallocated width
remaining after the number of fingers has been calculated must be added to the border, so the width of
the border (X
Equation 4-6
definitions).
Equation 4-6. Calculation for X
If the following measurements are used:
then the calculations using
This results in the pattern shown in
1. That is, the total length of the facing edge between the X and Y electrodes.
border
gives the equations that can be used to calculate X
X

X
Where:

T = 0.5 mm
W = 10 mm
H = 8 mm
Y
X
X
) must also be calculated.
fingers
border
width
fingers
border
number; that is, round down to the nearest integer. For example,

...
=0.1 mm

= (W - T - Y
=
is the FLOOR operator, defined as the largest integer not greater than the

W - 3T - Y
Equation 4-6
=
=
=
= 9
= (10 - 0.5 - 0.1 - 9 x (0.75 + 0.1)) / 2
= (9.4 - 7.65) / 2
= 0.875 mm
fingers



(10 - 1.5 - 0.1) / (0.75 + 0.1)
8.4 / 0.85
9.88
width
Figure 4-3 on page
width
and X

- X
is as follows:
) / (1.5T + Y

fingers

border

(1.5T + Y
width
Mutual-capacitance Zero-dimensional Sensors
4-4.
width
)

)) / 2


fingers
and X
border

(see
6.6

10620D–AT42–04/09
Figure 4-2
is 6.
(1)
fingers
between
) that
4-3
for