MGC3130 – Sabrewing Evaluation Board
2013 Microchip Technology Inc.
DS41685A-page 19
FIGURE 3-3:
ELECTRODE LAYOUT
The electrode layout is based on a four-layer PCB design using FR4 material.
Three functional layers are used:
- Layer 1 (Top): Rx electrodes
- Layer 3: Tx electrode and Rx feeding lines
- Layer 4 (Bottom): Ground
Layer 2 is not used.
FIGURE 3-4:
PCB LAYER STACK
The design of Rx electrodes includes four frame electrodes and one center electrode,
as shown in Figure 3-3. The frame electrodes are named according to their cardinal
directions - north, east, south and west. The dimensions of the four Rx frame elec-
trodes define the maximum sensing area. The center electrode is structured (hatched)
to get a similar input signal level as the four frame electrodes.
The Tx electrode spans over the complete area underneath the Rx electrodes. It is
structured to reduce the capacitances between Rx and Tx (C
RxTx
). The area below the
center electrode covers 50% of the copper plane, the area around only 20%.
The Rx feeding lines are also routed in the third layer. They are embedded into the Tx
electrode (refer to Figure 3-3 and Figure 3-4). This supports shielding of the feeding
lines.
Dimensions are given in Table 3-1.
Tx: 35 µm
Tx
Rx Electrode: 18 µm
GND: 18 µm
Not Used: 35 µm
0.25 mm
0.15 mm
935
µ
m
540
µm
1.546
m
m
Top layer
Bottom
layer
2
nd
layer
3
rd
layer
Rx feeding line
