MGC3140 datasheet(19/49 Pages) MICROCHIP

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Equation 5-1. Electrodes Equivalent Circuit

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A common example of an earth-grounded device is a notebook, even with no ground connection via

power supply or Ethernet connection. Due to its larger form factor, it presents a high earth-ground

capacitance in the range of 50 pF and, thus, it can be assumed as an earth-grounded GestIC system. For

further information on sensor designs with earth-grounded as well as nonearth-grounded devices, see

"GestIC Design Guide” (DS40001716).

A brief overview of the typical values of the electrode capacitances is summarized in the table below:

Table 5-1. Electrode Capacitances Typical Values

Capacity

Typical value

CRxTx

10...30 pF

CTxG

10...1000 pF

CRxG

10...30 pF

<1 pF

Important: Ideal designs have low CRxTx and CRxG to ensure higher sensitivity of the electrode

system. Optimal results are achieved with CRxTx and CRxG values being in the same range.

5.3.2

Standard Electrode Design

The MGC3140 electrode system is typically a double-layer design with a Tx transmit electrode at the

bottom layer to shield against device ground and, thus, ensure high-receive sensitivity. Up to five

comparably smaller Rx electrodes are placed above the Tx layer providing the spatial resolution of the

GestIC system. Tx and Rx are separated by a thin isolating layer. The Rx electrodes are typically

arranged in a frame configuration as shown in the following electrode diagrams.

The frame defines the inside sensing area.

Larger dimensions yield in higher sensitivity of the system.

For more information on sensor design as well as the function of the center electrode, see "GestIC

Design Guide" (DS40001716).

The electrode shapes can be designed solid or structured. In addition to the distance and the material

between the Rx and Tx electrodes, the shape structure density also controls the capacitance CRxTx and

thus, the sensitivity of the system.

MGC3140

System Architecture

DS40002037A-page 19

MGC3140 Arkusz danych(PDF) 19 Page - Microchip Technology