MGC3140 datasheet(18/49 Pages) MICROCHIP

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5.3

External Rx Electrodes

Rx electrodes are connected to the MGC3140. An electrode needs to be individually designed following

the guide lines from the "GestIC Design Guide” (DS40001716), for optimal E-field distribution and

detection of E-field variations inflicted by a user.

5.3.1

Electrode Equivalent Circuit

The hand position tracking and gesture recognition capabilities of a GestIC system depend on the

electrode design and their material characteristics.

A simplified equivalent circuit model of a generic GestIC electrode system is illustrated in the following

figure:

Figure 5-2. Electrodes Capacitive Equivalent Circuitry Earth Grounded

CRXTX

CTXG

CRXG

System ground

Transmitter signal

Electrode signal

Earth ground

E-field

VTX

System Ground

eRx

eTx

External Electrodes

VRXBUF

VTx

Tx electrode voltage

VRxBuf MGC3140 Rx input voltage

Capacitance between receive electrode and hand (earth ground). The user’s hand can always

be considered as earth-grounded due to the comparable large size of the human body.

CRxTx Capacitance between receive and transmit electrodes

CRxG Capacitance of the receive (Rx) electrode to system ground + input capacitance of the

MGC3140 receiver circuit

CTxG

Capacitance of the transmit (Tx) electrode to system ground

eRx

Rx electrode

eTx

Tx electrode

The Rx and Tx electrodes in a GestIC electrode system build a capacitance voltage divider with the

capacitances CRxTx and CRxG which are determined by the electrode design. CTxG represents the Tx

electrode capacitance to system ground driven by the Tx signal. The Rx electrode measures the potential

of the generated E-field. If a conductive object (e.g., a hand) approaches the Rx electrode, CH changes

its capacitance. Femtofarad changes are detected by the MGC3140 receiver. The equivalent circuit

formula for the earth-grounded circuitry is described in the following equation:

MGC3140

System Architecture

DS40002037A-page 18

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