MGC3030 datasheet(8/50 Pages) MICROCHIP

8 / 50 page

MGC3030/3130

DS40001667D-page 8

Advance Information

 2012-2015 Microchip Technology Inc.

1.0

THEORY OF OPERATION:

ELECTRICAL NEAR-FIELD

(E-FIELD) SENSING

Microchip’s GestIC is a 3D sensor technology which

utilizes an electric field (E-field) for advanced proximity

sensing. It allows realization of new user interface

applications by detection, tracking and classification of

a user’s hand gestures in free space.

E-fields are generated by electrical charges and

propagate three-dimensionally around the surface,

carrying the electrical charge.

Applying direct voltages (DC) to an electrode results in

a constant electric field. Applying alternating voltages

(AC) makes the charges vary over time and thus, the

field. When the charge varies sinusoidal with frequency

f, the resulting electromagnetic wave is characterized

by wavelength λ = c/f, where c is the wave propagation

velocity — in vacuum, the speed of light. In cases

where the wavelength is much larger than the electrode

geometry, the magnetic component is practically zero

and no wave propagation takes place. The result is

quasi-static electrical near field that can be used for

sensing conductive objects such as the human body.

Microchip’s GestIC technology uses transmit (Tx)

frequencies in the range of 100 kHz which reflects a

wavelength of about three kilometers. With electrode

geometries of typically less than fourteen by fourteen

centimeters, this wavelength is much larger in

comparison.

GestIC

systems

work

w/o

wave

propagation.

In case a person’s hand or finger intrudes the electrical

field, the field becomes distorted. The field lines are

drawn to the hand due to the conductivity of the human

body itself and shunted to ground. The three-

dimensional electric field decreases locally. Microchip’s

GestIC technology uses a minimum number of four

receiver (Rx) electrodes to detect the E-field variations

at different positions to measure the origin of the

electric field distortion from the varying signals

received. The information is used to calculate the

position, track movements (MGC3130) and to classify

movement patterns (gestures, MGC3X30).

Figure 1-1 and Figure 1-2 show the influence of an

earth-grounded body to the electric field. The proximity

of the body causes a compression of the equipotential

lines and shifts the Rx electrode signal levels to a lower

potential which is measured.

FIGURE 1-1:

EQUIPOTENTIAL LINES

OF AN UNDISTORTED

E-FIELD

FIGURE 1-2:

EQUIPOTENTIAL LINES

OF A DISTORTED E-FIELD

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