MXT1664T3-ABESSQTP datasheet(30/98 Pages) MICROCHIP

30 / 98 page

MXT1664T3 2.0

DS40002054A-page 30

 2018 Microchip Technology Inc.

6.6

Digital Filtering and Noise Suppression

The mXT1664T3 supports on-chip filtering of the acquisition data received from the sensor. Specifically, the Noise

Suppression T72 object provides an algorithm to suppress the effects of noise (for example, from a noisy charger

plugged into the user’s product). This algorithm can automatically adjust some of the acquisition parameters on-the-fly

to filter the analog-to-digital conversions (ADCs) received from the sensor.

Additional noise suppression is provided by the Self Capacitance Noise Suppression T108 object. Similar in both design

and configuration to the Noise Suppression T72 object, the Self Capacitance Noise Suppression T108 object is the

noise suppression interface for self capacitance touch measurements.

Noise suppression is triggered when a noise source is detected.

• A hardware trigger can be implemented using the NOISE_IN pin.

• The host driver code can indicate when a noise source is present.

• The noise suppression is also triggered based on the noise levels detected using internal line measurements.The

Noise Suppression T72 and Self Capacitance Noise Suppression T108 object selects the appropriate controls to

suppress the noise present in the system.

6.7

Shieldless Support and Display Noise Suppression

The mXT1664T3 can support shieldless sensor design even with a noisy LCD.

The Optimal Integration feature is not filtering as such, but enables the user to use a shorter integration window. The

integration window optimizes the amount of charge collected against the amount of noise collected, to ensure an optimal

SNR. This feature also benefits the system in the presence of an external noise source. This feature is configured using

the Shieldless T56 object.

Display noise suppression allows the device to overcome display noise simultaneously with external noise. This feature

is based on filtering provided by the Lens Bending T65 object (see Section 6.10 “Lens Bending”).

6.8

Retransmission Compensation

The device can limit the undesirable effects on the mutual capacitance touch signals caused by poor device coupling to

ground, such as poor sensitivity and touch break-up. This is achieved using the Retransmission Compensation T80

object. This object can be configured to allow the touchscreen to compensate for signal degradation due to these

undesirable effects. If self capacitance measurements are also scheduled, the Retransmission Compensation T80

object will use the resultant data to enhance the compensation process.

The Retransmission Compensation T80 object is also capable of compensating for water presence on the sensor if self

capacitance measurements are scheduled. In this case, both mutual capacitance and self capacitance measurements

are used to detect moisture and then, once moisture is detected, self capacitance measurements are used to detect

single touches in the presence of moisture.

6.9

Grip Suppression

The device has grip suppression functionality to suppress false detections from a user’s grip.

Mutual capacitance grip suppression works by specifying a boundary around a touchscreen, within which touches can

be suppressed whilst still allowing touches in the center of the touchscreen. This ensures that an accidental hand touch

on the edge is suppressed while still allowing a “real” (finger) touch towards the center of the screen. Mutual capacitance

grip suppression is configured using the Grip Suppression T40 object.

Self Capacitance grip suppression works by looking for characteristic shapes in the self capacitance measurement

along the touchscreen boundary, and thereby distinguishing between a grip and a touch further into the sensor. Self

capacitance grip suppression is configured using the Self Capacitance Grip Suppression T112 object.

6.10

Lens Bending

The device supports algorithms to eliminate disturbances from the measured signal.

When the sensor suffers from the screen deformation (lens bending) the signal values acquired by normal procedure

are corrupted by the disturbance component (bend). The amount of bend depends on:

• The mechanical and electrical characteristics of the sensor

• The amount and location of the force applied by the user touch to the sensor

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