Data Sheet

and composition of any overlaying panel material, and the degree of ground coupling of both sensor and

object.

2.4.2 Increasing Sensitivity

In some cases it may be desirable to increase sensitivity; for example, when using the sensor with very

thick panels having a low dielectric constant, or when the device is used as a proximity sensor. Sensitivity

can often be increased by using a larger electrode or reducing panel thickness. Increasing electrode size

can have diminishing returns, since high values of Cx will reduce sensor gain.

The value of Cs also has a dramatic effect on sensitivity, and this can be increased in value with the

trade-off of slower response time and more power. Increasing the electrode's surface area will not

substantially increase touch sensitivity if its diameter is already much larger in surface area than the

object being detected. Panel material can also be changed to one having a higher dielectric constant,

which will better help to propagate the field.

In the case of proximity detection, usually the object being detected is on an approaching hand, so a

larger surface area can be effective.

Ground planes around and under the electrode and its SNSK trace will cause high Cx loading and

destroy gain. The possible signal-to-noise ratio benefits of ground area are more than negated by the

decreased gain from the circuit so ground areas around electrodes are discouraged. Metal areas near the

electrode will reduce the field strength and increase Cx loading and should be avoided, if possible. Keep

ground away from the electrodes and traces.

2.4.3 Decreasing Sensitivity

In some cases the QT1011 may be too sensitive. In this case gain can be easily lowered further by

decreasing Cs.

2.4.4 Proximity Sensing

By increasing the sensitivity, the QT1011 can be used as a very effective proximity sensor, allowing the

presence of a nearby object (typically a hand) to be detected.

In this scenario, as the object being sensed is typically a hand, very large electrode sizes can be used,

which is extremely effective in increasing the sensitivity of the detector. In this case, the value of Cs will

also need to be increased to ensure improved sensitivity, as mentioned in Section 2.4.2. Note that,

although this affects the responsiveness of the sensor, it is less of an issue in proximity sensing

applications; in such applications it is necessary to detect simply the presence of a large object, rather

than a small, precise touch.

AT42QT1011

Datasheet

DS40001947A-page 9