Positive / Negative Drift

Drift in a general sense means adjusting reference level (of a sensor) to allow compensation for temperature (or other factor) effect on physical sensor characteristics. Decreasing reference level for such compensation is called Negative drift & increasing reference level is called Positive drift. Specifically, the drift compensation should be set to compensate faster for increasing signals than for decreasing signals.

Signals can drift because of changes in physical sensor characteristics over time and temperature. It is crucial that such drift be compensated for; otherwise false detections and sensitivity shifts can occur.

Drift compensation occurs only while there is no detection in effect. Once a finger is sensed, the drift compensation mechanism ceases since the signal is legitimately detecting an object. Drift compensation works only when the signal in question has not crossed the ‘Detect threshold’ level.

The drift compensation mechanism can be asymmetric; it can be made to occur in one direction faster than it does in the other simply by changing the appropriate setup parameters.

Signal values of a sensor tend to decrease when an object (touch) is approaching it or a characteristic change of sensor over time and temperature. Decreasing signals should not be compensated for quickly, as an approaching finger could be compensated for partially or entirely before even touching the channel (negative drift).

However, an object over the channel which does not cause detection, and for which the sensor has already made full allowance (over some period of time), could suddenly be removed leaving the sensor with an artificially suppressed reference level and thus become insensitive to touch. In the latter case, the sensor should compensate for the object’s removal by raising the reference level relatively quickly (positive drift).