STM8T141 Datasheet, PDF (13/50 Pages) STMicroelectronics – On-chip integrated voltage regulator

STM8T141
STM8T processing
5.3
Environment compensation filter (ECF)
5.3.1
ECF principle
The capacitive sensing channel reference value increases or decreases according to
environmental conditions such as temperature, power supply, moisture, and surrounding
conductive objects. The STM8T141 includes a built-in digital infinite impulse response (IIR)
filter capable of tracking slow changes in the environment called the Environment
Compensation Filter (ECF). This is a first order digital low pass filter with a gain of one. The
filter makes the reference follow slow changes of the signal while fast changes are
recognized as a touch or proximity.
When a touch or proximity condition is detected, the corresponding capacitive sensing
channel reference is frozen.
Figure 7. Environmental compensation filter (ECF) example 1
.UMBEROFCOUNTS
2EFERENCE
3IGNAL
2EFERENCE $4H
$ETECTION
:ONE
:ONE
:ONE
:ONE
:ONE
T
AI
Table 3. Explanation of ECF example 1
Zone 1
Zone 2
Zone 3
Zone 4
Event description
Detection state
ECF operation
The object (finger) is
outside the
electrode field
range.
Electrode
environment is
stable
The object, is inside the
electrode field range. It
induces a signal change
but, not large enough to
cross the detection
threshold (Dth).
The reference adapts
slowly to the object
proximity.
The object comes inside the
detection range before the
reference compensates for
its presence.
A touch or proximity event is
triggered because the
signal level falls below the
reference - D_Th.
The object exits
from the
electrode’s
detection range.
No detection
Detection
No detection
Active
Halt
Active
Reference
Adapting
Frozen
Adapting
Doc ID 15699 Rev 7
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