Freescale Semiconductor Evaluation Board MPR031/2 for 2- or 3-pad touch sensor controllers DEMOMPR031 DEMOMPR031 データシート
製品コード
DEMOMPR031
MPR03X
Sensors
20
Freescale Semiconductor
8
Filtering
8.1
Introduction
The MPR03X has three levels of filtering. The first and second level filters will allow the application to condition the signal for
undesired input variation. The third level filter can be configured to reject touch stimulus and be used as a baseline for touch
detection. Each level of filtering will be further described in this section.
undesired input variation. The third level filter can be configured to reject touch stimulus and be used as a baseline for touch
detection. Each level of filtering will be further described in this section.
8.2
First Level
The first level filter is designed to filter high frequency noise by averaging samples taken over short periods of time. The number
of samples can be configured to equal a set of values ranging from 6 to 34 samples. This value is set by the FFI in the AFE
Configuration Register (
of samples can be configured to equal a set of values ranging from 6 to 34 samples. This value is set by the FFI in the AFE
Configuration Register (
). The timing of this filter is also determined by the configuration of the electrode charge time
in the Filter Configuration Register (
Note that the electrode charge time must be configured for the capacitance in the application. The resulting value will affect the
period of the first level filter.
period of the first level filter.
8.3
Second Level
The second level filter is designed to filter low frequency noise and reject false touches due to inconsistent data. The number of
samples can be configured to equal a set of values ranging from 4 to 18. This value is set by the SFI in the Filter Configuration
Register (
samples can be configured to equal a set of values ranging from 4 to 18. This value is set by the SFI in the Filter Configuration
Register (
). The timing of this filter is also determined by the configuration of ESI in the Filter Configuration Register
(
).
Note that the ESI (Electrode Sample Interval) must be configured to accommodate the low power requirements of a system.
Thus, the resulting value will affect the period of the second level filter.
Thus, the resulting value will affect the period of the second level filter.
The raw data from the second level of filtering is output in the Filtered Data High and Filtered Data Low registers, as shown in
.
8.3.1
The Filter Configuration register is used to set the electrode charge/discharge time (CDT), second level filter iteration (SFI), and
electrode sample intervals (ESI). The address of the Electrode Configuration Register is 0x43.
electrode sample intervals (ESI). The address of the Electrode Configuration Register is 0x43.
Figure 26. Filter Configuration Register
7
6
5
4
3
2
1
0
R
CDT
SFI
ESI
W
Reset:
0
0
1
0
0
1
0
0
= Unimplemented