DA6505.005
11 June 2018
APPLICATION INFORMATION (continued)
Noise Resolution Improvement
Measurement noise resolution can be improved by
using high oversampling ratio (OSR) settings.
Additionally IIR filter options (see Table 3) can be
used to further improve the noise resolution. The IIR
filter has also impact on step response. Table 18
below shows noise scaling factors and step
responses at the different IIR filter options. However
note that the step response to the first measurement
result is immediate since the first result (CODEADC
)
is considered also as previous filtered output
(CODEOLD) in the filter equation 1 (see page 18).
Table 18. IIR filter noise reduction factor
Filter
Coefficient
Noise
Scale
Factor
[-]
Samples to reach
≥75% of step
response
Samples to reach
≥90% of step
response
[-]
[-]
[-]
No filtering
1
1
2
5
11
22
1
4
8
17
35
2
4
8
0.58
0.38
0.26
0.18
16
IIR Filter Step Responseto Input Signal Change
100 %
90 %
80 %
70 %
60 %
50 %
40 %
30 %
20 %
10 %
FILTER=1 (no filtering)
FILTER=2
FILTER=4
FILTER=8
FILTER=16
0 %
0
10
20
30
40
50
60
70
80
90
100
Sample Number [#]
Figure 16. IIR filter step response to input signal change
Example
GAIN=14.9, OSRP=16:
The input noise resolution in pressure mode using different filter options is as follows.
FILTER=1 (no filtering): typ 0.44µVRMS
.
FILTER=2: typ 0.58*0.44µVRMS 260nVRMS
FILTER=4: typ 0.38*0.44µVRMS 167nVRMS
FILTER=8: typ 0.26*0.44µVRMS 114nVRMS
FILTER=16: typ 0.18*0.44µVRMS 79nVRMS
.
.
.
.
40 (44)
MAS [ MICRO ANALOG SYSTEMS ]
