MAS6505 datasheet(40/44 Pages) MAS

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DA6505.005

11 June 2018

40 (44)

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

0.58

0.38

0.26

0.18

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.

0 %

10 %

20 %

30 %

40 %

50 %

60 %

70 %

80 %

90 %

100 %

100

Sample Number [#]

IIR Filter Step Response to Input Signal Change

FILTER=1 (no filtering)

FILTER=2

FILTER=4

FILTER=8

FILTER=16

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