Digital Filter Configuration - ST STM32F413 Reference Manual

RM0430
15.4.8

Digital filter configuration

DFSDM contains a Sinc
digital data stream filtering, which results in decreasing the output data rate (decimation)
and increasing the output data resolution. The Sinc
reach the required output data rates and required output data resolution. The configurable
parameters are:
• Filter order/type: (see FORD[2:0] bits in DFSDM_FLTxFCR register):
–
–
–
–
–
–
•
Filter oversampling/decimation ratio (see FOSR[9:0] bits in DFSDM_FLTxFCR
register):
–
–
–
The filter has the following transfer function (impulse response in H domain):
•
Sinc
•
FastSinc filter type:
x
type digital filter implementation. This Sinc
FastSinc
1
Sinc
2
Sinc
3
Sinc
4
Sinc
5
Sinc
FOSR = 1-1024 - for FastSinc filter and Sinc
FOSR = 1-215 - for Sinc
FOSR = 1-73 - for Sinc
x
filter type:
H z ( )
H z ( )
Figure 84. Example: Sinc
DocID029473 Rev 3
Digital filter for sigma delta modulators (DFSDM)
x
digital filter is configurable in order to
x
filter x = F
ORD
x
filter x = F
ORD
x
FOSR
⎛ ⎞
–
1 z
–
---------------------------- -
⎜ ⎟
=
1
–
⎝ ⎠
1 z
–
2
FOSR
⎛ ⎞
–
1 z
–
---------------------------- -
⋅ (
⎜ ⎟ 1
= +
1
–
⎝ ⎠
1 z
–
3
filter response
x
filter performs an input
x
filter x = F = 1..3
ORD
= 4
= 5
( 2 ⋅ FOSR )
–
)
z
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