ST STM32L4+ Series Reference Manual page 874

Digital filter for sigma delta modulators (DFSDM)
Bits 31:29 FORD[2:0]: Sinc filter order
0: FastSinc filter type
1
1: Sinc
2
2: Sinc
3
3: Sinc
4
4: Sinc
5
5: Sinc
6-7: Reserved
x
Sinc filter type transfer function:
FastSinc filter type transfer function:
This bit can only be modified when DFEN=0 (DFSDM_FLTxCR1).
Bits 28:26 Reserved, must be kept at reset value.
Bits 25:16 FOSR[9:0]: Sinc filter oversampling ratio (decimation rate)
0 - 1023: Defines the length of the Sinc type filter in the range 1 - 1024 (F
number is also the decimation ratio of the output data rate from filter.
This bit can only be modified when DFEN=0 (DFSDM_FLTxCR1)
Note: If FOSR = 0, then the filter has no effect (filter bypass).
Bits 15:8 Reserved, must be kept at reset value.
Bits 7:0 IOSR[7:0]: Integrator oversampling ratio (averaging length)
0- 255: The length of the Integrator in the range 1 - 256 (IOSR + 1). Defines how many samples
from Sinc filter will be summed into one output data sample from the integrator. The output data rate
from the integrator will be decreased by this number (additional data decimation ratio).
This bit can only be modified when DFEN=0 (DFSDM_FLTxCR1)
Note: If IOSR = 0, then the Integrator has no effect (Integrator bypass).
28.8.7 DFSDM filter x data register for injected group
(DFSDM_FLTxJDATAR)
Address offset: 0x118 + 0x80 * x, (x = 0 to 3)
Reset value: 0x0000 0000
31 30 29
r r r
15 14 13
r r r
874/2301
filter type
filter type
filter type
filter type
filter type
28 27 26 25
r r r r
12 11 10 9
JDATA[7:0]
r r r r
– FOSR

1 z –
H z ( )  ---------------------------- -
=
– 1

1 z –
– FOSR

1 z
–
H z ( ) ---------------------------- -
= 
–

1 z –
24 23 22
JDATA[23:8]
r r r
8 7 6
Res. Res.
r
RM0432 Rev 6
x



2

( ⋅ )
– 2 FOSR
⋅ ( )
 1 + z
1

= FOSR[9:0] +1). This
OSR
21 20 19 18
r r r r
5 4 3 2
Res. Res. Res.
r
RM0432
17 16
r r
1 0
JDATACH[2:0]
r r