cs5378 Cirrus Logic, Inc., cs5378 Datasheet - Page 40

• Manufacturer Part Number: cs5378
• Description: Low-power Single-channel Decimation Filter
• Manufacturer: Cirrus Logic, Inc.

12. SINC FILTER
The SINC filter primary purpose is to attenuate out-
of-band noise components from the ∆Σ modula-
tors. While doing so, they decimate 1-bit ∆Σ data
into lower frequency 24-bit data suitable for the
FIR and IIR filters.
The SINC filter has three cascaded sections,
SINC1, SINC2, and SINC3, which are each made
up of the smaller stages shown in Figure 23.
The selected output word rate in the FILTCFG reg-
ister automatically determines the coefficients and
decimation ratios selected for the SINC filters.
12.1 SINC1 Filter
The first section is SINC1, a single stage 5th order
fixed decimate by 8 SINC filter. This SINC filter
decimates the incoming 1-bit ∆Σ bit stream from
the modulators down to a 64 kHz rate.
DS639F1
4th order
sinc3
stage1
1-bit
∆−Σ
Input
5
4th order
5th order
sinc3
stage2
sinc1
5
8
4th order
sinc3
stage3
4th order
Figure 23. SINC Filter Block Diagram
5
sinc2
stage1
2
5th order
sinc3
stage4
4th order
5
sinc2
stage2
12.2 SINC2 Filter
The second section is SINC2, a multi-stage, vari-
able order, variable decimation SINC filter. De-
pending on the selected output word rate in the
FILTCFG register, different cascaded SINC2 stag-
es are enabled, as shown in Table 11.
12.3 SINC3 Filter
The last section is SINC3, a flexible multi-stage
variable order, variable decimation SINC filter.
Depending on the selected output word rate in the
FILTCFG register, different SINC3 stages are en-
abled, as shown in Table 11.
12.4 SINC Filter Synchronization
The SINC filter is synchronized to the external sys-
tem by the MSYNC signal, which is generated
from the SYNC input. The MSYNC signal sets a
reference time (time 0) for all filter operations, and
the SINC filter is restarted to phase align with this
reference time.
2
5th order
sinc3
stage5
5th order
2
sinc2
stage3
2
6th order
sinc3
stage6
3
6th order
sinc2
stage4
2
6th order
sinc3
stage7
2
CS5378
24-bit
Output
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