CS5376 View Datasheet(PDF) - Cirrus Logic

Part Name

Description

MFG CO.

CS5376

Low Power Multi-Channel Decimation Filter

Cirrus Logic 

CS5376

8.2 Hardware Sinc Filter

The hardware sinc filter provides high-order atten-

uation of out-of-band noise components from the

∆−Σ modulators. It also decimates the 512 kHz 1-

bit ∆−Σ data into lower frequency 24-bit data suit-

able for the FIR and IIR filters.

The hardware sinc filter is divided into two cascad-

ed sections, Sinc1 and Sinc2. Sinc1 is a fixed 5th

order decimate by 8 sinc filter while Sinc2 is a

multi-stage variable order sinc filter capable of

decimation ratios of 2, 4, 8, 12, or 16. The selected

output word rate and output filter stage from the

overall filter chain automatically determines the

decimation ratio selected for Sinc2.

Once the decimation ratio for Sinc2 is set, all en-

abled channels are decimated and filtered using an

identical hardware algorithm. The final output

from the sinc filter is 24-bit 2’s complement data

that passes to the decimation engine for further fil-

tering by the FIR and IIR stages.

8.2.1 SINC1 Filter

The first part of the hardware sinc filter is Sinc1, a

fixed 5th order decimate by 8 sinc filter. This filter

decimates the incoming 512 kHz (or oversampled

256 kHz) 1-bit ∆−Σ bit stream from the modulators

down to a 64 kHz rate.

This filter section can be modeled as a 5th order

sinc filter with a decimate by 8 output. The time do-

main coefficients are [1, 5, 10, 10, 5, 1], and the fre-

quency domain model is [(sin x)/x]5.

8.2.2 SINC2 Filter

The second part of the hardware sinc filter is Sinc2,

a multi-stage, variable order, variable decimation

sinc filter. Depending on the selected output word

rate and output filter stage from the overall filter

chain, different cascaded Sinc2 stages are enabled.

See Figure 37 for a listing of possible Sinc2 config-

urations.

Stage 1 of Sinc2 can be modeled as a 4th order sinc

filter with a decimate by 2 output. The time domain

1-bit ∆−Σ,

512 kHz

5th order

sinc1

8

4th order

sinc2

stage1

2

4th order

sinc2

stage3

2

5th order

sinc2

stage4

2

6th order

sinc2

stage5

2

24-bit,

4 kHz -

32 kHz

4th order

sinc2

stage2

3

Figure 36. Sinc1 and Sinc2 Filter Stages

DS256PP1

58

Share Link: