CS5378-ISZ datasheet(39/86 Pages) CIRRUS

39 / 86 page

CS5378

DS639F1

11.2.2 Output Word Rate

The CS5378 digital filter supports output word

rates (OWRs) between 4000 SPS and 1 SPS. The

output word rate is selected by the DEC bits in the

FILTCFG register.

When taking data directly from the SINC filter, the

decimation of the FIR1 and FIR2 stages is by-

passed and the actual output word rate is multiplied

by a factor of eight compared with the register se-

lection. When taking data directly from FIR1, the

decimation of the FIR2 stage is bypassed and the

actual output word rate is multiplied by a factor of

two. Data taken from the FIR2, IIR1, IIR2, or IIR3

filtering stages is output at the selected rate.

11.2.3 Digital Filter Clock

The digital filter clock rate is programmable be-

tween 8.192 MHz and 32 kHz by bits in the CON-

FIG register.

Computation Cycles

The minimum digital filter clock rate for a config-

uration depends on the computation cycles required

to complete digital filter convolutions at the select-

ed output word rate. All configurations work for a

maximum digital filter clock, but lower clock rates

consume less power.

Standby Mode

The CS5378 can be placed in a low-power standby

mode by sending the ‘Filter Stop’ configuration

command and programming the digital filter clock

to 32 kHz. In this mode the digital filter idles, con-

suming minimal power until re-enabled by later

configuration commands.

Bits

23:20

19:16

15:12

11:8

7:4

3:0

Selection

0000

IIR2

IIR1

FIR2

FIR1

Figure 22. FIR and IIR Coefficient Set Selection Word

Bits 15:12

IIR2 Coefficients

0000

3 Hz @ 2000 SPS

0001

3 Hz @ 1000 SPS

0010

3Hz @ 500SPS

0011

3Hz @ 333SPS

0100

3Hz @ 250SPS

Bits 11:8

IIR1 Coefficients

0000

3 Hz @ 2000 SPS

0001

3 Hz @ 1000 SPS

0010

3 Hz @ 500 SPS

0011

3 Hz @ 333 SPS

0100

3 Hz @ 250 SPS

Bits 7:4

FIR2 Coefficients

0000

Linear Phase

0001

Minimum Phase

Bits 3:0

FIR1 Coefficients

0000

Linear Phase

0001

Minimum Phase

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