CS5376 View Datasheet(PDF) - Cirrus Logic

Part Name

Description

MFG CO.

CS5376

Low Power Multi-Channel Decimation Filter

Cirrus Logic 

CS5376

purpose applications. The FIR1 reference coeffi-

cients are a compensation filter, with a slight rise in

the pass band magnitude to compensate for the sinc

filter droop. The FIR2 reference coefficients are a

brickwall filter with excellent stop band roll off and

out-of-band attenuation.

The FIR reference coefficients have a flat response

over a 40% fs pass band with in-band ripple less

than ±0.01 dB, a 10% fs stop band (from 40% fs to

50% fs), and out-of-band attenuation greater than

130 dB.

The FIR filter absolute performance characteristics

scale with sample frequency, fs. For a 1kHz output

word rate (1ms output period), using the FIR refer-

ence coefficients results in a 400 Hz pass band with

in-band ripple less than ±0.01 dB, a 100 Hz stop

band between 400 Hz and 500 Hz, and greater than

130 dB out-of-band attenuation for frequencies

above 500 Hz.

8.5.2 Reference IIR coefficient set

The reference IIR coefficients are separated into

1st order and 2nd order stages. The IIR stages im-

plement a 1st order and 2nd order Butterworth fil-

ter, with a 3rd order filter implemented by running

both stages. A listing of the reference IIR coeffi-

cients is provided in Figure 40.

The combined 1st order and 2nd order IIR refer-

ence coefficients provide excellent performance

for general purpose applications. Cascading the 1st

and 2nd order IIR coefficients creates a 3rd order

low-cut filter with a -3 dB corner at 2% fs.

The IIR filter low-cut corner frequency scales with

the sample frequency, fs. For a 1kHz output word

rate (1ms output period), the IIR reference coeffi-

cients cut frequencies as a 3rd order Butterworth

filter between DC and 2.0 Hz.

DS256PP1

64

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