Datasheet

½H(f) =½

sin

N fp

MOD

N sin´

MOD

½H(z) =½

1 Z-

- N

1 Z-

- 1

ADS131E04

ADS131E06

ADS131E08

SBAS561A –JUNE 2012–REVISED APRIL 2013

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DIGITAL DECIMATION FILTER

The digital filter receives the modulator output and decimates the data stream. By adjusting the amount of

filtering, tradeoffs can be made between resolution and data rate: filter more for higher resolution, filter less for

higher data rates. Higher data rates are typically used in power applications that implement software phase

adjustment.

The digital filter on each channel consists of a third-order sinc filter. The decimation ratio on the sinc filters can

be adjusted by the DR bits in the CONFIG1 register (see the Register Map section for details). This setting is a

global setting that affects all channels and, therefore, all channels operate at the same data rate in the device.

Sinc Filter Stage (sinx / x)

The sinc filter is a variable decimation rate, third-order, low-pass filter. Data are supplied to this section of the

filter from the modulator at the rate of f

MOD

. The sinc filter attenuates the high-frequency modulator noise, then

decimates the data stream into parallel data. The decimation rate affects the overall converter data rate.

Equation 4 shows the scaled sinc filter Z-domain transfer function.

(4)

The sinc filter frequency domain transfer function is shown in Equation 5.

where:

N = decimation ratio (5)

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