ADS5294IPFPR datasheet(33/81 Pages) TI1

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ADS5294

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SLAS776D – NOVEMBER 2011 – REVISED SEPTEMBER 2015

Feature Description (continued)

9.3.4 Decimation Filter

ADS5294 includes an option to decimate the ADC output data using filters. Once the decimation is enabled, the

decimation rate, frequency band of the filter can be programmed. In addition, the user can select either the pre-

defined or custom coefficients.

Table 1. Digital Filters(1)

USE

DATA

FILTERn

EN_CUSTOM

DECIMATION

TYPE OF FILTER

ODD_TAP

_FILTER

_RATE

_COEFF_SET

_FILT

_CHn

Built-in low-pass odd-tap filter (pass band = 0 to

000

fS / 4)

Decimate by 2

Built-in high-pass odd-tap filter (pass band = fS /

000

001

4 to fS /2)

Built-in low-pass even-tap filter (pass band = 0

001

010

to fS / 8)

Built-in first band pass even tap filter (pass band

001

011

= fS / 8 to fS / 4)

Decimate by 4

Built-in second band pass even tap filter (pass

001

100

band = fS / 4 to 3 fS / 8)

Built-in high pass odd tap filter (pass band = 3

001

101

fS / 8 to fS / 2)

Decimate by 2

Custom filter (user-programmable coefficients)

000

0 and 1

Decimate by 4

Custom filter (user-programmable coefficients)

001

000

0 and 1

Decimate by 8

Custom filter (user-programmable coefficients)

100

000

0 and 1

Bypass

Custom filter (user-programmable coefficients)

0 and 1

decimation

(1)

EN_CUSTOM_FILT is the D15 of register 5A (Hex) to B9 (Hex).

9.3.5 Decimation Filter Equation

In the default setting, the decimation filter is implemented as a 24-tap FIR filter with symmetrical coefficients

(each coefficient is 12-bit signed). By setting the register bit ODD_TAPn = 1, a 23-tap FIR is implemented

9.3.5.1 Pre-defined Coefficients

The built-in filters (lowpass, highpass, and bandpass) use pre-defined coefficients. The frequency responses of

the build-in decimation filters with different decimation factors are shown in Figure 48.

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