ADS5294 datasheet(56/67 Pages) TI1

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−80

−70

−60

−50

−40

−30

−20

−10

0.0

0.1

0.2

0.3

0.4

0.5

Normalized Frequency (fin/fs)

Low Pass

High pass

−80

−70

−60

−50

−40

−30

−20

−10

0.0

0.1

0.2

0.3

0.4

0.5

Normalized frequency (fin/fs)

Low Pass

Band−Pass1

Band−Pass2

High Pass

ADS5294

SLAS776B – NOVEMBER 2011 – REVISED JULY 2012

www.ti.com

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 9. Digital Filters

<USE

<DATA

FILTERn

<FILTERn

<EN CUSTOM

DECIMATION

TYPE OF FILTER

FILTER

RATE>

COEFF SET>

FILT>

CHn>

Built-in low-pass odd-tap filter (pass band = 0 to fS/4)

001

000

Decimate by 2

Built-in high-pass odd-tap filter (pass band = 0 to fS/4)

001

000

001

Built-in low-pass even-tap filter (pass band = 0 to fS/8)

010

001

010

Built-in first band pass even tap filter(pass band = fS/8 to fS/4)

010

001

011

Decimate by 4

Built-in second band pass even tap filter(pass band = fS/4 to 3

010

001

100

fS/8)

Built-in high pass odd tap filter (pass band = 3 fS/8 to fS/2)

010

001

101

Decimate by 2

Custom filter (user programmablecoefficients)

001

000

0 and 1

Decimate by 4

Custom filter (user programmablecoefficients)

010

001

000

0 and 1

Decimate by 8

Custom filter (user programmablecoefficients)

011

100

000

0 and 1

Bypass decimation

Custom filter (user programmablecoefficients)

0 and 1

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

Pre-defined Coefficients

The build-in filters (low pass, high pass an band pass) use pre-defined coefficients. The frequency responses of

the build-in decimation filters with different decimation factors are shown in Figure 62.

Figure 62. Decimation Filter Responses

Figure 63. Decimation Filter Responses

(Decimate by 2)

(Decimate by 4)

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