ADS5294 datasheet(43/67 Pages) TI1

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y(n) =

[x(n) x(n 1)+y(n 1)]

2 +1

ADS5294

www.ti.com

SLAS776B – NOVEMBER 2011 – REVISED JULY 2012

Coefficient Sets 1 and 2 are the most appropriate when Decimation by a factor of 2 is required, whereas

Coefficient Sets 3,4,5,6 are appropriate when Decimation by a factor of 4 is desired. The computation rate of the

filter output can be independently set using the bits FILTERn_RATE<2:0>. The settings are shown in Table 5.

Table 5. 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

The choice of the odd/even tap setting, filter coefficient set and the filter rate uniquely determines the filter to be

used. In addition to the preset filter coefficients, the coefficients for each of the eight filter channels can be

programmed by the user. Each of the eight channels has 12 programmable coefficients, each 12-bit long. The 96

registers with addresses from 5A (Hex) to B9 (Hex) are used to program these 8 sets of 12 programmable

coefficients. Registers 5A to 65 are used to program the 1st filter, with the 1st coefficient occupying the bits

D11..D0 of register 5A, the 2nd coefficient occupying the bits D11..D0 of register 5B, and so on. Similarly

registers 66(Hex) to 71(Hex) are used to program the 2nd filter, and so on.

When programming the filter coefficients, the D15 bit of each of the 12 registers corresponding to that filter

should be set to ‘1’. If the D15 bit of these 12 registers is set to ‘0’, then the preset coefficient (as programmed by

FILTERn_COEFF_SET<2:0>) is used even if the bits D11..D0 get programmed. By setting or not setting the D15

bits of individual filter channels to ‘1’, some filters can be made to operate with preset coefficient sets, and some

others can be made to simultaneously operate with programmed coefficient sets.

HIGH PASS FILTER

ADDR.

D15

D14

D13

D12

D11

D10

NAME

(HEX)

HPF_corner_CH1

HPF_EN_CH1

HPF_corner_CH2

HPF_EN_CH2

HPF_corner_CH3

HPF_EN_CH3

HPF_corner_CH4

HPF_EN_CH4

HPF_corner_CH5

HPF_EN_CH5

HPF_corner_CH6

HPF_EN_CH6

HPF_corner_CH7

HPF_EN_CH7

HPF_corner_CH8

HPF_EN_CH8

This group of registers controls the characteristics of a digital high pass transfer function applied to the output

data, useing Equation 3:

(3)

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