ADS5295IPFP datasheet(68/93 Pages) TI2

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y(n) =

[h6.x(n) + h7.x(n 1) +

h9.x(n 3) + h10.x(n 4)

h8.x(n 2) +

+ h11.x(n 5)

+ h11.x(n 6) +

h9.x(n 8) + h8.x(n 9)

+ h6.x (n 11)]

h10.x(n 7) +

+ h7.x(n 10)

ADS5295

SBAS595 – DECEMBER 2012

www.ti.com

Table 12. Predefined Coefficients for Decimate-by-4 Filters

DECIMATE-BY-4

COEFFICIENTS

LOW-PASS FILTER

1st BAND-PASS FILTER

2nd BAND-PASS FILTER

HIGH-PASS FILTER

–17

–7

–34

–50

–34

–15

–47

–101

–95

127

–8

–42

–28

–81

–100

–5

106

–97

117

–179

–62

–190

294

–97

202

–464

310

h10

414

–113

–563

–501

h11

554

526

352

575

Custom Filter Coefficients

In addition to the built-in filters described in the Predefined Coefficients section, customers also have the option

of using their own custom, 12-bit, signed coefficients. Because of the symmetric FIR implementation of the filters,

only 12 coefficients can be specified with the configuration of Equation 4 or Equation 5. These coefficients (h0 to

h11) must be configured in the custom coefficient registers as shown in Equation 6:

11)

(6)

The 12 custom coefficients must be loaded into 12 separate registers for each channel (refer to the custom

coefficient registers, 5Ah to B9h). The MSB bit of each coefficient register determines whether the built-in filters

or custom filters are used. If the EN_CUSTOM_FILT MSB bit is reset to '0', then the built-in filter coefficients are

used. Otherwise, the custom coefficients are used.

Custom Filter without Decimation

Another mode is available that enables the use of the digital filter without decimation. In this mode, the filter

behaves similar to a 12-tap symmetric FIR filter, as shown in Equation 7:

(7)

In Equation 7, h6 through h11 are 12-bit, signed, twos complement representations of the coefficients (–2048 to

+2047). x(n) is the filter input data sequence and y(n) is the filter output sequence.

In this mode, because the filter is implemented as a 12-tap symmetric FIR, only six custom coefficients must be

specified and loaded in registers h6 to h11 (refer to the custom coefficient registers, 5Ah to B9h). To enable this

mode, use the register setting specified in bit 15 of registers AEh to B9h.

Digital High-Pass Filter

In addition to the 12 tap filters described previously, the digital processing block also includes a separate high-

pass filter for each channel. The high-pass corner frequency can be programmed using bits D[14:10] in register

2Eh.

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