ADS1282IPW datasheet(22/52 Pages) TI

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Minimum Phase Response

HPF Stage

HPF(Z)=

-1

(9)

(

)

1+(1

(10)

Frequency(Hz)

100

120

140

160

180

200

LinearPhaseFilter

MinimumPhaseFilter

HPF[1:0]=65,536 1 -

cos

+sin

cos w

ADS1282

SBAS418E – SEPTEMBER 2007 – REVISED OCTOBER 2008 ........................................................................................................................................ www.ti.com

The minimum phase filter provides a short delay from

The last stage of the ADS1282 filter block is a

the arrival of an input signal to the output, but the

first-order HPF implemented as an IIR structure. This

relationship (phase) is not constant versus frequency,

filter

stage

blocks

signals

and

rolls

off

as shown in Figure 49. The filter phase is selected by

low-frequency

components

below

the

cut-off

the PHS bit, as Table 7 shows.

frequency. The transfer function for the filter is shown

in Equation 9:

where b is calculated as shown in Equation 10:

The high-pass corner frequency is programmed by

registers HPF[1:0], in hexadecimal. Equation 11 is

used to set the high-pass corner frequency. Table 8

lists example values for the high-pass filter.

Figure 49. FIR Group Delay (fDATA = 500Hz)

(11)

Where:

Table 7. FIR Phase Selection

HPF = High-pass filter register value (converted

to hexadecimal)

PHS BIT

FILTER PHASE

πf

HP/fDATA

(normalized

frequency,

Linear

radians)

Minimum

fHP = High-pass corner frequency (Hz)

fDATA = Data rate (Hz)

Table 8. High-Pass Filter Value Examples

fHP (Hz)

DATA RATE (SPS)

HPF[1:0]

0.5

250

0337h

1.0

500

0337h

1.0

1000

019Ah

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