ADS1278IPAPR datasheet(22/51 Pages) TI1

22 / 51 page

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NormalizedInputFrequency(f /f

DA A)

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IN DATA)

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ADS1274

ADS1278

SBAS367F

– JUNE 2007 – REVISED FEBRUARY 2011

www.ti.com

High-Speed, Low-Power, and Low-Speed Modes

The

digital

filter

configuration

the

same

High-Speed, Low-Power, and Low-Speed modes with

the oversampling ratio set to 64. Figure 58 shows the

frequency response in High-Speed, Low-Power, and

Low-Speed modes normalized to fDATA. Figure 59

shows the passband ripple. The transition from

passband to stop band is shown in Figure 60. The

overall frequency response repeats at 64x multiples

of the modulator frequency fMOD, as shown in

Figure 61.

Figure 60. Transition Band Response for

High-Speed, Low-Power, and Low-Speed Modes

Figure 58. Frequency Response for High-Speed,

Low-Power, and Low-Speed Modes

Figure 61. Frequency Response Out to fMOD for

High-Speed, Low-Power, and Low-Speed Modes

These image frequencies, if present in the signal and

not externally filtered, will fold back (or alias) into the

passband, causing errors. The stop band of the

ADS1274/78

provides

100dB

attenuation

frequencies that begin just beyond the passband and

continue out to fMOD. Placing an antialiasing, low-pass

filter

front

the

ADS1274/78

inputs

recommended

limit

possible

high-amplitude,

out-of-band signals and noise. Often, a simple RC

filter is sufficient. Table 4 lists the image rejection

Figure 59. Passband Response for High-Speed,

versus external filter order.

Low-Power, and Low-Speed Modes

Table 4. Antialiasing Filter Order Image Rejection

IMAGE REJECTION (dB)

(f–3dB at fDATA)

ANTIALIASING

FILTER ORDER

HS, LP, LS

111

129

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ADS1278IPAPR Datasheet(PDF) 22 Page - Texas Instruments

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