ASD1194 datasheet(22/76 Pages) TI

22 / 76 page

H(z)

H(f)

sin

N f

MOD

sin

MOD

ADS1194, ADS1196

ADS1198

SBAS471C

– APRIL 2010 – REVISED NOVEMBER 2011

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DIGITAL DECIMATION FILTER

The digital filter receives the modulator output and decimates the data stream. By adjusting the amount of

filtering, tradeoffs can be made between resolution and data rate: filter more for higher resolution, filter less for

higher data rates. Higher data rates are typically used in ECG applications for implement software pace detection

and ac lead-off detection.

The digital filter on each channel consists of a third-order sinc filter. The decimation ratio on the sinc filters can

be adjusted by the DR bits in the CONFIG1 register (see the Register Map section for details). This setting is a

global setting that affects all channels and, therefore, in a device all channels operate at the same data rate.

Sinc Filter Stage (sinx/x)

The sinc filter is a variable decimation rate, third-order, low-pass filter. Data are supplied to this section of the

filter from the modulator at the rate of fMOD. The sinc filter attenuates the high-frequency noise of the modulator,

then decimates the data stream into parallel data. The decimation rate affects the overall data rate of the

converter.

Equation 4 shows the scaled Z-domain transfer function of the sinc filter.

(4)

The frequency domain transfer function of the sinc filter is shown in Equation 5.

where:

N = decimation ratio

(5)

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ASD1194 Datasheet(PDF) 22 Page - Texas Instruments