ASD1194 datasheet(21/76 Pages) TI

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Max(INP

INN)<

REF

Gain

Full-ScaleRange=

REF

Gain

;

−160

−150

−140

−130

−120

−110

−100

−90

−80

−70

−60

−50

−40

−30

−20

−10

0.001

0.01

0.1

Normalized Frequency (fIN/fMOD)

G001

ADS1194, ADS1196

ADS1198

www.ti.com

SBAS471C

– APRIL 2010 – REVISED NOVEMBER 2011

Input Differential Dynamic Range

The differential (INP

– INN) signal range depends on the analog supply and reference used in the system. This

range is shown in Equation 3.

(3)

The 3V supply, with a reference of 2.4V and a gain of 6 for ECGs, is optimized for power with a differential input

signal of approximately 300mV. For higher dynamic range, a 5V supply with a reference of 4V (set by the

VREF_4V bit of the CONFIG3 register) can be used to increase the differential dynamic range.

ADC

ΔΣ Modulator

Each channel of the ADS1194/6/8 has a 16-bit

ΔΣ ADC. This converter uses a second-order modulator

optimized for low-power applications. The modulator samples the input signal at the rate of fMOD = fCLK/8. As in

the case of any

ΔΣ modulator, the noise of the ADS1194/6/8 is shaped until fMOD/2, as shown in Figure 20. The

on-chip digital decimation filters explained in the next section can be used to filter out the noise at higher

frequencies. These on-chip decimation filters also provide antialias filtering. This feature of the

ΔΣ converters

drastically reduces the complexity of the analog antialiasing filters that are typically needed with nyquist ADCs.

Figure 20. Modulator Noise Spectrum Up To 0.5

× fMOD

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