Datasheet

−160
−150
−140
−130
−120
−110
−100
−90
−80
−70
−60
−50
−40
−30
−20
−10
0
0.001 0.01 0.1 1
Normalized Frequency (f
IN
/f
MOD
)
Power Spectral Density (dB)
G001
Max(INP INN)<-
V
REF
Gain
Full-ScaleRange=
±V
REF
Gain
; =
2V
REF
Gain
AVDD 0.3- -
Gain V
MAX_DIFF
2
> CM > AVSS + 0.3 +
Gain V
MAX_DIFF
2
ADS131E04
ADS131E06
ADS131E08
www.ti.com SBAS561A –JUNE 2012–REVISED APRIL 2013
Input Common-Mode Range
The usable input common-mode range of the analog front-end depends on various parameters, including the
maximum differential input signal, supply voltage, and PGA gain. This range is described in Equation 2:
where:
V
MAX_DIFF
= maximum differential signal at the PGA input
CM = common-mode range (2)
For example:
If V
DD
= 3.3 V, gain = 2, and V
MAX_DIFF
= 1000 mV,
Then 1.3 V < CM < 2.0 V
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)
For higher dynamic range, a 5-V supply with a 4-V reference (set by the VREF_4V bit of the CONFIG3 register)
can be used to increase the differential dynamic range.
ADC ΔΣ Modulator
Each ADS131E0x channel has a ΔΣ ADC. This converter uses a second-order modulator optimized for low-
power applications. The modulator samples the input signal at the rate of [f
MOD
= f
CLK
/ 2]. As in the case of any
ΔΣ modulator, the ADS131E0x noise is shaped until f
MOD
/ 2, as shown in Figure 22. The on-chip digital
decimation filters also provide antialias filtering. This ΔΣ converter feature drastically reduces the complexity of
the analog antialiasing filters typically required with nyquist ADCs.
Figure 22. Modulator Noise Spectrum Up To 0.5 × f
MOD
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