Datasheet

ENOB = 2 log
V
REF
2 Gain RMS Noise´´
Noise-Free Bits = 2 log
2 V
REF
Gain Peak-to-Peak Noise´
SNR = ENOB 6.02´
ADS1291
ADS1292
ADS1292R
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SBAS502B DECEMBER 2011REVISED SEPTEMBER 2012
PARAMETER MEASUREMENT INFORMATION
NOISE MEASUREMENTS
The ADS1291, ADS1292, and ADS1292R noise performance can be optimized by adjusting the data rate and
PGA setting. As the averaging is increased by reducing the data rate, the noise drops correspondingly.
Increasing the programmable gain amplifier (PGA) value reduces the input-referred noise, which is particularly
useful when measuring low-level biopotential signals. Table 1 through Table 8 summarize the ADS1291,
ADS1292, and ADS1292R noise performance. The data are representative of typical noise performance at T
A
=
+25°C. The data shown are the result of averaging the readings from multiple devices and are measured with the
inputs shorted together. For the shown data rates, the ratio is approximately 6.6.
Table 1 through Table 8 show measurements taken with an internal reference. The data are also representative
of the ADS1291, ADS1292, and ADS1292R noise performance when using a low-noise external reference such
as the REF5025.
In Table 1 through Table 8, µV
RMS
and µV
PP
are measured values. SNR, noise-free bits, ENOB, and dynamic
range are calculated with Equation 1, Equation 2, and Equation 3.
(1)
(2)
(3)
Table 1. Input-Referred Noise (μV
RMS
/ μV
PP
) 3-V Analog Supply and 2.42-V Reference
(1)
PGA GAIN = 1 PGA GAIN = 2
DR BITS OUTPUT
OF DATA –3-dB NOISE- NOISE-
CONFIG1 RATE BANDWIDTH FREE FREE
REGISTER (SPS) (Hz) μV
RMS
μV
PP
SNR BITS ENOB μV
RMS
μV
PP
SNR BITS ENOB
000 125 32.75 1.5 10.3 121.0 18.83 20.10 0.8 5.6 120.0 18.71 19.94
001 250 65.5 2.2 14.4 117.8 18.34 19.58 1.2 7.5 117.1 18.29 19.46
010 500 131 3.0 18.9 115.1 17.95 19.11 1.7 10.9 113.9 17.75 18.91
011 1000 262 4.6 30.8 111.3 17.25 18.49 2.5 15.6 110.6 17.23 18.37
100 2000 524 10.1 99 104.5 15.57 17.36 5.3 48 104.0 15.60 17.28
101 4000 1048 55.2 563 89.7 13.06 14.91 26.0 265 90.3 13.14 15.00
110 8000 2096 287.3 2930 75.4 10.68 12.53 144.1 1470 75.4 10.67 12.52
111 NA NA
(1) At least 1000 consecutive readings were used to calculate the peak-to-peak noise values in this table.
Table 2. Input-Referred Noise (μV
RMS
/ μV
PP
) 3-V Analog Supply and 2.42-V Reference
(1)
PGA GAIN = 3 PGA GAIN = 4
DR BITS OUTPUT
OF DATA –3-dB NOISE- NOISE-
CONFIG1 RATE BANDWIDTH FREE FREE
REGISTER (SPS) (Hz) μV
RMS
μV
PP
SNR BITS ENOB μV
RMS
μV
PP
SNR BITS ENOB
000 125 32.75 0.6 4.1 119.2 18.58 19.80 0.5 3.4 117.9 18.42 19.58
001 250 65.5 0.9 5.5 115.9 18.15 19.26 0.8 5.0 114.8 17.88 19.07
010 500 131 1.3 7.7 113.0 17.67 18.77 1.1 6.6 111.9 17.47 18.59
011 1000 262 1.9 12.0 109.5 17.02 18.19 1.6 10.3 108.7 16.83 18.06
100 2000 524 3.7 31 103.7 15.65 17.23 2.9 23 103.2 15.69 17.14
101 4000 1048 17.0 173 90.5 13.18 15.03 12.2 124 90.8 13.24 15.09
110 8000 2096 91.9 937 75.8 10.74 12.59 66.8 681 76.1 10.78 12.63
111 NA NA
(1) At least 1000 consecutive readings were used to calculate the peak-to-peak noise values in this table.
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