ADS1246
ADS1247
ADS1248
SBAS426G –AUGUST 2008–REVISED OCTOBER 2011
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NOISE PERFORMANCE
The ADS1246/7/8 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 PGA value
reduces the input-referred noise, particularly useful when measuring low-level signals. Table 1 to Table 6
summarize noise performance of the ADS1246/7/8. The data are representative of typical noise performance at
T = +25°C. The data shown are the result of averaging the readings from multiple devices and were measured
with the inputs shorted together. A minimum of 128 consecutive readings were used to calculate the RMS and
peak-to-peak noise for each reading.
Table 1, Table 3, and Table 5 list the input-referred noise in units of μV
RMS
and μV
PP
for the conditions shown.
Table 2, Table 4, and Table 6 list the corresponding data in units of ENOB (effective number of bits) where:
ENOB = ln(Full-Scale Range/Noise)/ln(2) (1)
Table 3 to Table 6 use the internal reference available on the ADS1247 and ADS1248. The data though are also
representative of the ADS1246 noise performance when using a low-noise external reference such as the
REF5020.
Table 1. Noise in μV
RMS
and (μV
PP
)
at AVDD = 5V, AVSS = 0V, and External Reference = 2.5V
DATA PGA SETTING
RATE
(SPS) 1 2 4 8 16 32 64 128
5 1.1 (4.99) 0.68 (3.8) 0.37 (1.9) 0.19 (0.98) 0.1 (0.44) 0.07 (0.31) 0.05 (0.27) 0.05 (0.21)
10 1.53 (8.82) 0.82 (3.71) 0.5 (2.69) 0.27 (1.33) 0.15 (0.67) 0.08 (0.5) 0.06 (0.36) 0.07 (0.34)
20 2.32 (13.37) 1.23 (6.69) 0.71 (3.83) 0.34 (1.9) 0.18 (1.01) 0.12 (0.71) 0.10 (0.51) 0.09 (0.54)
40 2.72 (17.35) 1.33 (7.65) 0.68 (3.83) 0.38 (2.21) 0.22 (1.13) 0.14 (0.77) 0.15 (0.78) 0.14 (0.76)
80 3.56 (22.67) 1.87 (12.3) 0.81 (5.27) 0.5 (3.49) 0.3 (1.99) 0.19 (1.24) 0.19 (1.16) 0.18 (1.04)
160 5.26 (42.03) 2.52 (17.57) 1.32 (9.22) 0.67 (5.25) 0.41 (2.89) 0.26 (1.91) 0.27 (1.74) 0.26 (1.74)
320 9.39 (74.91) 4.68 (39.48) 2.69 (18.95) 1.24 (9.94) 0.68 (5.25) 0.45 (3.08) 0.38 (2.71) 0.36 (2.46)
640 13.21 (119.66) 6.93 (59.31) 3.59 (28.55) 1.53 (10.68) 0.95 (8.7) 0.63 (4.94) 0.53 (3.74) 0.5 (3.55)
1000 32.34 (443.91) 16.11 (185.67) 11.54 (92.23) 4.65 (37.55) 2.02 (23.14) 1.15 (12.29) 0.77 (7.42) 0.64 (4.98)
2000 32.29 (372.54) 15.99 (182.27) 8.02 (91.73) 4.08 (45.89) 2.19 (24.14) 1.36 (12.32) 1.08 (8.03) 1 (6.93)
Table 2. Effective Number of Bits From RMS Noise and (Peak-to-Peak Noise)
at AVDD = 5V, AVSS = 0V, and External Reference = 2.5V
DATA PGA SETTING
RATE
(SPS) 1 2 4 8 16 32 64 128
5 21.8 (19.6) 21.5 (19) 21.4 (19) 21.4 (19) 21.3 (19.2) 20.9 (18.7) 20.2 (17.8) 19.4 (17.2)
10 21.4 (18.8) 21.3 (19.1) 21 (18.5) 20.8 (18.6) 20.7 (18.6) 20.6 (18) 19.9 (17.5) 18.9 (16.5)
20 20.8 (18.2) 20.7 (18.2) 20.5 (18) 20.5 (18) 20.4 (18) 20 (17.5) 19.3 (16.9) 18.4 (15.9)
40 20.5 (17.8) 20.6 (18) 20.5 (18) 20.4 (17.8) 20.2 (17.8) 19.8 (17.4) 18.7 (16.3) 17.8 (15.4)
80 20.1 (17.5) 20.1 (17.3) 20.3 (17.6) 20 (17.2) 19.7 (17) 19.4 (16.7) 18.4 (15.7) 17.5 (14.9)
160 19.6 (16.6) 19.6 (16.8) 19.6 (16.8) 19.5 (16.6) 19.3 (16.4) 18.9 (16) 17.9 (15.2) 16.9 (14.2)
320 18.7 (15.7) 18.7 (15.7) 18.5 (15.7) 18.7 (15.7) 18.5 (15.6) 18.1 (15.3) 17.4 (14.5) 16.5 (13.7)
640 18.2 (15.1) 18.2 (15.1) 18.1 (15.1) 18.4 (15.5) 18 (14.8) 17.6 (14.7) 16.9 (14.1) 16 (13.1)
1000 17 (13.2) 17 (13.4) 16.4 (13.4) 16.7 (13.7) 17 (13.4) 16.8 (13.3) 16.4 (13.1) 15.6 (12.6)
2000 17 (13.4) 17 (13.5) 17 (13.4) 16.9 (13.4) 16.8 (13.4) 16.5 (13.3) 15.9 (13) 15 (12.2)
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