sx8725 Semtech Corporation, sx8725 Datasheet - Page 45
sx8725
Manufacturer Part Number
sx8725
Description
Sx8725 Zoomingadc? For Pressure And Temperature Sensing
Manufacturer
Semtech Corporation
Datasheet
1.SX8725.pdf
(53 pages)
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ADVANCED COMMUNICATIONS & SENSING
As an example, consider the system where: GD
V
we get: V
ADC. Considering 0.2 V (rms) maximum signal amplitude, the signal-to-noise ratio is 90dB.
Noise can also be reduced by implementing a software filter. By making an average on a number of subsequent
measurements, the apparent noise is reduced the square root of the number of measurement used to make the
average.
V1.5 © 2007 Semtech Corp.
REF
= 5 V. In this case, the noise contribution V
N,IN
= 6.4 µV (rms) at the input of the acquisition chain, or, equivalently, 0.85 LSB at the output of the
V
N,IN
Figure 23 - ADC Noise (PGA1, 2 & 3 Bypassed, OSR = 512, N
GD1
PGA1
GD1
PGA1
Figure 24 - Simple Noise Model for PGAs and ADC
V
N1
Figure 25 - Total Input Referred Noise
V
80
60
40
20
0
N1
-5
ZoomingADC™ for Pressure and Temperature Sensing
-4
GD2
Output Code Deviation From Mean Value [LSB]
PGA2
GD2
-3
PGA2
N1
2
-2
= 10 (GD
of PGA1 is dominant over that of PGA2. Using Equation 25,
V
45
-1
N2
V
N2
0
1
1
GD3
= 1; PGA3 bypassed), OSR = 512, N
PGA3
GD3
PGA3
2
3
V
4
N3
V
N3
5
ELCONV
ADC
f
s
ADC
f
s
= 2)
www.semtech.com
SX8725
ELCONV
= 2,