sx8724s Semtech Corporation, sx8724s Datasheet - Page 58

• Manufacturer Part Number: sx8724s
• Description: Zoomingadc For Sensing Data Acquisition
• Manufacturer: Semtech Corporation

Revision 1.0
© Semtech
V
respectively. V
The simple noise model of
chain in the model of
On the numerator of
1 the first parenthesis is the PGA1 gain amplifier contribution to noise
2 the second parenthesis is the PGA2 gain amplifier contribution to noise
3 the third parenthesis is the PGA3 gain amplifier contribution to noise
4 the fourth parenthesis is PGA2 and PGA3 offset amplifiers contributions to noise
5 the last parenthesis is the contribution of the noise on the references of the ADC
V
ADVANCED COMMUNICATIONS & SENSING
N1
Analog
Inputs
Reference
Inputs
N
,
, V
IN
2
N2
=
, and V
⎛
⎜ ⎜
⎝
GD
V
N
REFN,WB
1
N3
1
VSS
VREF
AC2
AC3
AC4
AC5
AC6
AC7
VBATT
VSS
VREF
VSS
⎞
⎟ ⎟
⎠
2
are the output RMS noise figures of
+
is the wide band noise on the reference voltage.
⎛
⎜ ⎜
⎝
Equation
Figure 54, page
GD
February 2011
V
1
Figure 52
N
⋅
V
GD
2
REFN,WB
28:
2
⎞
⎟ ⎟
⎠
2
Figure 52. Simple Noise Model for PGAs and ADC
+
is used to estimate the equivalent input referred RMS noise V
⎛
⎜ ⎜
⎝
59. This is given by the relationship:
gains:
offsets:
GD
V
S
V
REF,ADC
N
TOT
3
±
V
Vin
IN
⎞
⎟ ⎟
⎠
2
GD
+
(
PGA1
⎛
⎜ ⎜
⎝
OSR
1
Equation 28
Page 58
Table
V
REFN
⋅
N
V
,
WB
38, GD
N1
ELCONV
(
GD
±
±
Vin
Voff
ZoomingADC for sensing data acquisition
GD
2
1
)
GD
GD
, GD
⋅
GD
OFF2
PGA2
2
TOT
2
, and GD
OFF
2
V
+
N2
GD
3
are the PGA gains of stages 1 to 3
±
±
OFF
Vin
Voff
GD
GD
3
)
OFF3
⎞
⎟ ⎟
⎠
PGA3
3
2
+
⎛
⎜ ⎜
⎝
1
2
V
SX8724S
⋅
N3
N,IN
V
www.semtech.com
GD
REFN
of the acquisition
DATASHEET
TOT
,
WB
±
±
Vin
Vref
V
⎞
⎟ ⎟
⎠
2
IN,ADC
[
V
ADC
2
rms
]