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ADVANCED COMMUNICATIONS & SENSING
USER GUIDE
SX8724SEVK
Evaluation Kit for SX8724S Data Acquisition System
ACS - Revision 1.0 May 2011
© Semtech Corp.
of
PGA1
,
2
, and
3
, standard output deviation and output rms noise voltage.
V
N1
,
V
N2
, and
V
N3
are the
output rms noise figures (constants).
GD
1
,
GD
2
, and
GD
3
are the
PGA
gains of stages 1 to 3 respectively, set
by the user in the GUI:
Total gain
– the total gain of the acquisition chain is the product of all individual gains:
Total offset
– the total offset of the acquisition chain is computed according to the PGA2 and PGA3 offset
controls. Additionally, this total offset is function of the contribution of PGA3 gain. Therefore, the total
offset is computed as:
Output noise
– the output noise is computed using the input noise value multiplied by the total gain of
the PGAs as follows:
Resolution
– the theoretical resolution of the ADC, without considering thermal noise, is given by:
LSB
– the least-significant bit of ADC output codes. The total range (or span) of the 16-bit ADC is
LSBs,
ratiometric to the voltage reference:
T
CONV
– the time of the conversion sequence for one sample is computed as:
V
N IN
,
V
N1
GD
1
-----------
⎝
⎠
⎛
⎞
2
V
N2
GD
1
GD
2
⋅
---------------------------
⎝
⎠
⎛
⎞
2
V
N3
GD
TOT
------------------
⎝
⎠
⎛
⎞
2
+
+
OSR N
ELCONV
⋅
(
)
----------------------------------------------------------------------------------------------
=
Vrms
[
]
GD
TOT
GD
1
GD
2
GD
3
⋅
⋅
=
V
V
---
GDoff
TOT
GDoff
3
GD
3
+
GDoff
2
⋅
=
V
V
---
V
N OUT
,
V
N IN
,
GD
TOT
⋅
=
Vrms
[
]
Q
2 Log
2
OSR
(
)
Log
2
N
ELCONV
(
)
+
⋅
=
bit
[
]
2
16
LSB
V
REF
2
16
------------
=
V
[ ]
T
CONV
N
ELCONV
OSR
1
+
(
)
⋅
1
+
f
S
--------------------------------------------------------------
=
s
[ ]
