XE8000EV104 Semtech, XE8000EV104 Datasheet - Page 112

• Manufacturer Part Number: XE8000EV104
• Description: EVAL BOARD FOR XE8805AMI028LF
• Manufacturer: Semtech
• Type: MCUr

Specifications of XE8000EV104

• Contents: Fully Assembled Evaluation Board
• For Use With/related Products: XE88LC05AMI028
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

16.8.4
Ideally, a constant input voltage V
output code may vary for a fixed input voltage. Thus, a statistical analysis on the output code of 1200 conversions
for a constant input voltage was performed to derive the equivalent noise levels of PGA1, PGA2, and PGA3. The
extracted rms output noise of PGA1, 2, and 3 are given in Table 16-27: standard output deviation and output rms
noise voltage. Figure 16-17 shows the distribution for the ADC alone (PGA1, 2, and 3 bypassed). Quantization
noise is dominant in this case, and, thus, the ADC thermal noise is below 16 bits.
The simple noise model of Figure 16-18(a) is used to estimate the equivalent input referred rms noise V
acquisition chain in the model of Figure 16-18(b). This is given by the relationship:
where V
stages 1 to 3 respectively. As shown in this equation, noise can be reduced by increasing OSR and N
(increases the ADC averaging effect, but reduces noise).
© Semtech 2006
Table 16-27. PGA noise measurements (n = 16 bits, OSR = 512, N
V
N1
N
, V
,
Noise
IN
2
N2
=
, and V
(
V
N
1
/
GD
N3
Note: see noise model of Figure 16-18 and equation Eq. 21.
are the output rms noise figures of Table 16-27, GD
Output rms noise (µV)
1
Standard deviation at
)
2
ADC output (LSB)
+
Figure 16-16. Differential non-linearity of the ADC converter.
(
Parameter
V
N
2
IN
/(
should result in a constant output code. However, because of circuit noise, the
GD
(
OSR
1
⋅
GD
⋅
N
2
1
))
ELCONV
2
+
(
V
205 (V
)
N
PGA1
0.85
3
16-26
/(
GD
N1
)
1
⋅
GD
340 (V
PGA2
2
1.4
⋅
GD
N2
)
3
))
2
365 (V
PGA3
ELCONV
1.5
(V
1
, GD
2
N3
rms)
)
2
= 2, V
, and GD
(Eq. 21)
REF
= 5V)
3
XE8805/05A
are the PGA gains of
www.semtech.com
N,IN
ELCONV
of the