參數(shù)資料
型號: XE8805AMI028LF
廠商: Semtech
文件頁數(shù): 17/156頁
文件大?。?/td> 0K
描述: IC DAS 16BIT FLASH 8K MTP 64LQFP
標準包裝: 160
系列: XE880x
應用: 感測機
核心處理器: Coolrisc816?
程序存儲器類型: 閃存(22 kB)
控制器系列: XE8000
RAM 容量: 512 x 8
接口: UART,USRT
輸入/輸出數(shù): 24
電源電壓: 2.4 V ~ 5.5 V
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 64-LQFP
包裝: 托盤
供應商設備封裝: 64-LQFP(10x10)
產品目錄頁面: 585 (CN2011-ZH PDF)
配用: XE8000MP-ND - PROG BOARD AND PROSTART2 CARD
Semtech 2006
www.semtech.com
16-27
XE8805/05A
0
20
40
60
80
-5
-4
-3
-2
-1
0
1
2
3
4
5
Output Code Deviation From Mean Value [LSB]
O
ccu
ren
ces
[%
o
ftota
lsa
mp
le
s]
Figure 16-17. ADC noise (PGA1, 2 & 3 bypassed, OSR=512,NELCONV=2)
PGA1
PGA2
PGA3
ADC
GD1
GD2
GD3
V
N1
f
S
V
N2
V
N3
(a)
PGA1
PGA2
PGA3
ADC
GD1
GD2
GD3
V
N,IN
f
S
(b)
Figure 16-18. (a) Simple noise model for PGAs and ADC
and (b) total input referred noise
As an example, consider the system where: GD2 = 10 (GD1 = 1; PGA3 bypassed), OSR = 512, NELCONV = 2, VREF =
5V. In this case, the noise contribution VN1 of PGA1 is dominant over that of PGA2. Using equation Eq. 21, we get:
VN,IN = 6.4V (rms) at the input of the acquisition chain, or, equivalently, 0.85 LSB at the output of the ADC.
Considering a 0.2V (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.
16.8.5
Gain Error and Offset Error
Gain error is defined as the amount of deviation between the ideal transfer function (theoretical equation Eq. 18)
and the measured transfer function (with the offset error removed).
The actual gain of the different stages can vary depending on the fabrication tolerances of the different elements.
Although these tolerances are specified to a maximum of
±3%, they will be most of the time around ±0.5%.
Moreover, the tolerances between the different stages are not correlated and the probability to get the maximal
error in the same direction in all stages is very low. Finally, these gain errors can be calibrated by the software at
the same time with the gain errors of the sensor for instance.
Figure 16-19 shows gain error drift vs. temperature for different PGA gains. The curves are expressed in % of Full-
Scale Range (FSR) normalized to 25°C.
Not
Recommended
for
New
Designs
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