参数资料
型号: XE8805AMI028LF
厂商: Semtech
文件页数: 17/156页
文件大小: 0K
描述: IC DAS 16BIT FLASH 8K MTP 64LQFP
标准包装: 160
系列: XE880x
应用: 感测机
核心处理器: Coolrisc816?
程序存储器类型: 闪存(22 kB)
控制器系列: XE8000
RAM 容量: 512 x 8
接口: UART,USRT
输入/输出数: 24
电源电压: 2.4 V ~ 5.5 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 64-LQFP
包装: 托盘
供应商设备封装: 64-LQFP(10x10)
产品目录页面: 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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