參數(shù)資料
型號: SX8724E082TRT
廠商: Semtech
文件頁數(shù): 39/53頁
文件大?。?/td> 0K
描述: IC DAS PRESSURE/TEMP SENS 16MLPQ
標準包裝: 1
系列: ZoomingADC™
類型: 數(shù)據采集系統(tǒng)(DAS)
輸入類型: 差分
輸出類型: 數(shù)字
接口: I²C
安裝類型: 表面貼裝
封裝/外殼: 16-VQFN 裸露焊盤
供應商設備封裝: 16-MLPQ(4x4)
包裝: 標準包裝
配用: XE8000EV121-ND - BOARD EVAL FOR SX8723/24
其它名稱: SX8724E082DKR
ADVANCED COMMUNICATIONS & SENSING
V1.23 2009 Semtech Corp.
www.semtech.com
44
SX8724
ZoomingADC for Pressure and Temperature Sensing
Noise
Ideally, a constant input voltage VIN should result in a constant output code. However, because of circuit noise,
the 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 33: standard output deviation
and output rms noise voltage. Figure 24 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 25 is used to estimate the equivalent input referred rms noise VN,IN of the
acquisition chain in the model of Figure 26. This is given by the relationship:
(
)
ELCONV
N
IN
N
OSR
GD
V
GD
V
GD
V
+
+
=
2
3
2
1
3
2
1
2
1
2
,
(V
2rms)
Equation 25
where VN1, VN2, and VN3 are the output rms noise figures of Table 33, GD1, GD2, and GD3 are the PGA gains of
stages 1 to 3 respectively. As shown in this equation, noise can be reduced by increasing OSR and NELCONV
(increases the ADC averaging effect, but reduces noise).
Parameter
PGA1
PGA2
PGA3
Standard
deviation
at
ADC
output (LSB)
0.85
1.4
1.5
Output rms noise (V)
205 (VN1)
340 (VN2)
365 (VN3)
Table 33 - PGA Noise Measurements (n = 16 bits, OSR = 512, NELCONV = 2, VREF = 5 V)
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