www.semtech.com/products/ Page 48 ADVANCED COMMUNICATIONS & SENSING DATASHEET SX8724C ZoomingADC fo" />
參數(shù)資料
型號: SX8724CWLTDT
廠商: Semtech
文件頁數(shù): 43/67頁
文件大?。?/td> 0K
描述: IC DAS ADC 16BIT I2C/SRL
標準包裝: 1
系列: ZoomingADC™
類型: 數(shù)據(jù)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-WQFN 裸露焊盤
供應(yīng)商設(shè)備封裝: 16-MLPQ-EP(4x4)
包裝: *
其它名稱: SX8724CWLTDTDKR
www.semtech.com/products/
Page 48
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
SX8724C
ZoomingADC for sensing data acquisition
Revision 1.01
January 2011
Semtech
11.1.1 Switched Capacitor Principle
Basically, a switched capacitor is a way to emulate a resistor by using a capacitor. The capacitors are much easier to
realize on CMOS technologies and they show a very good matching precision.
A resistor is characterized by the current that flows through it (positive current leaves node V1):
One can verify that the mean current leaving node V1 with a capacitor switched at frequency f is:
Therefore as a mean value, the switched capacitor 1/(f x C) is equivalent to a resistor.
It is important to consider that this is only a mean value. If the current is not integrated (low impedance source), the
impedance is infinite during the whole time but the transition.
What does it mean for the ZoomingADC?
If the fs clock is reduced, the mean impedance is increased. By dividing the fs clock by a factor 10, the impedance is
increased by a factor 10.
One can reduce the capacitor that is switched by using an amplifier set to its minimal gain. In particular if PGA1 is used
with gain 1, its mean impedance is 10x bigger than when it is used with gain 10.
One can increase the effective impedance by increasing the electrical bandwidth of the sensor node so that the
switching current is absorbed through the sensor before the switching period is over. Measuring the sensor node will
Figure 26. The Switched Capacitor Principle
Equation 25
Equation 26
Figure 27. The Switched Capacitor Principle
V
1
V
2
R
V
1
f
fV
2
]
[
2
1
A
R
V
I
=
(
)
]
[
2
1
A
C
f
V
I
=
Sensor
C
ZoomingADC (model)
V
1
f
fV
2
Sensor
impedence
Node
Capacitance
Current
integration
Not
Recommended
for
New
Designs
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SX8724EVK 制造商:Semtech Corporation 功能描述:Evaluation Board for SX8724E082TRT Data Acquisition System
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SX8724SEVK 制造商:Semtech Corporation 功能描述: 制造商:Semtech Corporation 功能描述:Evaluation Kit for SX8724S