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參數(shù)資料
| 型號： | SX8723E083TRT |
| 元件分類： | ADC |
| 英文描述： | 5-CH 16-BIT PROPRIETARY METHOD ADC, SERIAL ACCESS, PDSO12 |
| 封裝： | 4 X 4 MM, ROHS COMPLIANT, MLPD-12 |
| 文件頁數(shù)： | 30/53頁 |
| 文件大?。?/td> | 3978K |
| 代理商： | SX8723E083TRT |
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ADVANCED COMMUNICATIONS & SENSING
V1.8 2009 Semtech Corp.
www.semtech.com
36
SX8723
ZoomingADC for Pressure and Temperature Sensing
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.
Figure 19 - The Switched Capacitor Principle
A resistor is characterized by the current that flows through it (positive current leaves node V1):
R
V
I
2
1
=
(A)
Equation 22
One can verify that the mean current leaving node V1 with a capacitor switched at frequency f is:
(
) C
f
V
I
=
2
1
(A)
Equation 23
Therefore as a mean value, the switched capacitor
C
f
1
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.
Figure 20 - The Switched Capacitor Principle
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 show short voltage spikes at the frequency fs, but these will not influence the measurement. Whereas
if the bandwidth of the node is lower, no spikes will arise, but a small offset can be generated by the integration
of the charges generated by the switched capacitors, this corresponds to the mean impedance effect.
Note:
One can increase the mean input impedance of the ZoomingADC by lowering the acquisition clock fs.
One can increase the mean input impedance of the ZoomingADC by decreasing the gain of the first enabled amplifier.
One can increase the effective input impedance of the ZoomingADC by having a source with a high electrical bandwidth (sensor electrical
bandwidth much higher than fs).
Sensor
C
ZoomingADC (model)
V
1
f
V
2
Sensor
impedence
Node
Capacitance
Current
integration
V
1
V
2
R
V
1
f
V
2
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| SX8723S | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:ZoomingADC for sensing data acquisition |
| SX8723SWLTDT | 制造商:Semtech Corporation 功能描述:2 INPUTS ZOOMING ADC WITH SPI |
| SX8724 | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:ZoomingADC? for Pressure and Temperature Sensing |
| SX8724C | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:ZoomingADC for sensing data acquisition |
| SX8724CEVK | 制造商:Semtech Corporation 功能描述: |
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