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參數(shù)資料
| 型號： | AD8137_05 |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | Low Cost, Low Power 12-Bit Differential ADC Driver |
| 中文描述： | 低成本，低功耗12位差分ADC驅(qū)動器 |
| 文件頁數(shù)： | 17/24頁 |
| 文件大小： | 597K |
| 代理商： | AD8137_05 |
AD8137
THEORY OF OPERATION
The AD8137 is a low power, low cost, fully differential voltage
feedback amplifier that features a rail-to-rail output stage,
common-mode circuitry with an internally derived common-
mode reference voltage, and bias shutdown circuitry. The
amplifier uses two feedback loops to separately control differ-
ential and common-mode feedback. The differential gain is set
with external resistors as in a traditional amplifier while the
output common-mode voltage is set by an internal feedback
loop, controlled by an external V
OCM
input. This architecture
makes it easy to arbitrarily set the output common-mode
voltage level without affecting the differential gain of the
amplifier.
Rev. B | Page 17 of 24
–OUT
+IN
A
CM
V
OCM
C
C
C
C
CP
+OUT
–IN CN
0
Figure 61. Block Diagram
From Figure 61, the input transconductance stage is an
H-bridge whose output current is mirrored to high impedance
nodes CP and CN. The output section is traditional H-bridge
driven circuitry with common emitter devices driving nodes
+OUT and OUT. The 3 dB point of the amplifier is defined as
C
m
C
g
×
BW
π
=
2
where
g
m
is the transconductance of the input stage and
C
C
is
the total capacitance on node CP/CN (capacitances CP and CN
are well matched). For the AD8137, the input stage g
m
is
~1 mA/V and the capacitance C
C
is 3.5 pF, setting the crossover
frequency of the amplifier at 41 MHz. This frequency generally
establishes an amplifier’s unity gain bandwidth, but with the
AD8137, the closed-loop bandwidth depends upon the feed-
back resistor value as well (see Figure 19). The open-loop gain
and phase simulations are shown in Figure 62.
FREQUENCY (MHz)
100
80
60
–60
–80
–40
–20
0
20
40
–120
–140
–100
–200
–180
–160
0.0001
0.01
0.001
0.1
1
10
100
0
OPEN-LOOP GAIN (dB)
PHASE (DEGREES)
Figure 62. Open-Loop Gain and Phase
In Figure 61, the common-mode feedback amplifier A
CM
samples the output common-mode voltage, and by negative
feedback forces the output common-mode voltage to be equal
to the voltage applied to the V
OCM
input. In other words, the
feedback loop servos the output common-mode voltage to the
voltage applied to the V
OCM
input. An internal bias generator
sets the V
OCM
level to approximately midsupply; therefore, the
output common-mode voltage will be set to approximately
midsupply when the V
OCM
input is left floating. The source
resistance of the internal bias generator is large and can be
overridden easily by an external voltage supplied by a source
with a relatively small output resistance. The V
OCM
input can
be driven to within approximately 1 V of the supply rails while
maintaining linear operation in the common-mode feedback loop.
The common-mode feedback loop inside the AD8137 produces
outputs that are highly balanced over a wide frequency range
without the requirement of tightly matched external compo-
nents, because it forces the signal component of the output
common-mode voltage to be zeroed. The result is nearly
perfectly balanced differential outputs of identical amplitude
and exactly 180° apart in phase.
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| AD8137ACP | 制造商:Analog Devices 功能描述:LOW COST 10-12 BIT DIFFERENTIAL ADC DRIVER - Bulk |
| AD8137AR | 制造商:Analog Devices 功能描述:LOW COST 10-12 BIT DIFFERENTIAL ADC DRIVER - Bulk |
| AD8137WYCPZ-R7 | 制造商:AAVID 制造商全稱:AAVID 功能描述:Low Cost, Low Power, Differential ADC Driver |
| AD8137YCP-EBZ | 制造商:Analog Devices 功能描述:AD8137 ADC DRIVER EVALUATION BOARD 制造商:Analog Devices 功能描述:AD8137, ADC DRIVER, EVALUATION BOARD |
| AD8137YCP-R2 | 制造商:Analog Devices 功能描述:SP Amp DIFF AMP Single R-R O/P ±6V/12V 8-Pin LFCSP EP T/R |
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