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參數資料
| 型號： | AD8138ARZ |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 通用總線功能 |
| 英文描述： | Low Distortion Differential ADC Driver |
| 中文描述： | LINE DRIVER, PDSO8 |
| 封裝： | LEAD FREE, MS-012AA, SOIC-8 |
| 文件頁數： | 17/24頁 |
| 文件大小： | 318K |
| 代理商： | AD8138ARZ |
AD8138
THEORY OF OPERATION
The AD8138 differs from conventional op amps in that it has
two outputs whose voltages move in opposite directions. Like
an op amp, it relies on high open-loop gain and negative
feedback to force these outputs to the desired voltages. The
AD8138 behaves much like a standard voltage feedback op
amp and makes it easy to perform single-ended-to-differential
conversion, common-mode level-shifting, and amplification of
differential signals. Also like an op amp, the AD8138 has high
input impedance and low output impedance.
Rev. F | Page 17 of 24
Previous differential drivers, both discrete and integrated
designs, have been based on using two independent amplifiers
and two independent feedback loops, one to control each of the
outputs. When these circuits are driven from a single-ended
source, the resulting outputs are typically not well balanced.
Achieving a balanced output has typically required exceptional
matching of the amplifiers and feedback networks.
DC common-mode level-shifting has also been difficult with
previous differential drivers. Level-shifting has required the use
of a third amplifier and feedback loop to control the output
common-mode level. Sometimes the third amplifier has also
been used to attempt to correct an inherently unbalanced
circuit. Excellent performance over a wide frequency range
has proven difficult with this approach.
The AD8138 uses two feedback loops to separately control the
differential and common-mode output voltages. The differential
feedback, set with external resistors, controls only the differential
output voltage. The common-mode feedback controls only the
common-mode output voltage. This architecture makes it easy
to arbitrarily set the output common-mode level. It is forced, by
internal common-mode feedback, to be equal to the voltage
applied to the V
OCM
input, without affecting the differential
output voltage.
The AD8138 architecture results in outputs that are very highly
balanced over a wide frequency range without requiring tightly
matched external components. The common-mode feedback
loop 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.
ANALYZING AN APPLICATION CIRCUIT
The AD8138 uses high open-loop gain and negative feedback to
force its differential and common-mode output voltages in such
a way as to minimize the differential and common-mode error
voltages. The differential error voltage is defined as the voltage
between the differential inputs labeled +IN and IN in Figure 42.
For most purposes, this voltage can be assumed to be zero.
Similarly, the difference between the actual output common-
mode voltage and the voltage applied to V
OCM
can also be
assumed to be zero. Starting from these two assumptions, any
application circuit can be analyzed.
SETTING THE CLOSED-LOOP GAIN
Neglecting the capacitors C
F
, the differential-mode gain of the
circuit in Figure 42 can be determined to be described by
S
G
S
F
dm
OUT
V
dm
OUT
V
R
R
=
,
,
This assumes the input resistors,
R
GS
, and feedback resistors,
R
FS
,
on each side are equal.
ESTIMATING THE OUTPUT NOISE VOLTAGE
Similar to the case of a conventional op amp, the differential
output errors (noise and offset voltages) can be estimated by
multiplying the input referred terms, at +IN and IN, by the
circuit noise gain. The noise gain is defined as
+
=
G
F
N
R
R
G
1
To compute the total output referred noise for the circuit of
Figure 42, consideration must also be given to the contribution
of the Resistors
R
F
and
R
G
. Refer to Table 8 for the estimated
output noise voltage densities at various closed-loop gains.
Table 8.
Gain
1
2
5
10
R
G
(Ω)
499
499
499
499
R
F
(Ω)
499
1.0 k
2.49 k
4.99 k
Bandwidth
3 dB
320 MHz
180 MHz
70 MHz
30 MHz
Output
Noise
AD8138
Only
10 nV/√Hz
15 nV/√Hz
30 nV/√Hz
55 nV/√Hz
Output
Noise
AD8138 +
R
G
, R
F
11.6 nV/√Hz
18.2 nV/√Hz
37.9 nV/√Hz
70.8 nV/√Hz
相關PDF資料 |
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|---|---|
| AD8138ARZ-R7 | Low Distortion Differential ADC Driver |
| AD8138ARZ-RL | Low Distortion Differential ADC Driver |
| AD8138 | Low Distortion Differential I/O Amplifier(小失真差分輸入/輸出放大器) |
| AD8139ARDZ-REEL | Low Noise Rail-to-Rail Differential ADC Driver |
| AD8139ARDZ-REEL7 | Low Noise Rail-to-Rail Differential ADC Driver |
相關代理商/技術參數 |
參數描述 |
|---|---|
| AD8138ARZ-R7 | 功能描述:IC AMP DIFF LDIST LP 95MA 8SOIC RoHS:是 類別:集成電路 (IC) >> 線性 - 放大器 - 專用 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:60 系列:- 類型:可變增益放大器 應用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤 供應商設備封裝:20-TQFN-EP（5x5） 包裝:托盤 |
| AD8138ARZ-RL | 功能描述:IC AMP DIFF LDIST LP 95MA 8SOIC RoHS:是 類別:集成電路 (IC) >> 線性 - 放大器 - 專用 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:60 系列:- 類型:可變增益放大器 應用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤 供應商設備封裝:20-TQFN-EP（5x5） 包裝:托盤 |
| AD8138-EVAL | 制造商:AD 制造商全稱:Analog Devices 功能描述:Low Distortion Differential ADC Driver |
| AD8138SRMZ-EP-R7 | 功能描述:IC ADC DRIVER DIFF 8MSOP RoHS:是 類別:集成電路 (IC) >> 線性 - 放大器 - 專用 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:60 系列:- 類型:可變增益放大器 應用:CATV 安裝類型:表面貼裝 封裝/外殼:20-WQFN 裸露焊盤 供應商設備封裝:20-TQFN-EP（5x5） 包裝:托盤 |
| AD8139 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Low Noise, Rail-to-Rail, Differential ADC Driver |
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