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| 型号： | AD8331ARQ-REEL |
| 厂商： | Analog Devices Inc |
| 文件页数： | 19/56页 |
| 文件大小： | 0K |
| 描述： | IC VGA SINGLE W/PREAMP 20-SSOP |
| 产品变化通告： | Product Discontinuance 27/Oct/2011 |
| 设计资源： | Interfacing the High Frequency AD8331 to AD9215 (CN0096) |
| 标准包装： | 2,500 |
| 系列： | X-AMP® |
| 类型： | 可变增益放大器 |
| 应用： | 信号处理 |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-SSOP（0.154"，3.90mm 宽） |
| 供应商设备封装： | 20-QSOP |
| 包装： | 带卷 (TR) |
| 配用： | AD8331-EVALZ-ND - BOARD EVAL FOR AD8331 |
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AD8331/AD8332/AD8334
Rev. G | Page 26 of 56
Active Impedance Matching
The LNA supports active impedance matching through an external
shunt feedback resistor from Pin LON to Pin INH. The input
resistance, RIN, is given in Equation 5, where A is the single-
ended gain of 4.5, and 6 kΩ is the unterminated input impedance.
IZ
IN
R
A
R
+
×
=
+
=
kΩ
33
kΩ
6
kΩ
6
1
(5)
CIZ is needed in series with RIZ because the dc levels at Pin LON
and Pin INH are unequal. Expressions for choosing RIZ in terms
at higher frequencies, where the loop gain is diminished, and
prevent peaking. Frequency response plots of the LNA are shown
130 MHz for matched input impedances of 50 Ω to 200 Ω and
declines at higher source impedances. The unterminated
bandwidth (when RIZ = ∞) is approximately 80 MHz.
Each output can drive external loads as low as 100 Ω in addition
to the 100 Ω input impedance of the VGA (200 Ω differential).
Capacitive loading up to 10 pF is permissible. All loads should
be ac-coupled. Typically, Pin LOP output is used as a single-ended
driver for auxiliary circuits, such as those used for Doppler
ultrasound imaging. Pin LON drives RIZ. Alternatively, a
differential external circuit can be driven from the two outputs
in addition to the active feedback termination. In both cases,
important stability considerations discussed in the Applications
Information section should be carefully observed.
The impedance at each LNA output is 5 Ω. A 0.4 dB reduction
in open circuit gain results when driving the VGA, and a 0.8 dB
reduction results with an additional 100 Ω load at the output.
The differential gain of the LNA is 6 dB higher. If the load is less
than 200 Ω on either side, a compensating load is recommended
on the opposite output.
LNA Noise
The input-referred voltage noise sets an important limit on
system performance. The short-circuit input voltage noise of
the LNA is 0.74 nV/√Hz or 0.82 nV/√Hz (at maximum gain),
including the VGA noise. The open circuit, current noise is
2.5 pA/√Hz. These measurements, taken without a feedback
resistor, provide the basis for calculating the input noise and
noise figure performance of the configurations in Figure 75.
results and the 4.1 dB noise figure (NF) measurement with the
input actively matched to a 50 Ω source. Unterminated (RIZ = ∞)
operation exhibits the lowest equivalent input noise and noise
figure. Figure 76 shows the noise figure vs. source resistance,
rising at low RS, where the LNA voltage noise is large compared
to the source noise, and again at high RS due to current noise.
The VGA input-referred voltage noise of 2.7 nV/√Hz is
included in all of the curves.
VOUT
UNTERMINATED
+
–
VIN
RIN
RS
VOUT
RESISTIVE TERMINATION
+
–
VIN
RIN
RS
VOUT
ACTIVE IMPEDANCE MATCH - RS = RIN
+
–
VIN
RIN
RIZ
1 + 4.5
RS
RIN =
03
19
9-
0
75
Figure 75. Input Configurations
7
6
5
4
3
2
1
0
50
100
1k
NO
IS
E
F
IG
UR
E
(
d
B)
RS ()
03
19
9-
0
76
INCLUDES NOISE OF VGA
RESISTIVE TERMINATION
(RS = RIN)
ACTIVE IMPEDANCE MATCH
UNTERMINATED
SIMULATION
Figure 76. Noise Figure vs. RS for Resistive,
Active Match, and Unterminated Inputs
7
6
5
4
3
2
1
0
50
100
1k
NO
IS
E
F
IG
UR
E
(
d
B)
RS ()
03
19
9-
0
77
INCLUDES NOISE OF VGA
RIN = 50
RIN = 75
RIN = 100
RIN = 200
RIZ = ∞
(SIMULATED RESULTS)
Figure 77. Noise Figure vs. RS for Various Fixed Values of RIN, Actively Matched
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| AD8331ARQ-REEL7 | 功能描述:IC VGA SINGLE W/PREAMP 20-SSOP RoHS:否 类别:集成电路 (IC) >> 线性 - 放大器 - 专用 系列:X-AMP® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:60 系列:- 类型:可变增益放大器 应用:CATV 安装类型:表面贴装 封装/外壳:20-WQFN 裸露焊盘 供应商设备封装:20-TQFN-EP（5x5） 包装:托盘 |
| AD8331ARQZ | 功能描述:IC VGA SINGLE W/PREAMP 20-QSOP RoHS:是 类别:集成电路 (IC) >> 线性 - 放大器 - 专用 系列:X-AMP® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:60 系列:- 类型:可变增益放大器 应用:CATV 安装类型:表面贴装 封装/外壳:20-WQFN 裸露焊盘 供应商设备封装:20-TQFN-EP（5x5） 包装:托盘 |
| AD8331ARQZ | 制造商:Analog Devices 功能描述:IC AMP VARIABLE GAIN 8331 QSOP20 |
| AD8331ARQZ-R7 | 功能描述:IC AMP VAR GAIN 1CHAN 20QSOP RoHS:是 类别:集成电路 (IC) >> 线性 - 放大器 - 专用 系列:X-AMP® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:60 系列:- 类型:可变增益放大器 应用:CATV 安装类型:表面贴装 封装/外壳:20-WQFN 裸露焊盘 供应商设备封装:20-TQFN-EP（5x5） 包装:托盘 |
| AD8331ARQZ-RL | 功能描述:IC VGA SINGLE W/PREAMP 20QSOP RoHS:是 类别:集成电路 (IC) >> 线性 - 放大器 - 专用 系列:X-AMP® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:60 系列:- 类型:可变增益放大器 应用:CATV 安装类型:表面贴装 封装/外壳:20-WQFN 裸露焊盘 供应商设备封装:20-TQFN-EP（5x5） 包装:托盘 |
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