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參數資料
| 型號： | AD8011AR-REEL |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 運動控制電子 |
| 英文描述： | 300 MHz, 1 mA Current Feedback Amplifier |
| 中文描述： | OP-AMP, 6000 uV OFFSET-MAX, PDSO8 |
| 封裝： | SOIC-8 |
| 文件頁數： | 13/16頁 |
| 文件大小： | 219K |
| 代理商： | AD8011AR-REEL |
AD8011
REV. B
–13–
INCREASING BW AT HIGH GAINS
As presented above, for a fixed R
F
(feedback gain setting resis-
tor) the AD8011 CLBW will decrease as R
N
is reduced (in-
creased G). This effect can be minimized by simply reducing R
F
and thus partially restoring the devices optimized BW for gains
greater than +2/
–
1. Note that the AD8011 is ac optimized (high
BW and low peaking) for A
V
=+2/
–
1 and R
F
equal to 1 k
.
Using this optimized G as a reference and the V
O
(s) equations
above, the following relationships results:
R
F
= 1
k
+ 2
–
G
/2
gm
for G
= 1+
R
F
/R
N
(noninverting) or:
R
F
= 1
k
+
G
+ 1/2
gm
for
G
=
–
R
F
/
R
N
(inverting)
Using 1/2 gm equal to 120
results in a R
F
of 500
for
G = 5/
–
4 and a corresponding R
N
of 125
. This will extend the
AD8011
’
s BW to near its optimum design value of typically 180
MHz at R
L
= 1 k
. In general, for gains greater than +7/
–
6, R
F
should not be reduced to values much below 400
else ac
peaking can result. Using this R
F
value as the a lower limit, will
result in BW restoration near its optimized value to the upper G
values specified. Gains greater than about +7/
–
6 will result
in CLBW reduction. Again, the derivations above are just
approximations.
DRIVING A SINGLE-SUPPLY A/D CONVERTER
New CMOS A/D converters are placing greater demands on the
amplifiers that drive them. Higher resolutions, faster conversion
rates and input switching irregularities require superior settling
characteristics. In addition, these devices run off a single +5 V
supply and consume little power, so good single-supply operation
with low power consumption are very important. The AD8011
is well positioned for driving this new class of A/D converters.
Figure 36 shows a circuit that uses an AD8011 to drive an
AD876, a single supply, 10-bit, 20 MSPS A/D converter that
requires only 140 mW. Using the AD8011 for level shifting and
driving, the A/D exhibits no degradation in performance com-
pared to when it is driven from a signal generator.
The analog input of the AD876 spans 2 V centered at about
2.6 V. The resistor network and bias voltages provide the level
shifting and gain required to convert the 0 V to 1 V input signal
to a 3.6 V to 1.6 V range that the AD876 wants to see.
Biasing the noninverting input of the AD8011 at 1.6 V dc forces
the inverting input to be at 1.6 V dc for linear operation of the
amplifier. When the input is at 0 V, there is 3.2 mA flowing out
of the summing junction via R1 (1.6 V/499
). R3 has a current
of 1.2 mA flowing into the summing junction (3.6 V
–
1.6 V)/
1.65 k
. The difference of these two currents (2 mA) must flow
through R2. This current flows toward the summing junction
and requires that the output be 2 V higher than the summing
junction or at 3.6 V.
When the input is at 1 V, there is 1.2 mA flowing into the sum-
ming junction through R3 and 1.2 mA flowing out through R1.
These currents balance and leave no current to flow through
R2. Thus the output is at the same potential as the inverting
input or 1.6 V.
The input of the AD876 has a series MOSFET switch that turns
on and off at the sampling rate. This MOSFET is connected to
a hold capacitor internal to the device. The on impedance of the
MOSFET is about 50
, while the hold capacitor is about 5 pF.
In a worst case condition, the input voltage to the AD876 will
change by a full-scale value (2 V) in one sampling cycle. When
the input MOSFET turns on, the output of the op amp will be
connected to the charged hold capacitor through the series
resistance of the MOSFET. Without any other series resistance,
the instantaneous current that flows would be 40 mA. This
would cause settling problems for the op amp.
The series 100
resistor limits the current that flows instanta-
neously after the MOSFET turns on to about 13 mA. This
resistor cannot be made too large or the high frequency perfor-
mance will be affected.
The sampling MOSFET of the AD876 is closed for only half of
each cycle or for 25 ns. Approximately 7 time constants are
required for settling to 10 bits. The series 100
resistor along
with the 50
on resistance and the hold capacitor, create a
750 ps time constant. These values leave a comfortable margin
for settling. Obtaining the same results with the op amp A/D
combination as compared to driving with a signal generator
indicates that the op amp is settling fast enough.
Overall the AD8011 provides adequate buffering for the AD876
A/D converter without introducing distortion greater than that
of the A/D converter by itself.
3.6V
1.6V
AD8011
+5V
10 F
R2
1k
R3
1.65k
R1
499k
3.6V
V
IN
50
0.1 F
1.6V
1V
0V
100
AD876
+1.6V
+3.6V
REFT
REFB
0.1 F
0.1 F
Figure 36. AD8011 Driving the AD876
相關PDF資料 |
PDF描述 |
|---|---|
| AD8011 | 300 MHz, 1 mA Current Feedback Amplifier |
| AD8011* | Micropower Op Amp, Comparator and Reference; Package: MSOP; No of Pins: 8; Temperature Range: 0°C to +70°C |
| AD8011-EB | 300 MHz, 1 mA Current Feedback Amplifier |
| AD8011AN | 300 MHz, 1 mA Current Feedback Amplifier |
| AD8011AR | 300 MHz, 1 mA Current Feedback Amplifier |
相關代理商/技術參數 |
參數描述 |
|---|---|
| AD8011AR-REEL7 | 功能描述:IC OPAMP CF LP LDIST 30MA 8SOIC RoHS:否 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 標準包裝:2,500 系列:- 放大器類型:通用 電路數:1 輸出類型:滿擺幅 轉換速率:0.11 V/µs 增益帶寬積:350kHz -3db帶寬:- 電流 - 輸入偏壓:4nA 電壓 - 輸入偏移:20µV 電流 - 電源:260µA 電流 - 輸出 / 通道:20mA 電壓 - 電源，單路/雙路(±):2.7 V ~ 36 V，±1.35 V ~ 18 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 供應商設備封裝:8-SO 包裝:帶卷 (TR) |
| AD8011ARZ | 功能描述:IC OPAMP CF LP LDIST 30MA 8SOIC RoHS:是 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 標準包裝:2,500 系列:- 放大器類型:通用 電路數:4 輸出類型:- 轉換速率:0.6 V/µs 增益帶寬積:1MHz -3db帶寬:- 電流 - 輸入偏壓:45nA 電壓 - 輸入偏移:2000µV 電流 - 電源:1.4mA 電流 - 輸出 / 通道:40mA 電壓 - 電源，單路/雙路(±):3 V ~ 32 V，±1.5 V ~ 16 V 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:14-TSSOP（0.173"，4.40mm 寬） 供應商設備封裝:14-TSSOP 包裝:帶卷 (TR) 其它名稱:LM324ADTBR2G-NDLM324ADTBR2GOSTR |
| AD8011ARZ | 制造商:Analog Devices 功能描述:Operational Amplifier (Op-Amp) IC 制造商:Analog Devices 功能描述:IC, OP-AMP, 300MHZ, 3500V/ us, SOIC-8 |
| AD8011ARZ | 制造商:Analog Devices 功能描述:IC AMPLIS |
| AD8011ARZ-REEL | 功能描述:IC OPAMP CF LP LDIST 30MA 8SOIC RoHS:是 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 其它有關文件:Automotive Product Guide 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:1 系列:- 放大器類型:通用 電路數:1 輸出類型:滿擺幅 轉換速率:3 V/µs 增益帶寬積:10MHz -3db帶寬:- 電流 - 輸入偏壓:1pA 電壓 - 輸入偏移:70µV 電流 - 電源:2.5mA 電流 - 輸出 / 通道:48mA 電壓 - 電源，單路/雙路(±):2.7 V ~ 5.5 V，±1.35 V ~ 2.75 V 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:SOT-23-6 供應商設備封裝:SOT-6 包裝:Digi-Reel® 其它名稱:MAX4475AUT#TG16DKR |
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