AD812AR Analog Devices Inc, AD812AR Datasheet - Page 12
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AD812AR
Manufacturer Part Number
AD812AR
Description
IC OPAMP DUAL CURR-FDBK 8-SOIC
Manufacturer
Analog Devices Inc
Datasheet
1.AD812ARZ.pdf
(16 pages)
Specifications of AD812AR
Slew Rate
1600 V/µs
Mounting Type
Surface Mount
Rohs Status
RoHS non-compliant
Applications
Current Feedback
Number Of Circuits
2
-3db Bandwidth
145MHz
Current - Supply
4.5mA
Current - Output / Channel
50mA
Voltage - Supply, Single/dual (±)
2.4 V ~ 36 V, ±1.2 V ~ 18 V
Package / Case
8-SOIC (0.154", 3.90mm Width)
No. Of Amplifiers
2
Bandwidth
145MHz
No. Of Pins
8
Settling Time
40ns
Operating Temperature Max
85°C
Peak Reflow Compatible (260 C)
No
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
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20 000
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Company:
Part Number:
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Manufacturer:
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Quantity:
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Part Number:
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Manufacturer:
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Quantity:
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Part Number:
AD812ARZ-REEL7
Manufacturer:
ADI/亚德诺
Quantity:
20 000
AD812
General Considerations
The AD812 is a wide bandwidth, dual video amplifier which
offers a high level of performance on less than 5.5 mA per am-
plifier of quiescent supply current. It is designed to offer out-
standing performance at closed-loop inverting or noninverting
gains of one or greater.
Built on a low cost, complementary bipolar process, and achiev-
ing bandwidth in excess of 100 MHz, differential gain and phase
errors of better than 0.1% and 0.1 (into 150 ), and output
current greater than 40 mA, the AD812 is an exceptionally
efficient video amplifier. Using a conventional current feedback
architecture, its high performance is achieved through careful
attention to design details.
Choice of Feedback and Gain Resistors
Because it is a current feedback amplifier, the closed-loop band-
width of the AD812 depends on the value of the feedback resis-
tor. The bandwidth also depends on the supply voltage. In
addition, attenuation of the open-loop response when driving
load resistors less than about 250
Table I contains data showing typical bandwidths at different
supply voltages for some useful closed-loop gains when driving a
load of 150 . (Bandwidths will be about 20% greater for load
resistances above a few hundred ohms.)
The choice of feedback resistor is not critical unless it is impor-
tant to maintain the widest, flattest frequency response. The
resistors recommended in the table are those (metal film values)
that will result in the widest 0.1 dB bandwidth. In those appli-
cations where the best control of the bandwidth is desired, 1%
metal film resistors are adequate. Wider bandwidths can be
attained by reducing the magnitude of the feedback resistor (at
the expense of increased peaking), while peaking can be reduced
by increasing the magnitude of the feedback resistor.
Table I. –3 dB Bandwidth vs. Closed-Loop Gain and
Feedback Resistor (R
V
+5
+3
15
5
S
(V)
Gain
+1
+2
+10
–1
–10
+1
+2
+10
–1
–10
+1
+2
+10
–1
–10
+1
+2
+10
–1
–10
L
= 150 )
will affect the bandwidth.
R
866
715
357
715
357
750
681
154
715
154
750
681
154
715
154
750
681
154
715
154
F
( )
BW (MHz)
145
100
65
100
60
90
65
45
70
45
60
50
35
50
35
50
40
30
40
25
–12–
To estimate the –3 dB bandwidth for closed-loop gains or feed-
back resistors not listed in the above table, the following two
pole model for the AD812 many be used:
where:
Appropriate values for the model parameters at different supply
voltages are listed in Table II. Reasonable approximations for
these values at supply voltages not found in the table can be
obtained by a simple linear interpolation between those tabu-
lated values which “bracket” the desired condition.
As discussed in many amplifier and electronics textbooks (such
as Roberge’s Operational Amplifiers: Theory and Practice), the
–3 dB bandwidth for the 2-pole model can be obtained as:
where:
and:
This model will predict –3 dB bandwidth within about 10 to
15% of the correct value when the load is 150 . However, it is
not an accurate enough to predict either the phase behavior or
the frequency response peaking of the AD812.
Printed Circuit Board Layout Guidelines
As with all wideband amplifiers, printed circuit board parasitics
can affect the overall closed-loop performance. Most important
for controlling the 0.1 dB bandwidth are stray capacitances at
the output and inverting input nodes. Increasing the space between
signal lines and ground plane will minimize the coupling. Also,
signal lines connecting the feedback and gain resistors should be
kept short enough that their associated inductance does not
cause high frequency gain errors.
Table II. Two-Pole Model Parameters at Various
Supply Voltages
V
+5
+3
A
15
5
S
CL
A
G
r
C
R
R
f
S
2
IN
CL
T
F
G
f
S
3
= closed-loop gain
= 1 + R
= input resistance of the inverting input
= “transcapacitance,” which forms the open-loop
= feedback resistor
= gain resistor
= frequency of second (nondominant) pole
= 2 j f
2
= f
d = (1/2) [f
dominant pole with the tranresistance
N
R
f
N
[1 – 2d
F
r
85
90
105
115
F
IN
2
/R
Gr
( )
G
f
R
IN
2
2
2
F
+ (2 – 4d
(R
C
Gr
F
T
f
+ Gr
2
G
IN
S R
C
2.5
3.8
4.8
5.5
2
IN
C
+ 4d
T
T
) C
(pF)
F
1 2 /
T
4
Gr
]
)
1/2
1/2
IN
]
1/2
C
T
f
150
125
105
95
2
(MHz)
1
REV. B