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AD812 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer AD812
Beschreibung Dual/ Current Feedback Low Power Op Amp
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 16 Seiten
AD812 Datasheet, Funktion
a
Dual, Current Feedback
Low Power Op Amp
AD812
FEATURES
Two Video Amplifiers in One 8-Lead SOIC Package
Optimized for Driving Cables in Video Systems
Excellent Video Specifications (RL = 150 ):
Gain Flatness 0.1 dB to 40 MHz
0.02% Differential Gain Error
0.02؇ Differential Phase Error
Low Power
Operates on Single +3 V Supply
5.5 mA/Amplifier Max Power Supply Current
High Speed
145 MHz Unity Gain Bandwidth (3 dB)
1600 V/s Slew Rate
Easy to Use
50 mA Output Current
Output Swing to 1 V of Rails (150 Load)
APPLICATIONS
Video Line Driver
Professional Cameras
Video Switchers
Special Effects
PRODUCT DESCRIPTION
The AD812 is a low power, single supply, dual video amplifier.
Each of the amplifiers have 50 mA of output current and are
optimized for driving one back-terminated video load (150 )
each. Each amplifier is a current feedback amplifier and fea-
tures gain flatness of 0.1 dB to 40 MHz while offering differen-
tial gain and phase error of 0.02% and 0.02°. This makes the
AD812 ideal for professional video electronics such as cameras
and video switchers.
PIN CONFIGURATION
8-Lead Plastic
Mini-DIP and SOIC
OUT1 1
–IN1 2
+
+IN1 3
V– 4
+
AD812
8 V+
7 OUT2
6 –IN2
5 +IN2
The AD812 offers low power of 4.0 mA per amplifier max (VS =
+5 V) and can run on a single +3 V power supply. The outputs
of each amplifier swing to within one volt of either supply rail to
easily accommodate video signals of 1 V p-p. Also, at gains of
+2 the AD812 can swing 3 V p-p on a single +5 V power sup-
ply. All this is offered in a small 8-lead plastic DIP or 8-lead
SOIC package. These features make this dual amplifier ideal
for portable and battery powered applications where size and
power is critical.
The outstanding bandwidth of 145 MHz along with 1600 V/µs
of slew rate make the AD812 useful in many general purpose
high speed applications where a single +5 V or dual power sup-
plies up to ± 15 V are available. The AD812 is available in the
industrial temperature range of –40°C to +85°C.
0.4
G = +2
0.3 RL = 150
0.2
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
–0.6
100k
VS = ؎15V
؎5V
5V
3V
1M 10M
FREQUENCY – Hz
100M
Figure 1. Fine-Scale Gain Flatness vs. Frequency, Gain
= +2, RL = 150
REV. B
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
0.06
DIFFERENTIAL GAIN
0.04
0.08
0.02
0.06
DIFFERENTIAL PHASE
0.04
0.02
0
5 6 7 8 9 10 11 12 13 14 15
SUPPLY VOLTAGE – ؎Volts
Figure 2. Differential Gain and Phase vs. Supply Voltage,
Gain = +2, RL = 150
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1998






AD812 Datasheet, Funktion
AD812–Typical Performance Characteristics
20 16
14
15
12
VS = ؎15V
10
5
0
0 5 10 15 20
SUPPLY VOLTAGE – ؎Volts
Figure 4. Input Common-Mode Voltage Range vs. Supply
Voltage
10
VS = ؎5V
8
6
4
–60 –40
–20 0 20 40 60 80 100
JUNCTION TEMPERATURE – ؇C
120 140
Figure 7. Total Supply Current vs. Junction Temperature
10
20 TA = +25 C
NO LOAD
9
15
8
10
7
RL = 150
56
0
0 5 10 15 20
SUPPLY VOLTAGE – ؎Volts
Figure 5. Output Voltage Swing vs. Supply Voltage
5
0 2 4 6 8 10 12 14 16
SUPPLY VOLTAGE – ؎Volts
Figure 8. Total Supply Current vs. Supply Voltage
30
؎15V SUPPLY
25
20
15
10
؎5V SUPPLY
5
0
10 100
1k 10k
LOAD RESISTANCE –
Figure 6. Output Voltage Swing vs. Load Resistance
25
20
15
10 –IB, VS = ؎5V
5
0
–5 +IB, VS = ؎5V, ؎15V
–10
–IB, VS = ؎15V
–15
–20
–25
–60 –40 –20 0 20 40 60 80 100 120 140
JUNCTION TEMPERATURE – ؇C
Figure 9. Input Bias Current vs. Junction Temperature
–6– REV. B

6 Page









AD812 pdf, datenblatt
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 will affect the bandwidth.
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 (RL = 150 )
VS (V)
Gain
RF ()
BW (MHz)
± 15 +1
+2
+10
–1
–10
866 145
715 100
357 65
715 100
357 60
± 5 +1
750 90
+2 681 65
+10 154 45
–1 715 70
–10 154 45
+5 +1
750 60
+2 681 50
+10 154 35
–1 715 50
–10 154 35
+3 +1
750 50
+2 681 40
+10 154 30
–1 715 40
–10 154 25
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:
( ) ( )ACL =
G
S2
RF
+ GrIN
 2πf2
CT
+
S
RF
+ GrIN

CT +1
where:
ACL = closed-loop gain
G = 1 + RF/RG
rIN = input resistance of the inverting input
CT = “transcapacitance,” which forms the open-loop
dominant pole with the tranresistance
RF = feedback resistor
RG = gain resistor
f2 = frequency of second (nondominant) pole
S = 2 πj f
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.
Table II. Two-Pole Model Parameters at Various
Supply Voltages
VS
rIN ()
CT (pF)
f2 (MHz)
± 15 85
2.5 150
± 5 90
3.8 125
+5 105 4.8 105
+3 115 5.5 95
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:
f3 = fN [1 2d2 + (2 4d2 + 4d4)1/2]1/2
where:
( )fN
=
RF
f
2
+ GrIN
1/ 2
CT
and:
d = (1/2) [f2 (RF + GrIN) CT]1/2
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.
–12–
REV. B

12 Page





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