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PDF AD818 Data sheet ( Hoja de datos )
| Número de pieza | AD818 | |
| Descripción | Low Cost/ Low Power Video Op Amp | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AD818 (archivo pdf) en la parte inferior de esta página. Total 15 Páginas | ||
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Low Cost, Low Power
Video Op Amp
AD818
FEATURES
Low Cost
Excellent Video Performance
55 MHz 0.1 dB Bandwidth (Gain = +2)
0.01% and 0.05؇ Differential Gain and Phase Errors
High Speed
130 MHz Bandwidth (3 dB, G = +2)
100 MHz Bandwidth (3 dB, G+ = –1)
500 V/s Slew Rate
80 ns Settling Time to 0.01% (VO = 10 V Step)
High Output Drive Capability
50 mA Minimum Output Current
Ideal for Driving Back Terminated Cables
Flexible Power Supply
Specified for Single (+5 V) and Dual (؎5 V to ؎15 V)
Power Supplies
Low Power: 7.5 mA Max Supply Current
Available in 8-Lead SOIC and 8-Lead PDIP
GENERAL DESCRIPTION
The AD818 is a low cost video op amp optimized for use in
video applications that require gains equal to or greater than +2
or –1. The AD818’s low differential gain and phase errors,
single supply functionality, low power, and high output drive
make it ideal for cable driving applications such as video
cameras and professional video equipment.
With video specs like 0.1 dB flatness to 55 MHz and low differ-
ential gain and phase errors of 0.01% and 0.05∞, along with
50 mA of output current, the AD818 is an excellent choice for
+15V
0.01F
2.2F
VIN
1k⍀
REV. D
AD818
0.1F
RBT
75⍀
75⍀
2.2F
RT
75⍀
–15V
1k⍀
Figure 1. Video Line Driver
CONNECTION DIAGRAM
8-Lead Plastic Mini-DIP (N) and SOIC (R) Packages
NULL 1
–IN 2
+IN 3
AD818
8 NULL
7 +VS
6 OUTPUT
–VS 4
TOP VIEW
5 NC
NC = NO CONNECT
any video application. The 130 MHz 3 dB bandwidth (G = +2)
and 500 V/ms slew rate make the AD818 useful in many high speed
applications including video monitors, CATV, color copiers,
image scanners, and fax machines.
The AD818 is fully specified for operation with a single +5 V
power supply and with dual supplies from ± 5 V to ± 15 V. This
power supply flexibility, coupled with a very low supply current
of 7.5 mA and excellent ac characteristics under all power sup-
ply conditions, make the AD818 the ideal choice for many
demanding yet power sensitive applications.
The AD818 is a voltage feedback op amp and excels as a gain
stage in high speed and video systems (gain ≥ 2, or gain £ –1). It
achieves a settling time of 45 ns to 0.1%, with a low input offset
voltage of 2 mV max.
The AD818 is available in low cost, small 8-lead PDIP and
SOIC packages.
DIFF GAIN
0.02
0.01
0.06
0.00
0.05
DIFF PHASE
0.04
0.03
5
10
SUPPLY VOLTAGE (؎V)
15
Figure 2. Differential Gain and Phase vs. Supply
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 that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective companies.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781.461-3113 ©2010 Analog Devices, Inc. All rights reserved.
1 page  
Typical Performance Characteristics–AD818
20 20
15
+VCM
10
–VCM
5
15
RL = 500⍀
10
RL = 150⍀
5
0
0 5 10 15 20
SUPPLY VOLTAGE (؎V)
TPC 1. Common-Mode Voltage Range vs. Supply
30
25
VS = ؎15V
20
15
10
VS = ؎5V
5
0
10 100
1k
LOAD RESISTANCE (⍀)
10k
TPC 2. Output Voltage Swing vs. Load Resistance
600
500
0
0 5 10 15 20
SUPPLY VOLTAGE (؎V)
TPC 4. Output Voltage Swing vs. Supply
8.0
7.5
+85؇C
+25؇C
7.0
–40؇C
6.5
6.0
0
5 10
SUPPLY VOLTAGE (؎V)
15
20
TPC 5. Quiescent Supply Current vs. Supply Voltage
100
10
400 1
300 0.1
200
0
5 10 15
SUPPLY VOLTAGE (؎V)
TPC 3. Slew Rate vs. Supply Voltage
20
0.01
1k
10k 100k 1M
10M
100M
FREQUENCY (Hz)
TPC 6. Closed-Loop Output Impedance vs. Frequency
REV. D
–5–
5 Page 
AD818
+VS may result in peaking. A small capacitance (1 pF–5 pF) may be
used in parallel with the feedback resistor to neutralize this effect.
Power supply leads should be bypassed to ground as close as
possible to the amplifier pins. Ceramic disc capacitors of 0.1 mF
are recommended.
OUTPUT
–IN +VS
+IN
NULL 1
NULL 8
–VS
Figure 4. AD818 Simplified Schematic
THEORY OF OPERATION
The AD818 is a low cost video operational amplifier designed to
excel in high performance, high output current video applications.
The AD818 (Figure 4) consists of a degenerated NPN differen-
tial pair driving matched PNPs in a folded-cascode gain stage.
The output buffer stage employs emitter followers in a class
AB amplifier that delivers the necessary current to the load, while
maintaining low levels of distortion.
The AD818 will drive terminated cables and capacitive loads of
10 pF or less. As the closed-loop gain is increased, the AD818
will drive heavier capacitive loads without oscillating.
INPUT CONSIDERATIONS
An input protection resistor (RIN in TPC 28) is required in
circuits where the input to the AD818 will be subjected to tran-
sients of continuous overload voltages exceeding the ± 6 V
maximum differential limit. This resistor provides protection for
the input transistors by limiting their maximum base current.
For high performance circuits, it is recommended that a “bal-
ancing” resistor be used to reduce the offset errors caused by
bias current flowing through the input and feedback resistors.
The balancing resistor equals the parallel combination of RIN
and RF and thus provides a matched impedance at each input
terminal. The offset voltage error will then be reduced by more
than an order of magnitude.
GROUNDING AND BYPASSING
When designing high frequency circuits, some special precautions
are in order. Circuits must be built with short interconnect leads.
When wiring components, care should be taken to provide a low
resistance, low inductance path to ground. Sockets should be
avoided, since their increased interlead capacitance can degrade
circuit bandwidth.
Feedback resistors should be of low enough value (£1 kW) to
ensure that the time constant formed with the inherent stray
capacitance at the amplifier’s summing junction will not limit
performance. This parasitic capacitance, along with the parallel
resistance of RFʈRIN, forms a pole in the loop transmission, which
AD818
10k⍀
–VS VOS ADJUST
Figure 5. Offset Null Configuration
OFFSET NULLING
The input offset voltage of the AD818 is inherently very low.
However, if additional nulling is required, the circuit shown
in Figure 5 can be used. The null range of the AD818 in this
configuration is ± 10 mV.
SINGLE SUPPLY OPERATION
Another exciting feature of the AD818 is its ability to perform
well in a single supply configuration. The AD818 is ideally
suited for applications that require low power dissipation and
high output current.
Referring to Figure 6, careful consideration should be given to
the proper selection of component values. The choices for this
particular circuit are: R1 + R3ʈR2 combine with C1 to form a
low frequency corner of approximately 10 kHz. C4 was inserted
in series with R4 to maintain amplifier stability at high frequency.
Combining R3 with C2 forms a low-pass filter with a corner
frequency of approximately 500 Hz. This is needed to maintain
amplifier PSRR, since the supply is connected to VIN through
the input divider. The values for R2 and C2 were chosen to
demonstrate the AD818’s exceptional output drive capability.
In this configuration, the output is centered around 2.5 V. In
order to eliminate the static dc current associated with this level,
C3 was inserted in series with R L.
VS
R3
100⍀
C2
3.3F
R4
1k⍀
C4
0.001F
C1
0.01F
VIN
R1
3.3k⍀
R2
3.3k⍀
1k⍀
3.3F
SELECT C1, R1, R2
FOR DESIRED LOW
FREQUENCY CORNER.
0.01F
AD818
VOUT
C3
0.1F
RL
150⍀
Figure 6. Single-Supply Amplifier Configuration
REV. D
–11–
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet AD818.PDF ] | |
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