AD8010AR-16 View Datasheet(PDF) - Analog Devices
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AD8010AR-16 Datasheet PDF : 12 Pages
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APPLICATIONS
Video Distribution Amplifier
The AD8010 is optimized for the specific function of providing
excellent video performance when driving multiple video loads
in parallel. Significant power is saved and heat sinking is greatly
simplified because of the ability of the AD8010 to obtain this
performance when running on a ± 5 V supply. However, due to
the high currents that flow when driving many parallel video
loads, special layout and bypassing techniques are required to
assure optimal performance.
When designing a video distribution amplifier with the AD8010, it
is very important to keep in mind where the high (ac) currents
will flow. These paths include the power supply pins of the chip
along with the bypass capacitors and the return path for these
capacitors, the output circuits and the return path of the output
current from the loads.
In general, any loops that are formed by any of the above paths
should be made as small as possible. Large loops are both gen-
erators and receivers of magnetic fields and can cause undesired
coupling of signals that lowers the performance of the amplifier.
Effects that have not been seen before in other op amp circuits
might arise because of the high currents. Most op amp circuits
output, at most, tens of milliamps and do not require extremely
tight video specifications, while a video distribution amplifier
can output hundreds of milliamps and require extremely low
differential gain and phase errors.
AD8010
The bypassing scheme that is used for the AD8010 requires
special attention. It was found that the conventional technique
of bypassing each power pin individually to ground can have an
adverse effect on the differential phase error of the circuit. The
cause of this is attributed to the fact that there is an internal
compensation capacitor in the AD8010 that is referenced to the
negative supply.
The recommended technique is to connect parallel bypass
capacitors from the positive supply to the negative supply and
then to bypass the negative supply to ground. For high fre-
quency bypassing, 0.1 µF ceramic capacitors are recommended.
These should be placed within a few millimeters of the power
pins and should preferably be chip type capacitors.
The high currents that can potentially flow through the power
supply pins require large bypassing capacitors. These should be
low inductance tantalum types and at least 47 µF. The ground
side of the capacitor that bypasses the negative supply should be
brought to a single point ground that is the common for the
returns of the outputs.
Figure 30 shows a circuit for making an N-channel video distri-
bution amplifier. As a practical matter, the AD8010 can readily
drive eight standard 150 Ω video loads. When driving up to 12
video loads, there is minimal degradation in video performance.
Another important consideration when driving multiple cables
is the high frequency isolation between the outputs of the
cables. Due to its low output impedance, the AD8010 achieves
better than 46 dB of output-to-output isolation at 5 MHz driv-
ing back terminated 75 Ω cables.
499⍀
+5V
FB
499⍀
VIN
75⍀
150⍀
AD8010
C1
C2
FB
75⍀
75⍀
75⍀ RL1
75⍀ RL2
–5V
75⍀
75⍀ RLN
Figure 30. An N-Channel Video Distribution Amplifier Using An AD8010.
NOTE: Please see Figure 29 for Recommended Bypassing Technique.
REV. B
–9–
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