ADA4411-3
Rev. 0 | Page 12 of 16
Figure 20 and Figure 21 illustrate several ways to use the
LEVEL1 and LEVEL2 inputs.
INPUT AND OUTPUT COUPLING
Figure 20 shows examples of how
to generate fully adjustable LEVEL1 and LEVEL2 voltages from
±5 V and single +5 V supplies. These circuits show a general
case, but a more practical approach is to fix one voltage and
vary the other.
Inputs to the ADA4411-3 are normally dc-coupled. Ac coupling
the inputs is not recommended; however, if ac coupling is
necessary, suitable circuitry must be provided following the ac
coupling element to provide proper dc level and bias currents at
the ADA4411-3 input stages. The ADA4411-3 outputs can be
either ac- or dc-coupled.
Figure 21 illustrates an effective way to produce
a 600 mV output offset voltage in a single-supply application.
Although the LEVEL2 input could simply be connected to
GND,
Figure 21 includes bypassed resistive voltage dividers for
each input so that the input levels can be changed, if necessary.
Additionally, many in-circuit testers require that I/O signals not
be tied directly to the supplies or GND. DNP indicates do not
populate.
When driving single ac-coupled loads in standard 75 Ω video
distribution systems, 220 µF coupling capacitors are recom-
mended for use on all but the chrominance signal output. Since
the chrominance signal is a narrow-band modulated carrier, it
has no low frequency content and can therefore be coupled with
a 0.1 µF capacitor.
05527-018
DUAL SUPPLY
0.1μF
LEVEL1
9.53kΩ
1kΩ
9.53kΩ
+5V
–5V
0.1μF
LEVEL2
9.53kΩ
1kΩ
9.53kΩ
+5V
–5V
SINGLE SUPPLY
0.1μF
LEVEL1
1kΩ
9.09kΩ
+5V
0.1μF
LEVEL2
1kΩ
9.09kΩ
+5V
There are two ac coupling options when driving two loads from
one output. One simply uses the same value capacitor on the
second load, while the other is to use a common coupling
capacitor that is at least twice the value used for the single load
(see
Figure 22 and Figure 23).
05527-020
75Ω
DA4411-3
75Ω
220μF
220μF
75Ω
75Ω
75Ω
CABLE
75Ω
CABLE
Figure 20. Generating Fully Adjustable Output Offsets
Figure 22. Driving Two AC-Coupled Loads with Two Coupling Capacitors
05527-021
75Ω
75Ω
75Ω
75Ω
470μF
75Ω
CABLE
75Ω
CABLE
ADA4411-3
05527-019
0.1μF
LEVEL1
634Ω
10kΩ
+5V
DNP
LEVEL2
0Ω
DNP
+5V
Figure 21. Flexible Circuits to Set the LEVEL1 and LEVEL2 Inputs to
Obtain a 600 mV Output Offset on a Single Supply
Figure 23. Driving Two AC-Coupled Loads with One Common Coupling Capacitor
When driving two parallel 150 Ω loads (75 Ω effective load),
the 3 dB bandwidth of the filters typically varies from that of
the filters with a single 150 Ω load. For the 9 MHz and 18 MHz
filters, the typical variation is within ±1.0%; for the 36 MHz
filters, the typical variation is within ±2.5%.
