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.

DUAL SUPPLY

0.1

μF

LEVEL1

9.53k

Ω

1k

Ω

9.53k

Ω

+5V

–5V

0.1

μF

LEVEL2

9.53k

Ω

1k

Ω

9.53k

Ω

+5V

–5V

SINGLE SUPPLY

0.1

μF

LEVEL1

1k

Ω

9.09k

Ω

+5V

0.1

μF

LEVEL2

1k

Ω

9.09k

Ω

+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).

75

Ω

ADA4411-3

75

Ω

220

μF

220

μF

75

Ω

75

Ω

75

Ω

CABLE

75

Ω

CABLE

Figure 20. Generating Fully Adjustable Output Offsets

Figure 22. Driving Two AC-Coupled Loads with Two Coupling Capacitors

75

Ω

75

Ω

75

Ω

75

Ω

470

μF

75

Ω

CABLE

75

Ω

CABLE

ADA4411-3

0.1

μF

LEVEL1

634

Ω

10k

Ω

+5V

DNP

LEVEL2

0

Ω

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%.