•

Observe the output current requirements of the driving

device.

Figure 16 and Figure 17 show DC and AC coupled interface

examples which meet these four conditions.

OUTPUT INTERFACES

SDO, SDO, SCO, and SCO swing at ECL logic levels when

the correct external components are used. However, the out-

puts are not standard emitter-coupled logic outputs. Instead,

the signals flow from the collectors of the output transistors.

The primary advantage of this architecture is lower power

dissipation. Some example interfaces follow.

Differential Load-Terminated Output Interface

Figure 18 shows an interface to drive signals differentially

over a coaxial cable. The diode establishes V

resistor network sets V

in its characteristic impedance.

Differential Source-Terminated Output Interface

Figure 19 is similar to Figure 18 except that the termination

is placed near the output pins.

Terminating Physically Separated Outputs

When the circuit design requires the outputs to be routed to

separate locations, the recommended interface is depicted

in

Figure 20. Choose the resistors for an equivalent 75

Ω ter-

mination of the cable impedance (or other cable characteris-

tic impedance, as appropriate).

DS100087-28

FIGURE 16. Differential 75

Ω Source

DS100087-29

FIGURE 17. AC Coupled Termination

DS100087-30

FIGURE 18. Differential Load-Terminated

Output Interface

DS100087-31

FIGURE 19. Differential Source-

Terminated Output Interface

www.national.com

14