CLC014 datasheet(10/17 Pages) NSC

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Output Interfacing (Continued)

DIFFERENTIAL SOURCE-TERMINATED OUTPUT

INTERFACE

Figure 6 is similar to Figure 5 except that the termination is

provided at the source. This configuration may also be used

for single-ended applications. However, the unused output

must still be terminated as shown.

TERMINATING PHYSICALLY SEPARATED OUTPUTS

When the two outputs must be routed to physically separate

locations, the circuit in Figure 6 may be applied. Alterna-

tively, if load termination is desired, the circuit in Figure 7

may be used. The resistive divider network provides 75

Ω

termination and establishes proper ECL levels. This circuit

consumes slightly more power than the previous circuits.

Design Guidelines

SELECTING THE AUTOMATIC EQUALIZER CAPACITOR

The AEC capacitor sets the loop time constant

τ for the

equalizer’s adaptive loop response time. The following for-

mula is used to set the loop time constant:

τ =R • C

AEC • 10

−6

R is a conversion factor that is set by internal equalizer

parameters and cable length. For Belden 8281 coaxial

cable, the R values are (

τ = µs, C

AEC in pF):

Cable

Length

R Value

(Ohms)

100 meters

15000

200 meters

20000

300 meters

32000

For example, a C

AEC value of 100 pF results in an adaptive

loop time constant of 2 µs at 200 meters of cable.

CONNECTION AND OPERATION OF CD AND MUTE

Carrier Detect (CD) is a CMOS output that indicates the

presence of equalized data from the filter. This CD output

can be connected to MUTE to suspend changes in the data

outputs DO and DO, if no valid signal exists. This simple

configuration prevents random output transitions due to

noise. For sparse transition patterns it is recommended that

a capacitor be connected to CD as shown in Figure 1.

Add a capacitor to pin 5 to slow the response time of Carrier

Detect when Carrier Detect is connected to MUTE. The

capacitor reduces sensitivity to pathological patterns. Patho-

logical patterns are defined as sparse data sequences with

few transitions.

OUTPUT EYE MONITOR OEM CONNECTIONS

The OEM is a high-speed, buffered output for monitoring the

equalized eye pattern prior to the output comparator. Its

output is designed to drive an AC-coupled 50

Ω coaxial cable

with a series 50

Ω backmatch resistor. The cable should be

terminated with 50

Ω at the oscilloscope. Figure 1 shows a

schematic with a typical connection.

10005625

FIGURE 5. Differential Load Terminated

Output Interface

10005626

FIGURE 6. Differential Source Terminated

Output Interface

10005627

FIGURE 7. Alternative Load Terminated

Output Interface

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