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 ter-

mination and establishes proper ECL levels. This circuit con-

sumes 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

−6

R is a conversion factor that is set by internal equalizer pa-

rameters and cable length. For Belden 8281 coaxial cable,

the R values are (

τ = µs, C

Cable

Length

R Value

(Ohms)

100 meters

15000

200 meters

20000

300 meters

32000

For example, a C

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

CONNECTION AND OPERATION OF LOS AND MUTE

Loss of Signal (LOS) is a CMOS output that indicates the

presence of equalized data from the filter. This LOS 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 LOS as shown in

Figure 1.

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

Signal when LOS is connected to MUTE. The capacitor re-

duces sensitivity to pathological patterns. Pathological pat-

terns are defined as sparse data sequences with few transi-

tions.

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 out-

put 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.

MINIMUM DATA TRANSITIONS

The CLC012 specifies a minimum transition rate. For the

CLC012 this sets the minimum data rate for transmitting data

through any cable medium. The CLC012 minimum average

transition density is found in the Electrical Characteristics

section of the datasheet.

POWER SUPPLY OPERATION AND THERMAL

CONSIDERATIONS

The CLC012 operates from either +5V or −5.2V single sup-

plies. Refer to

Figure 1 when operating the part from +5V.

When operating with a −5.2V supply, the V

bypassed to ground. The evaluation board and associated

literature provide for operation from either supply.

Maximum power dissipation occurs at minimum cable

length. Under that condition, I

Total power dissipated:

P

Power in the load:

P

Maximum power dissipated on the die:

P

Junction Temperature =

(

θ

Layout and Measurement

The printed circuit board layout for the CLC012 requires

proper high-speed layout to achieve the performance speci-

fications found in the datasheet. The following list contains a

few rules to follow:

1.

Use a ground plane.

2.

Decouple power pins with 0.1 µF capacitors placed

≤ 0.1” (3mm) from the power pins.

3.

Design transmission strip lines from the CLC012’s input

and output pins to the board connectors.

4.

Route outputs away from inputs.

5.

Keep ground plane

≥ 0.025” (0.06mm) away from the in-

put and output pads.

Figure 8 shows a block level measurement diagram, while

Figure 15 on depicts a detailed schematic. A pseudo-random

pattern generator with low output jitter was used to provide a

NRZI pattern to create the eye diagrams shown in the

Typi-

cal Performance Characteristics section.

Since most pattern generators have a 50

Ω output imped-

ance, a translation can be accomplished using a CLC005

Cable Driver as an impedance transformer. A wide band-

width oscilloscope is needed to observe the high data rate

eye pattern. When monitoring a single output that is termi-

nated at both the equalizer output and the oscilloscope, the

effective output load is 37.4

Ω. Consequently, the signal

swing is half that observed for a single-ended 75

Ω

termination.

DS100145-27

FIGURE 7. Alternative Load Terminated

Output Interface

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