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DETAILED DESCRIPTION

INPUT INTERFACING

SDI/SDI are

high impedance

differential inputs. Two

conditions must be observed when interfacing to these

inputs:

1. The input signal amplitude must be between 80mV and

1000mV.

2. The common mode voltage range must be as specified

in the DC Characteristics Table (page 2). For 800mV

input amplitude signals, this corresponds to a common

mode voltage range between 2.8 and 4.6 volts.

Figures 6 and 7 illustrate two methods of interfacing the

GS9028 to the Gennum GS9024 (Cable Equalizer), GS9035

(Reclocker) or the GS9025 (Receiver).

Figure

6

illustrates

the

simplest

interface

and

is

recommended when the trace lengths between the driver

and the GS9028 are less than 0.5in. The pull up resistors

should be placed near the GS9028 to serve as end

terminations.

GS9024 or

GS9035 or

GS9025

GS9028

75

Ω

75

Ω

10nF

+

_

+

_

Fig. 6

When trace lengths become longer than 0.5in and data

rates greater than 360Mb/s, electromagnetic reflections

begin to affect signal integrity. To minimize reflections,

controlled

impedance

traces

and

source

and

end

terminations should be used as shown in Figure 7. Although

terminations on both sides reduce the signal swing by a

factor of two, the GS9028 is designed to meet this need

with ultra low input amplitude requirements (as low as

80mV). This low input amplitude requirement also allows the

use of 50

Ω transmission lines (which are more robust and

easier to control in multilayer boards) to interconnect the

GS9024/25/35 and the GS9028.

GS9024 or

GS9035 or

GS9025

GS9028

+

_

+

_

75

Ω

100nF

10nF

75

Ω 75Ω

75

Ω

Fig. 7

The GS9028 can also be configured to accept ac coupled

input signals. In this case, the inputs must be dc biased as

illustrated in Figure 8.

R1

R1

10nF

1µF

1µF

R2

R2

GS9028

+

_

Fig. 8

The recommended values for R1 and R2 are:

For 75

Ω cable, R1 = 100Ω and R2 = 287Ω.

OUTPUT INTERFACING

Figure 9 illustrates the recommended interface for ac

coupled outputs.

GS9028

R

GS9028

R

L

L

+

_

10nF

1µF

1µF

Fig. 9