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6

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

GS9029 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 GS9029 are less than 0.5 in.

Fig. 6 Interfaces using Internal SDI Terminations

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 GS9029 is designed to meet this need

with ultra low input amplitude requirements (as low as

80mV).

Fig. 7 Interfaces using Internal SDI Terminations

Connected to AC Ground

The GS9029 can accept AC coupled input signals with no

extra configuration required.

OUTPUT INTERFACING

Figure 8 illustrates the recommended interface for ac

coupled outputs.

Fig. 8 Interfaces for AC Coupled Outputs

characteristic

impedance

of

the

cable.

Controlled

impedance traces should be used for the outputs and the

termination resistors should be placed near the GS9029.

The inductor (L) and resistor (R) are used to optimize the

output return loss and are PCB dependent. Typically, R

equals the transmission line characteristic impedance and

L is approximately 8.2nH.

OUTPUT AMPLITUDE ADJUSTMENT

The GS9029 outputs are adjustable from as low as 50mV to

as high as 1000 mV. The output amplitudes are set by the

is given by the equation below:

note that the above formula assumes that the transmission

line is properly end terminated.

10nF

+

_

SDI/T

SDI/T

GS9029

+

_

GS9028

+

_

SDI/T

10nF

SDI/T

GS9029

+

_

75

75

10nF

GS9028

R

GS9029

R

L

L

+

_

10nF

1µF

1µF

R

SET

1.154

Z

O

×

2V

OUT

×

-----------------------------

=