DETAILED DESCRIPTION
INPUT INTERFACING
OUTPUT INTERFACING
SDI/SDI are high impedance differential inputs. Two
conditions must be observed when interfacing to these
inputs:
Figure 8 illustrates the recommended interface for ac
coupled outputs.
V
1. The input signal amplitude must be between 80mV and
1000mV.
CC
R
= R = Z
T
O
10nF
R
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.
R
T
R
1µF
1µF
T
L
+
GS9028
L
_
R
Figures 6 and 7 illustrate two methods of interfacing the
GS9029 to the Gennum GS9024 (Cable Equalizer), GS9035
(Reclocker) or the GS9025 (Receiver).
GS9029
Fig. 8 Interfaces for AC Coupled Outputs
Figure
6
illustrates the simplest interface and is
The termination resistor (RT) value should be equal to the
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.
recommended when the trace lengths between the driver
and the GS9029 are less than 0.5 in.
+
+
_
GS9029
_
SDI/T
SDI/T
10nF
V
CC
OUTPUT AMPLITUDE ADJUSTMENT
Fig. 6 Interfaces using Internal SDI Terminations
The GS9029 outputs are adjustable from as low as 50mV to
as high as 1000 mV. The output amplitudes are set by the
RSET0 and the RSET1 resistors respectively. The relationship
between the approximate output amplitude (VOUT) and RSET
is given by the equation below:
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).
1.154 × Z
O
R
= ----------------------------
SET
2 × V
OUT
where ZO is in ohms and VOUT is in volts.
The minimum value of RSET is 43.2Ω. For 75Ω cable and
800mV output amplitudes, the value of RSET is 54.9Ω. Also,
note that the above formula assumes that the transmission
line is properly end terminated.
V
CC
10nF
75
75
+
+
_
GS9029
GS9028
_
SDI/T
10nF
SDI/T
Fig. 7 Interfaces using Internal SDI Terminations
Connected to AC Ground
The GS9029 can accept AC coupled input signals with no
extra configuration required.
6
521 - 97 - 02
GENNUM [ GENNUM CORPORATION ]
