GS9028 データシートの表示（PDF） - Gennum -> Semtech
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GS9028 Datasheet PDF : 7 Pages
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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.
VCC
10nF
75Ω
+
_
GS9024 or
GS9035 or
GS9025
75Ω
+
_
GS9028
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 50Ω transmission lines (which are more robust and
easier to control in multilayer boards) to interconnect the
GS9024/25/35 and the GS9028.
VCC
100nF
10nF
75Ω
+
75Ω 75Ω
_
GS9024 or
GS9035 or
GS9025
75Ω
+
_
GS9028
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.
VCC
10nF
R1
1µF
1µF
R2
R1
+
_
GS9028
R2
Fig. 8
The recommended values for R1 and R2 are:
R1 = 1.35ZO
R2 = 3.85ZO
where ZO is the transmission line characteristic impedance.
For 75Ω cable, R1 = 100Ω and R2 = 287Ω.
OUTPUT INTERFACING
Figure 9 illustrates the recommended interface for ac
coupled outputs.
VCC
10nF
RT
RT
+
GS9028
_
GS9028
RT = R = ZO
R
L 1µF
L 1µF
R
Fig. 9
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