HDMP-1012 Datasheet, PDF (40/42 Pages) Agilent(Hewlett-Packard) – 4Low Cost Gigabit Rate Transmit/Receive Chip Set

deliver ECL swings directly into
50 Ω. The output impedance is
matched to 50 Ω with a VSWR of
less than 2:1 to above 2 GHz. This
output is ideal for driving the I-
H50 input through a 50 Ω cable
and a 0.1 uF coupling capacitor.
The 150 Ω shunt resistor to
ground improves internal DC bias
of the O-BLL differential output
circuit. The O-BLL driver can also
be connected directly into a high
speed 50 Ω oscilloscope. For
optimum performance, both
output should see the same
impedance. It is necessary that all
used O-BLL outputs be
terminated into 50 Ω. Figure 23
shows various methods of
interfacing O-BLL to I-H50 and
standard ECL logic.
TTL and Positive 5 V
Operation
Many applications require the I/
Os to interface to the standard
TTL logic family. Such TTL/ECL
translators are available in the
industry from various
semiconductor manufacturers.
This works well, but requires two
power supplies since the system is
supporting two different logic
families. This technique is
preferred, since it is easier to
keep a single clean ground plane.
Although G-LINK has been
designed to work with conven-
tional ECL negative supply, a
single positive supply can also be
used. This basically replaces the
traditional ground and Vee planes
with the Vcc and ground planes.
Also, the termination plane Vtt is
shifted up to +3 V. In theory,
since voltages are all relative,
there should be no difference. In
practice, however, the differences
lie in how well the Vcc plane is
bypassed to ground, since all of
the I/Os are referenced to this
plane. It is therefore necessary to
separate any TTL or CMOS Vcc to
this chip set, so that the cleanest
Vcc plane can be achieved.
O-BLL
12
80
80
28 mA
V_EE
150
0.1 µF
HGND
Z_O = 50 Ω
150
50
50
Figure 22. I-H50 and O-BLL Simplified Circuit Schematic.
I-H50
50
50
V_EE
612