ICS889834 Datasheet, PDF (1/7 Pages) Integrated Circuit Systems – LOW SKEW, 2-TO-4 LVCMOS/LVTTL-TO-LVPECL/ECL CLOCK MULTIPLEXER

Integrated
Circuit
Systems, Inc.
HiPerClockS™ Application Note
3.3V LVPECL DRIVER TERMINATION
This application note provides termination examples for HiPerClockS^TM 3.3V LVPECL drivers. The HiPerClockS^TM
3.3V LVPECL driver is an open source/emitter driver as shown in Figure 1. Proper termination is required to
ensure proper function of the device and signal integrity. There are many different termination schemes for the
LVPECL drivers. This application note includes standard direct termination and AC coupled termination. The
following termination approaches are only general recommendations under ideal conditions. Board designers
should consult with their signal integrity engineers or verify through simulations in their system environment. The
trace length and physical location of the components can affect signal integrity. The 50-Ohm transmission lines
in the following diagrams indicate whether the components should be located near the driver or near the
receiver.
VCCO
VCCO
R1
R2
P.C. Board
Q
Zo = 50
nQ
LVPECL Driver
Zo = 50
R4
R3
50
50
VEE
VCCO-2V
Figure 1 HiPerClockS^TM LVPECL driver
Direct LVPECL Termination
The standard 3.3V LVPECL termination is shown in Figure 2. This termination scheme is used in
characterization. The draw back of using this termination scheme in real applications is that it requires an
additional power supply V_CCO-2V = 1.3V. In actual applications, the terminations shown in Figure 3 and Figure 4
are commonly used. These termination approaches eliminate the need of 1.3V power supply. In Figure 5, R1
and R2 located near the driver serve as current paths for the LVPECL outputs. The R3=100 Ohm located near
the receiving serves as matched load termination for the transmission lines.
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Aug 02, 2002