4608X-102-102 Datasheet, PDF (48/62 Pages) Bourns Electronic Solutions – Resistor Networks Product Selection Guide

Bourns Emitter Coupled Logic Terminator 800 Series
Typical Application
A typical application using a Bourns 801 RC Network in con-
junction with a 10K ECL design is shown below. Vee is typically
connected to -5.2 volts (10K ECL) or -4.5 volts (100K ECL). Vcc
is typically connected to GND. Vtt is typically connected to -2.0
volts. The 801 network shown below can terminate up to 6
transmission lines and provides a 0.01 µF capacitor to reduce
cross talk and feedthrough effects.
TRANSMISSION
LINES
BOURNS 801
10K ECL TERMINATOR
Vtt Vee
MC10H118 MECL 10KH
Vcc1
Aout
Vcc2
Bout
A1in
A1in
A1in
B1in
B1in
B1in
A2in
B2in
A2in
B2in
Vee
A2in,B2in
Transmission Line Considerations
In high speed circuit applications, the signal propagation delay
(Tpd) and characteristic impedance (zo), along a printed circuit
board line must be taken into consideration. In general, if the
two-way delay along the line is greater than the rise or fall time
of the signal, then controlled impedance techniques (i.e., termi-
nation) must be utilized to prevent undesirable ringing or over-
and undershoots. The delay and impedance can be calculated
by knowing the intrinsic inductance (Lo) and capacitance (Co) of
the line:
√ Tpd = LoCo
√ Zo =
Lo/Co
The actual, effective delay and impedance due to
loading from stubs or additional devices off the line will be:
√ Tpd’ = Tpd 1 + Cd/Co
Zo’ =
√ Zo
1 + (Cd/Co)
Where Co = intrinsic capacitance of the line
Cd = capacitance due to loading and stubs
off the line
Tpd = basic propagation delay of the line
Zo ....= basic impedance of the line
To formulate a guideline for when line termination is
necessary, take the ratio of the rise time or fall time and the two-
way delay along the line. The maximum length for unterminated
lines will result as follows:
Lmax = Tr
2Tpd’
Where Tr = rise or fall time
Tpd = propagation delay per unit length
The above equation implies that the faster the edge rate or the
higher the loading on the line (i.e., higher fanout), the more likely
that termination will be necessary for a given line length.
Parallel Termination
For maximum circuit performance or distributed loads, parallel
termination is the most appropriate technique. A parallel termi-
nated line uses a resistor connected to -2 volts (ECL application)
at the receiving end. The resistor value matches the characteris-
tic impedance of the line (Zo), thereby producing zero reflection
at the receiver. In addition, the terminating resistor also provides
output pull down, so a separate pull down resistor at the driving
end is unnecessary.
FOR PRODUCT SPECIFICATIONS, SEE PAGES 309 - 311.
324
Specifications are subject to change without notice.