4608X-102-102 Datasheet, PDF (46/62 Pages) Bourns Electronic Solutions – Resistor Networks Product Selection Guide

RC Terminator Networks 700 Series
General Description
This series of RC Networks is designed to eliminate transmis-
sion line effects, such as signal reflections and ringing which
influence high speed CMOS. The Networks capacitor blocks
DC currents while acting as a short circuit during signal transmi-
tions, thus reducing power consumption. The capacitor also
holds the bus at the last logic level to avoid excessive currents.
Block Diagram Of CPU/BUS Configuration
Bus Termination Applications Of Bourns Networks
At high frequencies, the traces on a printed circuit board act
as transmission lines—in which impedance mismatches can
cause distortion of signals on that line. Terminating the lines
with resistor or resistor-capacitor networks provides the means
to match impedances and reduce signal distortion.
Bus termination (in this case, RC termination technique)
considerably reduces overshoots and ringings.
Transmission lines require termination when the time it takes
the signal to travel from one end of the line to the other (the
propagation delay) amounts to 1/2 or more of the edge rate of
the signal (signal rise time or fall time). In other words, termina-
tion is required when:
Tpd > (1/2)Te
Te = edge rate
Tpd = propagation delay
Present high-speed logic families have typical rise times of 2
nanoseconds, while the propagation delay of a common PCB is
about 1.77 ns per foot. Applying the above relationship, a trans-
mission line will require termination if it is longer than 7 inches.
High performance systems will commonly need Bourns termi-
nation networks for CPU address, data, and control lines. In
addition, clock inputs, write and read strobe lines, chip select or
output enable lines of high speed devices such as static RAMs,
PROMs, and PLDs will also need termination networks.
TERMINATION TYPICAL ADDS RESISTOR CAPACITOR
TECHNIQUE POWER DELAY VALUE
VALUE
USAGE
RC
MEDIUM NO
Zo
200-500pF
FOR PRODUCT SPECIFICATIONS, SEE PAGES 307 AND 308.
322
Specifications are subject to change without notice.