4116R-R2R-503 datasheet(46/62 Pages) BOURNS

46 / 62 page

Specifications are subject to change without notice.

322

FOR PRODUCT SPECIFICATIONS, SEE PAGES 307 AND 308.

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

USAGE

MEDIUM

200-500pF

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.

RC Terminator Networks 700 Series

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