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Printed Circuit Board Termination Network for High Speed Signals

IP.com Disclosure Number: IPCOM000123591D
Original Publication Date: 1999-Jan-01
Included in the Prior Art Database: 2005-Apr-05
Document File: 8 page(s) / 268K

Publishing Venue

IBM

Related People

Chaudron, P: AUTHOR [+3]

Abstract

Disclosed is a Printed Circuit Board (PCB) layout fitted to allow optimal placement of termination networks around a Very Large Scale Integration (VLSI) module.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 39% of the total text.

Printed Circuit Board Termination Network for High Speed Signals

   Disclosed is a Printed Circuit Board (PCB) layout fitted
to allow optimal placement of termination networks around a Very
Large Scale Integration (VLSI) module.

   The increasing required bandwidth of communication systems
leads to high density and high speed active components performing
switching functions.  The amount of digital inputs/outputs terminals
of VLSI modules reaches several hundreds to meet the required
bandwidth.

   High density VLSI components are characterized by a matrix
pattern of I/O terminals as in Pin Grid Array or Ball Grid Array
packages.

   A 25 by 25 Ball Grid Array is shown on Figure 1.

   The I/O assignment of the module is very often liable to be
customized according to the logic functions to be performed.  Once
the power supply and other reserved I/O are assigned, there is some
freedom to allocate some package regions to some particular
functions.

   If the function is a 16 ports switch, one can expect that
there are two regions, one for input data flow, one for output data
flow, each region being composed of 16 sub regions.  One particular
sub region is therefore dedicated to a port.

   An input port sub region may consist in a set of I/O
terminals, generally located in the same area amidst the hundreds of
terminals of the VLSI module.  An input port may include 4, 8 or 16
bits, each bit requiring one wire (single ended transmission) or two
wires (differential transmission).  This also holds true for output
port.

   One has to consider what are the characteristics of the
signal carried by these wires, i.e. their rise and fall time, and the
distance between the module driving the signal, and the module
receiving it.

   Transmission line theory applies when twice the propagation
time becomes longer than the rise/fall time of the signal.  Over
this distance, the line requires proper termination network to be
implemented, either on the driver end, or on the receiver end, and
sometimes on both ends.

   In data transmission systems, the designer has to analyze
line reflections caused by improperly terminated lines, liable to
generate signal distortion at the receiver input.  It has been shown
that the most adequate termination is located as close as possible to
the end of a point to point transmission line.

   On the driver side, the number of components required to
adapt the line is generally less that the one required on the
receiver side, which also includes means to probe the signals with a
high bandwidth oscilloscope.  This is the reason why only the
receiver network termination, the most difficult to implement, will
be detailed hereafter.

   The problems consists in connecting the required
termination components (resistor, capacitor, test point) to the
point to point line under analysis.  First, the components have to be
placed on one side (and possibly on the two sides) of the PCB, then,
the connections should be...