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Efficient Wiring to Avoid "Crosstalk" Problems in Electronic Circuitry

IP.com Disclosure Number: IPCOM000040508D
Original Publication Date: 1987-Nov-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 15K

Publishing Venue

IBM

Related People

Hickson, JB: AUTHOR [+2]

Abstract

A technique is described whereby the physical layout of electronic circuitry is examined, and crosstalk-zone maps are maintained in the analysis of potential crosstalk problems. The crosstalk-zone maps contain the data needed to provide the required routing of wires and connections to avoid and solve electrical crosstalk problems. Crosstalk typically refers to an electrical phenomena which occurs as a result of wires or connections which are in close proximity to one another, whereby signals of one circuit affect the signals of other circuits. Crosstalk must be taken into account in the layout of a circuit chip, card, board or other packaging, so as to prevent erroneous functioning of the circuit.

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Efficient Wiring to Avoid "Crosstalk" Problems in Electronic Circuitry

A technique is described whereby the physical layout of electronic circuitry is examined, and crosstalk-zone maps are maintained in the analysis of potential crosstalk problems. The crosstalk-zone maps contain the data needed to provide the required routing of wires and connections to avoid and solve electrical crosstalk problems. Crosstalk typically refers to an electrical phenomena which occurs as a result of wires or connections which are in close proximity to one another, whereby signals of one circuit affect the signals of other circuits. Crosstalk must be taken into account in the layout of a circuit chip, card, board or other packaging, so as to prevent erroneous functioning of the circuit. Typically, logic design specifies the circuit layout and the points on the circuit which are connected to specified points of other circuits. A major task is to specify the exact routing of each connection between the circuits. Routing algorithms and other wiring procedures usually do not take into account crosstalk in their procedures. The technique described herein provides a method of identifying connections which may have potential crosstalk problems, determines a routing sequence for routing algorithms to follow, implements a crosstalk-zone map for re-routing of connections made by the algorithm and provides a final check of the crosstalk influence at each connection. Identifying crosstalk circuits: Crosstalk typically occurs when signals on a wire change, such as from +5 volts to 0 volts. When signals in a conductor are constant, no crosstalk occurs. Therefore, it is only necessary to examine sets of conductors which have changing signals. Determination of these sets is accomplished by examining the logic design, taking into account the circuits and the logic paths from input registers to each connection. A clock signal received by an input register initiates a time during which many circuits are affected by the settings of the registers. Clock signal connections are considered as being in the first set of connections for the analysis of crosstalk and is termed the "time 0" set. The outputs of the registers which feed into other circuits are the first set of connections to change signal levels, after arrival of the clock signal, therefore are termed "time 1" set.

If all circuits switch in the same length of time or have the same delay, then all outputs from circuits which are fed by "time 1" signals are members of the "time 2" set. As a result, any circuit whose inputs include one or more "time t" signals has its output connection in the "time t+1" set. If there are paths of different logical lengths between input registers and a particular circuit, then the output connection of that circuit is a member of more than one of the crosstalk sets. If the circuits do not all have the same delay, then the assignment of connections to crosstalk sets must take into accou...