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Method for crosstalk cancellation by alternating the signal transition polarity between lanes of an EPM data interface

IP.com Disclosure Number: IPCOM000132449D
Publication Date: 2005-Dec-16
Document File: 4 page(s) / 83K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for crosstalk cancellation by alternating the signal transition polarity between lanes of an edge position modulated (EPM) data interface. Benefits include improved functionality, improved performance, improved ease of implementation, and improved cost effectiveness

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Method for crosstalk cancellation by alternating the signal transition polarity between lanes of an EPM data interface

Disclosed is a method for crosstalk cancellation by alternating the signal transition polarity between lanes of an edge position modulated (EPM) data interface. Benefits include improved functionality, improved performance, improved ease of implementation, and improved cost effectiveness.

Background

      Crosstalk is caused by signal transitions on nearby data lanes which electromagnetically couple to susceptor lanes. As a result, several problems can occur, including the following:

•             Reduced signal-to-noise ratio

•             Lower maximum signaling rate

•             Requirements for higher receiver sensitivity and power

•             Requirement for wider physical separation of adjacent data lanes, increasing circuit board area and cost

•             Requirement for increased connector pin count and/or pin spacing for crosstalk isolation

•             Low-cost package options using closely spaced bond wires not optimal

•             Requirement for differential mode signaling, resulting in higher power and additional package and board interconnections

              Conventionally, crosstalk is minimized by reducing signal transition times to the minimum required to achieve the specified bit-error rate. This solution requires increasing the printed circuit board (PCB) trace spacing and adding guard traces between the PCB traces for isolation. Differential signaling improves noise immunity. Alternatively, connectors with low pin density or ground pins are added between signal pins. Active crosstalk cancellation circuitry is used in some situations.

      Conventional EPM signals and PCB traces can result in crosstalk (see Figure 1). The top and bottom traces are crosstalk aggressors in the single ended case while the center trace is the victim. Any signals on the victim are not illustrated for simplicity and only the crosstalk that is superimposed on the victim is depicted.

General description

      The disclosed method reduces crosstalk between parallel lanes of data interfaces by alternating the polarity of signal transitions on adjacent lanes. Signal transitions are arranged on the lanes to either side of a given susceptor to be nearly equal in amplitude and opposite in polarity.

      The method applies to interfaces having signals with regular transition polarity, such as with edge position modulation or other physical coding schemes. Additionally, the method applies to package interconnects, connect...