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Equalization Method for High-Speed Serial Links

IP.com Disclosure Number: IPCOM000015395D
Original Publication Date: 2002-Jan-11
Included in the Prior Art Database: 2003-Jun-20

Publishing Venue

IBM

Abstract

The present document describes the equalization of a serial data stream that is transmitted over a channel that has frequency dependent loss characteristics. The transmission channel used in serial link applications is typically a single ended wire, a differential wire pair or an optical channel including laser driver and photo receiver. All of these channels exhibit frequency dependent loss. If a bit stream is transmitted over a channel with frequency dependent loss, then the signal waveform at the receiver shows intersymbol interference (ISI) that can significantly reduce the eye opening. Tight timing margins with increased bit error rates are a result of that. A channel equalizer is a building block that has a frequency dependent gain curve represents the inverse of the loss of the channel, therefore canceling the channel effects. If a signal passes through both the channel and the equalizer, the resulting signal is showing no frequency-dependent loss anymore, and the unwanted ISI is reduced to zero in the ideal case, or to a small value in real world applications. The equalizing block can be located after the channel, in front of the channel or it can even be split with some portion of the equalizing filter be placed on the TX side and some portion on the RX side (Figure 1). Figure 1: Placement of channel equalizer: a) on both sides of the channel, b) after the channel, c) before the channel