Bus Expansion Encoder
When determining the performance of an off-chip bus, the worst-case noise magnitude must be considered in order to ensure a robust digital system. Chapter 11 presented an analytical model to predict the performance of an off-chip bus using the assumption that each of the noise sources within the package contributes its worstcase noise. Each source of noise within the package (Section 8.2) had a particular set of data sequences that resulted in the worst-case noise. This set of sequences dictates the highest performance that the package can achieve. The sequences that result in noise (from any noise source) above a certain magnitude can be avoided by designing an encoder which eliminates such sequences. This increases the performance of the package. By inserting this encoder in the signal path on the IC, it ensures that the off-chip data is encoded before traversing the package interconnect. In this way, data sequences which result in noise above a specified limit can be avoided and the bus performance can be increased.
KeywordsConstraint Equation Noise Source Noise Limit Mutual Capacitance Legal Transition
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