REDUCTION OF SIMULTANEOUS-SWITCHING NOISE IN LARGE CROSSBAR NETWORKS

A major problem in the design of VLSI crossbar networks is the simultaneous-switching noise (also known as Delta-I noise) caused by the simultaneous activation of a large number of line drivers at the output leads of the VLSI package. The Delta-I noise poses a severe limitation on the size of the individual crosspoint chips that can be used to synthesize a large crossbar network. We present an architectural solution for reduction of the Delta-I noise in a crossbar network by using one-sided crosspoint switching circuits. Because of the existence of multiple switching paths between any pair of terminals to be connected, these circuits provide the potential for minimizing the Delta-I noise by placing the active line drivers uniformly among the switching chips. We first show that when the sequence of connections and disconnections is arbitrary, and with a minimal nonblocking configuration of one-sided switching chips, no algorithm exists for allocation of paths in the network that can prevent the active line drivers from getting concentrated in a few chips. However, it is possible to reduce the maximum number of active line drivers in a chip by using extra columns of chips. We derive tight upper bounds for the number of additional columns required for a one-sided nonblocking crossbar network when a Delta-I constraint is imposed. Although these worst-case bounds apply to any algorithm for allocation of paths in the network, the Delta-I constraint can be satisfied by a much smaller number of columns in the average case by the use of algorithms that allocate paths intelligently. Simulation studies of two path-allocation algorithms, namely, the first-fit and the best-fit, for a 256-port network indicate that the Delta-I noise can be reduced by as much as 70% over a random allocation, with a blocking probability of less than 1%.