Bus Stuttering : An Encoding Technique to Reduce Inductive Noise in Off-Chip Data Transmission

Simultaneous switching noise due to inductance in VLSI packaging is a significant limitation to system performance. The inductive parasitics within IC packaging causes bounce on the power supply pins in addition to glitches and rise-time degradation on the signal pins. These factors bound the maximum performance of off-chip busses, which limits overall system performance. Until recently, the parasitic inductance problem was addressed by aggressive package design which attempts to decrease the total inductance in the package interconnect. In this work we present an encoding technique for off-chip data transmission to limit bounce on the supplies and reduce inductive signal coupling. This is accomplished by inserting intermediate (henceforth called "stutter") states in the data, transmission to bind the maximum number of signals that switch simultaneously, thereby limiting the overall inductive noise. Bus stuttering is cheaper than expensive package design since it increases the bus performance without changing the package. We demonstrate that bus stuttering can bound the maximum amount of inductive noise, which results in increased bus performance even after accounting for the encoding overhead. Our results show that the performance of an encoded bus can be increased up to 225% over using un-encoded data. In addition, synthesis results of the encoder in a TSMC 0.13mum process show that the encoder size and delay are negligible in a modern VLSI design