Modelling of Skin Effect in On-Chip VLSI RLC Global Interconnect

Abstract

This paper addresses one of the aspects of the high frequency effects, namely the skin effect. The basic
problem with skin effect is that it attenuates the high frequency components of a signal more than that of
the low frequency components. Due to the increase in operating frequency and die sizes, RC models are
becoming insufficient for analysis of global VLSI interconnects. Accurate noise modelling for RLC lines is
thus critical for timing and signal integrity analysis. Skin effect basically affects the resistance and also the
inductance, which in turn affects the system integrity in particular and its response as a whole. The current
distribution inside the conductor changes as frequency increases. These changes produced in the
conductors are known as skin and proximity effect. Till now the skin effect has been neglected for the
modelling the on-chip interconnects. But with the increase in frequency to the GHz range, the skin effect
has become prominent in performance parameter modelling. In this paper, firstly a crosstalk noise formula
for on chip VLSI interconnects has been proposed without considering the skin effect. The voltage
response at the output node is analytically derived and then the skin effect on the line resistance is
analysed. From that an efficient and novel model is derived to estimate the crosstalk in the on-chip
interconnects. On-chip inductive effects are becoming predominant in deep submicron interconnects due to
increasing clock speeds; circuit complexity and decreasing interconnect lengths. Inductance causes noise
in the signal waveforms, which can adversely affect the performance of the circuit and signal integrity. In
this paper, we have also proposed a novel analytical model to find the impact of the skin effect on the noise
in RLC interconnect without considering the skin effect on inductance because the value of the resistance
increases dramatically compared to that of the value of inductance. In this work, the resistance variation
due to the skin effect is considered in two wire transmission line model. The correlation between the skin
effect and the noise induced is also discussed. The simulation results justify the efficacy of the proposed
crosstalk noise model in the presence of skin effect.
Keywords: On-Chip Interconnect, Skin- Effect, Crosstalk, RLC Segments, Coupling, VLSI