Bus encoder design for crosstalk and power reduction in RLC modelled VLSI interconnects
Authors: Verma S.K. , Kaushik B.K. 
Published: June 2015

Purpose
– This paper aims to reduce the worst-case crosstalk effects for resistance, inductance and capacitance (RLC) interconnects using the bus encoding technique. In current nanoscale technology, power dissipation, propagation delay and crosstalk performance of interconnects determine the overall performance of a chip. Signal integrity issues due to crosstalk in the form of voltage glitches, overshoots, undershoots, undesirable noise, propagation speed ups and downs, etc. are some of the major deterrents for high-performance RLC modelled (VLSI) interconnects. This research paper primarily proposes two novel encoding methods (I and II) for RLC modelled interconnects to reduce the effect of crosstalk, simultaneous switching noise (SSN) and power consumption.

Design/methodology/approach
– The proposed methods are based on the bus encoding method that is effective and well-suited for the reduction of the crosstalk noise. This method encodes or transforms incoming data in a manner that encoded data contain minimum or no crosstalk effects. The proposed encoding method uses the bus invert (BI) method. The proposed encoding methods are able to avoid the worst-case crosstalks while consuming lesser power during transmission in VLSI interconnects.

Findings
– It is observed that the proposed encoders reduced/eliminated the worst-case crosstalk by reducing SSN. The encoding method I also reduces Type 0 crosstalk by 100 per cent, while Type 1 crosstalk is reduced by 36.4 per cent and Type 2 is reduced by 16.8 per cent. The average simultaneous switching is reduced by 51.1 per cent. Similarly, encoding method II reduces switching activity by 10.3 per cent, whereas the coupling activity is reduced by 35.4 per cent. Furthermore, encoding method II also reduced Type 0, Type 1 and Type 2 crosstalk by 100, 36.9 and 27.1 per cent, respectively. Hence, the proposed encoding methods reduced the worst-case crosstalk completely.

Research limitations/implications
– In VLSI technology, the reduction in feature size and the increase in operating frequency are quite rapid. This leads to higher propagation delay, crosstalk and power dissipation through the interconnects. Most of the previously proposed encoders/decoders have turned out to be unsuitable for RLC modelled interconnects. Hence, the proposed encoder would be extremely useful for crosstalk reduction in newer operating conditions.

Practical implications
– The encoding method I identifies the harsh crosstalks, that is Type 0 and Type 1, in the inverted and non-inverted forms of incoming data with respect to the previous data. The data having minimum crosstalk in the inverted and non-inverted forms are only sent through the transmission line. The encoding method I also removes the worst-case crosstalk and simultaneously reduces other mild crosstalks. The removal of worst-case crosstalk improves the overall performance of the interconnect. The encoding method II identifies Type 2 crosstalk along with Type 0 and Type 1 similar to encoding method I. Furthermore, the encoding method II exhibits an improvement over method I in terms of reduction in crosstalk and power dissipation.

Originality/value
– This paper proposes a novel encoding method to reduce worst-case crosstalk effects that reduces SSN. The proposed encoding methods achieve their purpose of crosstalk reduction for several technology nodes.