Effect of line resistance and driver width on crosstalk in coupled VLSI interconnects

Abstract

Purpose - This paper proposes to study the effect of line resistance and driver width on crosstalk noise for a CMOS gate driven inductively and capacitively coupled VLSI interconnects. Design/methodology/approach - The paper considers a distributed RLC interconnect topology. The interconnect length is 4 mm and far-end capacitive loading is 30 fF. The SPICE simulation set-up uses an IBM 0.13 μm, 1.2 V technology model. The input falling ramp has a transition time of 50 ps. The victim line is grounded through a driver resistance of 50 Ω at near end of interconnect. While observing the effect of line resistance, the aggressor driver has PMOS and NMOS widths of 70 and 30 μm, respectively, and the line resistance is varied from 0 to 500 Ω. For capturing the effect of driver width, SPICE waveforms are generated at far end of victim line for three different line resistances (R=0, 30, and 60 Ω respectively). In each case, the aggressor PMOS driver width is swept from 20 to 100 μm. The corresponding NMOS width is half of PMOS width. Findings - It is observed that, as line resistance increases, the noise peak reduces. This is due to the fact that with increasing resistance the incident and reflected waves traveling along the line experience increasing attenuation. Hence, the waves arriving at the far-end of the line are of smaller magnitude and larger time durations. This causes noise pulses in the lossy lines to be smaller and wider compared with those in a lossless line. The effect of driver width on noise waveforms is further observed. It is observed that, as the PMOS (and corresponding NMOS) driver width is increased, the victim line gets more prone to crosstalk noise. The crosstalk magnitude level increases alarmingly as driver width is increased, because the driver resistance decreases, which in turn increases the current driving capability of driver. Originality/value - While designing coupled interconnects, driver width and line resistance play an important role in deciding the crosstalk level. An interconnect designer often increases driver width and reduces line resistance for achieving lower propagation delays. This effort may result in higher crosstalk noise in coupled interconnect. Therefore, a designer should be concerned simultaneously for crosstalk noise while reducing delays. © Emerald Group Publishing Limited.