Crosstalk Noise Analysis for Nano-Meter VLSI Circuits.

Scaling of device dimensions into the nanometer process technology has led to a considerable reduction in the gate delays. However, interconnect delays have not scaled in proportion to gate delays, and global-interconnect delays account for a major portion of the total circuit delay. Also, due to process-technology scaling, the spacing between adjacent interconnect wires keeps shrinking, which leads to an increase in the amount of coupling capacitance between interconnect wires. Hence, coupling noise has become an important issue which must be modeled while performing timing verification for VLSI chips. As delay noise strongly depends on the skew between aggressor-victim input transitions, it is not possible to a priori identify the victim-input transition that results in the worst-case delay noise. This thesis presents an analytical result that would obviate the need to search for the worst-case victim-input transition and simplify the aggressor-victim alignment problem significantly. We also propose a heuristic approach to compute the worst-case aggressor alignment that maximizes the victim receiver-output arrival time with current-source driver models. We develop algorithms to compute the set of top-k aggressors in the circuit, which could be fixed to reduce the delay noise of the circuit. Process variations cause variability in the aggressor-victim alignment which leads to variability in the delay noise. This variability is modeled by deriving closed-form expressions of the mean, the standard deviation and the correlations of the delay-noise distribution. We also propose an approach to estimate the confidence bounds on the path delay-noise distribution. Finally, we show that the interconnect corners obtained without incorporating the effects of coupling noise could lead to significant errors, and propose an approach to compute the interconnect corners considering the impact of coupling noise.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/64663/1/gravkis_1.pd

Modeling crosstalk induced delay

V aggressor1 waveform The amplitude of coupled noise is often used in estimating the crosstalk effect. Coupling noise-induced delay measures the impact of crosstalk on circuit performance. Efficient computation of worst case noise-induced delays are essential, because such calculations are performed a huge number of times during timing analysis. In this paper we analyze the problem of crosstalk noise-induced delay in one logic stage. We observe that the popular method of crosstalk delay computation based on superposition of the victim’s switching waveform and the noise waveform determined when the victim is quiet, produces an underestimation of delay. To capture the crosstalk noise-induced delay, we introduce the concept of dynamic coupling noise waveform. We propose a method of synthesizing the dynamic noise waveform and using it to estimate the delay change.

Skybridge: 3-D Integrated Circuit Technology Alternative to CMOS

Continuous scaling of CMOS has been the major catalyst in miniaturization of integrated circuits (ICs) and crucial for global socio-economic progress. However, scaling to sub-20nm technologies is proving to be challenging as MOSFETs are reaching their fundamental limits and interconnection bottleneck is dominating IC operational power and performance. Migrating to 3-D, as a way to advance scaling, has eluded us due to inherent customization and manufacturing requirements in CMOS that are incompatible with 3-D organization. Partial attempts with die-die and layer-layer stacking have their own limitations. We propose a 3-D IC fabric technology, Skybridge[TM], which offers paradigm shift in technology scaling as well as design. We co-architect Skybridge's core aspects, from device to circuit style, connectivity, thermal management, and manufacturing pathway in a 3-D fabric-centric manner, building on a uniform 3-D template. Our extensive bottom-up simulations, accounting for detailed material system structures, manufacturing process, device, and circuit parasitics, carried through for several designs including a designed microprocessor, reveal a 30-60x density, 3.5x performance per watt benefits, and 10X reduction in interconnect lengths vs. scaled 16-nm CMOS. Fabric-level heat extraction features are shown to successfully manage IC thermal profiles in 3-D. Skybridge can provide continuous scaling of integrated circuits beyond CMOS in the 21st century.Comment: 53 Page

Clock Jitter in Communication Systems

For reliable digital communication between devices, the sources that contribute to data sampling errors must be properly modeled and understood. Clock jitter is one such error source occurring during data transfer between integrated circuits. Clock jitter is a noise source in a communication link similar to electrical noise, but is a time domain noise variable affecting many different parts of the sampling process. Presented in this dissertation, the clock jitter effect on sampling is modeled for communication systems with the degree of accuracy needed for modern high speed data communication. The models developed and presented here have been used to develop the clocking specifications and silicon budgets for industry standards such as PCI Express, USB3.0, GDDR5 Memory, and HBM Memory interfaces

Statistical static timing analysis considering process variations and crosstalk

Increasing relative semiconductor process variations are making the prediction of realistic worst-case integrated circuit delay or sign-off yield more difficult. As process geometries shrink, intra-die variations have become dominant and it is imperative to model them to obtain accurate timing analysis results. In addition, intra-die process variations are spatially correlated due to pattern dependencies in the manufacturing process. Any statistical static timing analysis (SSTA) tool is incomplete without a model for signal crosstalk, as critical path delays can increase or decrease depending on the switching of capacitively coupled nets. The coupled signal timing in turn depends on the process variations. This work describes an SSTA tool that models signal crosstalk and spatial correlation in intra-die process variations, along with gradients and inter-die variations

Early Estimation Of The Impact Of Delay Due To Coupling Capacitance In VSLI Circuits

University of Minnesota M.S.E.E. thesis.May 2019. Major: Electrical/Computer Engineering. Advisor: Sachin Sapatnekar. 1 computer file (PDF); vii, 54 pages.Coupling capacitance is becoming increasingly problematic at the more advanced technology nodes and affects the timing and sign-off timeline of integrated circuits (ICs). As the coupling capacitance information is only available after the detailed routing phase, it can be a difficult task to make any major changes post detailed routing towards fixing issues caused by coupling effects that were unaccounted for. The goal of the project is to come up with an estimate of coupling capacitance for a given net before the detailed routing phase with the help of congestion maps. This information can be fed back to the detailed router which can help avoid routes that are susceptible to heavy coupling effects. The first part of this thesis explains why beforehand knowledge of a net’s coupling capacitance is crucial for a timely tape-out. This thesis revisits the Elmore delay model and extends the analysis to coupled RC structures. The notion of considering the coupling capacitance as a random variable is described to model the uncertainties that are introduced into the delay analysis which is performed ahead in time. The second part of this thesis illustrates how congestion analysis can provide valuable information about the severity of coupling effects. A method for the expedited extraction of estimated parasitics using congestion maps and global router solutions is presented. Modification to existing driving-point analysis techniques is suggested to accommodate coupled RC structures with probabilistic coupling capacitance. The last part of this thesis compares the delay metrics obtained from an open-source timing analyzer with the delay metrics obtained through methods described in this thesis for a given net

Skybridge: A New Nanoscale 3-D Computing Framework for Future Integrated Circuits

Continuous scaling of CMOS has been the major catalyst in miniaturization of integrated circuits (ICs) and crucial for global socio-economic progress. However, continuing the traditional way of scaling to sub-20nm technologies is proving to be very difficult as MOSFETs are reaching their fundamental performance limits [1] and interconnection bottleneck is dominating IC operational power and performance [2]. Migrating to 3-D, as a way to advance scaling, has been elusive due to inherent customization and manufacturing requirements in CMOS architecture that are incompatible with 3-D organization. Partial attempts with die-die [3] and layer-layer [4] stacking have their own limitations [5]. We propose a new 3-D IC fabric technology, Skybridge [6], which offers paradigm shift in technology scaling as well as design. We co-architect Skybridge’s core aspects, from device to circuit style, connectivity, thermal management, and manufacturing pathway in a 3-D fabric-centric manner, building on a uniform 3-D template. Our extensive bottom-up simulations, accounting for detailed material system structures, manufacturing process, device, and circuit parasitics, carried through for several designs including a designed microprocessor, reveal a 30-60x density, 3.5x performance/watt benefits, and 10x reduction in interconnect lengths vs. scaled 16-nm CMOS [6]. Fabric-level heat extraction features are found to be effective in managing IC thermal profiles in 3-D. This 3-D integrated fabric proposal overcomes the current impasse of CMOS in a manner that can be immediately adopted, and offers unique solution to continue technology scaling in the 21st century

Novel Multicarrier Memory Channel Architecture Using Microwave Interconnects: Alleviating the Memory Wall

abstract: The increase in computing power has simultaneously increased the demand for input/output (I/O) bandwidth. Unfortunately, the speed of I/O and memory interconnects have not kept pace. Thus, processor-based systems are I/O and interconnect limited. The memory aggregated bandwidth is not scaling fast enough to keep up with increasing bandwidth demands. The term "memory wall" has been coined to describe this phenomenon. A new memory bus concept that has the potential to push double data rate (DDR) memory speed to 30 Gbit/s is presented. We propose to map the conventional DDR bus to a microwave link using a multicarrier frequency division multiplexing scheme. The memory bus is formed using a microwave signal carried within a waveguide. We call this approach multicarrier memory channel architecture (MCMCA). In MCMCA, each memory signal is modulated onto an RF carrier using 64-QAM format or higher. The carriers are then routed using substrate integrated waveguide (SIW) interconnects. At the receiver, the memory signals are demodulated and then delivered to SDRAM devices. We pioneered the usage of SIW as memory channel interconnects and demonstrated that it alleviates the memory bandwidth bottleneck. We demonstrated SIW performance superiority over conventional transmission line in immunity to cross-talk and electromagnetic interference. We developed a methodology based on design of experiment (DOE) and response surface method techniques that optimizes the design of SIW interconnects and minimizes its performance fluctuations under material and manufacturing variations. Along with using SIW, we implemented a multicarrier architecture which enabled the aggregated DDR bandwidth to reach 30 Gbit/s. We developed an end-to-end system model in Simulink and demonstrated the MCMCA performance for ultra-high throughput memory channel. Experimental characterization of the new channel shows that by using judicious frequency division multiplexing, as few as one SIW interconnect is sufficient to transmit the 64 DDR bits. Overall aggregated bus data rate achieves 240 GBytes/s data transfer with EVM not exceeding 2.26% and phase error of 1.07 degree or less.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Demonstration of SRAM Design with LED Cube Display

There is a constant push to reduce power consumption and increase speed in transistor memory devices. The goal of this project is to improve Allegro MicroSystems’ current Static Random Access Memory technology by designing and implementing a new sense amplifier. The final design is latch based and uses positive feedback to quickly display data at the output, which stops static current flow and dramatically reduces power consumption. Additionally a three-dimensional LED structure was designed and built to display a series of letters, characters or visual effects