IEEE transactions on computer-aided design of integrated circuits and systems : a publication of the IEEE Circuits and Systems Society

Clock networks account for a significant fraction of the power dissipation of a chip and are critical to performance. This paper presents theory and algorithms for building a low-power clock tree by distributing the clock signal at a lower voltage and translating it to a higher voltage at the utilization points. Two low-power schemes are used: reduced swing and multiple-supply voltages. We analyze the issue of tree construction and present conclusions relevant to various technology generations according to the NTRS. Our experimental results show that power savings of an average of 45% are possible for a 0.25 /spl mu/m technology using multiple supply voltages, and about 32% using a single external supply voltage.

/pdf/low-power-clock-distribution-using-multiple-voltages-and-18r0ucck38.pdf

Low-power clock distribution using multiple voltages and reduced swings

Increasingly significant variational effects present a great challenge for delivering desired clock skew reliably. Non-tree clock network has been recognized as a promising approach to overcome the variation problem. Existing non-tree clock routing methods are restricted to a few simple or regular structures, and often consume excessive amount of wire-length. In this paper, we suggest to construct a low cost non-tree clock network by inserting cross links in a given clock tree. The effects of the link insertion on clock skew variability are analyzed. Based on the analysis, we propose two link insertion schemes that can quickly convert a clock tree to a non-tree with significantly lower skew variability and very limited wirelength increase. In these schemes, the complicated non-tree delay computation is circumvented. Further, they can be applied to the recently popular non-zero skew routing easily. Experimental results on benchmark circuits show that this approach can achieve significant skew variability reduction with less than 2 increase of wirelength.

Reducing clock skew variability via cross links

Design of noise detector circuits as compact as standard logic cells is proposed. High-density large-scale digital integrated circuits that embed such built-in noise detectors enable in-depth characterization of dynamic power supply and ground noises. Dependence of power supply and ground voltage drops on the location of active cell rows within 1.8-V standard cell-based digital circuits are consistently measured by 1.8- and 2.5-V built-in detectors fabricated in a 0.18-/spl mu/m CMOS triple-well technology. Measurements also show that ground noise distribution is distinctively more localized than power supply counterparts due to the presence of a substrate.

A built-in technique for probing power supply and ground noise distribution within large-scale digital integrated circuits

Thermal effects are becoming a limiting factor in high-performance circuit design due to the strong temperature-dependence of leakage power, circuit performance, IC package cost and reliability. While many interconnect reliability models assume a constant temperature, this paper presents a physics-based model for estimating interconnect lifetime for any time-varying temperature/current profile. This model is verified with numerical solutions. With this model, we show that designers may be more aggressive with the temperature profiles that are allowed on a chip. In fact, our model reveals that when the temperature magnitude variation is small, average temperature (instead of worst-case temperature) can be used to accurately predict interconnect lifetime, allowing for significant design margin reclamation in reliability-aware design. Even when the variation of temperature magnitude is large, our model shows that using the maximum temperature is still too conservative for interconnect lifetime prediction. Therefore, our model not only increases the accuracy of reliability estimates, but also enables designers to consider more aggressive designs. This model is similarly useful for temperature-aware dynamic runtime management.

/pdf/interconnect-lifetime-prediction-under-dynamic-stress-for-2z9f7r7p9z.pdf

Interconnect lifetime prediction under dynamic stress for reliability-aware design

Clocks are perhaps the most important circuits in high-speed digital systems. The design of clock circuitry and the quality of clock signals directly impact the performance of a very large scale integrated chip. Clock skew verification requires high accuracy and is typically performed using circuit simulators. However in high-performance deep-submicrometer digital circuits, clocks are running at higher frequencies and are driving more gates than ever, thus presenting a higher current load on the power distribution network with the potential for substantial power grid voltage (IR)-drop. This IR-drop affects the clock timing and must be taken into account in the verification process. Since IR-drop is a full-chip phenomenon, the use of standard circuit simulation on both the clock circuitry and the power-grid is not practical. In this paper, we present a new methodology for the verification of clock delay and skew. An iterative technique is presented for clock simulation in the presence of full-chip dynamic IR-drop. The effect of IR-drop on the timing of clock signals is quantified on a small example, and demonstrated on a large chip.

Clock skew verification in the presence of IR-drop in the power distribution network

Reliability analysis has not been promoted to the full-chip realm because techniques to extract, manage, and process full-chip power grid and signal data have not been previously available. This paper introduces techniques that have been developed to permit both full-chip power grid and signal net electromigration and Joule heating analysis. Results of this analysis provide feedback to the designer to permit easy design modification to provide superior "designed-in" long term reliability.

Full-chip reliability analysis

Clock nets are the most important circuits in high-speed digital systems. The design of clock circuitry and the quality of the clock signal directly impacts the performance of a VLSI chip. Clock verification requires high accuracy and is typically performed using circuit simulators. In high-performance deep-submicron digital circuits, clocks are running at higher frequencies and are driving more gates than ever, thus presenting a higher load on the power distribution network with the potential of substantial IR-drop. However, as IR-drop is a full-chip phenomenon, circuit simulation is extremely time consuming. In this paper, we present a loosely coupled iterative technique for clock verification in the presence of full-chip dynamic IR-drop. The degradation in the clock signal due to dynamic IR-drop is demonstrated on a small example as well as upon a large chip. In addition, we also discuss risks associated with assuming a static IR-drop budget upon clock propagation.

http://courses.ece.ubc.ca/579/J7.TCAD.IRclk.pdf

S.Z. Hussain

Papers

Clock skew verification in the presence of IR-drop in the power distribution network

Full-chip reliability analysis

Clock verification in the presence of IR-drop in the power distribution network