Design and Analysis of Power Distribution Networks in VLSI Circuits.

Abstract

Rapidly switching currents of the on-chip devices can cause fluctuations in the supply voltage which can be classified as IR and Ldi/dt drops. The voltage fluctuations in a supply network can inject noise in a circuit which may lead to functional failures of the design. Power supply integrity verification is, therefore, a critical concern in high-performance designs. Also, with decreasing supply voltages, gate-delay is becoming increasingly sensitive to supply voltage variation. With ever-diminishing clock periods, accurate analysis of the impact of supply voltage on circuit performance has also become critical. Increasing power consumption and clock frequency have exacerbated the Ldi/dt drop in every new technology generation. The Ldi/dt drop has become the dominant portion of the overall supply-drop in high performance designs. On-die passive decap, which has traditionally been used for suppressing Ldi/dt, has become expensive due to its area and leakage power overhead. This has created an urgent need for novel circuit techniques to suppress the Ldi/dt drop in power distribution networks. We provide accurate algorithmic solutions for determining the worst-case supply-drop and the impact of supply noise on circuit performance. We propose a path-based and a block-based approach for computing the maximum circuit delay under power supply fluctuations. We also propose an early-mode supply-drop estimation approach and a statistical approach for power grid analysis. All the proposed approaches are vectorless and account for both IR and Ldi/dt drops. We also propose a performance-aware decoupling capacitance allocation technique which uses timing slacks to drive the optimization. Finally, we present analog as well as all-digital circuit techniques for inductive supply noise suppression. The proposed all-digital circuit techniques were implemented in a test-chip, fabricated in a 0.13µm CMOS process. Measurements on the test-chip demonstrate a reduction in the supply fluctuations by 57% for a ramp loads and by 75% during resonance. We also present a low-power, all-digital on-chip oscilloscope for accurate measurement of supply noise. Supply noise measurements obtained from the on-chip oscilloscope were validated to conform well to those obtained from a traditional supply-drop monitor and direct on-chip probing.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/58508/1/spant_1.pd