Transition-Aware Decoupling-Capacitor Allocation in Power Noise Reduction

Abstract-Dynamic power noises may not only degrade the circuit performance but also reduce the noise margin which may result in the functional errors in integrated circuit. Decoupling capacitor (decap) allocation is one of the most effective way in reducing serious dynamic power noises (hotspots). To allocate decap bef ore placement, we observed that not only locations but also rising time of functional cells are required to accurately predict power noises. Compared to a previous work which only takes neighborhood relation into consideration, our method is more efficient in reducing hotspots. Furthermore, to reduce the hotspots af ter placement, instead of only using the empty space as proposed in the previous work, we move out cells in the area with serious power noise area (hot area). The obtained empty space can be used to accommodate decaps to further reduce the hotspots. The experimental result shows, compared to the previous work [1], our estimation function to allocate decap before placement is 23% better in reducing power noises. Moreover, compared to a method which fills decaps to all remaining empty space, our cell move algorithm can almost eliminate all the remaining hot grid nodes and hot cells. In summary, compared to the original circuits (without decap), about 60% of hotspots can be removed using our prediction function before placement, and most of the remaining hotspots are removed by our cell moving step after placement

Design and Analysis of Power Distribution Networks in VLSI Circuits.

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.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/58508/1/spant_1.pd