August 2010: Early PI-aware design is a significant aspect of IC floorplanning, particularly in nanoscale systems where low power/energy and efficient use of chip/pkg metal and decoupling resources are key design constraints. The advent of 3D integration in the form of chip or package stacking makes early front-end analysis of PI through high levels of abstraction and physics-based simulations all the more necessary. Correlation between PI and thermal issues provides an added benefit in front-end PI analysis and optimization…
June 2010: Power Integrity (PI) analysis has traditionally been conducted using lumped, discrete elements and circuits, which lead to exponential simulation complexity, approximate models, and often, inaccurate results. In continuum-models based analysis, a chip power grid and distribution network is modeled as a continuous surface, employing distributed models for circuits and capacitance. This not only eliminates the exploding computational complexity for PI analysis in nanoscale chips, it facilitates physical, true-electromagnetic simulations for chips, packages, and 3D assemblies. Continuum-models based analysis is “analog” in the sense that a layer to be analyzed is treated as a spatial potential or voltage continuum, similar to analog signals being time-continuous in nature, as opposed to analyzing discrete elements and their interactions.
“Yield loss and timing problems undetected by traditional verification and validation methods can be traced to a significant decrease in supply noise margin in components using advanced fabrication processes at and below the 90nm node. A combination of increased current density at lower supply voltages and supply pathway impedance results in large, on and off chip, relative supply variations called voltage droops. These fluctuations make it more difficult to reduce static and dynamic power and energy consumption by further reductions in supply voltage, despite the scaling direction for semiconductors…”
Read more on how active noise regulation helps minimize power and energy consumption through noise minimization here (PDF) or view it here (web).
RLCSim is a Windows(tm) executable that performs noise analysis on a power grid over a circuit block. This tool, a pre-cursor of pi-fp, considers grid resistance (IR drop), inductance (L*di/dt) or voltage droop, and distributed capacitance that absorbs transients, and displays noise propagation and summing within the block.
Inputs include grid parameters, block power consumption profiles and capacitance.
Shown below is a noise simulation result using RLCSIM demonstrating detrimental effects of lens-shaped on-chip decoupling capacitance structure. Power grid noise from an on-chip source is focused behind the capacitance structure, illustrating distributed true-electromagnetic simulation capability absent in other power integrity analysis tools.
A power-integrity-aware physical design methodology enables front-end optimization of power grid metal resource usage, decoupling capacitance planning and placement, and significantly relaxes routing constraints.