Power integrity domains

Raj Nair -December 12, 2016

Dynamic voltage drop or DVD in a chip power grid segment is in essence transient noise. It is a complex superposition of various noise components of a typical chip power grid that reduces available power supply differential. DVD is a key measure of chip power integrity, and requires careful inspection during chip design. It is a sign-off gating aspect of chip power delivery.

Measured at points of interest on the grid, DVD is distinct from static (IR Drop) voltage reduction. But this distinction blurs at times depending upon the analysis method adopted. A review of such methods is thus useful - both to comprehend DVD and to recognize its derivation at present.

It is perhaps best to begin at the beginning as I've done in Chapter 1 of Power Integrity Analysis and Management for Integrated Circuits. In that chapter, 'Power, Delivering Power, and Power Integrity,' I delve into fundamental constituents of supply noise, introducing the 3 R's of Interconnect: Resistance, Reactance, and Resonance. Chapter 2 details the response of power delivery networks (PDN's) to load stimuli. A separation of transient (AC) and static (DC) noise becomes clear through such response. The analysis described therein captures circuit behavior in the TIME domain. Figure 1 displays an example.

Figure 1 
Time domain simulation of supply noise at the chip-pkg interface.

But such capture as in Figure 1 are nodal simulations: supply voltage variation at a circuit node with respect to an ideal ground. A chip is a two dimensional surface. Voltage variations across its power grid are typically captured as shown in Figure 2.

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