Impedance/Noise Issues in On-Chip Power Distribution Networks
The high frequency response of a power distribution system is the focus of this chapter. The impedance of the power distribution system at high frequencies is determined by the characteristics of the on-chip power distribution network. The impedance of a power system at a specific on-chip location is determined by the local resistive, inductive, and capacitive characteristics of the on-chip network. The resistive and inductive characteristics of the on-chip power distribution grids are characterized in Chapters 9 and 13. In this chapter, the impedance characteristics of both the on-chip power interconnect and the decoupling capacitors are combined to evaluate the noise characteristics of a power network. The inductance of an on-chip power distribution network is shown under specific conditions to be a significant design issue in high speed integrated circuits.
As discussed in Chapter 5, the inductance of the on-chip power and ground interconnect affects the impedance characteristics at relatively high frequencies; specifically, from the chip-package resonance to the highest frequencies of interest. The on-chip interconnect is a part of the current loop from the on-chip decoupling capacitors to the package decoupling capacitors. Typically, the inductance of this current loop is dominated by other parts of the loop – the bonding solder bumps, package conductors, and package decoupling capacitors. This situation is changing with technology scaling, as discussed in Section 20.1. The propagation of the power supply noise through the on-chip power distribution network is discussed in Section 20.2. The on-chip interconnect also provides a current path between the on-chip decoupling capacitors and the load. As the switching speed of the load increases, the inductance of the on-chip power lines can degrade the effectiveness of the on-chip capacitors, as discussed in Section 20.3. The chapter concludes with a summary.
KeywordsPower Distribution Impedance Characteristic Current Path Ground Line Noise Margin
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