Library-Based Gate-Level Current Waveform Modeling for Dynamic Supply Noise Analysis

Abstract

As the VLSI technology goes into the nanometer era, the device sizes and supply voltages are continually decreased. The smaller supply voltage reduces the power dissipation but also decreases the noise margin of devices. Therefore, the power integrity problem has become one of the critical issues that limit the design performance (Blakiewicz & Chrzaniwska-Jeske, 2007; kawa, 2008 & Michael et al., 2008). Most of the power supply noises (PSNs) come from two primary sources. One is the IR-drop and the other is the simultaneous switching noise (SSN). Figure 1(a) illustrates a typical RLC model for power supply networks, which is the combination of on-chip power grids and off-chip power pins. The IR-drop is a power supply noise when the supply current goes through those non-zero resistors and results in a I·R voltage drop. The simultaneous switching noise (SSN) is the supply noise which happens when large instantaneous current goes through those non-zero inductors on power networks and generates a L·(di/dt) voltage drop. When the supply voltage is reduced , the noise margin of devices also decreases as shown in Fig.1(b). It may induce worse performance because the driving capability of devices becomes week due to smaller supply voltage. If serious power supply noise occurs, the logic level may be changed, which causes function error in the circuit. The worst situation is the electronmigration (EM) effects. Supply wires are shorten or broken because a large current travels through the small supply wires. Therefore, the power supply noise analysis is reguired at design stages to evaluate the effects caused by power supply noise.