On-Board and On-Package Active Capacitors for High Current Systems

Due to scaling of semiconductors, the power density in VLSI circuits has increased dramatically. Furthermore, ON-chip power noise requirements have become more stringent as nominal voltages have decreased. As a result, the requirements for voltage variations have become more difficult to satisfy. Voltage drops below the noise margin may cause gate delays, false switching, and even system failure. Passive capacitors are often used to satisfy these stringent voltage drop requirements. However, due to ON-chip and on-package area constraints, including sufficient passive capacitors has become difficult. One solution is active capacitors, which provide a higher density capacitance than passive capacitors. On-package and on-board active capacitors are the focus of this article. An on-board active capacitor has been simulated and experimentally validated using an evaluation board, where a 97-mV reduction in voltage is observed in a 1.2-V system. The simulation model exhibits an accuracy within 10% of the experimental results. Furthermore, the performance of an on-package active capacitor is evaluated for high current conditions and compared with passive capacitors of equal area. A reduction in the voltage drop of 98 mV in an on-package system when compared with a system with on-package passive capacitors is demonstrated in an 800-mV, high current system.