Large scale integrated circuit for dynamically changing resonant point

#This application claims the benefit of priority from Japanese Patent Application No. 2007-260871 filed on Oct. 4, 2007, the entire contents of which are incorporated herein by reference.

#1. Field of the Invention

#This application relates to a large scale integrated circuit that suppresses power noise.

#FIG. 1 is a graph for illustrating a method for controlling power impedance;

#FIGS. 2A and 2B are diagrams for illustrating the different cases of a resonant frequency depending on an operation environment;

#FIGS. 3A and 3B are diagrams for illustrating the case of the resonant frequency depending on the difference between two applications;

#When the resonant frequency matches a spectrum of the operation current, the change in voltage caused by resonating power of the LSI amplifies the power noise. The power line inductance L or the decoupling capacitance C is adjusted at the design phase in order lo prevent the matching between the spectrum distribution of the operation current and the resonant frequency. It cannot be prevented on the LSI whose operation frequency is dynamically changed, thereby there is an operation frequency zone that cannot be used on the LSI. FIG. 1, shows a relationship between a frequency and power impedance with of operation current i. The power impedance is controlled in accordance with the operation frequency by using a variable inductance-capacitance-resistance (LCR). The resonant frequency that causes the power noise is changed. When the operation frequency is high, the variable LCR is controlled so as to generate the resonant frequency at a low frequency band (e.g., a resonant frequency fr-I), thereby operating the LSI at impedance (I). On the other hand, when the operation frequency is low, the variable LCR is controlled so as to generate the resonant frequency at a high resonant frequency band (e.g., a resonant frequency fr-II), thereby operating the LSI at impedance (II).

#As a consequence, power impedance determined by the LCR parasitic on the LSI is changed to suppress the power noise caused in the LSI.

#A frequency (hereinafter, referred to as a switching frequency) as the basis for switching to the resonant frequency fr-I or resonant frequency fr-II is predetermined in FIG. 1, and the variable LCR is controlled in accordance with the operation frequency,