Patent ID: 7701277

Claim:
An apparatus for controlling noise in a power system that includes a power rail and a ground rail, comprising: a decoupling capacitor having a first lead which is coupled to the ground rail; a MOS transistor coupled to the decoupling capacitor, wherein a source of the MOS transistor is coupled to the power rail and a drain of the MOS transistor is coupled to a second lead on the decoupling capacitor; an inductive packaging connection coupled to the power rail, wherein the MOS transistor and the decoupling capacitor are configured to be in parallel with the inductive packaging connection, thereby forming a resonant circuit; and a control circuit with an input coupled to the power rail and an output coupled to a gate of the MOS transistor, wherein the control circuit adjusts a voltage applied to the gate of the MOS transistor, thereby changing an impedance of the MOS transistor to reduce a noise in a frequency range near a frequency of interest (ω interest ) of the resonant circuit without causing an unnecessary increase in switching noise at other frequencies, the control circuit comprising; a noise-sensing mechanism configured to monitor the V dd signal and output a present amplitude of the noise in the V dd signal in a predetermined frequency range near ω interest and a present amplitude of the noise at least one other frequency range of the V dd signal; and a determination mechanism configured to determine the voltage applied to the gate of the MOS transistor by comparing the present amplitude of the noise in the V dd signal in the predetermined frequency range near ω interest to at least one previous amplitude of the noise in the V dd signal in the predetermined frequency range near ω interest and by comparing the present amplitude of the noise in at least one other frequency range of the V dd signal to at least one previous amplitude of the noise in at least one other frequency range of the V dd signal.