Accelerating microprocessor core wake up via charge from capacitance tank without introducing noise on power grid of running microprocessor cores

Abstract

A mechanism is provided for an integrated circuit with power gating. A power switch is configured to connect and disconnect circuits to a common voltage source. A capacitor tank is configured to supply wakeup charge to a given circuit. A controllable element is connected to the given circuit and to the capacitor tank. The controllable element is configured to controllably connect and disconnect the capacitor tank to the given circuit in order to supply the wakeup charge to the given circuit. The controllable element is configured to, responsive to the power switch disconnecting the given circuit from the common voltage source and to the given circuit being turned on to wakeup, supply the wakeup charge to the given circuit being turned on by transferring the wakeup charge from the capacitor tank to the given circuit. This reduces the electrical charge transferred from the circuits connected to the common voltage source.

What is claimed is: 
     
         1 . A method of operating an integrated circuit with power gating, the method comprising:
 configuring a power switch to connect and disconnect any one of a plurality of circuits to a common voltage source;   configuring a capacitor tank to supply wakeup charge to a given circuit of the plurality of circuits;   configuring a controllable element, which is connected to the given circuit and to the capacitor tank, to controllably connect and disconnect the capacitor tank to the given circuit in order to supply the wakeup charge to the given circuit; and   responsive to the power switch disconnecting the given circuit from the common voltage source and responsive to the given circuit being turned on to wake up, turning on the controllable element to supply the wakeup charge to the given circuit being turned on by transferring the wakeup charge from the capacitor tank to the given circuit, thereby reducing an amount of electrical charge transferred from the plurality of circuits connected to the common voltage source.   
     
     
         2 . The method of  claim 1 , wherein a feed transistor is connected to the capacitor tank and a capacitor voltage source;
 wherein the feed transistor is controllable to connect the capacitor voltage source to the capacitor tank in order to charge the capacitor tank when no circuit of the plurality of circuits is connected to the capacitor tank for supplying the wakeup charge.   
     
     
         3 . The method of  claim 1 , wherein the feed transistor connects the capacitor tank to a capacitor voltage source which charges the capacitor tank to a voltage potential higher than the common power supply. 
     
     
         4 . The method of  claim 1 , wherein the power switch for the given circuit is turned on as a single header transistor, in which the single header transistor does not require a sequence of header transistors to consecutively turn on before all of the headers transistors of power switch supplies are turned on to connect the common voltage source to the given circuit. 
     
     
         5 . The method of  claim 1 , wherein another controllable element is connected to another given circuit and to the capacitor tank such that the capacitor tank is shared by both the given circuit and the another given circuit in order to respectively supply the wakeup charge to either of the two circuits. 
     
     
         6 . The method of  claim 5 , wherein the another given circuit receives a smaller amount of the wakeup charge from the capacitor tank, after the given circuit has previously received the wakeup charge and when the capacitor tank is not recharged by the capacitor voltage source. 
     
     
         7 . The method of  claim 6 , wherein the power header switch for the another given circuit is turned on to connect the another given circuit to the common voltage source, based on the another controllable element disconnecting the another given circuit from the capacitor tank;
 wherein when the another given circuit receives the smaller amount of the wakeup charge from the capacitor tank, turning on the power switch for the another given circuit includes turning on at least one of a first header transistor through a last header transistor according to an amount of electrical charge received by the another given circuit from the capacitor tank.   
     
     
         8 . The method of  claim 1 , further comprising:
 providing another capacitor tank configured to supply wakeup charge to another given circuit of the plurality of circuits;   providing another controllable element connected to the another given circuit and to the another capacitor tank, wherein the another controllable element is configured to controllably connect and disconnect the another capacitor tank to the given circuit for supplying the wakeup charge; and   responsive to the power switch disconnecting the another given circuit from the common voltage source and responsive to the another given circuit being turned on to wake up, configuring the another controllable element to supply the wakeup charge to the another given circuit being turned on by transferring electrical charge from the another capacitor tank to the given circuit, without affecting power of currently running circuits of the plurality of circuits already connected to the common voltage source.