Abstract:
A system is disclosed. The system includes a central processing unit (CPU) to operate in one or more low power sleep states, and a power converter. The power converter includes phase inductors; and one or more power switches to drive the phase inductors. The one or more power switches are deactivated during the CPU sleep state.

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 11/416,534 filed on May 3, 2006. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to computer systems; more particularly, the present invention relates to regulating voltage in a microprocessor. 
     BACKGROUND 
     Growing demand for integrated circuits (ICs), for example microprocessors, with ever higher levels of performance and functionality have driven these devices to circuit densities beyond 100 million transistors per die. This number may soon exceed one billion transistors on a single die. The growth in transistor density has been made possible by the use of MOSFET transistors with gate lengths below 100 nm. As gate length has shortened, power supply voltages have fallen, in some cases, to below 1 V. 
     Even in a mobile computing environment (laptop), high-speed microprocessors, with clock speeds in excess of 2 GHz, may require in excess of 100 watts of power when operating at maximum load. With operating voltages below 1 V, this translates to power supply currents that reach beyond 100 A. Nevertheless, when used in a mobile environment, the same microprocessor must often draw less than 1 watt of “average power” due to battery considerations. 
     Integrated circuits are typically powered from one or more DC supply voltages provided by external supplies and converters. The power is provided through pins, leads, lands, or bumps on the integrated circuit package. The traditional method for providing such high power to integrated circuits may involve the use of a high-efficiency, programmable DC-to-DC (switch-mode) power converter located near the IC package. 
     This type of converter (buck regulator) may use a DC input voltage as high as 48V and provide a DC output voltage below 2 V. Conventional DC-to-DC power converters use switching frequencies in the neighborhood of 200 KHz, with some high-end units in the 1-2 MHz range. Such converters usually require a handful of relatively large components, including a pulse-width modulation (PWM) controller, one or more power transistors, filter and decoupling capacitors, and one or more large inductors and/or transformers. 
     Typical switch-mode power converters include one or more phases to supply the full output current. However, in many instances it may be inefficient to implement full operation of the converter, especially in applications that have low (e.g., nearly 0) current draw. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements, and in which: 
         FIG. 1  is a block diagram of one embodiment of a computer system; 
         FIG. 2  illustrates a block diagram of one embodiment of a central processing unit; 
         FIG. 3  illustrates one embodiment of a power converter; and 
         FIG. 4  illustrates a block diagram of one embodiment of a power control unit. 
     
    
    
     DETAILED DESCRIPTION 
     A voltage regulator having a suspend mode is described. In the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the present invention. 
     Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
       FIG. 1  is a block diagram of one embodiment of a computer system  100 . Computer system  100  includes a central processing unit (CPU)  102  coupled to interconnect  105 . In one embodiment, CPU  102  is a processor in the Itanium® family of processors including the Itanium® 2 processor available from Intel Corporation of Santa Clara, Calif. Alternatively, other CPUs may be used. 
     A chipset  107  may also be coupled to bus  105 . Chipset  107  includes a memory control hub (MCH)  110 . MCH  110  may include a memory controller  112  that is coupled to a main system memory  115 . Main system memory  115  stores data and sequences of instructions that are executed by CPU  102  or any other device included in system  100 . In one embodiment, main system memory  115  includes dynamic random access memory (DRAM); however, main system memory  115  may be implemented using other memory types. Additional devices may also be coupled to interconnect  105 , such as multiple CPUs and/or multiple system memories. 
     MCH  110  is coupled to an input/output control hub (ICH)  140  via a hub interface. ICH  140  provides an interface to input/output (I/O) devices within computer system  100 . In addition, computer system  100  includes a power supply  165  to provide power to CPU  102  and chipset  107 . In one embodiment, power supply  165  is implemented as multiple cascaded supplies, where a first supply converts the AC input from a wall outlet to a set of standard voltage rails, and a set of downstream supplies (often referred to as a point-of-load regulators) convert the standard voltages to the less standardized voltages directly used by advanced logic ICs. 
       FIG. 2  illustrates one embodiment of CPU  102  coupled to power converter  210 . In one embodiment, power converter  210  is a programmable DC-to-DC (switch-mode) power converter located near the CPU  102  IC package to provide high power to CPU  102 . However in other embodiments, power converter  210  may be located on the CPU  102  package. 
       FIG. 3  illustrates one embodiment of power converter  210 . Power converter  210  is a 2-phase converter that receives a 12V voltage input at each phase, which is converted to a 1.2V output voltage. According to one embodiment, each phase includes a set of power field effect transistors (FETs) and an inductor. The phases all couple into a shared bank of output filter capacitors, represented in  FIG. 3  as a single capacitor C. 
     Referring back to  FIG. 2 , CPU  102  includes processing cores  0 - 3  coupled to receive power from power converter  210 , and a power control unit  250 . Each processing core operates as an independent microprocessor to permit thread-level parallelism. Power control unit  250  regulates the voltage applied to CPU  102  by power converter  210 , based at least in part on the potential of the operational frequency of all or a subset of the operational circuit(s) of CPU  102 . 
       FIG. 4  illustrates one embodiment of power control unit  250 . Power control unit  250  includes a voltage regulator (VR) microcontroller  410 , a finite state machine (FSM) control block  420  and a VR  430 . VR microcontroller  410  provides voltage control configuration parameters that are implemented to control voltage. According to one embodiment, VR microcontroller  410  provides the configuration parameters via input/output (I/O) writes to addresses to add coefficients that define voltage control functionality. 
     FSM control block  420  implements various FSMs to control various voltage control parameters. In one embodiment, FSM control block  420  includes ramp rate control, power throttle and loadline adjust current. VR  430  includes a compensator  432  and a pulsewidth modulator  436 . Compensator  432  receives a target voltage from control block and compares the target voltage to an actual voltage received from one or more of the cores  0 - 3 . 
     In response, compensator  432  generates an error term that is used to drive to zero error using negative feedback. Pulsewidth modulator  436  generates pulse signals to control current based upon the error term received from compensator  432 . The pulse signals are transmitted from pulsewidth modulator  436  to power converter  210  to control the activation of the power FETs at each phase. 
     In normal operation, CPU  102  components may demand a very high current from power converter  210 , which is generally the motivation for designing a voltage regulator with multiple phases. In normal operation, the current demand is generally high enough that multiple phases can continuously be pulsed, and the energy lost in continuous pulsing is small compared to the total current draw. 
     However at certain instances (e.g., where CPU  102  goes into a sleep state), it would be inefficient for power converter  210  to continuously pulse even a single phase. According to one embodiment, whenever the CPU  102  cores go into a sleep state, power control unit  250  and power converter  210  go into a suspend mode. In such an embodiment, a clock supplying power control unit  250  is deactivated. 
     In such an embodiment, the current draw at CPU  102  is sufficiently low so as to enable the charge stored at the output filter capacitors to supply power to CPU for a predetermined period of time. For example, if the CPU  102  sleep state duration is in a range of a few (e.g., 2-4) milliseconds operation at power control unit  250  and power converter  210  may be suspended until CPU  102  is reactivated. Thus, the power FET switches at power converter  210  are deactivated (e.g., no current generated by power converter  210 ) until CPU  102  is reactivated. 
     In another embodiment, power control unit  250  monitors the CPU  102  voltage whenever it and power converter  210  are in the suspend state. In this embodiment, power converter  210  remains in the suspend state until the voltage falls below a predetermined threshold (e.g., 1.2V). Once the voltage falls below the threshold, VR  430  exits the suspend state and transmits a pulse to activate one or both of the phases at power converter  210  in order to supply current to CPU  102 . In a further embodiment, VR  430  may reenter the suspend state once current is supplied to CPU  102  as long as CPU  102  remains in the sleep state. Subsequently, the CPU  102  is again monitored by power control unit  250 . 
     In yet another embodiment, whenever CPU  102  is in the suspend state and the CPU  102  voltage is above the threshold voltage, power converter  210  will enter an adaptive diode emulation mode. In such a mode, one phase is repeatedly sequenced through the following states: only upper FET on (UPPER state), only lower FET on (LOWER state), both FETs off (OFF state). Further, the repeated sequencing is performed at a largely fixed frequency, and the portion of time spent in each state is adapted to maintain a desired voltage. In another embodiment, the UPPER state time and the LOWER state time may be largely fixed, while the OFF state time is adapted to maintain a desired voltage. 
     The above-described power management mechanism yields an increase in battery life in a mobile computer system. 
     Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that any particular embodiment shown and described by way of illustration is in no way intended to be considered limiting. Therefore, references to details of various embodiments are not intended to limit the scope of the claims which in themselves recite only those features regarded as essential to the invention.