Abstract:
In one embodiment, a computing system includes a switching voltage regulator having at least two inductors formed on a common toroidal core.

Description:
TECHNICAL FIELD 
   Various embodiments of the present invention concern voltage regulators, for example, voltage regulators used in computing devices, such as notebook computers. 
   BACKGROUND 
   Notebook computers are portable computing devices that have become very popular in recent years. Two components that contribute to their portability are the battery and the voltage regulator. 
   The battery supplies electrical power to the device, typically at a voltage level of 9-13 volts. However, this voltage level is typically higher than the voltage needed by many of the components in these devices. For example, a microprocessor—the brains of the computer—typically operates on approximately one to two volts. Converting the battery voltage to the right level for any given component is the job of the voltage regulator. 
   In addition to converting the voltage, the voltage regulator has the job of reducing fluctuations in its output voltage as demand for power fluctuates in response to changes in component workload. For example, when a microprocessor shifts from idle to active, it pulls the regulator output voltage downward from its desired level, and conversely, when the microprocessor shifts from active to idle, it pushes the regulator output voltage upward. In either case, a properly functioning voltage regulator quickly responds to the changing load conditions by increasing or decreasing its output voltage to counteract effects of loading. A consequence of the changing load and voltage levels is that the regulator output voltage generally ripples or oscillates back and forth about its desired voltage. 
   To reduce the magnitude of these ripples and their undesirable effects on processor operations, many computing devices employ a multi-phase voltage regulator. These multi-phase voltage regulators often include two or more separate inductors that are connected so that ripples at the output of one phase are opposite in direction or polarity to ripples on the other phase. The outputs of the two phases are added together, with the opposing ripples partially canceling each other and reducing the magnitude of ripples that reach the microprocessor. 
   At least one problem recognized by the inventors is that conventional multi-phase voltage regulators often use separate inductors which not only occupy significant space on the motherboard—that is, the printed circuit board that carries many components of the computer system—but also necessitate the use of other large components, such as several 300 microfarad capacitors. Thus, the use of separate inductors ultimately limits the ability of manufacturers to further reduce the size of the motherboard or to add other components to the same size motherboard. 
   Accordingly, the inventors have recognized a need for alternative circuitry for voltage regulators. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a circuit diagram of an exemplary two-phase switching voltage regulator circuit corresponding to one or more embodiments of the present invention; and 
       FIG. 2  is a block diagram of an exemplary computer system which incorporates a voltage regulator circuit and thus corresponds to one or more embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   This description, which references and incorporates the above-identified Figures and incorporates the appended claims, describes one or more specific embodiments of an invention. These embodiments, offered not to limit but only to exemplify and teach the invention, are shown and described in sufficient detail to enable those skilled in the art to implement or practice the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art. 
   Exemplary Voltage Regulator Circuit 
     FIG. 1  shows an exemplary two-phase switching voltage regulator circuit  100 . Circuit  100  includes a controller  110 , switching circuits  120  and  130 , a dual toroidal inductor  140 , an output capacitor  150 , power supply nodes VDC and GND, and an output node Vout. 
   Controller  110  includes conventional or advanced circuitry for sensing the voltage and/or current at output node Vout and controlling the switching of switching circuits  120  and  130 , both of which may operate in the 200 Kilohertz to 1 Megahertz range. Controller  110  includes circuitry for decreasing the magnitude of Vout as the load current increases. This optional feature is desirable, not only for increasing battery life, but also for reducing system design costs by reducing maximum thermal envelope. It also increases the amount of headroom available to accommodate load transients, and thus reduces the amount of required bulk output capacitance. 
   Switching circuit  120  includes a driver  122 , switching transistors (more generally switches)  124  and  126 , and an output node V 1 out. Switching transistors  124  and  126 , which are metal-oxide-semiconductor field-effect transistors (mosfets) in the exemplary embodiment, are coupled in series between power supply nodes VDC and GND. 
   Switching circuit  130  similarly includes a driver  132 , switching transistors  134  and  136 , and an output node V 2 out. Switching transistors  134  and  136 , which are metal-oxide-semiconductor field-effect transistors (mosfets) in the exemplary embodiment, are coupled in series between power supply nodes VDC and GND. 
   More specifically, each switching transistor includes a control node, such as a gate, and two controllable nodes, such as a source and a drain. Transistor  124  has its gate coupled to an output of driver  122 , its drain coupled to supply node VDC, and its source coupled to the drain of transistor  126  and to output V 1 out. Transistor  126  has its gate coupled to another output of driver  122 , and its source coupled to supply node GND. Transistor  134  has its gate coupled to an output of driver  132 , its drain coupled to supply node VDC, and its source coupled to the drain of transistor  136  and to output V 2 out. Transistor  136  has its gate coupled to another output of driver  132 , and its source coupled to supply node GND. Outputs V 1 out and V 2 out are coupled respectively to first and second nodes (or terminals) of dual toroidal inductor  140 . 
   Dual toroidal inductor  140 , which defines substantially equal inductances L 1  and L 2 , includes conductors  142  and  144  that are manually and oppositely wound or coiled the same number of turns around a toroidal or donut-shaped magnetic core  146 . In the exemplary embodiment, L 1  and L 2  are in the 200-800 nano-henry range with the conductors providing a direct-current (DC) resistance of approximately 500-1000 milliohms. A coupling factor in the range of 0.5 to 0.9 is generally desired; some embodiments use the following inclusive coupling factor ranges: 0.5-0.7, 0.6-0.8, 0.7-0.9, and 0.8-0.9. Other embodiments may use other ranges. 
   In the exemplary embodiment, magnetic core  146  takes the form of a substantially circular closed loop with a nominal inner diameter of approximately three to four millimeters and a nominal outer diameter of approximately seven millimeters. Some embodiments may use other core shapes, such as oval or elliptical. The cross-section of the core can be substantially circular with a nominal diameter of two millimeters. However, some embodiments employ other cross sections, for example: square, rectangular, oval or elliptical. The exemplary core consists essentially of a ferromagnetic material, such as Molypermalloy Powder (MPP). Some embodiments form the core of iron powder, power ferrite, or sendust. In some embodiments, the closed loop may be only substantially closed and/or only generally circular. 
   Still other variations are used in other embodiments.  FIG. 1  shows that dual toroidal inductor  140  may be replaced with dual toroidal inductor  140 ′, which has a bifilar conductor configuration. The spacing between conductors  142  and  144  can be used to set the coupling factor as desired. Conductors can be electrically coupled at one end to define output node Vout. 
   Output node Vout, which in operation is generally coupled to a load, such as the power pin of microprocessor or other circuit, is coupled to supply node GND via output capacitor  150 . In the exemplary embodiment, capacitor  150  comprises two or more banks of capacitors coupled in parallel. For example, some embodiments include a low frequency (less than 200 KHz) bulk capacitance, a mid-frequency (less than 10 MHz) bank of capacitors, and a high-frequency bank of capacitors. The low frequency bulk capacitors may include six 330-microfarad, 9 milliohm tantalum, electrolytic, or Polymerized Organic Semiconductor (POSCAP) type capacitors; the mid-frequency bank may include 30 22-microfarad multilayer ceramic capacitors (MLCC). The high-frequency bank of capacitors are generally integrated as part of a processor integrated circuit. Notably, in some embodiments, the dual toroidal inductor allows one to omit the low frequency bank of capacitors completely, not only saving considerable space on a printed circuit board, such as a motherboard, but also significantly reducing manufacturing cost. 
   In operation, voltage regulator circuit  100  provides a substantially constant output voltage which generally has lower output ripple due to the current cancellation effect within dual toroidal inductor  140  that reduces or minimizes peak current ripple. The current cancellation effect stems from generating opposite flowing currents in conductors  142  and  144 , which thus produce opposing magnetic fluxes that are substantially equal and confined to the toroidal shaped magnetic core. Additionally, peak current reductions generally also reduce switching losses in the mosfets of switching circuits  120  and  130 , yielding improved power-conversion efficiency. 
   Exemplary System Incorporating Voltage Regulator Circuit 
     FIG. 2  shows an exemplary mobile computing system  200 , which incorporates voltage regulator circuit  100 . (Circuit  100  can also be embodied within a non-mobile system and/or a system that does not use a battery.) System  200 , can take the form of a notebook or laptop computer, personal digital assistance, mobile telephone, or other battery-powered appliance or entertainment device. Specifically, system  200  includes a motherboard (printed circuit board)  210 . Motherboard  210 , which may take a variety of shapes and sizes, includes a battery assembly  220 , voltage regulator circuit  100 , a processor assembly  230 , a bus  240 , a memory assembly  250 , a display assembly  260 , a keyboard assembly  270 , and an accessory assembly  280 . 
   More specifically, battery assembly  220  includes a battery connector or battery socket  222  and a rechargeable battery  224 . Other embodiments may use different kinds of power sources, such as a fuel cell, a solar array, a super capacitor, a combination of two or more power sources, etc. In some embodiments, battery  224  is installed within socket  222  by an end user of system  200 . Socket  222  is electrically connected to power supply nodes VDC and GND of voltage regulation circuit  100 , which includes dual toroidal inductor  140  and has its output Vout coupled to a power pin (not shown separately) of processor assembly  230 , more precisely processor socket (or connector)  232 . In some embodiments, dual toroidal inductor  140  is directly soldered onto the motherboard; however, other embodiments could use specific sockets. 
   Processor assembly  230  also includes a processor  234  which mechanically engages and electrically connects with socket  232 . In some embodiments, processor  232  is sold and installed separately from other components of motherboard  210 . Processor assembly  230  is coupled to bus  240 . 
   Bus  240  couples processor assembly  230  to memory assembly  250 , display assembly  260 , keyboard assembly  270 , and accessory assembly  280 . Assemblies  250 - 280  are shown on the boundary of motherboard  210  to indicate that they may be wholly or only partly positioned on the motherboard. In some embodiments, the motherboard may only include sockets or connectors for one or more of the corresponding assemblies; whereas in other embodiments, the motherboard includes the sockets and one or more corresponding integrated circuits or other devices. 
   Memory assembly  250  includes one or more memory sockets or connectors and corresponding volatile or non-volatile memory circuits, data-storage device, such as hard drives or removable storage media. In general, memory assembly  250  can include any form of volatile or non-volatile data-storage. 
   Display assembly  260  includes one or more sockets and connectors and/or corresponding drivers and/or screens. In some embodiments, connectors and/or drivers are for liquid-crystal displays (LCD). 
   Keyboard assembly  270  includes one or more sockets, connectors, and/or corresponding drivers, keyboards or keypads. 
   Accessory assembly  280  includes sockets and interface circuitry for permanently or detachably adding functional modules to system  200 . Exemplary modules include mobile telephone transceivers, network communicators, memory extensions, infrared transceivers, digital cameras, barcode readers, digital media players, and so forth. 
   The embodiments described in this document are intended only to illustrate and teach one or more ways of practicing or implementing the present invention, not to restrict its breadth or scope. The actual scope of the invention, which embraces all ways of practicing or implementing the teachings of the invention, is defined only by the issued claims and their equivalents. Additionally, to comply with 37 C.F.R. Section 1.72(b), this document includes an abstract that is intended only for efficiently communicating the technical nature of the document. It is not intended for use in limiting or interpreting the scope or meaning of the claims.