Abstract:
A switching regulator includes an inductive element to provide a first voltage across the element and at least one switch to energize and de-energize the inductive element to produce an output voltage. A controller of the regulator constructs an indication of a current from the first voltage and operates the switch(es) to regulate the output voltage in response to the indication.

Description:
This is a divisional of application Ser. No. 09/717,766 filed on Nov. 21, 2000, now U.S. Pat. No. 6,534,962. 
    
    
     BACKGROUND 
     The invention generally relates to a voltage regulation system having an inductive current sensing element. 
     A DC-to-DC voltage regulator typically is used to convert a DC input voltage to either a higher or a lower DC output voltage. One type of voltage regulator is a switching regulator that is often chosen due to its small size and efficiency. The switching regulator typically includes one or more switches that are rapidly opened and closed to transfer energy between an inductor (a stand-alone inductor or a transformer, as examples) and an input voltage source in a manner that regulates the output voltage. 
     As an example, referring to FIG. 1, one type of switching regulator is a Buck switching regulator  10  that receives an input DC voltage (called V IN ) and converts the V IN  voltage to a lower regulated output voltage (called V OUT ) that appears at an output terminal  11 . To accomplish this, the regulator  10  may include a switch  20  (a metal-oxide-semiconductor field-effect-transistor (MOSFET), for example) that is operated (via a switch control signal called V SW ) in a manner to regulate the V OUT  voltage, as described below. 
     Referring also FIGS. 2 and 3, in particular, the switch  20  opens and closes to control energization/de-energization cycles  19  (each having a duration called T S ) of an inductor  14 . In each cycle  19 , the regulator  10  asserts, (drives high, for example) the V SW  signal during an on interval (called T ON ) to close the switch  20  and transfer energy from an input voltage source  9  to the inductor  14 . During the T ON  interval, a current (called I L ) of the inductor  14  has a positive slope. During an off interval (called T OFF ) of the cycle  19 , the regulator  10  deasserts (drives low, for example) the V SW  voltage to open the switch  20  and isolate the input voltage source  9  from the inductor  14 . At this point, the level of the I L  current is not abruptly halted, but rather, a diode  18  begins conducting to transfer energy from the inductor  14  to a bulk capacitor  16  and a load (not shown) that are coupled to the output terminal  11 . During the T OFF  interval, the I L  current has a negative slope, and the regulator  10  may close a switch  21  to shunt the diode  18  to reduce the amount of power that is otherwise dissipated by the diode  18 . The bulk capacitor  16  serves as a stored energy source that is depleted by the load, and additional energy is transferred from the inductor  14  to the bulk capacitor  16  during each T ON  interval. 
     For the Buck switching regulator, the ratio of the T ON  interval to the T S  interval (i.e., the summation of the T ON  and T OFF  intervals) is called a duty cycle of the regulator and generally governs the ratio of the V OUT  voltage to the V IN  voltage. Thus, to increase the V OUT  voltage, the duty cycle of the regulator may be increased, and to decrease the V OUT  voltage, the duty cycle may be decreased. 
     As an example, the regulator  10  may include a controller  15  (see FIG. 1) that regulates the V OUT  voltage by using a current mode control technique. In this manner, the controller  15  may include an error amplifier  23  that amplifies the difference between a reference voltage (called V REF ) and a voltage (called V P  (see FIG.  1 )) that is proportional to the V OUT  voltage to produce an error voltage (called V CNTRL ) that is used to control the levels of the V OUT  voltage and the I L  inductor current. 
     The controller  15  uses the V CNTRL  voltage and a voltage (called V CS ) that indicates the I L  inductor current to produce the V SW  switch control signal to control the switch  20 . More specifically, referring also to FIG. 5, the controller  15  may include a comparator  26  that compares the V CNTRL  and V CS  voltages. The V CS  voltage is provided by a differential amplifier  24  that senses the voltage difference (called V R ) across a current sensing resistor  29  that is coupled in series with the inductor  14 . 
     The output terminal of the comparator  26  may be coupled to a switch circuit  27  that generates the V SW  switch control signal. As an example of one type of current mode control, the switch circuit  27  may keep the T OFF  time interval constant and use the positive incline of the V CS  voltage to control the duration of the T ON  time interval. Thus, the T ON  time interval ends when the V CS  voltage reaches the V CNTRL  voltage and begins at the expiration of the constant T OFF  interval. 
     Due to the above-described arrangement, when the V OUT  voltage increases, the V CNTRL  voltage decreases and causes the duty cycle of the regulator  10  to decrease to counteract the increase in V OUT . Conversely, when the V OUT  voltage decreases, the V CNTRL  voltage increases and causes the duty cycle to increase to counteract the decrease in V OUT . When the average value, or DC component, of the I L  current increases, the DC component of the V CS  voltage increases and causes the duty cycle to decrease to counteract the increase in the I L  current. Conversely, when DC component of the I L  current decreases, the DC component of the V CS  voltage decreases and causes the duty cycle to increase to counteract the decrease in the I L  current. The switching frequency (i.e., 1/T S ) typically controls the magnitude of an AC ripple component (called V RIPPLE  (see FIG.  4 )) of the V OUT  voltage, as a higher switching frequency typically reduces the magnitude of the V RIPPLE  voltage. 
     The regulator  10  is a single phase regulator. However, multiple regulators may be coupled in parallel to form a multiple phase voltage regulation system. In this manner, the input terminals of the regulators are coupled together, and the output terminals of the regulators are coupled together. The energization/de-energization cycles of the regulators are controlled so that the cycles are interleaved, or phased, with respect to each other. Such an arrangement is desirable because the phasing ensures that the entire voltage regulation system operates at a higher frequency than the frequency of any of the individual regulators. 
     The current sensing resistor  29  may occupy a substantial amount of printed circuit board space, may contribute significantly to the cost of the voltage regulation system, and may dissipate a significant amount of power especially in a multiple phase voltage regulator system that includes a multiple number of regulators and current sensing resistors  29 . 
     Thus, there is a continuing need for an arrangement that addresses one or more of the problems that are stated above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic diagram of a switching voltage regulator of the prior art. 
     FIGS. 2,  3 ,  4  and  5  are waveforms that illustrate operation of the regulator of FIG.  1 . 
     FIG. 6 is a voltage regulation system according to an embodiment of the invention. 
     FIGS. 7,  8 ,  9 ,  10 ,  11  and  12  depict waveforms illustrating operation of the voltage regulation system of FIG. 6 according to an embodiment of the invention. 
     FIG. 13 depicts waveforms illustrating a current mode control scheme according to an embodiment of the invention. 
     FIG. 14 is a schematic diagram of an inductor of a regulator of the voltage regulation system of FIG. 6 according to an embodiment of the invention. 
     FIG. 15 is a schematic diagram of a controller of the voltage regulation system of FIG. 6 according to an embodiment of the invention. 
     FIG. 16 is a schematic diagram of a computer system according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 6, an embodiment  100  of a multiple phase voltage regulation system in accordance with the invention includes multiple Buck switching regulator stages, such as regulator stages  102   1  and  102   2  (each having a similar design denoted by the reference numeral “ 102 ”), that are coupled together in parallel to convert an input voltage (called V IN ) into an output voltage (called V OUT ). In this manner, both stages  102   1  and  102   2  receive the V IN  input voltage and cooperate in a phased relationship with each other to regulate the V OUT  voltage that appears at an output terminal  107  (of the system  100 ) that is common to both of the stages  102   1  and  102   2 . The V IN  voltage may be provided by a voltage regulator that receives an AC wall voltage, for example and produces a DC voltage that is filtered by a low pass filter (formed from an inductor  114  and a capacitor  116 ) to form the V IN  input voltage. The stages  102   1  and  102   2  share a bulk capacitor  109  in common, and the bulk capacitor  109  is coupled between the output terminal  107  and ground. As described below, the power subsystem  100  also includes a pulse width modulation (PWM) controller  104  that uses a current mode technique to control the operations of both stages  102   1  and  102   2 . 
     More particularly, in some embodiments of the invention, each stage  102  includes a switch  108  (a metal-oxide-semiconductor field-effect-transistor (MOSFET), for example) that is coupled between the positive terminal of an input voltage line  118  (that provides the V IN  input voltage) and a terminal  123  of an inductor  106  (of the stage  102 ). The other terminal of the inductor  106  is coupled to the output terminal  107 . For the stage  102   1 , a switch control signal (called V 1 ) controls the state (open or closed) of the switch  108  and for the stage  102   2 , a switch control signal (called V 3 ) controls the state (open or closed) of the switch  108 . 
     For each stage  102 , the closing of the switch  108  causes energy to be transferred from the input voltage line  118  and stored in the inductor  106  to energize the inductor  106 , and the opening of the switch  108  causes the stored energy to be transferred from the inductor  106  to the output terminal  107 , a transfer that de-energizes the inductor  106 . In this manner, when the switch  108  is open, a diode  112  (that has its anode couple to ground and its cathode coupled to the terminal  123 ) conducts and/or a switch  110  (that is controlled via a switch control signal called V 2  (for the stage  102   1 ) or a switch control signal called V 4  (for the stage  102   2 )) closes to couple the terminal  123  to ground to permit the flow of energy to the output terminal  107 . Thus, the V 1  and V 2  signals are generally complementary signals (one has a logic one state when the other has a logic zero state and vice-versa), and the V 3  and V 4  signals are complementary signals. 
     In some embodiments of the invention, the controller  104  generates the V 1  and V 3  signals in a manner that causes the inductor energization/de-energization cycles of the two stages  102   1  and  102   2  to be shifted 180° apart. Thus, the voltage regulation system  100  that is depicted in FIG. 6 is a two phase system. In other embodiments of the invention, the voltage regulation system may have a different number of phases (other than two), and in these embodiments, the controller  104  may generate signals to control the operation of the stages  102  so that the switch control signals have the proper phase relationship. As examples, for a three phase voltage regulation system (having three stages  102 ) the switch control signals to control the switching states of the three switches  108  are phased to place the energization/de-energization cycles 120° apart. For a four phase voltage regulation system, the switch control signals to control the four switches  108  are phased to place the energization/de-energization cycles 90° apart, etc. 
     Referring to FIGS. 7,  8 ,  9  and  10 , for the two phase design (assumed in the description below unless other-vise noted), the V 1  signal includes switching cycles  120  (see FIG.  7 ), each of which controls the switch  108  for a particular energization/de-energization cycle of the inductor  106  of the stage  102   1 . In this manner, each switching cycle  120  includes a pulse  130  that causes the switch  108  of the stage  102   1  to conduct and has a duration that sets the on time (called T ON ) of the switching cycle  120 . In some embodiments of the invention, the controller  104  controls the duration of the pulse  130  (i.e., controls the T ON  on time) to regulate the V OUT  voltage and sets a fixed duration for the off time (called T OFF ) of the switch  108 . Therefore, for the example that is depicted in FIG. 7, the pulse  130  lasts from the beginning (at time T 0 ) of the switching cycle  120  to time T 1 . Time T 2  marks the midpoint of the switching cycle  120 , and the switch  108  of the stage  102   1  remains off (from time T 1 ) until time T 3 , the time at which the switching cycle  120  ends. As depicted in FIGS. 7 and 8, the V 1  and V 2  signals are complementary. 
     For the other stage  102   2 , the V 3  signal includes switching cycles  122  that are complementary to the switching cycles  120 , as the stages  102   1  and  102   2  operate 180° out of phase. In this manner, as depicted in FIG. 9, a particular switching cycle  122  begins at time T 3  at the expiration of the switching cycle  120 . Each switching cycle  122  includes a pulse  132  in which the switch  108  of the stage  102   2  conducts and has a duration that sets the on time of the switching cycle  122 . When the switching cycle  122  elapses, another switching cycle  120  occurs, then another switching cycle  122  occurs, etc. As depicted in FIGS. 9 and 10, the V 3  and V 4  signals are complementary. 
     Unlike conventional systems, the system  100  uses a current mode control technique without using explicit current sensing devices (such as current sensing resistors) to sense inductor currents in the stages  102 . Instead, the system  100  uses the inductor  106  of each stage  102  as a current sensing element. In this manner, as described below, the PWM controller  104  measures the voltage (called V L1  (see FIG. 11) for the stage  102   1  called V L2  (see FIG. 12) for the stage  102   2 ) across each inductor  106  and uses these measured inductor voltages to sense the inductor currents in the stages  102   1  and  102   2 . 
     More specifically, as described below, the controller  104  uses a particular voltage of an inductor to reconstruct the current in the inductor. For example, for the stage  102   1 , the controller  104  uses the V L1  voltage to construct a representation of the current (called I L1  and depicted in FIG. 13) in the inductor  106 . As an example, the controller  104  may set an upper limit (called I C ) on the I L1  current and operate the switch  108  accordingly. In this manner, the controller  104  may establish a constant off time for the switch  108  of the stage  102   1  and establish the on time as the time for the I L1  current to rise from its minimum value to the I C  current. As described below, the level of the I C  current may vary with the level of the V OUT  voltage. The controller  104  may also construct a representation of the current (called I L2 ) of the inductor  106  of the stage  102   2  from the V L2  inductor voltage and control the operation of the switch  108  of the stage  102   2  in a similar manner. 
     The controller  104  may use various other current mode control schemes, depending on the particular embodiment of the invention. However, regardless of the type of current mode control that is used, the controller  104  uses the V L1  and V L2  inductor voltages to sense the I L1  and I L2  currents. 
     For purposes of constructing the inductor&#39;s current from its voltage, the controller  104  models the inductor according to an electrical model  106  that is depicted in FIG.  14 . As shown, the inductor may be modeled as an ideal winding  142  (that produces an AC voltage called V AC ) that is in series with an inherent winding resistor  140  (that produces a DC voltage called V DC ) that is introduced by the inherent winding resistance of the inductor. In this manner, the controller  104  derives the AC component of the inductor current from the V AC  component via integration and derives the DC component of the inductor current from the V DC  component. 
     More specifically, FIG. 15 depicts a possible embodiment of circuitry  105   a  (see FIG. 6) of the controller  104  to generate the V 1  and V 2  switch control signals. In this manner, the PWM controller  104  includes the circuitry  105   a  (see FIG. 6) to receive the V L1  voltage (via sense lines  113  and  115  that are coupled to different terminals of the inductor  106 ) and generates the V 1  and V 2  switch control signals, and the PWM controller  104  includes circuitry  105   b  (see FIG. 6) to receive the V L2  voltage (via sense lines  113  and  115 ) and generate the V 3  and V 4  switch control voltages. The circuitry  105   a  and  105   b  communicates with each other for purposes of interleaving the respective switching cycles. Because the circuitry  105   a  has a similar design to the circuitry  105   b , only the design of the circuitry  105   a  is described below. 
     As depicted in FIG. 15, in some embodiments of the invention, the circuitry  105   a  includes a differential amplifier  158  that has its input terminals coupled to the sense lines  113  and  115  to receive the V L1  inductor voltage. Thus, the output terminal of the differential amplifier  158  furnishes a signal that is indicative of the V L1  inductor voltage. A low pass filter (LPF)  160  of the circuitry  105   a  filters the signal from the output terminal of the differential amplifier  158  to provide a signal (at its output terminal) that indicates the DC component of the I L1  inductor voltage and thus, indicates the DC component of the inductor current. A bandpass filter (BPF)  162  of the circuitry  105  filters the signal that is provided by the output terminal of the differential amplifier  162  to provide a signal (at its output terminal) that indicates the AC component of the V L1  inductor voltage. An integrator  164  integrates the signal at the output terminal of the BPF  162  to produce a signal that indicates the AC component of the I L1  inductor current. An adder  166  of the circuitry  105  receives the signals from the output terminals of the LPF  160  and the integrator  164  and furnishes a signal (called V IL1 ) at its output terminal that indicates the I L1  inductor current. 
     In some embodiments of the invention, the circuitry  105   a  includes a comparator  168  that compares the V IL1  signal with a signal (called V C ) that sets the maximum level of the I L1  inductor current. In some embodiments of the invention, the V C  signal is finished by the output terminal of an error differential amplifier  170  that compares the V OUT  voltage with a reference voltage (called V REF ). Due to this arrangement, the signal at the output terminal of the comparator  168  indicates when the switch  108  should be opened and closed, as the signal transitions between states when the V IL1  voltage reaches the V C  voltage to indicate the end of the on time interval. A switch circuit  172  is coupled to the output terminal of the comparator  168  and is also coupled to the circuitry  105   b  to control the on and off time switching intervals (based on the signal at the output terminal of the comparator  168 ) during the appropriate switching cycle. 
     Referring to FIG. 16, in some embodiments of the invention, the voltage regulation system  100  may furnish power (via one or more voltage communication lines that extend from the output terminal  107 , for example) to a processor  401  and other components of a computer system  400 . In this context, the term “processor” may refer to, as examples, to at least one microcontroller, X86 microprocessor, Advanced RISC Machine (ARM) microprocessor or Pentium microprocessor. Other types of processors are possible and are within the scope of the following claims. 
     The processor  401  may be coupled to a local bus  402  along with a north bridge, or memory hub  404 . The memory hub  422  may represent a collection of semiconductor devices, or a “chip set,” and provide interfaces to a Peripheral Component Interconnect (PCI) bus  416  and an Accelerated Graphics Port (AGP) bus  410 . The PCI Specification is available from The PCI Special Interest Group, Portland, Oreg. 97214. The AGP is described in detail in the Accelerated Graphics Port Interface Specification, Revision 1.0, published on Jul. 31, 1996, by Intel Corporation of Santa Clara, Calif. 
     A graphics accelerator  412  may be coupled to the AGP bus  410  and provide signals to drive a display  414 . The PCI bus  416  may be coupled to a network interface card (NIC)  420 , for example. The memory hub  404  may also provide an interface to a memory bus  406  that is coupled to a system memory  408 . 
     A south bridge, or input/output (I/O) hub  424 , may be coupled to the memory hub  404  via a hub link  422 . The I/O hub  424  represents a collection of semiconductor devices, or a chip set, and provides interfaces for a hard disk drive  438 , a CD-ROM drive  440  and an I/O expansion bus  426 , as just a few examples. An I/O controller  428  may be coupled to the I/O expansion bus  426  to receive input data from a mouse  432  and a keyboard  434 . The I/O controller  428  may also control operations of a floppy disk drive  430 . 
     Other embodiments are within the scope of the following claims. For example, in other embodiments of the invention, a topology (a forward, flyback or a Boost converter topology, as examples) other than a Buck converter topology may be used for each stage  102 . A multiple phase converter (three phase or a four phase converter, as examples) other than a two phase converter may be used, in other embodiments of the invention. A single converter stage may be used in some embodiments of he invention. Other control schemes than the current mode control scheme described herein may be used in some embodiments of the invention. Other variations are possible. 
     While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of the invention.