Abstract:
A voltage proportional to a sum of currents flowing though first and second coupled inductors is developed across a first capacitor common to first and second series RC networks if the RC networks are time constant-matched to the inductors. The first and second inductors are coupled between a first and second switched drive phase input terminal, respectively, and an apparatus output terminal. The first and second RC networks are coupled in parallel with the first and second inductor, respectively. Inverting and non-inverting inputs of an amplifier are coupled to junctions of third and fourth time constant-matched series RC networks coupled in parallel with the first and second inductors, respectively. The amplifier subtracts voltages sensed at the junctions to generate a difference signal proportional to a magnitude difference of the currents flowing through the inductors.

Description:
TECHNICAL FIELD 
     Embodiments described herein relate to apparatus and systems associated with direct current voltage conversion, including coupled inductor current sensing. 
     BACKGROUND INFORMATION 
     Electronic circuits of various applications may include multiple inductors other than transformers sharing a single core. Using a common core may be employed for space and cost saving purposes rather than for the explicit purpose of coupling energy from one shared-core inductor to another. In fact, field coupling between shared-core inductors may yield undesirable consequences. For example, such coupling may complicate the sensing of current flowing through each of two shared-core inductors in a direct current (“DC”)-to-DC converter such as a multiphase buck converter. 
       FIG. 1A  is a prior-art schematic diagram of a two-phase DC-DC converter output section including time constant matched current sensing circuits  105  and  108  associated with each of the uncoupled output inductors L 1   110  and L 2   120 , respectively. The technique of sensing/measuring instantaneous current flow through an uncoupled inductor is described by Tateishi in U.S. Pat. No. 6,469,481, the latter incorporated herein by reference in its entirety. The terms “sensing” and “measuring” are used synonymously herein and mean obtaining a voltage analogue waveform that is instantaneously proportional to inductor current, whether or not magnitudes of particular points of the voltage waveform are reduced to numerical values. 
     Each current sensing circuit includes a series coupled sense resistor (e.g., the sense resistors R 1   125  and R 2   130  corresponding to the sensing circuits  105  and  108 , respectively) and sense capacitor (e.g., the sense capacitors C 1   135  and C 2   140  corresponding to the sensing circuits  105  and  108 , respectively). Each such series coupled RC sense network is coupled in parallel with a series combination of the corresponding inductor and a resistor representing the inductor&#39;s parasitic DC resistance (“DCR”) (e.g., DCR 1   145  and DCR 2   150  corresponding to the inductors L 1   110  and L 2   120 , respectively). The time constant of each inductor is equal to the inductance L of the inductor divided by the DCR of the inductor. The time constant of each RC sense network is the resistance R of the sense resistor multiplied by the capacitance C of the sense capacitor. The inductor time constant L/DCR is matched to the sense network time constant RC if L/DCR=R*C. 
       FIG. 1B  is a prior-art waveform diagram illustrating an example inductor current  165 B.  FIG. 1B  also illustrates a corresponding time constant matched voltage analogue  160 B of the inductor current  165 B. The sense voltage  160 A and  160 B are accurate representations of the current  165 A and  165 B flowing through the inductor L 1   110  if time constant matching is adhered to. 
     Accordingly, the sense resistor and capacitor (e.g., the sense resistor R 1   125  and the sense capacitor C 1   135 ) are chosen such that their time constant RC is equal to the corresponding inductor time constant (e.g., the inductance of L 1   110  divided by the resistance of DCR 1   145 ). So chosen, the voltage V_C 1   160 A and  160 B seen across the sense capacitor C 1   135  is instantaneously proportional to the current I 1   165 A and  165 B flowing through the inductor L 1   110 . Likewise, the voltage V_C 2   170  seen across the sense capacitor C 2   140  is instantaneously proportional to the current I 2   170  flowing through the inductor L 2   120 . 
     However, the simple time constant matched current sensing circuits  105  and  108  become considerably more complex if the inductors L 1   110  and L 2   120  are magnetically flux-coupled. Although such coupled inductor current sensing circuits are known, they suffer variously from high complexity and consequent large surface area requirements, difficulty in tuning for wide ranges of inductances and coupling coefficients, inaccuracy in the use for phase balancing due to offset and gain errors associated with cascaded amplifiers, and/or high quiescent current consumption when used in high switching speed applications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a prior-art schematic diagram of a two-phase DC-DC converter output section including a time constant matched current sensing circuit associated with each uncoupled output inductor. 
         FIG. 1B  is a prior-art waveform diagram illustrating an example inductor current and a corresponding time constant matched voltage analogue of the inductor current. 
         FIG. 2  is a schematic diagram of a coupled inductor current sensing apparatus according to various example embodiments. 
         FIG. 3  is a schematic diagram of a coupled inductor current sensing apparatus according to various example embodiments. 
         FIG. 4  is a schematic diagram of a coupled inductor current sensing apparatus according to various example embodiments. 
         FIG. 5  is a schematic diagram of a multiphase coupled inductor current sensed power converter according to various example embodiments. 
         FIG. 6  is a waveform diagram illustrating a load line curve associated with a load-line embodiment of a multiphase coupled inductor current sensed power converter. 
         FIG. 7  is a schematic diagram of a phase add/shed embodiment of a multiphase coupled inductor current sensed power converter. 
     
    
    
     SUMMARY OF THE INVENTION 
     A voltage proportional to a sum of currents flowing though first and second coupled inductors is developed across a first capacitor common to first and second series RC networks if the RC networks are time constant-matched to the inductors. The first and second inductors are coupled between a first and second switched drive phase input terminal, respectively, and an apparatus output terminal. The first and second RC networks are coupled in parallel with the first and second inductor, respectively. Inverting and non-inverting inputs of an amplifier are coupled to junctions of third and fourth time constant-matched series RC networks coupled in parallel with the first and second inductors, respectively. The amplifier subtracts voltages sensed at the junctions to generate a difference signal proportional to a magnitude difference of the currents flowing through the inductors. 
     DETAILED DESCRIPTION 
       FIG. 2  is a schematic diagram of a coupled inductor current sensing apparatus  200  according to various example embodiments. The apparatus  200  includes two switched voltage input terminals  205  and  208 . Each of the input terminals  205  and  208  is coupled to a multiphase drive voltage source (not shown). The multiphase voltage source may be associated with a DC-to-DC power converter but need not be. 
     The apparatus  200  receives a switched drive voltage (“drive phase”)  210  at the input terminal  205  and a drive phase  212  at the input terminal  208 . Waveforms representing the drive phases  210  and  212  are substantially rectangular-shaped. A phase difference between the drive phases  210  and  212  is typically 180 degrees but need not be. The drive phases  210  and  212  are typically duty cycle controlled and/or amplitude modulated by the multiphase drive voltage source in order to control a voltage level at an output terminal  218  of the apparatus  200 . 
     An inductor L 1   215  is coupled between the input terminal  205  and the apparatus output terminal  218 . An inductor L 2   222  is coupled between the input terminal  208  and the apparatus output terminal  218 . The inductance values of the inductors  215  and  222  are substantially equal. Parasitic DC resistance associated with the inductors  215  and  222  is modeled as resistors DCR 1   223  and DCR 2   224 , respectively. However it is noted that the resistors  223  and  224  are not discrete resistors but are merely representative of the parasitic DC resistance of each of the inductors  215  and  222 , respectively. The resistances  223  and  224  are substantially equal. 
     It is noted that some embodiments of the apparatus  200  as well as apparatus and systems described below may be implemented using discrete components. Other embodiments are implemented in silicon as integrated circuits (“ICs”) or as portions of IC-based systems. For example, some embodiments of coupled inductor current sum and/or difference sensing circuits may be included as sub-sections of a DC-DC voltage converter IC. Some components of a current sum and/or difference circuit or an array thereof implanted in silicon may include discrete components that are impractical or inconvenient to implement on-chip. In particular, the current-carrying inductors  215  and  222  may be included as components of some embodiments of the apparatus  200 , particularly embodiments implemented with discrete components. However, some embodiments of the apparatus  200 , including IC-implemented embodiments, do not include the inductors  215  and  222  as components but include terminals to connect to external versions of the inductors  215  and  222 . In the latter case the apparatus  200  senses inductor currents I 1   225  and I 2   228  but does not conduct the inductor currents  225  and  228  within the apparatus  200 . 
     The apparatus  200  includes a current sum sense capacitor CS  235 . The sum sense capacitor  235  is coupled between a summing node  238  and the apparatus output terminal  218 . A sum sense voltage proportional to an instantaneous sum of the currents I 1   215  and I 2   218  flowing through the two mutually coupled inductors  225  and  228  is developed across the sum sense capacitor  235 . The sum sense voltage is equal to the DCR resistance  223 / 224  divide by two multiplied by the sum of the magnitudes of the currents I 1   225  and I 2   228 :
 
 V _ CS=DCR/ 2*( I 1+ I 2)
 
     The apparatus  200  also includes a first current sum sense resistor RS 1   245  coupled between the first switched voltage input terminal  205  and the summing node  238 . The apparatus  200  further includes a second current sum sense resistor RS 2   250  coupled between the second switched voltage input terminal  208  and the summing node  238 . Resistance values of the resistors  245  and  250  are substantially equal. The sum sense voltage results from voltage drops across the first and second current sum sense resistors  245  and  250 . The voltage drops correspond to charging currents flowing through the sum sense resistors  245  and  250  and into or out of the current sum sense capacitor  235  as the first and second drive phases  210  and  212  are switched on and off. 
     The apparatus  200  also includes a current sum amplifier  260  coupled to the sum sense capacitor  235 . The sum amplifier  260  may be implemented with an operational amplifier, a transconductance amplifier or a sense amplifier, for example. Non-inverting and inverting input terminals  265  and  270  are coupled across the current sum sense capacitor  235 . The current sum amplifier  260  senses the sum sense voltage across the sum sense capacitor  235  and generates a sum signal α(I 1 +I 2 ) at an output terminal  275  of the sum amplifier  260 . The sum signal α(I 1 +I 2 ) is proportional to the instantaneous sum of the magnitudes of the currents I 1   225  and I 2   228  flowing through the two mutually coupled inductors L 1   215  and L 2   222 , respectively:
 
α( I 1+ I 2)= DCR/ 2*( I 1+ I 2)*(gain of the sum amp 260)
 
       FIG. 3  is a schematic diagram of a coupled inductor current sensing apparatus  300  according to various example embodiments. The apparatus  300  includes the two switched voltage input terminals  205  and  208 , the switched drive phases  210  and  212 , the output terminal  218 , the inductors L 1   215  and L 2   222 , the inductor currents I 1   225  and I 2   228 , the current sum sense capacitor  235 , the summing node  238 , the current sum sense resistors RS 1   245  and RS 2   250  and the current sum amplifier  260 , all as previously described with reference to the apparatus  200  of  FIG. 2 . 
     The apparatus  300  further includes a current difference sense capacitor CD  310  and a current difference sense resistor RD  315 . The capacitor  310  and the resistor  315  are coupled in series to form a current difference resistor-capacitor (“RC”) network. The current difference RC network is coupled between the first and second input terminals  210  and  212 . 
     A difference sense voltage is developed across the difference sense capacitor  310 . The difference sense voltage is proportional to an instantaneous difference between magnitudes of the currents I 1   225  and I 2   228  flowing through the two mutually coupled inductors L 1   215  and L 2   222 , respectively. The difference sense voltage results from a voltage drop across the current difference sense resistor  315 . The voltage drop corresponds to a charging current flowing through the current difference sense resistor  315  and into/out of the difference sense capacitor  310  as the first and second drive phases  210  and  212  are switched. 
     The coupled inductor current sensing apparatus  300  also includes a current difference amplifier  320 . Non-inverting and inverting input terminals  325  and  330  of the current difference amplifier  320  are coupled across the difference sense capacitor  310 . The current difference amplifier  320  senses the current difference sense voltage and generates a difference signal β(I 1 −I 2 ) at an output terminal  335 . The difference signal β(I 1 −I 2 ) is proportional to the instantaneous difference between the magnitudes of the currents  225  and  228  flowing through the two mutually coupled inductors L 1   215  and L 2   222 .
 
β( I 1− I 2)= DCR *( I 1− I 2)*(difference amp gain)
 
       FIG. 4  is a schematic diagram of a coupled inductor current sensing apparatus  400  according to various example embodiments. The apparatus  400  includes the two switched voltage input terminals  205  and  208 , the switched drive phases  210  and  212 , the output terminal  218 , the inductors L 1   215  and L 2   222 , the inductor currents I 1   225  and I 2   228 , the current sum sense capacitor  235 , the summing node  238 , the current sum sense resistors RS 1   245  and RS 2   250  and the current sum amplifier  260 , all as previously described with reference to the apparatus  200  of  FIG. 2   
     The apparatus  400  also includes a first current difference sense capacitor CD_A  410  and a first current difference sense resistor RD_A  415  coupled in series. The series combination of the capacitor  410  and the resistor  415  is coupled in parallel with a first inductor L 1   215  of the two mutually coupled inductors  215  and L 2   222  between the first switched voltage input terminal  205  and the apparatus output terminal  218 . A first sense voltage proportional to the instantaneous current flowing through the first inductor  215  is developed across the first current difference sense capacitor  410 . 
     The apparatus  400  further includes a second current difference sense capacitor CD_B  420  and a second current difference sense resistor RD_B  425  coupled in series. The series combination of the capacitor  420  and the resistor  425  is coupled in parallel with the second inductor L 2   222  between the second switched voltage input terminal  208  and the apparatus output terminal  218 . A second sense voltage proportional to the instantaneous current flowing through the second inductor  215  is developed across the second current difference sense capacitor  420 . 
     The apparatus  400  also includes a current difference amplifier  440 . A non-inverting input terminal  445  of the current difference amplifier  440  is coupled to a junction  448  of the first current difference sense resistor  415  and the first current difference sense capacitor  410 . An inverting input terminal  450  of the current difference amplifier  440  is coupled to a junction  453  of the second current difference sense resistor  425  and the second current difference sense capacitor  420 . The current difference amplifier  440  senses an instantaneous voltage difference between the first and second sense voltages across the current difference sense capacitors  410  and  420 . The amplifier  440  generates a difference signal β(I 1 −I 2 ) at an output  455  of the amplifier  440 . The difference signal β(I 1 −I 2 ) is proportional to the instantaneous voltage difference between the first and second sense voltages.
 
β( I 1− I 2)= DCR *( I 1− I 2)*(difference amp gain)
 
       FIG. 5  is a schematic diagram of a multiphase coupled inductor current sensed power converter  500  according to various example embodiments. The power converter  500  includes an array  510  of two or more coupled inductor current sum/difference sense modules (e.g., the modules M 1   515 , M 2   518  . . . MN  522 ). Each sum/difference sense module includes the circuit elements coupled together as previously described in the context of the apparatus  200 , the apparatus  300  or the apparatus  400  of  FIG. 2 ,  FIG. 3 , and  FIG. 4 , respectively. 
     Each sum/difference current sense module receives two switched drive phases (e.g., the drive phases  210  and  212  associated with the module  515 ). Each sum/difference sense module generates a sense module sum signal (e.g., the sum signal α(I 1 +I 2 ) from the module  515 ), a sense module difference signal (e.g., a difference signal β(I 1 −I 2 ) from the module  515 , not shown), or both. A module sum signal is proportional to an instantaneous sum of currents flowing through two mutually coupled inductors associated with the corresponding current sense module as previously described in the context of the apparatus  200 . A module difference signal is proportional to an instantaneous magnitude difference between the currents flowing through the two mutually coupled inductors associated with the corresponding current sense module as previously described in the context of the apparatus  300  of  FIG. 3  and the apparatus  400  of  FIG. 4 . 
     The power converter  500  also includes a multiphase DC-to-DC power converter drive phase voltage source  525 . The drive phase voltage source  525  is coupled to the array  510  of coupled inductor current sum/difference sense modules and generates the two drive phases associated with each sense module. 
     The power converter  500  further includes a summing device (e.g., the summing configured operational amplifier  540 ) coupled to the array  510  of sense modules. The summing device receives the sense module sum or difference signals from each of the plurality of sense modules at a first summing device input terminal  545 . The summing device also receives a reference signal (e.g., the voltage regulation signal V_REF) at a second summing device input terminal  550 . The summing device compares a sum of the sum or difference signals summed to the input terminal  545  to a magnitude of the reference signal at the input terminal  550 . The summing device generates a drive phase feedback signal (e.g., the load-line voltage regulation reference signal V_REF_LL  552 ) at an output terminal  555  of the summing device  540 . The drive phase feedback signal is responsive to the comparison of the signals received at the first and second summing device input terminals  545  and  550 . 
     The multiphase coupled inductor current sensed power converter  500  also includes a drive phase controller  570  communicatively coupled to the summing device  540 . The drive phase controller  570  receives the drive phase feedback signal and generates one or more drive phase source control signals. For the example power converter  500  of  FIG. 5 , the drive phase controller  570  is a voltage regulation controller. 
     In the example embodiment of the multiphase coupled inductor current sensed power converter  500  being a load-line regulator, the reference signal is a base reference voltage V_REF. The summing device  540  is an operational amplifier configured in a summing mode to receive V_REF and to generate the load-line voltage reference signal V_REF_LL  552  as the drive phase feedback signal. V_REF_LL  552  is used to maintain an output voltage level of the multiphase DC-to-DC converter as load current from the DC-to-DC converter changes. 
     The load-line embodiment also includes an amplifier  580 . The al amplifier  580  is input-coupled to the operational amplifier to receive V_REF_LL  552  at a first input terminal  583  of the amplifier  580 . The amplifier  580  receives a converter output voltage sample at a second input terminal  586  of the amplifier  580 . The amplifier  580  generates a converter output voltage feedback signal at an output terminal  589  of the amplifier  580 . 
     The voltage regulation controller is coupled to the output terminal of the amplifier  580  to receive the converter output voltage feedback signal. The voltage regulation controller generates one or more drive phase duty cycle control signals and/or one or more drive phase amplitude control signals responsive to the converter output voltage feedback signal. The drive phase source  525  is coupled to the voltage regulation controller to receive the drive phase control signals. The drive phase source  525  modifies the duty cycle and/or amplitude of one or more drive phases responsive to the drive phase control signals in order to maintain the converter output voltage within established regulation specifications. 
       FIG. 6  is a waveform diagram illustrating a load-line curve  600  associated with the load-line embodiment of the multiphase coupled inductor current sensed power converter  500  of  FIG. 5 . The load-line curve  600  illustrates V_REF_LL  552  of  FIG. 5  as a function of the sum of the load currents flowing through the inductors of the sense module array  510  as sensed at the input  545  of the operational amplifier  540 . 
       FIG. 7  is a schematic diagram of a phase add/shed embodiment of a multiphase coupled inductor current sensed power converter  700 . The power converter  700  includes the array  510  of current sense modules  515 ,  518  . . .  522  and the multiphase drive phase source  525  as previously described in the context of the power converter  500  of  FIG. 5 . 
     The power converter  700  also includes a signal comparator  710  coupled to the sense module array  510 . The comparator  710  receives a total phase current reference signal I_REF  715  at a comparator input  720 . The comparator  710  also receives and sums the sense module sum signals received from each sense module at a comparator input  725 . The sum of the sense module sum signals represents total instantaneous current flowing through all inductors. The comparator  710  compares the sum of the sense module sum signals to I_REF. The comparator  710  generates a drive phase add/shed trigger signal  725  at the comparator output  730  when the total instantaneous current flowing through all inductors crosses a threshold represented by I_REF. 
     The power converter  700  also includes a drive phase add/shed controller  750 . The add/shed controller  750  receives the add/shed trigger signal  725  as a drive phase feedback signal. The add/shed controller  750  generates add/shed control signals to cause the drive phase source  525  to selectively enable and disable drive phases associated with one or more sense modules in response to converter output load demand. 
     It is noted that the load-line regulation embodiment of the power converter  500  and the phase shedding/adding embodiment of the power converter  700  are example systems utilizing multi-module embodiments of coupled inductor current sensing apparatus described above. Both the load-line regulation system embodiment and the phase shedding/adding embodiment utilize sense module sum signals. Other system embodiments including intra-module current balancing systems utilize sense module difference signals. For example, a comparator associated with each sense module of an example multi-module system receives a sense module difference signal from the associated sense module. The difference signal is phase-compared to a reference phase to control the on time of drive phases associated with each sense module. Some systems including DC power converters may include multiple application embodiments such as load-line regulation in combination with phase shedding/adding. 
     Apparatus and systems described herein may be useful in applications other than multiphase DC-DC converters. The examples of the apparatus  200 ,  300  and  400  and the power converters  500  and  700  described herein are intended to provide a general understanding of the structures of various embodiments. They are not intended to serve as complete descriptions of all elements and features of systems and methods that might make use of these example structures. 
     By way of illustration and not of limitation, the accompanying figures show specific embodiments in which the subject matter may be practiced. It is noted that arrows at one or both ends of connecting lines are intended to show the general direction of electrical current flow, data flow, logic flow, etc. Connector line arrows are not intended to limit such flows to a particular direction such as to preclude any flow in an opposite direction. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be used and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. This Detailed Description, therefore, is not to be taken in a limiting sense. The breadth of various embodiments is defined by the appended claims and the full range of equivalents to which such claims are entitled. 
     Such embodiments of the inventive subject matter may be referred to herein individually or collectively by the term “invention” merely for convenience and without intending to voluntarily limit this application to any single invention or inventive concept, if more than one is in fact disclosed. Accordingly, although specific embodiments have been illustrated and described herein, any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. 
     The Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b) requiring an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In the preceding Detailed Description, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted to require more features than are expressly recited in each claim. Rather, inventive subject matter may be found in less than all features of a single disclosed embodiment. The following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.