Abstract:
An input-tracking and automatic output-margining system and method including: a logic board having a first load, a second load, and a first regulator disposed thereon; and a power supply having a bulk power source, a precision reference voltage, and a second regulator disposed therein; the first load supplied by a first voltage generated by the power supply, and the second load supplied by a second voltage generated by the first regulator; wherein a reference input to the first regulator comprises a first feedback voltage derived from the first voltage, such that a change in the value of the first voltage is tracked by the second voltage.

Description:
BACKGROUND 
   1. Field of the Invention 
   The present invention generally relates to regulators, and more specifically, to an input-tracking, automatic output-margining method and system. The present invention describes a method and system for controlling voltage margining of a small regulator located on a logic circuit in communication with an external power supply. 
   2. Description of Background 
   During manufacturing test routines, computer logic is often run for sustained periods at voltages higher or lower than the nominal. This is done to ensure the robustness of the product, and the procedure is referred to as margining. For most high-current power supply outputs, the voltage is adjusted dynamically through the use of a DAC (digital-to-analog converter) affecting the regulator&#39;s precision voltage reference. This DAC is controlled by a microprocessor internal to the power supply, and is issued instructions from an outside source. 
   On occasion, small regulators may be located on a system logic board, as opposed to within the power supply itself. These small regulators often have limited features, and it may not be possible to have computer control over voltage margining. Traditionally, two methods have been used to control voltage margining on small on-board regulators. 
   In a first method, an Intel VRM (Voltage Regulator Module) compliant regulator controller is used. These chipsets include a VID (Voltage ID) feature, which is a series of logic-level inputs that act as a DAC input and allow output voltage to be dynamically adjusted according to the applied bit pattern. This topology requires a digital interface to the regulator, which may not be easily available on a logic board external to the power supply. Additionally, margining capability is limited to the discrete voltage step sizes, which are determined by the chipset manufacturer. 
   In a second method, an external reference may be supplied on small linear or switch-mode regulators. Several resistor dividers may be used to combine an external margining circuit with the external precision reference, allowing for small voltage changes. Often times, the circuit is simply a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) with a series resistor that toggles a margin state either on or off (e.g., allowing a +/−7% change in output voltage) but does not allow fine resolution adjustability. This method is easier to interface to than the first method, and can offer more control over the maximum margin sizes, but does not have much flexibility. 
   Accordingly, it is desirable to implement a method that allows extensive margining capabilities, allows more granularity within voltage margining capabilities, and improves output voltage accuracy. 
   SUMMARY 
   One aspect of the invention is a logic circuit comprising: a first load and a second load; and a first regulator for converting a first voltage to a second voltage; wherein the regulator receives the first voltage that tracks an internal reference voltage of an external power supply having a second regulator. 
   Another aspect of the invention is an input-tracking and automatic output-margining system, the system comprising: a logic board having a first load, a second load, and a first regulator; and a power supply having a bulk power source, a precision reference voltage, and a second regulator; wherein the second regulator receives the precision reference voltage, the precision reference voltage being adjusted to vary a voltage of the second regulator. 
   Another aspect of the invention is a method for implementing input-tracking and automatic output-margining of a locally disposed voltage regulator on a logic board, the method comprising: receiving a first, externally generated voltage to supply a first load within the board; utilizing the first voltage as an input power source for the locally disposed generator to generate a second voltage to supply a second load within the board; and utilizing a first feedback voltage derived from the first voltage as a reference input to the local voltage regulator, wherein a change in the value of the first voltage is tracked by the second voltage. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures: 
       FIG. 1  illustrates a block diagram of an input-tracking, automatic output-margining system according to the exemplary embodiments of the present invention; and 
       FIG. 2  illustrates a circuit diagram of an input-tracking, automatic output-margining system according to the exemplary embodiments of the present invention. 
   

   DETAILED DESCRIPTION 
   One aspect of the exemplary embodiments is improving output voltage accuracy. Another aspect of the exemplary embodiments is eliminating the need for a potentially expensive external reference supplied on small linear or switch-mode regulators. In yet another exemplary embodiment, allowing for more granularity within voltage margining capabilities is presented. 
   The exemplary embodiments of the present invention permit a power supply&#39;s margining capabilities to be accurate and flexible by allowing a reference input to a regulator located on a logic board to have a first feedback voltage derived from a voltage supplied by an external power supply, such that a change in the value of the supplied voltage is tracked by an output voltage measured on the regulator located on the logic board. 
   In general, a power supply can have one or more output voltages feeding a logic board. In high-performance systems, the power supply has connections to the logic board, typically near a processor or other heavy load. The power supply as well as the circuit board each may include a separate regulator. The power supply regulator may feed a first load on the logic board and the logic board regulator may feed a second load on the logic board. A reference input to the logic board regulator may include a feedback voltage derived from a voltage supplied from the power supply to the logic board, such that a change in the value of the supplied voltage is tracked by a second voltage sensed on the logic board regulator located on the logic board. Therefore, the power supply ensures that the voltage sensed on the small regulator located on the logic board exactly matches the voltage of the power supply&#39;s internal precision voltage reference. As a result, if changes are made to the precision reference voltage of the power supply, as would be done for margining, the small regulator of the logic circuit changes its output voltage accordingly, effectively tracking the margined voltage level. 
   A small regulator located on the logic board uses the precision voltage reference that supplies voltage to the power supply regulator as a reference for voltage adjustment. A small regulator is basically a Point-of-load (“POL”) regulator, which is also referred to as a voltage regulator or a DC/DC converter, and is commonly used in conjunction with electronic circuits. This is because the voltage/current requirements of electronic circuits typically differ from the voltage that is readily available or the current that can practically be delivered. For example, some electronic devices only include a single voltage input but require different voltages for circuits contained within the electronic devices. Traditionally, POL regulators operate in conjunction with a power supply controller that activates, programs, and monitors the POL regulators. In one exemplary embodiment, the POL has low-power capability, configured to receive an input voltage of less than 3V and an output current of less than about 10 A. 
   Referring to  FIG. 1 , a block diagram of an input tracking, automatic output-margining system  10  is illustrated. The system  10  includes a power supply  12  and a logic board  14 . The power supply  12  includes a bulk power source  20 , a 2.5 VDC regulator  22 , a bulk power input  24  from the bulk power source  20  to the 2.5 VDC regulator  22 , and a precision voltage reference  26  input to the 2.5 VDC regulator  22 . The logic board  14  includes a 1.8 VDC regulator  30 , a first logic load  32  (Logic Load A), a second logic load  34  (Logic Load B), a 2.5 VDC input  52  from the 2.5 VDC regulator  22  to the first logic load  32 , a 2.5 VDC feedback output  38  from the first logic load  32  to the 2.5 VDC regulator  22 , a 1.8 VDC output  40  from the 1.8 VDC regulator  30  to the second logic load  34 , and a 1.8 VDC feedback output  42  from the second logic load  34  to the 1.8 VDC regulator  30 . 
   As illustrated in  FIG. 1 , the 2.5 VDC regulator  22  is used to power the first logic load  32 , as well as to supply bulk power to the 1.8 VDC regulator  30 . The 2.5 VDC feedback output  38  is used as a regulation feedback loop for the 2.5 VDC regulator  22 , as well as being a precision reference for the 1.8 VDC regulator  30 . In addition, the 2.5 VDC output  38  is scaled down by the regulator  30  to a more applicable voltage for the second logic load  34  (e.g., 1.8 VDC). 
   Referring to  FIG. 2 , a circuit diagram of an input tracking, automatic output-margining system is illustrated. The circuit diagram of  FIG. 2  is one exemplary circuit diagram that may be used to represent the 1.8 VDC regulator  30  of  FIG. 1 . The regulator circuit  30  includes two inputs, a 2.5 V input  52 , which is the input power from 2.5 VDC regulator and a sense input  26 , which is the precision voltage reference. 
   The 2.5 V input  52  is connected to a resistor R 1 , which is further connected to a circuit topology including a resistor R 2  in parallel with a capacitor C 1 . This three-component circuit configuration is connected to the positive input of an operation amplifier  72 . 
   The sense input  26  is connected to a resistor R 3 , which is connected to a circuit topology including a capacitor C 3  in series with a resistor R 5 , both capacitor C 3  and resistor R 5  in parallel with a resistor R 4 . In addition, resistor R 3  is connected to a capacitor C 2 , which is further connected to ground. Resistor R 4  is connected to a circuit topology including a resistor R 6  in parallel with a capacitor C 5 . Resistor R 7  is connected is series with capacitor C 6 , which is further connected to ground. This circuit configuration, including the elements resistor R 3 , capacitor C 3 , resistor R 5 , resistor R 4 , capacitor C 2 , resistor R 6 , capacitor C 5 , capacitor C 6 , and resistor R 7 , is connected to the negative input of the operational amplifier  72 . The positive power supply voltage of the operational amplifier  72  is connected to a capacitor C 4  and a 5V node  76 . The negative power supply voltage of the operational amplifier  72  is connected to ground. 
   The output of the operational amplifier  72  provides feedback to the negative input of the operational amplifier  72  via the resistor R 6 , which is in parallel with the capacitor C 5 . The output of the operational amplifier  72  is further connected to a resistor R 8 , which is connected to a transistor Q 1 . The input of the transistor Q 1  is connected to a capacitor C 7  and a 2.5 V node  52 . The output of the transistor Q 1  is connected to a 1.8 V node  40 . 
   In operation of the circuit  30 , the operational amplifier  72  establishes a reference comparison in order to regulate the output voltage  40 . In addition, the operational amplifier  72  is configured to reduce the error between the output voltage  40  and the positive input voltage  71  to a value of zero. Also, the output voltage  40  is read by the sense input  26 . This operation is performed in order to ensure that the system is stable and in order to avoid oscillation. In order to reduce the error between the output voltage  40  and the positive input voltage  71  to a value of zero, the transistor Q 1  is fed via the resistor R 8  in order to drive the transistor Q 1  as hard as desired. The amplifier  72  attempts to force the correct output voltage  40  by providing various levels of power to the transistor Q 1 . Thus, the transistor Q 1  acts as a variable resistor. In addition, the conductance is varied between the voltage output  40  and the 2.5V node  52  in order to accommodate for the varied levels of power required by the load connected to  40 . In  FIG. 2 , the 1.8 V output is connected to the logic, which it powers. The +sense input  26  is also connected to the logic at the point we want to regulate the voltage. The feedback is applied from that point to the +sense input  26 . This driving process provides for voltage-margining capabilities that are derived from a power supply that is of very high precision, where the regulator is forced to track its input. 
   The reference input to the logic circuit regulator includes a feedback voltage derived from a voltage supplied by the power supply, such that the change in the value of the precision voltage reference supplied to the power supply regulator is tracked by the measured voltage on the small regulator located on the logic circuit. The voltage measured on the small regulator on the logic circuit is as accurate as the precision voltage reference feeding the power supply regulator, which has a high degree of margining capability. Consequently, the small regulator on the logic circuit has an accurate voltage reference (typically more accurate than that supplied with small regulators) and margining capability that requires no external connections. Ordinarily margining requires separate inputs that control the regulator from a microprocessor or logical switch. These external connections to the 1.8V regulator are not needed when the exemplary embodiments of the present invention are employed because it inherently tracks margining applied to the 2.5V input. Note that a 1% shift in the 2.5V regulator output produces a 1% shift in the 1.8V output. 
   Essentially, by connecting the small, on-board regulator in this fashion, the small regulator can have similar voltage accuracy and margining capabilities as the main power supply regulators, while reducing overall circuit cost and complexity. The benefit of tracking the precision voltage reference supplied to the power supply regulator by the measured voltage on the small regulator located on the logic circuit is to accurately use the output voltage of the small regulator as a reference to an internal voltage of a power supply in order to control one or more loads located on the logic circuit. 
   While the invention has been described with reference to a preferred embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.