Abstract:
A system comprises an integrated circuit comprising one or more transistors that receive a supply voltage. The system also includes a reference transistor operable to receive a constant current and produce a reference voltage that varies according to temperature or process variations, wherein the reference transistor behaves similarly to at least one of the one or more transistors with respect to temperature or process variations. The system also includes a comparator operable to compare the reference voltage with the received supply voltage and produce an output based at least in part on the difference between the reference voltage and the received supply voltage. The system further includes a controller operable to adjust the received supply voltage based at least in part on the output of the comparator.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 60/915,850 filed on May 3, 2007. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates in general to electronic circuits and more particularly to a method and system for adaptive power management for integrated circuits, including enhancement JFET integrated circuits. 
       OVERVIEW 
       [0003]    As a result of the rapid technological growth of the past several decades, transistors and other semiconductor devices have become a fundamental building block for a wide range of electronic components. One or more operating characteristics of a transistor may be affected by temperature changes and process variations. In some applications, transistors may exhibit inconsistent performance across the range of operating temperatures and process variations. Such inconsistent performance can lead to excess power consumption and/or other operational inefficiencies. 
         [0004]    Advanced transistor devices can have a large positive temperature coefficient with respect to drive current. This may be a disadvantage in high performance chip design with a fixed supply voltage scheme. The lowest performance may happen in the lowest temperature when the drive current is the lowest. If a higher supply voltage is used, like 0.55 V instead of 0.5 V, the performance may be improved in low temperature. But at high temperature this can unnecessarily waste power and potentially cause thermal problems. In enhancement mode junction field effect transistor (JFET) technology, the gate pn-junction diode will be more strongly forward biased due to the negative temperature coefficient (˜−2 mV per degree Celsius), which can cause gate leakage problems. 
         [0005]    With an adaptive supply voltage scheme, the above problem can be resolved. Furthermore, the “large” and “positive” temperature coefficient can be turned into an advantage in advanced transistor circuit designs. The supply voltage may be adaptively adjusted using temperature sensing. At high chip temperature, the supply voltage can be lowered. At low chip temperature, the supply voltage can be raised so that the drive current can be kept relatively constant across a range of temperatures. Because the supply voltage can be lower for a given performance target at higher temperature, the power dissipation at higher temperature is lower, resulting in advantages in thermal design of the chip and packaging. 
       SUMMARY OF EXAMPLE EMBODIMENTS 
       [0006]    In accordance with one embodiment of the present disclosure, a system comprises an integrated circuit comprising one or more transistors that receive a supply voltage. The system also includes a reference transistor operable to receive a constant current and produce a reference voltage that varies according to temperature and process variations, wherein the reference transistor behaves similarly to at least one of the one or more transistors with respect to temperature or process variations. The system also includes a comparator operable to compare the reference voltage with the received supply voltage and produce an output based at least in part on the difference between the reference voltage and the received supply voltage. The system further includes a controller operable to adjust the received supply voltage based at least in part on the output of the comparator. 
         [0007]    In accordance with another embodiment of the present disclosure, a method includes providing a constant current to a reference transistor. The method also includes comparing a voltage associated with the reference transistor to a supply voltage of an integrated circuit, wherein the voltage associated with the reference transistor increases when a temperature associated with the reference transistor decreases and decreases when a temperature associated with the reference transistor increases, and wherein the voltage associated with the reference transistor varies according to temperature at a rate of approximately minus 2 millivolts per degree Celsius. The method further includes adjusting the supply voltage in response to a change in the voltage associated with the reference transistor. 
         [0008]    Numerous technical advantages are provided according to various embodiments of the present disclosure. Particular embodiments of the disclosure may exhibit none, some, or all of the following advantages depending on the implementation. In certain embodiments, substantially consistent performance can be maintained for one or more transistors across a wide range of temperatures. In certain other embodiments, on-chip structures may be used to measure temperature. In some embodiments, power dissipation may be decreased. 
         [0009]    Other technical advantages of the present disclosure will be readily apparent to one skilled in the art from the following figures, descriptions, and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
           [0011]      FIG. 1  illustrates a block diagram of an example system for adaptive power management; 
           [0012]      FIG. 2  illustrates current and voltage characteristics of a pn-junction at different temperatures; 
           [0013]      FIG. 3  illustrates an example JFET device that may be used in a digital logic circuit; 
           [0014]      FIG. 4  illustrates one example embodiment of a temperature-sensing device for use in an adaptive power management system; 
           [0015]      FIG. 5  illustrates an example power management system; and 
           [0016]      FIG. 6  is a flowchart illustrating one example method for adaptive power management. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  illustrates a block diagram of an example system  10  for adaptive power management. The components of system  10  may be situated or connected in any suitable arrangement. In certain digital logic circuits, one or more advanced transistor devices may have a positive temperature coefficient. Lower performance may occur at lower temperatures, and higher performance may occur at higher temperatures. Adaptive power management system  10  may be used to sense a temperature associated with at least one of the one or more devices and adaptively adjust a voltage supply to maintain a consistent performance across a range of temperatures. At high chip temperature the supply voltage can be lowered, and at low chip temperature the supply voltage can be raised. System  10  comprises digital logic  12 , voltage source  14 , temperature sensor  16 , controller  18 , and feedback loop  20 . 
         [0018]    Digital logic  12  can be located in an integrated circuit or in any suitable location. Digital logic  12  may comprise one or more transistors or other semiconductor components operable to perform one or more functions. In certain embodiments, digital logic  12  can be comprised of one or more junction field effect transistors (JFETs). Some JFETs may have low operating voltages and low threshold voltages. In some embodiments, operating voltages can be 0.5 volts or lower. 
         [0019]    A system can be used to increase or decrease the supply voltage as the temperature changes or process variations occur to ensure a consistent performance of the transistor across a wide range of temperatures or process variations. An adaptive power management system, like system  10 , may be used to decrease the supply voltage as the temperature at or near digital logic  12  increases, and increase the supply voltage as the temperature at or near digital logic  12  decreases. This system can also lead to reduced power consumption while maintaining consistent performance, such as consistent operating speeds and drive current across a range of temperatures. On-chip structures may be used to read the temperature near digital logic  12 . 
         [0020]    Voltage source  14  comprises any suitable circuitry operable to provide one or more voltages to digital logic  12 . In certain embodiments, voltage source  14  can provide a voltage of approximately 0.3 to 0.7 volts to digital logic  12  to power one or more transistors or other semiconductor components. In some embodiments, voltage source  14  provides a voltage to a gate terminal of one or more transistors within digital logic  12 , such as in enhancement mode JFETs. In certain other embodiments, voltage source  14  may provide a voltage to digital logic  12 , and suitable circuitry within digital logic  12  may convert that voltage to a higher and/or lower voltage for use within digital logic  12 . 
         [0021]    Temperature sensor  16  comprises any suitable component or set of components operable to detect, sense, or otherwise respond to one or more temperature changes in or near digital logic  12 . In some embodiments, temperature sensor  16  may comprise an on-chip semiconductor structure, such as a transistor or diode used for sensing purposes. For example, temperature sensor  16  may comprise a diode that reacts to temperature changes. The voltage across a pn-junction of a diode may change with temperature changes, and this voltage can be used in a feedback loop, such as feedback loop  20 , to adjust the voltage supplied by voltage source  14 . Temperature sensor  16  could also comprise a reference transistor that responds to a change in temperature. The response of the reference transistor may be sensed and used to adjust the voltage supplied by voltage source  14 . In certain embodiments, the reference transistor may be identical to at least one of the transistors in digital logic  12 . In certain embodiments, the reference transistor may comprise an enhancement mode JFET that operates with an operating voltage of approximately 0.5 volts. 
         [0022]    Controller  18  comprises any suitable combination of hardware, software, and firmware that adjusts the voltage provided by voltage source  14 . Controller  18  may adjust voltage source  14  in response to one or more signals from temperature sensor  16 . In certain embodiments, controller  18  can comprise a part of a feedback loop. 
         [0023]    Feedback loop  20  comprises temperature sensor  16 , controller  18 , and voltage source  14 . Feedback loop  20  may be used to measure and then adjust one or more voltages associated with digital logic  12  when the temperature changes. Feedback loop  20  may adjust a voltage in real time or periodically at set intervals. 
         [0024]    System  10  may also compensate for process or voltage variations in certain embodiments. For example, a voltage provided by voltage source  14  may fluctuate slightly due to device imperfections or limitations. These fluctuations could, in turn, raise or lower the temperature of one or more devices within digital logic  12 . Temperature sensor  16  could detect these temperature changes and controller  18  could use that information to alter the voltage provided by voltage source  14 . System  10  can thus compensate for fluctuations or variations in voltage source  14 . 
         [0025]    System  10  may also, in certain embodiments, compensate for process variations within one or more semiconductor devices. Process variations may cause one or more characteristics of a semiconductor device to vary from one device to another, such as a voltage threshold. System  10  may employ a sensor comprised of one or more semiconductor devices that are similar to the devices within digital logic  12 , which can be used to reduce the effect of process variations. 
         [0026]      FIG. 2  illustrates the current and voltage characteristics of a pn-junction of a low-power JFET device at two example temperatures. The pn-junction diode voltage decreases by approximately 2 mV/° C. when the current is constant in certain embodiments. Constant current is represented on the graph by a horizontal line. As shown on the graph, at a higher temperature the current/voltage curve moves to the left, resulting in a lower voltage if the current is constant. With a constant current, at a higher temperature the voltage will be lower. This voltage can be monitored and used for thermal management. 
         [0027]      FIG. 3  illustrates an example JFET device  90  that may be used in a digital logic circuit. JFET device  90  is not to scale and may comprise other structures and still fall within the scope of this disclosure. Device  90  comprises a p-type substrate  93  and an n-type channel  98 , source  94 , drain  95 , gate  92 , and pn-junction diodes  96 . When the current of pn-junction diode  96  is used for control, forward biasing of the diode can be prevented. In certain low-voltage technologies, such as enhancement mode JFET technologies, strong forward biasing of the pn-junction between gate  92  and source  94  (or between a back gate and source  94 ) can make the devices non-operating. Controlling the current through pn-junction diode  96  can prevent this. At the same time, the speed difference between hot and cold temperature operation can become smaller. 
         [0028]      FIG. 4  illustrates one example embodiment of temperature-sensor  16  for use in adaptive power management system  10 . Sensor  16  may comprise any component or number of components operable to measure a temperature at or near one or more semiconductor devices. In certain embodiments, multiple sensors may be implemented to have different optimal supply voltages at different specific locations on a chip. 
         [0029]    Sensor  16  comprises reference transistor  54 . In this embodiment, reference transistor  54  comprises a source terminal  72  and a drain terminal  74  connected to a ground node  56 . Reference transistor  54  also comprises a gate terminal  70  connected to a constant current source  52 . Although not shown in  FIG. 4 , reference transistor  54  may also comprise a body terminal, which may be connected to ground. In the illustrated embodiment, reference transistor  54  is a p-type JFET. In certain embodiments, reference transistor  54  should be similar to at least one of the one or more transistors that comprise digital logic  12 . If reference transistor  54  reacts similarly to temperature changes as the transistors in digital logic  12 , then reference transistor  54  can be monitored and used as a part of feedback loop  20  to adjust voltage source  14 . A voltage associated with reference transistor  54 , such as the voltage across a gate pn-junction, may change as the temperature changes, and this change may be used in feedback loop  20  to modify voltage source  14  to compensate for the temperature changes. 
         [0030]    Constant current source  52  operates to provide a constant current to gate terminal  70  of reference transistor  54 . Constant current source  52  comprises any component or system of components operable to perform this function, such as a simple transistor current source. Constant current source  52  may be connected to one or more voltage nodes, such as node  58 , which provides power to constant current source  52 . 
         [0031]    Sensor  16  may also comprise comparator  60 . Comparator  60  may be used as part of a feedback loop (positive or negative) that adjusts voltage source  14  to compensate for one or more temperature changes. In this example embodiment, comparator  60  comprises input node  66 , which receives as input the voltage at gate terminal  70  of reference transistor  54 . Comparator  60  also comprises input node  64 , which receives as input a supply voltage  62  used by one or more transistors in digital logic circuit  12 . In certain embodiments, this supply voltage  62  is applied to a gate terminal of one or more JFETs within digital logic  12 . Supply voltage  62  may be output from voltage source  14 , as illustrated in  FIG. 4 , or may come from within digital logic  12 . Comparator  60  compares supply voltage  62  to the voltage at gate terminal  70  of reference transistor  54  which is coupled to input node  66 . Comparator  60  is operable to output a voltage to node  68  based at least in part on the difference between supply voltage  62  and the reference voltage at input node  66 . The output voltage at node  68  changes depending on the difference between the voltages at the two comparator input nodes  64  and  66 . The output voltage at node  68  can be fed to controller  18  and used in feedback loop  20  to alter the supply voltage  62  until the two comparator input voltages (at input nodes  64  and  66 ) fall within an acceptable range of one another. 
         [0032]    Controller  18  may receive the output voltage at node  68  and adjust voltage source  14  either up or down based at least in part on the value of the voltage at node  68 . In certain embodiments, this adjustment alters supply voltage  62  until it is approximately identical to the voltage at gate terminal  70  of reference transistor  54 . 
         [0033]    In operation, sensor  16  works as follows. Reference transistor  54  receives a constant current from constant current source  52 . Reference transistor  54  comprises a pn-junction between its gate terminal and a channel of the transistor. Current from the constant current source  52  flows through this pn-junction and creates a voltage at the gate terminal. If the temperature at or near reference transistor  54  is constant, and the current from constant current source  52  is constant, then the voltage at gate terminal  70  of reference transistor  54  will also be relatively constant. 
         [0034]    As the temperature increases, the pn-junction diode voltage of reference transistor  54  decreases at approximately 2 mV/° C. when the current is constant. This relationship can be used to alter voltage source  14  in response to one or more temperature changes. For example, when the pn-junction diode voltage decreases, comparator  60  receives this decreased voltage at input node  66 . Supply voltage  62  will now be larger than the transistor reference voltage at node  66 , and comparator  60  will output a voltage at node  68  based at least in part on this difference. The voltage at node  68  can then be used by other components, such as controller  18 , to adaptively adjust voltage source  14  to decrease supply voltage  62  until it is approximately equal to the reference voltage at gate terminal  70  of reference transistor  54 . 
         [0035]    If the temperature decreases, the opposite effect occurs. The pn-junction diode voltage of reference transistor  54  increases and comparator  60  receives this increased voltage at input terminal  66 . Comparator  60  and controller  18  can then act to raise supply voltage  62  until it is approximately equal to the reference voltage at gate terminal  70  of reference transistor  54 . 
         [0036]    Thus, as the temperature increases, the speed or drive current of one or more transistors in digital logic circuit  12  also increases. To prevent excessive power dissipation and to create more consistent speed and drive current across a range of temperatures, system  10  can be used to lower supply voltage  62 , which may be used to operate one or more transistors in digital logic  12 . This can be done to slow down the transistors as the temperature increases or reduce the drive current of the transistors, which can prevent damage to the transistors and also prevent forward biasing of the transistors. Also, since the transistors are operating with a lower supply voltage  62 , power consumption may be reduced. In contrast, as the temperature decreases, the speed or drive current of the transistors may also decrease. In that situation, the present disclosure can be used to raise supply voltage  62  to increase the speed or drive current of the transistors to ensure consistent performance across a wide range of temperatures. In certain embodiments, a chip temperature range of −10° C. to 125° C. can lead to adaptive adjustments of up to 400 mV in the supply voltage. For example, a supply voltage may be adjusted to any value between 300 mV and 700 mV depending on temperature changes. 
         [0037]    Sensor  16  also operates to keep the gate pn-junction voltage of transistors within digital logic  12  below a cut-in voltage. As temperature increases, the cut-in voltage is reduced, and there is a risk that the transistors may become forward biased. However, supply voltage  62  is reduced when the temperature increases, which decreases the risk that the transistors will become forward biased. Conversely, as the temperature decreases, the cut-in voltage is increased, and thus supply voltage  62  can be increased without the risk of forward biasing the transistors. 
         [0038]      FIG. 5  illustrates an example power management system  100 . The components of power management system  100  may be situated or connected in any suitable arrangement. System  100  generates a control signal  118  based at least in part on a temperature change to adjust a supply voltage. Power management system  100  comprises pulse width modulator (PWM)  102 , sensor  104 , digital logic  106 , transistor  110  and  112 , inductor  114 , capacitor  116 , and isothermal environment  122 . 
         [0039]    In power management system  100 , sensor  104  can be used to detect a change in temperature near digital logic  106 . Sensor  104  and digital logic  106  exist in isothermal environmental  122 , which means that the temperature at sensor  104  is at or near the temperature of digital logic  106 . Because they are near the same temperature, the temperature changes detected by sensor  104  may be used to adjust the voltage at node  126  supplied to digital logic  106 . 
         [0040]    When a change in temperature is detected by sensor  104 , control signal  118  is sent to PWM  102 . PWM  102  uses control signal  118  to determine how to adjust the voltage supplied to digital logic  106 . PWM  102  can output one or more signals based at least in part on control signal  118 . The signals output by PWM  102  may be used to selectively turn transistors  110  and  112  on and off to produce an appropriate voltage at node  124 . Transistor  110  is coupled to external voltage supply  108  and node  124 . Transistor  112  is coupled to node  124  and ground node  120 . 
         [0041]    The voltage produced at node  124  can be filtered by inductor  114  and capacitor  116 . This L-C filter may be used to reduce the voltage ripple at node  126 . Thus, PWM  102  uses control signal  118  to determine whether the voltage supplied to digital logic  106  at node  126  should be adjusted up or down. The output of PWM  102  creates an appropriate voltage at node  124 , and this voltage is filtered and then sent to node  126 , where it can be used by digital logic  106 . By this process, power management system  100  is operable to adjust a supply voltage for digital logic  106  based at least in part on a temperature measured near digital logic  106  in order to maintain consistent performance across a range of temperatures. 
         [0042]      FIG. 6  is a flowchart illustrating one example method  300  for an adaptive power management system  10 . In particular, the illustrated method can adjust a voltage source  14  in response to one or more temperature changes. The steps illustrated in  FIG. 6  may be combined, modified, or deleted where appropriate. Additional steps may also be added to the example operation. Furthermore, the described steps may be performed in any suitable order. 
         [0043]    The method begins with step  310 . In step  310 , a constant current is provided to reference transistor  54 . In certain embodiments, reference transistor  54  is similar to at least one of one or more transistors within digital logic  12 . Reference transistor  54  also comprises a voltage that adjusts to one or more temperature changes at approximately −2 mV/° C. 
         [0044]    In step  320 , a voltage of reference transistor  54  that reacts to a change in temperature is monitored. In certain embodiments, this voltage can be a voltage at a gate terminal  70  of reference transistor  54 . The reference voltage can be monitored in a variety of ways. In some embodiments, a pn-junction voltage that changes with temperature may be monitored. 
         [0045]    In step  330 , the reference voltage of reference transistor  54  can be compared to supply voltage  62  for digital logic  12 . A comparator  60  may be used that accepts as input the reference voltage of reference transistor  54  and supply voltage  62 . Comparator  60  may output a value based at least in part on the difference between the reference voltage of reference transistor  54  and supply voltage  62 . This value may be used in feedback loop  20  to adjust supply voltage  62 . 
         [0046]    In step  340 , the reference voltage of reference transistor  54  and supply voltage  62  are compared to determine if they are approximately equal. If they are approximately equal, then no adjustment needs to be done, as illustrated in step  350 . If the voltages are not approximately equal, then the method continues to step  360 . “Approximately equal” in this case refers to the voltages being within a range of one another that is acceptable for the desired operation of the system. This range may vary depending on the details of digital logic  12  or any other circuit being monitored. 
         [0047]    At step  360 , the reference voltage of reference transistor  54  and supply voltage  62  are compared to determine which is greater. If the reference voltage is greater, the temperature of the circuit must have decreased, and supply voltage  62  can be increased in step  370  so that the speed and drive current of the transistors in digital logic  12  may also increase. This increase in supply voltage  62  can help to counter the effect of the decreased temperature, providing a more consistent performance for the transistors in digital logic  12  across a range of temperatures. 
         [0048]    If the reference voltage of reference transistor  54  is lower than supply voltage  62 , the temperature of the circuit must have increased, and supply voltage  62  can be decreased in step  380  to also decrease the speed and drive current of the transistors in digital logic  12 . This can prevent excess power consumption by the transistors. It can also prevent forward biasing of one or more transistors in digital logic  12 . It also may allow for more consistent performance of the transistors when the temperature increases. 
         [0049]    The output of comparator  60  may be used as an input in feedback loop  20  that continually adjusts supply voltage  62  until it approximately matches the voltage of reference transistor  54 . As the reference voltage of reference transistor  54  increases, supply voltage  62  can be increased. As the reference voltage of reference transistor  54  decreases, supply voltage  62  can be decreased. Steps  310 - 380  can be continually performed in a loop so that supply voltage  62  can be adaptively adjusted to any changes in temperature. The adjustments to supply voltage  62  can be made at any suitable time intervals. 
         [0050]    Although the present disclosure has been described with several embodiments, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present disclosure encompass such changes, variations, alterations, transformations, and modifications as fall within the scope of the appended claims.