Patent Publication Number: US-2022236119-A1

Title: Calibration and temperature sensing on integrated chrcuit chip

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to temperature sensing in an integrated circuit (IC) chip. More specifically, the present invention relates to calibration of a temperature sensor on an IC chip. 
     BACKGROUND OF THE INVENTION 
     Temperature has a significant impact on electronic devices. It can affect both the system performance and the expected life of such electronic devices. Furthermore, issues related to temperature can increase with the increasingly dense circuitry and reductions in package size. As such, measuring the temperature within an electronic device or system can allow an electronic device or system to compensate for the effects of temperature and/or to mitigate issues related to overheating of a device. Thus, many electronic devices and systems include one or more temperature sensors incorporated therein to quantify the temperature of the surrounding environment. Integrated temperature sensors based on CMOS technology have been developed to fulfill the function of temperature sensing in small devices in which area and power consumption are limited. 
     SUMMARY 
     Aspects of the disclosure are defined in the accompanying claims. 
     In a first aspect, there is provided An integrated circuit (IC) chip comprising a first temperature sensor of a first type and a second temperature sensor of a second type that differs from the first type, wherein the first temperature sensor is configured to be utilized to calibrate the second temperature sensor and the second temperature sensor is configured to be utilized for temperature sensing following calibration. 
     In a second aspect, there is provided a method implemented in an integrated circuit (IC) chip, the IC chip including a first temperature sensor of a first type and a second temperature sensor of a second type that differs from the first type, the method comprising calibrating the second temperature sensor utilizing the first temperature sensor and following the calibrating operation, sensing a temperature of the IC chip utilizing the second temperature sensor. 
     In a third aspect, there is provided an integrated circuit (IC) chip comprising a first temperature sensor of a first type characterized by a first operational voltage and a second temperature sensor of a second type that differs from the first type, the second type being characterized by a second operational voltage that is less than the first operational voltage, wherein the first temperature sensor is configured to be utilized to calibrate the second temperature sensor, the first temperature sensor is configured to be powered off following calibration, and the second temperature sensor is configured to be utilized for temperature sensing following calibration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying figures in which like reference numerals refer to identical or functionally similar elements throughout the separate views, the figures are not necessarily drawn to scale, and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention. 
         FIG. 1  shows a block diagram of an integrated circuit (IC) chip in accordance with an embodiment; 
         FIG. 2  shows a block diagram of an integrated circuit (IC) chip in accordance with another embodiment; 
         FIG. 3  shows a flowchart of a temperature sensing process implemented in connection with either of the IC chips of  FIGS. 1 and 2  in accordance with another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In overview, the present disclosure concerns integrated circuit (IC) chips having temperature sensors included therein and methodology for calibration and temperature sensing utilizing the temperature sensors. More particularly, an IC chip includes two temperature sensors of differing types. A first temperature sensor of one type is utilized to calibrate the second temperature sensor of another type. Following calibration, the first temperature sensor may be powered off and the second temperature sensor is utilized for temperature sensing. In some embodiments, the first temperature sensor may be a bipolar junction transistor-based (BJT-based) temperature sensor configured to undergo voltage calibration, and in other embodiments, the first temperature sensor may be a high accuracy thermal-diffusivity-based temperature sensor. The second temperature sensor utilized for temperature sensing may be any of a variety of temperature sensors suited for ultra-low-voltage operation. Thus, an accurate temperature sensor that may have a relatively high power consumption may be utilized to calibrate a lower-power temperature sensor. In some embodiments, calibration may be performed in a tester and in other embodiments, calibration may be performed as a background process during operation of the IC chip. In either instance, calibration accuracy may be increased and/or test time may be significantly decreased for improved efficiency and cost savings. 
     The instant disclosure is provided to explain in an enabling fashion at least one embodiment in accordance with the present invention. The disclosure is further offered to enhance an understanding and appreciation for the inventive principles and advantages thereof, rather than to limit in any manner the invention. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued. 
     Much of the inventive functionality and many of the inventive principles are best implemented with or in integrated circuits (ICs) including possibly application specific ICs or ICs with integrated processing or control or other structures. It is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such ICs and structures with minimal experimentation. Therefore, in the interest of brevity and minimization of any risk of obscuring the principles and concepts according to the present invention, further discussion of such structures and ICs, if any, will be limited to the essentials with respect to the principles and concepts of the various embodiments. 
     It should be understood that the use of relational terms, if any, such as first and second, top and bottom, and the like are used solely to distinguish one from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. 
     Temperature sensors often include a sensor that produces temperature dependent voltages and an analog-to-digital converter (ADC) that converts a ratio of the temperature dependent voltages to a digital output. During the integrated circuit (IC) fabrication process of a temperature sensor, process inconsistencies may occur that cause variability in the device parameters of the sensor (referred to as process spread) or plastic packaging may increase mechanical stress on the sensor&#39;s die and also cause variability, referred to as packaging shift. Such variability affects the initial inaccuracy of an uncalibrated temperature sensor, which may be as great as ±2.0° C. at room temperature. However, in a number of applications, requirements call for these temperature sensors to be calibrated to achieve better accuracy, for example, better than ±1.0° C. 
     The calibration of temperature sensors is nontrivial, especially in an industrial manufacturing process. One conventional approach includes using thermal calibration to trim the temperature sensor, which usually requires comparing a reading of the sensor with a reading of a reference thermometer of known accuracy at the same temperature as the sensor, and then adjusting a trim value. This approach usually requires bringing the sensor (or a batch of sensors) and the thermometer into good thermal contact using a thermally-conducting medium, such as a metal block (e.g., chuck) or a liquid bath, where a thermal equilibrium may be obtained after a minutes-long wait time. For example, achieving a stable temperature may require the sensors to be in an oven for minutes at a time, increasing calibration costs in both time and money. Additionally, due to thermal inertia, thermal calibration may also introduce error as large as, for example, several degrees Celsius because of poor heat distribution on the thermally-conducting medium (e.g., chuck). Performing additional trimming operations at different temperatures requires an even longer wait time and additional infrastructure, which further complicates the trimming operations. Accordingly, there are significant challenges in accurately applying heat and accurately measuring the temperature during a thermal calibration process. 
     Embodiments discussed in connection with  FIGS. 1 and 2  include IC chips that include two temperature sensors of differing types located in close proximity to one another. As will be discussed in significantly greater detail below, a first temperature sensor is utilized to calibrate a second temperature sensor without performing a thermal calibration process. Following calibration, the first temperature sensor can be powered off and the second temperature sensor can be utilized for temperature sensing. An embodiment discussed in connection with  FIG. 3  provides calibration methodology for calibrating the second temperature sensor of either of the IC chips of  FIGS. 1 and 2 , as well as temperature sensing in an operational mode utilizing the second temperature sensor. 
     Referring to  FIG. 1 ,  FIG. 1  shows a block diagram of an integrated circuit (IC) chip  100  in accordance with an embodiment. IC chip  100  includes a first temperature sensor  102  (labeled TS 1 ), a second temperature  104  (labeled TS 2 ), a processing element  106  electrically connected to each of the first and second temperatures sensors  102 ,  104 , and a memory element  108  associated with processing element  106 . IC chip  100  may be a stand-alone temperature sensing IC chip that may be incorporated at a suitable location within a larger electronic device or system (not shown). Alternatively, the elements of IC chip  100  may be incorporated into a packaged electronic device that further includes any suitable variety of active and/or passive components, as represented by a block  110 , for performing a function. Temperature sensing may be useful in any type of circuit that generates significant heat, such as a radar transceiver, a microcontroller, and so forth. The temperature information can be used to compensate for a temperature coefficient, to send out a warning when the temperature has crossed a certain threshold, and so forth. 
     In accordance with an embodiment, first temperature sensor  102  is utilized to calibrate second temperature sensor  104 . Following calibration, first temperature sensor  102  may be powered off and second temperature sensor  104  is utilized for temperature sensing. First and second temperature sensors  102 ,  104  may be physically close to one another in IC chip  100 . By way of example, first temperature sensor  102  is at a first location  112  within IC chip  100  and second temperature sensor  104  is at a second location  114  within IC chip  100  in which first and second locations  112 ,  114  are physically close enough to one another such that an ambient temperature at each of first and second locations  112 ,  114  is generally equivalent. The closer that first and second temperature sensors  102 ,  104  are to one another (e.g., within 1 mm of one another), the greater the probability that they are experiencing the same environmental temperature. Alternatively, since a silicon substrate is a good thermal conductor, a larger distance may be acceptable if other circuits within IC chip  100  are shut down during calibration so that they do not cause a temperature gradient. Regardless, it can be assumed that the same temperature would be sensed at respective first and second temperature sensors  102 ,  104  which is useful during calibration. 
     First and second temperature sensors  102 ,  104  operate under different principles, referred to herein as types. In accordance with some embodiments, first temperature sensor  102  may be a sensor of a first type, such as a bipolar junction transistor-based (BJT-based) temperature sensor. First temperature sensor  102  may therefore be referred to herein as BJT-based temperature sensor  102 . Second temperature sensor  104  may be a sensor of a second type that is suited for ultra-low-voltage (e.g., less than 1V) operation. Such temperature sensors can be, for example, resistor-based, capacitor-based, DTMOS-based (dynamic threshold metal oxide semiconductor-based), thermal-diffusivity-based, or another principle or type. Second temperature sensor  104  may generally be referred to herein as sensing temperature sensor  104  since it may be any of a variety of types of temperature sensors and, regardless of the type, is utilized for sensing temperature within IC chip  100  during normal operational use. 
     BJT-based temperature sensors are often used in electronic equipment because they can be included in a silicon integrated circuit (IC) at a relatively low cost. The principle of the sensor is that the forward voltage of a silicon diode, which may be the base-emitter junction of a bipolar junction transistor (BJT), is temperature dependent. A BJT-based temperature sensor is biased by a current source, and the voltage between its base and emitter (V BE ) is given as follows: 
     
       
         
           
             
               
                 
                   
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     where k is the Boltzman Constant, T is the absolute temperature, q is the electron charge, Ic is the bias current and Is is the saturation constant, with the saturation constant being strongly process-dependent. 
     V BE  is a non-linear function of temperature. Furthermore, process spread may cause larger errors in V BE  due to variations in Ic and Is. Therefore, V BE  is not suitable as a sensing signal. To eliminate the process error, the difference between the two voltages between base and emitter (V BE s) is determined. This difference, ΔV BE , is given by: 
     
       
         
           
             
               
                 
                   
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     As a result, the process-dependent saturation constant, Is, is canceled out and ΔV BE  can be determined by the ratio of the two currents, which can be made quite accurate. Ideally, ΔV BE  is proportional to the absolute temperature (PTAT). A BJT-based temperature sensor, can be calibrated utilizing a voltage calibration process instead of a thermal calibration process. Voltage calibration entails applying an accurate external reference voltage (in lieu of V BE ) and determining the value of ΔV BE  based on digital output of the BJT-based temperature sensor. In voltage calibration, the difference between the two V BE  voltages (e.g., ΔV BE ) can be made very accurate and can be used to measure the temperature of a die during calibration. As will be discussed in greater detail below, in  FIG. 1 , an external reference voltage  116 , labeled V REF , may be applied via a tester  118  during a voltage calibration process in order to calibrate BJT-based temperature sensor  102 . 
     A voltage calibration technique has a number of advantages. For example, in a single temperature trim, the ΔV BE  can be used to determine the temperature of IC chip  100  to be calibrated. Therefore, no externally applied temperature needs to be provided by a heater. Accordingly, voltage calibration speeds up the calibration process by orders of magnitude, thereby saving in calibration costs. Furthermore, since the ΔV BE  can be read per chip, heat distribution on the chuck becomes irrelevant as it will be calibrated out. 
     However, BJT-based temperature sensors may not be suitable for ultra-low-voltage operations because V BE  can be as high as 900 millivolts at temperatures lower than −40° C., thereby limiting their application in advanced technology nodes. That is, BJT-based temperature sensor  102  my be characterized by an operational voltage that is greater than the operational voltage of sensing temperature sensor  104 . On the other hand, alternative temperature sensors, such as sensing temperature sensor  104 , that rely on other sensing techniques may be implemented in applications calling for ultra-low-voltage operations and can have suitable accuracy. Unfortunately, calibration of those temperature sensors, such as sensing temperature sensor  104 , is limited to thermal calibration. 
     In accordance with some embodiments, BJT-based temperature sensor  102  is combined with sensing temperature sensor  104  of a different type to effectively enable voltage calibration for temperature sensors (such as to second temperature sensor  104 ) that are more suitable for ultra-low-voltage operations. During voltage calibration (discussed in greater detail in connection with  FIG. 3 ), reference voltage  116  is provided to BJT-based temperature sensor  102 . Reference voltage  116  is compared to ΔV BE  of BJT-based temperature sensor  102 , which is subsequently translated into a first current temperature  120  (labeled TEMP 1 ) of IC chip  100  by BJT-based temperature sensor  102 . First current temperature  120  is an accurate estimation of the temperature of IC chip  100 . Immediately thereafter, sensing temperature sensor  104  will measure a second current temperature  122  (labeled TEMP 2 ) of IC chip  100 . The difference of the two measurement results from BJT-based temperature sensor  102  and sensing temperature sensor  104  (e.g., the difference between first and second current temperatures  120 ,  122 ) can be used as information to calibrate sensing temperature sensor  104 . In an example, the difference may be used to determine calibration parameters  124 , or trim values, for sensing temperature second  104  that may be stored, for example, in memory element  108 . These calibration parameters  124  can then be communicated to sensing temperature sensor  104 . 
     Following calibration, BJT-based temperature sensor  102  can be powered down and with calibration parameters  124  applied, temperature sensing of IC chip  100  utilizing sensing temperature sensor  104  can be performed. That is, sensing temperature sensor  104  can thereafter output a calibrated output temperature  126  (labeled TEMP OUT ) that accurately represents the current temperature of IC chip  100  at second location  114  or at a location at which IC chip  100  is positioned within a larger system. 
     The inclusion of BJT-based temperature sensor  102  within IC chip  100  is advantageous for calibrating sensing temperature sensor  104  since voltage calibration can be performed in lieu of a thermal calibration process. Thus, voltage calibration can be performed in the absence of a temperature-controlled environment and an external temperature reference, thereby yielding calibration time savings, power savings, and potential inaccuracies due to the application of heat and poor heat distribution. More particularly and in accordance with the above described embodiment, BJT-based temperature sensor  102  can be utilized to enable voltage calibration for temperature sensors (e.g., sensing temperature sensor  104 ) that do not support voltage calibration. However, voltage calibration using BJT-based temperature sensor  102  calls for external reference voltage  116  provided by tester  118  during, for example, final test of IC chip  100  to yield high accuracy calibration. As such, sensing temperature sensor  104  cannot be calibrated during operational use of IC chip  100 . 
     Some configurations may call for periodic recalibration during operational use of the sensing temperature sensor or sensors. Besides accuracy, a temperature sensor&#39;s size and power consumption, and its ability to operate at a low supply voltage may also be important. A BJT-based temperature sensor is typically the most accurate type of on-chip temperature sensor. However, a BJT-based temperature sensor is relatively large, has moderate instead of low power consumption, and is not suited for low supply voltage operation. 
     Referring now to  FIG. 2 ,  FIG. 2  shows a block diagram of an integrated circuit (IC) chip  200  in accordance with another embodiment. IC chip  100  includes a first temperature sensor  202  (labeled TS 1 ), a second temperature  204  (labeled TS 2 ), a processing element  206  electrically connected to each of the first and second temperatures sensors  202 ,  204 , and a memory element  208  associated with processing element  206 . In some embodiments, IC chip  200  may include additional temperature sensors, as demonstrated by a third temperature sensor  210 . Like IC chip  100  ( FIG. 1 ), IC chip  200  may be a stand-alone temperature sensing IC chip that may be incorporated at a suitable location within a larger electronic device or system (not shown). Alternatively, the elements of IC chip  200  may be incorporated into a packaged electronic device that further includes any suitable variety of active and/or passive components, as represented by a block  214 , for performing a function. 
     In accordance with the illustrated an embodiment, first temperature sensor  202  is utilized to calibrate both of second and third temperature sensors  204 ,  210 . Following calibration, first temperature sensor  202  may be powered off and second and third temperature sensors  204 ,  210  may be utilized for temperature sensing. First, second, and third temperature sensors  202 ,  204 ,  210  may be physically close to one another in IC chip  200 . By way of example, first temperature sensor  202  is at a first location  216  within IC chip  200 , second temperature sensor  204  is at a second location  218  within IC chip  200 , and third temperature sensor  210  is at a third location  220  within IC chip  200  in which first, second, and third locations  216 ,  218 ,  220  are physically close enough to one another such that an ambient temperature at each of first, second, and third locations  216 ,  218 ,  220  is generally equivalent. Alternatively, first, second, and third temperature sensors  202 ,  204 ,  210  may be located relatively far apart from one another to monitor hotspots scattered at different places, as will be discussed in greater detail below. 
     First temperature sensor  202  operates under a different principle from second and third temperature sensors  204 ,  210 . That is, first temperature sensor  202  may be a sensor of a first type, such as a thermal-diffusivity-based temperature sensor. As such, first temperature sensor may therefore be referred to herein as thermal-diffusivity-based temperature sensor  202 . Second and third temperature sensors  204 ,  210  may be sensor of a second type that is suited for ultra-low-voltage (e.g., less than 1V) operation. Resistor-based temperature sensors may be an advantageous option for second and third temperature sensors  204 ,  210  since they make use of the same type of readout circuit as does thermal-diffusivity-based temperature sensor  202 . Further, both thermal-diffusivity-based temperature sensors and resistor-based temperature sensors can work with ultra-low supply voltages making them well suited for advance technology nodes. Nevertheless, other temperature sensor types may alternatively be used for second and third temperature sensors  204 ,  210  such as capacitor-based, DTMOS-based (dynamic threshold metal oxide semiconductor-based), a BJT-based temperature sensor (in lieu of voltage calibration) or another principle or type. Second and third temperature sensors  204 ,  210  may generally be referred to herein as sensing temperature sensors  204 ,  210  since they may be any of a variety of types of temperature sensors and, regardless of the type, they are utilized for sensing temperature within IC chip  200  during normal operational use. 
     Temperature sensors based on measuring thermal diffusivity of silicon to measure the temperature (e.g., thermal-diffusivity-based temperature sensor  202 ) can achieve acceptable accuracy without the need for individual calibration because the thermal diffusivity of silicon is a very weak function of process variation. However, a thermal-diffusivity-based temperature sensor typically includes an integrated heater (e.g., heater  222 ). Unfortunately, thermal-diffusivity-based temperature sensors are not prevalent for temperature sensing in low power chips and systems because the power consumed by the integrated heater (e.g., heater  222 ) results in an undesirably high power consumption by the thermal-diffusivity-based temperature sensor. Duty-cycling a thermal-diffusivity-based temperature sensor can help reduce the average power dissipation. However, a consequence is a reduction in the update speed of the temperature sensor. 
     In accordance with the embodiment of  FIG. 2 , background calibration may be implemented in temperature sensors without utilizing a tester (e.g., tester  118 ). In particular, thermal-diffusivity-based temperature sensor  202  may be used as an on-chip reference temperature sensor to calibrate one or more low-power temperature sensors, e.g., sensing temperature sensors  204 ,  210 . Furthermore, both thermal-diffusivity-based temperature sensors and, for example, resistor-based temperature sensors have a very small silicon footprint, thereby making the combination of both very appealing. In an example, a thermal-diffusivity-based temperature sensor may be approximately 1650 mm 2 , while a resistor-based temperature sensor may be approximately 5800 mm 2 . 
     Background calibration may be performed by executing a calibration algorithm  212  stored in memory  208 . During calibration, a first current temperature  224  (labeled TEMP 1 ) of IC chip  200  is measured by thermal-diffusivity-based temperature sensor  202 . First current temperature  224  is an accurate estimation of the temperature of IC chip  200 . Immediately thereafter, sensing temperature sensor  204  can measure a second current temperature  226  (labeled TEMP 2 ) of IC chip  200  and sensing temperature sensor  210  will measure a third current temperature  228  (labeled TEMP 3 ). The difference of the two measurement results from thermal-diffusivity-based temperature sensor  202  and sensing temperature sensor  204  (e.g., the difference between first and second current temperatures  224 ,  226 ) can be used as information to calibrate sensing temperature sensor  204 . In an example, the difference may be used to determine calibration parameters  230 , or trim values, for sensing temperature sensor  204  that may be stored, for example, in memory element  208 . These calibration parameters  230  can then be communicated to sensing temperature sensor  204 . Similarly, the difference of the two measurement results from thermal-diffusivity-based temperature sensor  202  and sensing temperature sensor  210  (e.g., the difference between first and third current temperatures  224 ,  228 ) can be used as information to calibrate sensing temperature sensor  210 . In an example, the difference may be used to determine calibration parameters  232 , or trim values, for sensing temperature sensor  210  that may be stored, for example, in memory element  208 . These calibration parameters  232  can then be communicated to sensing temperature sensor  210 . 
     Following calibration, thermal-diffusivity-based temperature sensor  202  can be powered down and with calibration parameters  230 ,  232  applied, temperature sensing of IC chip  200  utilizing sensing temperature sensors  204 ,  210  can be performed. That is, sensing temperature sensor  204  can thereafter output a calibrated output temperature  234  (labeled TEMP OUT1 ) that accurately represents the current temperature of IC chip  200  at second location  218  or a location at which IC chip  200  is positioned within a larger system. Likewise, sensing temperature sensor  210  can thereafter output a calibrated output temperature  236  (labeled TEMP OUT2 ) that accurately represents the current temperature of IC chip  200  at third location  220  or a location at which IC chip  200  is positioned within a larger system. 
     The inclusion of thermal-diffusivity-based temperature sensor  202  within IC chip  200  may be advantageous for calibrating sensing temperature sensors  204 ,  210  since thermal-diffusivity-based temperature sensor  202  does not need to be individually calibrated by an external tester to be accurate and no heat needs to be provided by an external heater to calibrate thermal-diffusivity-based temperature sensor  202 . Thus, thermal-diffusivity-based temperature sensor  202  can be used as an on-chip reference temperature sensor so that an external tester is not required. As such, background calibration can be performed efficiently and from time to time, for instance each time IC chip  200  starts up. Thermal-diffusivity-based temperature sensor  202  may be used only during the background calibration process to obtain the instantaneous temperature of IC chip  200  for the purpose of calibrating sensing temperature sensors  204 ,  210 . After background calibration and during normal operation, thermal-diffusivity-based temperature sensor  202  can be powered down to save power. Still further, both types of temperature sensors can be made extremely small so that the area impact of combining multiple sensors of varying types is not significant. 
     In some embodiments, a combined sensor may be limited to a one to one relationship, such as one thermal-diffusivity-based temperature sensor and one sensing temperature sensor. However, a combined sensor does not need to be limited to a one to one relationship. As shown in the example above, one accurate thermal-diffusivity-based temperature sensor (e.g., thermal-diffusivity-based temperature sensor  202 ) can be combined with one or multiple small sensing temperature sensors (e.g., sensing temperature sensors  204 ,  210 ) across a large IC chip or system to monitor for hotspots. In such a situation, calibration may be performed under conditions in which the temperature over the IC chip can still be considered to be the same, such as for instance during IC chip startup or in a tester. 
       FIG. 3  shows a flowchart of a temperature sensing process  300  implemented in connection with either of IC chips  100 ,  200  ( FIGS. 1 and 2 ) in accordance with another embodiment. For simplicity, temperature sensing process  300  collectively describes both calibration of the sensing temperature sensors as well as sensing during normal or operational use. Calibration may be performed as a background process during operational use, as mentioned above in connection with IC chip  200  ( FIG. 2 ). Alternatively, calibration may be performed as a process that is separate from sensing, as mentioned above in connection with IC chip  100  ( FIG. 1 ). For example, calibration may be performed during final test prior to the IC chip being placed in an intended operational environment. 
     At a block  302 , the sensing temperature sensors are calibrated utilizing the first temperature sensor. In the embodiment of  FIG. 1 , first current temperature  120  is determined in response to voltage calibration of BJT-based temperature sensor  102 , second current temperature  122  is determined by measurement at sensing temperature sensor  104 , and a difference (DIFF) of first and second current temperatures  120 ,  122  is determined. Thereafter, calibration parameters  124  may be determined from the difference and calibration parameters  124  are applied to sensing temperature sensor  104 . In the embodiment of  FIG. 2 , first current temperature  224  is determined by direction measurement via thermal-diffusivity-based temperature sensor  202 , second current temperature  226  is determined by measurement at sensing temperature sensor  204 , and a difference of first and second current temperatures  224 ,  226  is determined. Thereafter, calibration parameters  230  may be determined from the difference and calibration parameters  230  are applied to sensing temperature sensor  204 . In a configuration that includes additional sensing temperature sensors, the additional sensing temperature sensors may also be calibrated using thermal-diffusivity-based temperature sensor  202 . In this example, third current temperature  228  is determined by measurement at sensing temperature sensor  210  and a difference of first and third current temperatures  224 ,  228  is determined. Thereafter, calibration parameters  232  may be determined from the difference and calibration parameters  232  are applied to sensing temperature sensor  210 . 
     Process  300  continues with a query block  304 . At query block  304 , a determination is made as to whether calibration is complete. When calibration is not complete, process control may loop back to block  302  to repeat calibration. However, when a determination is made at query block  304  that calibration is complete, process control continues with a block  306 . 
     At block  306 , the first temperature sensor (e.g., BJT-based temperature sensor  102 ,  FIG. 1 , or thermal-diffusivity-based temperature sensor  204 ,  FIG. 2 ) is powered off. Accordingly, power savings can be achieved. At a block  308 , the IC chip (e.g., first or second IC chip  100 ,  200 ) is placed in operational mode. That is, the associated sensing temperature sensor(s) is/are utilized to sense temperature at a location within their associated IC chip. 
     At a query block  310 , a determination is made as to whether the IC chip is to continue in the operational mode. When the operational mode is to continue, process control may proceed with a query block  312 . 
     At query block  312 , a determination is made as to whether the calibration process is to be repeated. When the calibration process is not to be repeated (e.g., the configuration of  FIG. 1 ), process control loops back to block  308  to remain in the operational mode. However, as discussed above, the configuration of  FIG. 2  can allow for background calibration while IC chip  200  is in the operational mode. Hence, if a determination is made at query block  312  that calibration is to be repeated, process control continues at a block  314 . At block  314 , the first temperature sensor (e.g., thermal-diffusivity-based temperature sensor  204 ,  FIG. 2 ) is powered on. Thereafter, process control loops back to block  302  to calibrate sensing temperature sensors  204 ,  210  during a background calibration process. 
     Returning to query block  310 , the operational mode of the IC chip (IC chip  100  or IC chip  200 ) may be discontinued when, for example, the IC chip is powered down or otherwise signaled to terminate temperature sensing. When the operational mode is to be discontinued, execution of temperature sensing process  300  ends. 
     Thus, execution of the temperature sensing process described herein enables utilization of a first temperature sensor of one type integrated into an IC chip to accurately calibrate a second temperature sensor of another type that is also integrated into the IC chip. Thereafter, the second temperature sensor can be utilized for temperature sensing. It should be understood that certain ones of the process blocks depicted in  FIG. 3  may be performed in parallel with each other or with performing other processes. In addition, the particular ordering of the process blocks depicted in  FIG. 3  may be modified while achieving substantially the same result. Accordingly, such modifications are intended to be included within the scope of the inventive subject matter. 
     Embodiments described herein entail integrated circuit (IC) chips having temperature sensors included therein and methodology for calibration and temperature sensing utilizing the temperature sensors. More particularly, an IC chip includes two temperature sensors of differing types. A first temperature sensor of one type is utilized to calibrate the second temperature sensor of another type. Following calibration, the first temperature sensor may be powered off and the second temperature sensor is utilized for temperature sensing. In some embodiments, the first temperature sensor may be a bipolar junction transistor-based (BJT-based) temperature sensor configured to undergo voltage calibration, and in other embodiments, the first temperature sensor may be a high accuracy thermal-diffusivity-based temperature sensor. The second temperature sensor utilized for temperature sensing may be any of a variety of temperature sensors suited for ultra-low-voltage operation. Thus, an accurate temperature sensor that may have a relatively high power consumption may be utilized to calibrate a lower-power temperature sensor. In some embodiments, calibration may be performed in a tester and in other embodiments, calibration may be performed as a background process during operation of the IC chip. In either instance, calibration accuracy may be increased and/or test time may be significantly decreased for improved efficiency and cost savings. 
     This disclosure is intended to explain how to fashion and use various embodiments in accordance with the invention rather than to limit the true, intended, and fair scope and spirit thereof. The foregoing description is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The embodiment(s) was chosen and described to provide the best illustration of the principles of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims, as may be amended during the pendency of this application for patent, and all equivalents thereof, when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.