Abstract:
Integrated circuit with junction temperature sensing diode. An integrated circuit with temperature sensing capabilities is disclosed. The integrated circuit includes a substrate for containing circuitry on the surface thereof. At least one section of the circuitry on the surface of the substrate is operable, during a normal operating mode, to raise the surface temperature of the substrate. A sensing element is disposed within the at least one section for sensing temperature varying parameters that vary as a function of temperature. accessing circuitry then is operable for accessing the sensing element during a test mode for output of the sensed temperature varying parameters by the sensing element

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention pertains in general to systems for determining the operating temperature of a die in an integrated circuit package and, more particularly, to the use of a diode sensing device incorporated within the integrated circuit die for sensing temperature.  
         BACKGROUND OF THE INVENTION  
         [0002]    In systems utilizing integrated circuits, the operating temperature of the system has seen increasing attention due to the fact that a number of these integrated circuits operate at fairly high current levels, thus resulting in high die temperatures in the integrated circuit. Typically, these integrated circuits are singled out and heat sinks associated therewith, such as, for example, a CPU that has a heat sink with mini-fans associated therewith. In addition, there is provided a power supply fan and, to an increasing extent, extra ventilating fans for the case.  
           [0003]    As the die temperatures increase, the operating characteristics of the parts of the integrated circuit can be impeded, as well as there being a potential for a decrease in the useful life of the integrated circuit. A problem exists when dealing with fairly dense digital integrated circuits with a relatively high clock speed in that die temperature can be excessively high in certain regions. However, present ventilation/heat sink/cooling techniques may not be sufficient to maintain the die temperature for a particular integrated circuit at a sufficiently low enough temperature. The problem is that the die temperature is difficult to ascertain on these circuits without some complex modeling techniques that not only involve the integrated circuit, but also must consider the mounting PC boards, the enclosure, the surrounding integrated circuits, etc. There are some systems that actually provide for measurement of the package temperature. However, these types of systems have inaccuracies due to the thermal characteristics of the surrounding materials in the package. There are also some on-chip temperature measuring devices such as those associated with band-gap generators, that are used to measure ambient temperature. These systems actually measure the die temperature which is assumed to be substantially equal to the ambient temperature due primarily to the fact that these are very low power applications.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention disclosed and claimed herein, in one aspect thereof, comprises an integrated circuit with temperature sensing capabilities. The integrated circuit includes a substrate for containing circuitry on the surface thereof. At least one section of the circuitry on the surface of the substrate is operable, during a normal operating mode, to raise the surface temperature of the substrate. A sensing element is disposed within the at least one section for sensing temperature varying parameters that vary as a function of temperature. Accessing circuitry then is operable for accessing the sensing element during a test mode for output of the sensed temperature varying parameters by the sensing element.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying Drawings in which:  
         [0006]    [0006]FIG. 1 illustrates a diagrammatic view of an integrated circuit board containing a plurality of integrated circuits in a case;  
         [0007]    [0007]FIG. 2 illustrates a cross sectional view of an integrated circuit;  
         [0008]    [0008]FIG. 3 illustrates a top view of the integrated circuit of FIG. 2;  
         [0009]    [0009]FIG. 4 illustrates a side view of the integrated circuit of FIG. 3 with its temperature profile;  
         [0010]    [0010]FIG. 5 illustrates a schematic of the current source in the series with the temperature sensing diode;  
         [0011]    [0011]FIG. 5A illustrates a curve of voltage vs. temperature in ambient atmosphere for the diode of FIG. 5;  
         [0012]    [0012]FIG. 6 illustrates a perspective view of the diode incorporated in a sensing section;  
         [0013]    [0013]FIG. 7 illustrates a diagram of the test mode for an embodied temperature sensing diode;  
         [0014]    FIGS.  8 - 10  illustrate alternate embodiments of FIG. 7;  
         [0015]    [0015]FIG. 11 illustrates a diagrammatic view of the embodied diode within the sense section with a control section illustrated;  
         [0016]    [0016]FIG. 12 illustrates an alternate embodiment where multiple temperature sensing diodes are provided for;  
         [0017]    [0017]FIG. 13 illustrates a flow chart for the diode calibration operation; and  
         [0018]    [0018]FIG. 14 illustrates a flow chart for the measurement operation.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    Referring now to FIG. 1, there is illustrated a diagrammatic view of a computer case  102  having contained therein a PC board  104  with integrated circuits  106  disposed thereon. At least one of these integrated circuits  106  has contained therein the sensing device of the present disclosure. The case  102  has associated therewith a cooling fan  108 , which cooling fan  108  is operable to draw air through the case  102 . This is for the purpose of maintaining a low ambient temperature. It is desirable that the ambient temperature be maintained at such a level that the operating temperature on the die of any of the integrated circuits  106  is maintained below a maximum operating temperature for that die. However, depending upon how the integrated circuit  106  is mounted on the board  104  and the location within the case  102  can be determinative of how well the integrated circuit  106  is cooled. As such, the temperature of the ambient air will not necessarily be a valid representation of the actual die temperature.  
         [0020]    Referring now to FIG. 2, there is illustrated a cross sectional view of the integrated circuit  106 . The integrated circuit  106  is representative of any type of integrated circuit and typically includes a die  202  that is adhered to some type of substrate  204  associated with the package with a die attach layer  206 . This die attach layer  206  can be any type of attachment which is well known in the industry. The package will have a plurality of leads  208  that provide for mounting onto the board  104 , these leads shown with a conventional “pin.” However, various other types of attachment techniques can be utilized such as solder balls for “flip-chip” applications. With leads, the pads associated with input/output functions of the integrated circuit on the die  202  will need to be connected to the pins  208 . This will utilize bonding wires  210 . Disposed on the die  202  and integral with the integrated circuit is a sensing device  212  that is operable to determine the temperature on the surface of the die at a particular location on that die.  
         [0021]    The integrated circuit  106  with the die  202  disposed thereon will typically, in some applications, be encapsulated within some type of resin encapsulation  222 . Once the package is encapsulated in this instantiation, the thermal transfer characteristics of the materials surrounding the die  202  will greatly affect how heat is removed from the die  202 . Current, of course, is input to the device through one of the terminals and the bond wire and then dissipated within the die across the surface thereof. However, in present integrated circuits, there are many circuit “modules” or “sections” that require different levels of power. As such, one section of the die may have a different temperature profile than others due to the concentration of power therein and the thermal resistance in the horizontal direction extending outwards therefrom. This high power portion will, of course, result in the highest localized die temperature. This heat that is generated on the die at any particular location thereon, is pulled away from the die  202  through either the package at die attach layer  206 , through the bonding wires or through the encapsulated materials from the top of the die  202 . Since packages can take many forms, it can be appreciated that thermal transfer characteristics between the surface of the die  202  and the exterior of the package will vary greatly.  
         [0022]    Referring now to FIG. 3, there is illustrated a top view of the integrated circuit die  202  with a plurality of integrated circuit sections defined thereon. These are for exemplary purposes only, and it should be understood that any type of integrated circuit can be utilized. The reason to provide the different sections is that some sections will have significantly higher power consumption than others and, therefore, localized die temperature in that section will tend to be higher, such applications being those associated with circuitry having digital and analog sections on the same integrated circuit. One such application is a high speed Ethernet chip. One reason for the localized temperature of one section being higher than others is due to the fact that, as the size of the conventional die increases and the circuit density increases with high clocking rates, the lateral dissipation of heat is insufficient to adequately distribute heat across the integrated circuit which will result in localized temperature increases. There are illustrated four integrated circuit sections  302 ,  304 ,  306  and  308  on the die  202 , each have a different functionality associated therewith. For example, some of the sections may be associated primarily with analog functions, some with I/O functions and some with low power digital functions. However, the section  308 , for this example, is one that is associated with relatively high power circuitry that requires substantially more current to operate than the other sections and is also associated with fairly dense circuitry. As such, the surface temperature will be fairly high from a localized standpoint, as compared to the other sections. Of course, there could be other sections will relatively high power associated therewith also.  
         [0023]    The sensing device  212  is disposed within the circuitry  308  at a particular point. This point can be determined from actual measurements. However, it will in this embodiment be disposed within the substantial center at the most dense portion of the circuitry where the temperature would be expected to be highest. This sensing circuit  212  is connected through leads  310  to a test control circuit  312  which interfaces with two test control pins  314  and  316 . During tests, as will be described in more detail hereinbelow, this sensing device  212  is calibrated with the power consumption in the section  308  reduced to a minimal and insignificant level. In this manner, the output of the sensing device  212  can be measured as a function of the ambient temperature to generate a plot of voltage output vs. temperature. Thereafter, when the section  308  is fully powered and operational, the voltage output of the sensing device  212  can be measured in a test mode to provide a voltage output that is compared to the plot to determine the temperature of the die of the section  308  as opposed to the temperature of the package or the ambient temperature.  
         [0024]    Referring now to FIG. 4, there is illustrated a side view of an integrated circuit die  402  that illustrates on the surface thereof four integrated circuit sections  404 ,  406 ,  408  and  410 . A temperature profile is illustrated across the surface of the die  402  when it is operating. This profile illustrates that the section  408  has a substantially higher temperature than the other sections  404 ,  406  and  410 . As such, the temperature sensing device  410  is disposed in a select portion of the section  408 . By examining the output of this temperature sensing device  410 , the maximum operating temperature of the die can be determined, it being recognized that it is assumed that the highest temperature on the die in any localized region will be in substantially the region that the sensing device  410  is disposed.  
         [0025]    Referring now to FIG. 5, there is illustrated a schematic diagram of the sensing device  410 , which is substantially the same sensing device  212 . The sensing device  410  is a diode  502  which is oriented such that it will have a constant current applied thereto with a current source  504  that is disposed between the positive supply V DD  and the anode of diode  502 , the cathode of diode  502  connected to ground. This will result in a diode current I D  flowing through the diode  502 . The diode has the following relationship:  
         KT   q          ln   (     I     I   o       )                           
 
         [0026]    where K=Boltzmann&#39;s constant  
         [0027]    I O =a current constant  
         [0028]    The temperature coefficient for the diode  502  is approximately −2.5 mV/C. As such, measuring the voltage across the diode for a 10° C. difference in temperature will only require being able to resolve a 25 mV voltage difference. In FIG. 5A, it can be seen that measurement of the diode  502  in an ambient atmosphere would result in a curve of voltage vs. temperature that decreases as temperature increases. As will be described hereinbelow, the diode  502  is calibrated after the design has been implemented in a test mode. In this test mode, the primary power consuming circuitry is powered down and then the voltage across the PN junction of diode  502  measured as a function of temperature in a test oven. This will basically comprise the combination of the current source  504  and diode  502 . When the device is powered up at a later time, it is only necessary to measure the voltage and then correlate this voltage with the appropriate temperature which is known from the calibration curve.  
         [0029]    The current source  504  can be realized with a number of different configurations which, in this embodiment, is one that is fabricated on the semiconductor substrate with the other circuitry. One such embodiment utilizes a temperature independent voltage source to drive a temperature independent resistor to provide a temperature independent current. This can then be mirrored to provide the current to the diode  504 . The temperature independent voltage source can be realized with an on-chip band gap generator and the temperature independent resistor can be an external resistor that is disposed at the ambient temperature.  
         [0030]    Referring now to FIG. 6, there is illustrated a perspective view of the integrated circuit die  402  and the section  408  in which the sensing device  410  is disposed. The sensing device  410 , as described hereinabove with respect to FIG. 5, comprises the diode  502 . The diode  502  in the standard cell is inserted into the integrated circuit section  408  and at a predetermined location. In the present embodiment, the section  408  is comprised of a digital section in a circuit such as an Ethernet integrated circuit. These Ethernet integrated circuits operate in the 10 Megabit mode, the 100 Megabit mode and the 1 Gigabit mode. In the 1 Gigabit mode, the power consumption is the highest, due to the processing required in the digital section and the high clocking rate. It is at this level that the surface temperatures are of most concern. Therefore, there will exist in such a circuit a digital section or digital “route” which will generate the most heat due to power consumption. The diode  502  is placed in substantially the center of this section and leads run out from the diode  502  external to the section  408  to provide access to the diode  502  to allow measurement of the junction thereof.  
         [0031]    Referring now to FIGS.  7 - 10 , there are illustrated diagrammatic views of various embodiments of how the test mode is configured. With specific reference to FIG. 7, the integrated circuit section  408  is referred to as a “sense section.” The diode  502  has an anode  702  that is connected through a line  704  to the current source  504 . The cathode of the diode  502  is connected to a node  705  and to a line  706  that extends out of the sense section  408  and is connected to ground. In the embodiment of FIG. 7, the ground connection is illustrated as occurring outside of the sense section  408 . However, it should be understood that the diode  502  could be connected such that the node  705  is connected to ground within the sense section or at any place on the circuit where an adequate ground connection can be facilitated. It is only important that the node  705  be connected to a run that can be accessed for measuring the voltage across the diode  502 .  
         [0032]    Line  704  is connected to one side of a switch  710 , the other side thereof connected to an external terminal  712  in the integrated circuit. The line  706  connected to node  705  on the cathode of the diode  502  is connected to one side of a switch  714 , the other side thereof connected to an external terminal  716  on the integrated circuit. There is illustrated a box  718  around the switches  710  and  714 , this illustrated as a test mode box. This receives a test mode signal which is operable to connect the nodes  702  and  705  to the terminals  712  and  716  such that the voltage across the diode  502  can be measured in that mode.  
         [0033]    Referring now to FIG. 8, there is illustrated an alternate embodiment wherein the current source  504  is contained within the sense section  408  and the ground connection is also contained within the sense section  408 . As noted hereinabove, it should be understood that the current source  504  can be contained within the sense section  408  where it can be external thereto. Typically, it would be outside of this sense section due to the temperature variation associated with the higher temperature in the sense section  408 .  
         [0034]    Referring now to FIG. 9, there is illustrated an alternate embodiment of the embodiment of FIG. 7. In this embodiment, an external current source  902  is utilized that is connected to the external terminal  712  outside of the integrated circuit and a ground is connected to terminal  716  such that current is provided external to the integrated circuit, run through the pass through diode  502  and brought back out through terminal  716 . Of course, the diode  502  would be calibrated in this method also.  
         [0035]    Referring now to FIG. 10, there is illustrated an alternate embodiment to the embodiment of FIG. 7. In the embodiment of FIG. 10, the voltage across the nodes  702  and  705  of the diode  702  is measured by inputting the voltage on line  704  to the input of an analog-to-digital converter (A/D)  1002 . This allows the conversion of the analog voltage to a digital voltage for processing by a onboard microcontroller unit (MCU)  1004 . The MCU  1004  provides an internal voltage measurement and the calibration information that is derived during a calibration mode, wherein the sense section  408  is disabled and the voltage across the diode  502  measured. This is compared to a known temperature which is derived by the MCU  1004  utilizing an on-chip temperature sensor  1006 . This temperature sensor  1006  can be realized with circuitry such as a band gap reference generator. This band gap reference generator, when operating in a low power mode and a corresponding low temperature mode, i.e., wherein high power sections of the circuitry are disabled, can determine the temperature of the die which is substantially at the ambient temperature during operation. Therefore, the MCU  1004  with use of the temperature sensor  1006  will have information as to the ambient temperature. This is utilized to create a calibration table for storage in a calibration storage area  1008 . This is facilitated by placing the integrated circuit in an oven and cycling the temperature. As the temperature cycles, the MCU  1004  can take periodic measurements at predefined temperature increments. Since the high power section is disabled, the temperature measured is that of the ambient air. During normal operation with the high powered section powered and dissipating heat, the MCU  1004  can utilize this calibration information and the information from the A/D converter  1002  to determine the temperature of the chip proximate the high powered section. This can be used for various purposes.  
         [0036]    Referring now to FIG. 11, there is illustrated a more detailed diagram of the overall control of the test mode. The line  704  is input to one input of a multiplexer  1102 , the other input thereof connected to an internal pin function, and the output of multiplexer  1102  connected to terminal  716 . The multiplexer  1102  is operable to, in normal operation, utilize the terminal  712  for a predefined function. This predefined function is utilized except in the measurement or test mode wherein the line  704  is selected. Similarly, line  706  is input to one input of a multiplexer  1104 , the other input thereof connected to another internal pin function which is utilized in the normal operating mode. Multiplexers  1102  and  1104  are controlled by a control block  1106  which control section  1106  is operable to control the multiplexers  1102  when operating in the test mode. The control section has two modes of operation. The first mode is on where the system is calibrated and the second is one where it is merely tested in normal operation. In a calibration mode, the multiplexers  1102  and  1104  are set to select lines  704  and  706  to measure the voltage across the diode  502 . In the calibration mode, the control section  1106  is operable to disable the operation of the sense section  408 . This disabling operation can occur in a number of ways. Some digital circuitry can be powered down by forcing a predetermined condition thereto or the clock signal that runs the section  408  can be disabled. A power switch can also be provided for disconnecting power from the particular sense section  408 . Any type of system that will result in powering down the sense section  408  can be utilized. The control section  1106  is typically disposed outside of the sense section  408 . Therefore, a user need only write information to a test register  1110 , which test register is operable to set the control section to the appropriate mode. Although not shown, other circuitry on the integrated circuit will allow reading and writing of the test register.  
         [0037]    Referring now to FIG. 12, there is illustrated a diagrammatic view wherein the integrated circuit die has three sections  1202 ,  1204  and  1206  disposed thereon. All of these sections can have a separate sense diode  1208 ,  1210  and  1212 , respectively, disposed at predetermined locations therein. Each of the diodes  1208 - 1212  have associated therewith current sources (not shown) with voltage lines  1214  disposed thereacross and input to a multiplexer  1216 . The multiplexer  1216  is operable to select between one of three sets of the lines  1214  to measure the voltage across the associated diodes  1208 - 1212 . This multiplexer  1216  is controlled by a control block  1220 . The multiplexer  1216  is operable to provide outputs to the external terminals  712  and  716 , as described hereinabove. In general, the embodiment of FIG. 12 allows for more than one sense node to be disposed on an integrated circuit for the purpose of taking different readings at different locations.  
         [0038]    In the embodiment of FIG. 12, the current source is connected to the output of the multiplexer  1216  associated with the terminal  712  and a ground connection is associated with the output of the multiplexer  1216  that is connected to the terminal  716 . As such, whenever the multiplexer selects one of the sets of lines  1214  associated with the diodes  1208 ,  1210  or  1212 , current will be passed therethrough. This therefore allows a user to create a thermal profile of a chip. In some situations, it is desirable to have knowledge of localized heating at different areas on the chip. These can be one or two areas or any number of areas.  
         [0039]    Referring now to FIG. 13, there is illustrated a flowchart depicting the operation of profiling the diode. During manufacturing of a new part, the actual thermal profile of the part is difficult to model. However, if a thermal profile could be taken of the chip, this profile would be a fairly repeatable profile over all production parts. The problem is that this temperature profile is a relative temperature profile that is relative to the base temperature of the substrate, the type of heat sink that the package is disposed on, etc. Thus, having an on-chip temperature sensor will provide information as to the localized temperature.  
         [0040]    The program is initiated at a block  1302  and then proceeds to a block  1304  wherein the test mode is set in a register on-chip. Once this mode of operation is entered, the section to be sensed is disabled, as indicated by a function block  1306  such that the sensed section operates at a relatively low power level and the temperature profile of the chip is fairly flat. Of course, although the sense section is the section of interest, there may be other sections that also generate heat. These sections will also be disabled if necessary to ensure that there is substantially no heat generated by the part that cannot be extracted therefrom by the chip merely being mounted in a test socket, i.e., the temperature is fairly flat over the entire chip area and it is at substantially ambient temperature. The program then flows to a function block  1308  wherein the sense diode is connected to the test terminal. However, it should be understood that dedicated test terminals could be provided that would always be connected across the sense diode. The program then flows to a function block  1310  wherein a test is performed at ambient, i.e., room temperature. The program then flows to a function block  1312 , which consists of placing the test integrated circuit into an oven and then cycling the temperature thereof to measure the voltage across the sense diode at predefined increments of temperature. The program then flows to a function block  1314  wherein the diode is profiled over this temperature cycle and then to a decision block  1316  to determine if the profiling is done, i.e., if it has been cycled through all the desired temperatures. If not, the program proceeds along the “N” path back to the input of function block  1312 . When complete, the program will flow along the “Y” path to a function block  1318  to store the profile.  
         [0041]    Referring now to FIG. 14, there is illustrated a flowchart depicting a measurement mode. This is initiated at a block  1402  and then proceeds to a function block  1404  to set the system in the temperature measurement mode. In this mode, the chip operates as normal and the particular sense section is not disabled. As such, the temperature sensing diode will be disposed at the localized temperature of the sense section. The program will proceed to a function block  1406  to connect the sense diode to the test terminals, it being noted again that the anode and cathode of the sense diode could be connected to the terminal at all times. The program then flows to a function block  1408  to measure the sense diode voltage and then to a function block  1410  to compare the measured voltage to the stored profile. A determination can then be made as to the temperature of the surface proximate the sense diode, as indicated by function block  1412 . The program then proceeds to a Done block  1414 .  
         [0042]    Although the preferred embodiment has been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.