FUNCTIONAL AMPLIFIER F`VOUT
Contents
1. US005376819A United States Patent n9 11 Patent Number 5 376 819 Gay et al 45 Date of Patent Dec 27 1994 54 INTEGRATED CIRCUIT HAVING AN ON CHIP THERMAL CIRCUIT REQUIRING OTHER PUBLICATIONS ONLY ONE DEDICATED INTEGRATED MC88110 Second Generation RISC Microprocessor CIRCUIT PIN AND METHOD OF User s Manual Motorola Inc Dec 1991 pp 11 6 OPERATION i 11 8 11 17 75 Inventors James G Gay Pflugerville William Primary Examiner Ngan V Ngo p Ledbetter Jr Austin both of Attorney Agent or Firm Robert L King ex 57 ABSTRACT 73 Assignee Motorola Inc Schaumburg Ill 21 Appl No 158 323 An integrated circuit implements an on chip thermal No i circuit 12 for measuring temperature of an operating 22 Filed Nov 29 1993 integrated circuit die 10 by requiring only one dedi cated integrated circuit pin 16 A second integrated a a p KE Al BE rer circuit pin 18 is utilized but is also connected directly KE ol EE E Sal hol an 6 connected to ather sireyifrv 14 on he Integrated cir 58 Field of Search 257 467 776 777 Suit and is used by the other circuitry at the same time 338 22 that the integrated circuit die temperature is being mea sured In one form the second integrated circuit pin is 56 References Cited a ground terminal Error voltages coupled to the U S PATENT DOCUMENTS ground terminal may be removed from the temperature 5 140 394 8 1992 Co2. that the output voltage of operational amplifier 37 is Vereferenced to the ground potential The output volt age Vout may therefore be represented as Vout R2 RD VG Va 2 where R1 is the resistance of each of resistors 33 and 39 and R2 is the resistance of each of resistors 35 and 43 As can be seen from equation 2 the ground bounce noise is totally subtracted from the output voltage as a result of the subtraction of Vz from Vg In other words each of the Vr and VG voltages is referenced to ground and noise bounce which is injected into the ground is therefore neutralized and invisible to the final output voltage provided by differential amplifier 24 It should be noted that many integrated circuits have scores of circuit pins in which there is more than one ground reference terminal pin Any ground reference terminal may be used to implement the present inven tion but it is preferable to connect differential amplifier 24 to the same ground pin which the die thermal sensing circuit 18 is connected to If other ground pins are con nected to differential amplifier 24 than the ground pin which die thermal sensing circuit 18 is connected to inductance and other electrical properties may create differential voltage potentials between the various ground circuit pins when the integrated circuit is opera tional The present invention may alternately be used with out the assistance of external differential amplifier 24 and consta
3. as a packaged integrated circuit for purposes of illustrating the present invention integrated circuit die 10 should be considered as a fully encapsu lated die in a completed integrated circuit chip Inte grated circuit die 10 generally has a die thermal sensing circuit 12 a functional operating circuit 14 a first inte grated circuit pin 16 and a second integrated circuit pin 18 Also illustrated is a constant current source 20 and a differential amplifier 24 In the illustrated form die thermal sensing circuit 12 is implemented as a resistor having a first terminal con nected to first integrated circuit pin 16 and having a second terminal connected to second integrated circuit pin 18 In the illustrated form the second integrated circuit pin 18 is a ground reference pin of integrated circuit die 10 Functional operating circuit 14 has a terminal connected directly to the second integrated circuit pin 18 thereby making the second integrated circuit pin a common integrated circuit pin which is common to both the die thermal sensing circuit 12 and the functional operating circuit 14 A constant current source 20 has a first terminal connected to a power supply voltage such as V pp and has a second terminal connected to both the first integrated circuit pin 16 and 5 376 819 3 a first input of differential amplifier 24 A second input of differential amplifier 24 is connected to the second integrated circuit pin 18 An output of di
4. circuit pin the integrated circuit comprising a die a first integrated circuit pin which is dedicated solely for use with the on chip thermal circuit a second integrated circuit pin an integrated circuit die thermal sensing circuit lo cated on the die and directly connected to the first integrated circuit pin and to the second integrated circuit pin the integrated circuit die thermal sens ing circuit comprising a material which has a physi cal characteristic which varies in a manner propor tional to variation of temperature of the material and a functional operating circuit also located on the die and connected directly to the second integrated circuit pin the functional operating circuit per forming a predetermined operating function within the integrated circuit at the same time the inte grated circuit die thermal sensing circuit is provid ing an output signal which indicates an operating temperature of the die said second integrated circuit pin being used by both the integrated circuit die thermal sensing circuit and the functional operating circuit 2 The integrated circuit of claim 1 wherein the inte grated circuit die thermal sensing circuit is a resistor 3 The integrated circuit of claim 2 wherein the resis tor is made of metal 4 The integrated circuit of claim 1 wherein the sec ond integrated circuit pin is a fixed voltage potential terminal 5 The integrated circuit of claim 4 wherein the fixed
5. of die thermal sensing circuit 12 other than a resistor Further pins other than the illustrated ground pin which can function as the common inte grated circuit pin 18 between the die thermal sensing circuit 12 and other operating circuitry may be used For example any fixed voltage potential integrated circuit pin may be used to implement the function of the common integrated circuit pin 18 It should also be 5 376 819 10 20 65 6 noted that any type of circuitry whether digital or analog and regardless of process type may be used as the functional circuitry which is connected to the com mon integrated circuit pin 18 Another point which should be noted is that the present invention may be implemented by establishing a fixed voltage across the die thermal sensing circuit 12 and measuring the current thru die thermal sensing circuit 12 which is proportional to die temperature Although the present invention has been disclosed in the context of a specific differential amplifier structure other types of differential amplifiers may be used Those skilled in the art will recognize that modifications and variations can be made without de parting from the spirit of the invention Therefore it is intended that this invention encompass all such varia tions and modifications as fall within the scope of the appended claims We claim 1 An integrated circuit having an on chip thermal circuit requiring only one dedicated integrated
6. second inte grated circuit pin The integrated circuit die thermal sensing circuit comprises a material which has a physi cal characteristic which varies in a manner proportional to variation of temperature of the material A functional operating circuit is located on the die and is connected directly to the second integrated circuit pin The func tional operating circuit performs a predetermined oper ating function within the integrated circuit at the same time the integrated circuit die thermal sensing circuit provides an output signal which indicates an operating temperature of the die The second integrated circuit pin is used by both the integrated circuit die thermal sensing circuit and the functional operating circuit These and other features and advantages will be more clearly understood from the following detailed description taken in conjunction with the accompany ing drawings It is important to point out that there may be other embodiments of the present invention which are not specifically illustrated BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 illustrates in block diagram form an on chip die thermal sensing circuit in accordance with the pres ent invention and FIG 2 illustrates in partial schematic form the differ ential amplifier of FIG 1 DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Illustrated in FIG 1 is an integrated circuit die 10 in accordance with the present invention Although not fully illustrated
7. the integrated circuit die is the MC88110 reduced instruction set microprocessor The temperature of the integrated circuit having an on chip resistor is measured by using a current source reference and forcing a known current thru the known resistance of the on chip resistor A resulting voltage across the two dedicated integrated circuit pins is then measured The resulting voltage is proportional to the temperature of the operating integrated circuit In other words as the temperature of the operating integrated circuit die varies the resistance varies proportionately which results in a proportional change in voltage mea sured across the two dedicated integrated circuit pins The two dedicated integrated circuit pins are required in order to isolate internally generated noise and other circuit parameters from the two integrated circuit pins Any voltage current resistance or impedance which is coupled to the two integrated circuit pins from internal to the integrated circuit will modify the voltage poten tial between the two integrated circuit pins and result in an incorrect temperature measurement However the price of two dedicated integrated circuit pins to imple ment a measurement function is costly even in the most advanced very large scale integrated circuits Another type of integrated circuit which uses a plu rality of resistors connected between the integrated circuit s external pins is a resistor network integrated circui
8. a first integrated circuit pin which is dedicated solely for use in measuring a temperature of the inte grated circuit die when the integrated circuit is receiving electrical power a second integrated circuit pin a thermal sensing circuit integrated in the integrated circuit die the thermal sensing circuit having a first terminal directly connected to the first integrated circuit pin and having a second terminal directly connected to the second integrated circuit pin and circuitry connected directly to the second integrated circuit pin the circuitry being operational and utilizing the second integrated circuit pin concur rently while the first and second integrated circuit pins are used to provide a signal which is propor tional to the temperature of the integrated circuit die 12 The integrated circuit of claim 11 wherein the thermal sensing circuit is a resistor made of a material consisting of one of polysilicon and metal 13 The integrated circuit of claim 11 further com prising a constant current source external to the integrated circuit for providing a reference current to the first integrated circuit pin and a differential amplifier external to the integrated cir cuit and connected to the first and second inte grated circuit pins the differential amplifier remov ing a common mode error component from a volt age differential between the first and second inte grated circuit pins 14 The integrated circuit of cla
9. aries in a manner propor tional to variation of temperature of the material directly connecting a functional operating circuit integrated in the integrated circuit die to the sec ond integrated circuit pin the functional operating circuit performing a predetermined operating func tion within the integrated circuit and concurrent with the functional operating circuit per forming the predetermined operating function providing an output signal between the first inte grated circuit pin and the second integrated circuit which is mathematically proportional to the oper ating temperature of the die 8 The method of claim 7 wherein the step of connect ing an integrated circuit die thermal sensing circuit further comprises connecting a resistor directly to the first and second integrated circuit pins 9 The method of claim 7 wherein the step of select ing a second integrated circuit pin further comprises selecting a fixed voltage potential pin of the inte grated circuit as the second integrated circuit pin 10 The method of claim 7 further comprising the step of removing a common mode noise error from the out put signal before translating the output signal from an electrical value to a temperature value 5 10 15 20 25 30 40 45 50 55 65 8 11 An integrated circuit having an on chip integrated circuit die thermal circuit the integrated circuit com prising an integrated circuit die
10. bb Hl et al mm 257 467 Calculation by an external differential amplifier 24 5 141 334 8 1992 Castles 257 467 5 230 564 7 1993 Bartilson et al 257 467 14 Claims 1 Drawing Sheet DIFFERENTIAL FUNCTIONAL AMPLIFIER Vout OPERATING CIRCUIT 14 U S Patent Dec 27 1994 5 376 819 DIFFERENTIAL FUNCTIONAL i AMPLIFIER f gt Vout PERATING CIRCUIT p FIG 2 14 24 FIG 1 5 376 819 1 INTEGRATED CIRCUIT HAVING AN ON CHIP THERMAL CIRCUIT REQUIRING ONLY ONE DEDICATED INTEGRATED CIRCUIT PIN AND METHOD OF OPERATION FIELD OF THE INVENTION The present invention generally relates to integrated circuits and more particularly to the monitoring of thermal characteristics of an operating integrated cir cuit BACKGROUND OF THE INVENTION An important operating characteristic of an inte grated circuit is the temperature of the integrated cir cuit s die when the integrated circuit is fully powered and in a normal operating mode of operation Such a temperature measurement is often desired at a final package test when the integrated circuit is in the same form as will be used by an end user To satisfy this need others have used an on chip resistor connected to two dedicated external pins of the integrated circuit The external pins have no other function than to implement the temperature measurement function An example of an integrated circuit having two dedicated pins for temperature measurement of
11. fferential am plifier 24 provides an output voltage Vout which is referenced to a ground reference terminal and is pro portional to temperature In operation an operating temperature of integrated circuit die 10 may be accurately measured while circuit die 10 is fully operational Further this function only requires one dedicated integrated circuit pin the first integrated circuit pin because the second integrated circuit pin is used concurrently by the functional oper ating circuit 14 Functional operating circuit 14 per forms a predetermined operating function within the integrated circuit 10 at the same time the present inven tion is utilized to determine the die operating tempera ture Examples of the functionality of operating circuit 14 might include an execution unit digital logic cir cuitry address translation circuitry a memory etc In one form the die thermal sensing circuit 12 is imple mented as a resistor If a metal resistor is utilized a resistor may be formed which is susceptible to average temperature changes of the integrated circuit die 10 and which provides a temperature coefficient of approxi mately 1 2 Ohms degree Centigrade It should be well understood that other materials such as polysilicon for example may be used to implement die thermal sensing circuit 12 As constant current source 20 provides a constant reference current to integrated circuit die 10 a small predetermined voltage is developed acro
12. ground terminal from the functional operating circuit 14 can be substantial caus ing the ground potential to actually rise above zero volts Such an operating condition would therefore create an error voltage between the first integrated circuit pin 16 and the second integrated circuit pin 18 The error voltage is known in the art by the term ground bounce 10 20 25 30 35 45 50 55 60 65 4 The present invention however can still be utilized even when ground bounce errors exist The voltage variation across the resistance of die thermal sensing circuit 12 attributable to ground bounce is common mode with respect to the ground bounce voltage varja tion at the common or second integrated circuit pin 18 Recognizing that the voltage variation due to ground bounce error which occurs across die thermal sensing circuit 12 is common mode makes it possible to elimi nate the ground bounce error and thereby use only one dedicated integrated circuit pin for the die thermal sensing Differential amplifier 24 may be used to sub tract the common mode ground bounce noise from the output voltage between integrated circuit pins 16 and 18 Differential amplifier 24 therefore recovers a pure voltage which is proportional to the resistance of die thermal sensing circuit 12 In other words differential amplifier 24 removes a common mode error component from a voltage differential between the first and second integrated circui
13. im 11 further com prising circuitry connected to the first and second integrated circuit pins the circuitry removing a common mode noise error from the signal which is propot tional to the temperature of the integrated circuit before translating the signal from an electrical value to a temperature value
14. nt current source 20 For example the resis tance of die thermal sensing circuit 12 of integrated circuit die 10 may be measured at room temperature between integrated circuit pins 16 and 18 before the integrated circuit is powered up Then the integrated circuit may be powered up and is operational for a sufficient amount of time to allow the die to achieve a characteristic operating die temperature The power should then be disconnected from the integrated circuit and another resistance measurement of the die thermal sensing circuit 12 immediately made The differing re sistance values can be used in accordance with equation 1 to provide an average operating temperature of the integrated circuit In this technique ground bounce noise does not exist and is therefore irrelevant Thus it is apparent that there has been provided in accordance with the present invention an integrated circuit having an on chip thermal circuit requiring only one dedicated integrated circuit pin and a method of operating the unique integrated circuit An advantage of the present invention is the saving of an additional dedicated integrated circuit pin to provide a die temper ature when the die is powered up and operational Al though the invention has been described and illustrated with reference to specific embodiments thereof it is not intended that the invention be limited to these illustra tive embodiments For example one may utilize many different types
15. ss the resistance of die thermal sensing circuit 12 The resis tance of die thermal sensing circuit 12 is proportional to the temperature of the die in accordance with the fol lowing equation Resistance of circuit 12 Die Temp Temp Coefficient K 1 where the die temperature is in units of degrees Centi grade the temperature coefficient is in units of Ohms degree Centigrade and K is a minimum resistance in Ohms which circuit 12 has The temperature coefficient depends upon what material is selected as die thermal sensing circuit 12 but is conventionally known for a given temperature range As the die temperature changes so does the resistance of die thermal sensing circuit 12 An increase in die temperature causes an increase in the resistance of die thermal sensing circuit 12 and a decrease in die temperature causes a decrease in the resistance of die thermal sensing circuit 12 Since the current through the resistance of die thermal sens ing circuit 12 is constant the voltage which is devel oped across the resistance of die thermal sensing circuit 12 is also proportional to the temperature of the die In other words when the die temperature increases the voltage between the first integrated circuit pin 16 and the second integrated circuit pin 18 increases and vice versa In a highly integrated circuit such as a data processor for example the amount of electrical current normally channeled to or sunk by a
16. t However this type of integrated circuit func tions only to provide a user with a plurality of possible resistance values depending upon which pins of the integrated circuit are connected No other operating circuitry is typically implemented in such circuits Yet another known type of integrated circuit which provides a signal from which an operating die tempera ture may be derived utilizes a significant amount of dedicated internal circuitry such as an analog to digital A D circuit and a storage register to provide the signal at a single dedicated output pin of the integrated circuit The additional internal circuitry which is re quired to implement this temperature measurement function is often prohibitive in many large scale integra tion designs 10 15 20 25 30 35 40 45 50 60 65 2 SUMMARY OF THE INVENTION In accordance with one form of the invention there is provided an integrated circuit having an on chip ther mal circuit requiring only one dedicated integrated circuit pin and a method of implementing a single pin on chip thermal circuit in an integrated circuit The inte grated circuit comprises a die and a first integrated circuit pin which is dedicated solely for use with the on chip thermal circuit A second integrated circuit pin is also provided An integrated circuit die thermal sensing circuit is located on the die and directly connected to the first integrated circuit pin and to the
17. t pins Although two integrated circuit pins are utilized it should be noted that the common or second integrated circuit pin 18 is already present on the integrated circuit and is never taken out of operational use during the die thermal measuring process Ilustrated in FIG 2 is a detailed diagram of one form of a differential amplifier which may be used as differen tial amplifier 24 in connection with constant current source 20 and integrated circuit die 10 Elements in FIG 2 which are the same as elements in FIG 1 are identically numbered for clarification Differential am plifier 24 has a first operational amplifier 31 having a first noninverting positive input connected to inte grated circuit pin 16 As was illustrated in FIG 1 con stant current source 20 has the first terminal thereof connected to power supply voltage V ppand the second terminal thereof connected to integrated circuit pin 16 of integrated circuit die 10 A second inverting nega tive input of operational amplifier 31 is connected to an output thereof and to a first terminal of a resistor 33 A second terminal of resistor 33 is connected to a first terminal of a resistor 35 A second operational amplifier 37 has a first noninverting positive input connected to integrated circuit pin 18 which is a ground terminal on the integrated circuit package and therefore connected to ground A second inverting negative input of oper ational amplifier 31 is connected
18. to an output thereof and to a first terminal of a resistor 39 A second terminal of resistor 39 is connected to a first noninverting posi tive input of a third operational amplifier 41 and to a first terminal of a resistor 43 A second terminal of resistor 43 is connected to a ground reference terminal A second inverting negative input of operational amplifier 41 is connected to both the second terminal of resistor 33 and the first terminal of resistor 35 A second terminal of resistor 35 is connected to an output of operational amplifier 41 and provides the output volt age Vout In one form the three operational amplifiers may be obtained by using the commercially available integrated circuit LF347 from National Semiconductor Corporation which contains four operational amplifiers A fourth operational amplifier of an LF347 integrated circuit may be used as the constant current source 20 In operation operational amplifiers 31 and 37 are high impedance unity gain buffer stages which do not load integrated circuit pins 16 and 18 Operational am plifier 41 is configured as a differential amplifier and resistors 33 35 39 and 43 function to establish a gain of differential amplifier 24 For example assume that resis 5 tors 33 and 39 have the same resistance R1 and assume that resistors 35 and 43 have the same resistance R2 Further assume that the output voltage of operational amplifier 31 is Vg referenced to a ground potential and
19. voltage potential terminal is a ground reference termi nal 6 The integrated circuit of claim 4 further compris ing circuitry external to the integrated circuit and con nected to the first and second integrated circuit pins the circuitry measuring a voltage potential between the first integrated circuit pin and the second integrated circuit pin and removing any common mode voltage component coupled to the fixed voltage terminal to provide a voltage which is proportional to the operating temperature of the die 7 A method of measuring an operating temperature of an integrated circuit die of an integrated circuit re 5 376 819 7 sulting from the integrated circuit receiving electrical power comprising the steps of dedicating a single integrated circuit pin solely for use with the method of measuring the single inte grated circuit pin used as a first integrated circuit pin to measure the temperature selecting a second integrated circuit pin to use with the first integrated circuit pin the second inte grated circuit pin being used additionally as a func tional pin of the integrated circuit concurrent with measuring the temperature directly connecting a thermal sensing circuit which is integrated in the integrated circuit die to the first integrated circuit pin and to the second integrated circuit pin the integrated circuit die thermal sens ing circuit comprising a material which has a physi cal characteristic which v
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