Patent ID: 12209917

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The same elements have been designated with the same reference numerals in the different drawings. In particular, the structural and/or functional elements common to the different embodiments may be designated with the same reference numerals and may have identical structural, dimensional, and material properties.

For clarity, only those steps and elements which are useful to the understanding of the described embodiments have been shown and are detailed. In particular, the electronic circuits, particularly microcontrollers, where the described embodiments may be provided, have not been detailed, such embodiments being compatible with usual circuits.

Throughout the present disclosure, the term “connected” is used to designate a direct electrical connection between circuit elements with no intermediate elements other than conductors, whereas the term “coupled” is used to designate an electrical connection between circuit elements that may be direct, or may be via one or more intermediate elements.

In the following description, when reference is made to terms qualifying absolute positions, such as terms “front,” “back,” “top,” “bottom,” “left,” “right,” etc., or relative positions, such as terms “above,” “under,” “upper,” “lower,” etc., or to terms qualifying directions, such as terms “horizontal,” “vertical,” etc., unless otherwise specified, it is referred to the orientation of the drawings.

The terms “about,” “substantially,” and “approximately” are used herein to designate a tolerance of plus or minus 10%, preferably of plus or minus 5%, of the value in question.

In the rest of the description, when reference is made to a DC voltage, unless otherwise specified, this means a voltage having a substantially constant, preferably constant, value.

FIG.1schematically shows an embodiment of a device1of detection of at least one temperature, in this example, two temperatures.

Device1comprises a temperature sensor120that is a source of a detection voltage VT. Voltage VT varies substantially proportionally, preferably proportionally, to the temperature of device1. In the described example, the value of voltage VT increases as the temperature of device1increases. As a variation, the value of voltage VT decreases as the temperature of device1increases.

In an alternative embodiment, not illustrated, voltage source VT is external to device1, the source of voltage VT for example forming part of an electronic circuit comprising device1, for example, an integrated circuit such as a microcontroller.

Device1further comprises a circuit10receiving, between terminals101and102, a substantially constant, preferably constant, DC voltage VDD. Voltage VDD is for example positive and referenced to terminal102, for example, ground GND. Circuit10supplies, from power supply voltage VDD, N sets of DC voltages, N being an integer greater than 2, preferably greater than 3. Each set comprises a calibration voltage Vtrim-i, i being the index of the considered set in the range from 1 to N, and a voltage for each temperature which is desired to be detected, that is, in the present example, a voltage VS1-ito detect a temperature TS1and a voltage VS2-ito detect a temperature TS2, i being the index of the considered set. Voltages VS1-i, Vtrim-i, and VS2-ioutput by circuit10have substantially constant, preferably constant values, whatever the temperature of device1. As an example, circuit10is a resistive voltage dividing bridge.

In an alternative embodiment, not illustrated, circuit10is external to device1, circuit10for example forming part of an electronic circuit comprising device1, for example, an integrated circuit such as a microcontroller.

Voltages Vtrim-i have values different from one another. Preferably, voltages Vtrim-i follow an order, their values being either decreasing with index i as in the shown example, or increasing with index i. Voltages Vtrim-i are selected so that, at a calibration temperature Ttrim, two voltages Vtrim-i surrounding the real or practical value of voltage VT can be determined. When it is considered that two voltages selected from among the N voltages Vtrim-i surround voltage VT, this means that one of the two voltages is the closest to voltage VT among the voltages Vtrim-i greater than voltage VT, and that the other one of the two voltages is the voltage Vtrim-i closest to voltage VT from among the voltages Vtrim-i smaller than voltage VT. Voltages Vtrim-i are for example equal, to within a few millivolts, for example 10 mV, to the theoretical value of voltage VT at calibration temperature Ttrim. As an example, temperature Ttrim is in the range from 10 to 50° C., for example from 20 to 40° C., preferably from 25 to 35° C., more preferably still approximately equal to 30° C., for example, equal to 30° C. The interval between two successive voltages Vtrim-i is for example substantially constant, preferably constant.

In each set, a same substantially constant, preferably constant, voltage interval ΔV1separates voltages VS1-iand Vtrim-i of the set. Interval ΔV1is substantially equal, preferably equal, to the theoretical variation of voltage VT between calibration temperature Ttrim and temperature TS1. As an example, temperature TS1is greater than 100° C., for example, in the range from 100 to 150° C., preferably in the range from 120 to 130° C., for example, approximately equal to 125° C., preferably equal to 125° C. Temperature TS1is for example the high limit of a temperature range where an electronic circuit comprising device1is intended to operate.

Similarly, in each set, a same substantially constant, preferably constant, voltage interval ΔV2separates voltages VS2-iand Vtrim-i of the set. Interval ΔV2is substantially equal, preferably equal, to the theoretical variation of voltage VT between calibration temperature Ttrim and temperature TS2. As an example, temperature TS2is smaller than −20° C., preferably in the range from −25 to −35° C., for example, equal to approximately −30° C., preferably equal to −30° C. Temperature TS2is for example the low limit of a temperature range where an electronic circuit comprising device1is intended to operate.

Device1further comprises a circuit12of selection of a set of DC voltages from among the N sets of DC voltages. Circuit12comprises as many inputs121as there are voltages VS1-i(VS1-1, . . . , VS1-i, . . . , VS1-N), Vtrim-i (Vtrim-1, . . . , Vtrim-i, . . . , Vtrim-N), and VS2-i(VS2-1, . . . , VS2-i, . . . , VS2-N) output by circuit10, each input121receiving one of the voltages. Circuit12comprises as many outputs that there are voltages per set, that is, three outputs1221,1222, and1223in the present example. Circuit12also comprises an input123receiving a control signal TRIM, preferably a digital control signal, for example, coded over a plurality of bits. Circuit12is configured to select one of the N sets according to the value of signal TRIM and to supply voltages VS1-i, Vtrim-i, and VS2-iof the selected set on its respective outputs1221,1222, and1223.

In the shown example, circuit12comprises N switches125-i(with i varying from 1 to N), each switch125-icoupling the input121receiving voltage VS1-ito output1221. Circuit12also comprises N switches126-i(with i varying from 1 to N), each switch126-icoupling the input121receiving voltage Vtrim-i to output1222. Circuit12further comprises N switches127-i(with i varying from 1 to N), each switch127-icoupling the input121receiving voltage VS2-ito output1223. When signal TRIM controls the selection of the set having index i, switches125-i,126-iand127-iturn on, the other switches of circuit12being left off.

Device1also comprises a circuit13for selecting a threshold voltage Vcomp1from among voltages VS1-i, Vtrim-i, and VS2-iof the selected set, and more particularly, in the present embodiment, from among voltages VS1-iand Vtrim-i of the selected set. The selection of voltage Vcomp1from among these voltages is determined by a control signal MODE, preferably a digital control signal, for example, coded over a plurality of bits, received by an input131of circuit13.

In this example, inputs132and133of the circuit receive respective voltages VS1-iand Vtrim-i of the selected set, and an output134of circuit13supplies voltage Vcomp1. In the shown example, circuit13comprises two switches135coupling output134to respective inputs132and133. Switches135are controlled by signal MODE.

Threshold voltage Vcomp1is supplied to a voltage comparator C1of device1. Comparator C1compares voltage Vcomp1with voltage VT and supplies an output signal OUT1, preferably, a binary signal representative of this comparison, for example, in a first logic state when voltage VT is smaller than voltage Vcomp1, and in a second logic state otherwise. As an example, comparator C1is an operational amplifier having its inverting input (−) for example receiving voltage Vcomp1, and having its non-inverting input (+) for example receiving voltage VT.

In this example where device1is configured to detect two temperatures TS1and TS2, device1comprises another comparator C2. Comparator C2compares a threshold voltage Vcomp2with voltage VT and delivers an output signal OUT2, for example, a binary signal, representative of this comparison, for example, in a first logic state when voltage VT is smaller than voltage Vcomp2and in a second logic state otherwise. As an example, comparator C2is an operational amplifier having its inverting input (−) for example receiving voltage Vcomp2, and having its non-inverting input (+) for example receiving voltage VT.

In this embodiment, threshold voltage Vcomp2corresponds to the voltage VS2-iof the set selected by circuit12. In the shown example, voltage Vcomp2is supplied to comparator C2by an output136of circuit13, circuit13comprising an input137connected to output1223of circuit12and to output136of circuit13. As a variation, output1223of circuit12is directly connected to comparator C2, without using circuit13.

Device1described hereabove is capable of implementing a method of detecting temperatures TS1and TS2which will now be described in relation withFIG.2.

FIG.2shows, in the form of blocks, an embodiment of a temperature detection method. In the described example, the method is implemented by device1to detect temperatures TS1and TS2.

The method comprises calibration steps200,201, and202and steps203and204of detection of respective temperatures TS1and TS2.

At step200(block Device at Ttrim), device1is set to calibration temperature Ttrim. As an example, this step is carried out by means of a test bench enabling to control the temperature of an enclosure having device1placed therein, the temperature of the enclosure being then taken to and then maintained at calibration temperature Ttrim.

At the next step201(block Frame VT at Ttrim), carried out while the enclosure having device1arranged therein is maintained at temperature Ttrim, the two sets having their voltages Vtrim-i surrounding voltage VT at temperature Ttrim are determined. For this purpose, circuit13is controlled by signal MODE so that voltage Vcomp1is equal to voltage Vtrim-i received from circuit12. Further, circuit12is controlled by signal TRIM to successively select at least some, preferably all of, the N sets of voltages. Thus, for each selected set, output signal OUT1enables to determine whether the voltage Vtrim-i of this set is greater or smaller than the real or practical value of voltage VT at calibration temperature Ttrim. Knowing the values of voltages Vtrim-i, or at least the order of the values of voltages Vtrim-i, the two voltages Vtrim-i surrounding voltage VT at temperature Ttrim can be deduced. As an example, step201is implemented by determining the two voltages Vtrim-i of successive values corresponding to two different logic states of signal OUT1. As an example, information representative of the two voltages Vtrim-i surrounding voltage VT at temperature Ttrim is stored.

At the next step202(block Choose one set), one of the two sets determined at step201is selected. Signal TRIM corresponding to the selected set is stored, preferably non-volatilely.

The end of step202marks the end of the calibration. Once calibrated, device1is used to detect temperatures TS1and TS2, during respective steps203and204.

Step203(block Compare VS1-ito VT) following step202comprises comparing voltage VS1-iof the set selected at step202with voltage VT. For this purpose, circuit12selects the set selected at step202, for example, by supplying circuit12with the signal TRIM stored at step202, and circuit13is controlled by signal MODE so that voltage Vcomp1is equal to voltage VS1-iof the selected set. When the temperature of device1increases to reach and then exceed temperature TS1, voltage VT increases to reach and then exceed voltage Vcomp1, whereby signal OUT1switches state, which enables to detect temperature TS1.

In this example, the method further comprises step204(block Compare VS2-ito VT), which comprises comparing voltage VS2-iof the set selected at step202with voltage VT. In this embodiment, steps203and204are carried out simultaneously, that is, signals TRIM and MODE are identical for the two steps203and204. The comparison of voltage VS2-iof the set selected at voltage VT is here performed by comparator C2, the latter receiving voltage Vcomp2equal to voltage VS2-iof the selected set. When the temperature of device1decrease to reach and then become lower than temperature TS2, voltage VT decreases to reach and then become lower than voltage Vcomp2, whereby signal OUT2switches state, which enables to detect temperature TS2.

In the above method, the calibration enables to select a voltage Vtrim-i, and more generally of a set of voltages Vtrim-i, VS1-i, and VS2-i, taking into account the possible voltage offset of comparator C1and/or the possible offset between the theoretical and effective values of voltage VT. This results in a decrease, or even in a suppression, of the effect of such offsets on the detection of temperatures TS1and TS2, and thus in a better detection accuracy.

It could have been devised to perform, by means of a test bench, a calibration step at each of temperatures TS1and TS2to be detected, but this would however have resulted in an increase in the number of steps necessary to calibrate device1. Further, at the temperatures considered herein, a test bench provided for a temperature TS1or TS2is more complex and more expensive than a test bench provided for temperature Ttrim. Further, for the considered temperatures, the time necessary to obtain a stable temperature TS1or TS2in a test bench is significantly longer than that necessary to obtain a stable temperature Ttrim.

In an alternative embodiment of the method described hereabove, an additional step of testing the device implementing the method, and more particularly a step of testing the voltage comparators of the device, is provided. Two DC test voltages Vtest1and Vtest2, possibly selected from among respective voltages VS1-iand VS2-i, are then provided. One of voltages Vtest1and Vtest2, for example, voltage Vtest1, is selected to be greater than voltage VT at a test temperature, preferably the ambient temperature, the other one of voltages Vtest1and Vtest2being selected to be smaller than voltage VT at the test temperature, preferably with a security margin taking into account the possible interval between the theoretical and practical values of voltage VT at the test temperature and/or possible voltage offsets of the comparators. As an example, the security margin is in the range from 10 to 20 mV. According to a preferred embodiment, the calibration temperature is substantially equal to the test temperature and voltages Vtest1and Vtest2are respectively greater and smaller than voltages Vtrim-i, although, as a variation, they may be respectively greater and smaller than voltages Vtrim-i.

During a first phase of the test step implemented at the test temperature, one of the two voltages Vtest1and Vtest2is supplied to each comparator of the device. In a second phase of the test step, also implemented at the test temperature, the other one of voltages Vtest1and Vtest2is supplied to each comparator of the device. Each comparator is considered as functional if the output signal that it supplies switches state between the two test phases, the device being considered as functional if all the comparators are functional.

In another variation of the above-described method, an additional step of calibration of the device implementing the method is provided. Such an additional step is preferably carried out between steps200and201. This additional calibration step comprises applying, to all the DC voltages independent from temperature, a same determined offset to compensate for a possible interval between the inner temperature of the device and the temperature of the environment where it is placed during the calibration. Once determined, the offset is applied during the remaining calibration steps and during the temperature detection steps. This results in a better accuracy of the temperature detection. As an example, during this additional calibration step, the inner temperature of the device is measured, for example, by means of a temperature sensor, and the offset to be applied is for example selected to be substantially equal or equal to the theoretical variation of voltage VT between the calibration temperature Ttrim and the measured temperature.

The two above-described variations may be combined.

FIG.3shows an alternative embodiment of device1ofFIG.1. To simplify the description, only the differences between the device1ofFIG.1and the device1ofFIG.3are detailed. In this variation, device1is capable of implementing the alternative embodiment of the method ofFIG.2where an additional step of testing device1is provided.

In this example, voltages Vtest1and Vtest2are supplied by circuit10. In this embodiment, the calibration temperature is substantially equal to the ambient temperature and voltages Vtest1and Vtest2are respectively greater than and smaller than voltages Vtrim-i, although, as a variation, they may be respectively smaller and greater than voltages Vtrim-i.

Circuit13is configured to select voltages Vcomp1and Vcomp2from among voltages VS1-i, Vtrim-i, and VS2-iof the set selected by circuit12, and, further, from among voltages Vtest1and Vtest2. More particularly, when device1is being tested, circuit13is configured to select voltages Vcomp1and Vcomp2from among voltages Vtest1and Vtest2. Voltages Vcomp1and Vcomp2are for example equal to voltage Vtest1in the first phase of the test, and to voltage Vtest2in the second phase of the test. As a variation, voltages Vcomp1and Vcomp2may be different from each other during each of the first and second phases of the test.

In the example ofFIG.3, circuit13comprises two additional inputs1381and1382receiving respective voltages Vtest1and Vtest2. The circuit further comprises two switches1383and1384connecting output134to respective inputs1381and1382. The circuit further comprises switches1385,1386, and1387connecting output136to respective inputs1381,1382, and137. During the first test phase, one of switches1383and1384is on and one of switches1385and1386is on, the other switches of circuit13being left off, and, during the second test phase, the other one of switches1383and1384is on and the other one of switches1385and1386is on, the other switches of circuit13being left off. The off or on state of each switch of circuit13is determined by signal MODE, for example, at a first value during the calibration (steps200,201, and203,FIG.2), at a second value during the detection of temperatures TS1and TS2(steps203and204,FIG.2), at a third value during the first phase of the test step, and at a fourth value during the second phase of the test phase.

It should be noted that, in this example, on detection of temperature TS2(step204,FIG.2), switch1387is turned on while switches1385and1386are off so that voltage Vcomp2is equal to voltage VS2-iof the set selected by circuit12.

FIG.4shows another alternative embodiment of the device ofFIG.1. To simplify the description, only the differences between device1ofFIG.1and device1ofFIG.4are detailed. In this variation, device1is capable of implementing the alternative embodiment of the method ofFIG.2where an additional calibration step is provided.

Device1comprises a calibration device or circuit103, for example, internal to circuit10, controlled by a signal TRIM2, for example, received by an input104of circuit10. Device103is configured to apply, to all the voltages supplied by circuit10, a same offset to compensate for a possible interval between the inner temperature of device1and temperature Ttrim of the environment of device1during the calibration. In this example where circuit10is a resistive dividing bridge, circuit103is configured to modify the total resistance of dividing bridge10according to the signal TRIM2that it receives. As an example, circuit103comprises resistors R in series between terminal102and the portion of resistive bridge10supplying voltages Vtrim-i, VS1-i, and VS2-iand, for each connection node between two resistors R, between a resistor R and terminal102and/or between a resistor R and the rest of bridge10, a switch107coupling this node to terminal102. According to signal TRIM2, a selected switch107is maintained on, the other switches107being left off.

Device1further comprises a temperature sensor120. As a variation, the temperature sensor may be external to device1, for example, provided in an integrated circuit comprising device1. The value of the offset to be applied is determined from the output signal of the temperature sensor, this signal being representative of a measurement of the inner temperature of device1or of the integrated circuit comprising device1. Signal TRIM2is then determined so that circuit103applies this offset, or at least an offset substantially equal to the determined offset, to the voltages output by circuit10. Signal TRIM2thus determined is stored, preferably non-volatilely.

The alternative embodiments of the devices ofFIGS.3and4may be combined.

In another variation, not shown, the method ofFIG.2is provided to detect a single temperature TS1. In this case, step204is omitted. Further, device1ofFIGS.1,3, and4is accordingly adapted and comprises neither comparator C2, not any of the elements used to supply voltage Vcomp2to comparator C2.

FIG.5schematically shows another embodiment of a device5of detection of at least two temperatures, in the present example, the two temperatures TS1and TS2. To simplify the description, only the differences between device5and device1ofFIG.1are detailed.

In this embodiment, circuit10outputs an intermediate voltage Vint. Voltage Vint has a value smaller than the values of voltages VS1-iand greater than the values of voltages VS2-i. Voltage Vint is thus representative of an intermediate temperature Tint between temperatures TS1and TS2. In this example, voltage Vint is an additional voltage output by circuit10. As a variation, voltage Vint corresponds to one of voltages Vtrim-i.

In this embodiment, circuit13is configured to select voltage Vcomp1from among voltages Vtrim-i, VS1-i, and VS2iof the set selected by circuit12. More particularly, in the illustrated example, circuit13comprises a third switch135coupling its input137to its output134.

In this embodiment, voltage Vcomp2is equal to voltage Vint. In the shown example, voltage Vint is directly supplied to comparator C2. As a variation, voltage Vcomp2equal to Vint may be supplied to comparator C2via circuit13, for example, by an output of circuit13directly connected to an input of circuit13receiving voltage Vint.

In this embodiment, signal MODE is at least partly determined based on signal OUT2.

FIG.6shows, in the form of blocks, another embodiment of a method of detecting two temperatures, in this example, temperatures TS1and TS2. In the described example, the method is implemented by device5ofFIG.5.

The method comprises the same successive steps200,201, and202as the method described in relation withFIG.2. The method ofFIG.6also comprises steps203and204. However, unlike the method ofFIG.2where steps203and204are carried out simultaneously, in the method ofFIG.6, a single one of steps203and204is selected and implemented, according to the result of a test600(block Vint>VT?) following step202. In device5ofFIG.5, the test is implemented by comparator C2, signal OUT2being representative of the result of this test.

If voltage Vint is greater than voltage VT (output Yes of block600), this means that the temperature of device5is, like temperature TS2in the present example, smaller than intermediate temperature Tint, and step204is then implemented. To achieve this, signal MODE is determined based on signal OUT2so that voltage Vcomp1is equal to voltage VS2-iof the selected set. In other words, signal MODE is such that switch135connecting input137and output134of circuit13is on, the other switches135being off.

Conversely, if voltage Vint is smaller than voltage VT (output No of block600), this means that the temperature of device5is, like temperature TS1in the present example, greater than intermediate temperature Tint, and step203is then implemented. To achieve this, signal MODE is determined based on signal OUT2so that voltage Vcomp1is equal to voltage VS1-iof the selected set. In other words, signal MODE is such that switch135connecting input132and output134of circuit13is turned on, the other switches135being off.

As compared with device1where two different comparators C1and C2are used to compare voltage VT with the respective voltages VS1-iand VS2-iof the selected set, in device5, the same comparator C1is used to compare voltage VT with the two voltages VS1-iand VS2-i. Due to the fact that the calibration of the device (steps200,201, and203,FIG.2) takes into account the possible voltage offset of comparator C1, device5enables to detect temperature TS2more accurately than device1when comparators C1and C2have different voltage offsets.

The alternative embodiments of the method described in relation withFIG.2and their combination apply to the method ofFIG.6and the corresponding alternative embodiments of device1such as described in relation withFIGS.3and4can be transposed to device5ofFIG.5. For example, when the alternative embodiment ofFIG.3is applied to the device ofFIG.5, circuit13is configured to select, according to control signal MODE, voltage Vcomp1from among voltages Vtest1, Vtest2and voltages VS1-i, VS2-i, and Vtrim-i of the selected set, and voltage Vcomp2from among voltages Vtest1, Vtest2, and Vint. More particularly, when the device is testing comparators C1and C2, circuit13supplies voltage Vtest1or Vtest2to comparators C1and C2, when device5is being calibrated, circuit13supplies the voltage Vtrim-i that it receives to comparator C1and, when the device is in a phase of detection of temperatures TS1and TS2, circuit13supplies voltage Vint to comparator C2and, according to signal OUT2, one of the voltages VS1-iand VS2-ithat it receives to comparator C1.

Further, although devices1and5detecting two temperatures TS1and TS2have been described, these devices may be adapted to detect more than two temperatures, for example, by adapting the number of voltages of each set of DC voltages output by circuit10, circuit12, and by further adapting circuit13and, if necessary, the number of comparators, the methods ofFIGS.2and6and their variations being accordingly adapted.

Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations may be combined, and other variations will occur to those skilled in the art. In particular, although embodiments where voltage VT increases with temperature have been described herein, such embodiments and variations may be adapted to the case of a voltage VT decreasing as the temperature increases. Further, voltage VDD, and thus voltages VS1-i, Vtrim-i, VS2-i, Vtest1, Vtest2, and Vint, may all be negative.

Further, although this is not shown inFIGS.1,3,4, and5, each of devices1and5may comprise a processing and control circuit, for example, connected to the output of each comparator of the device and, if present, to a temperature sensor, the circuit being configured to determine and output signals MODE, TRIM and, possibly, TRIM2, and/or to store information relative to the implementation of the described methods.

Finally, the practical implementation of the described embodiments and variations is within the abilities of those skilled in the art based on the functional indications given hereabove. In particular, as concerns the selection of the values of voltages VS1-i, Vtrim-i, VS2-i, Vtest1, Vtest2, and Vint, it is within the abilities of those skilled in the art, in the light of the present description, to select these values, particularly according to the desired calibration and/or detection accuracy.

Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.