Temperature sensor

Abstract

A flexible integrated circuit comprising a temperature sensor is disclosed. The temperature sensor 100, 200 comprises an array of thermistors 101a-j, 201a-j coupled between a first voltage supply and

Description

TECHNICAL FIELD

[0001] The present disclosure concerns a temperature sensor. More particularly, but not exclusively, the present disclosure concerns an integrated circuit comprising a temperature sensor. The present disclosure also concerns a method of operating a temperature sensor in an integrated circuit. BACKGROUND

[0002] Temperature sensors are used in many different applications. Temperature sensors often incorporate a thermistor as a temperature sensing element. A thermistor is a type of resistor whose resistance is strongly dependent on temperature. There are two main categories of thermistor: negative temperature coefficient (NTC) thermistors and positive temperature coefficient (PTC) thermistors. NTC thermistors have a resistance that decreases as a temperature of the thermistor increases. PTC thermistors have a resistance that increases as a temperature of the thermistor increases. By monitoring the resistance of the thermistor, it is possible to monitor changes in temperature of the thermistor.

[0003] Thermistors are generally operated as contact temperature sensors (i.e. they are arranged to be in direct contact with the object they are sensing); however, this requirement can often mean that a thermistor should be located apart from its associated signal processing electronics. Thermistors are generally discrete components which are not integrated with the integrated circuit that processes their output. Thermistors are typically also relatively expensive compared to other temperature sensing technologies (such as thermocouples and thermopiles). There is therefore a need for low-cost temperature sensors that can be embedded within an integrated circuit.

[0004] The present disclosure seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present disclosure seeks to provide an improved temperature sensor. SUMMARY

[0005] A first aspect of the present disclosure relates to a flexible integrated circuit comprising a temperature sensor, the temperature sensor comprising: an array of thermistors coupled between a supply voltage and an output node of the temperature sensor; and a further thermistor coupled between the output node and ground.

[0006] A second aspect of the present disclosure relates to a method of operating a temperature sensor in a flexible integrated circuit, the method comprising: providing an array of negative temperature coefficient thermistors coupled between a supply voltage and an output node of the temperature sensor; providing a further thermistor coupled between the output node and ground; and determining, on the basis of a measured resistance of the thermistor, a temperature of the thermistor.

[0007] A third aspect of the present disclosure relates to an integrated circuit comprising a temperature sensor, the temperature sensor comprising: an array of thermistors coupled between a supply voltage and an output node of the temperature sensor; and a further thermistor coupled between the output node and ground.

[0008] A fourth aspect of the present disclosure relates to an integrated circuit comprising a temperature sensor, the temperature sensor comprising: a first thermistor coupled between a supply voltage and an output node of the temperature sensor; a second thermistor coupled between the output node and ground; and a heater element configured to heat the second thermistor.

[0009] It will of course be appreciated that features described in relation to one aspect of the present disclosure may be incorporated into other aspects of the present disclosure. For example, the method of the present disclosure may incorporate any of the features described with reference to the apparatus of the present disclosure and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 shows a schematic view of a temperature sensor according to the present disclosure; [0011 ] Figure 2 shows a schematic view of a temperature sensor according to the present disclosure;

[0012] Figure 3 shows a schematic view of a temperature sensor according to the present disclosure; and

[0013] Figure 4 shows a functional block diagram illustrating the steps of a method of operating a temperature sensor according to the present disclosure. DETAILED DESCRIPTION

[0014] Figure 1 shows a schematic view of a temperature sensor 100 according to the present disclosure. Temperature sensor 100 comprises part of an integrated circuit (for example, a flexible integrated circuit). Temperature sensor 100 may be configured to measure a temperature of an object (not shown). Temperature sensor 100 may be a contact temperature sensor (for example, configured to be in direct contact with the object).

[0015] Temperature sensor 100 comprises an array of thermistors 101 a-j. Array of thermistors 101 a-j is coupled between a supply voltage (VDD) and an output node (OUT) of the temperature sensor 100. Whilst the example temperature sensor 100 illustrated in Figure 1 comprises ten thermistors 101 a-j, it will be appreciated that other numbers of thermistors may alternatively be used. The array of thermistors may comprise at least two thermistors, at least three thermistors, at least four thermistors, at least five thermistors, at least six thermistors, at least seven thermistors, at least eight thermistors, at least nine thermistors, at least ten thermistors, at least eleven thermistors, at least twelve thermistors, at least thirteen thermistors, at least fourteen thermistors, at least fifteen thermistors, at least sixteen thermistors, at least seventeen thermistors, at least eighteen thermistors, at least nineteen thermistors, or at least twenty thermistors. The array of thermistors may comprise no more than fifty thermistors, no more than forty-five thermistors, no more than forty thermistors, no more than thirty-five thermistors, no more than thirty thermistors, no more than twenty-five thermistors, no more than fifteen thermistors, no more than ten thermistors, or no more than five thermistors.

[0016] Temperature sensor 100 comprises a further thermistor 103. Further thermistor 103 is coupled between the output node (OUT) and ground (GND).

[0017] Array of thermistors 101 a-j and further thermistor 103 may together form a potential divider. It will be appreciated that the supply voltage (VDD) causes a current to flow through the potential divider (i.e. through array of thermistors 101 a-j and further thermistor 103) to ground (GND). The output node (OUT) may be connected to a high-impedance input of signal processing circuitry (not shown). Thus, it may be that only a negligible amount of the current that passes through array of thermistors 101 a-j is diverted away from further thermistor 103. Thus, the array of thermistors 101 a-j and the further thermistor 103 may be configured such that current flow through the array of thermistors 101 a-j is substantially equal to current flow through the further thermistor 103.

[0018] It may be that at least two (for example, all) of thermistors 101 a-j in the array are coupled between the supply voltage and the output node in parallel. The array of thermistors 101 a-j and the further thermistor 103 may be configured such that current flow through any given thermistor 101 a-j in the array is less than the current flow through the further thermistor 103. Two or more (for example, all) of thermistors 101 a-j in the array may be coupled between the supply voltage and the output node in series. It may be that the two or more thermistors each have a lower resistance at a given temperature than that of further thermistor 103. It may be that the two or more thermistors each have a lower resistance at any given temperature than that of further thermistor 103. It will be appreciated that the resistance of a thermistor varies according to its temperature. The resistance of a thermistor is therefore defined in respect of specific temperatures. The given temperature may be 25 degrees Celsius. The array of thermistors 101 a-j may comprise both at least two thermistors coupled in parallel and two or more thermistors coupled in series. It will be appreciated that a given thermistor in the array may be one of both the at least two parallel thermistors and the two or more series thermistors. It will be appreciated that the array of thermistors 101 a-j can be treated as collectively having a single equivalent resistance. The equivalent resistance of the array of thermistors 101 a-j may be equal to a resistance of the further thermistor 103.

[0019] It may be that each individual thermistor in the array 101 a-j dissipates less power than further thermistor 103. Each individual thermistor in the array 101 a-j may undergo less self-heating than further thermistor 103. It will be appreciated that any resistor (including a thermistor) that carries a current will undergo some degree of self-heating due to power dissipation in the resistor. It will be further appreciated that the power dissipated in a resistor is a function of its resistance and the current flowing through the resistor. As discussed above, the thermistors 101 a-j in the array may collectively carry the same current as further thermistor 103. Providing at least two thermistors 101 a-j in the array coupled in parallel divides the current flowing through the potential divider between the at least two thermistors. In other words, it may be that providing at least two thermistors 101 a-j in the array coupled in parallel increases the number of electrical current paths through the array of thermistors 101 a-j. Thus, an array of thermistors 101a- j comprising parallel coupled thermistors may cause each of the parallel coupled thermistors to carry less current (and therefore dissipate less power) than further thermistor 103. It will be appreciated that two series coupled resistors will carry the same electrical current. However, by providing two or more thermistors 101a-j in the array coupled in series, it is possible to divide a total resistance of a current path through the array of thermistors 101 a-j between the two or more thermistors. Thus, each of the two or more thermistors individually may have a lower resistance than if the two or more thermistors were combined, and therefore each of the two or more thermistors may dissipate less power. An array comprising series coupled thermistors may also cause each individual thermistor in the array 101 a-j to dissipate less power (and therefore undergo less self-heating) than further thermistor 103. The temperature sensor may be configured such that each of thermistors 101 a-j in the array individually dissipates less power than further thermistor 103. It may be that each of thermistors 101 a-j in the array therefore undergoes less self-heating than further thermistor 103.

[0020] Thus, it may be that, for a given (for example, any given) temperature of the object being measured, each of thermistors 101 a-j in the array will (due to having reduced selfheating compared to further thermistor 103) be at a lower temperature than further thermistor 103. The array of thermistors 101 a-j and the further thermistor 103 may be configured to cause one or more (for example, all) of thermistors 101 a-j in the array to operate at a relatively low temperature. It may be that the array of thermistors 101 a-j and the further thermistor 103 are configured to cause the further thermistor 103 to operate at a relatively high temperature. In embodiments, the relatively low temperature is no more than 100°C, no more than 75°C, no more than 50°C, no more than 30°C, or no more than 20°C. In embodiments, the relatively low temperature is at least 10°C, at least 15°C, at least 20°C, or at least 25°C. In embodiments, the relatively high temperature is no more than 250°C, no more than 200°C no more than 180°C, no more than 160°C, or no more than 140°C. In embodiments, the relatively high temperature is at least 50°C, at least 75°C, at least 100°C, or at least 125°C.

[0021] A change in the temperature of the object may result (due to the influence of the differing self-heating) in the thermistors 101 a-j in the array undergoing a different change in temperature to that undergone by further thermistor 103. A given change in temperature of the object may therefore result in an equivalent resistance of array of thermistors 101 a-j changing by a different amount to the change in resistance of further thermistor 103. Thus, a change in the temperature of the object may give a change in the ratio of the resistances of array of thermistors 101 a-j and further thermistor 103. This change in ratio may give a change in the voltage of the output node (OUT). Thus, an output voltage indicative of a temperature of the object can be generated. The change in the resistance of a thermistor in response to a given change in temperature can be referred to as a “response” of the thermistor. Thus, operating the array of thermistors 101 a-j and further thermistor 103 at different temperatures may cause the array of thermistors 101 a-j to have a different response to a given change in temperature of the object being measured to that of further thermistor 103.

[0022] It will be appreciated that each of the thermistors in the array 101 a-j and further thermistor 103 have respective resistance-temperature relationships. The resistance-temperature relationships of each of the thermistors in the array 101 a-j and further thermistor 103 may have a linear performance region (for example, in which a given change in temperature yields substantially the same change in resistance regardless of the starting temperature I resistance) and a non-linear performance region (for example, in which the change in resistance arising due to a given change in temperature varies depending on the starting temperature I resistance). It will be appreciated that in this context a “change in resistance” is intended to refer to a percentage change in resistance. The linear performance region of resistance-temperature relationships may be at relatively low temperatures. The non-linear performance region of resistance-temperature relationships may be at relatively high temperatures. Thus, a thermistor can be said to have a critical temperature, below which the thermistor is operating the linear performance region and above which the thermistor is operating in the non-linear performance region.

[0023] It may be that, in the linear performance region, changes in the temperature do not affect the temperature coefficient of a thermistor. Thus, it may be that the temperature coefficient remains substantially constant in the linear region. In the non-linear performance region, the temperature coefficient of a thermistor may vary with temperature. Operating thermistors 101 a-j in the array at a relatively low temperature may comprise operating thermistor 101 a-j in the linear performance region. Operating thermistors 101 a-j in the array at a relatively low temperature may comprise operating each of the thermistors 101 a-j at a temperature below the critical temperature of the respective thermistor. Operating further thermistor 103 at a relatively high temperature may comprise operating further thermistor 103 in the non-linear performance region. Operating further thermistor 103 at a relatively high temperature may comprise operating further thermistor 103 at a temperature above the critical temperature of further thermistor 103.

[0024] Operating thermistors 101 a-j in the array and further thermistor 103 in different performance regions (for example, in the linear performance region and the non-linear performance region respectively) may result in the response of thermistors 101 a-j in the array to a given change in temperature of the object being measured differing from the response of further thermistor 103 to that change by a greater degree. Thus, operating thermistors 101 a-j in the array and further thermistor 103 in different performance regions can provide a greater change in output voltage for a given change in temperature. It may be that the relationship between the voltage of the output node (OUT) and the temperature of the object being measured is not linear. Temperature sensor 100 may comprise signal processing electronics (not shown) configured to evaluate the voltage of the output node (OUT) and determine, on the basis of the evaluated voltage (for example, by use of a lookup table), a temperature of the object.

[0025] Each of thermistors 101 a-j in the array may be of the same type. Further thermistor 103 may be of the same type as thermistors 101 a-j in the array. Each of thermistors 101a-j in the array may comprise a negative temperature coefficient thermistor. Further thermistor 103 may comprise a negative temperature coefficient thermistor. Such a negative temperature coefficient thermistor may comprise a doped metal oxide semiconductor material. For example, the doped metal oxide semiconductor material may comprise semiconductor materials selected from one or more of: ZnO, SnO2, NiO, SnO, CU2O, ln2O3, LiZnO, ZnSnO, InSnO, InZnO, HflnZnO, InGaZnO, ZnxNy, ZnOxNx, and any other suitable metal oxide semiconductor material. It will be appreciated that zinc oxynitride semiconductor materials have a general chemical formula of ZnOxNy. It will be further appreciated that this formula denotes a material composed of zinc (Zn), oxygen (0), and nitrogen (N) in varying proportions. The exact stoichiometry (the values of x and y) can vary depending on the synthesis method and the desired properties of the material. In some cases, the formula can be more specifically written as ZnO-i-xNx, where x represents the proportion of oxygen atoms that are replaced by nitrogen atoms.

[0026] Multiple (for example, all) thermistors 101 a-j in the array may be arranged at dispersed locations across the integrated circuit. At least one thermistor 101 a-j in the array may be located on the integrated circuit apart from one or more other thermistors in the array. Each thermistor 101 a-j in the array may be located on the integrated circuit apart from the other thermistors in the array. The temperature sensor may occupy a sensing region (not shown) of the integrated circuit. The sensing region may be arranged to be in direct contact with the object being measured. It may be that one or more (for example, all) of thermistors 101 a-j in the array are located in the sensing region. Multiple (for example, all) thermistors 101 a-j in the array may be distributed across the sensing region. Multiple (for example, all) of thermistors 201 a-j in the array may be distributed substantially evenly across the sensing region. It will be appreciated that substantially evenly in this context means that the density of thermistors located in any given area of the sensing region is substantially constant. Multiple (for example, all) of thermistors 201 a-j in the array may be distributed symmetrically across the sensing region. Further thermistor 103 may be located in the sensing region. Dispersing thermistors 101 a-j in the array across a sensing region of temperature sensor 100 can enable the array of thermistors 101 a-j to collectively provide a more representative measurement of the temperature of the object being measured (for example, by providing temperature sensing elements across a larger area of the object).

[0027] The supply voltage (VDD) may be a positive supply voltage. An increase in a temperature of the temperature sensor 100 may cause an increase in a voltage of the output node (OUT). The voltage of the output node (OUT) may be directly related (for example, directly proportional) to the temperature of the temperature sensor 100. The - 9 - supply voltage (VDD) may be a negative supply voltage. An increase in a temperature of the temperature sensor 100 may cause a decrease in a voltage of the output node (OUT). The voltage of the output node (OUT) may be inversely related (for example, inversely proportional) to the temperature of the temperature sensor 100.

[0028] It will be appreciated that a “positive supply voltage” in this context refers to a voltage supply that is at a positive voltage compared to ground (GND). Similarly, a “negative supply voltage” in this context refers to a voltage supply that is at a negative voltage compared to ground (GND). It will also be appreciated that references to “ground” are intended to refer merely to a reference voltage in the electronic circuit of temperature sensor 100 and are not limited to a connection to the Earth. It will further be appreciated that in this context, references to an “increase” in a voltage of a node indicate the voltage of that node becoming more positive (or less negative) relative to ground, and not necessarily an increase in magnitude of the potential difference between the node and ground. Similarly, references to a “decrease” in a voltage of a node indicate the voltage of that node becoming more negative (or less positive) relative to ground, and not necessarily a decrease in magnitude of the potential difference between the node and ground.

[0029] Thus, the temperature sensor 100 may be configurable to operate in two modes of operation. In a first mode of the two modes of operation, the supply voltage (VDD) may be configured to be a positive supply voltage. In the first mode of operation, an increase in a temperature of the temperature sensor 100 causes an increase in a voltage of the output node (OUT). In a second mode of the two modes of operation, the supply voltage (VDD) may be configured to be a negative supply voltage. In the second mode of operation, an increase in a temperature of the temperature sensor 100 may cause a decrease in a voltage of the output node (OUT). The supply voltage (VDD) may be configurable to be either a positive supply voltage or a negative supply voltage. The temperature sensor 100 may comprise a control circuit (not shown) configured to control the polarity of the supply voltage (VDD). For example, the control circuit may comprise an H-bridge.

[0030] Temperature sensor 100 may comprise a positive temperature coefficient resistor (not shown). The positive temperature coefficient resistor may be coupled between the output node (OUT) and ground (GND). The positive temperature coefficient resistor may be coupled in series with further thermistor 103.

[0031] As discussed above, temperature sensor 100 may comprise part of a flexible integrated circuit. In accordance with the present disclosure a “flexible integrated circuit” (flexible IC or flexIC) is a type of integrated circuit that is designed to be flexible and conformable, allowing it to bend, twist, and conform to non-flat or irregular surfaces. Unlike traditional rigid ICs, which are typically made on silicon wafers and are inflexible, flexible ICs, in accordance with the present disclosure, are fabricated on flexible substrates using appropriate materials and thin-film processes. The substrate is typically formed of an appropriate flexible polymer material. Nevertheless, the flexible substrate may be formed from any other materials that provide suitable electrical, chemical, and / or structural properties. The flexible substrate may be formed from a single common material, may be formed from a plurality of different materials, or may be formed from a plurality of different types of the same material. The flexible substrate may, for example, comprise one or more materials selected from the following list of materials: flexible glass, polymer materials, metal oxide materials, resin materials, resist materials, foil materials, paper, insulator coated metals, or any other suitable material.

[0032] Where a polymer based material is used, the substrate may comprise one or more polymers selected from: polyethylene naphthalates, polyethylene terephthalates; polymethyl methacrylates; polycarbonates, polyvinyl alcohols, polyvinyl acetates, polyvinyl pyrrolidones, polyvinyl phenols, polyvinyl chlorides, polystyrenes, polyimides, polyamides (e.g. Nylon); poly(hydroxy ethers), polyurethanes, polycarbonates, polysulfones, parylenes, polyarylates, polyether ether ketones (PEEKs); acrylonitrile butadiene styrene (ABS), 1 Methoxy 2 propyl acetates, Benzocyclobutenes (BCB), polylactic acid (PLA), polyhydroxyalkanoates (PHAs), polybutylene succinate (PBS), polybutylene adipate terephthalate (PBAT), cellulose polymers, or any other suitable polymer material.

[0033] Where a metal oxide based material is used, the substrate may comprise one or more metal oxides selected from: AI2O3, SiOxNy, SiO2, Si3N4, or any other suitable metal oxide. Where a resin based material is used, the substrate may comprise one or more resins selected from: a UV-curable resin or any other suitable resin. Where a resist based material is used, the substrate may comprise one or more resists selected from: nanoimprint resists, photoresists such as, for example, Bisphenol A novolac epoxy (SU-8) or polyhydroxybenzyl silsesquioxane, or any other suitable resist. Where a foil based material is used the substrate may comprise one or more foils selected from: polymeric foils or any other suitable foil. Where an insulator-coated metal is used, the substrate may comprise one or more insulator-coated metals selected from: insulator coated stainless-steel or any other suitable insulator-coated metal.

[0034] Additionally or alternatively, a flexible IC may not include the flexible substrate, which, for example, may be removed during a manufacturing step.

[0035] Figure 2 shows a schematic view of a temperature sensor 200 according to the present disclosure. Temperature sensor 200 may have similarities to temperature sensor 100 described above, but has one or more differences as described below. Any or all of the optional features described above in respect of temperature sensor 100 may also be present in temperature sensor 200. Like temperature sensor 100, temperature sensor 200 comprises part of an integrated circuit.

[0036] Temperature sensor 200 may further comprise a heater element 205 configured to heat further thermistor 203. Heater element 205 may be configured to provide supplementary heating of further thermistors 203. It will be appreciated that the heating performed by heater element 205 can be described as supplementary because it is provided in addition to the self-heating of further thermistor 203. Heater element 205 may comprise a metal heater track.

[0037] Figure 3 shows a schematic view of a temperature sensor 300 according to the present disclosure. Temperature sensor 300 has similarities to temperature sensors 100, 200 described above, but has one or more differences as described below. Any or all of the optional features described above in respect of temperature sensors 100, 200 may also be present in temperature sensor 300.

[0038] Temperature sensor 300 may comprise, in the place of array of thermistors 101a-j, 201 a-j, only a single thermistor 301. Thus, temperature sensor 300 may comprise a potential divider formed of only two thermistors. Thermistor 301 and further thermistor 303 may have the same resistance for at least one (for example, any) given temperature. Thermistor 301 and further thermistor 303 may be substantially identical.

[0039] It may be that temperature sensor 300 comprises heater element 305 configured to heat further thermistor 303. Thus, the operating of further thermistor 303 at a relatively high temperature may be performed by operating heater element 305 to heat further thermistor 303. The operating of further thermistor 303 at a higher temperature than thermistor 301 may be attributable (for example, solely attributable) to the heating of further thermistor 303 by heater element 305. There may be substantially no difference in self-heating between thermistor 301 and further thermistor 303. Thus, temperature sensor 300 can be said to operate on the basis of active heating of further thermistor 303 using heater element 305, as opposed to the passive self-heating of further thermistor 103 (or the combination of active and passive heating of further thermistor 203).

[0040] Figure 4 shows a functional block diagram illustrating the steps of a method of operating a temperature sensor according to the present disclosure.

[0041] A first step, represented by item 401, of method 400 comprises providing an array of thermistors coupled between a supply voltage and an output node of the temperature sensor. One or more (for example, all) of the thermistors in the array may comprise negative temperature coefficient thermistors. The one or more (for example, all) of the thermistors in the array may be formed of semiconductor materials selected from one or more of: ZnO, SnO2, NiO, SnO, Cu2O, ln2O3, LiZnO, ZnSnO, InSnO, InZnO, HflnZnO, InGaZnO, ZnxNy, ZnOxNx, and any other suitable metal oxide semiconductor material.

[0042] A second step, represented by item 403, of method 400 comprises providing a further thermistor coupled between the output node and ground. The further thermistor in the array may comprise a negative temperature coefficient thermistor. The further - 13 - thermistor may be formed of semiconductor materials selected from one or more of: ZnO, SnO2, NiO, SnO, CU2O, ln2O3, LiZnO, ZnSnO, InSnO, InZnO, HflnZnO, InGaZnO, ZnxNy, ZnOxNx, and any other suitable metal oxide semiconductor material.

[0043] An optional third step, represented by item 405, of method 400 comprises providing a heater element arranged to heat the further thermistor.

[0044] An optional fourth step, represented by item 407, of method 400 comprises operating each thermistor in the array at a relatively low temperature. Operating a thermistor in the array at a relatively low temperature may comprise operating the thermistor in a linear performance region.

[0045] An optional fifth step, represented by item 409, of method 400 comprises operating the further thermistor at a relatively high temperature. Operating the further thermistor at a relatively high temperature may comprise operating the further thermistor in a non-linear performance region. Operating the further thermistor at a relatively high temperature may comprise operating the heater element to heat the further thermistor.

[0046] A sixth step, represented by item 511, of method 400 comprises determining, on the basis of a voltage of the output node, a temperature of the temperature sensor.

[0047] An optional seventh step, represented by item 513, of method 400 comprises operating the temperature sensor in a first mode of operation. In such cases, it may be that operating the temperature sensor in the first mode of operation comprises applying a positive supply voltage. Operating the temperature sensor in the first mode of operation may comprise configuring the temperature sensor such that an increase in a temperature of the temperature sensor causes an increase in a voltage of the output node.

[0048] An optional eighth step, represented by item 515, of method 400 comprises operating the temperature sensor in a second mode of operation. In such cases, it may be that operating the temperature sensor in the second mode of operation comprises applying a negative supply voltage. Operating the temperature sensor in the second mode of operation may comprise configuring the temperature sensor such that an increase in a temperature of the temperature sensor causes a decrease in a voltage of the output node.

[0049] Whilst the present disclosure has been described and illustrated with reference to particular examples, it will be appreciated by those of ordinary skill in the art that the present disclosure lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0050] Whilst the illustrated examples show the array of thermistors as having ten thermistors, it will be appreciated that in other examples the array of thermistors has other numbers of thermistors. Similarly, whilst the illustrated examples show temperature sensors including only one resistor, it will be appreciated that, in other examples, more than one resistor may be present.

[0051] Whilst in some examples described above the array of thermistors and the further thermistor comprise negative temperature coefficient thermistors, it will be appreciated that this may not be the case in other examples. In such examples, it may be that each of the thermistors in the array comprises a positive temperature coefficient thermistor. In some such examples, the further thermistor comprises a positive temperature coefficient thermistor.

[0052] Whilst in the examples described above, temperature sensors have been said to measure the temperature of an object, it will be appreciated that this merely an example. For example, the temperature sensors may alternatively be used to measure air temperature (or the temperature of other things that might arguably not be considered to be objects).

[0053] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present disclosure, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the present disclosure that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the present disclosure, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. A flexible integrated circuit comprising a temperature sensor, the temperature sensor comprising:an array of thermistors coupled between a supply voltage and an output node of the temperature sensor; anda further thermistor coupled between the output node and ground.

2. A flexible integrated circuit according to claim 1, wherein at least two thermistors in the array are coupled between the supply voltage and the output node in parallel.

3. A flexible integrated circuit according to claim 1 or 2, wherein:two or more thermistors in the array are coupled between the supply voltage and the output node in series; andthe two or more thermistors each have a lower resistance at a given temperature than that of the further thermistor.

4. A flexible integrated circuit according to any preceding claim, wherein the array of thermistors and the further thermistor are configured such that current flow through the array of thermistors is substantially equal to current flow through the further thermistor.

5. A flexible integrated circuit according to claim 4, wherein the array of thermistors and the further thermistor are configured such that current flow through any given thermistor in the array is less than the current flow through the further thermistor.

6. A flexible integrated circuit according to any preceding claim, wherein the array of thermistors and the further thermistor are configured to cause each thermistor in the array to operate at a relatively low temperature and the further thermistor to operate at a relatively high temperature.

7. A flexible integrated circuit according to claim 6, wherein:operating a thermistor in the array at a relatively low temperature comprises operating the thermistor in a linear performance region; andoperating the further thermistor at a relatively high temperature comprises operating the further thermistor in a non-linear performance region.

8. A flexible integrated circuit according to claim 7, wherein:in the linear performance region, a temperature coefficient of the thermistor does not vary with temperature; andin the non-linear performance region, the temperature coefficient varies with temperature.

9. A flexible integrated circuit according to any preceding claim, wherein the thermistors in the array are arranged at dispersed locations across the flexible integrated circuit.

10. A flexible integrated circuit according to any preceding claim, further comprising a heater element configured to heat the further thermistor.

11. A flexible integrated circuit according to any preceding claim, wherein:the supply voltage is a positive supply voltage; andan increase in a temperature of the temperature sensor causes an increase in a voltage of the output node.

12. A flexible integrated circuit according to any of claims 1 to 10 wherein:the supply voltage is a negative supply voltage; andan increase in a temperature of the temperature sensor causes a decrease in a voltage of the output node.

13. A flexible integrated circuit according to any of claims 1 to 10, wherein the supply voltage is configurable to be either a positive supply voltage or a negative supply voltage.

14. A flexible integrated circuit according to claim 13, wherein the temperature sensor is configurable to operate in:a first mode of operation in which the supply voltage is configured to be a positive supply voltage and an increase in a temperature of the temperature sensor causes an increase in a voltage of the output node; anda second mode of operation in which the supply voltage is configured to be a negative supply voltage and an increase in a temperature of the temperature sensor causes a decrease in a voltage of the output node.

15. A flexible integrated circuit according to any preceding claim, wherein the thermistors in the array and the further thermistor each comprise a negative temperature coefficient thermistor.

16. A flexible integrated circuit according to claim 15, wherein the thermistors in the array and the further thermistor each comprise a doped metal oxide semiconductor material.

17. A flexible integrated circuit according to claim 16, wherein the doped metal oxide semiconductor material comprises one or more of: ZnO, SnO2, NiO, SnO, CU2O, 10263, LiZnO, ZnSnO, InSnO, InZnO, HflnZnO, InGaZnO, ZnxNy, and ZnOxNx.

18. A flexible integrated circuit according to any preceding claim, wherein the array of thermistors comprises at least two thermistors.

19. A flexible integrated circuit according to any preceding claim, wherein an equivalent resistance of the array of thermistors is equal to a resistance of the further thermistor.

20. A method of operating a temperature sensor in a flexible integrated circuit, the method comprising:providing an array of thermistors coupled between a supply voltage and an output node of the temperature sensor; andproviding a further thermistor coupled between the output node and ground.determining, on the basis of a voltage of the output node, a temperature of the temperature sensor.

21. A method of operating a temperature sensor according to claim 20, wherein the method further comprises:operating each thermistor in the array at a relatively low temperature; andoperating the further thermistor at a relatively high temperature.

22. A method of operating a temperature sensor according to claim 21, wherein:operating a thermistor in the array at a relatively low temperature comprises operating the thermistor in a linear performance region; andoperating the further thermistor at a relatively high temperature comprises operating the further thermistor in a non-linear performance region.

23. A method of operating a temperature sensor according to claim 21 or 22, wherein operating the further thermistor at a relatively high temperature comprises operating a heater element to heat the further thermistor.

24. A method of operating a temperature sensor according to any of claims 20 to 23, wherein the method further comprises:operating the temperature sensor in a first mode of operation by applying a positive supply voltage, such that an increase in a temperature of the temperature sensor causes an increase in a voltage of the output node; andoperating the temperature sensor in a second mode of operation by applying a negative supply voltage, such that an increase in a temperature of the temperature sensor causes a decrease in a voltage of the output node.

25. An integrated circuit comprising a temperature sensor, the temperature sensor comprising:an array of thermistors coupled between a supply voltage and an output node of the temperature sensor; anda further thermistor coupled between the output node and ground.

26. An integrated circuit comprising a temperature sensor, the temperature sensor comprising:a first thermistor coupled between a supply voltage and an output node of the temperature sensor;a second thermistor coupled between the output node and ground; anda heater element configured to heat the second thermistor.

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