Temperature sensor

Abstract

An integrated circuit comprising a temperature sensor. The temperature sensor is configured to measure temperature across a predetermined temperature range. The temperature sensor comprises a sensing resistor and a reference resistor. The sensing resistor comprises a metal track having a first temperature coefficient of resistance. The reference resistor has a second temperature coefficient of resistance less than the first temperature coefficient of resistance.

Description

TEMPERATURE SENSORTECHNICAL FIELD

[0001] The present disclosure concerns integrated circuits. More particularly, but not exclusively, the present disclosure concerns integrated circuits comprising temperature sensors.BACKGROUND

[0002] Temperature sensors are used in many different applications. Temperature sensors often incorporate a thermistor as a temperature sensing element. 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 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). Furthermore, typical NTC (negative temperature co-efficient of resistance) thermistors exhibit a non-linear variation in resistance with temperature, which may complicate the circuitry required to derive a temperature measurement. There is therefore a need for low-cost temperature sensors that can be embedded within an integrated circuit.

[0003] The present disclosure seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present disclosure seeks to provide an improved temperature sensor.SUMMARY

[0004] A first aspect of the present disclosure relates to an integrated circuit comprising a temperature sensor, the temperature sensor being configured to measure temperature across a predetermined temperature range, the temperature sensor comprising:a sensing resistor comprising a metal track having a first temperature coefficient of resistance; and a reference resistor having a second temperature coefficient of resistance less than the first temperature coefficient.

[0005] A second aspect of the present disclosure relates to an integrated circuit comprising a temperature sensor, the temperature sensor comprising: a sensing resistor comprising a metal track formed in a single layer of the integrated circuit; and a signal processing circuit formed at least partly in the single layer of the integrated circuit, the signal processing circuit being configured to determine, on the basis of the resistance of the sensing resistor, a temperature of the temperature sensor.

[0006] 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

[0007] Figure 1 shows a schematic view of a temperature sensor according to the present disclosure;

[0008] Figure 2 shows a schematic view of a temperature sensor according to the present disclosure;

[0009] Figure 3 shows a schematic view of a temperature sensor according to the present disclosure; and

[0010] Figure 4 shows a schematic view of a temperature sensor according to the present disclosure.DETAILED DESCRIPTION

[0011] The present disclosure provides a novel temperature sensor comprising first and second resistances having different temperature coefficients of resistance. Thus, it may be that a resistance of the first resistance varies with temperature differently to thatof the second resistance. It may be that the temperature sensor operates to exploit the different sensitivities of the first resistance and the second resistance to changes in temperature to generate a signal indicative of a temperature of the temperature sensor. It may be that the second resistance is relatively insensitive to changes in temperature compared to the first resistance. For example, it may be that the second resistance has a resistance that is substantially invariant with temperature. Thus, the second resistance may act as a reference resistance within the temperature sensor. It may be that the second resistance is sensitive to changes in resistance attributable to factors other than temperature, such that the effect of temperature on the first resistance can be determined by comparison to the second resistance. The following figures illustrate example configurations of temperature sensors based on such principles. It will be appreciated that many configurations other than those illustrated are also possible.

[0012] Figure 1 shows a schematic view of an example temperature sensor 100 according to the present disclosure. Temperature sensor 100 is comprised in an integrated circuit. It will be appreciated that an integrated circuit in this context refers to an electronic circuit formed on or comprising a piece of semiconductor material. It is not necessarily intended to require the presence in the circuit of transistors or of electronic components beyond those discussed below.

[0013] Temperature sensor 100 is configured to measure temperature across a predetermined temperature range. It may be that the predetermined temperature range includes 2 °C to 8 °C, 0%) to 20 °C, 0°C to 30%), 0°C to 40°C, -10%) to 40%), or -10%) to 60%). It will be appreciated that these temperature ranges are provided to the nearest degree Celsius.

[0014] Integrated circuit 100 comprises a sensing resistor 101 and a reference resistor 103. In this example temperature sensor 100, it may be that one of sensing resistor 101 and reference resistor 103 is coupled between a voltage supply (VDD) and an output node (OUT) of temperature sensor 100. It may be that the other of sensing resistor 101 and reference resistor 103 is coupled between the output node (OUT) and ground (GND). Thus, it may be that sensing resistor 101 and a reference resistor 103 together form a potential divider.

[0015] Sensing resistor 101 comprises a metal track. It may be that reference resistor 103 comprises a metal track. It may be that sensing resistor 101 comprises a winding (for example, serpentine) metal track. It may be that reference resistor 103 comprises a winding (for example, serpentine) metal track. It will be appreciated in this context that a serpentine structure is one which repeatedly turns back on itself to form a path that incorporates a series of alternating bends.

[0016] It may be that sensing resistor 101 has a resistance that varies depending on temperature. It may be that reference resistor 103 has a resistance that remains substantially constant irrespective of changes in temperature (for example, changes of temperature within the predetermined temperature range). It may be that reference resistor 103 has a resistance that varies depending on temperature, but to a lesser degree than sensing resistor 101 . Thus, it may be that a voltage of the output node (OUT) varies depending on the temperature of temperature sensor 100. It may be that the voltage of the output node (OUT) varies depending on the temperature of sensing resistor 101 .

[0017] It will be appreciated that the change in resistance of a material for a given change of temperature is characterised by the temperature coefficient of resistance of the material. Sensing resistor 101 has a first temperature coefficient of resistance. Reference resistor 103 has a second temperature coefficient of resistance. The second temperature coefficient of resistance is less than the first temperature coefficient of resistance. It may be that the second temperature coefficient is less than 20% of the first temperature coefficient, less than 10% of the first temperature coefficient, less than 5% of the first temperature coefficient, less than 1% of the first temperature coefficient, less than 0.5% of the first temperature coefficient, or less than 0.1 % of the first temperature coefficient. It may be that reference resistor 103 comprises a metal track.

[0018] It may be that the first temperature coefficient is substantially constant across the predetermined temperature range. It may be that the first temperature coefficient varies by less than 10% across the predetermined temperature range, less than 5% across the predetermined temperature range, less than 2% across the predetermined temperature range, less than 1% across the predetermined temperature range, or less than 0.5% across the predetermined temperature range. Thus, it may be that, within the predetermined temperature range, a given change of temperature ofsensing resistor 101 gives the same percentage change in resistance of sensing resistor 101 regardless of the initial temperature of sensing resistor 101. lt may be that the second temperature coefficient is negligibly small (for example, zero) across the predetermined temperature range. It may be that the use of a reference resistor 103 having a negligible temperature coefficient provides a temperature sensor 100 that is self-referenced. It may be that changes in the resistance of reference resistor 103 are attributable to causes other than changes in temperature (for example, variation in the voltage supply (VDD)). Hence, it may be that changes in the ratio of the resistance of sensing resistor 101 to the resistance of reference resistor 103 (and therefore also changes in the voltage of the output node (OUT)) are indicative of a change in temperature of temperature sensor 100 (for example, of sensing resistor 101 ).

[0019] It may be that the second temperature coefficient is substantially constant across the predetermined temperature range. It may be that the second temperature coefficient varies by less than 10% across the predetermined temperature range, less than 5% across the predetermined temperature range, less than 2% across the predetermined temperature range, less than 1% across the predetermined temperature range, or less than 0.5% across the predetermined temperature range. Thus, it may be that, within the predetermined temperature range, a given change of temperature of reference resistor 103 gives the same percentage change in resistance of reference resistor 103 regardless of the initial temperature of reference resistor 103. It will be appreciated that, where the first and second temperature coefficients are both substantially constant across the predetermined temperature range and the second temperature coefficient is less than the first temperature coefficient, a change in temperature of temperature sensor 100 (for example, of sensing resistor 101 and reference resistor 103) will give a change in the ratio of the resistance of sensing resistor 101 to the resistance of reference resistor 103 (and thereby also of the voltage of the output node (OUT)).

[0020] It may be that sensing resistor 101 and reference resistor 103 are coupled in series between a voltage supply (VDD) and ground (GND). In such cases it may be that sensing resistor 101 and reference resistor 103 together form a potential divider.

[0021] It may be that sensing resistor 101 (for example, the metal track of sensing resistor 101 ) comprises one or more of: Titanium, Nickel, Palladium, Platinum, Iron, Osmium, Molybdenum, Tungsten, Aluminium, Copper, Silver, Palladium, Platinum, Gold, Rhodium, Iridium, Zinc, Steel, Nichrome, and Nichrome V. It may be that sensing resistor 101 (for example, the metal track of sensing resistor 101 ) comprises a layered structure (for example, a sandwich structure). It may be that the metal track is formed of a plurality of layers of material (for example, two or more different materials).

[0022] It may be that reference resistor 103 (for example, the metal track of reference resistor 103) comprises one or more of: Manganin (RTM), German silver, Constantan (RTM), and Nichrome (RTM).

[0023] As mentioned above, temperature sensor 100 is comprised in an integrated circuit. The integrated circuit may be a flexible integrated circuit.

[0024] 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, mechanical, optical, biological 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.

[0025] 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.

[0026] 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.

[0027] Additionally or alternatively, a flexible IC may not include the flexible substrate, which, for example, may be removed during a manufacturing step.

[0028] Figure 2 shows a schematic view of an example 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 features described above in respect of temperature sensor 100 may also be present in temperature sensor 200.

[0029] It may be that temperature sensor 200 comprises a plurality of sensing resistors 201 a-e. Where a resistor is formed by one or more metal tracks, it will be appreciated that any parallel track paths can be considered to be distinct resistors. Whilst Figure 2 shows temperature sensor 200 as having five sensing resistors 201 a-e, it will be appreciated that any number of sensing resistors may be used. Temperature sensor 200 may comprise at least two sensing resistors, at least three sensing resistors, at least four sensing resistors, at least five sensing resistors, at least six sensing resistors, at leastseven sensing resistors, at least eight sensing resistors, at least nine sensing resistors, or at least ten sensing resistors. Temperature sensor 200 may comprise no more than twenty sensing resistors, no more than fifteen sensing resistors, no more than ten sensing resistors, no more than five sensing resistors, or no more than three sensing resistors, or no more than one sensing resistor. Each of the sensing resistors 201 a-e may be coupled between the voltage supply (VDD) and the output node (OUT). Two or more (for example, all) of the plurality of sensing resistors 201 a-e may be connected in series. Two or more (for example, all) of the plurality of sensing resistors 201 a-e may be connected in parallel. Four or more (for example, all) of the plurality of sensing resistors may be connected in parallel. Four or more (for example, all) of the plurality of sensing resistors may be connected in series.

[0030] It may be that each of sensing resistors 201 a-e has a resistance that varies depending on temperature. It may be that the plurality of sensing resistors 201 a-e each have substantially the same resistance at a given temperature.

[0031] It may be that each of the plurality of sensing resistors 201 a-e comprises a metal track. In such cases it may be that the metal tracks of the sensing resistors are all substantially the same width and length. It will be appreciated that the reference to the width of a track refers in this context to an individual track (i.e. to the width of a single length of track), rather than to the dimensions of the overall resistor. It may be that the sensing resistors in the plurality each comprise (for example, consist of) a metal track having the same dimensions (for example, the same shape and dimensions) as the other sensing resistors in the plurality.

[0032] It may be that a first sensing resistor 201 a in the plurality is formed on a first layer of the integrated circuit. It may be that a second sensing resistor 201 b in the plurality is formed on a different, second layer of the integrated circuit. It may be that each of the sensing resistors 201 a-e in the plurality is formed on a respective separate layer of the integrated circuit. Thus, it may be that none of sensing resistors 201 a-e in the plurality are formed on the same layer of the integrated circuit as any of the other sensing resistors 201 a-e in the plurality.

[0033] It will be appreciated that each component in an integrated circuit occupies a respective portion of the area of the integrated circuit (when the integrated circuit isviewed in plan view - i.e. in a direction orthogonal to a plane of the layers of the integrated circuit). The area of the integrated circuit occupied by a component can be referred to as a footprint of the component. It will be further appreciated that, where an integrated circuit comprises multiple layers, it may be that the footprints of components can overlap (for example, where those components exist within different ones of the multiple layers). It may be that a footprint of the first sensing resistor 201 a at least partially overlaps a footprint of the second sensing resistor 201 b. It may be that the footprint of the first sensing resistor 201 a encompasses the footprint of the second sensing resistor 201 b. Thus, it may be that the footprint of the second sensing resistor 201 b is entirely within the footprint of the first sensing resistor 201 a. It may be that no portion of the footprint of the second sensing resistor 201 b is outside of the footprint of the first sensing resistor 201 b. It may be that the first sensing resistor 201 a and the second sensing resistor 201 b have the same footprint. Thus, it may be that the first sensing resistor 201 a and the second sensing resistor 201 b occupy the same area of the integrated circuit (when viewed in plan view). It may be that the first resistor 201 a has a footprint which does not overlap one or more (for example, any) of the footprints of the other resistors 201 b-e in the plurality. It may be that each resistor in the plurality 201 a-e has a footprint which does not overlap any of the footprints of the other resistors in the plurality 201 a-e.

[0034] Figure 3 shows a schematic view of an example temperature sensor 300 according to the present disclosure. Temperature sensor 300 may have similarities to temperature sensors 100, 200 described above but has one or more differences as described below. Any or all of the features described above in respect of temperature sensors 100, 200 may also be present in temperature sensor 300.

[0035] It may be that temperature sensor 300 further comprises a signal processing circuit 305. It may be that signal processing circuit 305 is configured to determine a temperature of temperature sensor 300 (for example of sensing resistors 301 a-e). It may be that signal processing circuit 305 is configured to determine the temperature on the basis of the resistance of sensing resistors 301 a-e. It may be that signal processing circuit 305 comprises an analogue-to-digital converter (ADC). It may be that the ADC comprises a successive approximation ADC, a Flash ADC, a dual-slope ADC, or a delta-sigma ADC. It will be appreciated that other types of ADC may also beused. It may be that signal processing circuit 305 has a sampling range that is set based on the voltage supply (VDD). It may be that the sampling range is of the ADC (which may, for example, be powered using and / or have a reference voltage set based on the voltage supply (VDD)).

[0036] As discussed above, it may be that sensing resistors 301 a-e and reference resistor 303 are coupled in series between a voltage supply (VDD) and ground (GND), such that sensing resistors 301 a-e and reference resistor 303 together form a potential divider. It may be that one of (a) sensing resistors 301 a-e and (b) reference resistor 303 is coupled between the voltage supply (VDD) and an output node (OUT) of temperature sensor 300. It may be that the other of (a) sensing resistors 301 a-e and (b) reference resistor 303 is coupled between the output node (OUT) and ground (GND). In such cases, it may be that signal processing circuit 305 is configured to determine the temperature based on a voltage of the output node (OUT).

[0037] It may be that signal processing circuit 305 is configured to determine the temperature of temperature sensor 300 (for example of sensing resistors 301 a-e) by evaluating a voltage of the output node (OUT). It may be that signal processing circuit 305 is configured to determine the temperature by comparing the voltage of the output node (OUT) as measured by the ADC to one or more predetermined thresholds. Where signal processing circuit 305 comprises an ADC, it may be that the ADC is configured to measure the voltage of the output node (OUT). It may be (for example, where the ADC comprises a successive approximation ADC) that the ADC comprises one or more comparators. In such cases, it may be that each of the one or more comparators is configured to compare the voltage of the output node (OUT) to a respective one of a plurality of reference voltages. It may be that the plurality of reference voltages are generated by a potential divider. It may be that the potential divider comprises a plurality of resistors connected in series, with one or more nodes between the resistors in the plurality providing the plurality of reference voltages. It may be that the potential divider is formed as a single track resistor, with one or more taps at intervals along its length providing the reference voltages. It may be that the potential divider is formed by sensing resistor 301 . It may be that the potential divider is formed by reference resistor 303. It may be that the potential divider is formed by a further resistor (i.e. not one of sensingresistor 301 and reference resistor 303). It may be that the ADC is configured to select one of the nodes (or taps) to obtain a reference voltage against which to compare the voltage of the output node (OUT). It may be that signal processing circuit 305 is configured to determine the temperature by use of a look-up table (for example, containing stored correspondences between voltages of the output node (OUT) and the temperature of temperature sensor 300). It may be that signal processing circuit 305 is configured to generate a digital signal (TEMP) indicative of the measured temperature.

[0038] Figure 4 shows a schematic view of an example temperature sensor 400 according to the present disclosure. Temperature sensor 400 may have similarities to temperature sensors 100, 200, 300 described above but has one or more differences as described below. Any or all of the features described above in respect of temperature sensors 100, 200, 300 may also be present in temperature sensor 400.

[0039] In this example, it may be that temperature sensor 400 comprises a first oscillator 407a and a second oscillator 407b. It may be that first oscillator 407a and second oscillator 407b each comprises an RC oscillator. It may be that first oscillator 407a comprises a first RC network. In such cases, it may be that the first RC network is configured to set an oscillation frequency of first oscillator 407a. Similarly, second oscillator 407b may comprise a second RC network. In such cases, it may be that the second RC network is configured to set an oscillation frequency of second oscillator 407b. It may be that sensing resistor 401 forms part of the first RC network. It may be that reference resistor 403 forms part of the second RC network. Thus, the oscillation frequency of first oscillator 407a may be determined by the resistance of sensing resistor 401 . Similarly, the oscillation frequency of second oscillator 407b may be determined by the resistance of reference resistor 403.

[0040] It may be that first oscillator 407a is configured to generate a first periodic signal 409a having a first frequency. It may be that second oscillator 407b is configured to generate a second periodic signal 409b having a second frequency. It may be that the first frequency is indicative of a resistance of sensing resistor 401 . It may be that the second frequency is indicative of a resistance of reference resistor 403. Signal processing circuit 405 may be configured to determine the temperature of temperature sensor 400 (for example, of sensing resistor 401 ) on the basis of the first periodic signal 409a andthe second periodic signal 409b (for example, of the basis of the first and second frequencies).

[0041] 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.

[0042] Whilst the examples illustrated in the figures show sensing resistor 101 as being coupled between the voltage supply (VDD) and the output node (OUT) and reference resistor 103 as being coupled between the output node (OUT) and ground (GND), it will be appreciated that this need not necessarily be the case. In an alternative example, reference resistor 103 is coupled between the voltage supply (VDD) and the output node (OUT) and sensing resistor 101 is coupled between the output node (OUT) and ground (GND).

[0043] Whilst the illustrated examples show implementations of temperature sensors based on potential divider and dual oscillator arrangements, it will be appreciated that the present disclosure provides general teaching of temperature sensors based on the combination of a first resistance having a relatively high temperature coefficient of resistance and a second resistance having a relatively low temperature coefficient of resistance. Thus, it will be appreciated that temperature sensors according to the present disclosure may be configured in alternative arrangements. For example, the temperature sensor could alternatively utilise a Wheatstone bridge to measure the resistance of the sensing resistor (and thereby to determine the temperature of the temperature sensor). In such cases, it may be that the known resistors and potentiometer comprise reference resistors (for example, having a negligible temperature coefficient of resistance as described above).

[0044] A further example temperature sensor in an integrated circuit (for example, a flexible integrated circuit) comprises a sensing resistor. It may be that the temperature sensor does not comprise a reference resistor. The sensing resistor comprises a metal track formed in a single layer of the integrated circuit. The temperature sensor further comprises a signal processing circuit. The signal processing circuit is formed at leastpartly in the single layer of the integrated circuit. Forming the signal processing circuit at least partly in the single layer of the integrated circuit can simplify the design of the temperature sensor and facilitate easier manufacture of the temperature sensor (for example, by reducing the number of process steps involved in manufacturing the temperature sensor). The signal processing circuit is configured to determine, on the basis of the resistance of the sensing resistor, a temperature of the temperature sensor. It will be appreciated in this context that the single layer of the integrated circuit refers to a layer of metal and / or semiconductor material between two layers of dielectric. In an arrangement where, for example, a metal track within the integrated circuit is formed of multiple layers of different metals (for example, all in direct contact such that they form a single track), the single layer of the integrated circuit is intended to refer to the metal layer of the track as a whole, not to the individual metal layers making up the metal track. It may be that the metal track of the sensing resistor is formed in the same layer as a metal feature of the signal processing circuit. The metal feature may for example comprise one or more of: a source, drain or gate terminal of a transistor; a capacitor electrode; a resistor terminal; or a memory device element. As the temperature sensor is comprised in an integrated circuit, the sensing resistor and / or the signal processing circuit can be said to be comprised in the integrated circuit. The temperature sensor may include one or more (for example, all) of the features described above in respect of temperature sensors 100, 200, 300, 400.

[0045] 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 examples of the present disclosure, may not be desirable, and may therefore be absent, in other examples.

Claims

CLAIMS:

1. An integrated circuit comprising a temperature sensor, the temperature sensor being configured to measure temperature across a predetermined temperature range, the temperature sensor comprising: a sensing resistor comprising a metal track having a first temperature coefficient of resistance; and a reference resistor having a second temperature coefficient of resistance less than the first temperature coefficient.

2. An integrated circuit according to claim 1 , wherein the first temperature coefficient is substantially constant across the predetermined temperature range.

3. An integrated circuit according to claim 1 or 2, wherein the second temperature coefficient of resistance is less than 20% of the first temperature coefficient of resistance.

4. An integrated circuit according to any preceding claim, wherein the predetermined range includes 2 °C to 8 °C.

5. An integrated circuit according to claim 4, wherein the predetermined range includes 0°C to 409C.

6. An integrated circuit according to claim 5, wherein the predetermined range includes - 'C to 60 °C.

7. An integrated circuit according to any preceding claim, wherein the sensing resistor comprises a plurality of resistors.

8. An integrated circuit according to claim 7, wherein the resistors in the plurality each have substantially the same resistance at a given temperature.

9. An integrated circuit according to claim 7 or 8, wherein each of the plurality of resistors comprises a metal track.

10. An integrated circuit according to claim 9, wherein the metal tracks of the resistors in the plurality are all substantially the same width and length.1 1. An integrated circuit according to any of claims 7 to 10, wherein: a first resistor in the plurality is formed on a first layer of the integrated circuit; and a second resistor in the plurality is formed on a different, second layer of the integrated circuit.

12. An integrated circuit according to claim 11 , wherein a footprint of the first resistor at least partially overlaps a footprint of the second resistor.

13. An integrated circuit according to claim 12, wherein the footprint of the first resistor encompasses the footprint of the second resistor.

14. An integrated circuit according to claim 12, wherein the first and second resistors have the same footprint.

15. An integrated circuit according to any preceding claim, wherein the sensing resistor comprises a winding serpentine metal track.

16. An integrated circuit according to any preceding claim, further comprising a signal processing circuit configured to determine, on the basis of the resistance of the sensing resistor, a temperature of the temperature sensor.

17. An integrated circuit according to claim 16, wherein the signal processing circuit comprises an analogue-to-digital converter.

18. An integrated circuit according to any preceding claim, wherein the sensing resistor and the reference resistor are coupled in series between a voltage supply and ground, such that the sensing resistor and the reference resistor together form a potential divider.

19. An integrated circuit according to claim 18, wherein: one of the sensing resistor and the reference resistor is coupled between a voltage supply and an output node of the temperature sensor; and the other of the sensing resistor and the reference resistor is coupled between the output node and ground.

20. An integrated circuit according to claim 19 when dependent on claim 16 or 17, wherein the signal processing circuit is configured to determine the temperature based on a voltage of the output node.21 . An integrated circuit according to any preceding claim, wherein the metal track comprises one or more of: Titanium, Nickel, Palladium, Platinum, Iron, Osmium,Molybdenum, Tungsten, Aluminium, Copper, Silver, Palladium, Platinum, Gold, Rhodium, Iridium, Zinc, Steel, Nichrome, and Nichrome V.

22. An integrated circuit according to claim 21 , wherein the metal track comprises a sandwich structure comprising layers of different materials.

23. An integrated circuit according to any preceding claim, wherein the integrated circuit comprises a flexible integrated circuit.

24. An integrated circuit comprising a temperature sensor, the temperature sensor comprising: a sensing resistor comprising a metal track formed in a single layer of the integrated circuit; and a signal processing circuit formed at least in part in the single layer of the integrated circuit, the signal processing circuit being configured to determine, on the basis of the resistance of the sensing resistor, a temperature of the temperature sensor.

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