Current-based temperature measuring devices and methods

Abstract

Temperature measuring system (100) which features: a Proportional-To-Absolute-Temperature (PTAT) current source (120); a capacitor (130) which is selectively connected to the PTAT current source (120) by means of a controllable switch (132); a controller coupled to a timer and configured to control the switch (132) to couple the capacitor (130) to the PTAT power source (120) for a charging time determined by the timer, wherein the capacitor (130) is charged to a voltage during the charging time; an analog-to-digital converter (ADC) (140) having an input coupled to the capacitor (130) and configured to generate a digital representation of the voltage across the capacitor (130) after the capacitor (130) has been charged for the charging time predetermined by the timer; and an electronic circuit (144, 142) configured to calculate a temperature based on the digital representation of the voltage across the capacitor (130).

Description

[0001] The present disclosure relates to temperature measuring devices and methods, and in particular to current-based temperature measuring devices and methods, e.g. using a proportional-to-absolute temperature (PTAT) current source for temperature measurement.

[0002] Various electronic methods are used for temperature measurement. For example, some devices or methods employ resistance-based temperature measurement, such as driving a resistor with a fixed current source, measuring the voltage across the resistor, and determining a temperature value as a function of the measured voltage. However, resistance-based techniques often have limited accuracy and / or conversion speed.

[0003] Another example is the use of a resistance divider technique for temperature measurement, e.g., by using resistors in the divider circuit with different known temperature coefficients. However, this technique typically suffers from slow response times, limited accuracy, and / or linearity problems.

[0004] As another example, some devices or techniques use diode-based temperature measurement, e.g., by driving a diode with a fixed current source, measuring the voltage across the diode, and determining a temperature value as a function of the measured voltage. However, diode-based techniques often suffer from a slow response time, limited accuracy, and / or low resolution.

[0005] A high-resolution temperature measurement device is known from US patent application US 2013 / 0 121 372 A1. A temperature sensor is known from US patent application US 2010 / 0 123 510 A1. A temperature sensor is known from US patent US 6078208 A. A thermal detection circuit is known from German patent application DE 10 2016 100 061 A1. A time-domain temperature sensor is known from Chinese patent application CN 1 02 865 943 A. A DRAM temperature measurement system is known from US patent application US 2006 / 0 190 210 A1. A precision reference circuit and associated method are known from US patent application US 2014 / 0 084 899 A1. A thermal sensor with temperature control is known from US patent application US 2014 / 0 269 839 A1. A ratio meter for a thermal sensor is known from US patent application US 2014 / 0 211 905 A1.A temperature sensor and a temperature measurement method are known from US patent application US 2013 / 0 272 341 A1. A temperature sensor integrated in a time domain is known from US patent application US 2017 / 0 016 776 A1.

[0006] Therefore, an accurate, fast, reliable, and cost-effective method for temperature measurement is required. This and other tasks are solved by the independent claims. Further developments are described in the dependent claims.

[0007] According to one embodiment, a temperature measurement system may comprise: a proportional-to-absolute temperature (PTAT) current source; a capacitor selectively connected to the PTAT current source by a controllable switch; a controller configured to control the switch to couple the capacitor to the PTAT current source for a charging period, during which the capacitor may be charged to a voltage; an analog-to-digital converter (ADC) with an input coupled to the capacitor, configured to generate a digital representation of the voltage across the capacitor; and an electronic circuit configured to calculate a temperature based on the digital representation of the voltage across the capacitor.

[0008] According to another embodiment, a zero-change-to-absolute-temperature (ZTAT) current sink can be configured to adjust a capacitor charging current to a desired value. According to another embodiment, PTAT and ZTAT currents can be generated by bandgap circuits. According to another embodiment, a current mirror can be provided to increase the current available from the PTAT current source. According to another embodiment, a current mirror can be provided to adjust a temperature coefficient of the PTAT current source. According to another embodiment, a current mirror can be provided to enhance the current processing capacity of the ZTAT current sink.

[0009] According to another embodiment, the temperature measurement system can have a temperature measurement resolution selected from a group consisting of less than 1 °C, less than 0.5 °C, less than 0.2 °C, less than 0.1 °C, and less than 0.05 °C. According to another embodiment, the charging time can be selected from a group consisting of less than 1 second, less than 100 milliseconds, less than 10 milliseconds, less than 1 millisecond, less than 100 µs, less than 10 µs, less than 1 µs, and less than 100 ns. According to a further embodiment, the charging time can be approximately 625 ns.

[0010] According to another embodiment, the temperature measurement system can include a microcontroller. According to another embodiment, the microcontroller can include: a microprocessor; a memory coupled to the microprocessor that stores a program for determining the temperature from the digital representation of the voltage across the capacitor. According to another embodiment, the microcontroller can include the ADC and the controllable switch. According to another embodiment, a short-circuit switch can be provided to discharge the capacitor before charging during the charging process. According to another embodiment, the controller controls the short-circuit switch.

[0011] According to another embodiment, a method for measuring the temperature may comprise the following steps: providing a current proportional to the absolute temperature (PTAT) from a current source; charging a capacitor with the current from the PTAT current source for a charging time; measuring a voltage across the capacitor after the charging time; and converting the measured voltage into a temperature.

[0012] According to a further embodiment of the method, the step of converting the measured voltage into a temperature can comprise the following steps: determining a reference voltage across the capacitor, where the reference voltage can be equal to the current from the PTAT current source at a given temperature multiplied by the charging time divided by a capacitance of the capacitor; determining a current / temperature slope of the PTAT current source; converting the current / temperature slope into a voltage / temperature slope over the charging time; and calculating the temperature from the reference voltage and the voltage / temperature slope.

[0013] According to another embodiment of the method, the step of adjusting the capacitor charging current to a desired value can be performed using a current sink with zero change with absolute temperature (ZTAT). According to another embodiment of the method, the step of increasing the current from the PTAT current source can be performed using a mirror current source. According to another embodiment of the method, the step of increasing the temperature coefficient of the PTAT current source can be performed using a mirror current source.

[0014] According to yet another embodiment, a device for measuring temperature may comprise: a microcontroller having a microprocessor with memory, an analog-to-digital converter (ADC) with an output coupled to the microprocessor, a capacitor coupled to an input of the ADC, a first switch coupled between a first node and the capacitor, a second switch coupled between the capacitor and a common voltage (ground), a switching control coupled to the microprocessor and the first and second switches, and a timer coupled to the microprocessor and the switching control; and a current source proportional to the absolute temperature (PTAT) coupled between a supply voltage and the first node; wherein the first switch closes for a certain time and then opens; the ADC measures a voltage across the capacitor after a certain time;and the microprocessor converts the measured voltage into a temperature reading.

[0015] According to another embodiment, the second switch can close and discharge the capacitor before the first switch closes. According to yet another embodiment, a zero-change-to-absolute-temperature (ZTAT) current sink can be configured to set a charging current to the capacitor.

[0016] A more complete understanding of the present arrangement can be obtained by referring to the following description in conjunction with the accompanying drawings, which: Fig. Figure 1 illustrates a schematic block diagram of a PTAT-based temperature measurement system according to a specific exemplary embodiment of this arrangement.

[0017] While the present disclosure is accessible for various modifications and alternative forms, specific exemplary embodiments thereof have been shown in the drawings and are described in detail here. It should be understood, however, that the description of specific exemplary embodiments herein is not intended to limit the disclosure to the embodiments disclosed herein.

[0018] Exemplary aspects of the present disclosure are discussed below in connection with Fig. 1 described, which shows an exemplary system for temperature measurement using a PTAT current source according to an exemplary embodiment.

[0019] Embodiments of the present arrangement provide systems, devices, and methods for providing high-resolution temperature measurement using a proportional-to-absolute temperature (PTAT) current source. Some embodiments use a PTAT current source to charge a capacitor for a fixed period of time, applying a voltage to the capacitor that is proportional to the current and thus proportional to the temperature of the PTAT, which may substantially correspond to the temperature surrounding it. This voltage can be measured, and a temperature can be calculated or determined from the measured voltage.

[0020] Some embodiments use analog signals generated by a bandgap. For example, a bandgap can be designed to generate a reference voltage that is stable over temperature. Additionally, a bandgap can generate three basic currents: 1. PTAT - Proportional to absolute temperature. The PTAT delivers a current that has a linear relationship to temperature. 2. ZTAT - Zero change to absolute temperature. The ZTAT provides a current that is stable and does not change with temperature. This current can be used to adjust the offset of the temperature measuring circuit to the desired value, as fully disclosed below. 3. NTAT - Negatively proportional to the absolute temperature. The NTAT delivers a current that has a negative temperature coefficient.

[0021] Some embodiments of the present invention, e.g. the one in Fig. The example discussed below uses the PTAT and ZTAT currents generated by a bandgap to provide high-resolution temperature measurement. For instance, some embodiments can use the ZTAT to set the offset to the desired PTAT value, as discussed below. A current mirror circuit can be used in combination with the bandgap to provide PTAT and / or ZTAT with higher current capacity and to set the operating current of PTAT and / or ZTAT. A current mirror circuit can also provide a setting for the change in current per degree of temperature, such as the slope in microamperes per degree Celsius (mA / °C). The delta of temperature change per degree Celsius and Kelvin is the same and is used interchangeably here.

[0022] With reference to the drawing, the details of exemplary embodiments are shown schematically. Identical elements in the drawings are represented by the same numbers, and similar elements are represented by the same numbers with a different lowercase suffix. With reference to Fig. Figure 1 shows a schematic block diagram of a PTAT-based temperature measurement system according to a specific exemplary embodiment of this arrangement. Fig. Figure 1 shows an exemplary temperature measurement system, generally represented by the numeral 100, for temperature measurement using PTAT and ZTAT current sources, e.g., generated by a band gap. The temperature measurement system 100 can comprise a PTAT current source 120, a ZTAT current sink 122, a capacitor 130, switches 132 and 134, an analog-to-digital converter (ADC) 140, a microprocessor 144, a memory 142, a timer 146, and a switch controller 148. All of the aforementioned components, with the exception of the PTAT 120 and the ZTAT 122, can be provided in a microcontroller 102. It is considered, and is within the scope of protection of this disclosure, that current mirrors can be used to increase the current output / reduction of the PTAT 120 and / or ZTAT 122, as well as the amount of current supplied / reduced by each device.Additionally, the current change in relation to the temperature change (slope of current / temperature transfer) can be adjusted using an associated current mirror.

[0023] The microprocessor 144 can instruct the switch controller 148 to open switch 132 and close switch 134 to reset the charge on capacitor 130 to zero, and then open switch 134. The microprocessor 144 can also instruct the timer 146 to start and close switch 132, and then open switch 132 when timer 146 expires. This provides a precise charging time for capacitor 130, which stores a voltage. The ADC 140 converts this voltage into a digital value, which is provided to the microprocessor 144. The microprocessor 144 is controlled by a program in memory 142, which can be used to convert the digital value of the capacitor voltage into a temperature reading. The ZTAT current sink 122 can be used as an offset to adjust the charging current to the capacitor 130 to a desired value (diverting excess current from the PTAT).

[0024] Capacitor 130 can be integrated into or separate from a sampling and holding capacitor associated with ADC 140. Switch 132 can be controlled by suitable control electronics, such as microprocessor 144, timer 146, and switch controller 148, to close switch 132 at T1 and open it at T2 after a predefined duration (e.g., determined by timer 146), so that capacitor 130 is charged during a charging time from T2 to T1. The charging time (via the opening and closing of switch 132) can be controlled based on a clock signal from timer 146. System 100 can use any suitable charging time for capacitor 130, e.g., 625 ns, which is used in the following example.

[0025] An exemplary implementation of System 100 can be designed as follows. Two equations apply to this example implementation: (Equation 1) I = C * (V / T), where I is current, C is capacitance, V is voltage and T is time; (Equation 2) I = 40 * K, where 40 equals 40 nA per degree K (slope) and K is the temperature in Kelvin.

[0026] At -40 °C (Celsius), the current I = 40(273 - 40) or 9.32 microamperes (µA) according to Equation 2. For Equation 1, we use: C = 5 picofarads (pF), V = 0.2 volts (V), and T = 625 nanoseconds (ns). Therefore, I = 1.6 µA. From Equations 1 and 2, two different values ​​for I are obtained: 1.6 µA and 9.32 µA. The current of 9.32 µA can be supplied by the PTAT 120 ( Fig. 1) The difference can be corrected by replacing ZTAT 122 ( Fig. 1) is set to 7.72 µA to ensure the desired current of 1.6 µA at 233 K (-40 °C). The final equation is then: I=C*(V / T)+offset Combining equations 1 and 2 C*(V / T)+offset−6=slope*K Solving for K K=(C*(V / T)+offset)−slope

[0027] Furthermore, the resulting slope is = 40 nA / °C * 625 ns / 5 pF = 5.0 millivolts (mV) / °C. In other words, the PTAT 120 current source exhibits a voltage / temperature relationship of 5.0 mV / °C. It should be noted that the temperature change per degree Celsius corresponds to the temperature change per degree Kelvin.

[0028] The example 12-bit ADC with 3.3 V offers an ADC resolution of 3.3 V / 4096 = 806 microvolts (µV) / number (CNT). Therefore, the temperature resolution of this example implementation is = (806 µV / CNT / (5.0 mV / °C) = 0.161 °C / CNT.

[0029] It should be noted that the components discussed above are only an example. Therefore, different PTAT current sources and ADC components with different operating parameters can be used.

[0030] The present invention can provide one or more advantages. For example, the invention utilizes a linear relationship between current and temperature. As another example, the offset and gain can be easily adjusted to enable higher temperature resolution. As yet another example, the invention can provide fast measurements, e.g., less than 2 µs. Furthermore, the invention can have a very small or minimal impact on chip area (e.g., no operational amplifiers are required for improved resolution). Additionally, the disclosed system can generate less noise than conventional systems. Furthermore, the disclosed system can be easier to calibrate than conventional systems.

[0031] The present invention has been described in relation to one or more preferred embodiments, and it should be acknowledged that many equivalents, alternatives, variations and modifications, apart from those expressly stated (e.g. manufacturing process, product according to process, etc.), are possible and fall within the scope of protection of the invention.

Claims

[1] Temperature measuring system (100) comprising: a Proportional-To-Absolute-Temperature (PTAT) current source (120); a capacitor (130) which is selectively connected to the PTAT current source (120) by means of a controllable switch (132); a controller coupled to a timer and configured to control the switch (132) to couple the capacitor (130) to the PTAT power source (120) for a charging time determined by the timer, wherein the capacitor (130) is charged to a voltage during the charging time; an analog-to-digital converter (ADC) (140) having an input coupled to the capacitor (130) and configured to generate a digital representation of the voltage across the capacitor (130) after the capacitor (130) has been charged for the charging time predetermined by the timer; and an electronic circuit (144, 142) configured to calculate a temperature based on the digital representation of the voltage across the capacitor (130). [2] Temperature measuring system (100) according to claim 1, further comprising a zero-change-to-absolute temperature (ZTAT) current sink (122) configured to adjust a capacitor charging current to a desired value. [3] Temperature measuring system (100) according to claim 2, wherein PTAT and ZTAT currents are generated by band gap circuits. [4] Temperature measuring system (100) according to one of claims 1 to 3, further comprising a first current mirror to increase the current available from the PTAT current source (120). [5] Temperature measuring system (100) according to one of claims 1 to 4, further comprising a second current mirror to adjust a temperature coefficient of the PTAT current source (120). [6] Temperature measuring system (100) according to one of claims 2 to 5, further comprising a third current mirror to increase the current handling of the ZTAT current sink. [7] Temperature measuring system (100) according to any one of claims 1 to 6, wherein the temperature measuring system has a temperature measurement resolution of less than 1 °C, less than 0.5 °C, less than 0.2 °C, less than 0.1 °C or less than 0.05 °C. [8] Temperature measuring system (100) according to one of claims 1 to 7, wherein the charging time consists of less than 1 second, less than 100 milliseconds, less than 10 milliseconds, less than 1 millisecond, less than 100 µs, less than 10 µs, less than 1 µs or less than 100 ns. [9] Temperature measuring system (100) according to one of claims 1 to 7, wherein the charging time is 625 ns. [10] Temperature measuring system (100) according to any one of claims 1 to 9, wherein the temperature measuring system comprises a microcontroller (102). [11] Temperature measuring system (100) according to claim 10, wherein the microcontroller (102) comprises: a microprocessor (144); and a memory (142) which is coupled to the microprocessor (144) and stores a program for determining the temperature from the digital representation of the voltage across the capacitor (130). [12] Temperature measurement system (100) according to one of claims 10 to 11, wherein the microcontroller (102) comprises the ADC (140) and the controllable switch (132). [13] Temperature measuring system (100) according to one of claims 1 to 12, which further comprises a short-circuit switch (134) for discharging the capacitor (130) before charging. [14] Temperature measuring system (100) according to claim 13, wherein the controller controls the short-circuit switch (134). [15] Method for measuring temperature, wherein the method comprises the steps for operating one of the temperature measuring systems (100) according to claims 1 to 14.

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