Method and apparatus for temperature compensation of low battery voltage threshold and voltage droop detection in medical devices

Abstract

A method for operating a medical device includes activating a processor that receives power from a battery within the medical device, measuring a temperature within a housing of the medical device, identifying a low battery voltage threshold based on the temperature, measuring a first voltage level of the battery, initiating an operational sequence after measuring the first voltage level of the battery, generating a plurality of voltage comparisons between a reference voltage level and a voltage level supplied by the battery during the operational sequence, and generating an output indicating a low battery condition if at least one of the first voltage levels of the battery is less than the low battery voltage threshold and greater than a predetermined minimum operational voltage threshold or if at least one voltage comparison indicates that the voltage level of the battery is less than the reference voltage level during the operational sequence.

Description

[Technical Field]

[0001] Priority claim This application claims the benefit of U.S. Provisional Patent No. 63 / 068,633, filed August 21, 2020, entitled "Method and Apparatus For Temperature Compensation of Low Battery Voltage Thresholds and Voltage Droop Detection in a Medical Device," the entire contents of which are incorporated herein by reference.

[0002] FIELD OF THE INVENTION FIELD OF THE DISCLOSURE The present disclosure relates generally to the field of battery-powered medical devices, and more particularly to battery-powered medical devices including blood glucose test meters. [Background technology]

[0003] Background of the Invention Analyte test meters known in the art enable the analysis of a bodily fluid sample provided by a user to identify the level of one or more analytes in the user's body using electronic devices and one or more electrochemical reactions. These analyte meters offer significant advantages in the accurate measurement of analytes in an individual user's fluid sample (i.e., biological or environmental). The analyte meter applies an electrical signal to a combination of a reagent and the fluid sample and records the response to the applied electrical signal. The combination of electronic hardware and software in the analyte test meter implements a detection engine that detects the level of an analyte in the user's body based on the recorded response to the electrical signal. For example, a person with diabetes can benefit from measuring glucose by providing a fluid sample of blood or another bodily fluid to a reagent formed on an electrochemical test strip electrically connected to a blood glucose meter (BGM). The BGM provides a measurement of the user's blood glucose level, and many BGM devices use disposable electrochemical test strips that are discarded after each blood glucose measurement. Analyte test meters can also benefit users at risk for heart disease by providing measurements of cholesterol and triglycerides, among other analytes. However, these are just a few of the advantages of measuring analytes in biological samples. Advances in medical science have identified an increasing number of analytes that can be electrochemically analyzed in fluid samples.

[0004] Many existing analyte test meters use batteries as an energy source to power the analyte meter's electronic components, providing a compact, portable test meter carried by a person with diabetes (PwD) or other medical user. In typical use, the test meter is activated for use for a relatively short period, usually one minute or less, to obtain a blood glucose reading. During this period, one or more batteries provide current to operate the components in the test meter. The test meter may be in a stopped or "hibernate" mode for a relatively long period, during which the test meter is deactivated and the battery in the test meter provides a small amount of current, or no current, to the test meter. Even in a high-use scenario, for example, a PwD testing their blood glucose 10 times a day, the blood glucose meter spends most of the day in stopped mode, and many blood glucose meters experience less frequent use, creating longer periods of inactivity. For example, some PwDs test their blood glucose only three times a day, and some PwDs who employ continuous glucose monitors (CGMs) use portable blood glucose meters only occasionally (e.g., once every few days or even once every few weeks / months) to verify and complement the data from the CGM.

[0005] During periods of inactivity, the internal temperature of the BGM may change as the BGM is transported to different environments where it may be exposed to cooler or hotter temperatures for extended periods of time. Temperature changes can affect the nominal voltage of one or more batteries within the BGM, particularly when the BGM is started from an extended period of inactivity in which the battery was not monitored to detect whether discharge had occurred. Temperature fluctuations can lead to false detection of a low-battery condition or failure to detect a low-battery condition, depending on the temperature. Furthermore, the nominal battery voltage measured during operation of the BGM, in a hibernation or light-load state, may not provide sufficient information to identify all low-battery conditions that may occur during operation of the BGM when the battery operates under higher load conditions. Consequently, improvements to blood glucose meters and other battery-powered medical devices that detect low-battery conditions over a wide range of operating temperatures and during operating sequences would be beneficial. Summary of the Invention

[0006] Summary of the Invention In one embodiment, a method for operating a medical device includes activating a processor within the medical device, the processor receiving power from a battery electrically connected to the medical device; measuring, by the processor, a temperature within a housing of the medical device; identifying, by the processor, a first low battery voltage threshold based on the temperature; measuring, by a voltage sensor operably connected to the processor, a first voltage level of the battery; initiating an operational sequence of the medical device after measuring the first voltage level of the battery; generating, by a voltage comparator operably connected to the processor, a plurality of voltage comparisons between a reference voltage level and a voltage level supplied by the battery during the operational sequence; and generating, by the processor, an output using an output device within the medical device, an output indicating a low battery condition in response to at least one of: the first voltage level of the battery being less than the first low battery voltage threshold and greater than a predetermined minimum operating voltage threshold, wherein the predetermined operating voltage threshold is less than the first low battery voltage threshold; or at least one voltage comparison in the plurality of voltage comparisons indicating that the voltage level of the battery is less than the reference voltage level during the operational sequence.

[0007] In another embodiment, a method for operating a medical device includes activating a processor within the medical device, the processor receiving power from a primary battery electrically connected to the medical device; activating, by the processor, at least one peripheral device within the medical device, the at least one peripheral device receiving power from a secondary battery electrically connected to the medical device; measuring, by the processor, a temperature within a housing of the medical device; identifying, by the processor, a first low battery voltage threshold based on the temperature; identifying, by the processor, a second low battery voltage threshold based on the temperature; and determining, by a voltage sensor operably connected to the processor, a first low battery voltage threshold of the primary battery. measuring a voltage level of the secondary battery with a voltage sensor operatively connected to the processor; and generating, by the processor, using an output device within the medical device, an output indicative of a low battery condition in response to at least one of: a first voltage level of the primary battery that is less than a first low battery voltage threshold and above a first predetermined minimum operating voltage threshold of the primary battery, where the first predetermined operating voltage threshold is less than the first low battery voltage threshold; or a second voltage level of the secondary battery that is less than a second low battery voltage threshold and above a second predetermined minimum operating voltage threshold of the secondary battery, where the second predetermined operating voltage threshold is less than the second low battery voltage threshold.

[0008] In another embodiment, a method for operating a medical device includes activating a processor within the medical device, the processor receiving power from a battery electrically connected to the medical device; initiating an operation sequence of the medical device; generating, with a voltage comparator operably connected to the processor, a plurality of voltage comparisons between a reference voltage level and a voltage level supplied by the battery during the operation sequence; and generating, with an output device within the medical device, an output indicating a low battery condition in response to at least one voltage comparison in the plurality of voltage comparisons indicating a voltage level of the battery is less than the reference voltage level during the operation sequence.

[0009] In another embodiment, a method for operating a medical device includes activating a processor within the medical device, the processor receiving power from a battery electrically connected to the medical device; measuring, by the processor, a temperature within a housing of the medical device; identifying, by the processor, a first low battery voltage threshold based on the temperature; measuring, by a voltage sensor operably connected to the processor, a first voltage level of the battery; and generating, by the processor, using an output device within the medical device, an output indicating a low battery condition in response to the first voltage level of the battery being less than the first low battery voltage threshold and greater than a first predetermined minimum operating voltage threshold of the battery, wherein the first predetermined operating voltage threshold is less than the first low battery voltage threshold. [Brief explanation of the drawings]

[0010] Further advantages, benefits, features and objects will become more readily apparent from a consideration of the following detailed description, which refers to the following drawings.

[0011] [Figure 1] FIG. 1 is a schematic diagram of a battery-powered medical device, further depicted as a blood glucose monitor that operates using a single battery. [Figure 2] FIG. 1 is a schematic diagram of a battery-powered medical device further depicted as a blood glucose monitor that operates using two batteries. [Figure 3] 1 is a graph illustrating a temperature dependent low battery threshold function for a primary battery. [Figure 4] 10 is a graph illustrating another temperature dependent low battery threshold function for a secondary battery. [Figure 5] 10 is a graph illustrating an example of voltage droop detected during a series of operations of a battery-powered medical device. [Figure 6] FIG. 3 is a block diagram of a process for detecting a low battery condition during operation of the battery-powered medical device of FIGS. 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0012] Detailed Description of the Invention These and other benefits, advantages, features and objects will be better understood from the following description, in which reference is made to the accompanying drawings which form a part hereof and in which are shown by way of example, and not limitation, embodiments of the inventive concepts. Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

[0013] While the inventive concept is susceptible to various modifications and alternative forms, exemplary embodiments thereof have been shown by way of example in the drawings and are described in detail herein. However, it should be understood that the following description of exemplary embodiments is not intended to limit the inventive concept to the particular form disclosed; rather, the intention is to cover all advantages, effects, and features included within the spirit and scope defined by the embodiments described herein and the following embodiments. Therefore, reference should be made to the embodiments described herein and the following embodiments to interpret the scope of the inventive concept. Therefore, it should be noted that the embodiments described herein may have advantages, effects, and features useful for solving other problems.

[0014] The devices, systems, and methods will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventive concepts are shown. Indeed, the devices, systems, and methods may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

[0015] Similarly, many modifications and other embodiments of the devices, systems, and methods described herein will come to mind to one skilled in the art to which this disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. It is therefore to be understood that the devices, systems, and methods are not limited to the particular embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the embodiments. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the methods, the preferred methods and materials are described herein.

[0017] Furthermore, reference to an element by the indefinite article "a" or "an" does not exclude the possibility that a plurality of elements are present, unless the context clearly requires that one and only one element is present. Thus, the indefinite article "a" or "an" normally means "at least one." Similarly, the terms "have," "comprise," or "include," or any grammatical variations thereof, are used in a non-exclusive manner. Thus, these terms may refer both to a situation in which, in addition to the feature introduced by these terms, no further features are present in the entity described in this context, and to a situation in which one or more additional features are present. For example, the expressions "A has B," "A comprises B," and "A includes B" can all refer to a situation in which no other elements are present in A besides B (i.e., a situation in which A consists solely and exclusively of B), or to a situation in which, in addition to B, one or more further elements are present in A, such as element C, elements C and D, or additional elements.

[0018] FIG. 1 shows a schematic diagram of a battery-powered medical device 100 configured to identify a low-battery condition during an operating sequence over a range of operating temperatures. A housing 50 in the medical device 100 includes a receptacle for a replaceable battery 128 electrically connected to the medical device 100 and encloses the other components of the medical device 100. The medical device 100 operates using power provided by the battery 128 to operate the following peripherals: a processor 104, a memory 116, a user input / output (I / O) peripheral 140, and a wireless transceiver 144. In the illustrative embodiment of FIG. 1, the battery 128 is a single lithium battery, commercially available as a CR2032 coin cell battery with a nominal 3V voltage level when the battery is fully charged. However, in alternative embodiments, the battery 128 is a different type of battery. Furthermore, in alternative embodiments, what is referred to as a single battery 128 further includes multiple battery cells electrically connected in a series, parallel, or series-parallel configuration to act as a power source for components in the medical device. 1, medical device 100 is a blood glucose meter that includes a test strip port 136. Test strip port 136 receives a portion of an electrochemical test strip and provides an electrical connection between electrodes on the test strip and processor 104, allowing processor 104 to apply signals in an electrical test sequence and receive response signals from the test strip, enabling measurement of the glucose level in a blood sample applied to test strip 136. Other medical device embodiments that do not perform blood glucose measurements or other forms of electrochemical analyte measurements do not include test strip port 136.

[0019] In medical device 100, processor 104 includes one or more digital logic devices, such as a microcontroller, microprocessor, application specific integrated circuit (ASIC), or any other electronic device or devices that implement digital logic functions for performing operations to detect a low battery condition and for the operation of medical device 100. Although not depicted in further detail herein, processor 104 also incorporates or is operatively connected to digital-to-analog converters, drive signal generators, signal measurement circuits, and analog-to-digital converters, as well as any other electronic components necessary for processor 104 to generate electrical test sequences that are applied to electrodes in the electrochemical test strip through test strip port 136 and for processor 104 to detect electrical response signals from the electrochemical test strip in response to the electrical test sequences. Although not depicted in further detail herein, processor 104 also includes input / output (I / O) hardware that operatively connects processor 104 to I / O peripherals 140, wireless transceiver 144, and memory 116.

[0020] In medical device 100, processor 104 is operatively connected to clock generator 106, voltage sensor 108, temperature sensor 110, and voltage comparator 112. In the exemplary embodiment of FIG. 1, processor 104 incorporates clock generator 106, voltage sensor 108, temperature sensor 110, and voltage comparator 112 in a system-on-chip configuration to achieve the operative connection, although in other configurations, these components are separate and processor 104 may incorporate the clock generator 106, voltage sensor 108, temperature sensor 110, and voltage comparator 112 in a system-on-chip configuration to achieve the operative connection. 2 The peripheral interconnect may be operably connected thereto via a peripheral interconnect interface such as C, SPI, RS-232 / RS-485, PCI or PCIe, or any other suitable peripheral interconnect.

[0021] In medical device 100, clock generator 106 includes oscillators and other electronic components commonly known in the art for generating clock signals that synchronize the execution of operations of processor 104. Clock generator 106 generates clock signals of at least two different frequencies that regulate the rate of execution of instructions in processor 104 and, in turn, affect the level of power consumption of processor 104 while operating at lower-frequency clock rates, which draw lower power levels than higher-frequency clock rates. In one configuration, processor 104 operates clock generator 106 in a low-power operating mode to generate a 1 MHz clock signal, and processor 104 operates clock generator 106 in a high-power operating mode to generate a 16 MHz clock signal. Of course, alternative processor configurations employ clock generators that generate different specific clock frequencies, and clock generators that are configurable to generate clock signals at three or more different frequencies as well.

[0022] In the medical device 100, the voltage sensor 108 includes an analog voltage measurement device and an analog-to-digital converter (ADC) that provides digital data corresponding to the voltage of the battery 128 to the processor 104. The voltage sensor 108 is operably connected to the battery 128 and to a switchable battery test resistor 132. The voltage sensor 108 detects the voltage across the terminals of the battery 128 both when there is a minimal load on the battery 128 and when the battery 128 is connected to the switchable battery test resistor 132. The switchable battery test resistor 132 includes a resistor of a predetermined resistance level (e.g., 820 ohms) that applies a high impedance load across the terminals of the battery 128. The high impedance load draws minimal current from the battery 128 but allows the voltage sensor 108 to measure both open circuit and loaded voltage levels of the battery 128. The processor 104 operates a switch, such as a solid-state switching transistor or relay, to connect the resistor to the battery 128, allowing the voltage sensor 108 to measure the voltage of the battery 128 under a predetermined load and, after measuring the voltage, to disconnect the battery test resistor 132 from the battery 128. In the embodiments of the medical device 100 and medical device 200 described herein, the ADC in the voltage sensor 108 is connected to different components within the medical device using a multiplexer or other suitable switching element during different portions of an operational sequence within the medical device. For example, the ADC converts analog voltage levels of electrical signal responses from electrodes in a test strip inserted into the test strip port 136 into digital data for the processor 104 during different portions of an analyte measurement operational sequence. Therefore, the voltage sensor 108 cannot be used to perform battery voltage measurements while the ADC is connected to different components within the medical device.

[0023] In the medical device 100, the temperature sensor 110 is a thermocouple, thermistor, resistance temperature detector (RTD), solid-state temperature sensor, or any other suitable device that enables the processor 104 to electronically measure temperature levels. Suitable temperature sensing devices are generally known in the art and will not be described in further detail herein. In the configuration of the medical device 100, the temperature sensor 110 provides an internal temperature measurement corresponding to components, including the battery 128, that are internal to the housing 50 of the medical device 100, and this temperature measurement is not necessarily equivalent to the ambient air temperature of the environment surrounding the medical device 100. Generally, the interior of the medical device 100 is compact, and the components within the medical device 100 will have a substantially uniform temperature when the medical device 100 is shut down or in a low-power operating state. Thus, the processor 104 is configured to receive temperature measurements from the temperature sensor 110 within the housing 50 of the medical device 100 and use the temperature measurements to determine the internal temperature of the battery 128, which the processor 104 further uses to determine a low battery voltage threshold for the battery 128, as described in more detail below.

[0024] In the medical device 100, the voltage comparator 112 is a sensor that compares a predetermined reference voltage with the power supply voltage input from the battery 128. The voltage comparator may be, for example, an operational amplifier (Op-Amp) or other suitable circuit having a first input for a reference voltage signal and a second input that receives the voltage from the battery. The reference voltage may be generated, for example, by a digital-to-analog converter (DAC) utilizing a resistor ladder network, which generates an analog voltage level that is generally below the voltage level supplied by the battery 128 during operation, although the exact voltage level of the reference voltage need not be set to a fixed threshold. In the medical device 100, if the voltage supplied by the battery 128 falls below the reference voltage level during operation of the medical device 100, the voltage comparator 112 generates an output indicating that a voltage droop has occurred, but the voltage comparator does not determine the magnitude by which the voltage droop is below the reference voltage level. 1 , the voltage comparator 112 is gated by a clock signal from the clock generator 106, and the voltage comparator 112 identifies whether a voltage droop of the battery 128 occurs during a single clock cycle, where zero, one, or multiple voltage droops can occur over a series of clock cycles. The output of the voltage comparator 112 sets a binary status flag or counter to enable the processor 104 to identify the detection of one or more voltage droops over a series of clock cycles. The voltage comparator 112 detects transient voltage droops in the voltage level of the battery 128, which is subjected to various loads during operation of the medical device 100 more quickly and efficiently than the voltage sensor 108. However, the voltage comparator 112 does not generate precise voltage measurements; it only detects whether a transient voltage droop occurs during a clock cycle. In contrast, the voltage sensor 108 generates accurate voltage level measurements of the battery 128 during device startup and other low-load conditions when the battery 128 is at or near rest, but as described above, the ADC in the voltage sensor 108 is connected to different components within the medical device during different parts of the operating sequence, while the voltage comparator 112 remains connected to the battery 128 during the operating sequence.

[0025] In medical device 100, memory 116 is a digital data storage device including at least one non-volatile data storage device, such as EEPROM, NAND or NOR flash, phase change memory, or other suitable data storage device, that retains stored digital data even without power from battery 128. Memory 116 further includes one or more volatile memory devices, including static random access memory (RAM) or dynamic RAM, either integrated with processor 104 or embodied as a separate memory device. Memory 116 holds a set of battery voltage thresholds 118 and stored program instructions 122 that processor 104 executes to perform low battery detection operations and other functions of the medical device as described herein.

[0026] The battery voltage thresholds 118 include both fixed and temperature-dependent low battery voltage threshold data that the processor 104 uses to determine the status of the battery 128 based on voltage measurements received from the voltage sensor 108. In the embodiment of FIG. 1, the fixed battery voltage thresholds include a minimum operating voltage threshold required for the medical device 100 to perform normal operation and a fixed dead battery voltage threshold at which the battery 128 is considered discharged to a point where the medical device 100 shuts down without further operation. In one non-limiting configuration, the minimum operating voltage threshold is approximately 2.46 V and the dead battery voltage is approximately 2.40 V. If the battery 128 exhibits a nominal voltage below the minimum operating voltage threshold but greater than the dead battery voltage, the processor 104 generates an error using a display screen, indicator light, or other output device within the user I / O peripherals 140 indicating the need to replace the battery 128, and the medical device 100 does not continue other operations, such as generating blood glucose measurements. If the voltage of the battery 128 is below the dead voltage threshold, the processor 104 immediately shuts down the medical device 100 without generating a battery replacement output.

[0027] The battery voltage threshold 118 also includes a temperature-dependent low battery voltage threshold that is higher than a predetermined minimum battery operating voltage and that the processor 104 uses to identify a low battery condition. If the voltage of the battery 128 is above the temperature-dependent low battery threshold, however, the medical device 100 continues with its normal operating sequence. If the processor 104 identifies that the voltage of the battery 128 is below the temperature-dependent low battery threshold, the processor 104 generates an output using a display screen, indicator light, or other output device within the user I / O peripherals 140 indicating a low battery condition, but because the voltage of the battery 128 is still above the minimum operating voltage threshold, the medical device 100 continues normal operation.

[0028] In one configuration, the medical device 100 implements the temperature-dependent low battery voltage threshold using a piecewise linear function. FIG. 3 shows a graph 300 of an example piecewise linear function for a primary battery in a medical device, such as the battery 128 of FIG. 1. In the graph 300, the temperature-dependent low battery threshold 304 is a piecewise linear function including a first segment 306A that establishes a low battery threshold voltage of approximately 2.46 V for cooler operating temperatures ranging from −10° C. to 5° C. The second segment 306B is another linear segment with a positive slope relative to operating temperature that increases the low battery voltage threshold level as the temperature increases from 5° C. to 60° C. within the operating temperature range of the medical device 100. FIG. 3 illustrates an operating temperature range of −10° C. to 60° C. for the medical device 100. As noted above, these temperatures correspond to internal temperatures measured within the medical device 100 and are not necessarily the same as the ambient air temperature surrounding the medical device 100 during operation. Thus, a temperature of 60°C may correspond to the internal temperature of the medical device 100 when stored in a vehicle in the summer, even if the ambient air temperature is not 60°C, for example.

[0029] 3 also shows a prior art fixed low battery voltage threshold 302 for illustrative purposes, although the medical device 100 does not use the fixed low battery voltage threshold 302. During operation, if the processor 104 and voltage sensor 108 measure a battery voltage level that exceeds the temperature-dependent low battery threshold 304, the medical device 100 continues normal operation, while any voltage measurement below the temperature-dependent low battery voltage threshold 304 but above the minimum operating voltage threshold 312 at the measured temperature allows the medical device 100 to continue normal operation and causes the processor 104 to generate a low battery indicator to alert the user that the battery 128 is approaching the replacement point. The temperature-dependent low battery threshold 304 is lower than the fixed low battery threshold 302 at lower temperatures from −10° C. to 10° C. and higher than the fixed low battery threshold 302 at higher temperatures above 10° C. to 60° C. Therefore, the temperature dependent low voltage threshold 304 reduces the occurrence of false positive low battery voltage detections at lower temperatures and reduces the occurrence of false negative failures to detect low battery conditions at higher temperatures. For all temperature ranges, the temperature dependent low battery threshold 304 is higher than the minimum operating voltage threshold 312.

[0030] In medical device 100, memory 116 stores parameters describing the piecewise linear function, such as the slope, Y-intercept, and breakpoints between segments of the piecewise linear function, and processor 104 calculates the low battery voltage threshold using temperature measurements from temperature sensor 110 as independent variables of the piecewise linear function. In another embodiment, memory 116 stores a lookup table in which processor 104 uses temperature measurements as indexes to identify voltage thresholds stored in the lookup table. In this embodiment, processor 104 optionally interpolates between entries in the lookup table to identify the low battery voltage threshold if the measured temperature value does not match an exact entry value in the lookup table.

[0031] 3 shows an example of a temperature-dependent low battery voltage threshold 304, although the exact voltage threshold levels for different operating temperatures may vary in different medical device embodiments. Furthermore, the temperature-dependent low battery threshold may be formed from a single linear function, a piecewise linear function with two or more segments, or a non-linear function that adjusts the low battery voltage threshold over a temperature range.

[0032] 1 , the user I / O peripherals 140 include input and output devices that allow a user to interact with the medical device 100. Examples of input devices include touchpad and touchscreen input, buttons, switches, dials, and the like. At least some types of input devices receive power from the battery 128, either directly or through drive circuitry in the processor 104. Output devices include displays such as LCD or OLED display screens, indicator lights, audio output speakers, electromechanical actuators for tactile feedback devices, and the like, which also draw power from the battery 128, either directly or through drive circuitry in the processor 104.

[0033] The wireless transceiver 144 may be, for example, a Bluetooth, Bluetooth Low Energy (BLE), IEEE 802.11 "Wi-Fi," Near Field Communication (NFC), cellular, or other wireless transceiver that enables the medical device 100 to communicate wirelessly with external computing devices, including, but not limited to, smartphones, personal computers (PCs), and network services over a data network. In one non-limiting embodiment, the wireless transceiver 144 is implemented as a BLE transceiver with an antenna contained within the housing 50. The wireless transceiver 144 receives power from the battery 128 either directly or via driver circuitry in the processor 104. In some medical device embodiments, the wireless transceiver 144 draws a significant level of power from the battery 128 during operation, particularly during wireless transmission operations. Because some medical devices are not configured for wireless communication with external computing devices, the wireless transceiver 144 is an optional component that need not be included in all embodiments of the medical device.

[0034] FIG. 2 shows a schematic diagram of another battery-powered medical device 200. The medical device 200 includes several elements common to the medical device 100, including the housing 50, the processor 104, the memory 116, the user I / O peripherals 140, and the wireless transceiver 144. The medical device 200 is also depicted as a blood glucose meter that includes a test strip port 136. Unlike the medical device 100, the medical device 200 includes receptacles for two different replaceable batteries, depicted as a primary battery 228 and a secondary battery 254, both electrically connected to the medical device 200. In the configuration of FIG. 2, the primary battery 228 provides power to the processor 104, including the components that generate the electrical test signals for the test strip port 136, and the memory 116. The secondary battery 254 provides power to power the wireless transceiver 144 and the user I / O peripherals 140. In medical device 200, processor 104 uses voltage sensor 108 and switchable battery check resistor 132 to measure the voltage level of primary battery 228, similar to that described above with respect to Figure 1, while a separate power management integrated circuit (PMIC) 250 provides processor 104 with voltage measurements of secondary battery 254. In the illustrative example of Figure 2, primary battery 228 and secondary battery 254 are both lithium batteries commercially available as CR2032 coin cell batteries with a nominal 3V voltage level when the batteries are fully charged.

[0035] 2, the processor 104 also includes a clock generator 106, a voltage sensor 108, a temperature sensor 110, and a voltage comparator 112. In the medical device 200, the voltage comparator 112 is connected only to the primary battery 228. However, in alternative configurations, a second voltage comparator is connected to the secondary battery, or a multiplexer connects the voltage comparator 112 to both the primary battery 228 and the secondary battery 254 at different times.

[0036] 2, the primary battery 228 and the secondary battery 254 can generate different voltage levels during operation of the medical device 200. The memory 116 stores battery voltage threshold data 218 similar to the battery thresholds 118 of the medical device 100, but possibly including separate sets of fixed and temperature-dependent low battery voltage thresholds for the primary battery 228 and the secondary battery 254, although in some embodiments, both the primary battery 228 and the secondary battery 254 use the same voltage thresholds. In the exemplary embodiment of FIG. 2, the battery threshold data 218 includes two different temperature-dependent low battery voltage thresholds used to detect low voltage conditions for the primary battery 228 and the secondary battery 254 based on temperature measurements. In the embodiment of FIG. 2, the medical device 200 uses the temperature-dependent low battery voltage threshold 304 shown above in FIG. 3 for the primary battery 228 and the second temperature-dependent low battery voltage threshold shown in FIG. 4 for the secondary battery 254.

[0037] 4, a graph 400 illustrates a temperature-dependent low battery voltage threshold 404 and a minimum operating voltage threshold 412 for the secondary battery 254. In the graph 400, the temperature-dependent low battery threshold 404 is a piecewise linear function including a first segment 406A that establishes a low battery threshold voltage of approximately 2.41 V for cooler operating temperatures ranging from −10° C. to 5° C. The second segment 406B is another linear segment with a positive slope relative to operating temperature that increases the low battery voltage threshold level as the temperature increases from 5° C. to 60° C. within the operating temperature range of the medical device 100. In the illustrative example of FIG. 4, the low battery voltage threshold and minimum operating voltage threshold for the secondary battery 254 are lower than those for the primary battery 228 at a given temperature. The memory 116 stores temperature-dependent low battery voltage data 218 that also corresponds to a piecewise linear function that enables the determination of the low battery voltage threshold based on temperature measurements. During operation, if the processor 104 and PMIC 250 measure a secondary battery voltage level that exceeds the temperature-dependent low battery threshold 404, the medical device 200 continues normal operation, while any voltage measurement below the temperature-dependent low battery voltage threshold 404 but above the minimum operating voltage threshold 412 at the measured temperature allows the medical device 200 to continue normal operation and causes the processor 104 to generate a low battery indicator to alert the user that the secondary battery 254 is approaching the point of replacement. The processor 104 also performs the same low battery voltage detection operation on the primary battery 228 using the temperature-dependent low battery voltage threshold 304 described above.

[0038] The temperature-dependent low battery threshold 404 is lower than the fixed low battery threshold 402 (shown as a reference) of the prior art at low temperatures from −10° C. to 10° C., and higher than the fixed low battery threshold 402 at high temperatures from above 10° C. to 60° C. Thus, the temperature-dependent low voltage threshold 404 reduces the occurrence of false positive low battery voltage detections of the secondary battery 254 at lower temperatures and reduces the occurrence of false negative failures for detecting a low battery condition at higher temperatures. The temperature-dependent low battery threshold 404 is also greater than the minimum operating voltage threshold 412 of the secondary battery 254 at any temperature within its operating range.

[0039] In medical device 200, memory 116 stores parameters describing the piecewise linear function, such as the slope, Y-intercept, and breakpoints between segments of the piecewise linear function, and processor 104 calculates the low battery voltage threshold using temperature measurements from temperature sensor 110 as independent variables of the piecewise linear function for both primary battery 228 and secondary battery 254 using the selected parameters of both the temperature-dependent low battery voltage threshold. In another embodiment, memory 116 stores one or more lookup tables in which processor 104 uses temperature measurements as indexes into the lookup table to identify voltage thresholds stored in the lookup table. In this embodiment, processor 104 optionally interpolates between entries in the lookup table to identify the low battery voltage threshold if the measured temperature value does not match an exact entry value in the lookup table.

[0040] 6 shows a block diagram of a process 600 for detecting a low battery condition in a medical device. In particular, the process 600 is applicable to a medical device 100 that uses a single battery 128, as well as the primary battery 228 and the secondary battery 254 in the medical device 200. These medical devices and batteries are referred to interchangeably in the context of the process 600 unless otherwise stated herein. In the following description, references to the process 600 performing a function or action refer to the operation of a processor that executes stored program instructions and performs the function or action with respect to other components of the medical device.

[0041] Process 600 begins with the medical device waking up (block 604). In medical device 100 / 200, processor 104 wakes up either upon wake-up from hibernation mode if the medical device is dormant, or in reset mode if the main battery 128 / 228 has been replaced. In either mode, processor 104 operates in a low-power state at a reduced frequency clock speed controlled by clock generator 106 to perform initial battery checks and other start-up procedures before commencing operational sequences to perform analyte tests or other operations.

[0042] The process continues by processor 104 using temperature sensor 110 to measure the temperature within housing 50 of medical device 200, which corresponds to the temperature of primary battery 128 / 228 and secondary battery 254 of medical device 100 / 200 (block 608). As described above, processor 104 also uses temperature measurements and temperature-dependent threshold data 118 / 218 to identify low battery voltage thresholds for primary battery 128 / 228 and, in medical device 200, secondary battery 254 (block 612). Processor 104 also measures the voltage level of primary battery 128 / 228 using voltage sensor 108, and, in medical device 200, measures the voltage of secondary battery 254 using PMIC 250 (block 616). The temperature sensing and battery voltage measurement operations described above with reference to blocks 608 and 616 can be performed in any order or simultaneously.

[0043] During process 600, if the measured voltage level of the primary battery 128 / 228 or the secondary battery 254 is below the identified temperature-dependent low battery voltage threshold (block 620), the processor 104 further determines whether the measured voltage level also exceeds a predetermined operating voltage threshold (block 624). If the measured voltage level of the primary battery 128 / 228 or the secondary battery 254 is also below the corresponding minimum operating voltage threshold, the processor 104 generates a replace battery indicator output or immediately shuts down the medical device 100 / 200 (block 632). In the medical device 100 / 200, the processor 104 operates a display screen, indicator lights, audio output device, or other output device user I / O peripheral 140 to indicate the need to replace the battery 128 or batteries 228 and 254, and the processor 104 prevents further operation of the medical device 100 / 200. If the measured voltage level falls below the dead battery threshold, the processor 104 immediately shuts down the medical device 100 / 200.

[0044] During process 600, if the measured voltage level of primary battery 128 / 228 or secondary battery 254 is below the identified temperature-dependent low battery voltage threshold (block 620), but processor 104 further determines that the measured voltage level exceeds a predetermined minimum operating voltage threshold (block 624), processor 104 generates a low battery status output and continues the standard operating sequence of medical device 100 / 200 (block 628). In medical device 100 / 200, processor 104 operates a display screen, indicator lights, audio output device, or other output device user I / O peripheral 140 to indicate that battery 128 or one or both batteries 228 and 254 are in a low charge state, but the battery does not require immediate replacement for medical device 100 / 200 to execute the operating sequence.

[0045] If the measured voltage level of one or more batteries in the medical device 100 / 200 is greater than the temperature-dependent low battery voltage threshold (block 620), or if the medical device 100 / 200 generates a low battery indicator but one or more batteries are greater than the minimum operating voltage threshold (block 628), the process 600 continues as the medical device 100 / 200 initiates an operational sequence (block 636). As used herein, the term "operational sequence" refers to an operation or series of operations that the medical device 100 / 200 performs during normal operation when one or more batteries can provide sufficient power to enable the execution of the operational sequence. In the medical device 100 / 200, the processor 104 transitions operation to a high-power mode using a high-frequency clock signal from the clock generator 106, and the processor 104 operates other components in the medical device 100 / 200 that increase the load placed on the battery 128 or batteries 228 and 254 during the operational sequence. 6, the operational sequence described below is a measurement sequence for detecting an analyte in a fluid sample, such as a blood glucose measurement. In particular, processor 104 uses voltage comparator 112 to identify voltage droop in primary battery 128 / 228 during an operational sequence in which primary battery 128 / 228 experiences an increased load level. However, other medical devices perform different specific operational sequences that may also generate voltage droop in a manner similar to medical device 100 / 200, and one skilled in the art will recognize that process 600 is also applicable to these medical devices.

[0046] During process 600, processor 104 performs a quality check sequence in response to the insertion of a test strip into test strip port 136 (block 640). During the quality check sequence, processor 104 applies a series of electrical signals to the test strip to ensure that the test strip is not damaged, and processor 104 further verifies that other components within meter 100 / 200 are also operational. Voltage comparator 112 generates a voltage comparison between a reference voltage and the voltage level of primary battery 128 / 228 during each clock cycle of clock generator 106 during the quality check sequence. If all voltage comparisons indicate that the voltage level of primary battery 128 / 228 is greater than the reference voltage (block 644), processor 104 does not identify a voltage droop during the quality check and continues to wait for the fluid sample sequence. However, if the voltage comparator 112 generates one or more voltage comparisons where the voltage of the primary battery 128 / 228 is below the reference voltage for one or more clock cycles, the processor 104 detects one or more voltage droops (block 644), and the processor 104 generates a battery low indicator (block 648). In the medical device 100 / 200, the processor 104 generates a battery low indicator in the same manner as described above with reference to the processing of block 628. Furthermore, if the medical device 100 / 200 has already generated a battery low indicator at any point during the process 600, the previous battery low indicator remains active during the remaining operational sequences and other portions of the process 600.

[0047] The process 600 continues as the processor 104 executes a wait for fluid sample operation in which the processor 104 monitors the test strip to detect when a fluid sample, such as a blood sample, has been applied to the test strip (block 652). The voltage comparator 112 continues to generate voltage comparisons during each clock cycle. If all voltage comparisons indicate that the voltage level of the primary battery 128 / 228 is greater than the reference voltage (block 656), the processor 104 does not identify a voltage droop during the wait for fluid sample operation and continues executing the analyte testing sequence. However, if the voltage comparator 112 generates one or more voltage comparisons in which the voltage of the primary battery 128 / 228 is below the reference voltage for one or more clock cycles, the processor 104 detects one or more voltage droops (block 656), and the processor 104 generates a low battery indicator (block 660).

[0048] Process 600 continues as processor 104 performs an analyte test sequence operation in which, after the test strip receives a fluid sample, such as a blood sample, processor 104 applies a series of electrical signals to the electrodes to detect the presence of an analyte, such as glucose, and provides the results to the user via user I / O peripherals 140 and / or wireless transceiver 144 (block 664). Voltage comparator 112 continues to generate voltage comparisons during each clock cycle. If all voltage comparisons indicate that the voltage level of primary battery 128 / 228 is greater than the reference voltage (block 668), processor 104 identifies that there is no voltage droop during the analyte test sequence, and processor 104 terminates the analyte test sequence operation (block 676). However, if the voltage comparator 112 generates one or more voltage comparisons in which the voltage of the primary battery 128 / 228 is below the reference voltage for one or more clock cycles, the processor 104 detects one or more voltage droops (block 668), and the processor 104 generates a low battery indicator (block 672). After completing the operation, the analyte meter 100 / 200 may remain powered on, and the user I / O device 140 continues to provide a low battery indicator (block 676) if one was generated during one or more of the low battery checks that occur during the process 600. The medical device 100 / 200 can remain powered on to perform another operation sequence or to perform a different operation, such as uploading stored blood glucose data to an external computing device using the wireless transceiver 144. The processor 104 optionally measures the battery voltage of the battery 128 or batteries 228 and 254 using a temperature-dependent low battery voltage threshold before each subsequent operation sequence to continue to identify low battery conditions during operation of the medical device 100 / 200.

[0049] As described above, medical device 100 / 200 and process 600 implement two different techniques for identifying a low battery condition: the use of a temperature-dependent voltage low battery threshold using DC voltage measurements of one or more batteries prior to an operational sequence, and the use of a voltage comparator to identify voltage droop of a primary battery during an operational sequence. While FIG. 5 illustrates a graph 500 showing a series of analyte measurement tests performed in an embodiment of medical device 200 based on a primary battery 228 discharging during the series of tests, a medical device 100 using a single battery 128 would produce results similar to those of graph 500. Each test number in graph 500 corresponds to a single activation of the test meter and execution of an operational sequence for testing an analyte in a fluid sample. Graph 500 includes measurements of voltage thresholds 504, 508, and 512, a nominal battery voltage measurement curve 516, and voltage droops 520 and 524 that occur during the quality check and analyte test sequences, respectively. Thresholds 504, 508, and 512 represent the low battery voltage threshold, minimum operating voltage threshold, and dead battery voltage threshold, respectively. As described above, medical device 100 / 200 identifies the low battery voltage threshold based on temperature, and low battery voltage 504 is shown for a fixed temperature used during testing for illustrative purposes. Voltage measurement curve 516 illustrates the gradual decrease in the nominal voltage of primary battery 228, as measured by processor 104 using voltage sensor 108, while primary battery 228 is in a low-load condition. Voltage droop curves 520 and 524 illustrate the total number of voltage droops detected by processor 104 during either the quality check (520) or analyte test sequence (524) of a single test sequence. Process 600 also includes waiting for the fluid drop portion of the operating sequence; however, voltage droop during this portion of the sequence occurs infrequently and is omitted from FIG. 5 for simplicity. Graph 500 shows that the number of detected voltage droops generally increases as the battery discharges over multiple test sequences, although the voltage droop counts can vary between individual test sequences.In particular, at reference numeral 522, analyte test sequence curve 524 experiences an initial voltage droop, while standard battery voltage curve 516 remains well above low battery voltage threshold 504. Similarly, at reference numeral 526, quality check curve 520 experiences a first voltage droop, while standard battery voltage curve 516 remains above low battery voltage threshold 504. As shown in FIG. 5 , detecting a voltage droop allows processor 104 to detect a low battery condition earlier during operation compared to simply measuring the battery's nominal voltage. Similarly, a temperature-dependent low battery voltage threshold increases the accuracy of identifying whether the battery's nominal voltage actually indicates a low battery condition during operation of the medical device.

[0050] While the embodiments described herein use both a temperature-dependent low battery voltage threshold and detection of voltage droop during an operating sequence to improve the accuracy of detecting a low battery condition, those skilled in the art will recognize that these features can be implemented independently of one another. For example, an alternative embodiment of a medical device may use the temperature-dependent low battery voltage threshold described herein to detect a low battery condition over a wide range of operating temperatures without further detecting voltage droop. Similarly, another embodiment of a medical device may perform the voltage droop detection described herein while not measuring the nominal battery voltage or using a conventional fixed voltage threshold to detect a low battery condition. However, the two techniques described herein provide particular advantages to the medical device 100 / 200. As mentioned above, the first method, using an ADC in the voltage sensor 108, returns a digital value that can then be used to compensate the battery voltage for temperature. The processor 104 incorporates a single ADC but uses a multiplexer to select different inputs for measurement, including the electrodes in the test strip. When the medical device 100 / 200 is not performing time-critical measurements, the ADC can be used to measure the battery voltage. If the processor 104 is performing a time-critical measurement, such as measuring the voltage and current of an analyte measurement test strip during a blood glucose or other analyte measurement, the processor 104 cannot interrupt this critical timing to measure the battery voltage. The second method, using the voltage comparator 112, provides a yes / no status for the primary battery 128 and does not affect the processor 104's timing. Thus, the processor 104 is configured to check for voltage droop based on a status flag received from the voltage comparator 112 after the time-critical measurement is completed and determine whether the battery voltage fell below a reference voltage while the processor was performing other time-critical functions. In this way, the medical device 100 / 200 can monitor one or more batteries during both device initialization and sleep periods, as well as during operational sequences, to improve detection of low battery conditions.

[0051] The present disclosure will be described in connection with what are considered to be the most practical and preferred embodiments. However, these embodiments are presented by way of example, and the scope of protection is not intended to be limited to the disclosed embodiments. Accordingly, those skilled in the art will understand that the present disclosure encompasses all modifications and alternative arrangements within the spirit and scope of the present disclosure and as set forth in the following claims.

Claims

1. 1. A method for operating a medical device, comprising: activating a processor within the medical device that receives power from a battery electrically connected to the medical device; measuring, with the processor, a temperature within a housing of the medical device; identifying, by the processor, a first low battery voltage threshold based on the temperature; measuring a first voltage level of the battery with a voltage sensor operably connected to the processor; initiating an operation sequence of the medical device after measuring the first voltage level of the battery; generating, with a voltage comparator operatively connected to the processor, a plurality of voltage comparisons between a reference voltage level and a voltage level supplied by the battery during the operating sequence; by the processor using an output device within the medical device; a) the first voltage level of the battery that is less than the first low battery voltage threshold and greater than a predetermined minimum operating voltage threshold, the predetermined minimum operating voltage threshold being less than the first low battery voltage threshold; or b) at least one voltage comparison in the plurality of voltage comparisons indicating that the voltage level of the battery is less than the reference voltage level during the operating sequence; generating an output indicative of a low battery condition in response to at least one of: A method comprising:

2. Identifying the first low battery voltage threshold comprises: The method of claim 1 , further comprising: identifying, by the processor, the first low battery voltage threshold using a predetermined piecewise linear function stored in a memory of the medical device.

3. The method of claim 2 , wherein the memory stores parameters of the piecewise linear function, and the processor uses the parameters to calculate the first low battery voltage threshold.

4. 3. The method of claim 2, wherein the memory stores a lookup table corresponding to the piecewise linear function, and the processor uses the lookup table to identify the first low battery voltage threshold.

5. The operation sequence is quality check process, A fluid sample waiting process; and 5. The method of claim 1, further comprising an analyte test sequence process, wherein the voltage comparator generates the plurality of voltage comparisons during each of the quality check process, the fluid sample waiting process, and the analyte test sequence process.

6. A medical device configured to carry out the method according to any one of claims 1 to 5.

7. 1. A method for operating a medical device, comprising: activating a processor within the medical device that receives power from a primary battery electrically connected to the medical device; activating, by the processor, at least one peripheral device within the medical device that receives power from a secondary battery electrically connected to the medical device; measuring, with the processor, a temperature within a housing of the medical device; identifying, by the processor, a first low battery voltage threshold based on the temperature; identifying, by the processor, a second low battery voltage threshold based on the temperature; measuring a first voltage level of the primary battery with a voltage sensor operably connected to the processor; measuring a second voltage level of the secondary battery with the voltage sensor operably connected to the processor; by the processor using an output device within the medical device; a) the first voltage level of the primary battery that is less than the first low battery voltage threshold and greater than a first predetermined minimum operating voltage threshold of the primary battery, the first predetermined minimum operating voltage threshold being less than the first low battery voltage threshold; or b) the second voltage level of the secondary battery that is less than the second low battery voltage threshold and greater than a second predetermined minimum operating voltage threshold of the secondary battery, the second predetermined minimum operating voltage threshold being less than the second low battery voltage threshold; generating an output indicative of a low battery condition in response to at least one of: A method comprising:

8. initiating an operation sequence of the medical device after measuring the first voltage level of the primary battery and the second voltage level of the secondary battery; generating, with a voltage comparator operatively connected to the processor, a plurality of voltage comparisons between a reference voltage level and a voltage level supplied by the primary battery during the operating sequence; generating, by the processor, the output device within the medical device, the output indicative of the low battery condition in response to at least one voltage comparison in the plurality of voltage comparisons indicating that the voltage level of the primary battery is less than the reference voltage level during the operating sequence; The method of claim 7 further comprising:

9. A medical device configured to perform the method according to claim 7 or 8.

10. 1. A method for operating a medical device, comprising: activating a processor within the medical device that receives power from a battery electrically connected to the medical device; initiating an operation sequence of the medical device; generating, with a voltage comparator operatively connected to the processor, a plurality of voltage comparisons between a reference voltage level and a voltage level supplied by the battery during the operating sequence; generating, by the processor, an output device within the medical device, an output indicative of a low battery condition in response to at least one voltage comparison in the plurality of voltage comparisons indicating that the voltage level of the battery is less than the reference voltage level during the operating sequence; A method comprising:

11. A medical device configured to perform the method of claim 10.

12. 1. A method for operating a medical device, comprising: activating a processor within the medical device that receives power from a battery electrically connected to the medical device; measuring, with the processor, a temperature within a housing of the medical device; identifying, by the processor, a first low battery voltage threshold based on the temperature; measuring a first voltage level of the battery with a voltage sensor operably connected to the processor; generating, by the processor, an output device within the medical device, an output indicative of a low battery condition in response to the first voltage level of the battery being less than the first low battery voltage threshold and greater than a first predetermined minimum operating voltage threshold of the battery, the first predetermined minimum operating voltage threshold being less than the first low battery voltage threshold; A method comprising:

13. A medical device configured to perform the method of claim 12.

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