Patent Description:
Devices, systems, and methods for assaying analytes in body fluids, as well as biosensors for use therein, are well known. For example, electrochemical-based measuring methods are known that generally rely upon correlating a current (amperometry), a potential (potentiometry), or an accumulated charge (coulometry) to an analyte concentration, typically in conjunction with a detection reagent that produces charged-carriers when combined with an analyte of interest. Common types of single-use biosensors include test strips that conduct such electrochemical tests when connected to a meter that generates a series of test signals to analyze reactions that occur between a body fluid sample and one or more reagents that are formed on the test strip.

In general, test strips have a reaction zone that includes measurement electrodes in communication with one or more detection reagents that come into direct contact and thus chemically interact with a body fluid sample. In some amperometric and coulometric electrochemical-based measurement systems, the measurement electrodes are attached to electronic circuitry in an analyte test meter that supplies an electrical potential to the measurement electrodes and measures a response of the test strip to this potential (e.g., current, impedance, charge, etc.). As such, the biosensor is attached or inserted into the analyte test which then measures a reaction between an analyte in the body fluid sample and the detection reagent to determine the analyte concentration, where the measurement of the electrical signal response indicates the analyte concentration.

The analyte measurement process requires a user to place a dose of the fluid sample, which is typically blood but may be a different type of bodily fluid, onto a predetermined region of the test strip that includes the reagent. Ensuring that the proper amount of the fluid is applied to the test strip is one part of the operation of the test strip and analyte test meter, which is sometimes referred to as "sample sufficiency" detection. The sample sufficiency detection ensures that the user has applied enough blood or other bodily fluid to the test strip, but some modern test strips only require a small sample on the order of, for example, <NUM>µL, or a fraction of a microliter such as a range of <NUM>µL to <NUM>µL to provide a proper sample. In some situations, the user does not retract his or her finger or other body part from the test strip even after the test strip has received a sufficiently large sample to conduct an analyte measurement. The contact between the body of the user and the reagents and electrodes in the test strip may reduce the accuracy of detecting the analyte in the fluid sample. Given these challenges, improvements to analyte test meters that reduce or eliminate the issues produced by contact between a user and the electrochemical test strip during analyte measurement would be beneficial.

<CIT> discloses a hand-held test meter with body portion proximity sensor module. <CIT> discloses an analyte meter and method of operation. <CIT> discloses analyte measurements for electrochemical test strip based on multiple calibration parameters.

In one embodiment, an analyte test meter includes a test strip port configured to receive a first portion of an electrochemical test strip, a capacitive sensor positioned proximate to the test strip port and coupled to at least one electrode in the electrochemical test strip, and a controller connected to the test strip port and the capacitive sensor. The controller is configured to identify insertion of the first portion of the electrochemical test strip into the test strip port, apply a drive signal to the capacitive sensor after the insertion, measure a first response to the drive signal from the capacitive sensor corresponding to a first level of capacitance in the capacitive sensor, identify dosing of a fluid sample on a second portion of the electrochemical test strip that is outside of the analyte test meter after the measurement of the first response, apply the drive signal to the capacitive sensor after the identification of the dosing, measure a second response to the drive signal from the capacitive sensor corresponding to a second level of capacitance in the capacitive sensor, and detect contact between a body of a user and at least one electrode in the electrochemical test strip in the second portion of the electrochemical test strip in response to a difference between the first response and the second response exceeding a predetermined threshold.

In another embodiment, a method for operating an analyte test meter to detect contact with a user and an electrochemical test strip has been developed. The method includes identifying, with a controller in the analyte test meter, insertion of the first portion of the electrochemical test strip into a test strip port in the analyte test meter, applying, with the controller, a drive signal to a capacitive sensor in the analyte test meter after the insertion, measuring, with the controller, a first response to the drive signal from the capacitive sensor corresponding to a first level of capacitance in the capacitive sensor, identifying, with the controller, dosing of a fluid sample on a second portion of the electrochemical test strip that is outside of the analyte test meter after the measurement of the first response, applying with the controller, the drive signal to the capacitive sensor after the identification of the dosing, measuring, with the controller, a second response to the drive signal from the capacitive sensor corresponding to a second level of capacitance in the capacitive sensor, and detecting, with the controller, contact between a body of a user and at least one electrode in the electrochemical test strip in the second portion of the electrochemical test strip in response to a difference between the first response and the second response exceeding a predetermined threshold.

The advantages, effects, features and objects other than those set forth above will become more readily apparent when consideration is given to the detailed description below. Such detailed description makes reference to the following drawings, wherein:.

These and other advantages, effects, features and objects are better understood from the following description. In the description, reference is made to the accompanying drawings, which form a part hereof and in which there is shown by way of illustration, not limitation, embodiments of the inventive concept. Corresponding reference numbers indicate corresponding parts throughout the several views of the drawings.

While the inventive concept is susceptible to various modifications and alternative forms, exemplary embodiments thereof are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description of exemplary embodiments that follows is not intended to limit the inventive concept to the particular forms disclosed, but on the contrary, the intention is to cover all advantages, effects, and features falling within the scope thereof as defined by the embodiments described herein and the claims below. Reference should therefore be made to the embodiments described herein and claims below for interpreting the scope of the inventive concept. As such, it should be noted that the embodiments described herein may have advantages, effects, and features useful in solving other problems.

The devices, systems and methods now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventive concept 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.

Likewise, many modifications and other embodiments of the devices, systems and methods described herein will come to mind to one of skill in the art to which the disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the devices, systems and methods are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art to which the disclosure pertains. Although any methods and materials similar to 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.

Moreover, reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one element is present, unless the context clearly requires that there be one and only one element. The indefinite article "a" or "an" thus usually means "at least one. " Likewise, the terms "have," "comprise" or "include" or any arbitrary grammatical variations thereof are used in a non-exclusive way. For example, the expressions "A has B," "A comprises B" and "A includes B" may refer both to a situation in which, besides B, no other element is present in A (i.e., a situation in which A solely and exclusively consists of B) or to a situation in which, besides B, one or more further elements are present in A, such as element C, elements C and D, or even further elements.

The embodiments described herein enable detection of contact between the finger or other body part of a user and exposed electrodes in a portion of a test strip that is located outside of the housing of an analyte test meter. As used herein, the term "contact" with a user refers any of direct contact with the skin of the user and an electrode in the test strip <NUM> after the electrode has been dosed with a fluid sample, where the contact electrically connects the body of the user to one or more electrodes in the test strip <NUM>. The contact between the user and the exposed electrode occurs via blood or another bodily fluid that provides an electrically conductive path between the electrodes of the test strip and the body of the user. The illustrative examples provided herein often refer to detection of contact of a finger of the analyte meter user with the test strip, but any reference to a finger should be understood to be generally applicable to a body part of a human, including the user of the analyte test meter or any other person handling the analyte test meter.

<FIG> depicts an example of an analyte test meter <NUM> with a removable test strip <NUM> that is depicted as being inserted into the analyte test meter <NUM> via a test strip port <NUM>. The test strip <NUM> is an electrochemical test strip that includes both a chemical reagent that reacts with a fluid sample and electrodes that enable the analyte test meter <NUM> to apply electrical signals to the reagent and to detect response signals from the reagent to detect levels of one or more analytes in the fluid sample. All references to a "test strip" herein refer to an electrochemical test strip such as the test strip <NUM> or other suitable electrochemical test strip configuration.

The analyte test meter <NUM> of <FIG> is further embodied as a blood glucose meter that detects and displays a level of glucose in a blood sample that is applied to the test strip <NUM> for illustrative purposes. The analyte test meter <NUM> includes at least one output device, which is depicted as the display device <NUM> in <FIG>, and at least one input device, which is depicted as the control buttons <NUM> in <FIG>. Additional examples of output devices include indicator lights, audio alarms or synthesized speech audio outputs, haptic feedback devices, and the like. Additional examples of input devices include touchscreen input devices, speech recognition devices, keypads, and the like. While the analyte test meter <NUM> of <FIG> measures a glucose analyte in a blood sample, the embodiments described herein are not limited to blood glucose meters since the embodiments described herein are suitable for use in analyte test meters that measure different types of analytes contained in blood or other bodily fluid samples. Examples of other analytes include, but are not limited to, alcohols, amino acids, <NUM>,<NUM>- anhydroglucitol, cholesterols, fructosamine, glycerines, HbA1c, HDL <NUM> ketones/ketone bodies, lactates, lactate dehydrogenase, malates, pyruvates, sorbitol, creatinine, triglycerides, and uric acid.

The test strip <NUM> is formed from an electrically non-conductive base layer, electrodes formed on the non-conductive base layer, and a non-conductive spacer layer <NUM> that covers a portion of the electrodes leaving exposed electrodes at both ends of the test strip <NUM>. In some test strip embodiments, a separate non-conductive cover layer (shown in <FIG>) is placed over the spacer layer to form a fluid chamber over the reagent that is formed on the second portion <NUM> of the test strip <NUM>, although in other embodiments the reagent is left exposed. Examples of electrodes include, but are not limited to, one or more working electrodes, reference electrodes, counter electrodes, and sample-sufficiency electrodes. The electrodes extend along the length of the test strip <NUM> from a first portion of the test strip (not shown in <FIG>) that includes electrode contacts that are electrically connected to components in the analyte test meter <NUM> via electrical contacts contained in the test strip port <NUM> to a second portion of the test strip <NUM> that is located outside of the analyte test meter <NUM>. The second portion of the test strip <NUM> includes the exposed electrodes and at least one reagent that is applied to the electrodes. The second portion <NUM> of the test strip <NUM> receives a fluid sample and the analyte test meter <NUM> applies electrical signals to the electrodes via the connection in the test strip port <NUM> for the measurement of an analyte that is present in the sample and that produces a chemical reaction in the reagent. The exposed second portion <NUM> is also referred to as a sample chamber since this portion of the tests strip <NUM> receives the sample of the fluid that contains the analyte. Alternative embodiments of test strips include different arrangements of layers and electrode configurations that provide electrical connections between one or more reagents that receive a fluid sample and an analyte test meter.

<FIG> is a depiction of selected components that are contained within the housing <NUM> of the analyte test meter <NUM>. <FIG> depicts a printed circuit board (PCB) <NUM>, the test strip port <NUM>, and a capacitive sensor <NUM> that is formed in the PCB <NUM> and contained within the housing <NUM> of the analyte test meter <NUM>. While not shown in greater detail, the PCB <NUM> also provides electrical connections to the controller, batteries, and other electronic components in the blood glucose meter <NUM>. <FIG> also depicts the test strip <NUM> removed from the test strip port <NUM> to depict the first portion <NUM> at one end of the test strip <NUM> that includes the exposed electrode terminals that enable electrical connection of the test strip <NUM> to the analyte test meter <NUM> when the first portion <NUM> is inserted into the test strip port <NUM>. As depicted in <FIG>, the capacitive sensor <NUM> is located proximate to the test strip port <NUM> and to the electrodes in the test strip <NUM> when the first portion <NUM> of the test strip <NUM> is inserted into the test strip port <NUM>. In the embodiment of <FIG>, the capacitive sensor <NUM> is integrated into the PCB <NUM>, although in other embodiments the capacitive sensor <NUM> can be a separate component instead of being integrated into the PCB <NUM>.

<FIG> depicts additional aspects of the arrangement of the capacitive sensor <NUM> in the analyte test meter <NUM> and the test strip <NUM> including a portion of the PCB <NUM> and the test strip port <NUM>. <FIG> depicts layers of the test strip <NUM> including a non-conductive base layer <NUM> that is formed from plastic or another non-conductive material, the electrodes <NUM> in the test strip <NUM>, the non-conductive spacer layer <NUM>, and the non-conductive cover <NUM> that protects the electrodes outside of the exposed first portion <NUM> that connects the electrodes to the test strip port <NUM> and the second portion <NUM> that bears the reagent. In <FIG>, the cover layer <NUM> overhangs the spacer layer <NUM> to form a fluid chamber that receives a blood sample from a finger <NUM> of the user, although alternative test strip configurations receive other types of fluid samples. Additionally, in some test strip embodiments a cover layer does not overhang the second portion <NUM> of the test strip, such as the test strip embodiment depicted in <FIG>, which leaves the second portion of the test strip exposed to receive the fluid sample.

<FIG> depicts the capacitive sensor <NUM> with a capacitor that is formed by a first conductive plate <NUM>, which is formed as a planar conductor in a layer of copper or other electrically conductive material in the PCB <NUM>, and a second conductive plate that is formed by the electrical contacts <NUM> in the test strip port <NUM> that are configured to establish electrical connections between the electrodes <NUM> in the test strip <NUM> and to a controller and other components in the analyte test meter <NUM>. The conductive plate <NUM> is, for example, a copper pad or a pad formed from another conductor with a square, rectangular, circular, or other planar shape that acts as a plate in a capacitor. The two plates <NUM> and <NUM> are formed in a substantially parallel orientation with a predetermined separation in the PCB <NUM>. The PCB <NUM> provides an electrical insulative layer that forms a dielectric between the conductive plate <NUM> and the contacts <NUM>. In the embodiment of <FIG>, the thickness of the dielectric is on the order of <NUM> to <NUM>, although smaller or larger dielectric thicknesses can be used in different configurations based on the designed capacitance level and the relative permittivity of the dielectric material. While <FIG> depicts a dielectric formed by one or more layers in the PCB, in alternative configurations one or more dielectric materials including air gaps or other non-conductive materials such as glass or a ceramic, and combinations thereof, form the dielectric.

The PCB <NUM> includes additional conductive layers, such as the conductive layers 210A - 210D in the illustrative example of <FIG>, which are arranged to minimize interference with the capacitive sensor <NUM>. For example, the conductive layer 210D includes an aperture to ensure that no conductive elements are interposed in the dielectric between the conductive plate <NUM> and the electrical contacts <NUM>. The conductive plate <NUM> is formed from a portion of the conductive layer 210C, and a gap around the conductive plate <NUM> isolates the layer 210C from the conductive plate <NUM> to enable capacitive coupling with the electrical contacts <NUM>. Of course, those if skill in the art will note that the presence of multiple conductive layers in the PCB <NUM> produces parasitic capacitances. However, the configuration of the capacitive sensor <NUM> reduces the effects of these parasitic capacitances and, as described below, the operation of the capacitive sensor <NUM> in the analyte test meter <NUM> relies on relative changes in capacitance levels, which reduce or eliminate the influence of parasitic capacitances during the detection of user contact with the test strip <NUM>.

In the embodiment of <FIG>, the capacitive sensor <NUM> is connected to a resistor <NUM>, and the capacitive sensor <NUM> and resistor <NUM> form a resistor-capacitor (RC) circuit that is depicted schematically as RC circuit <NUM> in <FIG>. The resistor <NUM> is electrically connected to the conductive plate <NUM> by a set of vias that are depicted in <FIG> and to at least one of the electrical contacts <NUM> in the PCB <NUM> via electrical traces in the PCB <NUM> (not shown) that also connect the electrical contacts <NUM> to the controller <NUM>. For example, in one configuration one or more of the contacts <NUM> that are configured to be electrically connected to the counter electrode in the test strip <NUM> form the second plate in the capacitive sensor <NUM> and these contacts are connected to the resistor <NUM>. The resistor <NUM> is depicted as a surface-mount resistor with a resistance of <NUM> MΩ for illustrative purposes, but other resistor configurations with a higher or lower resistance are used in different embodiments. Additionally, <FIG> depicts the resistor <NUM> in close proximity to the conductive plate <NUM> and the electrical contacts <NUM> for illustrative purposes, but the resistor <NUM> can be placed in a different location of the PCB. The RC circuit <NUM> is electrically connected to a signal generator <NUM> within the analyte test meter <NUM> that is described in further detail below.

During operation of the analyte test meter <NUM>, the electrodes <NUM> in the test strip <NUM> are inserted into the test strip port <NUM>, which enables the electrodes <NUM> to increase the effective size of the electrical contacts <NUM> that form one of the conductive plates in the capacitive sensor <NUM>. Because the electrodes <NUM> extend outside of the housing <NUM> of the analyte test meter <NUM> and come into contact with the body of the user <NUM>, the capacitive sensor <NUM> that is located within the analyte test meter <NUM> can detect contact between the user and the second portion of the test strip <NUM> that is located outside of the housing <NUM> of the analyte test meter <NUM>. As depicted in <FIG>, the body of the user <NUM> acts as an electrical ground when placed in contact with the electrodes <NUM> via a blood sample <NUM> or other fluid sample. When in contact with the electrodes <NUM>, the electrical ground increases the effective capacitance of the capacitive sensor <NUM>. As described in further detail below, a controller in the analyte test meter <NUM> identifies the relative difference between the capacitance level in the capacitive sensor <NUM> prior to when the test strip <NUM> receives the dose of the fluid sample and the larger capacitance level that occurs when then user <NUM> contacts the test strip <NUM> after dosing to detect the contact.

<FIG> is a schematic diagram that depicts additional components of the analyte test meter <NUM>. The analyte test meter <NUM> includes a controller <NUM> that is operatively connected to the test strip port <NUM>, the capacitive sensor <NUM>, the display or other output devices <NUM>, and the input devices <NUM>. The controller <NUM> includes one or more digital logic devices <NUM> such as a microcontroller, microprocessor, application specific integrated circuit (ASIC), or any other electronic device or devices that implement the digital logic functions to perform the operations to detect contact between a user and a test strip that is inserted in the test strip port <NUM> and to perform the analyte measurement process. While not depicted in greater detail, the controller <NUM> also includes input/output (I/O) hardware that operatively connects the controller <NUM> to the display and output devices <NUM>, the input devices <NUM>, and the memory <NUM>.

The controller <NUM> further incorporates one or more signal generators <NUM> that generate a drive signal for the capacitive sensor <NUM> and that generate alternating current (AC), direct current (DC), or sequences of AC and DC signals that are applied to electrodes in a test strip via the test strip port <NUM> to perform an analyte measurement process. The signal generators <NUM> include, for example, oscillators, modulators, amplifiers, and other circuits that generate DC and AC output signals with controlled output amplitudes, duty cycles, frequencies, and waveforms. The controller <NUM> further incorporates one or more signal measurement devices <NUM> including, for example, digital and analog filters, amplifiers, voltage and current sensors, analog-to-digital converters that convert an analog response signal to digital data for processing by the digital logic devices in the controller <NUM>, and any other suitable signal measurement components. For illustrative purposes, the signal generators <NUM> and the signal measurement devices <NUM> refer to separate signal generators and signal measurement devices that are connected to the capacitive sensor <NUM> and to signal generators and signal measurement devices that are connected to the electrodes in the test strip <NUM> via the electrical contacts <NUM> in the test strip port <NUM>. In one embodiment, the signal generators <NUM> and the signal measurement devices <NUM> that are connected to the capacitive sensor <NUM> are specifically configured as touch sensors that, in the embodiments described herein, detect contact between the user and the exposed portion of the test strip <NUM> that is outside of the housing <NUM> of the analyte test meter <NUM>. A separate signal generator <NUM> and signal measurement device <NUM> combination that is connected to the electrical contacts <NUM> in the test strip port <NUM> generates the signals and measures signal responses for analyte detection in the test strip <NUM>.

As described in further detail below, the controller <NUM> detects contact between the user and the test strip <NUM> prior to measuring the concentration of the analyte in the fluid sample on the test strip <NUM>. However, in an alternative configuration a single signal generator and signal measurement device can implement the functions described herein in two different operating modes that detect contact between the test strip and the user and that perform the analyte test sequence after detecting that the user is not in contact with the test strip. While <FIG> depicts the controller <NUM> as one device, such as a System-on-a-Chip (SoC), for illustrative purposes, in other embodiments the controller <NUM> includes multiple digital and analog devices that are connected to each other to implement the controller <NUM>.

The memory <NUM> includes, for example, one or more non-volatile and volatile digital data storage devices. The memory <NUM> holds stored program instructions <NUM> that the controller <NUM> executes to implement the functions described herein. The memory <NUM> further stores a threshold <NUM> that corresponds, either directly or indirectly, to a change in capacitance level in the capacitive sensor <NUM>, which enables the controller <NUM> to determine if the user is in contact with one or more electrodes in a test strip. In one embodiment, the threshold <NUM> is a time threshold that the controller <NUM> uses to detect contact with the user based on a change in the amount of time required for the voltage of the capacitive sensor <NUM> in the RC circuit <NUM> to discharge to a predetermined threshold level, where this discharge time is affected by the capacitance level. While not depicted in greater detail herein, the memory <NUM> also stores any other data used for the operation of the analyte test meter <NUM> including, but not limited to, a history of analyte test results, fixed parameter values used in the analyte measurement process, and personalized user setting parameters.

<FIG> is a block diagram of a process <NUM> for operation of an analyte test meter that detects contact between a finger or other body part of a user and electrodes in a portion of a test strip that is located outside of the analyte test meter. In the description below, a reference to the process <NUM> performing a function or action refers to the operation of a controller to execute stored program instructions to perform the action in association with components in an analyte test meter. The process <NUM> is described in conjunction with the analyte test meter <NUM> and the foregoing embodiments for illustrative purposes.

The process <NUM> begins as the controller <NUM> detects the insertion of a test strip in the test strip port <NUM> (block <NUM>). In one embodiment, the controller <NUM> detects the insertion of the first portion <NUM> of the test strip <NUM> into the test strip port <NUM> based on an electrical continuity test through a circuit that a conductor in the test strip <NUM> closes upon insertion in the test strip port <NUM> or via any other suitable sensor that detects insertion of the test strip <NUM>. Upon initial insertion, the test strip <NUM> has not received a dose of the fluid sample.

The process <NUM> continues as the controller <NUM> applies a first drive signal to the capacitive sensor <NUM> to identify a baseline capacitance level in the capacitive sensor prior to dosing of the test strip <NUM> (block <NUM>). The controller <NUM> activates the signal generator <NUM> to apply a drive signal to the capacitive sensor <NUM> and measures a discharge time of the capacitor formed in the RC circuit <NUM>. In the analyte test meter <NUM>, the controller <NUM> operates the signal generator <NUM> to apply a pulsed DC drive signal to the capacitive sensor <NUM>, which charges the capacitor that is formed by the conductive plate <NUM> in the capacitive sensor <NUM> and the electrodes in the test strip <NUM>. The pulsed DC drive signal is, for example, a digital logic output signal that is generated at a predetermined voltage level (e.g. <NUM>. 3V or 5V although other embodiments use different voltage levels) or another DC output signal that is generated for a predetermined period of time to charge the capacitor in the RC circuit <NUM> to a sufficiently high level to enable measurement of the amount of time that the RC circuit takes to discharge to a low-voltage threshold level. In one embodiment, the controller <NUM> applies the pulsed DC drive signal for a length of time that charges the capacitor to nearly the same voltage level as the DC signal, although the capacitor may be charged to a somewhat lower predetermined voltage level as well. After applying the pulsed DC drive signal for a predetermined time period, the controller <NUM> deactivates the signal from the signal generator <NUM> and uses a voltage sensor or other signal measurement device <NUM> to monitor the discharge of the voltage as the RC circuit <NUM> discharges over time. In one embodiment, the controller <NUM> starts a timer, such as an incrementable counter or another suitable timer, upon deactivation of the pulsed DC drive signal. The timer runs until a voltage sensor <NUM> detects that the measured voltage level of the RC circuit <NUM> has discharged to a predetermined low-voltage threshold (e.g. <NUM> V although other embodiments use different low-voltage levels). The elapsed time that the RC circuit <NUM> takes to discharge indicates the level of the capacitance of the capacitor as described in further detail below.

The time taken for the measured voltage from the RC circuit <NUM> to discharge to a reference voltage level provides a baseline capacitive sensor response for the capacitive sensor <NUM> prior to dosing of the test strip <NUM> while the electrical contacts <NUM> are connected to the electrodes <NUM> in the test strip <NUM>. The time required for the capacitive sensor <NUM> to charge and discharge is related to the RC time constant: τ = RC where R is a resistance in Ohms and C is the capacitance in Farads. In the embodiments described herein, R has a predetermined value of the resistor <NUM> (e.g. 1MΩ) and C is the capacitance of the capacitive sensor (e.g. <NUM> picoFarads (pF)), although the values presented herein are non-limiting and, as described below, the embodiments described herein can accommodate RC circuits that have varying Rand C values. The precise capacitance level of the capacitive sensor <NUM> may vary somewhat from a nominal value due to environmental factors such as temperature and humidity, and the controller <NUM> measures a first response from the capacitive sensor that corresponds to the capacitance level prior to dosing as a baseline measurement to ensure accurate detection of contact with the user <NUM> during the process <NUM>. The duration of each pulse in the pulsed DC drive signal varies based on the configuration of the RC circuit, but in one illustrative embodiment the pulse duration is <NUM> millisecond, which charges an RC circuit with a 1MΩ resistor and a <NUM> pF capacitor to approximately <NUM>% of maximum charge where τ = (<NUM>MΩ)(<NUM>pF) = <NUM> * <NUM>-<NUM> sec and <NUM> millisecond represents five of the time constant periods τ. The nominal <NUM> MΩ and <NUM> pF values provided above are not necessarily precise values of the capacitor and resistor in this illustrative embodiment of the RC circuit <NUM> since these values may vary during operation, but are estimates that are sufficiently accurate to ensure that the capacitive sensor <NUM> charges to approximately full capacity. Upon deactivation of the signal, the capacitive sensor <NUM> discharges through the resistor <NUM> at substantially the same rate as the charge rate, and in this example the capacitor discharges to a charge level of approximately <NUM>% after <NUM> millisecond. As is known to the art, the time constant τ indicates the amount of time taken for the capacitor in the RC circuit to charge to <NUM> - e-<NUM> of the total capacity of the capacitor (approximately <NUM>%) or to discharge to e-<NUM> of the total capacity of the capacitor (approximately <NUM>%). The capacitor charge and discharge times follow an exponential curve, and the capacitor asymptotically approaches maximum or minimum charge over additional time periods. The signal measurement circuits <NUM> measure the voltage level of the capacitive sensor <NUM> during the discharge process, and the controller <NUM> measures the amount of time required for the capacitor to discharge to the predetermined low voltage level. The measured discharge time corresponds to the capacitance level of the capacitive sensor <NUM> since the measured discharge time is related to the capacitance level of the capacitive sensor <NUM> with longer times indicating larger capacitances and shorter times indicating smaller capacitances.

The process <NUM> continues as the controller <NUM> detects the dosing of the test strip with the fluid sample (block <NUM>). In the analyte test meter <NUM>, the controller <NUM> detects the application of the fluid sample to the second portion <NUM> of the test strip <NUM> by generating a detection signal through two sample sufficiency electrodes that are exposed to the fluid sample. A sufficiently large fluid sample applied to the second portion <NUM> of the test strip <NUM> establishes a reduced-impedance electrical connection between the sample sufficiency electrodes, and the controller <NUM> identifies that the test strip <NUM> has received a fluid sample of sufficient size to conduct the analyte measurement process.

The process <NUM> continues as the controller <NUM> applies the drive signal to the capacitive sensor <NUM> to identify the capacitance level in the capacitive sensor after detecting that the test strip <NUM> has received a dose of the fluid sample (block <NUM>). In the analyte test meter <NUM>, the controller <NUM> generates the same drive signal both before and after detecting dosing of the test strip <NUM>. The controller <NUM> measures the discharge time for the capacitive sensor <NUM> to discharge to the predetermined voltage level in the same manner as described above to measure a second response to the drive signal from the capacitive sensor corresponding to the second level of capacitance in the capacitive sensor after the dosing has occurred. In at least some instances, the addition of the fluid sample to the electrodes in the second portion of the test strip <NUM> increases the capacitance level of capacitive sensor <NUM>. However, this contribution to the capacitance is substantially smaller in magnitude than the increase in capacitance that occurs in response to contact between the user <NUM> with the electrodes <NUM> in the test strip <NUM> after the blood or other fluid sample is applied to the test strip to establish an electrical connection between the body of the user <NUM> and the capacitive sensor <NUM> via the test strip electrodes <NUM> and the contacts <NUM> in the test strip port <NUM>. As described above, the body of the user <NUM> effectively acts as an electrical ground that increases the capacitance level of the capacitive sensor, and consequently increases the discharge time of the capacitive sensor in response to the drive signal relative to the baseline discharge time that is measured prior to dosing the test strip <NUM>.

During process <NUM>, the controller <NUM> identifies a difference between the pre-dosing and post-doing signal responses from the capacitive sensor <NUM> to detect user contact with the test strip <NUM> after dosing if the differences exceed a predetermined threshold (block <NUM>). In the embodiment of <FIG>, the contact detection threshold data <NUM> in the memory <NUM> corresponds to a maximum time delta from the pre-dosing discharge time that the controller <NUM> uses to identify contact with the user <NUM> if the contact detection threshold time is exceeded. For example, if the maximum time delta is <NUM> × <NUM>-<NUM> sec and the pre-dosing measured signal response from the capacitive sensor <NUM> indicates a discharge time of <NUM> × <NUM>-<NUM> sec, then a post-dosing signal response discharge time of <NUM> × <NUM>-<NUM> sec lies within the maximum time threshold (<NUM> × <NUM>-<NUM> sec + <NUM> × <NUM>-<NUM> sec), which indicates that the user <NUM> is not in contact with the test strip <NUM>. However, if the discharge time exceeds the predetermined threshold <NUM>, such as a post-dosing discharge time of <NUM> × <NUM>-<NUM> sec, then controller <NUM> detects that the user <NUM> is in contact with the test strip <NUM>. The controller <NUM> optionally performs a series of signal response measurements and averages the measurement values to identify if the signal response exceeds the predetermined threshold to reduce or eliminate the effects of transient noise in the capacitive sensor <NUM>. As described above, some changes in the signal response from the capacitive sensor <NUM> after the test strip receives the fluid dose may occur, and the controller <NUM> uses the contact detection threshold <NUM> to distinguish between a smaller change in capacitance that occurs due to receiving the fluid sample compared to the larger change in capacitance that occurs due to contact with the user <NUM>. In another embodiment, the threshold <NUM> represents a percentage of the pre-dosing discharge time, such as a threshold of <NUM>% of the measured pre-dosing discharge time in the signal response from the capacitive sensor <NUM>. As described above, during the process <NUM> the controller <NUM> detects contact or non-contact with the user <NUM> based on relative changes in the measured signal response from the capacitive sensor <NUM> in the RC circuit <NUM> in the pre-dosing baseline state and post-dosing of the test strip <NUM>. As such, the precise values of the capacitor in the capacitive sensor <NUM> and the resistor <NUM> may vary both over time in a single analyte test meter <NUM> and between different analyte test meters <NUM> while the analyte test meter <NUM> provides accurate contact detection by measuring the relative changes in capacitance instead of the precise absolute capacitance and resistance values of the capacitive sensor <NUM> and the resistor <NUM>, respectively.

If the controller <NUM> measures that the difference between the first response to the drive signal prior to dosing the test strip <NUM> and the second response to the drive signal after dosing the test strip <NUM> does not exceed the predetermined threshold (i.e. the difference between the first response and the second response is less than the predetermined threshold) (block <NUM>), then the controller <NUM> identifies that the user <NUM> is not in contact with the test strip <NUM> (non-contact) and the analyte test meter <NUM> generates an measurement signal sequence to identify the level of analyte in the fluid sample that is applied to the test strip <NUM> (block <NUM>). In one embodiment where the analyte test meter is a blood glucose meter, the controller <NUM> operates the signal generator <NUM> to apply a test sequence including a series of AC, DC, or AC and DC voltage signals to the electrodes <NUM> in the test strip <NUM> via the contacts <NUM> in the test strip port <NUM>. The signal measurement device <NUM> in the controller <NUM> detects responses to the test sequence signals, typically in the form of electrical current responses, and the controller <NUM> measures the analyte level based on the responses to the test sequence signals. The measurement of analytes in electrochemical test strips is generally known to the art and is not described in further detail herein. In some embodiments, the controller <NUM> also deactivates the pulsed DC signal used for contact detection with the user <NUM> prior to initiating the test sequence to measure the analyte.

If the controller <NUM> measures that the difference between the first response to the drive signal prior to dosing the test strip <NUM> and the second response to the drive signal after dosing the test strip <NUM> exceeds the predetermined threshold (block <NUM>), then the controller <NUM> identifies that the user <NUM> is in contact with the test strip <NUM> and the analyte test meter <NUM> generates an output to request that the user <NUM> withdraw from contact with the test strip <NUM> (block <NUM>). Using the analyte test meter <NUM> as an example, the controller <NUM> operates the display device <NUM> to produce an output message including text, graphics, or both text and graphics to request that the user remove a finger or other body part from contact with the second portion <NUM> of the test strip <NUM>. In other configurations, the controller <NUM> operates an indicator light, generates an audible output using a speaker, or operates a haptic feedback device to produce an output request for the user to remove contact from the test strip <NUM>. In one embodiment, the controller <NUM> incorporates a short delay (e.g. <NUM> - <NUM> seconds) from the dose detection until generating the output message to provide the user <NUM> time to withdraw the finger from the test strip <NUM> before generating the request message.

During the process <NUM> the controller <NUM> continuously detects the contact with the user <NUM> as described above with reference to the processing of blocks <NUM>, <NUM>, and <NUM> until the user <NUM> either releases contact to enable measurement of the analyte level as described above with reference to block <NUM>, or the process <NUM> exceeds a maximum contact time threshold that has elapsed since detecting the dosing of the test strip <NUM> (block <NUM>). If the user <NUM> does not release contact with the test strip <NUM> before exceeding the maximum time from dosing, then the controller <NUM> terminates the process <NUM> without measuring the analyte level and generates an output request, using the display device <NUM> or other suitable output device, for the user to remove the test strip <NUM> and to test again with a different test strip (block <NUM>). The controller <NUM> terminates the process <NUM> after maximum time threshold is reached to avoid measurement errors that may occur when a fluid sample remains on the test strip <NUM> for a sufficiently long period that evaporation of the fluid occurs, which can reduce the accuracy of the analyte measurement. In one embodiment the maximum time period threshold is <NUM> seconds, but the maximum time threshold may vary based on the configuration of the test strip <NUM>.

The specific configuration of the capacitive sensor <NUM> and operation in the analyte test meter <NUM> described above is provided for illustrative purposes, and other capacitive sensor configurations are also suitable for use in the analyte test meter <NUM>. For example, a mutual capacitive sensor that employs mutual capacitance includes capacitors that are formed in the capacitive sensor itself in the same location as the conductive plate <NUM> depicted above. In this embodiment, the contacts <NUM> in the test port <NUM> and the electrodes <NUM> in the test strip <NUM> are not directly part of the capacitive sensor, but these elements still affect the mutual capacitance between these capacitors within the capacitive sensor. The contact between the user and the electrodes in the test strip <NUM> further changes the mutual capacitance levels in the capacitive sensor, which the controller <NUM> detects to identify that the user is in contact with the electrodes in the second portion <NUM> of the test strip <NUM>. Additionally, while the embodiments described herein measure changes in capacitance indirectly based on the measured time for discharge of an RC circuit, other embodiments that measure the capacitance of one or more capacitors indirectly or directly to detect contact with the user are also suitable for use in the analyte test meter <NUM> and other analyte test meter embodiments. More generally, the analyte test meter <NUM> employs a capacitive sensor that incorporates or is capacitively coupled to the electrodes <NUM> in the test strip <NUM> to detect a change in capacitance that occurs in response to contact with the finger or other body part of a user.

As described above, the embodiments described herein enable an analyte test meter to detect contact between the body of the user and one or more electrodes in a biochemical test strip that are located outside of the analyte test meter. The detection of user contact with the electrodes in the test strip enables the analyte test meter to avoid the generation of a test sequence for measurement of the analyte while the user is in contact with the electrodes in the test strip, which reduces the likelihood of interference with the analyte measurement process to improve the accuracy of the analyte detection meter.

Claim 1:
An analyte test meter (<NUM>) comprising:
a test strip port (<NUM>) configured to receive a first portion (<NUM>) of an electrochemical test strip (<NUM>);
a capacitive sensor (<NUM>) positioned proximate to the test strip port and configured to be capacitively coupled to at least one electrode (<NUM>) in the electrochemical test strip so as to detect contact between a body of a user and at least one electrode in the electrochemical test strip in a second portion (<NUM>) of the electrochemical test strip; and
a controller (<NUM>) connected to the test strip port and the capacitive sensor, the controller being configured to:
identify insertion of the first portion of the electrochemical test strip into the test strip port;
apply a drive signal to the capacitive sensor after the insertion;
measure a first response to the drive signal from the capacitive sensor corresponding to a first level of capacitance in the capacitive sensor;
identify dosing of a fluid sample on the second portion of the electrochemical test strip that is outside of the analyte test meter after the measurement of the first response;
apply the drive signal to the capacitive sensor after the identification of the dosing;
measure a second response to the drive signal from the capacitive sensor corresponding to a second level of capacitance in the capacitive sensor; and
detect contact between a body of a user and at least the one electrode in the electrochemical test strip in the second portion of the electrochemical test strip in response to a difference between the first response and the second response exceeding a predetermined threshold.