Patent Description:
Biosensors provide an analysis of a biological fluid, such as whole blood, urine, or saliva. Measuring the concentration of substances in biological fluids is an important tool for the diagnosis and treatment of many medical conditions. For example, the measurement of glucose in body fluids, such as blood, is crucial to the effective treatment of diabetes. The sample of biological fluid may be directly collected or may be a derivative of a biological fluid. Typically, biosensors have a nondisposable measurement device or test meter that is used to analyze the sample of biological fluid that is placed on the test strip.

Many biosensor systems provide calibration information to the measurement device prior to the analysis. The measurement device typically uses this information to adjust the analysis of the biological fluid in response to one or more parameters. The accuracy and precision of the analysis is improved by using the calibration information. If the calibration information is not used, the measurement device may not complete the analysis or may make a wrong analysis of the concentration of the analyte in the biological fluid.

It is common practice in such test meter/test strip systems to ensure proper identification of the test strip in order to ensure proper test results. For example, a single test meter may be able to analyze several different types of test strips, wherein each type of test strip is designed to test for the presence or concentration of a different analyte in the biological fluid. In order to properly conduct the test, the test meter must know which type of test is to be performed for the test strip currently in use.

Also, lot-to-lot variations in the test strips normally require calibration information to be loaded into the test meter in order to ensure accurate test results. A common practice for downloading such calibration information into the test meter is the use of an electronic read-only memory key (ROM key) that is inserted into a corresponding slot or socket of the test meter. Because this calibration data may only be accurate for a particular production lot of test strips, the user is usually asked to confirm that the lot number of the test strip currently in use matches the lot number for which the ROM key was programmed.

Many other instances in which it is desirable to have information relating to the test strip are known to those having skill in the art. Prior art attempts to code information onto the test strip for reading by the test meter have suffered from many problems, including a severely limited amount of information that can be coded and the use of relatively large amounts of test strip surface area for the information coding function.

<CIT> discloses encoded biosensors and methods of manufacture and use thereof. <CIT> discloses identification of a type by the meter using conductive patterns on the strip. <CIT> discloses autocoded analyte sensors and apparatus, systems and methods for detecting same. <CIT> discloses a thick film resistor. <CIT> discloses a measurement instrument and concentration measurement apparatus.

Thus, a system and method are needed that will allow information to be coded onto a biosensor for reading of the information by the test meter.

In accordance with the present invention, there is disclosed an analyte test strip for performing at least one of quantitative and qualitative analysis of an analyte in a sample of fluid, the analyte test strip comprising: a non-conductive substrate; a working electrode; a counter electrode; a reagent layer at the distal end of the analyte test strip, the reagent layer covering at least a portion of the working electrode and the counter electrode; and a circuit on the non-conductive substrate, the circuit comprising: primary resistive element on the non-conductive substrate having a first end and a second end, wherein the configuration of the primary resistive element is a serpentine configuration; and a secondary resistive element on the non-conductive substrate having a third end and a plurality of taps connected to the primary resistive element at a plurality of predetermined connection points on the serpentine configuration, the plurality of predetermined connection points defining a plurality of unique resistive paths running from the third end, through the predetermined connection points, through at least a portion of the serpentine configuration and to either of the first and second ends; wherein the plurality of unique resistive paths have a plurality of resistance values, the plurality of resistance values having a non-linear distribution, the non-linear distribution comprising a power function, an exponential function, or a sinusoidal function.

The unique resistive path through the predetermined configuration has associated therewith a resistance falling within a respective one of a plurality of ranges of resistances. The resistance is determined based on or as a function of a location of the predetermined connection point on the predetermined configuration. The unique resistive path may be associated with an attribute of the analyte test sensor strip. An attribute of the strip should be broadly understood to refer to any information relating to the strip, such as strip type, calibration information, manufacturing information, country information, etc. Essentially any information pertaining to the strip which may be desirable to convey to a meter with which the strip is used.

In order to provide an opportunity to define the unique resistive path from among more than one possible unique resistive paths each having an associated resistance correlating to a different attribute, the secondary resistive element includes a plurality of taps. The respective tap that is connected with the predetermined configuration at the predetermined connection point is formed or maintained in a closed state and all other taps of the plurality of taps are opened or formed in an open state.

The first end of the primary resistive element may be connected with a first contact pad and the second end may be connected with a second contact pad. The secondary resistive element has a third end, which may be connected with a third contact pad.

One tap of the plurality of taps may be connected with the primary resistive element at a predetermined location thereby being formed and/or maintained in a closed state and defining a unique resistive path through at least a portion of the primary resistive network. The remaining taps of the plurality of taps may be opened or formed in an open state thereby being disconnected from the primary resistive network. A portion of the secondary resistive element may be connected with a secondary resistive element contact pad.

In one form, the taps that are in the open state are ablated with a laser. The unique resistive path is associated with an attribute of the analyte test sensor strip. In one form, the attribute is associated with one or more algorithm variables, such as slope and/or intercept for a linear correlation algorithm, associated with the test sensor strip. In yet another form, the analyte test sensor strip includes an optical code formed on the non-conductive substrate. The optical code can contain information related to the test sensor strip such as a product expiration date, product identification (countries or regions), intercepts of blood and control solutions, strip lot identification, and other features. In addition, the test sensor strip can also include a first resistance loop formed on the non-conductive substrate comprising a first measurement sense electrode in a spaced apart relationship from a first measurement electrode. In one form, the first measurement electrode is connected with the second end of the primary resistive element.

In accordance with the invention, there is also disclosed a method of forming a circuit on a biosensor test strip, the method comprising: forming a primary resistive element on a non-conductive substrate, wherein the configuration of the primary resistive element is a serpentine configuration including a first end and a second end; and forming a secondary resistive element on the non-conductive substrate having a third end and at least one of a plurality of taps connected to a predetermined connection location on the primary resistive element thereby defining a plurality of unique resistive paths running from the third end, through the predetermined connection location, through at least a portion of the serpentine configuration and to either of the first and second ends, wherein the test strip comprises a working electrode, a counter electrode, and a reagent layer at the distal end of the analyte test strip, the reagent layer covering at least a portion of the working electrode and the counter electrode; wherein each of the plurality of taps has associated therewith a resistance falling within a respective one of a plurality of ranges of resistances having a non-linear distribution, the non-linear distribution comprising a power function, an exponential function, or a sinusoidal function.

The secondary resistive element is formed to include a plurality of taps. All of the plurality of taps but the tap connected to the predetermined location on the primary resistive element may be ablated thereby disconnecting the ablated taps from the primary resistive element. The primary resistive element includes a plurality of predetermined connection locations. A connection location to be connected with the tap can be selected as a function of an attribute associated with the biosensor test strip. The unique resistive path through the secondary and primary resistive elements may be associated with an attribute of the biosensor test strip. Further, each range of resistances contained in the plurality of ranges of resistances may be associated with a unique attribute of the biosensor test strip.

In one form, a ratio of the first resistance and the second resistance may selectively correlate to an attribute of the analyte test sensor strip. The first end may be connected with a first contact pad, the second end may be connected with a second contact pad, and the third end may be connected with a third contact pad. The predetermined configuration comprises a serpentine configuration, which has a plurality of proximal ends and a plurality of distal ends. The closed tap may be connected to a respective proximal end of the serpentine configuration. The tap that comprises the closed tap may be selected as a function of an attribute of the analyte test sensor strip.

The method may further comprise the step of providing a test meter. The working electrode on the non-conductive substrate may be connectable to the test meter; The counter electrode on the non-conductive substrate may be connectable to the test meter; the first end may be connectable to the test meter and the second end may be connectable to the test meter; and the third end may be connectable to the test meter, wherein the secondary resistive element has a tap connected to the primary resistive element at a predetermined connection point on the predetermined configuration thereby defining a unique resistive path through at least a portion of the predetermined configuration having a resistance value; receiving the test strip into the test meter; operatively connecting the working electrode, the counter electrode, the primary resistive element, and the secondary resistive element with the test meter; and determining an attribute associated with the test strip as a function of a measurement associated with at least the resistance value associated with the unique resistive path.

In one form, the primary resistive element has a primary element resistance value and the attribute is determined as a function of a resistance ratio determined by comparing the resistance value of the unique resistive path with the primary element resistance value. The test meter is adjusted to output a concentration measurement output associated with the analyte as a function of the attribute. In one form, an end of the primary resistive element is connected with the counter electrode.

The invention is further elucidated in the following on the basis of an exemplary embodiment shown in the drawings. Embodiments of a test strip described in <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG> and <FIG> are not encompassed by the wording of the appended claims but are considered useful for understanding the invention.

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings, and specific language will be used to describe that embodiment. It will nevertheless be understood that no limitation of the scope of the invention is intended. Alterations and modifications in the illustrated device, and further applications of the principles of the invention as illustrated therein, as would normally occur to one skilled in the art to which the invention relates are contemplated, are desired to be protected. In particular, although the invention is discussed in terms of a blood glucose meter, it is contemplated that the invention can be used with devices for measuring other analytes and other sample types. Such alternative embodiments require certain adaptations to the embodiments discussed herein that would be obvious to those skilled in the art.

Referring to <FIG>, a concentration measuring device or test meter <NUM> is disclosed with an analyte test sensor strip <NUM> mounted thereto that is used to measure the presence or concentration of an analyte in a biological fluid, such as whole blood, urine, or saliva. In this form, the test strip <NUM> is removably inserted into a connection terminal <NUM> of the test meter <NUM>. Upon insertion of the test strip <NUM>, the test meter <NUM> is configured to automatically turn on and begin the measuring process, as set forth in greater detail below. The test meter <NUM> includes an electronic display <NUM> that is used to display various types of information to the user including the test results.

Referring to <FIG>, a general test strip <NUM> is illustrated for background purposes and includes several components. The test strip <NUM> comprises a small body defining a chamber in which the sample fluid is received for testing. This sample-receiving chamber is filled with the sample fluid by suitable means, preferably by capillary action, but also optionally assisted by pressure or vacuum. The sample-receiving chamber includes electrodes and chemistry suitable for producing an electrochemical signal indicative of the analyte in the sample fluid.

In this illustrated form, the test strip <NUM> includes a base substrate <NUM>, a spacing layer <NUM> and a covering layer <NUM> comprising body cover <NUM> and chamber cover <NUM>. The spacing layer <NUM> includes a void portion <NUM> to provide a sample receiving chamber extending between the base substrate <NUM> and the covering layer <NUM>. The base substrate <NUM> carries an electrode system <NUM> including a plurality of electrodes <NUM> and electrode traces <NUM> terminating in contact pads <NUM>. The electrodes <NUM> are defined as those portions of the electrode traces <NUM> that are positioned within the sample-receiving chamber. A suitable reagent system <NUM> overlies at least a portion of the electrodes <NUM> within the sample-receiving chamber.

The body cover <NUM> and the chamber cover <NUM> overlying the spacing layer <NUM> define a slot therebetween, the slot defining a vent opening communicating with the sample-receiving chamber to allow air to escape the chamber as a sample fluid enters the chamber from the edge opening or fluid receiving opening. The test strip <NUM> therefore includes a dosing end <NUM> and a meter insertion end <NUM>. The shape of the dosing end <NUM> is typically distinguishable from the meter insertion end <NUM> so as to aid the user. The body cover <NUM> and chamber cover <NUM> are preferably secured to the spacing layer <NUM> by an adhesive layer <NUM>. Further, a second adhesive layer <NUM> secures the spacing layer <NUM> to the base substrate <NUM>. A more detailed discussion of the test strip <NUM> illustrated in <FIG> can be found in commonly owned <CIT>.

Referring to <FIG>, a more detailed image of one form of a test strip <NUM>, useful for understanding the invention, that is configured for use with the test meter <NUM> is illustrated having spacer, covering and adhesive layers removed to reveal the electrode system <NUM> of the test strip <NUM>. The test strip <NUM> includes a non-conductive base substrate <NUM> having formed thereon a plurality of electrodes, traces and contact pads, as will be discussed in greater detail below. Such formation may be achieved by using any of a number of known techniques, such as screen printing, lithography, laser scribing or laser ablation. For purposes of illustration, formation using a broad field laser ablation technique is generally described herein.

Prior to formation of the electrodes, traces and contact pads, the non-conductive substrate is coated on its top surface with a conductive layer (by sputtering or vapor deposition, for example). The electrodes, traces and contact pads are then patterned in the conductive layer formed on the non-conductive substrate by a laser ablation process using a mask defining the desired design for the electrical aspects of the test strip. A more detailed discussion of the laser ablation process is set forth in commonly owned <CIT>.

The conductive layer may contain pure metals or alloys, or other materials, which are metallic conductors. The conductive material is generally absorptive at the wavelength of the laser used to form the electrodes, traces and contact pads on the non-conductive substrate <NUM>. Non-limiting examples include aluminium, carbon, copper, chromium, gold, indium tin oxide, palladium, platinum, silver, tin oxide/gold, titanium, mixtures thereof, and alloys or metallic compounds of these elements. In some forms, the conductive material includes noble metals or alloys or their oxides.

The test strip <NUM> includes a working electrode <NUM>, a working sense trace <NUM>, a counter electrode <NUM>, and a counter sense trace <NUM> formed on the non-conductive substrate <NUM>. The test strip <NUM> includes a distal end or reaction zone <NUM> and a proximal end or contact zone <NUM> extending along a longitudinal axis. As set forth in greater detail below, the test strip <NUM> includes a working electrode trace 54a that is used to connect the working electrode <NUM> to a contact pad <NUM>. Further, the test strip <NUM> includes a counter electrode trace 58a that is used to connect the counter electrode <NUM> to a contact pad <NUM>. As illustrated, the proximal end <NUM> of the test strip <NUM> includes a plurality of contact pads that are configured to be conductively connected with the connection terminal <NUM> of the test meter <NUM>. In one form, the test meter <NUM> is configured to determine the type of test strip <NUM> inserted into the test meter <NUM> based on the configuration, including, e.g., any interconnection, of the contact pads. The distal end <NUM> of the test strip <NUM> includes a reagent layer <NUM> that covers at least a portion of the working electrode <NUM> and counter electrode <NUM>.

The reagent layer <NUM> of the test strip <NUM> may comprise reagents of a chemical or biochemical nature for reacting with a target analyte to produce a detectable signal that represents the presence and/or concentration of the target analyte in a sample. The term "reagent", as used herein, is a chemical, biological or biochemical reagent for reacting with the analyte and/or the target to produce a detectable signal that represents the presence or concentration of the analyte in the sample. Suitable reagents for use in the different detection systems and methods include a variety of active components selected to determine the presence and/or concentration of various analytes, such as glucose for example. The selection of appropriate reagents is well within the skill in the art. As is well known in the art, there are numerous chemistries available for use with each of various targets. The reagents are selected with respect to the target to be assessed. For example, the reagents can include one or more enzymes, co-enzymes, and co-factors that can be selected to determine the presence of glucose in blood.

The reagent chemistry may include a variety of adjuvants to enhance the reagent properties or characteristics. For example, the chemistry may include materials to facilitate the placement of the reagent composition onto the test strip <NUM> and to improve its adherence to the strip <NUM>, or for increasing the rate of hydration of the reagent composition by the sample fluid. Additionally, the reagent layer can include components selected to enhance the physical properties of the resulting dried reagent layer <NUM>, and the uptake of a liquid test sample for analysis. Examples of adjuvant materials to be used with the reagent composition include thickeners, viscosity modulators, film formers, stabilizers, buffers, detergents, gelling agents, fillers, film openers, coloring agents, and agents endowing thixotropy.

As further illustrated in <FIG>, a proximal end <NUM> of the working electrode trace 54a is connected with a working electrode measurement contact pad <NUM>. A distal end <NUM> of the working electrode trace 54a is connected with the working electrode <NUM>. A proximal end <NUM> of the working sense trace <NUM> is connected with a working sense measurement contact pad <NUM>. As further illustrated, a distal end <NUM> of the working sense trace <NUM> is connected with the distal end <NUM> of the working electrode trace 54a thereby defining a working resistance loop.

In one form, the working resistance loop has a resistance value within a predetermined range of resistance values, which range corresponds to an attribute of the test strip <NUM>. Forming the working resistance loop to have a resistance value that falls within one or another predetermined range of resistance values is within the ordinary skill in the art of forming thin conductive layers. Nevertheless, for purposes of illustration, it is known that conductive materials, such as thin layers of metals such as gold and palladium, have a characteristic sheet resistance dependent upon the thickness of the conductive layer. Sheet resistance is essentially a multiplier for calculating a predicted resistance through a path of a particular configuration (e.g. length and width) for a particular material of a particular thickness. Thus, sheet resistance and/or the configurational aspects of the conductive trace can be altered in order to achieve a desired resistance through a particular path, such as the working resistance loop.

Thus, for example, a gold layer having a thickness of <NUM>ηm has a sheet resistance of <NUM> ohms/square. A "square" is a unitless measure of the aspect ratio of the conductive path, broken down into the number of square sheets (based on the width) that can be actually or theoretically determined in the conductive path. In one sense, the effective surface area of the conductive path is approximated as a number of squares. The number of squares that can be determined in the conductive path is multiplied by the sheet resistance to give a calculation for a predicted resistance through that conductive path.

Illustrative examples will typically be described in the context of <NUM> thick layers of gold, thus a sheet resistance of <NUM> ohms/square. Thus, in order to manipulate the resistance along any conductive paths being described in the various contexts of this disclosure (as will be clear to persons of ordinary skill in the art), one may alter the length or width of the conductive path (thus change the number of "squares") or one may alter the thickness or material of the conductive layer (thus changing the sheet resistance) in order to increase or decrease a predicted resistance value for that particular conductive path to fall within a desired range of resistance values, wherein the range of such values is indicative of an attribute of the test strip. Determining the number of squares for a particular conductive path in a variety of patterns and configurations other than generally straight line paths is within the ordinary skill in the art and requires no further explanation here.

As will be further described, actual measured resistance values through variously identified conductive paths are used in various manners for purposes of indicating one or more attributes of a test strip. In this regard, it will be understood that the measured resistance values, or predetermined ranges of resistance values in which a measured resistance value lies, or ratios of the measured resistance values between different conductive paths, may correspond to a particular attribute. Which of these manners is employed for corresponding the resistance value of a conductive path to an attribute is within the discretion of one of skill in the art.

Generally, the measured resistance value itself is useful in the event the actual, measured resistance value closely corresponds to the predicted resistance value (calculated as described above). If manufacturing tolerances are such that the measured value does not correspond well to the predicted value, then it may be advisable to predetermine a range of resistance values within which a conductive path having a certain predicted resistance value will almost certainly have a measured resistance value. In that case, the system measures the actual resistance value of a conductive path, identifies the predetermined the range within which the resistance value lies, and corresponds that identified predetermined range with the attribute of the test strip. Finally, if manufacturing tolerances are simply not conducive to accurately predicting the actual measured resistance value for a conductive path, or simply as desired, it may be useful to ratio one measured resistance value against another measured resistance value through a different conductive path, in order to determine an essentially normalized value. The normalized value may be used similarly as a measured resistance value or compared against one or more predetermined ranges of values in order to identify a corresponding attribute of the test strip. It is generally in this context of measured, predicted, and normalized resistance values that the present invention will be further described and understood.

For illustrative purposes only, in one form the working resistance loop has a resistance value of approximately <NUM> Ohms. (In this illustrative form, it is assumed that <NUM> thick gold is used to form the traces and contact pads and that the surface area associated with the traces and contact pads of the working resistance loop equates to approximately <NUM> squares. As such, the working resistance loop has a resistance value of approximately <NUM> Ohms. ) In one embodiment, this resistance value is within a predetermined range, e.g. <NUM>-<NUM> Ohms, and corresponds to an attribute such as the strip type, i.e. a reagent deposited on the strip that is configured for determination of glucose concentration. By way of example, a different predetermined range, e.g. <NUM>-<NUM> Ohms, for the resistance value of the working resistance loop may correspond to a different strip type, such as for determination of ketone concentration. As with all forms, and as described above, the resistance value of the working resistance loop as well as all resistance values disclosed herein can be adjusted by various methods, such as, for example, by adjusting the length, width, and thickness of the working sense trace <NUM> as well as the material from which the working sense trace <NUM> is manufactured. See, e.g., <CIT>.

A proximal end <NUM> of the counter electrode trace 58a is connected with a counter electrode measurement contact pad <NUM>. A distal end <NUM> of the counter electrode trace 58a is connected with the counter electrode <NUM>. In addition, a proximal end <NUM> of the counter sense trace <NUM> is connected with a counter sense measurement contact pad <NUM>. A distal end <NUM> of the counter sense trace <NUM> is connected with the distal end <NUM> of the counter electrode trace 58a thereby defining a counter resistance loop. In one form, the counter resistance loop has a resistance value within a predetermined range of resistance values, which range corresponds to an attribute of the test strip <NUM>. For illustrative purposes only, in one form the counter resistance loop has a resistance value of approximately <NUM> Ohms, based on a <NUM> thick layer of gold and a surface area configuration of approximately <NUM> squares. In one embodiment, this resistance value is within a predetermined range, e.g. <NUM>-<NUM> Ohms, which range corresponds to an attribute of the test strip. In other embodiments, the resistance value of the working resistance loop is ratioed with the resistance value of the counter resistance loop wherein the ratio value corresponds to an attribute of the strip, such as strip type or geographic market of distribution.

As will be generally understood, designating an electrode as a "working" or "counter" electrode is merely an indication of a particular predetermined functionality or intended use for an electrode during an electrochemical measurement method as either an anode or cathode in the presence of a particular electrical field or applied potential. Those of ordinary skill in the art will similarly understand reference to such electrodes generically as first and second measurement electrodes (and corresponding traces, sense traces, contact pads, etc.), inasmuch as such electrodes participate in the measurement of a particular analyte or target, in contrast to, for example, electrodes that may be specifically designated solely for use as dose detecting and/or sample sufficiency electrodes according to known techniques; see, for e.g., <CIT>. In view of these understandings, the designations "working" and "counter" are used solely for contextual illustration and description, and are not intended to limit the scope of the present invention, whether or not recited in the claims, to a particular measurement electrode functionality.

Generally speaking, to commence an assay, the test sensor <NUM> is inserted into the connection terminal <NUM> of the test meter <NUM> such that all of the contact pads of the test sensor <NUM> are connected to contact pins within the connection terminal <NUM>. The working electrode <NUM> and counter electrode <NUM> remain in an open state with respect to each other (i.e. generally electrically isolated from each other) until an adequate amount of fluid, such as blood, is placed on the test sensor <NUM>. The application of an adequate amount of fluid onto the reagent layer <NUM> creates an electrochemical reaction that can be detected by the test meter <NUM>.

In a general sense, the test meter <NUM> applies a predetermined voltage across the working electrode measurement contact pad <NUM> and the counter electrode measurement contact pad <NUM> to create a potential difference between the working electrode <NUM> and counter electrode <NUM>, and then measures the resulting current flow. The magnitude and direction of the voltage is selected based on the electrochemical activation potential for an electrical measurement species to be detected which is generated from the electrochemical reaction of the reagent <NUM> and applied fluid. For glucose, for example, an applied potential difference typically is between about +<NUM> mV and +<NUM> mV when using a DC potential. When using AC potentials these can be between about +<NUM> mV and + <NUM> mV RMS but can also have larger amplitude depending on the purpose for applying the AC potential. The measured amount of current flow, particularly resulting from a DC potential or sufficiently large amplitude AC potential, is indicative of the concentration of the analyte to be measured. The exact manner in which this process works is beyond the scope of the present invention but known to those skilled in the art. See, for example, <CIT>; <CIT>; and <CIT>.

To compensate for the parasitic I-R (current x resistance) drop in the working electrode trace 54a and the counter electrode trace 58a, the test sensor <NUM> includes the working sense trace <NUM> and the counter sense trace <NUM>. As set forth above, the working sense trace <NUM> is connected with the working electrode trace 54a at the distal end <NUM> of the test sensor <NUM> and the working sense measurement contact pad <NUM> at the proximal end <NUM> of the test sensor <NUM>. The counter sense trace <NUM> is connected with the counter electrode trace 58a at the distal end <NUM> of the test sensor <NUM> and the counter sense measurement contact pad <NUM> at the proximal end <NUM> of the test sensor <NUM>.

In one form, during a test procedure a voltage potential is applied to the counter electrode measurement contact pad <NUM>, which will produce a current between the counter electrode <NUM> and the working electrode <NUM> that is proportional to the amount of analyte present in the biological sample applied to the reagent layer <NUM>. To ensure that the proper voltage potential is applied to the counter electrode <NUM>, the test meter <NUM> includes circuitry (not shown) that ensures that a voltage potential (or absolute potential difference) applied to the counter sense trace <NUM> is the same as the desired voltage potential (or absolute potential difference) at the counter electrode <NUM>. Typically, the test meter <NUM> will ensure that little to no current will flow through the counter sense trace <NUM>, thereby assuring that the voltage potential seen at the counter electrode <NUM> corresponds to the desired voltage potential. For a more detailed discussion on the compensation functionality of the working sense trace <NUM> and the counter sense trace <NUM> reference can be made to commonly owned <CIT>.

The ability to code information directly onto the test strip <NUM> can dramatically increase the capabilities of the test strip <NUM> and enhance its interaction with the test meter <NUM>. For example, it is well known in the art to supply the test meter <NUM> with calibration information or data applicable to multiple lots of test strips <NUM>. Prior art systems have relied on a read-only-memory key (ROM key) that is supplied, for example, with each vial of test strips and is inserted into a corresponding socket or slot in the test meter <NUM> when the applicable vial of test strips is utilized by the user. Because this process relies upon the user to perform this task, there is no way to guarantee that it is done or if it is, that it is done correctly or each time a new vial of strips is used. In order to remove the possibility of human error or neglect, the code, such as a code corresponding to preset and pre-stored calibration data, can be placed directly on the test strip <NUM>. This information may then be read by the test meter <NUM>, which has the preset or pre-stored calibration data stored in internal memory, to adjust the test meter <NUM> so that it can provide precise measurements.

To achieve such encoding, in one embodiment, the test strip <NUM> includes a secondary or inner resistive element <NUM> and a primary or outer resistive element <NUM> that form a base resistance network <NUM> on the surface of the substrate <NUM>. An end of the secondary resistive element <NUM> is connected with a secondary resistive element contact pad <NUM>. The primary resistive element <NUM> has a first end <NUM>, a second end <NUM> and a predetermined shape or configuration. In one form, the primary resistive element <NUM> has a serpentine shape or configuration running parallel with the longitudinal axis of the test strip <NUM>. However, it is envisioned that the primary resistive element <NUM> may have other shapes and configurations in different forms. In one form, the primary resistive element <NUM> has a predicted resistance value associated with it falling within a predetermined range of resistance values which may be indicative of an attribute of the test strip <NUM>. The resistance value can be measured by the test meter <NUM> using first and second primary resistive element contact pads <NUM> and <NUM> (as defined below).

In <FIG>, the second end <NUM> of the primary resistive element <NUM> is defined by proximal end <NUM> of the counter electrode trace 58a, and thus contact pad <NUM> is generally coextensive with counter electrode contact pad <NUM>. Except as otherwise specifically required for a particular use or purpose, it will be understood that whether either end <NUM> or <NUM> of the primary resistive element <NUM> are defined by proximal end <NUM> of working electrode trace 54a or proximal end <NUM> of counter electrode trace 58a is a matter of design choice, and described are examples in which ends <NUM> and <NUM> are separate and distinct structures from the aspects of the working electrode <NUM> and counter electrode <NUM> and the traces 54a, 58a and proximal ends <NUM>, <NUM> thereof. See, for example, <FIG>; in contrast, see description above regarding use of one or both sense traces <NUM>, <NUM> for purposes of voltage compensation where one or both of contact pads <NUM>, <NUM> may be coextensive with contact pads <NUM>, <NUM>. The reagent layer <NUM> has been removed from the remaining figures for ease of reference but it should be appreciated that each test strip <NUM> disclosed herein will include a reagent layer <NUM> relevant for the particular analysis desired to be performed.

In particular, the test meter <NUM> can measure the resistance value of the primary resistive element <NUM> by applying a voltage across the primary resistive element contact pads <NUM>, <NUM> and then measuring the amount of current that flows through the primary resistive element <NUM>. In one form, the surface area associated with the primary resistive element <NUM> is equal to approximately <NUM> squares. As such, for illustrative purposes only, for a <NUM> thick layer of gold, the predicted resistance value associated with the primary resistive element <NUM> is approximately <NUM>,<NUM> Ohms.

Referring to <FIG>, another portion of a test strip <NUM> useful for understanding the invention is illustrated in which the secondary resistive element <NUM> and primary resistive element <NUM> have a different predetermined configuration. As set forth in detail below, the secondary resistive element <NUM> includes a plurality of taps 120a-g that are connected to the primary resistive element <NUM> at a plurality of predetermined connection points 122a-g. All other features and aspects of this representative embodiment remain the same as described below in connection with the embodiment illustrated in connection with <FIG>, <FIG> and <FIG>.

Referring to <FIG>, which illustrates a simplistic view of the electrical aspects of the test strip <NUM> illustrated in <FIG> but without the non-conductive substrate <NUM>, the secondary resistive element <NUM> includes a plurality of taps 120a-g that are connected to the primary resistive element <NUM> at a plurality of predetermined connection points 122a-g. In the illustrated form, the primary resistive element <NUM> has a serpentine shape or configuration which comprises a proximal end <NUM> and a distal end <NUM>. The taps 120a-g are connected to the connection points 122a-g at the proximal end <NUM> of the primary resistive element <NUM>. In particular, the taps 120a-g are connected at the proximal ends of each rung of the serpentine configuration. However, it should be appreciated that the taps 120a-g could be connected to the primary resistive element <NUM> at other locations as well, such as illustrated in <FIG> and <FIG>.

In the form illustrated in <FIG>, a first end <NUM> of the primary resistive element <NUM> is connected with a first primary resistive element contact pad <NUM>. A second end end <NUM> of the primary resistive element <NUM> is connected with the counter electrode trace 58a, thereby connecting the second end <NUM> of the primary resistive element <NUM> to the counter electrode contact pad <NUM>. As set forth above, in other forms, the second end <NUM> of the primary resistive element <NUM> could be connected to a different contact pad <NUM> other than the counter electrode contact pad <NUM>. See, e.g., <FIG>.

As illustrated in <FIG> and <FIG>, the base resistance network <NUM> is initially structured on the non-conductive substrate <NUM> by the original process that forms the overall electrodes, traces and contact pads on the test strip <NUM>, such as by broad field laser ablation. As set forth in greater detail below, during secondary processing a code may be placed on the test strip <NUM> by severing all but one of the taps 120a-g of the secondary resistive network <NUM>. As such, the severed taps among 120a-g are placed in an open or non-conductive state while the one remaining tap 120a-g is placed in a closed or conductive state in relation to the primary resistive element <NUM>. Severing may be accomplished by manual or other means, such as ablation or scribing with an appropriate laser.

During manufacturing, once a respective lot of test strips <NUM> is produced having the base resistance network <NUM> formed thereon, one or more pertinent attributes of the lot are determined in order to encode each test strip <NUM> in the lot accordingly for communicating the attribute(s) to the test meter <NUM>. For example, in one embodiment one or more of the test strips <NUM> from the lot are tested with a target analyte having a known concentration. The test results typically indicate an attribute comprising calibration data, such as values for slope and intercept for an algorithm based on a generally linear relationship for measurement of the target analyte, which calibration data should be employed by the test meter <NUM> in a final measurement determination that uses the test strips <NUM>. In a secondary processing of the remaining lot of test strips <NUM>, the base resistance network <NUM> is modified in order to place a code on the test strip <NUM> that is associated with the calibration data for that lot of test strips <NUM>.

In one form, the attribute comprising calibration data for the lot of test strips <NUM> permits the test meter <NUM> to automatically adjust itself to provide precise measurements of the target analyte. In particular, the resistive network that is created on the test strip <NUM> during secondary processing is used to convey information to the test meter <NUM> related to strip performance such as algorithm slopes and product type. In one particular embodiment, the secondary resistive element <NUM> is modified to exhibit only one of a plurality of possible states, wherein each state comprises at least a portion of the code on the test strip <NUM>.

According to one aspect, the base resistance network <NUM> is formed such that all taps 120a-g are in a closed state by manufacturing default. The default state conveys to the meter <NUM> a so-called nominal code for a particular test strip type, e.g. a nominal slope and/or intercept values for a linear correlation algorithm. Each of the plurality of possible other states created by later severing or opening all but one of the taps 120a-g (detected as set forth further below) may then convey incremental adjustment values to the nominal code or to values calculated from the algorithm using the nominal code. For example, for taps 120a-g there are seven possible states in which only one tap remains closed. Each such state may represent a positive or negative factor (e.g. a multiplier) which when conveyed to meter <NUM> is employed by the meter to adjust calculated output upwardly or downwardly depending on how the particular strip lot is evaluated compared to the nominal code. Thus, states <NUM>-<NUM> may represent multipliers -<NUM>%, -<NUM>%, and -<NUM>% respectively, while states <NUM>-<NUM> may represent multipliers +<NUM>%, +<NUM>%, +<NUM>% and +<NUM>% respectively. Such embodiments provide an alternative to the states each representing a set of code values (e.g. slope and intercept) pre-stored in the meter <NUM> that are then employed by the meter in the correlation algorithm.

In an alternative form, all of the taps 120a-g may be ablated or placed in an open state during primary processing. In this form, a respective tap 120a-g is placed in a closed state during secondary processing depending on the test results of the lot of test strips <NUM>. The tap 120a-g that is required to be placed in the closed state may be placed in the closed state during secondary processing by ink jet printing, soldering, drop dispensing, screen printing, conductive taping, and so forth. In other alternative forms, the masks used to form the test strips <NUM> may be formed already having one tap 120a-g placed in a closed state and the remaining in an open state thereby eliminating the need for secondary processing of the test strips <NUM>.

Referring to <FIG>, during secondary processing of the test strips <NUM>, the base resistance network <NUM> is modified such that code information indicative of an attribute associated with the test strip <NUM> is placed on the test strips <NUM>. As set forth above, the modified base resistance network <NUM> can be utilized to transfer basic information to the test meter <NUM> related to strip performance such as algorithm slopes and product type. As illustrated in <FIG>, during secondary processing all but one of the taps 120a-g, which are taps 120a-f in this illustrative example, have been ablated by a laser thereby defining a first state (State <NUM>) that the test strip <NUM> may be produced in. In particular, in State <NUM> only tap <NUM> remains connected to the primary resistive element <NUM> at location <NUM> thereby defining a first unique resistive path for secondary resistive element <NUM> through a portion of the primary resistive element <NUM>. The ablated taps 120a-f are thereby placed in an open state and the non-ablated tap <NUM> is in a closed state thereby allowing current to flow through the secondary resistive element <NUM>, and into a select portion of the primary resistive element <NUM>.

As illustrated in <FIG>, a first unique resistive path is defined from the secondary resistive element contact pad <NUM> through the secondary resistive element <NUM> including the non-ablated tap <NUM> and a portion of the primary resistive element <NUM> between location <NUM> and the contact pad <NUM> at the second end <NUM>. The first unique resistive path is defined at least in part by the non-ablated tap <NUM> and a portion of the primary resistive element <NUM>. In one form, for purposes of illustration, in State <NUM> the first unique resistive path has a resistance value associated with it of approximately <NUM> Ohms. For illustrative clarity, the first unique resistive path is shown in <FIG> between contact pads <NUM> and <NUM> in hashed line shading.

As with all of the forms discussed below, the resistance value associated with the first unique resistive path can be measured by the test meter <NUM> using the secondary resistive element contact pad <NUM> and the contact pad <NUM> (which as illustrated is co-extensive with counter electrode contact pad <NUM>). In particular, the resistance value can be measured by the test meter <NUM> by applying a predetermined voltage across the secondary resistive element contact pad <NUM> and the contact pad <NUM> and then by measuring the resulting current flow through the first unique resistive path and then calculating resistance according to Ohm's Law, R = V/I.

Alternatively, a second unique resistive path is defined by State <NUM> from the secondary resistive element contact pad <NUM> through the secondary resistive element <NUM> including the non-ablated tap <NUM> and a portion of the primary resistive element <NUM> between location <NUM> and the primary resistive element contact pad <NUM> at first end <NUM>. In this alternative form, the second unique resistive path has a resistance value associated with it of approximately <NUM> Ohms. As with all of the forms discussed below, the resistance value associated with the second unique resistive path for each state can be measured by the test meter <NUM> using the secondary resistive element contact pad <NUM> and the primary resistive element contact pad <NUM>. The resistance value can be measured by the test meter <NUM> by applying a predetermined voltage across the secondary resistive element contact pad <NUM> and the primary resistive element contact pad <NUM> and then by measuring the resulting current flow through the second unique resistive path and calculating resistance as described above.

Referring to <FIG>, additional states (e.g., States <NUM>-<NUM>) each including first and second unique resistive paths for each state may be defined on the basis of which tap 120a-120f remains unablated. In each instance, a first unique resistive path is defined from secondary resistive element contact pad <NUM> through the secondary resistive element <NUM> including the particular non-ablated tap 120f-120a (such as shown in <FIG>, respectively) and a portion of the primary resistive element <NUM> between particular location 122f-122a (respectively) and contact pad <NUM> at second end <NUM>. (For illustrative clarity, the first unique resistive path in each of <FIG> is shown between contact pads <NUM> and <NUM> in hashed line shading. ) Conversely, in each instance a second unique resistive path is defined from secondary resistive element contact pad <NUM> through the secondary resistive element <NUM> including the particular non-ablated tap 120f-120a (such as shown in <FIG>, respectively) and a portion of the primary resistive element <NUM> between particular location 122f-122a (respectively) and contact pad <NUM> at first end <NUM>.

For purposes of further illustration, Table <NUM> sets forth exemplary resistance values associated with the first and second unique resistive paths ("URP") defined for each of States <NUM>-<NUM> shown in <FIG>, in which the paths are formed from gold having <NUM>ηm thickness. It will be understood that other materials, thicknesses and path configurations will have different associated resistance values for each state.

As set forth above with respect to <FIG>, the test strip <NUM> disclosed herein can be configured during manufacturing to transmit a minimum of seven (<NUM>) basic states of product performance and attribute information from the comparative analysis of resistance traces on the test sensor strip <NUM>. Although discrete resistance values have been set forth above in the illustrative forms and as described further above with regard to predicted resistance values, it should be appreciated that in some embodiments these values will vary somewhat because of variances in the manufacturing process. As such, each state that the test strip <NUM> may be manufactured in during secondary processing will typically fall within a range of resistance values. Thus, in one embodiment, each discrete range of resistance values rather than the discrete resistance values themselves, will correspond to a state of the test strip <NUM>. For example, in one form, the resistance value of the first unique resistive path in State <NUM> could fall within a range of <NUM>-<NUM> Ohms, in State <NUM> could fall within a range of <NUM>-<NUM> Ohms, and so forth.

The method used to measure resistance and other factors, such as the temperature of the test strip <NUM> and the internal electronics configuration of test meter <NUM>, can also affect the resistance measured by the test meter <NUM> and thus minimize the size of each discrete range of resistances that may be used. For example, the measured resistance may also include the resistance of at least one switch internal to the test meter <NUM>, where the resistance of the switch varies depending on the temperature of the switch and manufacturing tolerances. In one embodiment, the internal switch resistances as well as contact resistances (i.e., the resistance from the contact of a contact pin of the meter to a particular contact pad) are accounted for and thus automatically compensated in the calculation of resistance values for each primary resistive element <NUM> and secondary resistive element <NUM>.

In other forms, the test meter <NUM> can be configured to determine the state of the test strip <NUM> in a manner in which the resistance values are ratioed, or proportionally compared, with at least one other resistance value on the test strip <NUM>. As such, the test meter <NUM> can be configured to measure the resistance value of the first or second unique resistive path through the secondary resistive element <NUM> and primary resistive element <NUM> and then compare it to another measured resistive value of the test strip <NUM>. For example, the test meter <NUM> could ratio the measured resistance value of the first or second unique resistive path of the secondary resistive element <NUM> and primary resistive element <NUM> against the measured resistance of one or more of the primary resistive element <NUM>, the working resistance loop, and the counter resistance loop to determine the state of the test strip <NUM>.

Referring back to <FIG>, in another form the test strip <NUM> useful for understanding the invention is provided with an optical two dimensional code <NUM> on the proximal end <NUM> of the test strip <NUM>. In some forms, the test meter <NUM> is provided with an optical code reader (not shown) that allows the test meter <NUM> to read the optical two dimensional code <NUM>. Additional information that may be provided by the optical two dimensional code <NUM> can be product expiration date, product identification (countries or regions), intercepts of blood and control solutions, strip lot identification, and other features.

Referring to <FIG>, another form of a test strip <NUM> useful for understanding the invention is disclosed that may incorporate the features disclosed herein. In this form, wherein like-numbered elements correspond to the same features, the primary resistive element <NUM> is formed having a different serpentine shape. In particular, instead of running parallel to the longitudinal axis of the test strip <NUM>, the serpentine configuration runs perpendicular to the longitudinal axis of the test strip <NUM>. This configuration also modifies where the connection points 122a-g of the secondary resistive element <NUM> connect to the primary resistive element <NUM>. In addition, the taps 120a-g of the secondary resistive element <NUM> are oriented perpendicular to the longitudinal axis of the test strip <NUM>.

In this form, the second end <NUM> of the primary resistive element <NUM> is connected with a second primary resistive element contact pad <NUM>. In the previous form illustrated in <FIG>, the second end <NUM> of the primary resistive element <NUM> is formed with the counter electrode trace 58a (with counter electrode contact pad <NUM> shown as coextensive with contact pad <NUM>). However, as discussed above, the second end <NUM> of the primary resistive element <NUM> can be connected with contact pad <NUM> separate from counter electrode trace 58a and counter electrode contact pad <NUM>, as illustrated in <FIG>. As with the form illustrated in <FIG>, during secondary processing of the test strips <NUM>, all but one of the taps 120a-g is ablated to place the test strip <NUM> in a predefined state (e.g., States <NUM>-<NUM>). In this form, the test meter <NUM> is configured to determine the resistance of the primary resistive element <NUM> by using the first primary resistive element contact pad <NUM> and the second primary resistive element contact pad <NUM>. All other features remain the same as discussed in connection with the form illustrated in <FIG>.

Referring to <FIG>, another form of a test strip <NUM> useful for understanding the invention is illustrated that includes a working sense serpentine <NUM> in the working resistance loop. In this form, the working sense serpentine <NUM> is used to code additional information on the test strip <NUM> related to an attribute of the test strip <NUM>. As depicted, the working sense trace <NUM> has been formed to include the working sense serpentine <NUM>, which in the illustrated embodiment is located on the distal end <NUM> of the test strip <NUM>. The working sense serpentine <NUM> allows the working resistance loop to be selectively formed having a predetermined resistance value that falls within a range of resistances. The resistance value can vary depending on the presence or absence of working sense serpentine <NUM>, and in the present thereof then also depending on the width, length, thickness and conductive material used to form the working sense serpentine <NUM> on the test strip. The resistance value of the working resistance loop can be measured by the test meter <NUM> by applying a predetermined voltage across the working sense measurement contact pad <NUM> and the working electrode measurement contact pad <NUM> and then measuring the resulting current flow and calculating resistance accordingly.

Referring to <FIG>, another form of a test strip <NUM> useful for understanding the invention is illustrated that includes a counter sense serpentine <NUM> in the counter resistance loop. As with the form illustrated in <FIG>, in this form the counter sense serpentine <NUM> is used to code additional information on the test strip <NUM> related to an attribute of the test strip <NUM>. The counter sense trace <NUM> has been formed to include the counter sense serpentine <NUM>, which in the illustrated embodiment is located on the distal end of the test strip <NUM>. The counter sense serpentine <NUM> allows the counter resistance loop to be selectively formed having a predetermined resistance value that falls within a range of resistances. The resistance value of the counter resistance loop can be measured by the test meter <NUM> by applying a predetermined voltage across the counter sense measurement contact pad <NUM> and the counter electrode measurement contact pad <NUM> and then measuring the resulting current flow.

Referring to <FIG>, an alternative form of a test strip <NUM>, useful for understanding the invention, that is configured to test for the concentration of an analyte is disclosed that is encoded with information pertaining to at least two attributes of the test strip <NUM>. In this form, a first resistive element <NUM> is defined between a first contact pad <NUM>, such as, for example, a counter electrode contact pad, and a second contact pad <NUM>. As illustrated, a second resistive element <NUM> including a first set of taps 308a-I is connected with the first resistive element <NUM>. As with the previous forms, all but one of the first set of taps 308a-I has been ablated thereby placing taps 308a-b and 308d-I in an open state. Tap 308c is in a closed state thereby defining a first unique resistive path from a third contact pad <NUM> through the second resistive element <NUM> and at least a portion of the first resistive element <NUM> to the first contact pad <NUM>. A second unique resistive path is also defined from the third contact pad <NUM> through the second resistive element <NUM> and a least a portion of the first resistive element <NUM> to the second contact pad <NUM>. In this form, up to twelve (<NUM>) states can be defined by the first and second unique resistive paths depending on which tap 308a-I is placed in the closed state.

A third resistive element <NUM> including a second set of taps 314a-I is also connected with the first resistive element <NUM>. Once again, all but one of the second set of taps 314a-I has been ablated thereby placing taps 314a-d and 314f-I in an open state. For illustrative purposes only, tap 314e has been placed in a closed state thereby defining a third unique resistive path from a fourth contact pad <NUM> through the third resistive element <NUM> and at least a portion of the first resistive element <NUM> to the first contact pad <NUM>. A fourth unique resistive path is also defined from the fourth contact pad <NUM> through the third resistive element <NUM> and at least a portion of the first resistive element <NUM> to the second contact pad <NUM>. In this form, up to twelve (<NUM>) states can be defined by the third and fourth unique resistive paths depending on which tap 314a-I is placed in the closed state. The number of taps 314a-I associated with the third resistive element <NUM> dictates how many states may be defined on the test strip <NUM>. In other forms, additional resistive elements, contact pads and taps could be placed on the test strips to encode additional information on the test strips.

Referring to <FIG> and <FIG>, a general description of a representative process that allows the test meter <NUM> to measure the concentration of an analyte in a biological fluid is set forth. The process begins by inserting a test strip <NUM> (step <NUM>) into the test meter <NUM>. In this form, the test meter <NUM> is configured to automatically turn on once a test strip <NUM> is inserted into the test meter <NUM>. At this point, the test meter <NUM> is configured to measure the conductivity of the base resistance network <NUM> to ascertain at least one attribute associated with the test strip <NUM>, which is represented at step <NUM>. In one form, the test meter <NUM> is configured to apply a predetermined voltage across the secondary resistive element contact pad <NUM> and one of the contact pads <NUM>, <NUM> (depending on whether the first or second unique resistive path is being queried) and then measure the resulting current flow to calculate resistance and determine the state of the test strip <NUM> (e.g. one of States <NUM>-<NUM>). As set forth above, the state of the test strip <NUM> is determined as a function of a first resistance value that is associated with either the first or second unique resistive path that defines the secondary resistive element <NUM>.

In other forms, the test meter <NUM> is also configured to determine a second resistance value associated with the primary resistive element <NUM>. In this form, the test meter <NUM> is configured to apply a predetermined voltage across the primary resistive element contact pads <NUM>, <NUM> and then measure the resulting current flow and calculate resistance accordingly. The test meter <NUM> then calculates a ratio of the first resistance value (i.e. the resistance associated with the selected unique resistive path) and the second resistance value (i.e. the resistance associated with the primary resistive element <NUM>) and then correlates this ratio to an attribute of the test strip <NUM> such as by a look-up table pre-stored in the memory of test meter <NUM>. As set forth above, in one form the attribute that the test meter <NUM> determines during this process correlates to an algorithm slope and intercept determined for the particular lot of the test strip <NUM>.

Once the test meter <NUM> determines the attribute, the test meter <NUM> is configured to automatically utilize the information relating to the attribute, which is represented at step <NUM>. For example, in one embodiment the test meter <NUM> is instructed to perform a particular type of test specific to the test strip <NUM> that has been inserted; or the test meter <NUM> calibrates the meter according to pre-stored calibration information for the lot of test strips. The test meter <NUM> is configured as a function of the attribute that is determined at step <NUM>. Thus, in the calibration embodiment, depending on the determined state of the test strip <NUM>, the test meter <NUM> includes algorithm slopes stored in memory that allow the test meter <NUM> to be adjusted for the particular type of test strip <NUM> that has been inserted into the test meter <NUM>. This allows the test meter <NUM> to provide more precise results without requiring the user to have to interact with the test meter <NUM> during the testing process.

After the test meter <NUM> is configured according to the coded attribute information, the measurement sequence is ready to begin such as by prompting a user to apply blood, for example, to the test strip <NUM>, which is represented at step <NUM>. Once blood has been applied to the test strip <NUM>, the test meter <NUM> then begins the blood glucose measurement cycle, which is represented at step <NUM>. After the test meter <NUM> performs the blood glucose measurement cycle, the test meter is configured to display the results on the display <NUM> (step <NUM>). It should be appreciated that this illustrative example is just a basic example and that the test meter <NUM> is configured to do many other tasks as well. For example, the test meter <NUM> can be configured to store the test results in memory so that the user can view test results from the past.

As used herein, the term ablate should be broadly construed to mean to remove or destroy, which can be done by, for example, cutting, abrading, or vaporizing. In one form, at least a portion of the taps 120a-g is ablated by a laser, which can be a diode-pumped solid state laser or a fiber laser. In an illustrative form, the diode-pumped solid state laser is a <NUM> nanometer diode-pumped solid state laser and the fiber laser is a <NUM> nanometer fiber laser.

Illustrated embodiments of the secondary resistive element <NUM> show that seven states are possible depending on which one of taps 120a-g are left closed. It will be well understood by those of ordinary skill in the art that the number of states may be increased or decreased as desired or needed by adding or removing taps <NUM> from the design for the base resistance network <NUM>, with corresponding increase or decrease in the number of predetermined connection points <NUM>.

As stated above, a series of resistor taps can be created along a network of resistors on a test strip <NUM>, which can allow for the selection of one or more taps along the overall network. This use of resistor taps can address the limitations associated with creating precision resistors in a loosely-controlled conductive layer, such as the layers used in test strips <NUM>. For example, available space on substrate, spacing requirements, trace materials, etc., can all limit an ability to design precision resistors in a loosely controlled conductive layer. By creating two or more related circuits using a plurality of taps along the overall network, the circuits can be separately measured and arranged in desired ratios that control the effects of variations in the test strips. For example, conductivity variations, temperature variations, contact resistance variations, etc. can be compensated or controlled. Further, when measuring small resistances, such as those used on test strips <NUM>, parasitic (series) resistances can influence measurements. Additionally, contact resistance can be difficult to control using thin layers of relatively soft materials on a flexible substrate, such as those on test strip <NUM>. Allowing for non-linear distribution of selectable resistances via a plurality of taps can reduce sensitivities associated with contact resistances. In some embodiments, only one tap can remain intact. Alternatively, combinations of taps can remain intact if all the contact resistances are adequately compensated and/or insignificant compared to a measured resistance.

Turning now to <FIG>, a two resistor network <NUM> is illustrated. In this configuration, the encoding resistors are made up of a first resistor R1 and a second resistor R2. In this configuration, only two resistor measurements (R1 and R2) are needed to determine the information encoded by the resistors. This can be accomplished by measuring each of the encoding resistors (R1 and R2) individually. Alternatively, the overall encoding resistive network (R1 + R2) less an individual encoding resistance (R1 or R2) can be used to encode information. The encoded information can then be computed by determining a ratio of resistances to control or minimize the effects of the material's conductivity and/or temperature sensitivity. Example ratios of the resistive elements (R1, R2) can be:
<MAT>.

Regardless of which possible ratio calculation is selected, encoding resistors R1 and R2 can generally be measured along with the contact resistance associated with each of a plurality of connections points. Connection points RNET <NUM>, RTAP <NUM>, and connection point CES <NUM> can be seen in <FIG>. Connection point RNET <NUM> has a connection resistance represented by R(RNET); connection point RTAP <NUM> has a connection resistance represented by R(RTAP); and connection point CES <NUM> has a connection resistance represented by R(CES). In this configuration, the contact resistances R(RNET), R(RTAP), R(CES) are not significant, if RA and RB are significantly greater than the contact resistances R(RNET), R(RTAP), R(CES). In one non-limiting example, R1 and R2 are significantly greater than the contact resistances R(RNET), R(RTAP), R(CES) where R1 and R2 have values more than ten-times greater than the contact resistances R(RNET), R(RTAP), R(CES). Alternatively, in some configurations, R1 and R2 can have values less than ten-times greater than the contact resistances R(RNET), R(RTAP), R(CES). However, where R1 and R2 do not have a significantly higher resistance value than the contact resistances R(RNET), R(RTAP), R(CES), the contact resistances R(RNET), R(RTAP), R(CES) can overwhelm the encoding resistances R1 and R2. In this scenario, another implementation may be used to account for or mitigate parasitic contact resistance.

In particular, <FIG> illustrates a cluster of an actual test strip contact resistances <NUM>. <FIG> shows the configuration of a test strip <NUM> used to gather the data in <FIG>. The test strip <NUM> has eight connection points. However, it should be known that the test strip <NUM> could have more than eight connection points or less than eight connection points. The test strip <NUM> can have four loop resistances formed using the eight connection points. A first resistance loop <NUM> can be the loop formed between connection points WES and WE. A second resistance loop <NUM> can be formed between connect points RNET and RTAP. Further, a third resistance loop <NUM> can be formed between connection points CE and CES. A fourth resistance loop <NUM> can be formed between connection points CES and RNET.

Returning now to <FIG>, the test strip contact resistance was measured on fifty strips, useful for understanding the invention, as shown in <FIG>. In this example, each of the strips was measured at room temperature. An appropriately configured biosensor test meter was first used to measure the resistance loops <NUM>, <NUM>, <NUM>. Alternatively, redundant connections to each contact were used to implement a <NUM>-wire digital Ohm meter (Kelvin contact/connection) to measure the resistance loops <NUM>, <NUM>, <NUM>. The difference between the test meter and the <NUM>-wire digital Ohm meter was then computed for each resistance loop <NUM>, <NUM>, <NUM>. The results are shown in <FIG>. The data shows that the mean test contact resistance <NUM> is typically about <NUM> ohm per contact.

As such, a system and method to reduce the impact of contact resistances can be created by measuring resistances using a <NUM>-wire resistance measurement device. However, additional contact wires, contact pads, or contact points per pad are often needed when using <NUM>-wire measurement techniques. This can result in additional, undesirable redundancy or complexity on connector contact density, contact pitch, and/or manufacturing tolerance. This can result in biosensor errors.

One of skill in the art understands that using Kelvin contacts/connections (remote sensing or <NUM>-point probes) is an electrical impedance measuring technique having separate pairs of current-carrying and voltage-sensing electrode leads or wires to enable more accurate measurement of unknown load impedances. Adding a pair of remotely connected sense leads can allow for the excitation circuit to detect the true potential dynamically available at or near the load. An excitation circuit can then be configured to actively adjust the source or force a potential based on the sensed potential error signal, typically driving the error signal towards zero. The desired potential is then actively maintained at the load over a wide range of lead and load resistances. This can be accomplished by increasing the source potential to the desired potential difference V + I*RWIRE. This scheme can effectively compensate for IR losses in a current carrying path between the source and the load's sense connections. This manner of operation is analogous for more dynamic excitations and loads. The scheme is generally limited, however, by the adjustment range and speed of the excitation circuit coupled with the magnitude of the current and wire resistances. Moreover, space can often be a factor in devices such as biosensors, and Kelvin contacts/connections often require additional contacts, pads or dual contacts per pad, which may not always be feasible.

Turning now to <FIG>, useful for understanding the invention, a shared connection and partial contact resistance compensation scheme <NUM> is shown that is designed to measure a resistor network terminated at the CES <NUM> and RNET <NUM> contacts. Contact points CES <NUM> and RNET <NUM> can form a first resistance loop <NUM>. A first end of the resistor loop <NUM> can be connected to one or more contacts shared with an electrochemical cell (not shown) for facilitating electrochemical reactions on biological samples, as described above. In one example, the first end of the resistor loop <NUM> is the CES <NUM> contact point. In one configuration, the CES <NUM> contact point can be actively driven by a driver <NUM>. The driver <NUM> can be a driver of a <NUM>-wire resistance measurement device. Alternatively, the driver <NUM> can be a driver of a <NUM>-wire resistance measurement circuit <NUM> contained in a test meter <NUM>. The driver <NUM> can drive contact point CES <NUM> by providing a voltage signal, thereby exciting the first resistance loop <NUM>. Contact point RNET <NUM> can act as the reference point for controlling the voltage signal. Contact point RNET <NUM> can also serve as an uncompensated negative sense point, which can be coupled into the inverting inputs on amplifiers <NUM> and <NUM> of the <NUM>-wire resistance measurement circuit <NUM>. This connection scheme can compensate for the contact resistance of contact pad CES <NUM>. This connection scheme can also compensate for a lead resistance between contact point CES <NUM> and an end point <NUM>. By compensating for the contact resistance of contact point CES <NUM> and the lead resistance between contact point CES <NUM> and the end point <NUM>, the <NUM>-wire measuring circuit <NUM> can determine a resistance between the end point <NUM> and contact point RNET <NUM>, including the contact resistance of contact point RNET <NUM>. By using contact point RNET <NUM> as both a return path and an uncompensated negative sense point, Kelvin-type resistance measurements can be obtained without adding additional connections points or additional test leads to the test meter <NUM> of <FIG>.

Turning to <FIG>, useful for understanding the invention, another shared connection and partial contact resistance compensation scheme <NUM> is illustrated. This shared connection and partial contact resistance compensation scheme <NUM> can measure a resistor network terminated at the contact point RTAP <NUM> and contact point RNET <NUM>. Contact points RTAP <NUM> and RNET <NUM> can form a first resistance loop <NUM>. A first end of the resistance loop <NUM> can be connected to one or more contacts shared with an electrochemical cell (not shown) for facilitating electrochemical reactions on biological samples, as described above. In one example, the first end of the resistance loop <NUM> is contact point RTAP <NUM>. In one configuration, the contact point RTAP <NUM> can be actively driven by a driver <NUM>. The driver <NUM> can be a driver of a <NUM>-wire resistance measurement device, taking measurements at RTAP <NUM>, RNET <NUM>, and CES <NUM>. Alternatively, the driver <NUM> can be a driver of a <NUM>-wire resistance measurement circuit <NUM> contained in the test meter <NUM> of <FIG>. The driver <NUM> can drive contact point RTAP <NUM> by providing a voltage signal, thereby exciting the first resistance loop <NUM>. Subsequently, contact point RNET <NUM> can act as the return path for the voltage signal. Contact point RNET <NUM> can also serve as a negative sense point or reference, which can be coupled into the inverting inputs on amplifiers <NUM> and <NUM> of the <NUM>-wire resistance measurement circuit <NUM>. This connection scheme can compensate for contact resistance of contact pad RTAP <NUM>. This connection scheme <NUM> can also compensate for a lead resistance between contact point RTAP <NUM> and one of a plurality of end points 1516a-f, depending on which traces (taps) have been cut, as described above. If no traces have been cut, the connection scheme <NUM> can compensate for a lead resistance between contact point RTAP <NUM> and an end point <NUM>. By compensating for the contact resistance of contact point RTAP <NUM> and the lead resistance between contact point RTAP <NUM> and at least one of the end points 1516a-f, the <NUM>-wire measuring circuit <NUM> can determine a resistance between the contact point RNET <NUM> and one of the plurality of end points 1516a-f, including the contact point RNET <NUM> contact resistance, and excluding the RTAP <NUM> contact resistance and trace resistance from contact point CES <NUM> to end point <NUM> or end points 1516a-f. The above arrangement can allow for improved accuracy of resistance measurements by allowing for one or more Kelvin connections to be made through shared interconnections, while using existing measurement resources and techniques. Additionally, the above connection schemes <NUM> and <NUM> can provide improved resistance measurement accuracy with little or no additional biosensor real estate, or modifications to meter electronics. In some examples, the meter electronics can be modified by including a programmable analog switch matrix and/or appropriate switch control.

Turning now to <FIG>, a plurality of test strips 1600a-g useful for understanding the invention can be seen. The plurality of test strips 1600a-g represent seven primary states for resistor networks 1602a-g, having taps 1604a-g for encoding information. The test strip <NUM> has all trace paths intact, with no taps <NUM> being cut. The test strip <NUM> can represent the nominal or default manufactured configuration, State <NUM> in which all taps 1604a-g are connected to the primary resistance loop. The test strips 1600a-f represent six first order modifications that may be selected after the manufacturing process is completed and the material characterized by cutting all but one of the six available taps 1604a-f. The test strips 1600a-f represent operational states <NUM>-<NUM>. In each of the test strips 1600a-f, all but one of the tap traces 1604a-g have been cut as discussed above.

In one configuration, the taps 1604a-f can be cut using a laser. For example, the taps 1604a-f can be cut using a <NUM> wavelength single laser diode emitter focused to a small linear spot. Using a fast response power supply, a laser diode can be pulsed on/off for a programmed sequence based on a feedback signal. In one example, the laser can be pulsed based on a signal provided by a registration sensor while a biosensor passes underneath.

Turning now to <FIG> and <FIG>, a biosensor test strip <NUM> useful for understanding the invention is illustrated that includes a symmetrical resistance network having connection points RNET <NUM>, RTAP <NUM>, CES <NUM>, and CE <NUM>. <FIG> illustrates the biosensor test strip <NUM> in physical form, and <FIG> is a schematic representation of test strip <NUM>. The test strip <NUM> can have a resistance network <NUM>, having uniformly distributed, nearly equal distance resistance taps 1712a-f. The resistance taps 1712a-f result in resistor values R1-R7. While the test strip <NUM> has six resistance taps 1712a-f, it should be known that a test strip can have more than six resistance taps or less than six resistance taps. A first resistance loop <NUM> can be formed between contact point RTAP <NUM> and contact point RNET <NUM>. A second resistance loop <NUM> can be formed between contact point CES <NUM> and contact point RNET <NUM>. The ratio of measured resistances between the first resistance loop <NUM> and the second resistance loop <NUM> can be calculated and used to determine the state of the test strip <NUM>. In one configuration, the ratio of the resistance of the first resistance loop <NUM> and the second resistance loop <NUM> may be designed to always be less than one. Alternatively, an inverse ratio of resistance of the first resistance loop <NUM> and the second resistance loop <NUM> can be used such that the ratio is always be greater than one.

As stated above, the test strip <NUM> has six resistance taps 1712a-f. Where the taps 1712a-f are configured such that either none of the taps 1712a-f are cut (State <NUM>), or all but one of the taps 1712a-f are cut (States <NUM>-<NUM>), there are seven primary states. However, in some configurations, more than one tap 1712a-f can remain uncut, allowing for additional resistance options. Where only one tap 1712a-f is left uncut, the following equations can determine the ratio of the first resistance loop <NUM> and the second resistance loop <NUM> for each State, for biosensor test strip <NUM>. <MAT><MAT><MAT><MAT><MAT><MAT>.

Likewise, definitions of the seven first order non-evident code (NEC) states available can be as follows:.

State <NUM> can subsequently be determined using various computations due to the multiple parallel paths available. As shown above, the smallest ratio (here, in a non-limiting example, assigned to State <NUM>) can be determined by dividing R7 by the resistor sum of the second resistor loop <NUM> (R1+R2+R3+R4+R5+R6+R7). The largest ratio can be limited by R1 as a portion of the resistor sum. In one configuration, a linear distribution of resistance values can be selected for resistors R2-R6. A linear distribution of the resistance values can be determined using the equation <MAT>; where N is equal to the total number of desired taps. Furthermore, as the resistance measurement connection methods described in <FIG> and <FIG>, above, can effectively nullify contact resistances at contact points CES <NUM> and RNET <NUM>, the actual ratio can be represented by the below equation:
<MAT>.

Turning now to <FIG>, a distribution chart <NUM> showing actual ratios calculated from approximately <NUM> paired network measurements of test strips with uniform linear distributions of resistance values for R1-R7 (useful for understanding the invention) can be seen. Each State (<NUM>-<NUM>) can have an experimental error rate shown by the vertical bars for each State value. While most States have an adequate "buffer" between each other, it can be seen that there is the possibility of a "failure" between State <NUM> and State <NUM>. This possible "failure" between State <NUM> and State <NUM> can be due to additional uncompensated contact resistances. This potential failure can cause several issues.

First, the ratio associated with State <NUM> could possibly be misjudged as State <NUM>, were there is additional contact resistance associated with RNET <NUM>. Second, as the overall resistance (RNET <NUM>) decreases, the available tap resistances (R1-R7) can be proportionately lower. The can result in a higher susceptibility to misidentified states by a device or test meter <NUM> due to uncompensated resistance at the contact point RNET <NUM>. Finally, when using linearly distributed resistance values for R1-R7, State <NUM> may not be symmetrically located between the remaining six states. In one example, it would be desirable to have an equal number of State (ratio) options located on either side of State <NUM>. This can allow for concentric transitions from a central default state to encoded information States.

Accordingly, an alternate resistance value scheme can be implemented to mitigate the influence of parasitic resistances in determining resistance ratios. In one configuration, the alternate resistance value scheme can rely on a non-linear distribution of the resistance values for R1-R7. By utilizing non-linear resistance values for R1-R7, the resistance ratio method described above can be used for determining States. In one configuration, no absolute resistances are used to decode state information. Additionally, the device or test meter <NUM> can be more reliable in that there can be fewer incorrect state determinations due to uncompensated contact resistances at contact point RNET <NUM> of <FIG>. Further, the resistance values (R2-R6) can be recomputed to more equally distribute the impact of uncompensated contact resistance at contact point RNET <NUM> across all States. For example, the resistance values (R2-R6) can be at their largest values when the RNET to RTAP value is the smallest (lowest ratio). Finally, as State <NUM> can be considered the nominal value, allowing for non-linear distribution of resistance values R2-R6 can allow for the total number of States to be increased, allowing for multiple, centrally distributed States or ratios to be assigned as State <NUM>.

Several different methods can be used to distribute resistances R2-R6. Generally, R1 and R7 are limited by the conductivity of the trace material, the trace dimensions, the area available for the trace routing, and the lowest resistance the system can reliably measure. The remaining resistors (R2-R6) can be distributed by any function that addresses the issues discussed above. According to the present invention the non-linear distribution comprises a power function, an exponential function or a sinusoidal function. For example, <FIG> illustrates several resistance ratios over multiple States for different functions. For example, the ratio distribution per State using a linear function can be seen on plot <NUM>. A ratio distribution per State using a sinusoidal function can be seen on plot <NUM>. A ratio distribution per State using a exponential function can be seen on plot <NUM>. A ratio distribution per State using a k/x<NUM> function can be seen on plot <NUM>. Finally, a ratio distribution per State using a k/√x function can be seen on plot <NUM>.

It can be seen from <FIG> that a sinusoidal function <NUM> can result in only a minor improvement over a linear function <NUM> in regards to ratio separation for low states. However, a simple power function, such as the exponential function shown in plot <NUM> can produce a marked improvement in separation between low ratios. The general form of a power function can be represented by the equation y = AxB , where A and B are constants. This function can be rewritten as Rsum = R<NUM> * αN, and applied to determine at least one ratio for the resistance values of a test strip, where N represents the total number of states. In one embodiment, the R1 value can be selected to be a resistance value within a measureable range, and N can be selected based on a desired value of Rsum. Additionally, constraints such as available space on the test strip, conductivity of the materials, etc., can be used as factors in determining an N value. Once the Rsum and N values have been selected, α can be solved for, using the equation <MAT>.

Turning now to <FIG>, a distribution plot <NUM> is provided that illustrates the effects of varying the constant "N" in the above power equation on resistance ratios. As can be seen, the higher the "N" value, for example N = <NUM>, the resistance ratios become closer to a linear value. Thus, the N value should not be increased arbitrarily.

The above process was applied to a physical biosensor having specific design constraints (width, length, number and size of contact pads, recommended trace width / spacing, etc.). The physical implementation resulted in a slightly higher R1 (i.e. <NUM> squares) than that used in the theoretical implementation (i.e. <NUM> squares). Further, N was set to equal <NUM>, which provided a maximum (nominal) ratio of <NUM>, and a minimum ratio of <NUM>. The resistance values for the individual resistors (R1 - R7 for N=<NUM>) were calculated, and can be seen below in Table <NUM>.

Turning now to <FIG>, a distribution plot <NUM> can be seen comparing a linear distribution of resistance ratios to the non-linear resistance ratios using the values in Table <NUM>. In this example, the central three of the nine computed ratios are reserved / assigned to State <NUM>. The lowest of the three ratios can be the target for the State <NUM> resistance ratio. By using the lowest of the three ratios for State <NUM>, additional margin can be provided for the default (State <NUM>) condition.

The physical implementation values above can be input into a set of fabrication and layout guidelines to produce a test strip layout for implementation. For example, <FIG> illustrates one possible implementation of a test strip <NUM> based on the physical implementation values above, illustrating resistors R1-R7, and which utilizes an asymmetrical resistance network (i.e., a of set non-uniformly distributed resistor taps). The set of non-uniformly distributed resistor taps, biased toward the network's maximum value, helps reduce the impact of contact resistance on the measurement. Also, <FIG> shows control nodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> corresponding to the cutting locations required for implement each state. Advantageously, the non-uniformly distributed resistor taps can permit the resistance ratio method for NEC determination to be used for all codes and also be robust enough detect incorrect NEC determinations due to uncompensated contact resistances at RNET. Additionally, the non-uniformly distributed resistor taps can allow for redistribution of the tap resistance in order to "equalize" the impact of uncompensated RNET contact resistance across all NEC codes.

Turning to <FIG>, one possible set of configurations of test strips <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, is shown. In <FIG>, each of test strips <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> has a single intact control nodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or all intact contact nodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, to illustrate each of seven possible states. The test strip <NUM>, representing State <NUM>, is shown with only contact node <NUM> intact. The test strip <NUM>, representing State <NUM>, is shown with only contact node <NUM> intact. The test strip <NUM>, representing State <NUM>, is shown with only contact node <NUM> intact. The test strip <NUM>, representing State <NUM>, is shown with only contact node <NUM> intact. The test strip <NUM>, representing State <NUM>, is shown with only contact node <NUM> intact. The test strip <NUM>, representing State <NUM>, is shown with only contact node <NUM> intact. The test strip <NUM>, representing State <NUM>, is shown with all contact nodes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> intact.

Multiple test strips of each state were then analyzed to measure the resistance ratios associated with each State, with the resistance values of R1-R7 being those shown in Table <NUM>, and N being equal to <NUM>. Setting N equal to <NUM> allows the total resistance to be divided into nine segments, with three assigned to default state <NUM>. Returning to <FIG>, a distribution chart <NUM> showing actual ratios calculated from approximately <NUM> paired network measurements of test strips with uniform linear distributions of resistance values for R1-R7 can be seen. Each State (<NUM>-<NUM>) can have an experimental error rate shown by the vertical bars for each State value. While most States have an adequate "buffer" between each other, it can be seen that there is the possibility of a "failure" between State <NUM> and State <NUM>. This possible "failure" between State <NUM> and State <NUM> can be due to additional uncompensated contact resistances. This potential failure can cause several issues. <FIG> shows a distribution plot showing a range of resistances at each state <NUM>-<NUM>, illustrating how any potential overlap with States <NUM> and/or <NUM> can be corrected by asymmetrical distribution. Additionally, <FIG> shows a distribution plot <NUM> showing the range of resistance ratios at each state, <NUM>-<NUM>. As shown in plot <NUM> the area above line <NUM> was reserved for ratio's associated with default state <NUM>. As can be seen by the distribution of resistance ratios associated state <NUM> (ranging from <NUM> to <NUM>), the reserved margin was necessary for the default state. The measured data can further be seen in Table <NUM>, below.

The above data was taken from approximately <NUM> paired network measurements. An analysis of the data showed approximately a <NUM>% increase in the amount of parasitic resistance needed to cause one of the seven states into the next highest adjacent state, when using the above power function. This increase of <NUM>% was based on the above constraints (trace width and length, number and size of contact pads, spacing requirements, etc.). Additionally, other physical constraints can exist in different applications and would need to be accounted for when determining non-linear resistance values. In some embodiment, modifying the constraints for certain applications can increase or decrease the effect of parasitic resistance on the circuit; however, by using a power based function, as opposed to a linear function to distribute the resistance values, the parasitic contact resistance can be more evenly distributed across a range of nominal ratio values.

Another configuration of a resistive tap circuit <NUM> is provided in <FIG>. In this configuration, three separate resistance measurements can be made. First, a four wire resistance measurement can be made of the resistive circuit RNET <NUM> to CES <NUM>. The four-wire measurement can be made using the RNET <NUM> contact, the RNET sense <NUM> contact, the CES <NUM> contact, and the CES sense <NUM> contact. A three wire resistance measurement of RNET <NUM> to RTAP <NUM> can be determined. RTAP <NUM> does not have a corresponding RTAP sense contact point, and therefore only a three-wire measurement is available. This measurement can compensate for RNET <NUM> contact resistance; however, due to the limitation to a three-wire measurement, the RNET <NUM> to RTAP <NUM> measurement may include unintended and/or variable resistances associated with the RTAP <NUM> contact or trace. Additionally, a further three wire resistance measurement can be taken between RTAP <NUM> and CES <NUM>, to compensate for CES contact resistance. However, due to the limitation to a three-wire measurement (again due to RTAP <NUM> not having a RTAP sense contact point), the RTAP <NUM> to CES <NUM> measurement can include unintended or variable resistance associated with the RTAP <NUM> contact or trace.

Once the three measurements, above, have been measured, the approximate value of the RTAP <NUM> parasitic resistance can be determined by adding the two three-wire partial network measurements to estimate a total network resistance. The four-wire total network measurement can then be subtracted from the sum of the three-wire partial measurements. This can be seen in the equation below:
<MAT>.

The computed RTAP <NUM> parasitic resistance can then be subtracted from the RTAP <NUM> measurements to obtain both a corrected (RNET <NUM> to RTAP <NUM>) and (RTAP <NUM> to CES <NUM>). Using the corrected network resistance values, corrected ratios [(RNET <NUM> to RTAP <NUM>) / (RNET <NUM> to CES <NUM>)] and/or [(RTAP <NUM> to CES <NUM>) / (RNET <NUM> to CES <NUM>)] can be determined. Alternatively, reciprocal ratio values can also be determined using the corrected values.

Although embodiments of the invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations obvious to the skilled artisan are to be considered within the scope of the claims that follow.

Claim 1:
An analyte test strip (<NUM>) for performing at least one of quantitative and qualitative analysis of an analyte in a sample of fluid, the analyte test strip comprising:
a non-conductive substrate;
a working electrode (<NUM>);
a counter electrode (<NUM>);
a reagent layer (<NUM>) at the distal end of the analyte test strip, the reagent layer covering at least a portion of the working electrode and the counter electrode; and
a circuit on the non-conductive substrate, the circuit comprising:
a primary resistive element on the non-conductive substrate having a first end and a second end, wherein the configuration of the primary resistive element is a serpentine configuration; and
a secondary resistive element on the non-conductive substrate having a third end and a plurality of taps connected to the primary resistive element at a plurality of predetermined connection points (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) on the serpentine configuration, the plurality of predetermined connection points defining a plurality of unique resistive paths running from the third end, through the predetermined connection points, through at least a portion of the serpentine configuration and to either of the first and second ends;
wherein
the plurality of unique resistive paths have a plurality of resistance values (R2, R3, R4, R5, R6), the plurality of resistance values having a non-linear distribution,
characterised in that the
non-linear distribution comprises a power function, an exponential function, or a sinusoidal function.