Sensor comprising a measurement circuit for determining resistance and capacitance of an

Abstract

A sensor for measuring environmental conditions is provided. The sensor includes a sensing element having a resistance and a capacitance sensitive to environmental conditions; a first measurement circuit for determining a resistance of the sensing element using logarithmic scaling; a second measurement circuit comprising an integral amplifier for determining a capacitance of the sensing element; and a switching circuit for sequentially switching the sensing element to the first measurement circuit and the second measurement circuit such that the resistance and capacitance can be determined within a predicted period of time.

Description

Technical Field

[0001] The present application relates to an electronic sensor for measuring environmental conditions and a method of operating such a sensor. Background Art

[0002] Electronic sensors are widely used to determine environmental conditions. As a simple example, temperature can be measured electronically by passing a current from a constant current source through a wire that has a temperature-dependent resistance. The resistance of the wire can then be determined by measuring the voltage across the wire, providing a temperature measurement.

[0003] In this simple example, the environmental condition to be measured consists of a single physical parameter (temperature), which allows the implementation of the electronic sensor to be relatively simple. However, in other cases, the environmental condition to be measured may be more complex, involving multiple physical parameters, such as different gases (volatiles) produced in a specific scenario with their own concentrations, such as exhaust products of fuel combustion or decay emissions produced by biological processes.

[0004] Sensors that detect odors in various gas mixtures are sometimes called electronic noses. Lalberte and Porter discuss such devices in “White Paper-How Does An Electronic Nose Work”, January 2017, available at https: / / www.researchgate.net / publication / 320455411, which provides information on various sensors used to detect odors.

[0005] To better determine such complex environmental conditions, sensing operations can include measuring the resistance and capacitance of the sensor (or its specific components, often referred to as transducers or sensing elements). In addition, such measurements can be repeated over a given period of time to provide an indication of the evolution of environmental conditions over time.

[0006] However, existing sensors used to make such measurements of complex environmental conditions are typically either complex (and therefore expensive) devices, or simpler devices that are limited in performance, such as providing limited measurement accuracy and / or poor temporal resolution. Summary of the invention

[0007] The invention is defined in the appended claims.

[0008] The present invention provides a sensor for measuring environmental conditions. The sensor includes a sensing element having a resistance and a capacitance that are sensitive to the environmental conditions; a first measurement circuit for determining the resistance of the sensing element using logarithmic scaling; a second measurement circuit including an integrating amplifier for determining the capacitance of the sensing element; and a switching circuit for switching the sensing element to the first measurement circuit and the second measurement circuit in sequence, so that the resistance and the capacitance are determined within a predetermined time period.

[0009] In some implementations, the first measurement circuit includes a logarithmic amplifier.

[0010] In some embodiments, the first measurement circuit is configured to measure a resistance whose resistance range covers at least 6 orders of magnitude, preferably at least 7 orders of magnitude, and more preferably at least 8 orders of magnitude.

[0011] In some embodiments, the first measurement circuit is configured to measure resistance within a certain range, the lower limit of which is not greater than 2500ohm, preferably not greater than 1000ohm, preferably not greater than 500ohm and the upper limit is not less than 1gOhm, preferably not less than 5gOhm, preferably not less than 25gOhm.

[0012] In some implementations, the integrating amplifier includes an operational amplifier integrator.

[0013] In some implementations, the sensor is configured to provide a step change voltage to an integrating amplifier, and the slope of the output of the integrating amplifier depends on the capacitance to be measured.

[0014] In some embodiments, the second measurement circuit further comprises a time-to-digital converter (TDC), and optionally, wherein the TDC can be used to measure the slope of the output of the integrating amplifier.

[0015] In some embodiments, the sensor is configured to correct the measured capacitance based on the measured resistance.

[0016] In some embodiments, the correction is only applied if the measured resistance is below a threshold, optionally wherein the threshold is below 100 kOhm, such as below 40 kOhm.

[0017] In some embodiments, the second measurement circuit is configured to measure a capacitance within a certain range, the lower limit of which is no greater than 5F, preferably no greater than 1F, and the upper limit of which is no less than 100F, preferably no less than 200F.

[0018] In some implementations, operations of the first measurement circuit for determining resistance are performed independently and sequentially from operations of the second measurement circuit for determining capacitance.

[0019] In some embodiments, the resistance and capacitance may be determined within a predetermined 0.1 s time period, such as within 0.01 s, such as within 1 ms.

[0020] In some embodiments, as a calibration mode, the sensor further comprises at least one channel for providing a known resistor measured by the first measurement circuit and / or for providing a known capacitor measured by the second measurement circuit.

[0021] In some embodiments, the sensor comprises a plurality of sensing elements, optionally wherein the number of sensing elements is in the range of 1-6, optionally in the range of 1-20, or optionally in the range of 1-50.

[0022] In some embodiments, the sensor is configured to switch each sensing element into the first measurement circuit and the second measurement circuit in sequence.

[0023] In some embodiments, the sensing elements are repeatedly switched to the first measurement circuit and the second measurement circuit in sequence, and the duration for which all the sensing elements are switched to the first measurement circuit and the second measurement circuit in sequence and the resistance and capacitance of all the sensing elements are measured is no more than 1 second, for example, no more than 0.1 second, for example, no more than 20 ms.

[0024] In some embodiments, the sensing element comprises an electronic nose comprising an array of polymer semiconductor-based sensors.

[0025] In some embodiments, the environmental condition to be measured corresponds to soil health.

[0026] The present disclosure also provides a method for measuring environmental conditions using a sensor, the sensor including a sensing element having a resistance and a capacitance that are sensitive to the environmental conditions. The method includes: switching the sensing element into a first measurement circuit; using the first measurement circuit to determine the resistance of the sensing element using logarithmic scaling; switching the sensing element into a second measurement circuit; and using the second measurement circuit to determine the capacitance of the sensing element using an integrating amplifier.

[0027] For example, the above method may be implemented using a suitable implementation of the sensor as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Various embodiments of the claimed invention will now be described, by way of example only, with reference to the following drawings.

[0029] Figure 1 is a schematic diagram of a sensor according to the present invention, which can be used to measure (detect) environmental conditions.

[0030] Figure 2is a schematic diagram of a logarithmic amplifier, which can be used as Figure 1 An example of a resistive detector is shown in FIG.

[0031] Figure 3 is a more detailed diagram of the logarithmic amplifier (with Figure 2 Compared to ), the logarithmic amplifier can be used as Figure 1 An example of a resistor detector is shown.

[0032] Figure 4 is the resistance of the sensing element and the Figure 1 An example graph of the relationship between the outputs of the resistive detectors in a sensor is shown.

[0033] Figure 5 Yes, you can Figure 1 Schematic diagram of an example of a capacitive detector used in a sensor.

[0034] Figure 6 are example graphs showing the deviation of an op amp integrator from the ideal integrator behavior.

[0035] Figure 7 is shown for operation such as Figure 1 An example flow chart of a sensor method is shown. DETAILED DESCRIPTION

[0036] Figure 1 is a schematic diagram of a sensor 50 for measuring (detecting) a condition of an environment 10. The sensor 50 comprises at least one sensing element 120 acting as a transducer, wherein an electrical characteristic of the sensing element 120 depends on the condition of the environment 10, so that measurement of the electrical characteristic of the sensing element can provide information about the condition of the environment 10.

[0037] The sensor 50 also includes a sensor control system 130. The sensor control system 130 has a detector 150 for measuring the resistance of the sensing element 120 (sometimes referred to as the sensor element) and a detector 160 for measuring the capacitance of the sensing element 120. Figure 1 , the sensor control system 130 is shown as being separate from the sensing element 120, however, in many embodiments, the sensor control system 130 and the sensing element 120 may be combined or integrated into a single unit. Although some sensors only measure resistance (without making any capacitance measurements), Figure 1The sensor supports measuring the resistance and capacitance of one or more sensing elements 120. The provision of resistance and capacitance measurements provides better data for analyzing the sample being sensed (especially when the analysis is performed using an artificial intelligence / machine learning system, as further described below). However, the measurement of resistance and capacitance places additional demands on the detectors 150, 160 and the sensor control system 130, as discussed in more detail below.

[0038] The sensor control system 130 provides interface electronics for performing, storing, and transmitting resistance and capacitance measurements obtained from the detectors 150, 160. As described above, the sensor 50 including one or more sensing elements 120, detectors 150, detectors 160, and sensor control equipment can be integrated into a single device. Typically, such devices are portable and can run on batteries for a long time. This in turn imposes some practical limitations on the power consumption levels that the sensor control system 130 and sensors in general can support.

[0039] By way of example, to outline potential applications of the sensor 50, the sensor 50 may be used, for example, for farmers to check soil properties (environmental conditions), but is not limited thereto. Specifically, the sensor 50 may be used to provide information about various biological, chemical, and physical soil health indicators, including microbial biomass and soil organic matter content, which depends on the activity and diversity of the soil microbial community. It is noteworthy that deteriorating soil health may reduce or limit crop yields, reduce crop resistance to pests and diseases, and reduce crop resistance to drought. To support such monitoring, the sensor 50 is typically portable and capable of being held in one hand. As described above, the sensor 50 may be designed to have sufficiently low power consumption to allow the sensor to run on batteries for a considerable period of time (e.g., a full day).

[0040] In a typical embodiment, the sensor 50 is a handheld, battery-powered device that can be controlled, for example, using an application on a smartphone 205. The sensor is used to measure and analyze soil samples directly on-site without the need for additional sample preparation. In addition, by using the sensor 50 to analyze the activity and diversity of microbial communities in a soil sample, many different information about soil health indicators can be obtained without having to perform multiple different tests to obtain information on different aspects of soil health. The measurement process and analysis can be completed in a few minutes, providing virtually real-time information about environmental conditions at the current location.

[0041] Sensor 50 may also include a global positioning system (GPS) detector and / or any other system that supports location monitoring ( Figure 1This allows each sample analyzed by the sensor and the associated measurements to be tagged with GPS location (and time) coordinates. The user can then track how environmental conditions (e.g. soil properties) change over time at a particular location being monitored.

[0042] In operation, a small soil sample (e.g., about 100 grams) may be scooped from the ground and placed into a cavity or drawer of the sensor 50 (the drawer or cavity for holding the sample is not in the Figure 1 ). The sensing element 120 may include a test strip that can be removed from the protective packaging and inserted into the sensor 50 (either before or after soil enters the sensor device 50). In some embodiments, the sensing element 120 may include a disposable test strip, whereby a new test strip is input into the sensor 50 each time a new measurement is taken. In some embodiments, the sensing element 120 may be reusable, such as to clean the sensor between consecutive readings. In some cases, sensor cleaning may be performed in situ (i.e., within the sensor 50 itself); in other cases, the sensing element 120 may be removed from the sensor 50 for cleaning prior to reuse. It should be understood that some sensors may support both disposable and reusable sensing elements 120.

[0043] Once the relevant measurements have been performed, in particular, when the sensor 50 has obtained a series of measurements of the resistance and capacitance of one or more sensing elements 120 for determining the conditions of the environment 10, in some embodiments, the data can be transmitted to an application (app) on the smartphone 205. Data communication between the sensor 50 and the smartphone can be performed, for example, by using a wireless Bluetooth connection. The smartphone can perform local analysis on the measurement data and / or can send the measurement data to a remote location (e.g., a computer server 208) to perform analysis of the measurement data. In some embodiments, the computer server can be part of (or provided by) a cloud computing service. In other embodiments, the sensor 50 can communicate with the smartphone 205 via an appropriate network (e.g., a wireless Bluetooth connection). Figure 1 ) communicates directly with the computer server 208 without going through the smartphone 205.

[0044] In some embodiments, an artificial intelligence (AI) or machine learning (ML) system ( Figure 1The analysis of the soil measurements is performed on any suitable device (e.g., smartphone 205 or computer server 208) (not shown in the figure), and the artificial intelligence or machine learning system can be implemented on any suitable AI platform, such as TensorFlow (see https: / / www.tensorflow.org / ) or Azure from Microsoft Corporation. The AI / ML software analyzes the measurement data from the sensor 60 and can identify values ​​for various soil health indicators. These results can then be returned from the cloud (such as computer server 208) to the smartphone 205 and presented to the user at the smartphone 205 for review and any appropriate action.

[0045] Figure 1 The sensor 50 is designed to process measurements of a high impedance sensing element 120, such as may be used in (among other things) an electronic nose. Such a sensing element 120 may include, for example, a substrate made of a semiconductor material such as metal oxide silicon (MOS), or may be provided as part of a sensor array based on a polymer semiconductor. More details on various types of sensing elements 120 may be found, for example, in the white paper cited above by Lalberte and Porter.

[0046] although Figure 1 The sensor 50 shown has one sensing element, but in many embodiments of the sensor 50, there are multiple sensing elements. In some cases, the sensing elements generally all have the same substrate, but different sensing elements may have different coatings from one another. These different coatings may affect how specific gases interact with the substrate and therefore how they change the electrical properties (particularly resistance and capacitance) of the sensing element 120.

[0047] In such Figure 1 In some embodiments of the illustrated sensor 50, the sensor 50 has six sensing elements 120, but other sensors may have a different number of sensing elements. It should be understood that increasing the number of sensing elements may provide greater discrimination and accuracy when measuring environmental conditions, however, increasing the number of sensing elements may also result in a larger size of the sensor 50 and increased power consumption. Therefore, the number of sensing elements provided for a given sensor 50 may be selected based on the circumstances of any particular application.

[0048] If the sensor has N sensing elements, each with a different coating, each sensing operation actually produces a 2N-dimensional vector, which includes values ​​r1, c1, r2, c2...rN, cN. Therefore, for each sensing element (1, 2, ...N), two sensed values ​​are obtained, namely the measured resistance of the sensing element 120 (e.g., r1) and the measured capacitance of the sensing element 120 (e.g., c1). Therefore, the sensing operation provides a 2N-dimensional space, and the specific location of the sensor result in the 2N-dimensional space corresponds to the determined environmental condition. (The environmental condition can be based on a variety of different physical parameters, such as the respective concentrations of a variety of different gases (target analytes) generated from a sample such as a soil sample).

[0049] In many cases, the sensing operation may include a group (time series) of individual sensing measurements that are spread out over a period of time (e.g., within a few minutes). Such time series measurements (readings) provide additional information for measuring environmental conditions (compared to measurements at only a single time point). However, during the time series, when one or more sensing elements are exposed to a target analyte (e.g., a gas or volatile organic compound released by a sample), the resistance R of one or more sensing elements 120 will typically change by several orders of magnitude. In particular, when gases, volatiles, etc. bind or adhere to the surface of the sensing element, the resistance will tend to decrease and help provide a conductive (low resistance) path on the sensing element. This reduction in resistance (impedance) within a few minutes may, for example, include a resistance drop from a giga-Ohm level to an ohm level. Therefore, the resistance detector 150 is designed to accommodate a wide range of resistance measurements, as discussed in more detail below.

[0050] The capacitance detector 160 measures the capacitance relative to one or more sensing elements, typically in the order of picofarads (pF). The capacitance level of a sensing element typically varies less than the large changes in resistance over a measurement period (e.g., several minutes). In some embodiments, although there may be some variation in the capacitance level over a measurement period, the capacitance of one or more sensing elements may remain in the order of picofarads during the measurement period.

[0051] It should be understood that the above-mentioned resistance and capacitance values ​​of one or more sensing elements, the length of the measurement period, and the change of the resistance and capacitance values ​​of one or more sensing elements during the measurement period are provided only as examples. Sensing operations implemented using different sensors and / or performed on other types of samples (rather than soil) may involve different values, and the sensor 50 can be appropriately designed to accommodate these different values.

[0052] The sensor 50 including the resistance detector 150, the capacitance detector 160 and the sensor control system 130 is generally designed to support multiple sensing elements 120. In addition, the various sensing elements 120 must generally be read within short time intervals because the signals (i.e., the resistance and capacitance values ​​of the various sensing elements) may change rapidly to reflect changes in the concentration of the target analyte in the measured environment. For example, the desired time sampling rate of each sensing element 120 may be on the order of milliseconds or lower. Having multiple sensing elements that are repeatedly read at short intervals generally increases the size and consumes the battery used to power the sensor 50, which is challenging for the implementation of handheld sensors.

[0053] Currently, there are various methods for measuring the resistance and capacitance of sensing elements, such as impedance spectroscopy, frequency conversion method and RC curve method. Impedance spectroscopy usually requires a good mathematical model and usually needs to sweep from very low to very high frequencies to obtain the best results. The resulting sensors usually include relatively expensive and complex hardware.

[0054] In an attempt to simplify hardware and reduce costs, some implementations may focus on a few key frequencies to overcome, but mathematical modeling is still required. Such modeling may be difficult in the absence of a physical context that can properly interpret the results. For example, it is difficult to develop a suitable model for soil sampling because the interaction between the target analyte and / or non-target analyte and the sensing element 120 has not been properly characterized (and such characterization would be a difficult and time-consuming task).

[0055] Measuring the resistance (R) and capacitance (C) from the sensor's RC curve is another known method of obtaining the output of a sensing element, since the RC curve naturally contains information about R and C. A limiting factor here is the time required for the RC curve to rise to a suitable level from which measurement data can be extracted. This is usually not a problem at low R, but becomes a problem at high R. For example, reasonable range limits for the resistance and capacitance of the sensing element 120 are: 450Ohm to 25gOhm for resistance and 1pF to 100pF for capacitance. The combination of 1pF capacitance and 450Ohm resistance means an RC value of 450 picoseconds (ps), which is very fast and therefore difficult to measure accurately; while the combination of 100pF capacitance and 25gOhm resistance means an RC value of 2.5 seconds (s), which is too long for many applications due to the lack of sufficient time resolution to track significant changes in the time domain.

[0056] The frequency conversion method is described in “A CMOS integrated low-voltage low-power time-controlled interface for chemical resistive sensors” by Marcellis et al., November 2012, available at: https: / / www.researchgate.net / publication / 236346603_A_CMOS_integrated_low-voltage_low-power_time-controlled_interface_for_chemical_resistive_sensors.

[0057] This approach allows for faster measurements at high R, in fact by limiting the maximum length of time that a measurement may take. However, even with this approach, the measurement time at high R may be as high as several seconds per data point per sensing element, so a complete scan of the entire system may take tens of seconds. In addition, the equations used in this approach are only valid in a specific region of the parameter space, which is narrower than the entire range of resistance values ​​experienced by the sensing element. The usable range can be extended by measuring pure frequency characteristics instead of using equations, and correlating these characteristics with the response of the sensor to known analyte concentrations or known characteristics of the analyzed sample through machine learning. However, this approach has significant disadvantages, because changes in the hardware electronics of the sensor 50 may require the construction of a completely new machine learning training data set, because the measured electronic characteristics no longer directly correspond to the physical properties of the sensor.

[0058] Rather than using such existing methods to measure the resistance and / or capacitance of a sensing element (e.g., based on impedance spectroscopy, RC curves, or frequency conversion methods), the sensor 50 described herein uses a different method to perform separate measurements of the resistance and capacitance of the detectors 150, 160. In this method, the resistance and capacitance are measured separately from each other (rather than using a single measurement to extract both values). It has been found that using two separate but effective measurement techniques for the resistance detector 150 and the capacitance detector 160 supports faster and more accurate results (compared to using a single measurement technique that attempts to determine the resistance and capacitance of the sensing element in a single operation).

[0059] exist Figure 1 In an embodiment, resistance and capacitance measurements may be performed sequentially, one at a time, using a switch system such as schematically represented by switch S1 140. For example, when a resistance measurement is to be performed, switch S1 is set to Figure 1 The configuration shown, in which the sensing element 120 is connected to the resistance detector 150 (but not to the capacitance detector). This enables the resistance detector 150 to make the desired measurement of the resistance of the sensing element 120.

[0060] Once the first sense measurement of the resistance of sense element 120 has been completed, the setting of switch S1 is changed to connect sense element 120 to capacitance detector 160 (instead of the resistance detector). This enables capacitance detector 160 to perform the required measurement of the capacitance of sense element 120.

[0061] The operation of switch S1 140 may be managed by the sensor control system 130. For example, the sensor control system may initially set the switch to Figure 1 The resistance detector 150 may then notify the sensor control system 130 when the resistance detector 150 has completed the resistance measurement, so that the sensor control system 130 may change the setting of the switch S1 to allow the capacitance detector 160 to perform the capacitance measurement. It should be understood that this switching back and forth between the resistance detector 150 and the capacitance detector may continue during the measurement cycle (typically several minutes).

[0062] As described above, in some embodiments, there may be multiple sensing elements. In this case, more complex switch configurations and sequences may be provided to allow the resistance detector 150 and the capacitance detector to measure each sensing element in sequence. For example, if there are two sensing elements, denoted as SE1 and SE2, the sensor control system may control the switch 140 to sequentially measure the resistance and capacitance of sensor SE1, and then sequentially measure the resistance and capacitance of SE2. Other modes may be used to sequence the sensing. For example, in some embodiments, the sensor control system 130 may control the switch settings so that the resistance detector 150 first (sequentially) determines the resistance of each sensing element 120, and then the capacitance detector 160 (sequentially) determines the capacitance of each sensing element 120. The sensor control system may manage other measurement modes for different sensing elements 120 based on various factors, such as the total number of sensing elements and the specific environment of any given embodiment (e.g., the switching time scale of the sensor control system 130 compared to the time scale of the target analyte concentration change).

[0063] In more detail, for the resistance detector 150, it can be configured to provide a logarithmically scaled output, for example according to the following equation:

[0064] V out = k log(V in / V ref )+c(Equation 1)

[0065] Among them, V ref is related to the input voltage (V in ) is the reference voltage for comparison, k and c are constants, k determines the gradient, c is the gradient to V out Note that k can also be viewed as a factor that changes the base of the logarithm (e.g., converting between base 10 and natural logarithm), while c can be viewed as adjusting V ref The value of parameter V ref , k, and c may be configured by the implementation to provide a suitable range of output voltages for a particular range of input voltages. For example, if the desired output voltage range is 0-5 volts for a particular range of input voltages, the value of k may be selected such that the range between the lowest and highest input voltage values ​​is 5 volts (for V in ), and c(and / or V ref ) can be chosen so that the lowest input voltage corresponds to one end of the voltage range, typically 0 volts.

[0066] To provide this logarithmic scaling, the implementation of the resistor detector may include a logarithmic amplifier, see for example: https: / / en.wikipedia.org / wiki / Log_amplifier and https: / / www.tutorialspoint.com / linear_integrated_circuits_appl ications / linear_integrated_circuits_applications_log_and_anti_log_amplifiers.htm.

[0067] Figure 2 is a schematic diagram of a logarithmic amplifier (log amp) 110, which can be used as Figure 1 An example of a resistor detector in a sensor is shown. The logarithmic amplifier includes a resistor R, a diode D, and an operational amplifier (op amp) OA. Figure 2 Medium input voltage (V in ) and output voltage (V out ) usually follows the above equation 1, V ref The values ​​of , k and c are determined in particular by the value of the resistor R and the characteristics of the diode D.

[0068] In general, grounding an op amp means that the voltage at both the positive and negative (inverting) inputs of the op amp is zero, so no current flows through the op amp (for an ideal device). Therefore, the current I flowing through resistor R matches the current flowing through diode D, and the current through the resistor is given by I = V in / R is given, so with the voltage Vin The voltage across the diode is (negative) V out , the current through the diode is exponentially related to the voltage, I~(exp V out ) represents the non-saturated region. Therefore, the current flowing through resistor R matches (with V in The only way to achieve a linear relationship is to out With V in logarithmically proportional (as shown in equation 1 above), because of this, the current flowing through the diode can be obtained as I~exp V out = > I ~ exp (log V in )=>I~V in Therefore, the current flowing through the resistor R and the current flowing through the diode D are both related to V in In linear proportion.

[0069] Figure 3 shows a logarithmic amplifier 110A, which can also be used in Figure 1 of the resistance detector 150. Although Figure 2 Only the core components of logarithmic amplifier 110 are shown to allow a high level understanding of such a device, but Figure 3 The logarithmic amplifier 110A represents a production model, i.e., the LOG114 logarithmic amplifier available from Texas Instruments (TI), see https: / / www.ti.com / product / LOG114. It is worth noting that the discussion of the LOG114 device herein will be limited to aspects directly related to the sensor of the present application. More information about the LOG114 device can be found in the vendor data sheet, which can be obtained from https: / / www.ti.com / lit / ds / symlink / log114.pdf?ts=1664175290746&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLOG114 (hereinafter referred to as the data sheet).

[0070] This application Figure 3 Based on the datasheet of the LO114 device dual supply configuration Figure 1 , which can be used to provide an output voltage representing the logarithmic comparison of two currents. Figure 3 As shown, the LOG114 device can be configured to have an input that provides a reference current I ref (also marked as I1), the reference current I ref is through the known reference resistance R ref Apply a known reference voltage V refThe reference current I ref The input is provided to the inverting terminal of the operational amplifier A1. Similarly, through the (unknown, to be measured) resistance R of the sensing element 120 s Apply a known reference voltage V ref The second current I2 is used to generate the second current I2. The second current I2 is provided as an input to the inverting terminal of the operational amplifier A2. The positive (non-inverting) inputs of the operational amplifiers A1 and A2 are both grounded.

[0071] It is worth noting that logarithmic amplifiers A1 and A2 use diode-connected transistors in their feedback paths, where the voltage across the diode is proportional to the logarithm of the current flowing through it. This configuration is similar in design to Figure 2 The example is slightly different because a transistor is used in the feedback loop (rather than a diode), but the overall mode of operation is still similar to the one described above for Figure 2 More information on log amplifier operation, including transistors, can be found at: https: / / electricalvoice.com / log-amplifier-circuit-applications / .

[0072] The two voltage outputs from log amplifiers A1 and A2 are fed to the corresponding ports of differential amplifier A3, and the output of differential amplifier A3 represents the voltage difference between the two. Specifically, the output of log amplifier A1 is passed to the inverting input of A3, and the output of log amplifier A2 is passed to the positive (non-inverting) input of A3. Amplifiers A4 and A5 of LOG114 are used for scaling and various other auxiliary functions.

[0073] The LOG114 device in conjunction with the present application operates as follows. Reference current input I ref By V ref / R ref The other current input I2 is given by V ref / R s Given, where R s is the resistance of the sensing element 120, i.e., the parameter to be measured. The output voltage of the logarithmic amplifier A1 can be expressed as V(A1)=k log V ref / R ref +c, and the output voltage of logarithmic amplifier A2 can be expressed as V(A2) = k log V ref / R s + c (as in Equation 1 above, k and c are constants corresponding to the scaling and base point, and may be known or measured properties of the device).

[0074] The output voltage of logarithmic amplifier A3 is proportional to V(A2)-V(A1) (because the output of op amp A1 is used as the inverting input of A3), which can be rewritten as k(log V ref / R s -log V ref / R ref ). This can be simplified to -k(logR s / R ref ). This expression gives the ratio of the resistance of the sensing element to the reference resistance. Furthermore, since the reference resistance is known, this ratio allows the resistance of the sensing element 120 to be determined.

[0075] The total output of a LOG114 device is generally given by:

[0076] V out =0.375log 10 (I1 / I2)+V offset (Equation 2)

[0077] (See Equation 2 of the datasheet.) It should be appreciated that this has the same overall format as Equation 1 above. In this configuration, for every ten-fold (power of 10) change in the input current, the output voltage changes by 0.375 volts relative to the reference current.

[0078] There are certain benefits to using such a logarithmic amplifier 110 as part of a resistance detector to measure the resistance of the sensing element 120. Thus, the logarithmic amplifier 110 is able to support input (voltage or current) measurements across several orders of magnitude, so that the measured resistance can span several orders of magnitude. This resistance measurement range is very useful in a variety of application areas, such as the soil sample research discussed above. In addition, the logarithmic amplifier 110 enables fast measurement of the resistance of the sensing element, with a timing (duration) typically in the range of μs to ms. Importantly, the timing is not dependent on the RC value, but is typically independent of the values ​​of R (resistance) and C (capacitance). This allows the timing performance of the resistance detector 150 to be specified as a predetermined period, such as less than 0.1 seconds, optionally less than 0.01 seconds, or optionally less than 0.001 microseconds. Because the predetermined period is typically applicable to situations that are independent of the resistance level, this method provides more consistent and predictable measurement results.

[0079] Furthermore, even if the sensor 50 has multiple sensing elements 20, the resistance detector 150 is able to read the measurement value of each of the multiple sensing elements (sequentially) in a total time much less than 1 second. This in turn supports measuring each of the multiple sensing elements at a high measurement frequency (significantly greater than 1 Hz).

[0080] As mentioned above, for the data table Figure 1The LOG114 logarithmic amplifier 110A calculates the logarithmic ratio of the input current to the reference current in a dual supply configuration. (The LOG114 logarithmic amplifier 110A also supports a single supply configuration). The LOG114 device has two logarithmic amplifier sections A1, A2 to compensate for various factors, such as temperature, using a differential amplifier A3. The LO114 device has additional operational amplifiers built in to provide scaling, biasing, filtering, and other functions.

[0081] The resistance of the sensing element 120 is typically in the range of 500 Ohms to 25 gOhms (although this range may vary depending on the type of sample being studied). Since current is inversely proportional to resistance (for a fixed voltage), the logarithmic range of the current input accepted by the logarithmic amplifier 110 should approximately correspond to the logarithmic range of the resistance to be measured in order to provide measurements over the resistance range of interest. The LOG114 logarithmic amplifier 110A meets this condition, supporting current inputs spanning eight orders of magnitude from 100 pA to 10 mA.

[0082] It is worth noting that if the resistance is above about 1 gOhm, the sensitivity to noise increases, which makes it more difficult to achieve stable and accurate measurements (the current signal level reflecting high resistance is low.) Careful shielding and reliable grounding can be provided to reduce the noise level within the resistance detector 150, so that accurate results can be obtained (even for high resistance measurements).

[0083] While the above description focuses on the use of a logarithmic amplifier to provide logarithmic scaling, such logarithmic scaling can also be obtained by other forms of circuits, such as by using a set of "range resistors". In the latter approach, different resistors are switched into the circuit using a chip that can electronically tell the circuit how to wire so that the output of the operational amplifier measurement circuit remains within a specific measurable voltage range. The chip can include a multiplexer chip, or in some cases two or more such multiplexer chips. For example, the multiplexer chip in one embodiment is limited to 6 channels, and there are 8 resistor ranges that need to be switched, namely: 10GOhm, 1GOhm, 100MOhm, 10MOhm, 1MOhm, 100kOhm, 10kOhm and 1kOhm, so two 6-channel multiplexer chips are required to handle the full set of range resistors. In such an embodiment, one or more multiplexer chips are used to switch the range resistors down or up based on the output voltage reaching a threshold voltage. Specifically, if the output voltage begins to exceed the range, the next time the circuit is measured, the resistors of the lower (or higher) range will be switched as appropriate. Thus, the final output of such a circuit is substantially similar to the output provided by log amp chip 110 (described above).

[0084] Figure 4 It is shown as Figure 1 An example graph of the relationship between the resistance of the sensing element 120 and the output of the resistance detector 150 in the sensor is shown. Specifically, Figure 4 The results of a simulation of measuring a resistor using a resistor detector 160 including a LOG114 logarithmic amplifier 120A are presented. The X-axis is used to represent the resistance values ​​from 1kOhm to 10gOhm, that is, spanning seven orders of magnitude. The Y-axis is used to represent the voltage output from the logarithmic amplifier 120A, which has a value in the range of 1-4 volts. Four lines are plotted showing the change in voltage output relative to known (simulated) resistance values. Three of the lines describe the measured voltage output of the logarithmic amplifier when three capacitors (0pF, 10pF and 68pF) are connected across the resistor being measured. The Vlogout line represents the "ideal" logarithmic amplifier output based on the equation in the datasheet of the LOG114 device. The graph shows the 0pF line (top) as red, the 68pF line (middle) as light blue, and the Vlogout line (bottom) as dark blue. The legend references the green 10pF line, however this line is essentially the same as the 0pF red (top) line, so in Figure 4 It is hidden, that is, it cannot be seen alone.

[0085] It can be seen that there is a linear relationship between the (logarithmic) resistance value and the voltage output. The voltage drops from about 3.75V to about 1.25V, a drop of 2.5V, while the resistance drops from 10 3 Ohm up to 10 10 Ohm, that is, spanning 7 orders of magnitude. This means that the voltage drops by about 0.36V per order of magnitude, which is comparable to the gradient of 0.375 in equation 2 above. 9 At higher resistances of 1 Ohm, there is a small change in slope (gradient). As mentioned above, this may be an artifact of increased sensitivity to noise at these high resistance levels.

[0086] All three measured outputs for different capacitance values ​​follow very close lines, with the output voltage typically varying by much less than 0.1V. This confirms that the resistance detector 150 can accurately measure the resistance of the sensing element 120 independently of the capacitance of the sensing element. The Vlogout curve (bottom, dark blue) shows that the measurements deviate slightly from the "ideal" log amp voltage. This deviation, which is typically about 0.1V, can be viewed as reflecting the constant c in Equation 1 (or Voffset in Equation 2). The deviation can be reduced by calibration of the sensor 50 to allow for the deviation and / or by further improving the circuitry of the resistance detector 150 (including shielding, etc.).

[0087] In summary, providing the logarithmic amplifier 110 in the resistance detector 150 can quickly, accurately and reliably measure the resistance of the sense element that spans multiple (eg, 7-8) orders of magnitude as may be experienced in various sense elements, regardless of the sense element capacitance.

[0088] Turning now to the capacitance of sensor 160, Figure 5 It is available for Figure 1 Schematic diagram of an example of a capacitive detector 160 in a sensor. Figure 5 The top portion of shows a sensing element 120 with an associated resistance and capacitance. As described above, sensor 50 may include multiple sensing elements 120 to be read sequentially. Figure 5 It is also shown schematically Figure 1 An example implementation of a capacitive detector is shown.

[0089] Figure 5 The capacitance detector includes an operational amplifier (op amp) U3 configured as an integrator. Specifically, the output voltage (V out ) is the input voltage (V in ) is the integral over time. Figure 5 As shown, the sensing element 120 is actually located in the feedback loop of the operational amplifier U3. The input of the capacitance detector 160 is provided in the form of a voltage pulse, such as a square wave, a top hat function, etc. The capacitance detector 160 performs a capacitance measurement on the "on" transition from low to high, which is actually a step-up of the input voltage pulse. This is followed by the falling portion of the pulse, i.e., the "off" transition from high back to low, however, this fall is not used for the capacitance measurement itself (except to reset the input to allow another rising pulse for the next measurement). The input voltage signal passes through the resistor R before reaching the operational amplifier U3. int .

[0090] Intuitively, if R sensor Higher (i.e. much larger than the range resistance (R int )), then R sensor In this case, the feedback network from the sensing element 120 can be considered as a pure capacitor (C sensor ), which will actually Figure 5 The circuit is converted into an integrating op amp circuit (see for example https: / / en.wikipedia.org / wiki / Op_amp_integrator and https: / / www.electronics-tutorials.ws / opamp / opamp_6.html). This integrating op amp can be largely independent of the sensor resistance R sensor The effect of the sensor capacitance (Csensor ).

[0091] In operation, the input voltage V out Provides a voltage pulse (step). Ignoring R sensor (very large), when the voltage is first applied, the sensor capacitor has no charge and thus behaves like a short circuit. In this case, the voltage at the inverting input of op amp U3 remains at zero, and no current flows into that input (in line with ideal op amp behavior). Therefore, the (effective) current flowing through the resistor (given by V in / R int given) must be equal to the current flowing through the capacitor (given by dQ / dt = -CdV out / dt) (again assuming ideal operation of the op amp so that the output voltage corresponds to the voltage across the sensing element capacitance), so V in / R int =-CdV out / dt. Integrating both sides of the equation over time yields the following equation:

[0092] V out =-(1 / R int C sensor )∫V in dt

[0093] In other words, the output voltage is the input voltage V in Integration over time.

[0094] For the specific case where the input voltage comprises a single step at time T, such that V in From 0 before time T to a known constant value (V p ), then V out It has the form of a straight-line ramp starting at time = T, with a slope that depends on the product R int C sensor (and the voltage step V of the input voltage pulse p In other words, there is a linear relationship between the ramp-up time and the capacitance of the sensing element 120. Therefore, for a known V p and R int The capacitance of the sensing element 120, C sensor .

[0095] Importantly, this determination of the capacitance of the sensing element 120 does not rely on any duration (e.g., measuring a time constant to determine RC). Instead, RC (and C) can be measured once the ramp has increased sufficiently to allow the slope (gradient) of the ramp to be determined. sensor). For example, assuming that we consider the time T of the voltage pulse to represent time = 0, then the output voltage V can be measured at time T. out , then the slope is determined by V out / t is given (independent of any RC timing constant). In practice, the measurement of the capacitance of the sensing element 120 by the capacitance detector 160 can be performed quickly with an operational amplifier integrator, so that even for a sensing element with a high resistance, the measurement of the capacitance typically takes no more than a few microseconds. In addition, by appropriately selecting Rint and the step input amplitude, the timing for the measurement can be configured so that the time can be brought into a reasonable range to make the desired capacitance measurement.

[0096] In some embodiments, two comparators with set voltage levels (thresholds), one high and one low, are used to perform the determination of capacitance. In particular, when the output voltage exceeds the voltage level of the low-level comparator, this can start a timer. Then, when the output voltage exceeds the voltage level of the high-level comparator, this can stop the timing. The capacitance of the sensing element 120 can be determined based on the (known) voltage difference between the low level and the high level, plus the measured time for the voltage output to rise from the low level to the high level (plus the knowledge of R and C). In an example embodiment, the comparator can be implemented using the TLV3601 device from Texas Instruments (TI), see https: / / www.ti.com / product / TLV3601 and the associated data sheet. However, it should be understood that any other suitable comparator can be used instead. With these comparators, capacitance changes of 1 pF can be detected (when the resistance of the sensing element is low).

[0097] In this approach, the output voltage must pass through both a low and high threshold to trigger the comparator. This can be accomplished by increasing the pulse amplitude and / or reducing the integrating resistor. Both approaches result in larger (steeper) ramp slopes. It should be appreciated that these steeper ramp slopes can provide more reliable comparator activation, but they also typically require faster timing. Another approach is to add an additional comparator at the mid-rail to time the 50% rise time of the RC curve when the op amp is not saturated. Having this mid-rail can impose very tight timing requirements for measuring the full range of possible time values ​​of practical interest (time values ​​can be as short as about 300ps at one end of the range to achieve the desired resolution of the measured capacitance value).

[0098] In some embodiments, a time-to-digital converter (TDC) is used to make very precise measurements of the time between start and stop pulses, such as the time generated by the two (low and high) comparators described above. For example, the Texas Instruments (TI) TDC7201 device is capable of performing such high-precision time measurements (see https: / / www.ti.com / product / TDC7201 and associated datasheet). The TDC has a timing resolution of 55 picoseconds, with an example measurement range of 0.25 nanoseconds to 8 milliseconds (varying depending on the specific operating mode selected). It is worth noting that the TDC is primarily used for ranging applications, however, the ability to discern very short time intervals is also useful and relevant to timing measurements used to discern the capacitance of a sensing element as described herein.

[0099] It has been found that the present method is relatively insensitive to the parameters of the particular type or configuration of the operational amplifier (there are many different types of operational amplifiers available). For example, the operational amplifier does not have to have a high input impedance. In one example implementation, the Texas Instruments (TI) OPA357 operational amplifier has been used for the capacitance detector 160, see https: / / www.ti.com / product / OPA357 and associated data sheets. However, any other suitable operational amplifier may be used depending on the particular circumstances of any given implementation.

[0100] In the method discussed above, the capacitance of one or more sensing elements can be obtained independently of the resistance of one or more sensing elements, which is actually achieved by assuming that the sensor resistance is infinite. However, as the resistance of the sensing element 120 decreases to a level that becomes significant compared to the integrating resistance, that is, when R sensor No longer much larger than R int , the behavior of the capacitance detector 160 begins to deviate from that of an ideal integrator.

[0101] Figure 6 is a graph based on simulation results, showing the Figure 5 The X-axis represents the resistance of the sensing element 120 in Ohms, while the Y-axis represents the actual rise time for a given resistance compared to a very large resistance (i.e., R sensor Much larger than R int ) is a percentage deviation from an ideal rise time of the sensing element 120. (The rise time represents the time interval between triggering the first comparator and the second comparator as described above, which then directly affects the measured value of the capacitance of the sensing element 120). Figure 6 The curve is based on a 470Ohm R in the capacitance detector int Value, see Figure 5 As can be seen, the percentage deviation (offset) is very small (a few percent at most) when the resistance is reduced to 40kOhm. The deviation increases to 10% at 20kOhm and then increases rapidly, so 10kOhm actually represents the practical measurement limit of this configuration.

[0102] It should be noted that Figure 6 The curves of only show resistances up to 100 kOhm, however, as mentioned above, the range of interest for resistance measurement can extend to about 25 GOhm. This shows that for much of the desired resistance measurement range, say from 25 GOhm down to 40 kOhm, an ideal op amp integrator assuming the sense element resistance is effectively infinite works well and provides high accuracy for the capacitance measurement of the sense element. Furthermore, although Figure 6 The practical limit for measuring the resistance and capacitance of the sensor is shown to be at least 10kOhm, but this can be reduced if necessary by int value to reduce this limit, since the circuit operation depends on R sensor With R int ratio.

[0103] It should also be noted that if Figure 6 As shown, for R sensor and R int For any given value of , the deviation of the rise time (and the capacitance of the sensing element) measured can be determined, for example, by simulating Figure 5 The behavior of the op amp integrator circuit shown is characterized. Figure 6 Shows the known R int Values ​​and Assumptions R sensor For example, based on Figure 6 The graph can be inverted to obtain R sensor The measured value of the resistance (obtained by the logarithmic amplifier as described above) is used to determine the deviation of the measured resistance value from the ideal rise time. Given this known deviation, it is possible to work backwards from the measured (actual) rise time to determine the corresponding ideal rise time and thus obtain a reliable value (e.g. within a few percent, e.g. within the range of 3-6%) of the capacitance of the sensing element. Furthermore, although Figure 6 The curve is obtained from simulation, but it can also (or alternatively) be derived from measurements of actual rise times using capacitors of known capacitance to provide an estimate of Figure 6 (Further) calibration of the curve.

[0104] Figure 7 is shown for operation such as Figure 11 and 1 . An example flow chart of a method for using the sensor 50 (or any other suitable sensor) shown in FIG. 7A . The method begins at operation 710 by switching the sensing element 120 of the sensor to a resistance detector. This switching can be accomplished in any suitable manner using a switching circuit within the sensor 50 (typically under the control of the sensor control system 130). At operation 720, the resistance detector 150 measures the resistance of the sensing element 120 using a logarithmic scaling as discussed above. When the resistance measurement has been completed, at operation 730, the sensing element is switched out of the resistance detector 150 and into the capacitance detector 160. At operation 740, the capacitance detector 160 is used to measure the capacitance of the sensing element 120 using an integrator as discussed above. In some embodiments, the capacitance detector 160 may include a time-to-digital converter (TDC) as described above.

[0105] When the capacitance measurement has been completed, the sensor is ready to return to Figure 7 The process shown in FIG. 1 may be started to perform updated resistance and capacitance measurements on the same sensing element, and / or to perform resistance and capacitance measurements on one or more additional sensing elements therein. In the latter case, it should be understood that the switching circuit is capable of switching between different sensing elements (and between different sensing elements such as Figure 1 Switching between resistance detector and capacitance detector as shown).

[0106] In the above method, the resistance measurement and the capacitance measurement are made independently of each other. (As described above, the measured resistance can be used to adjust the capacitance measured by the sensing element at low resistance levels, however, this adjustment does not affect the device measurement process itself, but rather adjusts the results of the process.) The resistance measurement and the capacitance measurement are usually made in rapid succession to each other within a period of time, such as a few milliseconds (such as 10 or 5 milliseconds) apart from each other, and sometimes a few microseconds (such as 10 or 5 microseconds) apart from each other. For most sensing operations, this allows the resistance measurement and the capacitance measurement to be considered simultaneous with each other. Although Figure 7 The resistance measurement is shown to be performed before the capacitance measurement, but in some embodiments, this order can be reversed.

[0107] Exemplary embodiments of the sensor 50 as disclosed herein may include a battery and power management to generate a voltage rail. A logarithmic amplifier associated with a reference voltage is used to measure the resistance of the sensing element, typically to an accuracy of about 5%. In addition, in some embodiments, an analog-to-digital converter (ADC) is included to obtain the output of the logarithmic amplifier; an operational amplifier integrator for measuring capacitance; and in some embodiments, a time-to-digital converter (TDC) is included to achieve tight timing resolution; switching circuits, such as using instrument multiplexers or reed relays, for switching between the resistance detector 150 and the capacitance detector 160 and / or for switching between different sensing elements; two channels for providing calibration resistance and calibration capacitance; a processor for controlling operations such as converting the ADC voltage into resistance and converting the TDC result into capacitance, as well as controlling the sensor and providing additional functions (including Figure 1 Bluetooth support; and temperature and humidity indicators. It should be understood that other sensors may utilize components of different packages, and thus the above-described package components should not be considered limiting.

[0108] In addition, it should be noted that the LOG114 device and other devices specifically identified herein are provided as examples only. In particular, it will be understood that other embodiments may use other hardware components that are different from those specified herein but provide similar functions. (Such other hardware components may be provided by the same supplier as those hardware components explicitly specified herein, or may be provided by a different supplier).

[0109] The sensors disclosed herein can support a very wide range of resistance measurements, for example from 450Ω to 25GΩ (assuming careful shielding at higher resistance levels). Capacitance measurements are typically made in the range of 1pF to 100pF. The capacitance detector may include a TDC chip to provide precise time resolution and detection down to the nanosecond level. Measuring circuit timing using a TDC chip can achieve a resolution of ±1pF. In general, for resistances ≤1GΩ<200μs, the time for resistance measurement (including setup time) may be less than 200μs, for resistances >1GΩ<3ms, the time may be less than 3ms, and the timing for capacitance measurement is typically a few μs, and in some embodiments may be less than 1μs.

[0110] Such timing supports fast switching between resistance and capacitance detectors and between different sensing elements. In particular, this allows the resistance and capacitance of a given sensing element to be effectively measured simultaneously (within a few ms (e.g., 10 or 5 ms) of each other in the worst case, and within 200 μs of each other in many cases). In addition, the sensor is able to cycle through the respective R and C measurements of each sensing element in sequence, with the duration of the cycle being short enough to provide a high sampling frequency (and therefore fine time resolution) for the output from each sensing element.

[0111] An example of a sensor 50 described herein is an electronic device that can accurately and (nearly) simultaneously measure the capacitance and resistance of high impedance sensing elements located in an array of sensing elements with good time resolution, the resistance of these high impedance sensing elements varying over time covering a range from the order of gigahertz to the order of ohms, and the capacitance being the order of picofarads. Resistance and capacitance are measured independently, but within 10ms of each other. To achieve this, a low impedance switching circuit can be used to switch specific circuits optimized for measuring resistance and capacitance, respectively, such as the resistance detector 150 and the capacitance detector 160 described above.

[0112] Resistance can be measured using a logarithmic amplifier with a wide dynamic input range and on-chip temperature drift compensation. This technique relies on the current through the sensor (rather than the RC curve) and can therefore make very fast measurements. The logarithmic amplifier converts the input current into an output voltage that directly corresponds to the sensor resistance, which can then be measured using an analog-to-digital converter and processed to provide the measured resistance.

[0113] By switching the sensor into the feedback loop of an op amp integrator configuration, the capacitance can be measured with pF resolution. When a step input is applied, the output of the integrator is a ramp whose slope depends on the sensor capacitance, the step amplitude, and the integrating resistor, which are fixed by design. If the sensor resistance is higher than the integrating resistor, the measured ramp rise time is proportional to the capacitance.

[0114] The integrating resistor and step amplitude are chosen so as to extend the ideal integrator behavior of the circuit to the lowest possible sensor resistance values ​​(down to a few kΩ). The rise time is approximately 0.1ns for each 1pF change in capacitance. To time the rise time with sufficient resolution, a time-to-digital converter (TDC) can be used, which can time (measure) pulses as short as 0.25ns with a resolution of 55ps.

[0115] Thus, resistance detectors and capacitance detectors as described herein can be used with sensing elements whose resistance changes by several orders of magnitude when exposed to an analyte. The capacitance of the sensing element will also change synchronously with time, which is also measured (but typically with a lower magnitude of change than resistance).

[0116] Two additional fixed resistance / capacitance channels may be provided to allow the processor to compensate for any minor circuit tolerance differences. This provides a form of calibration that helps achieve consistent results between systems. In some embodiments, a machine learning (ML) system may be used to analyze the measured resistance and capacitance values, and having more consistent resistance and capacitance values ​​helps the ML system learn faster and provide more consistent outputs.

[0117] Therefore, sensor 50 can be used for sensing environmental conditions, which involves sensing multiple physical parameters.Sensor 50 can include an array of sensing elements, all of which are (for example) combined in a battery-powered handheld device.In one example, environmental conditions relate to the health of the soil, and multiple physical parameters reflect the concentration of different gases (volatiles).Sensor 50 can have multiple sensing elements, which can include multiple copies of the same sensing element (for redundancy, better accuracy, etc.) and additional (or alternative) different versions of the sensing element.For example, in the latter case, different sensing elements can have different coatings, which interact with the target analyte in different ways and / or quantities.Different sensing elements can be used, for example, to distinguish different target analytes and / or expand the set of target analytes that can be detected and measured by the sensor.

[0118] The sensor can be used for a gas sensor or an electronic nose, for example including a polymer semiconductor-based sensor array for the sensing element. Such a device has a wide range of potential applications. In addition, the sensor 50 can be used for a biosensor in the medical field, which checks for the presence of a target analyte immersed in a liquid, for example.

[0119] In some embodiments, the electronic nose may contain sensing elements specifically designed to measure different substances, for example, each sensing element may be configured to detect the presence or concentration of a given gas. In other cases, the various sensing elements may not have such specific, individual measurement goals, but rather the readings from multiple sensors may be used in combination to provide a useful characterization of a given analyte (perhaps based on ML analysis). For example, in the case of a device that monitors soil health, the device may provide a yes / no output as to whether the soil is considered healthy. In other cases, the device may output a score (metric) that provides some numerical representation of overall soil health, for example, the score may range from 1 to 10, with 1 representing poor soil and 10 representing very healthy soil. Other embodiments of such a device may provide outputs regarding multiple metrics related to environmental conditions, where each parameter may be determined from one or more sensing elements. For example, such a sensor for soil health analysis may provide information about soil acidity / alkalinity, nutrient levels, water retention, and / or microbial populations.

[0120] Although the above description is primarily directed to the context of determining soil health, it will be appreciated that sensors such as those disclosed herein may be used in many other (different) contexts, such as for inspecting food, for detecting contamination in various environments, for monitoring exhaust products, etc. Different sensors may be used in different contexts, and various aspects of the sensor may vary depending on the context. For example, the present application references resistance ranges and capacitance ranges to be measured for the sensing element, but it will be appreciated that in other contexts and / or for other types of sensors, the resistance and / or capacitance ranges to be measured may be adjusted accordingly.

[0121] In summary, although various embodiments and examples have been described herein, they are provided by way of illustration, and many potential modifications will be apparent to those skilled in the art, taking into account the details of any given embodiment. Therefore, the scope of the invention should be determined by the appended claims and their equivalents.

Claims

1. A sensor for measuring environmental conditions, the sensor comprising: a sensing element having a resistance and a capacitance that are sensitive to environmental conditions; a first measurement circuit for determining the resistance of the sensing element using logarithmic scaling; a second measurement circuit including an integrating amplifier for determining the capacitance of the sensing element; as well as A switch circuit is used to switch the sensing element to the first measurement circuit and the second measurement circuit in sequence, so that the resistance and the capacitance are determined within a predetermined time period.

2. The sensor according to claim 1, wherein: The first measurement circuit includes a logarithmic amplifier.

3. The sensor according to claim 1 or 2, wherein: The first measurement circuit is configured to measure a resistance having a range covering at least six orders of magnitude, preferably at least seven orders of magnitude, preferably at least eight orders of magnitude.

4. A sensor according to any one of the preceding claims, wherein: The first measurement circuit is configured to measure resistance within a certain range, the resistance range being: The lower limit is not more than 2500 Ohm, preferably not more than 1000 Ohm, preferably not more than 500 Ohm, and The upper limit is not less than 1 gOhm, preferably not less than 5 gOhm, and preferably not less than 25 gOhm.

5. A sensor according to any one of the preceding claims, wherein: The integrating amplifier comprises an operational amplifier integrator.

6. A sensor according to any one of the preceding claims, wherein: The sensor is configured to provide a step change voltage to the integrating amplifier, and wherein the slope of the output of the integrating amplifier depends on the capacitance to be measured.

7. A sensor according to any one of the preceding claims, wherein: The second measurement circuit further comprises a time-to-digital converter TDC, and optionally, wherein the TDC is used to measure the slope of the output of the integrating amplifier according to claim 6.

8. A sensor according to any one of the preceding claims, wherein: The sensor is configured to correct the measured capacitance based on the measured resistance.

9. The sensor according to claim 8, wherein: The correction is only applied if the measured resistance is below a threshold, optionally wherein the threshold is below 100 kOhm, preferably below 40 kOhm.

10. A sensor according to any one of the preceding claims, wherein: The second measurement circuit is configured to measure a capacitance within a range: The lower limit is not more than 5F, preferably not more than 1F, and The upper limit is not less than 100F, preferably not less than 200F.

11. A sensor according to any one of the preceding claims, wherein: The operation of the first measurement circuit for determining resistance is performed independently and sequentially from the operation of the second measurement circuit for determining capacitance.

12. The sensor according to claim 11, wherein: The resistance and capacitance are determined within a predetermined time period of 0.1 s, preferably within 0.01 s, and more preferably within 1 ms.

13. The sensor according to any of the preceding claims, further comprising at least one channel for providing a known resistor for measurement by the first measurement circuit and / or for providing a known capacitor for measurement by the second measurement circuit as a calibration mode.

14. A sensor according to any one of the preceding claims, wherein: The sensor comprises a plurality of sensing elements, optionally wherein the number of sensing elements is in the range of 1 to 6, and optionally in the range of 1 to 20, and optionally in the range of 1 to 50.

15. The sensor according to claim 14, wherein: The sensor is configured to switch each sensing element into the first and second measurement circuits in sequence.

16. The sensor according to claim 15, wherein: The sensing elements are repeatedly switched to the first measurement circuit and the second measurement circuit in sequence, and the duration for which all sensing elements are switched to the first measurement circuit and the second measurement circuit in sequence to measure the resistance and capacitance of all sensing elements is no more than 1 second, preferably no more than 0.1 second, and preferably no more than 20 ms.

17. A sensor according to any one of the preceding claims, wherein: The sensing element comprises an electronic nose comprising a polymer semiconductor based sensor array.

18. A sensor according to any one of the preceding claims, wherein: The environmental conditions to be measured correspond to the soil health status.

19. A method of measuring an environmental condition using a sensor, the sensor comprising a sensing element having a resistance and a capacitance that are sensitive to the environmental condition, the method comprising: switching the sensing element into a first measurement circuit; determining the resistance of the sensing element by logarithmic scaling using the first measurement circuit; switching the sensing element into a second measurement circuit; as well as The capacitance of the sensing element is determined using the second measurement circuit via an integrating amplifier.

20. The method according to claim 19, wherein: The sensor comprises the sensor according to any one of claims 1 to 18.

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