阅读说明：本技术 集成电路和测量方法 (Integrated circuit and measurement method ) 是由 赖纳·斯塔尔德迈尔 弗朗茨·阿姆特曼 于 2020-08-03 设计创作，主要内容包括：根据本公开的第一方面,提供了一种包括电流源和参考电容器的集成电路,所述集成电路被配置成：使用所述电流源在外部测量电容器中注入第一电流,并且确定所述测量电容器上的所得电压达到电压阈值的第一时间量；使用所述电流源在所述参考电容器中注入第二电流,并且确定所述参考电容器上的所得电压达到所述电压阈值的第二时间量；使用所述第一时间量与所述第二时间量之间的差来检测所述测量电容器上电容的变化。根据本公开的第二方面,提出了一种相应的测量方法。(According to a first aspect of the present disclosure, there is provided an integrated circuit comprising a current source and a reference capacitor, the integrated circuit being configured to: injecting a first current in an external measurement capacitor using the current source and determining a first amount of time for a resulting voltage on the measurement capacitor to reach a voltage threshold; injecting a second current in the reference capacitor using the current source and determining a second amount of time for a resulting voltage on the reference capacitor to reach the voltage threshold; detecting a change in capacitance on the measurement capacitor using a difference between the first amount of time and the second amount of time. According to a second aspect of the disclosure, a corresponding measurement method is presented.)

1. An integrated circuit comprising a current source and a reference capacitor, wherein the integrated circuit is configured to:

injecting a first current in an external measurement capacitor using the current source and determining a first amount of time for a resulting voltage on the measurement capacitor to reach a voltage threshold;

injecting a second current in the reference capacitor using the current source and determining a second amount of time for a resulting voltage on the reference capacitor to reach the voltage threshold;

detecting a change in capacitance on the measurement capacitor using a difference between the first amount of time and the second amount of time.

2. The integrated circuit of claim 1, further configured to inject the second current in the reference capacitor at the same time as the first current is injected in the measurement capacitor.

3. The integrated circuit of claim 1 or 2, wherein the first current is a configurable current and the second current is a constant current.

4. An integrated circuit as claimed in any preceding claim, wherein the first current is configured such that the slope of the voltage on the measurement capacitor is substantially the same as the slope of the voltage on the reference capacitor.

5. An integrated circuit as claimed in any preceding claim, configured to determine the value of the first current after the integrated circuit has been calibrated.

6. The integrated circuit of any preceding claim, further configured to:

determining a third amount of time that a resulting voltage on the measurement capacitor reaches a further voltage threshold;

determining a fourth amount of time for the resulting voltage on the reference capacitor to reach the further voltage threshold;

detecting a change in capacitance on the measurement capacitor using a difference between the third amount of time and the fourth amount of time.

7. A radio frequency identification, RFID, or near field communication, NFC, tag comprising an integrated circuit according to any of the preceding claims.

8. A measuring system comprising an integrated circuit according to any of the preceding claims, and the measuring capacitor.

9. A tamper detection system, characterized in that it comprises a measuring system according to claim 8.

10. A method of measurement, comprising:

injecting a first current in a measurement capacitor by means of a current source in an integrated circuit and determining a first amount of time for a resulting voltage on the measurement capacitor to reach a voltage threshold;

injecting a second current in a reference capacitor by means of the current source and determining a second amount of time for a resulting voltage on the reference capacitor to reach the voltage threshold;

detecting, by the integrated circuit, a change in capacitance on the measurement capacitor using the difference between the first amount of time and the second amount of time.

Technical Field

The present disclosure relates to an integrated circuit. Furthermore, the present disclosure relates to a measurement method.

Background

Capacitance-based measurement systems and methods may be used in a variety of applications. For example, they may be used in tamper detection devices. While many tamper detection devices include resistance-based measurement systems, it may be beneficial to use a capacitance-based measurement system. Since it is easier to re-establish a current connection than to restore the capacitance value, capacitance-based measurement systems can enable more reliable tamper detection. Capacitance-based measurement systems and methods may also be used in other fields, such as measuring physical parameters such as humidity. The presently disclosed systems and methods may be applied in tamper detection devices and other types of devices that require accurate capacitance measurements.

For example, a capacitance-based tamper detection device includes an integrated circuit (i.e., chip) coupled to a capacitor. The integrated circuit may for example be comprised in a Radio Frequency Identification (RFID) tag or a Near Field Communication (NFC) tag. In operation, a change in capacitance on the capacitor may indicate a tampering attempt on the product, and information indicative of such a tampering attempt may be stored in the integrated circuit. This information can then be read out by an RFID reader or an NFC reader.

For example, the capacitor may be a plate capacitor consisting of two metal foils and a plastic foil as a dielectric in between. This capacitor can be fixed to the stopper to protect the expensive wine from counterfeiting and, once the bottle is opened, the capacitor is damaged or at least the capacitance value changes significantly. The information indicative of the counterfeit may be stored in an Integrated Circuit (IC) of the tag. The RFID tag affixed to the capacitor can then be read out with the cell phone and a display can be made on the cell phone that someone has handled the bottle. In another example, the tamper detection device may be applied to envelopes, with the paper being a dielectric. Thus, it is possible to detect whether the envelope is changed or manipulated.

It is important that the capacitance measurement is as accurate as possible. The presently disclosed systems and methods help to improve this accuracy.

Disclosure of Invention

According to a first aspect of the present disclosure, there is provided an integrated circuit comprising a current source and a reference capacitor, the integrated circuit being configured to: injecting a first current in an external measurement capacitor using the current source and determining a first amount of time for a resulting voltage on the measurement capacitor to reach a voltage threshold; injecting a second current in the reference capacitor using the current source and determining a second amount of time for a resulting voltage on the reference capacitor to reach the voltage threshold; detecting a change in capacitance on the measurement capacitor using a difference between the first amount of time and the second amount of time.

In one or more embodiments, the integrated circuit is further configured to inject the second current in the reference capacitor at the same time as the first current is injected in the measurement capacitor.

In one or more embodiments, the first current is a configurable current and the second current is a constant current.

In one or more embodiments, the first current is configured such that a slope of a voltage on the measurement capacitor is substantially the same as a slope of a voltage on the reference capacitor.

In one or more embodiments, the integrated circuit is configured to determine the value of the first current after the integrated circuit is calibrated.

In one or more embodiments, the integrated circuit is configured to store the determined value of the first current in a non-volatile memory of the integrated circuit.

In one or more embodiments, the determined value of the first current is a value that results in a minimum difference between the first amount of time and the second amount of time, the minimum difference being stored as a calibration offset in the non-volatile memory.

In one or more embodiments, the integrated circuit additionally includes a counter for determining the first amount of time and the second amount of time.

In one or more embodiments, the counter is configured to start counting upon reaching a trigger voltage and stop counting upon reaching the voltage threshold.

In one or more embodiments, the integrated circuit is further configured to: determining a third amount of time that a resulting voltage on the measurement capacitor reaches a further voltage threshold; determining a fourth amount of time for the resulting voltage on the reference capacitor to reach the further voltage threshold; detecting a change in capacitance on the measurement capacitor using a difference between the third amount of time and the fourth amount of time.

In one or more embodiments, a Radio Frequency Identification (RFID) tag or a Near Field Communication (NFC) tag includes an integrated circuit of the kind set forth.

In one or more embodiments, the measurement system includes an integrated circuit of the kind set forth, and a measurement capacitor.

In one or more embodiments, a tamper detection system includes a measurement system of the kind set forth.

According to a second aspect of the present disclosure, there is provided a measurement method comprising: injecting a first current in a measurement capacitor by means of a current source in an integrated circuit and determining a first amount of time for a resulting voltage on the measurement capacitor to reach a voltage threshold; injecting a second current in a reference capacitor by means of the current source and determining a second amount of time for a resulting voltage on the reference capacitor to reach the voltage threshold; detecting, by the integrated circuit, a change in capacitance on the measurement capacitor using the difference between the first amount of time and the second amount of time.

In one or more embodiments, the integrated circuit injects the second current in the reference capacitor at the same time as injecting the first current in the measurement capacitor.

Drawings

Embodiments will be described in more detail with reference to the accompanying drawings, in which:

FIG. 1 shows an example of a measurement system;

FIG. 2 shows an exemplary embodiment of a measurement system;

FIG. 3 shows an exemplary embodiment of a measurement method;

fig. 4 shows another exemplary embodiment of a measuring system.

Detailed Description

Fig. 1 shows an example of a measurement system 100. The system 100 includes a passive RFID tag having a sensor interface 102 and a device under test capacitor 108 (i.e., a measurement capacitor). As mentioned above, tamper detection devices typically include an integrated circuit (i.e., a chip) coupled to a capacitor. As can sensors for physical parameters such as humidity. The integrated circuit may for example be comprised in a Radio Frequency Identification (RFID) tag or a Near Field Communication (NFC) tag. In operation, a change in capacitance on the capacitor may indicate a tampering attempt on the product or a change in a sensed physical parameter, and information indicative of such a tampering attempt may be stored in the integrated circuit. This information can then be read out by an RFID reader or an NFC reader. Alternatively, the reader may trigger the tag to measure the device under test capacitor 108 by sending a command to the tag; the tag may then transmit the measurement back to the reader without storing the measurement in the integrated circuit. The change in capacitance can be detected by measuring the slope of the voltage across the capacitor. When the capacitance value changes due to tampering or changes in the physical parameter, because the current injected during the measurement remains substantially the same: since Δ V/Δ t is I/C, the voltage slope changes. The passive RFID tag 102 shown in fig. 1 includes an integrated circuit 104 (i.e., a chip) of the kind set forth, and an antenna 106. Furthermore, the device under test capacitor 108 is an example of a measurement capacitor of the kind set forth. An external RFID reader (not shown) may be configured to read data from the RFID tag through the antenna 106 of the RFID tag 102. It should be noted that the coupling between the capacitor and the chip may be referred to as a sensor interface.

The change in capacitance across the device under test capacitor 108 is measured using the charging current and the reference voltage. However, these charging currents and reference voltages may be susceptible to variations (i.e., tolerances), such as process, voltage, temperature, and time-related variations that exist between different integrated circuits. These variations limit the achievable accuracy of the measurement. The presently disclosed systems and methods help to improve the accuracy of the measurements.

Fig. 2 shows an exemplary embodiment of a measurement system 200. The measurement system 200 includes a measurement capacitor 202 (i.e., a device under test capacitor) and an integrated circuit 204. The integrated circuit 204 includes a current source 206 and a reference capacitor 208. The measurement capacitor 202 may be included in or attached to an external product (not shown), such as a bottle stopper (which may be tampered with), or the measurement capacitor 202 may be configured to sense a physical or environmental parameter. In accordance with the present disclosure, the integrated circuit 204 is configured to inject a first current in the measurement capacitor 202 using the current source 206 and determine a first amount of time for a resulting voltage on the measurement capacitor 202 to reach a voltage threshold. Further, the integrated circuit 204 is configured to inject a second current in the reference capacitor 208 using the same current source 206 and determine a second amount of time for the resulting voltage on the reference capacitor 208 to reach the same threshold voltage. Further, the integrated circuit 204 is configured to detect a change in capacitance on the measurement capacitor using a difference between the first amount of time and the second amount of time.

In this way, the accuracy of the capacitance measurement can be improved. In particular, applying differential measurement cancels out process, voltage, temperature and time dependent variations, since both measurements are affected by said variations in the same way. Accordingly, both measurement paths use current from the same current source: the external measurement capacitor 202 is charged through a first measurement path, while the internal reference capacitor 208 is charged through a second measurement path. Since both measurements drive the measured measurement current from the same source current, variations in the measurement current will affect both measurements in the same way. As does the voltage threshold. Thus, these effects cancel each other out. The measurement of the capacitance on the measurement capacitor 202 and the reference capacitor 208 is performed by determining the amount of time required to reach the voltage threshold. Because the capacitance on the reference capacitor 208 remains substantially the same to the extent that the capacitance on the reference capacitor 208 within the IC 204 is not affected by an external event (e.g., tampering or change in a physical parameter) that should be detected, a change in capacitance on the measurement capacitor 202 can be readily detected by comparing the amount of time required to measure the capacitor 202 with the amount of time required for the reference capacitor 208. For example, if the difference is less than a predetermined threshold, it will be assumed that the capacitance on the measurement capacitor has not changed, and if the difference is greater than the predetermined threshold, it will be assumed that the capacitance on the measurement capacitor has changed.

Fig. 3 shows an exemplary embodiment of a measurement method 300. The method 300 includes the following steps. At 302, an Integrated Circuit (IC) injects a first current in a measurement capacitor using a current source and determines a first amount of time for a resulting voltage on the measurement capacitor to reach a voltage threshold. At 304, the IC injects a second current in the reference capacitor using the same current source and determines a second amount of time for the resulting voltage on the reference capacitor to reach the same voltage threshold. Further, at 306, the IC detects a change in capacitance on the measurement capacitor using the difference between the first amount of time and the second amount of time. For example, the steps may be performed or controlled by a controller of the integrated circuit. In this way, as explained above, the accuracy of the capacitance measurement can be improved.

In one or more embodiments, the integrated circuit is configured to inject a second current in the reference capacitor at the same time as the first current is injected in the measurement capacitor. By charging the measurement capacitor and the reference capacitor simultaneously, the measurement system may be immune to current variations or noise coupling over time. Therefore, the accuracy of capacitance measurement can be further improved.

In one or more embodiments, the first current is a configurable current and the second current is a constant current. In other words, the first current may be adjustable, which helps to match the charging slope of the internal capacitor (i.e., the reference capacitor) to the charging slope of the external capacitor (i.e., the measurement capacitor) whose capacitance should be measured. Thus, in one or more embodiments, the first current is configured such that the slope of the voltage on the measurement capacitor is substantially the same as the slope of the voltage on the reference capacitor. In this way, the accuracy of the capacitance measurement can be further improved. In a practical and effective embodiment, the value of the first current is determined after the integrated circuit has been calibrated. Further, in one or more embodiments, the determined value of the first current is stored in a non-volatile memory of the integrated circuit. This facilitates retrieval of the determined value upon power-down. It should be noted that since the tag may be a device powered by the field, power may only be available for a short time. Further, in one or more embodiments, the determined value of the first current is a value that results in a minimum difference between the first amount of time and the second amount of time, wherein the minimum difference is stored as a calibration offset in the non-volatile memory. In this way, the accuracy of the capacitance measurement can be further improved. In particular, the calibration offset may reflect quantization errors caused by the finite granularity of the adjustable current. Thus, a calibration step may be performed to find the correct current setting needed to match the measurement slope (i.e. the charging slope or voltage slope of the respective capacitor) and to detect quantization errors caused by the limited granularity of the adjustable current. In a practical embodiment, the integrated circuit additionally comprises a counter for determining the first amount of time and the second amount of time. Further, in one or more embodiments, the counter starts counting after a trigger voltage is reached and stops counting after a voltage threshold is reached. As will be explained below with reference to fig. 4, waiting to count after the trigger voltage is reached reduces the inaccuracy of the ground level, thereby further improving the measurement.

In one or more embodiments, the integrated circuit is further configured to: the method further includes determining a third amount of time for the resulting voltage on the measurement capacitor to reach a further voltage threshold, determining a fourth amount of time for the resulting voltage on the reference capacitor to reach the further voltage threshold, and detecting a change in capacitance on the measurement capacitor using a difference between the third amount of time and the fourth amount of time. In this way, the voltage slopes of the measurement capacitor and the reference capacitor may be segmented, which may further improve the measurement accuracy. In particular, the further voltage threshold may be an intermediate voltage threshold between the trigger voltage and the (final) voltage threshold. Thereby, two segments are formed. The skilled person will appreciate that to the extent that additional intermediate threshold voltages may be used, more segments may be formed by extending this embodiment. In this case, the further amounts of time, in particular the resulting voltages over the respective capacitors (i.e. the voltages generated by the injected first and second currents) reaching the further intermediate threshold voltages, will be compared with each other. It should be noted that the principle of segmentation has been described in the content of the tamper detection of the european patent application with application number 18192899.5 entitled "System and method for detecting tampering with a product" filed on 6.9.2018.

More specifically, segmentation may be achieved by using different threshold voltages (e.g., start, intermediate, and end voltages). The current injected into the respective capacitor remains the same, but the counter value can be read out multiple times. In this way, the voltage slope is segmented. Specifically, if the threshold voltages are equally distributed, an equal counter value is desired for each voltage slope. By means of the comparator it can be detected whether a certain threshold voltage is reached. In particular, the comparators may be configured to take different threshold voltages (i.e., reference voltages) as inputs, or additional comparators may be provided that take a particular intermediate threshold voltage as an input.

Fig. 4 shows another illustrative embodiment of a measurement system 400. System 400 may be divided into an analog domain 402 and a digital domain 414. Analog domain 402 includes measurement capacitors (i.e., device under test capacitors), and analog components of the integrated circuit that are coupled to the measurement capacitors through inductive pads. Digital domain 414 contains the digital components of the integrated circuit. Analog domain 402 includes current reference 404, current mirror 406 connected to the supply voltage, voltage reference 408, and comparators 410, 412. The current reference 404 and the current mirror 406 implement a current source of the kind set forth. Digital domain 414 contains digital logic 416 and a time reference 418. The integrated circuit may be in a calibration state and a measurement state. In the calibration state, the integrated circuit is calibrated. More specifically, in this state, the current setting for the measurement capacitor is determined, and the calibration offset is determined. In the measuring state, a change in capacitance on the measuring capacitor is detected.

In a practical and efficient implementation, the integrated circuit may operate as follows in the measurement state. The measurement can be started by discharging both capacitors to zero. Once the discharge switch is released, the internal reference capacitor will be charged by the reference current (i.e. the second current) while the external capacitor will be charged with the previously defined external current (i.e. the first current determined in the calibration state). Once a certain reference voltage (i.e., trigger voltage) is reached, the counter will start counting until the final reference voltage (i.e., voltage threshold) is reached. Separate counters are used for the two measurement paths. Not starting the counter while the discharge switch is released reduces the inaccuracy of the ground level, thereby further improving the measurement. Since both measurements drive the measured measurement current from the same source current, variations in the measurement current will affect both measurements in the same way. As does the voltage reference. Thus, those effects cancel each other out. Additionally, multiple reference voltages (i.e., additional voltage thresholds) may be selected to further segment the measurement slope. When the measurement is complete, the difference between the two counter values plus the calibration offset may be evaluated. A change detection threshold may be defined that indicates for which counter difference the capacitance on the measurement capacitor is assumed to have changed. Since the components are not perfectly matched, only a certain resolution can be obtained, and the change detection threshold should be chosen to be higher than the minimum achievable accuracy.

In a practical and efficient implementation, the integrated circuit may operate as follows in the calibration state. During calibration, measurements are taken and the measurement current is adjusted until the difference between the two counters is minimal. It should be noted that the successive approximation algorithm will give the minimum number of measurement steps needed to get the minimum difference between the two counters. The current setting for charging the external measurement capacitor (DUT) is stored in a non-volatile memory, and the difference between the two counters is also stored therein. This difference can be used as a calibration offset to compensate for quantization errors caused by the limited amount of available current settings.

It should be noted that the above embodiments have been described with reference to different subject matters. In particular, some embodiments may have been described with reference to method class claims, while other embodiments may have been described with reference to device class claims. However, a person skilled in the art will gather from the above that, unless other notified, in addition to any combination of features belonging to one type of subject-matter also any combination of features relating to different subject-matters, in particular combinations of features of the method class of claims and features of the apparatus class of claims, is considered to be disclosed with this document.

Further, it should be noted that the drawings are schematic. The use of the same reference symbols in different drawings indicates similar or identical items. Furthermore, it should be noted that in order to provide a concise description of the exemplary embodiments, implementation details that are conventional to the skilled artisan may not be described. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

Finally, it should be noted that the skilled person will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The measures recited in the claims can be implemented by means of hardware comprising several distinct elements, and/or by means of a suitably programmed processor. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

List of reference numerals

100 measurement system

102 RFID tag with sensor interface

104 chip (Integrated circuit)

106 antenna

108 Device Under Test (DUT) capacitor

110 capacitor electrode

112 capacitor electrode

200 measuring system

202 measurement capacitor (DUT capacitor)

204 Integrated Circuit (IC)

206 current source

208 reference capacitor

300 measurement method

The 302 IC injects a first current in a measurement capacitor included in or attached to the product using a current source and determines a first amount of time for a resulting voltage on the measurement capacitor to reach a voltage threshold

304 IC injects a second current in the reference capacitor using the current source and determines a second amount of time for the resulting voltage on the reference capacitor to reach the voltage threshold

306 IC uses the difference between the first amount of time and the second amount of time to detect a change in capacitance on the measurement capacitor

400 measuring system

402 analog domain

404 current reference

406 current mirror

408 voltage reference

410 comparator

412 comparator

414 digital domain

416 digital logic

418 time reference.