CN114189212B - Method and circuit for automatically compensating RFID resonance frequency statistics and temperature drift - Google Patents

Method and circuit for automatically compensating RFID resonance frequency statistics and temperature drift Download PDF

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CN114189212B
CN114189212B CN202210140671.2A CN202210140671A CN114189212B CN 114189212 B CN114189212 B CN 114189212B CN 202210140671 A CN202210140671 A CN 202210140671A CN 114189212 B CN114189212 B CN 114189212B
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compensation
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CN114189212A (en
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吴边
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Excelio Technology Shenzhen Co Ltd
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
    • H03B5/00—Generation of oscillations using amplifier with regenerative feedback from output to input
    • H03B5/02—Details
    • H03B5/04—Modifications of generator to compensate for variations in physical values, e.g. power supply, load, temperature
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03B—GENERATION OF OSCILLATIONS, DIRECTLY OR BY FREQUENCY-CHANGING, BY CIRCUITS EMPLOYING ACTIVE ELEMENTS WHICH OPERATE IN A NON-SWITCHING MANNER; GENERATION OF NOISE BY SUCH CIRCUITS
    • H03B5/00—Generation of oscillations using amplifier with regenerative feedback from output to input
    • H03B5/08—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element comprising lumped inductance and capacitance
    • H03B5/12—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element comprising lumped inductance and capacitance active element in amplifier being semiconductor device
    • H03B5/1237—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element comprising lumped inductance and capacitance active element in amplifier being semiconductor device comprising means for varying the frequency of the generator
    • H03B5/1262—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element comprising lumped inductance and capacitance active element in amplifier being semiconductor device comprising means for varying the frequency of the generator the means comprising switched elements
    • H03B5/1265—Generation of oscillations using amplifier with regenerative feedback from output to input with frequency-determining element comprising lumped inductance and capacitance active element in amplifier being semiconductor device comprising means for varying the frequency of the generator the means comprising switched elements switched capacitors

Abstract

The invention belongs to the technical field of radio frequency identification, and particularly relates to a method and a circuit for automatically compensating RFID resonance frequency statistics and temperature drift. The method and the device provide a complete calibration compensation technology aiming at the influence of the statistical drift and the temperature drift faced by the radio frequency identification tag chip product on the resonance performance, and automatically compensate the statistical drift, so that a process of calibrating by special equipment is omitted in the processing process of the radio frequency identification tag finished product, and the production efficiency and the yield are greatly improved. The application also comprises an automatic compensation technology of the temperature drift of the resonant circuit, and the influence of the temperature drift on the resonant frequency is fundamentally solved by using various different implementation schemes aiming at different products with refined logic control requirements. The frequency calibration process after power-on reset provided by the application explicitly provides control steps for implementing statistical drift and temperature drift compensation, and the guiding idea can be extended to a more general circuit compensation technology in the field of low-power wireless communication.

Description

Method and circuit for automatically compensating RFID resonance frequency statistics and temperature drift
Technical Field
The invention belongs to the technical field of radio frequency identification, and particularly relates to a method for automatically calibrating and compensating the drift of the resonant frequency of a passive radio frequency identification tag (RFID) resonant circuit due to statistical factors and temperature factors, and a circuit for realizing the method.
Background
The radio frequency identification technology is one of the lowest core hardware technologies in the field of internet of things, and a radio frequency identification tag chip which is manufactured by adopting an integrated semiconductor manufacturing process in the form of an integrated circuit is a basic component concerned by the core technology in the field. Packaging the radio frequency identification tag chip in a certain form, and connecting the radio frequency identification tag chip with a plurality of peripheral devices to form a radio frequency identification tag core circuit system; the core circuit system is sealed and packaged by a plastic package process or a glass package process, and a finished product of the radio frequency identification tag suitable for various application occasions can be manufactured. The function of the finished product of the radio frequency identification tag in the main application fields of logistics management, article monitoring and the like is mainly response, the response content can be as simple as reporting the ID number of the tag for data entry and tracking, and the finished product of the radio frequency identification tag also can comprise some advanced applications, such as reading and writing the finished product of the tag, writing user data into the finished product tag and the like. The written data is stored in a Non-Volatile Memory (NVM) Memory cell built in the tag chip, such as an OTP (One-Time program), MTP (Multiple-Time program) or EEPROM (electrically Erasable Programmable Read-Only Memory) Memory cell.
The passive radio frequency identification tag is a tag product without an external power supply or battery power supply, and has a more suitable popularization value in market application because of lower manufacturing cost and maintenance cost. The electric energy source of the passive radio frequency identification tag is the energy of magnetic field around the peripheral inductance coil connected with the radio frequency identification chip, and the electric energy source generates resonance to form alternating current in the coil, namely the Faraday electromagnetic induction principle. Because the energy obtained by induction is very limited, the read-write operation of the memories with different specifications is also limited to different degrees; this limitation becomes a challenge for low power system design in microelectronics for chip design.
Generally, in a communication process of passive radio frequency identification, a magnetic induction coil of a tag reading and writing device firstly emits electromagnetic field energy with a certain specific frequency, and serves as a connection port with the outside world, an external inductance coil of a passive radio frequency identification tag can couple surrounding electromagnetic field energy and forms an LC resonance circuit with a capacitor on a port connected inside a chip, the magnetic field energy is converted into alternating current in the resonance circuit, and the alternating current is converted into direct current after rectification, so that the chip is powered. The main performance index of the passive radio frequency identification tag is the communication distance of the passive radio frequency identification tag, namely the radio frequency identification tag can also perform reliable uplink and downlink transmission at a far end away from the read-write equipment; the farther the uplink and downlink communication distances are, the higher the performance of the system is, which is the focus of product competition in the industry.
In order to obtain a longer communication distance, the passive rfid tag chip itself needs to have a smaller power consumption, i.e., the electric energy required for its operation is as small as possible. This involves a series of issues related to low power communication circuit design, which are not within the scope of the problems set forth in the present application and will not be discussed here. Under the condition of meeting the same power consumption, the energy collection and coupling efficiency of a resonant circuit consisting of an inductance coil and a built-in capacitor on a passive radio frequency identification tag chip becomes the key for improving the communication distance of the passive radio frequency identification tag chip.
The international standard for animal Radio Frequency Identification (RFID) of ISO11784/11785 defines a half-duplex RFID technology standard which mainly adopts a half-duplex communication technology. In this technical standard, a Frequency Shift Keying (FSK) technique is used for the rfid tag chip to perform uplink transmission from the tag to the reader/writer device. The resonance frequency is directly determined by the inductance value and the capacitance value in the resonance circuit, and is irrelevant to the radio frequency field frequency issued by the reader-writer equipment, and the reader-writer equipment is in a turn-off state during uplink transmission according to the technical standard of ISO11784/11785 animal radio frequency identification, so the antenna is named as 'half-duplex'. In the frequency shift keying technique, data "1" and "0" are represented by two different frequencies respectively, which are achieved by switching a capacitor array switch inside a radio frequency identification tag resonant circuit. Therefore, the accuracy of capacitance, i.e., the frequency, directly affects the performance of frequency shift keying communications.
As is well known, the resonant circuit of a conventional passive rfid tag is an LC resonant circuit consisting of an inductor and a capacitor. The inductance and capacitance values must satisfy:
Figure 339398DEST_PATH_IMAGE001
the resonant circuit will have a higher degree of coupling, i.e. a higher energy pick-up, where f0L is an inductance value of the inductor coil, and C is a capacitance value of the built-in resonance capacitor. For passive radio frequency identification tags in a low frequency band, such as the low frequency resonant frequency of 134.25KHz specified in international standards for animal radio frequency identification (rfid) of ISO11784/11785, complete integration inside the chip is not possible because the inductance and capacitance must both reach relatively large values, and particularly, the inductance value is far beyond the range that can be achieved by the inductive device in the integrated circuit chip, and the resonant inductor must be external to the chip. In the small-sized glass tube radio frequency identification label packaging process, a magnetic core made of ferrite materials is often adopted as the core of an external coil winding, and the quality factor of an inductor is improved by means of the high magnetic conductivity of the magnetic core, so that the performance of resonant coupling is improved, and under certain conditions, the performance of resonant coupling is improvedIn order to save the manufacturing cost of the chip, part of the resonant capacitor is also arranged outside the chip, so that the resonant capacitor of the whole resonant circuit is formed by adding a discrete capacitor element outside the chip and a capacitor inside the chip.
In the production practice of mass production of passive rfid tags, the inductance of the external inductor or the capacitance of the capacitor exhibits a certain statistical rule, such as gaussian distribution, along with the variation of the batch of discrete components, and the magnetic core adopted also has a deviation in the manufacturing process, which causes the magnetic permeability to exhibit a certain statistical distribution, and the drifts of these parameters can be classified into the same category and referred to as statistical drift. The statistical drift of the parameters causes the central frequency of the resonant circuit of the passive radio frequency tag to drift. The amplitude of the resonance versus frequency curve, I, as shown in FIG. 10At the maximum value of the resonance amplitude, corresponding to the optimum resonance frequency f0(ii) a And 0.707 times of I0For the resonance amplitude to reach-3 dB of maximum amplitude, i.e. the power to reach 50% of the optimum resonance power, corresponding to less than and greater than the optimum resonance frequency f on the frequency axis, respectively0Two frequency points fLAnd fHIt can be seen from the curve of fig. 1 that the amplitude of the resonant waveform changes with the frequency, when the frequency of the resonant circuit formed by the inductor and the capacitor deviates from the value of achieving the optimal resonance, the coupling efficiency of the resonant circuit is greatly reduced, so that the passive rfid tag cannot achieve the optimal resonance amplitude, and the yield of the tag finished product is reduced due to insufficient communication distance. Therefore, the primary factor of the design of the resonant circuit is to ensure that the external discrete inductor and capacitor can achieve the optimal resonance amplitude f0The numerical value of (c).
In order to solve the problem of statistical drift, a method of switching in or switching out a part of resonant capacitors according to the deviation of devices outside the resonant circuit is mostly adopted in chip design. The specific method is that a switch composed of a group of MOS transistors in the chip is respectively connected in series with an adjustable internal resonance capacitor, when the system determines to connect the capacitor, the MOS switch is connected and closed, the capacitor and other resonance capacitors form a parallel connection relationship, and then the capacitance value is added to the resonance capacitor, as shown in FIG. 2.
The prior art approach brings about two new problems, which are described below.
First, since our rfid tag chips of interest are passive, all of their energy sources come from field energy coupled through resonance; only when the field energy is large enough, the power-on reset signal of the chip system is triggered, after the power-on reset signal is activated, the digital logic circuit in the chip enters a normal working state, and then the control logic signal can distinguish high level voltage or low level voltage with electrical significance, namely, the function of switch control is started. The adjustable partial resonance capacitor to be accessed by the resonance circuit can be accessed only by the switch control signal, so that the optimal resonance state is achieved. It is apparent that the resonant circuit of a passive radio frequency identification tag is in a detuned state before the coupled energy reaches a power-on-reset level. In a detuning state, the efficiency of the resonant circuit coupling field energy is low, and in addition, the resonant circuit and its system load circuit inevitably have a reason of a leakage current flowing into the ground, the voltage at the two ends of the resonant circuit will present a gradually increasing process curve along with the accumulation of the coupling energy, and the process curve is relatively flat in a relatively long time, that is, the passive radio frequency identification tag must be coupled for a relatively long time to obtain sufficient energy, and further enter an optimal resonance state to start working. In the communication performance of a tag of the same type at a longer distance than the distance from the reader device, the energy coupling stage with gentle rise may not reach a certain energy level and eventually may not obtain enough energy. Therefore, the coupling process with low efficiency directly influences the communication distance of the passive radio frequency identification tag.
Second, even when the first problem is solved, the devices in the resonant circuit of the passive rfid tag chip may still experience a drift in inductance and capacitance with the change in ambient temperature. The problem of device characteristics changing with temperature changes is well known in the art and is an inherent non-ideal characteristic of the device. When the environmental temperature changes, both the inductance and the capacitance change to a certain degree, and the magnetic permeability of the magnetic core also changes, and the capacitance which is switched in or out by the resonant circuit through the on or off of the MOS switch mentioned in the above statistical drift problem also changes along with the temperature change, and the drift of this part is not solved by the prior art. Thus, in an application, the passive rfid tag chip may exhibit different communication performance under different temperature conditions, which is obviously not an optimal product design. In summary, the resonant frequency of the rfid tag directly affects the energy transmission efficiency from the reader/writer to the tag during the energy collection stage, and also affects the accuracy of the uplink FSK frequency during the uplink transmission stage from the tag to the reader/writer. Both phases of temperature drift must be taken into account in the design phase and compensated for in circuit technology.
In order to improve the detuning state of a passive radio frequency identification tag chip before a resonant capacitor controlled by an MOS switch is switched in, the prior art usually reduces the proportion of an adjustable resonant capacitor in a total resonant capacitor, namely, only a logic switch is used for controlling the switching in of a small part of the resonant capacitor, so that the detuning of a resonant circuit is reduced to a small degree before the resonant capacitor controlled by the MOS switch is switched in, and thus, the passive radio frequency identification tag can quickly cross a stage with low coupling efficiency, and the optimal resonance is quickly reached. However, the range in which the resonant capacitor can be adjusted becomes very small, and for the case that the inductance value or capacitance value of the external discrete inductor or capacitor changes greatly and exceeds the adjustable range, the method of supplementing the internal capacitor to the resonant circuit by switching the MOS switch is still insufficient to achieve the optimal resonant frequency.
In the production practice of rfid tags, calibration equipment needs to be specially equipped in the process of mass production for the resonant frequency deviation caused by the statistical drift of discrete components, so as to calibrate certain search algorithm for passive rfid tags one by one through antenna coupling. Different brands of radio frequency identification tags have different calibration instructions and read-write instructions, so that a batch production processing factory has to finely distinguish the matching of the calibration read-write equipment and the chip model of incoming material processing. Obviously, this additional step greatly increases the production cost.
In order to improve the temperature drift of the resonant circuit device of the passive rfid tag chip, a device with a smaller drift degree with the temperature change, such as a capacitor with a higher manufacturing grade or a magnetic rod using a ferrite material with a better temperature characteristic as an inductor, is used as much as possible. This inevitably increases the manufacturing cost, and cannot fundamentally solve the problem.
Disclosure of Invention
The invention aims to solve the problem that the conventional RFID resonant circuit has drift due to statistical factors and temperature factors, and provides a method and a circuit structure for carrying out automatic calibration compensation on the drift so as to improve the production efficiency and the yield of products.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a method for automatically compensating for RFID resonant frequency statistics and temperature drift, the method comprising the acts of:
s0, after the passive radio frequency identification label system is powered on and reset, firstly checking whether a compensation code exists in a preset non-volatile memory address, if no compensation code exists, the passive radio frequency identification label system enters a statistical drift compensation process of resonance frequency, after the statistical drift compensation process is finished, the passive radio frequency identification label system finishes the automatic resonance frequency compensation process and enters a normal starting state, if the compensation code exists and the compensation code does not need to be updated, the passive radio frequency identification label system finishes the automatic resonance frequency compensation process and enters the normal starting state; if the compensation code exists and needs to be updated, judging whether the statistical drift compensation needs to be carried out, and if so, entering a statistical drift compensation process of the resonant frequency by the passive radio frequency identification tag system until the end;
and S1, the statistical drift compensation process is to control the adjustable capacitor array, adjust the number of capacitors connected to the resonant circuit in the adjustable capacitor array to obtain an improved resonance effect, write the state value of the capacitor array switch in this state, i.e. the first compensation code, into the non-volatile memory unit, and end the statistical drift compensation process.
Further, in the automatic resonant frequency compensation process, when it is determined that statistical drift compensation is not required, the passive radio frequency identification tag system enters a temperature drift compensation process, the temperature drift compensation process is to control and adjust the number of capacitors connected to the resonant circuit in the adjustable capacitor array so that the resonant amplitude can be maximized under the condition of temperature change, and after the temperature drift compensation is finished, the passive radio frequency identification tag system writes the state value of the capacitor array switch in this state, i.e., the second compensation code, into the non-volatile memory unit, and then finishes the temperature drift compensation process.
The technical solution for achieving the object of the present invention further includes that the method for generating the first compensation code by the statistical drift compensation process includes: the passive radio frequency identification tag system generates an initial compensation code to control the on or off of the capacitor array switch, and starts a statistical drift compensation process; in the process, a peak detection circuit is adopted to extract the resonance amplitude value of the resonance circuit in the state, a digital code representing the resonance amplitude is obtained through the conversion of an analog-digital converter, namely a first peak code in the statistical drift compensation process, the first peak code is temporarily stored in a register, and then the statistical drift compensation process mathematically forms an optimization process taking the first peak code as a target function and the compensation code as an independent variable; after the logic control module obtains the first peak code, searching independent variables through an optimization algorithm to obtain the values of the searched independent variables, namely, the new compensation code drives the switch control signal in the adjustable capacitor array to control the on or off of the capacitor array switch, and measuring the resonance amplitude under the current switch signal setting condition to obtain a new first peak code, searching and adjusting the search algorithm again according to the newly obtained first peak code, and then obtaining a new peak value code and a new compensation code again, searching repeatedly in such a way until the compensation process meets a convergence condition and converges to a capacitor array switch combination with the maximum resonance amplitude, wherein the compensation code in the state is the first compensation code generated by the statistical drift compensation process, writing the first compensation code into the non-volatile memory, and ending the statistical drift compensation process.
The technical solution for achieving the object of the present invention further includes that the method for generating the second compensation code in the temperature drift compensation process includes: the passive radio frequency identification tag system controls the on or off of a capacitor array switch by using a compensation code which exists, starts a temperature detection and control circuit to work to obtain a PTAT voltage which is in a direct proportion relation with absolute temperature, the PTAT voltage is converted by an analog-digital converter to obtain a PTAT code, the PTAT code is input into a digital logic module to be processed, the digital logic module obtains a second compensation code in a temperature drift compensation process by looking up a table by the PTAT code, and controls the on or off of the switch in the adjustable capacitor array by using the second compensation code, so that the number of capacitors connected into a resonance circuit in the capacitor array and the total resonance capacitance value are changed to obtain an improved resonance amplitude at the temperature, the second compensation code is written into a non-volatile memory, and the temperature drift compensation process is ended.
Or the passive radio frequency identification label system controls the on or off of the capacitor array switch by the existing compensation code, starts the temperature detection and control circuit to work, obtains the PTAT voltage in direct proportion to the absolute temperature, the PTAT voltage is converted by an N-way parallel processing architecture to obtain PTAT codes, the PTAT code is input into a digital logic module for processing, the digital logic module obtains a second compensation code in the temperature drift compensation process by looking up a table of the PTAT code, the second compensation code is used for conducting on or off control on the switch in the adjustable capacitor array, therefore, the number of capacitors connected into the resonant circuit in the capacitor array and the total resonant capacitance value are changed, the improved resonant amplitude at the temperature is obtained, the second compensation code is written into the nonvolatile memory, and the temperature drift compensation process is ended.
Another technical solution of the present invention is to provide a control circuit for implementing the above statistical drift compensation process, where the control circuit includes a resonant circuit composed of a resonant inductor and a resonant capacitor, a peak detection module, an analog-to-digital converter, and a logic control module, the resonant capacitor includes two parts, i.e., a fixed capacitor array and an adjustable capacitor array, the fixed capacitor array and the adjustable capacitor array are connected in parallel to two ends of the resonant inductor, an input end of the peak detection module is connected to an output end of the resonant circuit, an output end of the peak detection module is connected to an input end of the analog-to-digital converter, an output end of the analog-to-digital converter is connected to an input end of the logic control module, an output end of the logic control module is connected to the adjustable capacitor array in the resonant circuit, the peak detection module is configured to extract a resonant amplitude value of the resonant circuit, and obtain a digital code representing the resonant amplitude after passing through the analog-to-digital converter, the first peak code in the statistical drift compensation process is temporarily stored in a register, and then the statistical drift compensation process mathematically forms an optimization process taking the first peak code as a target function and a compensation code as an independent variable; and the logic control module obtains a new compensation code according to the implemented optimization search algorithm after obtaining the first peak code, controls the on or off of the capacitor array switch again by the new compensation code so as to obtain a new resonance amplitude and a new peak code, obtains the new compensation code again by the logic control module according to the optimization search algorithm, and repeats the process until the logic control module converges to a switch combination with the maximum resonance amplitude, wherein the compensation code in the state is the first compensation code generated by the statistical drift compensation process, writes the first compensation code into the non-volatile memory, and ends the statistical drift compensation process.
The technical scheme of the invention also comprises providing a control circuit for realizing the temperature drift compensation process, wherein the control circuit comprises a resonance circuit consisting of a resonance inductor and a resonance capacitor, a rectification circuit, a power management module and a temperature detection and control circuit, the resonance capacitor comprises a fixed capacitor array and an adjustable capacitor array, the fixed capacitor array and the adjustable capacitor array are connected with two ends of the resonance inductor in parallel, the output end of the resonance circuit is connected with the input end of the rectification circuit, the output end of the rectification circuit is connected with the power management module, the output end of the power management module is connected with the temperature detection and control circuit,
the temperature detection and control circuit comprises a reference generation and PTAT voltage generation module, an analog-digital converter and a digital logic module, wherein the output end of the power management module is respectively connected to the reference generation and PTAT voltage generation module, the analog-digital converter and the digital logic module, the output end of the digital logic module is connected to an adjustable capacitor array in the resonance circuit, the reference generation and PTAT voltage generation module measures the internal temperature of a chip and converts a temperature physical quantity into PTAT voltage in a positive proportion relation with absolute temperature, the PTAT voltage is converted into a binary code representing the temperature physical quantity through the analog-digital converter, namely a PTAT code, the binary code is input into the digital logic module for processing, and the digital logic module obtains a second compensation code in a temperature drift compensation flow through the binary code lookup table, and controlling the on or off of a switch in the adjustable capacitor array by the second compensation code, so that the number of capacitors connected into the resonant circuit in the capacitor array and the total resonant capacitance value are changed, an improved resonant amplitude at the temperature is obtained, the second compensation code is written into the non-volatile memory, and the temperature drift compensation process is ended.
The control circuit may further be: the temperature detection and control circuit comprises a resonant circuit consisting of a resonant inductor and a resonant capacitor, a rectifying circuit, a power supply management module and a temperature detection and control circuit, wherein the resonant capacitor comprises a fixed capacitor array and an adjustable capacitor array, the fixed capacitor array and the adjustable capacitor array are connected to two ends of the resonant inductor in parallel, the output end of the resonant circuit is connected to the input end of the rectifying circuit, the output end of the rectifying circuit is connected to the power supply management module, the output end of the power supply management module is connected to the temperature detection and control circuit,
the temperature detection and control circuit comprises a reference generation and PTAT voltage generation module, a plurality of comparators and a plurality of digital logic modules, wherein the reference generation and PTAT voltage generation module outputs a PTAT voltage and a plurality of paths of reference voltages which are uniformly distributed, the comparators are respectively corresponding to the output of the plurality of paths of reference voltages, the PTAT voltage generation module generates a PTAT voltage which is in a positive proportional relation with absolute temperature and inputs the PTAT voltage to the positive input end of each comparator, the plurality of paths of reference voltages are respectively input to the negative input end of each comparator, the plurality of paths of comparators respectively output PTAT codes according to comparison results, the PTAT codes are input to the digital logic module for processing, the digital logic module obtains a second compensation code in a temperature drift compensation flow by looking up a table through the PTAT codes, and controls the second compensation code to conduct or shut off a switch in the adjustable capacitor array, so that the number and the total resonant capacitance value of the resonant circuit accessed in the capacitor array are changed, obtaining an improved resonance amplitude at the temperature, writing the second compensation code into the non-volatile memory, and ending the temperature drift compensation process.
The invention has the beneficial effects that: the method and the device provide a complete calibration compensation technology aiming at the influence of the statistical drift and the temperature drift faced by the radio frequency identification tag chip product on the resonance performance, particularly, the automatic compensation of the statistical drift enables a procedure of calibrating by special equipment to be omitted in the radio frequency identification tag finished product processing procedure, the production efficiency and the yield are greatly improved, and the method and the device have remarkable economic value. The technology also comprises an automatic compensation technology of the temperature drift of the resonant circuit, and the influence of the temperature drift on the resonant frequency is fundamentally solved by using various different implementation schemes aiming at different products with refined logic control requirements. The frequency calibration process after power-on reset provided by the application technology explicitly provides control steps for implementing statistical drift and temperature drift compensation, and the guiding idea can be extended to a more general circuit compensation technology in the field of low-power wireless communication.
Drawings
FIG. 1 is a graph of antenna coupling signal amplitude versus resonant frequency;
FIG. 2 is a circuit diagram of a switch-controlled capacitor array;
FIG. 3 is a block diagram of an embodiment of an automatic resonant frequency compensation control process according to the present invention;
FIG. 4 is a block diagram of a second embodiment of an automatic resonant frequency compensation control process according to the present invention;
FIG. 5 is a circuit diagram of the statistical drift compensation feedback control of the present invention;
FIG. 6 is a control circuit diagram of a temperature drift compensation embodiment of the present invention;
FIG. 7 is a schematic diagram of a second exemplary embodiment of the temperature detection and control circuit shown in FIG. 6;
FIG. 8 shows the second reference voltage, V, of the temperature drift compensation embodiment of FIG. 7PTATVoltage versus temperature graph.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
First, several terms used in the present technical solution are defined:
peak code-a binary code obtained by performing analog-to-digital conversion on the harmonic amplitude;
the compensation code is a binary code formed by the adjustable capacitor array switch control signals, for example, the switch is turned on to be '1', and the switch is turned off to be '0';
PTAT Voltage-Voltage that is directly proportional to Absolute temperature (i.e., PTAT isProportional To Absolute Temperature)
PTAT code-a binary code obtained by analog-to-digital conversion of PTAT voltage.
Fig. 3 is a block diagram of an automatic resonant frequency compensation control process according to the present invention, where the automatic resonant frequency compensation process includes two parts, namely, statistical drift compensation and temperature drift compensation, and the specific process includes:
s0, after the passive radio frequency identification label system is powered on and reset, firstly checking whether a compensation code exists in a preset non-volatile memory address, if no compensation code exists, the passive radio frequency identification label system enters a statistical drift compensation process of resonance frequency, after the statistical drift compensation process is finished, the passive radio frequency identification label system finishes the automatic resonance frequency compensation process and enters a normal starting state, if the compensation code exists and the compensation code does not need to be updated, the passive radio frequency identification label system finishes the automatic resonance frequency compensation process and enters the normal starting state; if the compensation code exists and needs to be updated, judging whether the statistical drift compensation needs to be carried out, and if so, entering a statistical drift compensation process of the resonant frequency by the passive radio frequency identification tag system until the end;
and S1, the statistical drift compensation process is to control the adjustable capacitor array, adjust the number of capacitors connected to the resonant circuit in the adjustable capacitor array to obtain an improved resonance effect, write the state value of the capacitor array switch in this state, i.e. the first compensation code, into the non-volatile memory unit, and end the statistical drift compensation process.
The method for generating the first compensation code in the statistical drift compensation process includes: the passive radio frequency identification tag system generates an initial compensation code to control the on or off of the capacitor array switch, and starts a statistical drift compensation process; in the process, a peak detection circuit is adopted to extract the resonance amplitude value of the resonance circuit in the state, a digital code representing the resonance amplitude is obtained through the conversion of an analog-digital converter, namely a first peak code in the statistical drift compensation process, the first peak code is temporarily stored in a register, and then the statistical drift compensation process mathematically forms an optimization process taking the first peak code as a target function and the compensation code as an independent variable; after the logic control module obtains the first peak code, searching independent variables through an optimization algorithm to obtain the values of the searched independent variables, namely, the new compensation code drives the switch control signal in the adjustable capacitor array to control the on or off of the capacitor array switch, and measuring the resonance amplitude under the current switch signal setting condition to obtain a new first peak code, searching and adjusting the search algorithm again according to the newly obtained first peak code, and then obtaining a new peak value code and a new compensation code again, searching repeatedly in such a way until the compensation process meets a convergence condition and converges to a capacitor array switch combination with the maximum resonance amplitude, wherein the compensation code in the state is the first compensation code generated by the statistical drift compensation process, writing the first compensation code into the non-volatile memory, and ending the statistical drift compensation process.
The initial compensation code may be chosen to be any intermediate value, minimum value (i.e., all "0" codes, representing fully off), or maximum value (i.e., all "1" codes, representing fully on) of the maximum number allowed by the compensation code without loss of generality. The flow of statistical drift compensation may also be controlled by a convergence control signal, which may stop the operation of statistical drift compensation after the compensation result meets the convergence condition. The convergence control signal has several optional convergence conditions, for example, the difference between the compensation codes or the peak codes which are continuously carried out twice or several times is within an allowable range, which indicates that the compensation has been in an optimal state, and almost no room for improvement exists; or, the compensation operation can be stopped when the number of times of statistical compensation reaches a preset number of times. In the optimization theory branch of the applied mathematics, there are many search algorithms with different characteristics, and the search algorithm implemented by the logic control circuit is not described in detail here. The peak detection circuit can be implemented by referring to the grant publication number of the applicant filed on 28/5/2021: CN 113255382B, entitled discharge control circuit and method driven by RF field envelope peak detection signal.
For a fixed radio frequency identification tag, the statistical drift of the resonant circuit element is a fixed offset, so in the application scenario of the actual radio frequency identification tag, the statistical drift compensation operation of the resonant frequency does not need to be performed in a normalized manner, and only the radio frequency field energy is obtained and activated once in the quality inspection of the first batch of products. The non-volatile memory of the radio frequency identification tag can be set to avoid compensating the statistical drift, so that the current local temperature drift compensation operation process can be directly entered in the next power-on process. Of course, for rfid tags with longer service life, the compensation of statistical drift is also optional, so that the communication performance of rfid tag products with long service life can be further optimized.
In the automatic resonant frequency compensation process, if a compensation code exists and needs to be updated, judging whether statistical drift compensation needs to be carried out, if so, entering the statistical drift compensation process by the passive radio frequency identification tag system until the end, and entering a temperature drift compensation process by the passive radio frequency identification tag system when judging that the statistical drift compensation does not need to be carried out, wherein the temperature drift compensation process is to control and adjust the number of capacitors connected to a resonant circuit in an adjustable capacitor array so that the resonant amplitude can still reach the maximum under the condition of temperature change, and after the temperature drift compensation is finished, writing the state value of a capacitor array switch in the state, namely a second compensation code, into a non-volatile memory unit by the passive radio frequency identification tag system, and finishing the temperature drift compensation process.
As shown in fig. 3, the method for generating the second compensation code in the temperature drift compensation process includes: the passive radio frequency identification tag system controls the on or off of a capacitor array switch by using a compensation code which exists, starts a temperature detection and control circuit to work to obtain a PTAT voltage which is in a direct proportion relation with absolute temperature, the PTAT voltage is converted by an analog-digital converter to obtain a PTAT code, the PTAT code is input into a digital logic module to be processed, the digital logic module obtains a second compensation code in a temperature drift compensation process by looking up a table by the PTAT code, and controls the on or off of the switch in the adjustable capacitor array by using the second compensation code, so that the number of capacitors connected into a resonance circuit in the capacitor array and the total resonance capacitance value are changed to obtain an improved resonance amplitude at the temperature, the second compensation code is written into a non-volatile memory, and the temperature drift compensation process is ended.
The method for generating the second compensation code in the temperature drift compensation process may further include: the passive radio frequency identification tag system controls the on or off of a capacitor array switch by using a compensation code which exists, starts a temperature detection and control circuit to work to obtain a PTAT voltage which is in a direct proportion relation with absolute temperature, the PTAT voltage is converted by an N-path parallel processing structure to obtain a PTAT code, the PTAT code is input into a digital logic module to be processed, the digital logic module obtains a second compensation code in a temperature drift compensation process by looking up a table by the PTAT code, and controls the on or off of the switch in the adjustable capacitor array by using the second compensation code, so that the number of capacitors accessed into a resonance circuit in the capacitor array and the total resonance capacitance value are changed, an improved resonance amplitude at the temperature is obtained, the second compensation code is written into a non-volatile memory, and the temperature drift compensation process is ended.
The operation method of the digital logic module for obtaining the compensation code by the PTAT code lookup table comprises the following steps: the method comprises the steps of storing a table in which PTAT codes representing temperature information and compensation codes are in one-to-one correspondence in a non-volatile memory inside a chip in advance, reading out the compensation code corresponding to the PTAT code obtained by closest measurement from a storage medium during calibration, wherein the compensation code is the compensation code in a temperature drift compensation process and is used for controlling the on or off of a capacitor array switch, so that temperature compensation is completed.
In the temperature drift compensation process, after a certain time delay, the temperature detection and control circuit measures the temperature again to obtain a new PTAT code, and obtains an updated second compensation code after table look-up operation again, the updated second compensation code controls the on or off of the capacitor array switch again, and the process is repeated in such a way until the temperature drift compensation process is finished, and the updated second compensation code is written into the non-volatile memory. The rate at which temperature drift compensation is iteratively adjusted is dependent upon the setting of the delay time in the block diagrams of fig. 3 and 4, for example, when the rfid tag is operated in a widely varying temperature environment for an extended period of time, a built-in counter counts the number of clock cycles, sets a suitable maximum count value, and when the count reaches the maximum, the temperature drift compensation process resumes. Of course, when the working time of the radio frequency identification tag is only dozens of milliseconds and is not influenced by the condition of continuous temperature change, the maximum count value is not reached, and the radio frequency identification tag is automatically powered off to complete one response operation; in the latter application example, the temperature drift compensation is usually performed only once. The result of the temperature drift compensation is a new compensation code that is used to further update the control of the capacitor array so that the resonance performance is still optimized under temperature variations.
After the temperature drift compensation process is finished, the passive radio frequency identification tag system selectively writes the compensation code into the non-volatile memory unit according to the working environment of the passive radio frequency identification tag system, namely, if the radio frequency identification tag works in the environment with relatively constant temperature, the compensation code written into the non-volatile memory unit is a second compensation code; if the temperature when the radio frequency identification tag is activated next time can not be guaranteed to be consistent with the ambient temperature for temperature drift compensation at present, only the first compensation code is written.
In fig. 3, 4, the system retains the option of updating the compensation code because the external resonant device also changes its characteristics over time. If the compensation code is updated, a compensation operation of statistical drift can be performed on the basis of the existing compensation code, otherwise, a temperature drift compensation phase can be directly entered, so as to ensure that the temperature factor is considered in the adjustment optimization of the resonance performance when the compensation code is applied at present.
All the options can be set by reading the configuration bit, that is, the determination of "yes" and "no" of each option is stored in the memory cell of the specific address in the nonvolatile memory of the rfid tag. For non-volatile memory, these settings may also be updated and adjusted by a write operation of the identification tag by the reader device.
The method and the device provide a complete calibration compensation technology aiming at the influence of the statistical drift and the temperature drift faced by the radio frequency identification tag chip product on the resonance performance, particularly, the automatic compensation of the statistical drift enables a procedure of calibrating by special equipment to be omitted in the radio frequency identification tag finished product processing procedure, the production efficiency and the yield are greatly improved, and the method and the device have remarkable economic value. The technology also comprises an automatic compensation technology of the temperature drift of the resonant circuit, and the influence of the temperature drift on the resonant frequency is fundamentally solved by using various different implementation schemes aiming at different products with refined logic control requirements. The frequency calibration process after power-on reset provided by the application technology explicitly provides control steps for implementing statistical drift and temperature drift compensation, and the guiding idea can be extended to a more general circuit compensation technology in the field of low-power wireless communication.
Another technical object of the present invention is to provide a feedback control circuit for implementing the above mentioned automatic resonance frequency statistical drift compensation and temperature drift compensation of the rfid tag.
FIG. 5 is a diagram of a statistical drift compensation feedback control circuit according to the present invention, where the control circuit includes a resonant circuit composed of a resonant inductor and a resonant capacitor, a peak detection module, an analog-to-digital converter, and a logic control module, where the resonant capacitor includes two parts, a fixed capacitor array and an adjustable capacitor array, the fixed capacitor array and the adjustable capacitor array are connected in parallel to two ends of the resonant inductor, an input end of the peak detection module is connected to an output end of the resonant circuit, an output end of the peak detection module is connected to an input end of the analog-to-digital converter, an output end of the analog-to-digital converter is connected to an input end of the logic control module, an output end of the logic control module is connected to the adjustable capacitor array in the resonant circuit, the peak detection module is configured to extract a resonant amplitude value of the resonant circuit, and obtain a digital code representing the resonant amplitude of the resonant circuit after passing through the analog-to-digital converter, the first peak code in the statistical drift compensation process is temporarily stored in a register, and then the statistical drift compensation process mathematically forms an optimization process which takes the first peak code as a target function and takes a compensation code as an independent variable; and the logic control module obtains a new compensation code according to the implemented optimization search algorithm after obtaining the first peak code, controls the on or off of the capacitor array switch again by the new compensation code so as to obtain a new resonance amplitude and a new peak code, obtains the new compensation code again by the logic control module according to the optimization search algorithm, and repeats the process until the logic control module converges to a switch combination with the maximum resonance amplitude, wherein the compensation code in the state is the first compensation code generated by the statistical drift compensation process, writes the first compensation code into the non-volatile memory, and ends the statistical drift compensation process.
The analog-to-digital converter (ADC) in fig. 5 may be an analog-to-digital converter with various low power consumption architectures, such as a primary-secondary approximation analog-to-digital converter and a time domain digital converter, and will not be described herein again.
The resonant frequency statistical drift compensation feedback control circuit is a negative feedback loop structure. As can be seen from the resonance amplitude versus frequency curve shown in fig. 1, the resonance amplitude reaches a maximum when the resonance frequency reaches the optimum frequency point. According to the principle, in the circuit technology shown in fig. 5, a structure that a peak detection circuit extracts a resonance amplitude value of a resonance circuit is adopted, and a digital code representing the resonance amplitude is obtained through a low-power consumption analog-digital converter, namely, the first compensation code in the statistical drift compensation process in fig. 3 and 4.
The output of the peak detection circuit is used as a standard structure for judging and optimizing the adjustable capacitor array in the resonant circuit, and the method can be extended to the resonant frequency compensation technology generated by temperature drift. For the application field of active power supply or semi-active power supply radio frequency identification tags, the radio frequency identification tags often have some real-time monitoring functions, such as temperature monitoring, humidity monitoring, or object proximity monitoring, and the like, and the continuous change of the environmental temperature can affect the resonant frequency of the radio frequency identification tags, thereby causing the drift of the communication performance. In this case, as shown in fig. 5, the statistical drift compensation process with the peak detection circuit as the core is also performed based on the ambient temperature of the current passive rfid tag, and in the process of performing the statistical drift compensation process, the temperature drift compensation is also performed on the tag at the ambient temperature.
In a system with a resonant circuit in a continuous working state, a resonant frequency compensation technology taking a peak detection circuit as a core, and an ultra-low power consumption analog-digital converter and a digital logic control module matched with the ultra-low power consumption analog-digital converter can play a key role in adjusting the performance of the resonant circuit in real time. Based on the same signal processing concept, the peak detection circuit may be replaced by common mode voltage detection of input signal voltages at two ends of the antenna, or mean voltage detection, which respectively corresponds to a slightly different common mode voltage extraction circuit, mean voltage extraction circuit, and the like.
For passive radio frequency identification tags, the compensation of the resonance frequency caused by the statistical drift by adopting the technology can be realized by adopting a one-time operation process, so that the performance requirement required by product application can be met; for frequency compensation caused by temperature drift, a more concise technology in the application is more suitable for the low power consumption requirement of a passive radio frequency identification tag chip, fig. 6 is a control circuit diagram of a temperature drift compensation embodiment of the invention, the control circuit comprises a resonance circuit consisting of a resonance inductor and a resonance capacitor, a rectification circuit, a power management module and a temperature detection and control circuit, the resonance capacitor comprises a fixed capacitor array and an adjustable capacitor array, the fixed capacitor array and the adjustable capacitor array are connected in parallel at two ends of the resonance inductor, the output end of the resonance circuit is connected to the input end of the rectification circuit, the output end of the rectification circuit is connected to the power management module, the output end of the power management module is connected to the temperature detection and control circuit,
the temperature detection and control circuit comprises a reference generation and PTAT voltage generation module, an analog-digital converter and a digital logic module, wherein the output end of the power management module is respectively connected to the reference generation and PTAT voltage generation module, the analog-digital converter and the digital logic module, the output end of the digital logic module is connected to an adjustable capacitor array in the resonance circuit, the reference generation and PTAT voltage generation module measures the internal temperature of a chip and converts a temperature physical quantity into PTAT voltage in a positive proportion relation with absolute temperature, the PTAT voltage is converted into a binary code representing the temperature physical quantity through the analog-digital converter, namely a PTAT code, the binary code is input into the digital logic module for processing, and the digital logic module obtains a second compensation code in a temperature drift compensation flow through the binary code lookup table, and controlling the on or off of a switch in the adjustable capacitor array by using the second compensation code, so that the number of capacitors connected into the resonance circuit in the capacitor array and the total resonance capacitance value are changed, an improved resonance amplitude at the temperature is obtained, the second compensation code is written into the non-volatile memory, and the temperature drift compensation process is finished.
The fixed capacitor part in the internal resonant circuit of the semiconductor chip and the rule that the characteristics of the semiconductor device of the adjustable capacitor array change along with the temperature drift can be described by an accurate semiconductor device model. In the OEM model, which is the model of semiconductor wafer production that is mostly entrusted with manufacturing, the device models of the foundry contain parameters whose key characteristics vary with temperature, so that the performance variation can be accurately estimated and simulated in the computer simulation. Based on this knowledge, fig. 6 gives the architecture of the temperature drift compensation circuit control circuit. The loop structure of fig. 6 simplifies the sense-sense part with respect to the sense-feedback-re-sense loop structure of fig. 5, i.e. this loop structure does not measure physical quantities related to the resonance parameters from the resonance circuit, except for the rectified dc power supply as a supply; for the resonance frequency compensation caused by the temperature drift, a method of detecting the voltage difference between semiconductors P-N representing the temperature physical quantity on a chip is adopted, the voltage difference is converted into a digital binary code, and the switch combination control of the adjustable capacitor array is adopted by contrasting the direct corresponding relation between the binary code and the resonance frequency compensation.
As shown in fig. 6, the rfid tag circuit rectifies ac power into dc power vdda as an input of the power management module through the energy collection function of the resonant circuit; the output of the power management module enables the reference generation and PTAT voltage generation module to be started; then the reference generation and PTAT voltage generation module measures the internal Temperature of the chip, and converts the Temperature physical quantity into PTAT voltage according to the Temperature characteristic of the semiconductor P-N junction, namely the current (Proportional to Absolute Temperature) in a direct proportion relation with the Absolute Temperature; the PTAT voltage is converted by a low-power consumption analog-digital converter (ADC), and a binary code representing a temperature physical quantity is obtained and input into a digital logic module for processing; the digital logic module can perform the operation of compensating the adjustable capacitor array according to the known physical characteristic that the capacitance value of the adjustable capacitor changes along with the temperature, namely a lookup table which is built in the non-volatile memory unit array.
The analog-to-digital converter (ADC) in fig. 6 may be an analog-to-digital converter with various low power consumption architectures, such as a primary-secondary approximation analog-to-digital converter and a time domain digital converter, and will not be described herein again.
Further, under the guidance of the same spirit of signal processing idea, the portion of fig. 6 where the PTAT temperature physical quantity is output to the analog-to-digital converter-to-digital Logic module may have various simplified implementation forms, i.e. a form of Direct Switch Logic Control (Direct Switch Logic Control). This embodiment bypasses the analog-to-digital conversion and is suitable for simple adaptive logic control. The logic for temperature drift compensation can be simplified to direct switching logic, mainly because the temperature drift characteristics of the capacitor array are known at the design stage and can be easily obtained from device models by simulation. Therefore, in addition to the quantization of the physical temperature quantity into the binary code, the analog-to-digital converter can be simplified into a series of parallel comparators, wherein the input of each comparator is a simple divided output from the PTAT physical quantity, as shown in fig. 8, the temperature point corresponding to each divided output is known, and the capacitance change of the capacitor array at each temperature point is also known; the outputs of the n parallel comparators are respectively connected to the corresponding switch control gates in the tunable capacitor array to achieve the purpose of improving the resonance performance according to the temperature detection result, as shown in fig. 7, an implementation structure diagram of the temperature detection and control circuit in this embodiment is shown, and a digital logic control part is omitted in the implementation structure.
In this embodiment, the control circuit includes a resonant circuit composed of a resonant inductor and a resonant capacitor, a rectifying circuit, a power management module, and a temperature detection and control circuit, the resonant capacitor includes two parts, a fixed capacitor array and an adjustable capacitor array, the fixed capacitor array and the adjustable capacitor array are connected in parallel to two ends of the resonant inductor, an output end of the resonant circuit is connected to an input end of the rectifying circuit, an output end of the rectifying circuit is connected to the power management module, an output end of the power management module is connected to the temperature detection and control circuit,
the temperature detection and control circuit comprises a reference generation and PTAT voltage generation module, a plurality of comparators and a plurality of digital logic modules, wherein the reference generation and PTAT voltage generation module outputs a PTAT voltage and a plurality of paths of reference voltages which are uniformly distributed, the comparators are respectively corresponding to the output of the plurality of paths of reference voltages, the PTAT voltage generation module generates a PTAT voltage which is in a direct proportion relation with absolute temperature and inputs the PTAT voltage to the positive input end of each comparator, the plurality of paths of reference voltages are respectively input to the negative input end of each comparator, the plurality of paths of comparators respectively output and obtain PTAT codes according to comparison results, the PTAT codes are input to the digital logic module for processing, the digital logic module obtains a second compensation code in a temperature drift compensation flow by looking up a table through the PTAT codes, and controls the second compensation code to conduct or shut off a switch in the adjustable capacitor array, so that the number and the total resonant capacitance value of the capacitor array which is accessed to the resonant circuit are changed, obtaining an improved resonance amplitude at the temperature, writing the second compensation code into the non-volatile memory, and ending the temperature drift compensation process.
In the control circuit of the temperature drift compensation process, after the passive radio frequency identification tag system obtains the second compensation code by looking up the table, the control circuit controls the temperature detection and control circuit to measure the temperature again after a certain time delay to obtain a new PTAT code, and obtains an updated second compensation code after the table look-up operation again, the updated second compensation code controls the on or off of the capacitor array switch again, the process is repeated in such a circulating way until the temperature drift compensation process is finished, and the updated second compensation code is written into the non-volatile memory. The rate at which the temperature drift compensation is iteratively adjusted is dependent upon the setting of the delay time in the block diagrams of fig. 3 and 4, for example, when the identification tag is operated in a widely varying temperature environment for an extended period of time, a built-in counter counts the number of clock cycles, sets a suitable maximum count value, and when the count reaches the maximum, the temperature drift compensation process resumes. Of course, when the working time of the radio frequency identification tag is only dozens of milliseconds and is not influenced by the condition of continuous temperature change, the maximum count value is not reached, and the radio frequency identification tag is automatically powered off to complete one response operation; in the latter application example, the temperature drift compensation is usually performed only once. The result of the temperature drift compensation is a new compensation code that is used to further update the control of the capacitor array so that the resonant performance of the passive rfid tag is still optimized under temperature variations.

Claims (12)

1. A method for automatically compensating RFID resonance frequency statistics and temperature drift, characterized in that the method comprises the following procedures:
s0, after the passive radio frequency identification label system is powered on and reset, firstly checking whether a compensation code exists in a preset non-volatile memory address, if no compensation code exists, the passive radio frequency identification label system enters a statistical drift compensation process of resonance frequency, after the statistical drift compensation process is finished, the passive radio frequency identification label system finishes the automatic resonance frequency compensation process and enters a normal starting state, if the compensation code exists and the compensation code does not need to be updated, the passive radio frequency identification label system finishes the automatic resonance frequency compensation process and enters the normal starting state; if the compensation code exists and needs to be updated, judging whether the statistical drift compensation needs to be carried out, and if so, entering a statistical drift compensation process of the resonant frequency by the passive radio frequency identification tag system until the end;
s1, the flow of the statistical drift compensation is to control the adjustable capacitor array, adjust the number of capacitors connected to the resonance circuit in the adjustable capacitor array to obtain improved resonance effect, write the state value of the capacitor array switch in this state, i.e. the first compensation code, into the non-volatile memory unit, and then end the flow of the statistical drift compensation;
the statistical drift compensation process is performed based on the ambient temperature of the current passive radio frequency identification tag, so that the process of performing the statistical drift compensation process is substantially equivalent to performing temperature drift compensation at the ambient temperature at the same time;
the compensation code is a binary code composed of the adjustable capacitor array switch control signal, and is generated by the previous compensation process and written into the chip memory unit.
2. The method according to claim 1, wherein in the automatic resonant frequency compensation process, when it is determined that the statistical drift compensation is not required, the passive RFID tag system enters a temperature drift compensation process, the temperature drift compensation process is performed by controlling and adjusting the number of capacitors connected to the resonant circuit in the tunable capacitor array, so that the resonant amplitude can still be maximized under the condition of temperature change, and after the temperature drift compensation is completed, the passive RFID tag system writes the state value of the capacitor array switch in this state, i.e., the second compensation code, into the non-volatile memory unit, and then completes the temperature drift compensation process.
3. The method of claim 2, wherein after the temperature drift compensation process is completed, the passive RFID tag system selectively writes the compensation code into the non-volatile memory unit according to the operating environment of the passive RFID tag system, that is, if the passive RFID tag operates in an environment with a relatively constant temperature, the compensation code written into the non-volatile memory unit is a second compensation code; if the temperature when the radio frequency identification tag is activated next time can not be guaranteed to be consistent with the ambient temperature for temperature drift compensation at present, only the first compensation code is written.
4. The method of claim 1, wherein the statistical drift compensation process generates the first compensation code by: the passive radio frequency identification tag system generates an initial compensation code to control the on or off of the capacitor array switch, and starts a statistical drift compensation process; in the process, a peak detection circuit is adopted to extract the resonance amplitude value of the resonance circuit in the state, a digital code representing the resonance amplitude is obtained through the conversion of an analog-to-digital converter, namely a first peak code in the statistical drift compensation process is temporarily stored in a register, and then the statistical drift compensation process mathematically forms an optimization process taking the first peak code as a target function and the compensation code as an independent variable; after the logic control module obtains the first peak code, searching independent variables through an optimization algorithm to obtain the values of the searched independent variables, namely, the new compensation code drives the switch control signal in the adjustable capacitor array to control the on or off of the capacitor array switch, and measuring the resonance amplitude under the current switch signal setting condition to obtain a new first peak code, searching and adjusting the search algorithm again according to the newly obtained first peak code, and then obtaining a new peak value code and a new compensation code again, searching repeatedly in such a way until the compensation process meets a convergence condition and converges to a capacitor array switch combination with the maximum resonance amplitude, wherein the compensation code in the state is the first compensation code generated by the statistical drift compensation process, writing the first compensation code into the non-volatile memory, and ending the statistical drift compensation process.
5. The method of claim 4, wherein the statistical drift compensation process is controlled by a convergence control signal, the convergence control signal stops the operation of statistical drift compensation after the compensation result meets a convergence condition, and the convergence condition of the convergence control signal includes, but is not limited to, that the peak code phase difference of two or more consecutive times is within an allowable range, or that the compensation code phase difference of two or more consecutive times is within an allowable range, or that the number of times of statistical drift compensation reaches a preset number.
6. The method of claim 2, wherein the temperature drift compensation process generates the second compensation code by: the passive radio frequency identification tag system controls the on or off of a capacitor array switch by using a compensation code which exists, starts a temperature detection and control circuit to work to obtain a PTAT voltage which is in a direct proportion relation with absolute temperature, the PTAT voltage is converted by an analog-to-digital converter to obtain a PTAT code, the PTAT code is input into a digital logic module to be processed, the digital logic module obtains a second compensation code in a temperature drift compensation process by looking up a table by the PTAT code, the second compensation code is used for controlling the on or off of the switch in the adjustable capacitor array, so that the number of capacitors connected into a resonance circuit in the capacitor array and the total resonance capacitance value are changed, an improved resonance amplitude at the temperature is obtained, the second compensation code is written into a non-volatile memory, and the temperature drift compensation process is ended.
7. The method of claim 2, wherein the temperature drift compensation process generates the second compensation code by: the passive radio frequency identification tag system controls the on or off of a capacitor array switch by using a compensation code which exists, starts a temperature detection and control circuit to work to obtain a PTAT voltage which is in a direct proportion relation with absolute temperature, the PTAT voltage is converted by an N-path parallel processing structure to obtain a PTAT code, the PTAT code is input into a digital logic module to be processed, the digital logic module obtains a second compensation code in a temperature drift compensation process by looking up a table by the PTAT code, and controls the on or off of the switch in the adjustable capacitor array by using the second compensation code, so that the number of capacitors accessed into a resonance circuit in the capacitor array and the total resonance capacitance value are changed, an improved resonance amplitude at the temperature is obtained, the second compensation code is written into a non-volatile memory, and the temperature drift compensation process is ended.
8. The method of any of claims 6 or 7, wherein the digital logic module obtains the compensation code from a PTAT code lookup table by the operation method of: the method comprises the steps of storing a table in which PTAT codes representing temperature information and compensation codes are in one-to-one correspondence in a non-volatile memory inside a chip in advance, reading out the compensation code corresponding to the PTAT code obtained by closest measurement from a storage medium during calibration, wherein the compensation code is the compensation code in a temperature drift compensation process and is used for controlling the on or off of a capacitor array switch, so that temperature compensation is completed.
9. The method according to any one of claims 6 or 7, wherein in the temperature drift compensation process, after a certain delay, the temperature detection and control circuit measures the temperature again to obtain a new PTAT code, and performs a table look-up operation again to obtain an updated second compensation code, and controls the capacitor array switch to be turned on or off again with the updated second compensation code, and the above steps are repeated until the temperature drift compensation process is completed, and the updated second compensation code is written into the non-volatile memory, and the temperature drift compensation process is completed.
10. A control circuit for implementing the method of any one of claims 1 or 4, wherein: the control circuit comprises a resonant circuit consisting of a resonant inductor and a resonant capacitor, a peak value detection module, an analog-to-digital converter and a logic control module, wherein the resonant capacitor comprises a fixed capacitor array and an adjustable capacitor array, the fixed capacitor array and the adjustable capacitor array are connected to two ends of the resonant inductor in parallel, the input end of the peak value detection module is connected to the output end of the resonant circuit, the output end of the peak value detection module is connected to the input end of the analog-to-digital converter, the output end of the analog-to-digital converter is connected to the input end of the logic control module, the output end of the logic control module is connected to the adjustable capacitor array in the resonant circuit, the peak value detection module is used for extracting a resonant amplitude value of the resonant circuit, a digital code representing the resonant amplitude of the resonant circuit is obtained after the analog-to-digital converter, and the first peak value code in the drift compensation process is counted, temporarily storing the first peak code in a register, and then mathematically forming an optimization process by the statistical drift compensation process, wherein the optimization process takes the first peak code as a target function and takes a compensation code as an independent variable; and the logic control module obtains a new compensation code according to the implemented optimization search algorithm after obtaining the first peak code, controls the on or off of the capacitor array switch again by using the new compensation code so as to obtain a new resonance amplitude and a new peak code, obtains the new compensation code again by using the logic control module according to the optimization search algorithm, and repeats the steps until the logic control module converges to a switch combination with the maximum resonance amplitude, wherein the compensation code in the state is the first compensation code generated by the statistical drift compensation process, writes the first compensation code into the non-volatile memory, and ends the statistical drift compensation process.
11. A control circuit for implementing the method of any one of claims 2 or 6, wherein: the control circuit comprises a resonant circuit consisting of a resonant inductor and a resonant capacitor, a rectifying circuit, a power management module and a temperature detection and control circuit, wherein the resonant capacitor comprises a fixed capacitor array and an adjustable capacitor array, the fixed capacitor array and the adjustable capacitor array are connected to two ends of the resonant inductor in parallel, the output end of the resonant circuit is connected to the input end of the rectifying circuit, the output end of the rectifying circuit is connected to the power management module, the output end of the power management module is connected to the temperature detection and control circuit,
the temperature detection and control circuit comprises a reference generation and PTAT voltage generation module, an analog-to-digital converter and a digital logic module, wherein the output end of the power management module is respectively connected to the reference generation and PTAT voltage generation module, the analog-to-digital converter and the digital logic module, the output end of the digital logic module is connected to the adjustable capacitor array in the resonance circuit, the reference generation and PTAT voltage generation module measures the internal temperature of a chip and converts a temperature physical quantity into a PTAT voltage in a direct proportion relation with absolute temperature, the PTAT voltage is converted into a binary code representing the temperature physical quantity through the analog-to-digital converter, namely a PTAT code, the binary code is input into the digital logic module for processing, the digital logic module obtains a second compensation code in a temperature drift compensation process through table lookup of the binary code, and controls the on or off of a switch in the adjustable capacitor array through the second compensation code, therefore, the number of capacitors connected into the resonant circuit in the capacitor array and the total resonant capacitance value are changed, the improved resonant amplitude at the temperature is obtained, the second compensation code is written into the nonvolatile memory, and the temperature drift compensation process is ended.
12. A control circuit for implementing the method of any one of claims 2 or 7, wherein: the control circuit comprises a resonant circuit consisting of a resonant inductor and a resonant capacitor, a rectifying circuit, a power management module and a temperature detection and control circuit, wherein the resonant capacitor comprises a fixed capacitor array and an adjustable capacitor array, the fixed capacitor array and the adjustable capacitor array are connected to two ends of the resonant inductor in parallel, the output end of the resonant circuit is connected to the input end of the rectifying circuit, the output end of the rectifying circuit is connected to the power management module, the output end of the power management module is connected to the temperature detection and control circuit,
the temperature detection and control circuit comprises a reference generation and PTAT voltage generation module, a plurality of comparators and a digital logic module, wherein the reference generation and PTAT voltage generation module outputs a PTAT voltage and a plurality of reference voltages with uniformly distributed voltages, the comparators respectively correspond to the outputs of the reference voltages with uniformly distributed voltages, the PTAT voltage generation module generates a PTAT voltage in a positive proportional relation with absolute temperature and inputs the PTAT voltage to the positive input ends of the comparators, the reference voltages with uniformly distributed voltages are respectively input to the negative input ends of the comparators, the comparators respectively output PTAT codes according to comparison results, the PTAT codes are input to the digital logic module for processing, the digital logic module obtains a second compensation code in a temperature drift compensation process by looking up a table through the PTAT codes, and controls the on or off of a switch in the adjustable capacitor array by the second compensation code, therefore, the number of capacitors connected into the resonant circuit in the capacitor array and the total resonant capacitance value are changed, an improved resonant amplitude at the temperature is obtained, the second compensation code is written into the nonvolatile memory, and the temperature drift compensation process is finished.
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