WO2023155459A1

WO2023155459A1 - Automatic compensation method for statistical drift and temperature drift of rfid resonant frequency, and circuits

Info

Publication number: WO2023155459A1
Application number: PCT/CN2022/126033
Authority: WO
Inventors: 吴边
Original assignee: 卓捷创芯科技（深圳）有限公司
Priority date: 2022-02-16
Filing date: 2022-10-19
Publication date: 2023-08-24
Also published as: CN114189212B; CN114189212A

Abstract

The present invention belongs to the technical field of radio frequency identification. Specifically provided are an automatic compensation method for statistical drift and temperature drift of RFID resonant frequency, and circuits. The present application provides a complete calibration compensation technique for the impact of statistical drift and temperature drift on resonance performance, which a radio frequency identification tag chip product faces; and the automatic compensation for statistical drift enables a step, in which a special device is used for calibration, to be omitted from a finished product production process for a radio frequency identification tag, thus greatly increasing the production efficiency and yield. The present application further comprises an automatic compensation technique for temperature drift of a resonance circuit, in which multiple different implementation solutions are used for products having different fine logical control requirements, thus fundamentally solving the impact of temperature drift on resonant frequency. A frequency calibration process performed after power-on reset, which is disclosed by the present application, definitely provides control steps for statistical drift and temperature drift compensation, and a guiding thought thereof can be developed into a more general circuit compensation technique in the field of low-power-consumption wireless communications.

Description

Method and circuit for automatically compensating RFID resonant frequency statistics and temperature drift

technical field

The invention belongs to the technical field of radio frequency identification, and specifically refers to a method for automatic calibration and compensation for the drift of the resonant frequency of a passive passive radio frequency identification tag (RFID) resonant circuit due to statistical factors and temperature factors, and realizes the method circuit.

Background technique

Radio frequency identification technology is one of the lowest core hardware technologies in the field of Internet of Things. The radio frequency identification tag chip made of radio frequency identification technology in the form of an integrated circuit using an integrated semiconductor manufacturing process is the basic component of the core technology in this field. The radio frequency identification tag chip is packaged in some form and connected with a number of peripheral devices to form the core circuit system of the radio frequency identification tag; the core circuit system is sealed and packaged by plastic packaging technology or glass packaging technology, which can be made into a suitable RFID tags for various applications. The role of finished radio frequency identification tags in the main application fields such as logistics management and item monitoring is mainly to respond, and the content of the response can be as simple as reporting the ID number of the tag itself for data entry and tracking purposes, and can also include Some advanced applications, such as reading and writing operations on the finished label, writing user data into the finished label, and so on. Among them, the written data is stored in the non-volatile NVM (Non-Volatile Memory) memory unit, such as OTP (One-Time Programmable), MTP (Multiple-Time Programmable) or EEPROM (Electronically Erasable Programmable Read-Only Memory) and other storage units.

Passive RFID tags are tag products that do not have an external power supply or battery power supply. Because of their low manufacturing and maintenance costs, they are more suitable for promotion in market applications. The power source of the passive passive RFID tag is to rely on the peripheral inductive coil connected to the RFID chip to couple the surrounding magnetic field energy, and generate resonance to form an alternating current in the coil, which is the so-called Faraday electromagnetic induction principle. Since the energy obtained by induction is very limited, there are different degrees of restrictions on the read and write operations of memories with different specifications; for chip design, this limitation becomes a challenge for low-power system design in the field of microelectronics.

Usually, the communication process of passive passive radio frequency identification is that the magnetic induction coil of the tag reading and writing device first emits electromagnetic field energy of a specific frequency, and as a connection port with the outside world, the external inductive coil of the passive passive radio frequency identification tag can couple the surrounding The electromagnetic field energy, and the capacitor connected to the port inside the chip form an LC resonant circuit, which converts the magnetic field energy into AC power in the resonant circuit, and after rectification, it becomes a DC current, thereby supplying power to the chip. The main performance index of the passive passive RFID tag is its communication distance, that is, the RFID tag can also perform reliable uplink and downlink transmission at the far end of the read-write device; the farther the uplink and downlink communication distance can be guaranteed, the better its performance. The higher it is, the focus of product competition in the industry.

In order to obtain a longer communication distance, the passive passive RFID tag chip itself needs to achieve very small power consumption, that is, the power required for its operation is as small as possible. This involves a series of low-power consumption communication circuit design issues, which are not within the scope of the issues described in this application, and will not be discussed here. Under the condition of satisfying the same power consumption, the energy collection and coupling efficiency of the resonant circuit composed of the inductance coil and the built-in capacitor on the passive passive RFID tag chip becomes the key to improving the communication distance of the passive RFID tag chip.

The ISO11784/11785 animal radio frequency identification international standard defines a half-duplex radio frequency identification technology standard based on half-duplex communication technology. In this technical standard, the radio frequency identification tag chip adopts frequency shift keying technology (Frequency Shift Keying, or FSK). Among them, the resonant frequency is directly determined by the inductance value and capacitance value in the resonant circuit, and has nothing to do with the frequency of the radio frequency field issued by the reader device, because according to the ISO11784/11785 animal radio frequency identification technical standard, during uplink transmission, the reader The writer device is in the off state, hence the name "half-duplex". In frequency shift keying technology, the data "1" and "0" are represented by two different frequencies, and these two different frequencies are switched by the capacitor array switch in the resonant circuit of the RFID tag. of. Therefore, the accuracy of the capacitance value, that is, the accuracy of the frequency will directly affect the communication performance of FSK.

As we all know, the resonant circuit of a common passive passive RFID tag is an LC resonant circuit composed of an inductor and a capacitor. The inductor and capacitor values must meet:

The resonant circuit will have a higher coupling degree, that is, obtain higher energy, where f ₀ is the coupled external input carrier resonance frequency, L is the inductance value of the inductor coil, and C is the capacitance value of the built-in resonant capacitor. For passive RFID tags in the low-frequency band, such as the low-frequency resonant frequency specified in the ISO11784/11785 animal RFID international standard is 134.25KHz, because the inductance and capacitance must reach relatively large values and not It may be completely integrated inside the chip, especially the inductance value is far beyond the range that the inductance device in the integrated circuit chip can achieve, and its resonant inductance coil must be external to the chip. In the packaging process of small-sized glass tube RFID tags, a magnetic core made of ferrite material is often used as the core of the external coil winding, and the high magnetic permeability of the magnetic core is used to improve the quality factor of the inductance, thereby improving the resonance coupling In some cases, in order to save the manufacturing cost of the chip, part of the resonant capacitor will also be placed outside the chip, so the resonant capacitor of the entire resonant circuit is added by the discrete capacitive components outside the chip and the internal capacitance of the chip made.

In the production practice of large-scale mass production of passive passive RFID tags, because the inductance value of the external inductor or the capacitance value of the capacitor presents a certain statistical law with the change of the production batch of the discrete component, such as Gaussian distribution, etc., at the same time The magnetic cores used will also have deviations in the manufacturing process, resulting in a certain statistical distribution of the magnetic permeability. The drift of these parameters can be classified into the same category and called statistical drift . The statistical drift of the above parameters causes the drift of the center frequency of the resonant circuit of the passive radio frequency tag. As shown in the relationship curve between resonance amplitude and frequency as shown in Figure 1, I ₀ is the maximum value of the resonance amplitude, corresponding to the optimum resonance frequency f ₀ ; while I ₀ of 0.707 times is -3dB when the resonance amplitude reaches the maximum amplitude, that is, the power Reaching 50% of the optimum resonant power corresponds to two frequency points f _L and f _H on the frequency axis that are less than and greater than the optimum resonant frequency f ₀ respectively; it can be seen from the curve of the resonance waveform amplitude changing with frequency in Figure 1 It is shown that when the frequency of the resonant circuit formed by the inductance and capacitance deviates from the value that reaches the optimal resonance, the coupling efficiency of the resonant circuit will be greatly reduced, making the passive passive RFID tag unable to achieve the optimal resonance amplitude, thus As a result, the yield rate of finished label products is reduced due to insufficient communication distance. Therefore, the primary element of resonant circuit design is to ensure that the external discrete inductance and capacitance can achieve the value that produces the optimal resonance amplitude f ₀ .

In order to solve the above-mentioned problem of statistical drift, a method of connecting or not connecting part of the resonant capacitor according to the deviation of the external components of the resonant circuit is mostly adopted in chip design. The specific method is that a switch composed of a group of MOS transistors inside the chip is connected in series with the adjustable internal resonant capacitor. When the system decides to connect the capacitor, the MOS switch is connected and closed, and the capacitor is connected in parallel with other resonant capacitors. The relationship, so its capacitance is added to the resonant capacitor, as shown in Figure 2.

The practice of the prior art will bring two new problems, which are respectively elaborated as follows.

First, since the RFID tag chip we are concerned about is passive, all its energy sources come from the field energy coupled through resonance; only when the field energy is large enough will the power-on reset of the chip system be triggered Signal, after the power-on reset signal is activated, the digital logic circuit inside the chip will enter the normal working state, and then the control logic signal will distinguish the high-level voltage or low-level voltage with electrical significance, that is, it will start to play The role of the switch control. With the above switch control signal, the adjustable part of the resonant capacitor to be connected to the above resonant circuit can be connected, so as to achieve the best resonant state. It is clear that the resonant circuit of the passive RFID tag is detuned until the coupled energy reaches the power-on-reset level. In the detuned state, the efficiency of the resonant circuit coupling field energy is low, and the resonant circuit and its system load circuit inevitably have leakage current flowing into the ground, the voltage on both ends of the resonant circuit will be coupled with The accumulation of energy shows a gradually increasing process curve, and the process curve is relatively flat in a long period of time, that is, the passive RFID tag must be coupled for a long period of time before it can obtain enough energy and further Enter the best resonance state and start working. When comparing the communication performance of similar tags with a longer distance from the reader device, this period of energy coupling stage with a gentle rise may fail to reach a certain energy level and ultimately fail to obtain enough energy. Therefore, such an inefficient coupling process directly affects the communication distance of the passive passive RFID tag.

Second, even if the above-mentioned first problem is solved, the devices in the resonant circuit of the passive passive RFID tag chip will still drift with the change of the ambient temperature in terms of inductance and capacitance. The problem of device characteristics changing with temperature changes is well known in the industry and becomes an inherent non-ideal characteristic of the device. When the ambient temperature changes, the inductance and capacitance will change to a certain extent, and the magnetic permeability of the magnetic core will also change. In the above statistical drift problem, the resonant circuit is turned on or off by the MOS switch. The capacitance that is connected or disconnected due to disconnection will also change with the change of temperature, and this part of the drift is not solved by the existing technology. Therefore, in the application, the passive passive RFID tag chip will 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 not only directly affects the energy transmission efficiency from the reader to the tag in the energy harvesting stage, but also affects the accuracy of the uplink FSK frequency in the uplink transmission stage from the tag to the reader. The temperature drift of these two stages must be considered in the design stage and compensated by circuit technology.

In order to improve the detuning state of the passive passive RFID tag chip before the resonant capacitor controlled by the MOS switch is connected, the existing technology tends to reduce the proportion of the adjustable resonant capacitor in the total resonant capacitor, that is, only a few logic switches are used to control Part of the resonant capacitor is connected or not, so that before the resonant capacitor controlled by the MOS switch is connected, the detuning of the resonant circuit is reduced to a small degree, which allows the passive radio frequency tag to quickly cross the lower The stage of even and efficiency, so as to quickly reach the best resonance. However, this approach makes the adjustment range of the resonant capacitor very small. For the case where the inductance or capacitance of the external discrete inductor or capacitor changes greatly and exceeds the adjustable range, the internal capacitance is supplemented by switching the MOS switch. The approach to the resonant circuit is still not enough to achieve the optimum resonant frequency.

In the production practice of RFID tags, for the resonance frequency deviation caused by the statistical drift of discrete components, calibration equipment needs to be specially equipped in the mass production process, and passive passive RFID tags are searched one by one through antenna coupling. Algorithm Calibration. Different brands of radio frequency identification tags have different calibration instructions and read-write instructions, so that mass production and processing plants have to finely distinguish the matching between the calibration read-write equipment and the chip type processed by the incoming material. Obviously, this extra step greatly increases the production cost.

In order to improve the drift of the resonant circuit device characteristics of the passive passive RFID tag chip with temperature, the current practice is to use devices with relatively small drift with temperature changes, such as capacitors with higher manufacturing grades, or temperature characteristics A better ferrite material is used as a magnetic bar for an inductance coil, etc. This inevitably increases the manufacturing cost and cannot fundamentally solve this problem.

technical problem

The purpose of the present invention is to solve the problem that the existing RFID resonant circuit drifts due to statistical factors and temperature factors, and proposes a method and circuit structure for automatic calibration and compensation for the drift, so as to improve the production efficiency and yield of products.

technical solution

In order to achieve the above object, the technical solution adopted by the present invention is: a method for automatically compensating RFID resonance frequency statistics and temperature drift, and the process included in the method is:

S0, after the passive RFID tag system is powered on and reset, first check whether there is a compensation code in the preset non-volatile memory address, if there is no compensation code, then the passive RFID tag system enters the statistical drift of the resonance frequency Compensation process, after the statistical drift compensation process ends, the passive radio frequency identification tag system ends the automatic resonance frequency compensation process and enters the normal startup state; if there is already a compensation code and the compensation code does not need to be updated, the passive radio frequency identification tag system ends automatically The resonant frequency compensation process enters the normal startup state; if there is already a compensation code and the compensation code needs to be updated, it is judged whether statistical drift compensation is required. If necessary, the passive RFID tag system enters the statistical drift compensation process of the resonant frequency until the end ;

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, and switch the capacitor array in this state The state value, that is, the first compensation code, is written into the non-volatile memory unit, and the statistical drift compensation process is ended.

Further, in the automatic resonant frequency compensation process, when it is judged that statistical drift compensation is not required, the passive radio frequency identification tag system enters the temperature drift compensation process, and the temperature drift compensation process is to access the adjustable capacitor array The number of capacitors in the resonant circuit is controlled and adjusted so that the resonance amplitude can still reach the maximum under the condition of temperature change. After the temperature drift compensation is completed, the passive RFID tag system will use the state value of the capacitor array switch in this state, namely The second compensation code is written into the non-volatile memory unit, and the temperature drift compensation process is ended.

The technical solution to achieve the purpose of the present invention further includes that the method for generating the first compensation code in the statistical drift compensation process is as follows: the passive radio frequency identification tag system generates the initial compensation code to control the on or off of the capacitor array switch, and starts Statistical drift compensation process; in the process, a peak value detection circuit is used to extract the resonance amplitude value of the resonant circuit in this state, and a digital code representing its resonance amplitude is obtained through conversion of an analog-to-digital converter, that is, in the statistical drift compensation process The first peak code, the first peak code is temporarily stored in the register, and then the statistical drift compensation process forms an optimization with the first peak code as the objective function and the compensation code as the independent variable in mathematics Process; after the logic control module obtains the first peak value code, the search of the independent variable is carried out through the optimization algorithm, and the value of the searched independent variable group, that is, the new compensation code, is used to drive the switch control signal in the adjustable capacitor array to control The capacitor array switch is turned on or off, and the resonance amplitude amplitude under the current switch signal setting condition is measured to obtain a new first peak code, and the search algorithm is searched and adjusted again according to the newly obtained first peak code, so as to obtain A new peak code and a new compensation code are searched repeatedly until the compensation process satisfies a convergence condition and converges to a capacitor array switch combination with the maximum resonance amplitude. The compensation code in this state is statistical drift compensation The process generates the first compensation code, writes the first compensation code into the non-volatile memory, and ends 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 is: the passive radio frequency identification tag system uses the existing compensation code to control the switching on or off of the capacitor array switch, Start the temperature detection and control circuit to work to obtain a PTAT voltage proportional to the absolute temperature. The PTAT voltage is converted by an analog-to-digital converter to obtain a PTAT code, and the PTAT code is input into a digital logic module for processing. The digital logic The module obtains the second compensation code in the temperature drift compensation process from the PTAT code look-up table, and uses the second compensation code to control the switch in the adjustable capacitor array to be turned on or off, thereby changing the The number of capacitors connected to the resonant circuit and the overall resonant capacitance value are obtained to obtain an improved resonance amplitude at the temperature, the second compensation code is written into the non-volatile memory, and the temperature drift compensation process is ended.

Alternatively, the passive radio frequency identification tag system uses the existing compensation code to control the on or off of the capacitor array switch, starts the temperature detection and control circuit to work, and obtains the PTAT voltage proportional to the absolute temperature, and the PTAT voltage passes through The conversion of an N-way parallel processing structure obtains the PTAT code, and the PTAT code is input into the digital logic module for processing, and the digital logic module obtains the second compensation code in the temperature drift compensation process by looking up the table of the PTAT code, so that The above-mentioned second compensation code controls the switches in the adjustable capacitor array to be turned on or off, thereby changing the number of capacitors connected to the resonant circuit in the capacitor array and the overall resonant capacitance value, and obtaining an improved The resonant amplitude, write the second compensation code into the non-volatile memory, and end the temperature drift compensation process.

Another technical solution of the present invention is to provide a control circuit for implementing the above statistical drift compensation process, 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: a fixed capacitor array and an adjustable capacitor array, the fixed capacitor array and the adjustable capacitor array are connected in parallel to both ends of the resonant inductor, and the input terminal of the peak detection module is connected to the output of the resonant circuit end, the output end of which 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, and the output end of the logic control module is connected to the resonant circuit. Capacitor adjustment array, the peak detection module is used to extract the resonance amplitude value of the resonance circuit, and obtain a digital code representing its resonance amplitude after passing through the analog-to-digital converter, that is, the first peak code in the statistical drift compensation process, and the described In the first peak code temporary storage register, then the statistical drift compensation process forms an optimization process with the first peak code as the objective function and the compensation code as the independent variable in mathematics; the logic control module obtains the obtained After the first peak code, a new compensation code is obtained according to the optimized search algorithm implemented, and the new compensation code is used to control the conduction or shutdown of the capacitor array switch again, thereby obtaining a new resonance amplitude and a new peak code, and again The new compensation code is obtained by the logic control module according to the optimization search algorithm, and the cycle is repeated until the logic control module converges to a switch combination with the maximum resonance amplitude. The compensation code in this state is the first compensation code generated by the statistical drift compensation process , write the first compensation code into the non-volatile memory, and end the process of statistical drift compensation.

The technical solution of the present invention also includes providing a control circuit for realizing the above-mentioned temperature drift compensation process, the control circuit includes a resonant circuit composed of a resonant inductor and a resonant capacitor, a rectifier 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 both ends of the resonant inductor, and the output end of the resonant circuit is connected to the input end of the rectifier circuit , the output end of the rectification circuit is connected to the power management module, and the output end of the power management module is connected to the temperature detection and control circuit,

The temperature detection and control circuit includes a reference generation and PTAT voltage generation module, an analog-to-digital converter and a digital logic module, and the output terminals of the power management module are respectively connected to the reference generation and PTAT voltage generation module, the analog-to-digital converter and a digital logic module, the output of the digital logic module is connected to the adjustable capacitor array in the resonant circuit, the reference generation and PTAT voltage generation module measures the internal temperature of the chip, and converts the temperature physical quantity into an absolute temperature The PTAT voltage in direct proportion, the PTAT voltage is converted into a binary code representing the physical quantity of temperature through an analog-to-digital converter, that is, a PTAT code, and the binary code is input into the digital logic module for processing, and the digital logic module is determined by the The second compensation code in the temperature drift compensation process is obtained by looking up the binary code table, and the switch in the adjustable capacitor array is controlled to be turned on or off with the second compensation code, thereby changing the access resonance in the capacitor array The number of capacitors of the circuit and the overall resonance capacitance value obtain an improved resonance amplitude at the temperature, write the second compensation code into the non-volatile memory, and end the temperature drift compensation process.

The control circuit can also be: a resonant circuit composed of a resonant inductor and a resonant capacitor, a rectifier 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 both ends of the resonant inductor, the output end of the resonant circuit is connected to the input end of the rectifier circuit, the output end of the rectifier circuit is connected to the power management module, and the power management module The output terminal is connected to the temperature detection and control circuit,

The temperature detection and control circuit includes a reference generation and a PTAT voltage generation module, which outputs one PTAT voltage and a reference voltage with uniform distribution of multiple voltages, and a plurality of comparators respectively corresponding to the output of the multiple reference voltages, the The PTAT voltage generating module generates a PTAT voltage proportional to the absolute temperature and inputs it to the positive input terminals of the comparators, and the multiple reference voltages are respectively input to the negative input terminals of the comparators, and the multiple comparators According to the results of the comparison, the PTAT codes are output respectively, and the PTAT codes are input into the digital logic module for processing, and the digital logic module obtains the second compensation code in the temperature drift compensation process from the table lookup of the PTAT code, and uses the second The compensation code controls the switch on or off in the adjustable capacitor array, thereby changing the number of capacitors connected to the resonant circuit in the capacitor array and the overall resonant capacitance value, and obtaining an improved resonance amplitude at this temperature , write the second compensation code into the non-volatile memory, and thus end the temperature drift compensation process.

Beneficial effect

The beneficial effect of the present invention is that: this application proposes a complete calibration compensation technology for the impact of statistical drift and temperature drift on resonance performance faced by radio frequency identification tag chip products, especially, the automatic compensation for statistical drift makes the radio frequency identification tag A process of calibration with special equipment is omitted in the finished product processing process, which greatly improves production efficiency and yield, and has significant economic value. The technology of this application also includes the automatic compensation technology for the temperature drift of the resonant circuit, and uses a variety of different implementation schemes for products with different refined logic control requirements, fundamentally solving the influence of temperature drift on the resonant frequency. The frequency calibration process after power-on reset proposed by the technology of this application clearly proposes control steps for implementing statistical drift and temperature drift compensation, and its guiding idea can be extended to a more general circuit compensation technology in the field of low-power wireless communication.

Description of drawings

Figure 1 is a graph showing the relationship between antenna coupling signal amplitude and resonance frequency;

Fig. 2 is the capacitor array circuit diagram of switch control;

Fig. 3 is a block diagram of an embodiment of the automatic resonance frequency compensation control process of the present invention;

Fig. 4 is a block diagram of the second embodiment of the automatic resonance frequency compensation control process of the present invention;

Fig. 5 is the circuit diagram of statistical drift compensation feedback control of the present invention;

FIG. 6 is a control circuit diagram of Embodiment 1 of temperature drift compensation of the present invention;

Fig. 7 is a schematic structural diagram of Embodiment 2 of the temperature detection and control circuit in Fig. 6;

FIG. 8 is a graph showing the relationship between the reference voltage, V _PTAT voltage and temperature in the second embodiment of temperature drift compensation in FIG. 7 .

Embodiments of the present invention

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

First define several nouns used in this technical solution:

Peak Code – the binary code obtained after analog-to-digital conversion of the resonance amplitude;

Compensation code – the binary code composed of the switch control signal of the adjustable capacitor array, such as "1" when the switch is turned on, and "0" when the switch is turned off;

PTAT voltage - the voltage proportional to the absolute temperature (PTAT is Proportional T o A bsolute T temperature)

PTAT Code - The binary code obtained after analog-to-digital conversion of the PTAT voltage.

As shown in Figure 3, it is a block diagram of the automatic resonance frequency compensation control flow of the present invention. The automatic resonance frequency compensation flow includes two parts: statistical drift compensation and temperature drift compensation. The specific flow is:

The method for generating the first compensation code in the above-mentioned statistical drift compensation process is as follows: the passive radio frequency identification tag system generates an initial compensation code to control the conduction or shutdown of the capacitor array switch, and starts the statistical drift compensation process; The circuit extracts the resonance amplitude value of the resonant circuit in this state, and through the conversion of the analog-to-digital converter, a digital code representing its resonance amplitude is obtained, that is, the first peak code in the statistical drift compensation process, and the first peak code is converted to In the temporary storage register, then the statistical drift compensation process forms an optimization process with the first peak code as the objective function and the compensation code as the independent variable in mathematics; after the logic control module obtains the first peak code , search the independent variables through the optimization algorithm, and use the searched independent variable group value, that is, the new compensation code, to drive the switch control signal in the adjustable capacitor array to control the on or off of the capacitor array switch, and measure the current Switch the resonance amplitude under the condition of signal setting to obtain a new first peak code, and the search algorithm performs search adjustment again according to the newly obtained first peak code, so as to obtain a new peak code and a new compensation code again, and so on. Search repeatedly until the compensation process satisfies a convergence condition and converges to a capacitor array switch combination with the maximum resonance amplitude. The compensation code in this state is the first compensation code generated by the statistical drift compensation process. The compensation code is written to non-volatile memory, and the statistical drift compensation process is ended.

The initial compensation code can select any intermediate value, minimum value (that is, all "0" codes, representing all off), or maximum value (that is, all "1" codes, represents full conduction). The statistical drift compensation process can also be controlled by a convergence control signal, and the signal can stop the statistical drift compensation operation after the compensation result satisfies the convergence condition. There are several optional convergence conditions for the convergence control signal. For example, if the difference between two or several consecutive compensation codes or peak codes is within an allowable range, it indicates that the compensation has reached the best state and there is almost no room for further improvement; Alternatively, the compensation operation can be stopped when the number of times of statistical compensation reaches a preset number of times. There are many search algorithms with different characteristics in the optimization theory branch of applied mathematics, and no specific description will be given here for the search algorithms implemented by the logic control circuit. The specific implementation of the peak detection circuit can refer to the authorized announcement number applied by the applicant on May 28, 2021: CN 113255382 B, titled "A Discharge Control Circuit and Method Driven by a Radio Frequency Field Envelope Peak Detection Signal".

For a fixed RFID tag, the statistical drift of the resonant circuit components is a fixed offset, so in the actual application scenario of the RFID tag, the statistical drift compensation operation of the resonant frequency does not need to be normalized, but It is only necessary to obtain the RF field energy activation once in the quality inspection of the first batch of products. In the non-volatile memory of the radio frequency identification tag, it can be set that the statistical drift compensation operation will no longer be performed, so that in the next power-on process, the process can directly enter the local temperature drift compensation operation process at that time. Of course, for RFID tags with a long service life, it is also optional to perform statistical drift compensation again, so that the communication performance of the RFID tag products with a long service life can be further optimized.

In the automatic resonant frequency compensation process, if there is already a compensation code and the compensation code needs to be updated, it is judged whether statistical drift compensation is required, if necessary, the passive radio frequency identification tag system enters the above statistical drift compensation process until the end, when judged When statistical drift compensation is not required, the passive RFID tag system enters the temperature drift compensation process, which is to control and adjust the number of capacitors connected to the resonant circuit in the adjustable capacitor array, so that the resonance The amplitude can still reach the maximum under the condition of temperature change. After the temperature drift compensation is completed, the passive RFID tag system writes the state value of the capacitor array switch in this state, that is, the second compensation code, into the non-volatile memory unit, and This completes the temperature drift compensation process.

As shown in Figure 3, the method for generating the second compensation code in the above temperature drift compensation process is as follows: the passive RFID tag system uses the existing compensation code to control the conduction or shutdown of the capacitor array switch, and starts the temperature detection and control circuit to work , to obtain the PTAT voltage proportional to the absolute temperature, the PTAT voltage is converted by an analog-to-digital converter to obtain a PTAT code, and the PTAT code is input into a digital logic module for processing, and the digital logic module is checked by the PTAT code The second compensation code in the temperature drift compensation process is obtained from the table, and the switch in the adjustable capacitor array is controlled to be turned on or off by using the second compensation code, thereby changing the capacitance of the capacitor array connected to the resonant circuit. number and the overall resonance capacitance value to obtain an improved resonance amplitude at the temperature, write the second compensation code into the non-volatile memory, and end the temperature drift compensation process.

The method for generating the second compensation code in the temperature drift compensation flow can also be: the passive radio frequency identification tag system uses the existing compensation code to control the conduction or shutdown of the capacitor array switch, and starts the temperature detection and control circuit to work to obtain the same The absolute temperature is directly proportional to the PTAT voltage. The PTAT voltage is converted by an N-way parallel processing structure to obtain the PTAT code. The PTAT code is input into the digital logic module for processing, and the digital logic module looks up the table by the PTAT code. Obtain the second compensation code in the temperature drift compensation process, and use the second compensation code to control the switch on or off in the adjustable capacitor array, thereby changing the number of capacitors connected to the resonant circuit in the capacitor array and the overall resonance capacitance value to obtain an improved resonance amplitude at the temperature, write the second compensation code into the non-volatile memory, and end the temperature drift compensation process.

The operation method for the digital logic module to obtain the compensation code by looking up the table of the PTAT code is as follows: pre-store the one-to-one correspondence table between the PTAT code representing the temperature information and the compensation code in the non-volatile memory inside the chip, and store the most The compensation code corresponding to the measured PTAT code is read from the storage medium. This compensation code is the compensation code in the temperature drift compensation process, which is used to control the on or off of the capacitor array switch, thereby completing the temperature compensate.

In the above temperature drift compensation process, after a certain delay in the passive RFID tag system, the temperature detection and control circuit measures the temperature again to obtain a new PTAT code, and obtains an updated second compensation code after another table lookup operation , using the updated second compensation code to control the on or off of the capacitor array switch again, repeating this cycle until the end of the temperature drift compensation process, and writing the updated second compensation code into the non-volatile memory . The rate of repeated adjustment of temperature drift compensation depends on the setting of the delay time in the block diagrams shown in Figure 3 and Figure 4. For example, when the RFID tag works in an environment with a large temperature change for a long time, a built-in counter is used to count The number of clock cycles, set an appropriate maximum count value, when the count reaches the maximum number, the temperature drift compensation process starts again. Of course, when the working time of the RFID tag is only tens of milliseconds and is not affected by the condition of continuous temperature change, the maximum count value has not yet been reached, and the RFID tag will automatically power off and complete a response operation; in the latter In an application example, temperature drift compensation is often performed only once. As a result of the temperature drift compensation, a new compensation code is generated, which is used to further update the control of the capacitor array, so that the resonance performance can still be optimized under the condition of temperature change.

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 its working environment, that is, if the RFID tag works in an environment with a relatively constant temperature , then the compensation code written into the non-volatile memory unit is the second compensation code; if it cannot be guaranteed that the temperature when the RFID tag is activated next time is consistent with the current ambient temperature for temperature drift compensation, then only the first compensation code is written. compensation code.

In Figure 3 and Figure 4, because the external resonant device will also change its characteristics over time, the system retains the option to update the compensation code. If you want to update the compensation code, you can perform a statistical drift compensation operation on the basis of the existing compensation code, otherwise, you can directly enter the temperature drift compensation stage to ensure that the temperature factor is considered in the resonance performance adjustment and optimization in the current application. within.

The setting of all the above-mentioned option judgments can be performed by reading the configuration bits, that is, the determination of "yes" and "no" of the above-mentioned options is stored in a memory unit at a specific address in the non-volatile memory of the radio frequency identification tag. For the non-volatile memory, these settings can also be updated and adjusted through the operation of writing the identification tag by the card reader device.

This application proposes a complete calibration compensation technology for the impact of statistical drift and temperature drift on the resonance performance faced by radio frequency identification tag chip products. In particular, the automatic compensation for statistical drift saves the A process of calibration with special equipment greatly improves production efficiency and yield, and has significant economic value. The technology of this application also includes the automatic compensation technology for the temperature drift of the resonant circuit, and uses a variety of different implementation schemes for products with different refined logic control requirements, fundamentally solving the influence of temperature drift on the resonant frequency. The frequency calibration process after power-on reset proposed by the technology of this application clearly proposes control steps for implementing statistical drift and temperature drift compensation, and its guiding idea can be extended to a more general circuit compensation technology in the field of low-power wireless communication.

Another technical purpose of the present invention is to provide a feedback control circuit for realizing the automatic resonant frequency statistical drift compensation and temperature drift compensation of the radio frequency identification tag.

Fig. 5 is the statistical drift compensation feedback control circuit diagram of the present invention, and described control circuit comprises the resonant circuit that is made up of resonant inductance and resonant capacitor, peak detection module, analog-to-digital converter and logic control module, and described resonant capacitor includes fixed capacitance array and There are two parts of the adjustable capacitor array, the fixed capacitor array and the adjustable capacitor array are connected in parallel to both ends of the resonant inductor, the input end of the peak detection module is connected to the output end of the resonant circuit, and its output end is connected to the 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, and the peak detection module It is used to extract the resonant amplitude value of the resonant circuit, and obtain a digital code representing its resonant amplitude after passing through the analog-to-digital converter, that is, the first peak code in the statistical drift compensation process, and store the first peak code in the temporary register, Then the statistical drift compensation process forms an optimization process with the first peak code as the objective function and the compensation code as the independent variable in mathematics; after the logic control module obtains the first peak code, according to the implemented The optimized search algorithm obtains a new compensation code, and the new compensation code is used to control the conduction or shutdown of the capacitor array switch again, thereby obtaining a new resonance amplitude and a new peak code, which are obtained by the logic control module according to the optimized search algorithm. The new compensation code is repeated in this way until the logic control module converges to a switch combination in which the resonance amplitude reaches the maximum. The compensation code in this state is the first compensation code generated by the statistical drift compensation process. Write the first compensation code into non-volatile memory and the statistical drift compensation process ends.

The analog-to-digital converter (ADC) in Figure 5 can choose a variety of analog-to-digital converters in the form of low-power architectures, such as primary and secondary approximation analog-to-digital converters and time-domain digital converters. repeat.

The above-mentioned resonance frequency statistical drift compensation feedback control circuit is a structure of a negative feedback loop. It can be seen from the relationship curve between resonance amplitude and frequency shown in Figure 1 that when the resonance frequency reaches the optimum frequency point, the resonance amplitude reaches the maximum. According to this principle, in the circuit technology shown in Figure 5, we adopt the structure of extracting the resonant amplitude value of the resonant circuit by the peak detection circuit, through a low-power analog-to-digital converter, we obtain a value representing the resonant amplitude The digital code is the first compensation code in the flow of statistical drift compensation in Fig. 3 and Fig. 4 .

Using the output of the peak detection circuit as the standard structure for judging and optimizing the adjustable capacitor array in the resonant circuit, of course, can also be extended to the resonant frequency compensation technology for temperature drift. For the application field of RFID tags with active power supply or semi-active power supply, RFID tags often have some real-time monitoring functions, such as temperature monitoring, humidity monitoring, or object proximity monitoring, etc. At this time, the continuous change of ambient temperature will It affects the resonant frequency of the RFID tag, resulting in a drift in communication performance. In this case, as shown in Figure 5, the statistical drift compensation process with the peak detection circuit as the core is also carried out based on the current ambient temperature of the passive RFID tag. In the process of performing the statistical drift compensation process, essentially It is also possible to compensate the temperature drift of the label at the ambient temperature.

Further expansion, in a system where the resonant circuit is in a continuous working state, the resonant frequency compensation technology with the peak detection circuit as the core, plus an ultra-low power analog-to-digital converter and the digital logic associated with it The control module can play a key role in real-time adjustment of the performance of the resonant circuit. Based on the same signal processing idea, the peak detection circuit can be replaced by the common-mode voltage detection of the input signal voltage at both ends of the antenna, or the average voltage detection, corresponding to slightly different common-mode voltage extraction circuits, average voltage extraction circuits, etc.

For passive RFID tags, the compensation for the resonant frequency caused by statistical drift using the above technology can only use a one-time operation process, which is sufficient to meet the performance requirements required by product applications; for frequency compensation caused by temperature drift , a more concise technology in this application is more suitable for the low power consumption requirements of passive radio frequency identification tag chips. Figure 6 is a control circuit diagram of a temperature drift compensation embodiment of the present invention. A resonant circuit, a rectifier circuit, a power management module, and a temperature detection and control circuit are formed. The resonant capacitor includes two parts: a fixed capacitor array and an adjustable capacitor array, and the fixed capacitor array and the adjustable capacitor array are connected in parallel to the resonant capacitor. Both ends of the inductor, the output end of the resonant 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, and the output end of the power management module is connected to the temperature detection and control circuit,

The fixed capacitor part in the internal resonant circuit of the semiconductor chip, and the law of the semiconductor device characteristics of the adjustable capacitor array changing with the temperature drift, can often be described by an accurate semiconductor device model. In today's semiconductor wafer production mostly adopts the OEM mode of entrusted processing and production, the device models of the wafer foundry include parameters that key characteristics change with temperature changes, so that such performance changes can be accurately calculated in computer simulations. Estimation and Simulation. Based on this cognition, Figure 6 shows the architecture of the temperature drift compensation circuit control circuit. Compared with the detection-sensing-feedback-re-detection loop structure in Figure 5, the loop structure in Figure 6 simplifies the detection-sensing part, that is, in addition to rectifying the DC power supply as a power supply, this loop structure does not get from the resonant circuit Measure the physical quantity related to the resonance parameter; for the resonance frequency compensation caused by the temperature drift, the method of detecting the voltage difference between the semiconductor P-N representing the temperature physical quantity on the chip is adopted, and the voltage difference is converted into a digital binary code, by comparing the binary code The direct corresponding relation between compensation and resonant frequency adopts the combined switch control of the adjustable capacitor array.

As shown in Figure 6, the radio frequency identification tag circuit rectifies the AC power into a DC power supply vdda through the energy harvesting function of the resonant circuit, which is used as the input of the power management module; the output of the power management module enables the reference generation and the PTAT voltage generation module to start; then the reference The generation and PTAT voltage generation module measures the internal temperature of the chip. According to the temperature characteristics of the semiconductor P-N junction, it converts the temperature physical quantity into a PTAT voltage, that is, a current proportional to the absolute temperature (Proportional to Absolute Temperature); the PTAT voltage passes through A low-power analog-to-digital converter (ADC) is converted to obtain a binary code representing a physical quantity of temperature and input it to the digital logic module for processing; the digital logic module is based on the known physical characteristics of the variable capacitance of the adjustable capacitor with temperature , that is, the look-up table built in the non-volatile memory cell array can perform an operation of compensating the adjustable capacitor array.

The analog-to-digital converter (ADC) in Figure 6 can choose a variety of analog-to-digital converters in the form of low-power architectures, such as primary and secondary approximation analog-to-digital converters and time-domain digital converters, etc. repeat.

Further, under the guidance of the same spirit of signal processing ideas, the part of the PTAT temperature physical quantity output to the analog-digital converter-digital logic module in Figure 6 can have a variety of simplified implementation forms, that is, direct switch logic control (Direct Switch Logic Control). This implementation bypasses the analog-to-digital conversion and is suitable for simple adaptive logic control. The reason why the logic of temperature drift compensation can be simplified into direct switching logic is mainly because the temperature drift characteristics of the capacitor array are known at the design stage and can be easily obtained from the device model through simulation. Therefore, in addition to quantizing the physical quantity of temperature to binary code, the analog-to-digital converter can be simplified as a series of parallel comparators, where the input of each comparator is a simple voltage-divided output from the PTAT physical quantity, as shown in Figure 8 It shows that the temperature point corresponding to each divided voltage output is known, and the capacitance value change of the capacitor array at each temperature point is also known; the outputs of n parallel comparators are respectively connected to the corresponding The gate is controlled by the switch to achieve the purpose of improving the resonance performance according to the temperature detection result. As shown in FIG. 7, it is a schematic diagram of the implementation structure of the temperature detection and control circuit in this embodiment, and the digital logic control part is omitted in this implementation structure.

In this embodiment, the control circuit includes a resonant circuit composed of a resonant inductor and a resonant capacitor, a rectifier 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 both ends of the resonant inductor, the output end of the resonant 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, and the power management The output terminal of the module is connected to the temperature detection and control circuit,

The temperature detection and control circuit includes a reference generation and PTAT voltage generation module, which outputs one PTAT voltage and a reference voltage with uniform distribution of multiple voltages, and a plurality of comparators respectively corresponding to the output of the multiple reference voltages, the PTAT The voltage generation module generates a PTAT voltage proportional to the absolute temperature and inputs it to the positive input terminal of each comparator, and the multiple reference voltages are respectively input to the negative input terminals of each comparator, and the multiple comparators are based on The results of the comparison are respectively output to obtain PTAT codes, and the PTAT codes are input into the digital logic module for processing, and the digital logic module obtains the second compensation code in the temperature drift compensation process by looking up the table of the PTAT code, and uses the second compensation code The code controls the switch in the adjustable capacitor array to be turned on or off, thereby changing the number of capacitors connected to the resonant circuit in the capacitor array and the overall resonant capacitance value, and obtaining an improved resonance amplitude at this temperature. Write the second compensation code into the non-volatile memory, and end the temperature drift compensation process.

In the control circuit of the above temperature drift compensation process, after the passive radio frequency identification tag system obtains the second compensation code from the table, the control circuit controls the temperature detection and control circuit to measure the temperature again after a certain delay to obtain a new PTAT code , and an updated second compensation code is obtained after the table lookup operation again, and the switching on or off of the capacitor array switch is controlled again with the updated second compensation code, and the cycle repeats until the end of the temperature drift compensation process , writing the updated second compensation code into a non-volatile memory. The rate of repeated adjustment of temperature drift compensation depends on the setting of the delay time in the block diagrams shown in Figure 3 and Figure 4. For example, when the identification tag works in an environment with a large temperature change for a long time, a built-in counter is used to count the clock The number of cycles, set an appropriate maximum count value, when the count reaches the maximum number, the temperature drift compensation process will start again. Of course, when the working time of the RFID tag is only tens of milliseconds and is not affected by the condition of continuous temperature change, the maximum count value has not yet been reached, and the RFID tag will automatically power off and complete a response operation; in the latter In an application example, temperature drift compensation is often performed only once. As a result of the temperature drift compensation, a new compensation code is generated, which is used to further update the control of the capacitor array, so that the resonance performance of the passive RFID tag can still be optimized under the condition of temperature change.

the

Claims

A method for automatically compensating RFID resonant frequency statistics and temperature drift, characterized in that the method includes the following processes:

S0, after the passive RFID tag system is powered on and reset, first check whether there is a compensation code in the preset non-volatile memory address, if there is no compensation code, then the passive RFID tag system enters the statistical drift of the resonance frequency Compensation process, after the statistical drift compensation process ends, the passive radio frequency identification tag system ends the automatic resonance frequency compensation process and enters the normal startup state; if there is already a compensation code and the compensation code does not need to be updated, the passive radio frequency identification tag system ends automatically The resonant frequency compensation process enters the normal startup state; if there is already a compensation code and the compensation code needs to be updated, it is judged whether statistical drift compensation is required. If necessary, the passive RFID tag system enters the statistical drift compensation process of the resonant frequency until the end ;

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, and switch the capacitor array in this state The state value, that is, the first compensation code, is written into the non-volatile memory unit, and the statistical drift compensation process is ended.
The method for automatically compensating for RFID resonance frequency statistics and temperature drift according to claim 1, wherein, in the automatic resonance frequency compensation process, when it is judged that statistical drift compensation is not required, the passive radio frequency identification tag system enters 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 resonance amplitude can still reach the maximum under the condition of temperature change, and the temperature drift compensation ends Afterwards, the passive RFID tag system writes the state value of the capacitor array switch in this state, that is, the second compensation code, into the non-volatile memory unit, and thus ends the temperature drift compensation process.
The method for automatically compensating for RFID resonant frequency statistics and temperature drift according to claim 2, wherein after the temperature drift compensation process ends, the passive radio frequency identification tag system selectively uses the compensation code according to its working environment Writing to the non-volatile memory unit, that is, if the radio frequency identification tag works in an environment with a relatively constant temperature, the compensation code written into the non-volatile memory unit is the second compensation code; if it cannot be guaranteed that the next time the radio frequency identification tag is If the temperature at the time of activation is consistent with the current ambient temperature for temperature drift compensation, only the first compensation code is written.
The method for automatically compensating for RFID resonance frequency statistics and temperature drift according to claim 1, wherein the method for generating the first compensation code in the statistical drift compensation process is: the passive radio frequency identification tag system generates an initial compensation code to control the capacitance The array switch is turned on or off, and the statistical drift compensation process is started; in the process, the peak value detection circuit is used to extract the resonance amplitude value of the resonant circuit in this state, and a value representing its resonance is obtained through the conversion of the analog-to-digital converter. The digital code of the amplitude, that is, the first peak code in the statistical drift compensation process, temporarily stores the first peak code in the register, and then the statistical drift compensation process forms a mathematical formula with the first peak code as The objective function is an optimization process with the compensation code as an independent variable; after the logic control module obtains the first peak value code, the search of the independent variable is carried out through an optimization algorithm, and the value of the searched independent variable group is the new compensation code, Drive the switch control signal in the adjustable capacitor array to control the on or off of the capacitor array switch, and measure the resonance amplitude under the current switch signal setting conditions to obtain the new first peak code. The search algorithm is based on the newly obtained first peak code. A peak code is searched and adjusted again, so that a new peak code and a new compensation code are obtained again, and the search is repeated in this way until the compensation process satisfies a convergence condition and converges to a capacitance array switch combination with the maximum resonance amplitude. The compensation code in this state is the first compensation code generated by the statistical drift compensation process, and the first compensation code is written into the non-volatile memory, and the statistical drift compensation process is ended.
The method for automatically compensating RFID resonance frequency statistics and temperature drift according to claim 4, wherein the statistical drift compensation process is controlled by a convergence control signal, and the convergence control signal stops statistics after the compensation result meets the convergence condition The operation of drift compensation, the convergence condition of the convergence control signal includes but not limited to two or several consecutive peak code phase differences within the allowable range, or two or several consecutive compensation code phase differences within the allowable range , or the number of statistical drift compensation reaches the preset number.
The method for automatically compensating for RFID resonant frequency statistics and temperature drift according to claim 2, wherein the method for generating the second compensation code in the temperature drift compensation process is: the passive radio frequency identification tag system uses the existing compensation code Control the on or off of the capacitor array switch, start the temperature detection and control circuit, and obtain the PTAT voltage proportional to the absolute temperature. The PTAT voltage is converted by the analog-to-digital converter to obtain the PTAT code. The PTAT code Input to the digital logic module for processing, the digital logic module obtains the second compensation code in the temperature drift compensation process from the PTAT code look-up table, and conducts the switch in the adjustable capacitor array with the second compensation code or conducts Turn off control, thereby changing the number of capacitors connected to the resonant circuit in the capacitor array and the overall resonant capacitance value, obtaining an improved resonant amplitude at this temperature, and writing the second compensation code into a non-volatile memory , and thus ends the temperature drift compensation process.
The method for automatically compensating for RFID resonant frequency statistics and temperature drift according to claim 2, wherein the method for generating the second compensation code in the temperature drift compensation process is: the passive radio frequency identification tag system uses the existing compensation code Control the on or off of the capacitor array switch, start the temperature detection and control circuit, and obtain the PTAT voltage proportional to the absolute temperature. The PTAT voltage is converted by an N-way parallel processing structure to obtain the PTAT code. The PTAT code is input into the digital logic module for processing, and the digital logic module obtains the second compensation code in the temperature drift compensation process from the table look-up of the PTAT code, and guides the switches in the adjustable capacitor array with the second compensation code On or off control, thereby changing the number of capacitors connected to the resonant circuit in the capacitor array and the overall resonant capacitance value, obtaining an improved resonance amplitude at this temperature, and writing the second compensation code into the non-volatile memory, and the temperature drift compensation process ends.
According to the method for automatically compensating RFID resonance frequency statistics and temperature drift according to claim 6 or 7, it is characterized in that, the operation method of the digital logic module to obtain the compensation code from the PTAT code look-up table is: pre-representing the temperature information The one-to-one correspondence between the PTAT code and the compensation code is stored in the non-volatile memory inside the chip, and the compensation code corresponding to the closest measured PTAT code is read from the storage medium during calibration, and the compensation code is The compensation code in the temperature drift compensation process is used to control the on or off of the capacitor array switch, so as to complete the temperature compensation.
According to the method for automatically compensating RFID resonant frequency statistics and temperature drift according to any one of claims 6 or 7, it is characterized in that, in the temperature drift compensation process, after a certain time delay, the passive radio frequency identification tag system detects the temperature Measure the temperature with the control circuit again to obtain a new PTAT code, and obtain an updated second compensation code after another table lookup operation, and use the updated second compensation code to control the on or off of the capacitor array switch again , repeating this cycle until the end of the temperature drift compensation process, writing the updated second compensation code into the non-volatile memory, and thus ending the temperature drift compensation process.
A control circuit for implementing the method according to any one of claims 1 and 4, characterized in that: the control circuit comprises a resonant circuit composed of a resonant inductance and a resonant capacitor, a peak detection module, an analog-to-digital converter, and a logic control module , 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 both ends of the resonant inductor, and the input terminal of the peak detection module is connected to the resonant circuit output terminal, the output terminal of which is connected to the input terminal of the analog-digital converter, the output terminal of the analog-digital converter is connected to the input terminal of the logic control module, and the output terminal of the logic control module is connected to the resonant circuit An adjustable capacitor array, the peak detection module is used to extract the resonance amplitude value of the resonance circuit, and obtain a digital code representing its resonance amplitude after passing through the analog-to-digital converter, that is, the first peak code in the statistical drift compensation process, and the obtained In the first peak code temporary storage register, then the statistical drift compensation process forms an optimization process with the first peak code as the objective function and the compensation code as the independent variable in mathematics; the logic control module obtains After the first peak code, a new compensation code is obtained according to the optimized search algorithm implemented, and the new compensation code is used to control the conduction or shutdown of the capacitor array switch again, thereby obtaining a new resonance amplitude and a new peak code, Again, the logic control module obtains a new compensation code according to the optimization search algorithm, and repeats this cycle until the logic control module converges to a switch combination with the maximum resonance amplitude. The compensation code in this state is the first compensation generated by the statistical drift compensation process. code, write the first compensation code into the non-volatile memory, and end the statistical drift compensation process.
A control circuit for implementing the method of any one of claims 2 or 6, characterized in that: the control circuit includes a resonant circuit composed of a resonant inductor and a resonant capacitor, a rectifier 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 both ends of the resonant inductor, and the output end of the resonant circuit is connected to the rectifier circuit The input end, the output end of the rectification circuit are 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 includes a reference generation and PTAT voltage generation module, an analog-to-digital converter and a digital logic module, and the output terminals of the power management module are respectively connected to the reference generation and PTAT voltage generation module, the analog-to-digital converter and a digital logic module, the output of the digital logic module is connected to the adjustable capacitor array in the resonant circuit, the reference generation and PTAT voltage generation module measures the internal temperature of the chip, and converts the temperature physical quantity into an absolute temperature The PTAT voltage in direct proportion, the PTAT voltage is converted into a binary code representing the physical quantity of temperature through an analog-to-digital converter, that is, a PTAT code, and the binary code is input into the digital logic module for processing, and the digital logic module is determined by the The second compensation code in the temperature drift compensation process is obtained by looking up the binary code table, and the switch in the adjustable capacitor array is controlled to be turned on or off with the second compensation code, thereby changing the access resonance in the capacitor array The number of capacitors of the circuit and the overall resonance capacitance value obtain an improved resonance amplitude at the temperature, write the second compensation code into the non-volatile memory, and end the temperature drift compensation process.
A control circuit for implementing the method of any one of claims 2 or 7, characterized in that the control circuit includes a resonant circuit composed of a resonant inductor and a resonant capacitor, a rectifier 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 both ends of the resonant inductor, and the output end of the resonant circuit is connected to the rectifier circuit The input end, the output end of the rectification circuit are 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 includes a reference generation and PTAT voltage generation module, which outputs one PTAT voltage and a reference voltage with uniform distribution of multiple voltages, and multiple comparisons corresponding to the output of the reference voltage with uniform distribution of multiple voltages. The PTAT voltage generating module generates a PTAT voltage proportional to the absolute temperature and inputs it to the positive input terminals of the plurality of comparators, and the reference voltages with uniform distribution of multiple voltages are respectively input to the negative terminals of each comparator. At the input end, the plurality of comparators respectively output PTAT codes according to the comparison results, and the PTAT codes are input to the digital logic module for processing, and the digital logic module obtains the first step in the temperature drift compensation process from the table lookup of the PTAT codes. Two compensation codes, using the second compensation code to control the switches in the adjustable capacitor array to be turned on or off, thereby changing the number of capacitors connected to the resonant circuit in the capacitor array and the overall resonant capacitance value, and obtaining a For the improved resonance amplitude at this temperature, write the second compensation code into the non-volatile memory, and thus end the temperature drift compensation process.

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