Passive impedance type sensor, sensing circuit and low-power-consumption passive electronic tag

Abstract

The invention discloses a passive impedance type sensor and a low-power-consumption passive electronic tag design method, is applied to the field of wireless sensor networks, and aims to solve the problems that a multi-stage operational amplifier or an instrument amplifier needs to be integrated in a signal conditioning circuit of an existing impedance type sensing circuit, and the integration number of the amplifiers is in direct proportion to the total power consumption of the sensing circuit; and a high-power-consumption sensing circuit is not suitable for realization of a passive electronic tag needing energy self-sustaining. The sensor is designed to be of a double-coil transformer structure, alternating current signal excitation is adopted, a signal conditioning circuit is achieved by adopting a voltage doubling circuit matched with a passive band-pass filter, the power consumption and the area of an impedance type sensing circuit are effectively reduced, and the impedance type sensing circuit is suitable for implementation of a passive electronic tag needing energy self-sustaining.

Description

Technical Field

[0001] The invention belongs to the field of wireless sensor networks, and in particular relates to a sensor circuit and a tag design technology. Background Art

[0002] With the progress and development of science and technology, Wireless Sensor Networks (WSN) technology has played a huge role in various production activities of human society. WSN is a distributed sensor network whose terminals are sensors that can sense and detect the outside world. Sensors in WSN communicate wirelessly, so the network settings are flexible, the location of the equipment can be changed at any time, and it can also connect and communicate with the Internet by wired or wireless means. At present, the most suitable WSN node is the passive electronic tag, that is, the passive radio frequency tag.

[0003] Passive electronic tags use frequency hopping working mode and have anti-interference ability. Users can customize the reading and writing standard data, and the reading distance can reach more than ten meters. Passive radio frequency tags have a wide working frequency band, which not only complies with relevant industry regulations, but also can be flexibly developed and applied. Its dedicated reader can read and write multiple tags at the same time. Due to its passive working characteristics, no battery is required in the tag design, and the tag's memory can be repeatedly erased and written more than 100,000 times. Since passive electronic tags do not have built-in batteries, when they are within the communication identification range of the reader, the electronic tags collect the power required for their work from the radio frequency energy emitted by the reader. Passive electronic tags generally use backscattering to complete the transmission of electronic tag information to the reader, so passive electronic tags can also be called passive tags. Radio Frequency Identification (RFID) technology is a traditional wireless communication identification technology that can realize non-line-of-sight communication and is widely used in intelligent logistics, transportation, multi-target identification, direction tracking and other fields. RFID technology is applied in wireless sensor networks and has the technical characteristics of both RFID and wireless sensor networks. It automatically identifies the characteristics of the target through RFID radio frequency signals and can simultaneously realize the functions of wireless sensor networks in perceiving information and communicating.

[0004] There are many types of sensors, including impedance sensors, resonant sensors, etc., especially impedance sensors, whose materials and structures make the impedance value of the sensor itself change due to changes in the sensing parameters, so that under a specific excitation signal, the amplitude parameter of the output signal can be collected as sensing information to reflect the size of the environmental target sensing parameter. Considering the miniaturization of nodes, the application prospects of impedance sensors in WSN systems are broader. It is not difficult to see that the miniaturization of sensors and their excitation and signal conditioning circuits is an important design indicator for passive electronic sensing tags. However, the industry currently does not have a low-power impedance sensing circuit design method for passive electronic sensing tags, and this invention is based on this and is detailed.

[0005] Existing impedance-type sensing circuits mostly use DC voltage source excitation, based on the principle that the sensor material changes its own impedance due to its sensitivity to the environmental target sensing parameters, to obtain a proportional change in the output signal amplitude, and to collect the output signal after amplifying and filtering it.

[0006] The disadvantages of the prior art are that the signal conditioning circuit of the existing impedance-type sensor circuit needs to integrate multiple operational amplifiers or instrumentation amplifiers, and the number of integrated amplifiers is proportional to the overall power consumption of the sensor circuit. The high-power sensor circuit is not suitable for the implementation of passive electronic tags that require energy self-sustaining. Summary of the invention

[0007] In order to solve the above technical problems, the present invention proposes a passive impedance sensor and a low-power passive electronic tag design method. The sensor is designed as a double-coil transformer structure, and AC signal excitation is adopted. The signal conditioning circuit adopts a voltage doubling circuit with a passive bandpass filter, which effectively reduces the power consumption and area of ​​the impedance sensor circuit, and is suitable for the implementation of passive electronic tags that require energy self-sustaining.

[0008] One of the technical solutions adopted by the present invention is: a passive impedance sensor adopts a double-coil transformer structure, and the double-coil transformer structure adopts a conductive material that is sensitive to environmental target parameters.

[0009] The second technical solution adopted by the present invention is: a low-power impedance sensing circuit, including: an excitation circuit, a passive impedance sensor, and a conditioning circuit; the input port of the passive impedance sensor is connected to the excitation circuit, and the output port of the passive impedance sensor is connected to the conditioning circuit.

[0010] The conditioning circuit includes: a passive bandpass filter, a voltage doubler circuit, a passive low-pass filter and an ADC; the output port of the passive impedance sensor is connected to the input end of the passive bandpass filter, the output end of the passive bandpass filter is connected to the input end of the voltage doubler circuit, the output end of the voltage doubler circuit is connected to the input end of the passive low-pass filter, the output end of the passive low-pass filter is connected to the ADC, and the ADC outputs a digital signal.

[0011] The voltage doubling circuit includes a multi-stage sub-voltage doubling circuit, each stage of the sub-voltage doubling circuit includes 2 diodes and 2 capacitors, wherein the first end of the first capacitor serves as the input end of the sub-voltage doubling circuit of this stage, the second end of the first capacitor is connected to the cathode of the first diode, the anode of the first diode is grounded, the cathode of the first diode is connected to the anode of the second diode, the cathode of the second diode is connected to the first end of the second capacitor, and the second end of the second capacitor is grounded; the cathode of the second diode serves as the output end of the sub-voltage doubling circuit of this stage.

[0012] The voltage amplitude output by the passive impedance sensor is greater than the threshold voltage of the diode in the voltage doubler circuit.

[0013] The third technical solution adopted by the present invention is: a low-power passive electronic tag, including: a low-power impedance sensor circuit, an MCU baseband processing unit circuit, an impedance matching and backscattering modulation circuit, a power divider, an antenna, a demodulation circuit, a rectification and energy management circuit;

[0014] The RF signal and RF energy sent by the reader are transmitted to the impedance matching and backscattering modulation circuit through the antenna port. The RF signal and energy output by the impedance matching and backscattering modulation circuit are divided into two paths through the power divider, one path transmits the RF signal and the other transmits the RF energy. The RF energy is transmitted to the rectification and energy management circuit for conversion and collection; the RF signal is transmitted to the demodulation circuit for demodulation, and the baseband signal obtained by demodulation is input into the MCU baseband processing unit circuit; the MCU baseband processing unit circuit generates a modulation signal based on the data collected by the low-power impedance sensor circuit, and the modulation signal is transmitted through the antenna port after the impedance matching and backscattering modulation circuit.

[0015] Beneficial effects of the invention: The invention aims to solve the problem that the existing impedance-type sensing circuit needs to integrate multi-stage operational amplifiers or instrumentation amplifiers, which leads to high power consumption and is not suitable for passive electronic tags that require energy self-sustaining. The invention proposes an impedance-type sensing circuit and design method suitable for passive electronic tags. The sensor is designed as a double-coil transformer structure, using AC signal excitation, and the signal conditioning circuit is implemented by a rectifier circuit with a passive filter, which effectively reduces the power consumption and area of ​​the impedance-type sensing circuit and is suitable for the design and implementation of passive electronic tags that require energy self-sustaining. At the same time, the invention is also suitable for the design and application of low and micro-power consumption sensor modules, has the characteristics of simplicity and universality, and has considerable scientific research and commercial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the equivalent circuit of transformer type sensor.

[0017] Figure 2 This is a low-power impedance sensing circuit architecture diagram.

[0018] Figure 3 It is a voltage doubler circuit architecture.

[0019] Figure 4 It is a low-power passive sensor tag circuit architecture.

[0020] Figure 5 Software workflow for the baseband processing unit circuit.

[0021] Figure 6 Design a flow chart for passive electronic tags.

[0022] Figure 7 A partial circuit diagram of a low-power passive sensor tag. DETAILED DESCRIPTION

[0023] To facilitate those skilled in the art to understand the technical content of the present invention, the present invention is further explained below with reference to the accompanying drawings.

[0024] The equivalent circuit diagram of the sensor structure proposed by the present invention is as follows: Figure 1 As shown, R 01 and R 02 is the equivalent resistance, L1 and L2 are the equivalent inductors. While using sensitive materials (conductive materials that are sensitive to environmental target parameters), the sensor is manufactured according to a two-stage induction coil structure to form a transformer structure, and the voltage amplification ratio is adjusted to the maximum when the size allows. Based on this sensor architecture, when it is excited by an AC signal with the same resonant frequency as its own, the output AC signal voltage amplitude increases proportionally, thereby reducing the dependence of the subsequent signal conditioning circuit on the amplifier, thereby reducing the overall power consumption of the sensing circuit.

[0025] The sensitive material in this embodiment may be: palladium (Pd) that is sensitive to hydrogen, ferrite that is sensitive to magnetic field, platinum resistor that is sensitive to temperature, carbon film resistor, etc.

[0026] The above-mentioned two-stage induction coil is made of sensitive materials. Under different environmental target parameters, the electrical properties of the sensitive materials of the sensor change, so that the resonant frequency of the sensor and the impedance characteristics at the original resonant frequency change due to the material change. Therefore, under the excitation of the original resonant frequency excitation signal, the amplitude of the sensor output signal will change proportionally with the change of the environmental target parameters, thereby achieving the effect that the amplitude of the sensor output signal reflects the environmental target parameters.

[0027] Based on the above sensor, the present invention proposes Figure 2The low-power impedance sensing circuit shown in the figure should be implemented by an oscillator, such as a crystal oscillator, which outputs an AC signal of a fixed frequency (sensor resonant frequency) on demand to excite the sensor, and controls the excitation signal current through a current-limiting resistor to achieve the purpose of controllable power consumption.

[0028] The output port of the sensor is connected to a passive bandpass filter to achieve impedance matching between the output port of the sensor and the input port of the subsequent voltage doubler circuit, while filtering out the noise in the sensor output signal to improve the signal-to-noise ratio. After the bandpass filter, the voltage doubler circuit is connected to a passive low-pass filter and ADC. The voltage doubler circuit is mainly composed of a diode and a capacitor, such as Figure 3 As shown, the sensor signal Vin output by the passive bandpass filter is output as the sensor signal Vout after passing through the voltage doubling circuit. Since the transformer structure of the sensor can boost the sensor output signal, the output voltage amplitude can be greater than the threshold voltage of the diode. Therefore, based on the sorting function of the diode, the voltage doubling circuit can also convert the AC signal output by the sensor into a DC signal. Figure 3 The voltage doubler circuit in the circuit is composed of 4 sub-voltage doubler circuits, each of which is composed of 2 diodes and 2 capacitors. Figure 3 As shown in the box in , the voltage doubler circuit raises the output DC voltage before entering the post-stage low-pass filter. The low-pass filter filters out the noise to facilitate the subsequent ADC circuit to collect and convert the sensor data, and obtain a high-precision digital signal for subsequent processing.

[0029] In summary, the transformer structure, excitation circuit, and signal conditioning circuit of the sensor avoid the addition of high-power and low-efficiency amplifiers, which can effectively reduce the overall power consumption of the sensor circuit and is suitable for the integration and implementation of passive sensing electronic tags. Therefore, the design of the passive sensing electronic tag based on this low-power sensor circuit is as follows Figure 4 shown.

[0030] The passive sensing electronic tag includes an antenna, an impedance matching and backscattering modulation circuit, a rectification and energy management circuit, a demodulation circuit, an MCU baseband processing unit circuit, and the above-mentioned low-power impedance sensing circuit. When it is working, the radio frequency signal and energy sent by the reader are transmitted from the antenna port to the impedance matching and backscattering modulation circuit, which is composed of an impedance matching circuit, a backscattering modulation circuit, and a power divider circuit. The radio frequency signal and energy are transmitted to the rectification and energy management circuit through the impedance matching circuit and the power divider circuit, and are converted and collected, and the input radio frequency signal is transmitted to the demodulation circuit for demodulation.

[0031] The rectification and energy management circuit provides DC (Direct Current) power to the demodulation circuit and the MCU baseband processing unit circuit.

[0032] The demodulation circuit consists of an envelope detection circuit, an average circuit, and a comparator. The demodulated signal processed by the envelope detection circuit is transmitted to the comparator together with the output signal of the average circuit. After the comparator receives power from the rectification and energy management circuit, it outputs the baseband signal and transmits it to the MCU baseband processing unit circuit for analysis and processing.

[0033] The single-chip microcomputer in the MCU baseband processing unit circuit receives power from the rectification and energy management circuit, processes and analyzes the reader / writer commands transmitted by the demodulation circuit, and when it receives the reader / writer command to sense environmental parameters, it sends a collection enable signal from the single-chip microcomputer to the impedance type sensing circuit, which is also the power supply voltage of the impedance type sensing circuit. At the same time, it processes the sensing signal transmitted by the impedance type sensing circuit, converts the collected parameters into modulation signals, transmits them to the impedance matching and backscattering modulation circuit, and transmits the measured environmental parameters back to the reader / writer by backscattering.

[0034] The software workflow of the MCU baseband processing unit circuit of the present invention is as follows: Figure 5 As shown, the MCU baseband processing unit mainly implements the RFID protocol based on ISO / IEC 18000. When the rectification and energy management circuit starts to supply power to the MCU baseband processing unit circuit, the MCU baseband processing unit circuit will start working, first initialize the working state of each pin of the single-chip microcomputer and configure the module receiving data accordingly, and then start to receive the command of the host computer. When the host computer sends a general RFID command, the sensing tag executes the command like a general RFID tag, and determines whether to return a signal according to the protocol; when the host computer sends an environmental parameter sensing command, the tag parses the command and obtains the number of acquisitions, then enables the impedance sensing circuit, and waits for the impedance sensing circuit to stabilize, then configures the ADC, and collects data, saves the collected data so that it can be read at any time, and then reduces the number of acquisitions by 1, and then determines whether the number of acquisitions is zero. If it is not zero, continue to collect, otherwise return the collected data to the reader.

[0035] Based on the above-mentioned low-power impedance sensor circuit and the passive electronic tag circuit architecture based on the circuit, the present invention proposes a passive electronic tag design method and process. Figure 6 shown.

[0036] The design method includes the following steps:

[0037] Firstly, according to the needs of practical application, an impedance-type sensitive material for the environmental parameter to be measured is selected, and a two-stage induction coil in a passive impedance-type sensor is prepared according to the selected sensitive material;

[0038] The second step is to make a passive impedance sensor with a permitted size;

[0039] The third step is to determine the frequency of the passive impedance sensor excitation signal;

[0040] The fourth step is to choose to design the oscillator circuit;

[0041] The fifth step is to determine the current limiting resistor value according to the maximum input current of the sensor;

[0042] The sixth step is to design the passive bandpass filter in the signal conditioning circuit according to the output frequency of the sensor, which mainly includes designing the resistance, capacitance and inductance values ​​of the bandpass filter;

[0043] The seventh step is to design the voltage doubler rectifier in the signal conditioning circuit. The specific circuit structure is as follows: Figure 3 As shown;

[0044] The eighth step is to design a low-pass filter in the signal conditioning circuit; the low-pass filter is implemented by a parallel capacitor;

[0045] Step 9: Choose a low-power MCU with ADC;

[0046] The tenth step is to design the MCU baseband processing unit circuit; this design process is a known technology and will not be described in detail in this embodiment;

[0047] The eleventh step is to design the demodulation circuit. The demodulation circuit is as follows Figure 7 As shown;

[0048] The twelfth step is to design the rectification and energy management circuit. The specific circuit structure is as follows: Figure 7 As shown;

[0049] The thirteenth step is to design the impedance matching and backscatter modulation circuit. The fourteenth step is to select or design the tag antenna. The specific circuit structure is as follows: Figure 7 As shown;

[0050] Step 15: Design the baseband software workflow;

[0051] The sixteenth step is processing and testing, observing the design effect and evaluating whether the label has achieved the expected characteristics. If not, optimize the circuits of each module. If it has, the design is completed.

[0052] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. For those skilled in the art, the present invention may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A passive impedance sensor, characterized in that: A double-coil transformer structure is adopted, wherein the double coils are made of conductive materials that are sensitive to environmental target parameters.

2. A passive impedance sensor according to claim 1, characterized in that: The conductive material sensitive to the environmental target parameter is one of palladium sensitive to hydrogen, ferrite sensitive to magnetic field, platinum resistor sensitive to temperature, and carbon film resistor.

3. A low power consumption impedance type sensing circuit, characterized in that: include: An excitation circuit, the passive impedance sensor according to claim 2, and a conditioning circuit; the input port of the passive impedance sensor is connected to the excitation circuit, and the output port of the passive impedance sensor is connected to the conditioning circuit.

4. A low power consumption impedance type sensing circuit according to claim 3, characterized in that: The conditioning circuit includes: a passive bandpass filter, a voltage doubler circuit, a passive low-pass filter and an ADC; the output port of the passive impedance sensor is connected to the input end of the passive bandpass filter, the output end of the passive bandpass filter is connected to the input end of the voltage doubler circuit, the output end of the voltage doubler circuit is connected to the input end of the passive low-pass filter, the output end of the passive low-pass filter is connected to the ADC, and the ADC outputs a digital signal.

5. A low power consumption impedance type sensing circuit according to claim 4, characterized in that: The voltage doubling circuit includes a multi-stage sub-voltage doubling circuit, each stage of the sub-voltage doubling circuit includes 2 diodes and 2 capacitors, wherein the first end of the first capacitor serves as the input end of the sub-voltage doubling circuit of this stage, the second end of the first capacitor is connected to the cathode of the first diode, the anode of the first diode is grounded, the cathode of the first diode is connected to the anode of the second diode, the cathode of the second diode is connected to the first end of the second capacitor, and the second end of the second capacitor is grounded; the cathode of the second diode serves as the output end of the sub-voltage doubling circuit of this stage.

6. A low power consumption impedance type sensing circuit according to claim 5, characterized in that: The voltage amplitude output by the passive impedance sensor is greater than the threshold voltage of the diode in the voltage doubler circuit.

7. A low power consumption impedance type sensing circuit according to claim 6, characterized in that: The excitation circuit is implemented by an oscillator, and the oscillator outputs an AC signal with a fixed frequency equal to the resonant frequency of the passive impedance type sensor.

8. A low power consumption impedance type sensing circuit according to claim 7, characterized in that: The excitation circuit also includes a current limiting resistor, and the AC signal output by the oscillator is input into the passive impedance sensor after passing through the current limiting resistor.

9. A low power consumption impedance type sensing circuit according to claim 8, characterized in that: The current limiting resistor is an adjustable resistor, and its minimum resistance is determined according to the maximum input current of the sensor.

10. A low-power passive electronic tag, characterized in that: include: The low-power impedance sensing circuit, MCU baseband processing unit circuit, impedance matching and backscatter modulation circuit, power divider, antenna, demodulation circuit, rectification and energy management circuit as described in any one of claims 3 to 9; The RF signal and RF energy sent by the reader are transmitted to the impedance matching and backscattering modulation circuit through the antenna port. The RF signal and energy output by the impedance matching and backscattering modulation circuit are divided into two paths through the power divider, one path transmits the RF signal and the other transmits the RF energy. The RF energy is transmitted to the rectification and energy management circuit for conversion and collection; the RF signal is transmitted to the demodulation circuit for demodulation, and the baseband signal obtained by demodulation is input into the MCU baseband processing unit circuit; the MCU baseband processing unit circuit generates a modulation signal based on the data collected by the low-power impedance sensor circuit, and the modulation signal is transmitted through the antenna port after the impedance matching and backscattering modulation circuit.

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