Low-power backscatter communication tag considering negative resistance amplification characteristics

Abstract

The application relates to a low-power backscatter communication tag considering a negative resistance amplification characteristic, and belongs to the technical field of radio frequency identification. The tag comprises a signal receiving matching module for receiving a downlink signal from a transmitter and matching impedance with subsequent circuits; an envelope detection module for demodulating the downlink signal and extracting a baseband signal from a carrier signal; a low-pass filter module for processing the baseband signal after envelope detection and filtering high-frequency components in the signal; a comparator module for comparing two signals output by the low-pass filter module to compare a digital baseband signal; a negative resistance amplification module for reflecting and amplifying the downlink signal; and a main control module for processing the digital baseband signal and controlling the on-off between the signal receiving matching module and the envelope detection module and the negative resistance amplification module. The communication tag has low overall power consumption, small volume and can be conveniently applied to the industry of Internet of Things interconnection.

Description

Technical Field

[0001] The present invention belongs to the technical field of radio frequency identification and relates to a low-power backscattering communication tag taking into account negative resistance amplification characteristics. Background Art

[0002] With the continuous development of the Internet of Things (IoT), wireless communication technology is playing an increasingly important role in various application scenarios. In particular, in low-power, long-distance communication scenarios, backscatter communication technology has attracted much attention due to its low power consumption and low cost. Backscatter communication tags transmit data by reflecting received radio frequency signals, without actively transmitting signals, thus significantly reducing power consumption. This technology can be applied to hundreds of millions of low-power IoT platforms in the future. Among them, it has great development potential in logistics and supply chain management, manufacturing, retail, healthcare, transportation, agriculture and animal husbandry, environmental monitoring, smart homes and other fields, and can realize the true interconnection of everything.

[0003] RFID radio frequency identification technology is based on backscattering technology, but existing backscattering tags have problems with power consumption and communication distance. That is, reducing power consumption will lead to a shortened communication distance, which cannot meet the requirements of long-distance low-power transmission. At the same time, backscattering will experience about twice the path loss, resulting in a further shortening of the communication distance. The power consumption problem will also lead to an increase in subsequent maintenance costs. The lack of commercial interest drive has caused a bottleneck in the development of the Internet of Things. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a low-power backscatter communication tag that takes into account the negative resistance amplification characteristics. Backscatter communication is used to make the tag independent of high-power modulation and demodulation circuits. At the same time, the introduction of negative resistance amplification greatly improves the communication distance of the tag, which not only meets the low power consumption requirements but also increases the transmission distance.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A low-power backscattering communication tag considering negative resistance amplification characteristics, the communication tag comprising:

[0007] A signal receiving and matching module is used to receive the downlink signal from the transmitter and perform impedance matching with the subsequent circuit;

[0008] Envelope detection module, used to demodulate the downlink signal and extract the baseband signal from the carrier signal;

[0009] The low-pass filter module is used to process the baseband signal after envelope detection and filter out the high-frequency components in the signal;

[0010] A comparator module is used to compare the two signals output by the low-pass filter module to obtain a digital baseband signal;

[0011] A negative resistance amplifier module, used to reflect and amplify the downlink signal;

[0012] The main control module is used to process the digital baseband signal and control the connection and disconnection between the signal receiving and matching module and the envelope detection module and the negative resistance amplification module respectively.

[0013] Furthermore, the signal receiving and matching module includes an antenna, an SMA interface, a multiplexer, and a matching circuit. The antenna's input receives downlink signals, while its output is connected to the input of the SMA interface. The output of the SMA interface is connected to the first port of the multiplexer. The second port of the multiplexer is connected to the input of the matching circuit, while the third port is connected to the negative resistance amplifier module. The output of the matching circuit is connected to the envelope detection module. Through the multiplexer, the main control module controls the communication between the antenna and the matching circuit and the negative resistance amplifier module, thereby achieving reflection of the downlink signal.

[0014] Furthermore, the envelope detection module includes a detector diode D1, a filter capacitor C2, and a load resistor R1. The anode of the detector diode is connected to the output of the matching circuit. The filter capacitor C2 and the load resistor R1 are connected in parallel and then in series between the cathode of the detector diode D1 and ground. One end of the load resistor R1 is connected to the low-pass filter module.

[0015] Furthermore, the low-pass filter module includes a primary low-pass filter circuit and a secondary low-pass filter circuit. The primary low-pass filter circuit has an input connected to a load resistor R1, and its output is connected to the input of the secondary low-pass filter circuit and the input of the comparator module, respectively. The output of the secondary low-pass filter circuit is connected to the input of the comparator module. The primary low-pass filter circuit has a higher cutoff frequency than the secondary low-pass filter circuit.

[0016] Furthermore, the comparator module is implemented using a comparator, the positive input end of the comparator is connected to the output end of the first-level low-pass filter circuit, the negative input end is connected to the output end of the second-level low-pass filter circuit, and the output end of the comparator is connected to the input end of the main control module.

[0017] Furthermore, the negative resistance amplifier module includes a DC blocking capacitor C5, a resonant circuit composed of a resonant inductor L3 and a resonant capacitor C7, a transistor Q1, an inductor L4, a DC bias circuit composed of a bias resistor R4 and a DC power supply, and a positive feedback circuit composed of a feedback inductor L5, a feedback capacitor C6 and a feedback capacitor C8.

[0018] Among them, the first end of the DC blocking capacitor C5 is connected to the third port of the multiplexer, and the second end is connected to the first end of the resonant inductor L3; the second end of the resonant inductor L3 is respectively connected to the first end of the resonant capacitor C7 and the collector of the transistor Q1; the second end of the resonant capacitor C7 is grounded; the emitter of the transistor Q1 is grounded, and the base is connected to the second end of the bias resistor R4; the first end of the bias resistor R4 is respectively connected to the positive electrode of the DC power supply and the first end of the inductor L4; the negative electrode of the DC power supply is grounded, and the second end of the inductor L4 is connected to the collector of the transistor Q1; the first end of the feedback inductor L5 is connected to the second end of the bias resistor R4, and the second end of the feedback inductor L5 is connected to the first end of the feedback capacitor C8; the first end of the feedback capacitor C6 is connected to the first end of the resonant inductor L3, and the second end is connected to the first end of the feedback capacitor C8; the second end of the feedback capacitor C8 is grounded.

[0019] In the negative resistance amplification module, the transistor Q1 is made to operate at a static operating point through the DC bias circuit, so that the negative resistance amplification module is in a negative resistance amplification state.

[0020] The beneficial effects of the present invention are as follows: the present invention determines the matching frequency and receives the radio frequency signal in the working range through the signal receiving and matching module, and demodulates the original digital baseband signal through matching, filtering, comparison and other operations; the present invention adopts the design principle of the Class E oscillator to design the negative resistance amplifier module. The Class E oscillator can achieve an efficiency of more than 70%, and has a simple structure. At the same time, it can provide a higher output power, which has great advantages in modulating the carrier to generate an uplink signal; the communication tag proposed by the present invention has low overall power consumption, can meet the requirements of the radio frequency tag, and is small in size, and can be conveniently applied to the industry of Internet of Things interconnection.

[0021] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0023] Figure 1 A schematic diagram of the structure of a low-power backscatter communication tag provided by one embodiment of the present invention;

[0024] Figure 2 It is a schematic diagram of the static operating point of the transistor;

[0025] Figure 3 is the input impedance of the negative resistance amplifier circuit;

[0026] Figure 4 is the gain of the negative resistance amplifier circuit. DETAILED DESCRIPTION

[0027] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0028] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0029] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0030] like Figure 1 As shown, a low-power backscatter communication tag considering the negative resistance amplification characteristics is provided in one embodiment of the present invention, which includes: a signal receiving and matching module, an envelope detection module, a low-pass filtering module, a comparator module, a main control module, and a negative resistance amplification module.

[0031] The RF matching receiving module receives the downlink signal from the transmitter and transmits the received signal to the envelope detection module. The envelope detection module demodulates the downlink signal, removes the baseband signal from the carrier signal, and transmits the baseband signal to the low-pass filtering module. In the low-pass filtering module, the first-stage low-pass filter filters out some high-frequency components in the baseband signal, and the second-stage low-pass filter further filters out some high-frequency components, resulting in a certain voltage difference between the signals generated by the two filters. The signals are then transmitted to the comparator module. The comparator module compares the signals transmitted by the two low-pass filters to generate a digital baseband signal, which is then transmitted to the main control module. The main control module is responsible for processing the digital baseband signal and generating a digital baseband signal to be reflected back. The digital baseband signal generated here is used to control the selection of the multiplexer in the signal receiving and matching module. That is, when the signal "0" appears, the multiplexer connects the signal receiving and matching module and the envelope detection module. When the signal "1" appears, the multiplexer connects the antenna and the negative resistance amplifier module, which directly reflects and amplifies the downlink signal received by the antenna. It can be seen that in the communication tag proposed by the present invention, the signal receiving and matching module has a bidirectional transmitting and receiving function.

[0032] The low-power backscatter communication tag provided in this embodiment complies with the radio frequency identification protocol, namely the Class-1 Generation-2 UHF RFID 860 MHz to 960 MHz communication protocol. The transmitter transmits a carrier with a center frequency of 915 MHz, which also determines the center frequency of the signal receiving and matching module to be 915 MHz. The downlink uses AM modulation, and the code elements use the PIE encoding format.

[0033] The matching circuit must ensure that the subsequent impedance matches the characteristic impedance, meaning that the reflection coefficient at the port is zero or approximately zero, ensuring that the downlink signal is fully received by the system without any reflections. The system input impedance must first be simulated using the electromagnetic simulation software Advanced Design System (ADS). The simulated system input impedance is then matched to the source impedance of 50 ohms using a Smith chart. This embodiment uses a π-type matching circuit, which offers greater flexibility and facilitates subsequent adjustments. After receiving the matched signal, it is input into the filtering circuit, which utilizes an L-type low-pass filter with a cutoff frequency of f = 12πRC. The first-stage low-pass filter removes high-frequency components above 1.6 MHz and outputs the signal to the positive terminal of the comparator; the second-stage low-pass filter removes high-frequency components above 0.16 MHz and outputs the signal to the negative terminal of the comparator. The comparator uses the MAX962 ultra-high-speed comparator to compare high-frequency signals to avoid errors. The propagation delay is 4.2 ns, sufficient for tag signal requirements. The negative resistance amplifier module is responsible for reflecting and amplifying the carrier signal emitted by the transmitter. The negative resistance amplifier principle is to use the "negative resistance" characteristics of the transistor in the working range to achieve amplification, that is, as the current increases, the voltage decreases. In order to make the transistor in the "negative resistance" state, it is necessary to use ADS to determine the static operating point of the transistor, such as Figure 2 Then, the static operating point is set by the bias circuit, and the complete circuit is built and the measured impedance is negative, as shown in Figure 3 The gain is shown as Figure 4 As shown in the figure, S11 is about 19dB, which means that the reflected signal power is amplified by about 65 times, achieving the purpose of amplifying and reflecting the carrier.

[0034] Specifically, if Figure 1 As shown, the signal receiving matching module includes an antenna, an SMA port, a multiplexer MUX, matching inductors L1, L2 and a matching capacitor C1. When receiving an input signal, the signal receiving matching module connects the multiplexer to the matching circuit and the SMA port so that the signal is fully received.

[0035] The envelope detection module includes a detection diode D1, a filter capacitor C2 and a load resistor R1. The diode D1 is connected to the matching inductor L2 and the matching capacitor C1. The filter inductor C2 is connected in parallel with the load resistor R1 and then connected in series between the diode D1 and the ground. Among them, the detection diode D1 uses a Schottky diode. The forward voltage drop of the Schottky diode is much lower than that of an ordinary silicon diode, which further reduces the power consumption, and the fast recovery time of the diode is also very short, only a few nanoseconds, which meets the demodulation requirements of the RF signal. The filter capacitor C2 is responsible for smoothing the signal after detection, removing the high-frequency component, and making the processed signal smoother. The load resistor R1 converts the current flowing through into a voltage, thereby forming a corresponding voltage signal at both ends of the resistor.

[0036] The low-pass filter module includes a first-order low-pass filter and a second-order low-pass filter. The first-order low-pass filter includes a filter capacitor C3 and a filter resistor R2, one end of the filter resistor R2 is connected to one end of the load resistor R1, the other end of the resistor R2 is connected to one end of the filter capacitor C3, and the other end of the capacitor C3 is grounded. The second-order low-pass filter includes a filter capacitor C4 and a filter resistor R3, one end of the filter resistor R3 is connected to the output end of the first-order low-pass filter, and the other end is connected to one end of the filter capacitor C4, and the other end of the capacitor C4 is grounded. The cut-off frequency of the first-order low-pass filter is slightly higher than that of the second-order low-pass filter. The two low-pass filters will produce a certain voltage difference, so that the subsequent comparator can compare the corresponding characters.

[0037] The negative resistance amplifier module is connected to a port of multiplexer P2. Within the negative resistance amplifier module, blocking capacitor C5 isolates DC signals while allowing AC signals to pass through, protecting subsequent circuits from the effects of DC components. One end of capacitor C5 is connected to multiplexer P2, and the other end is connected to a subsequent resonant network. The resonant network includes a resonant inductor L3 and a resonant capacitor C7. One end of resonant inductor L3 is connected to blocking capacitor C5, and the other end is connected to resonant capacitor C7. The other end of resonant capacitor C7 is grounded. The resonant network ensures signal frequency selectivity and ensures that the circuit can self-oscillate at a specific frequency. The resonant network acts as a filter, filtering out frequencies outside the resonant frequency to ensure proper system operation. Transistor Q1 has its emitter connected to ground, and its collector connected to resonant capacitor C7 and resonant inductor L3, respectively. Transistor Q1 is the core component of the negative resistance amplifier module. Operating at a quiescent point through a bias circuit, transistor Q1 presents a negative impedance to the overall circuit and amplifies the input signal. The feedback circuit ensures stable system operation. The DC power supply DC and bias resistor R4 form a DC bias circuit. Bias resistor R4 and inductor L4 are connected in series to ensure the transistor operates at its quiescent operating point. Feedback inductor L5, feedback capacitor C6, and feedback capacitor C8 together form a feedback circuit, which feeds back a certain proportion of the output signal's energy to the input to ensure stable operation of the transistor oscillator circuit.

[0038] The working principle of the present invention is as follows:

[0039] After transmission, the downlink signal passes through the antenna and SMA interface to the multiplexer. The multiplexer generates a digital signal when modulating the carrier signal. When the antenna is connected to the matching circuit via multiplexer port P1, a digital signal "0" is generated. When the antenna is connected to the negative resistance amplifier module via multiplexer port P2, a digital signal "1" is generated. The downlink signal is output from the multiplexer to the matching circuit, which matches the modulated signal with a center frequency of 915 MHz. The received amplitude modulated signal is then transmitted to the envelope detection module for detection. In the envelope detection module, the envelope is first extracted using a Schottky diode. Filter capacitor C2 smoothes the extracted signal. Load resistor R1 converts the current signal into a voltage signal for subsequent filtering. When the input signal is positive, diode D1 conducts and charges capacitor C2. When the input signal voltage drops below the cutoff voltage, diode D1 turns off, discharging capacitor C2. The signal after envelope detection is input into the low-pass filter module. It first passes through a primary low-pass filter circuit to remove high-frequency noise above 1.6 MHz, and then through a secondary low-pass filter circuit to remove high-frequency noise above 0.16 MHz. This creates a certain voltage difference between the primary and secondary low-pass filter circuits. The comparator module receives the two voltage signals output by the low-pass filter module. The primary low-pass filter circuit is connected to the positive terminal of the comparator CMP, and the secondary low-pass filter circuit is connected to the negative terminal of the comparator CMP. Due to the certain voltage difference between the two filter circuits, the comparator can compare the two voltage signals and transmit them to the subsequent main control chip for demodulation. The main control chip uses the low-power MSP430FR5969 chip, which has a 12-bit ADC with a maximum acquisition rate of 200 kbps. The negative resistance amplifier module is connected to port P2 of the multiplexer to reflect and amplify the downlink signal. The downlink signal enters the circuit through the DC blocking capacitor C5. In the negative resistance amplifier module, inductor L3 and capacitor C7 form a resonant network, which also has a certain frequency selection function. When the input signal is close to the resonant frequency, transistor Q1 maintains a fixed frequency. At this time, the circuit presents negative impedance and amplifies the input signal. The amplification gain is achieved through negative resistance. Transistor Q1 operates in a stable region through a DC bias circuit formed by resistor R4 and a DC power supply DC. Inductor L5 and capacitors C8 and C6 form a positive feedback circuit, feeding the output signal back to the input terminal, thus stabilizing the negative resistance amplifier module.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A low-power backscatter communication tag considering negative resistance amplification characteristics, characterized in that: It includes: A signal receiving and matching module is used to receive the downlink signal from the transmitter and perform impedance matching with the subsequent circuit; Envelope detection module, used to demodulate the downlink signal and extract the baseband signal from the carrier signal; The low-pass filter module is used to process the baseband signal after envelope detection and filter out the high-frequency components in the signal; A comparator module is used to compare the two signals output by the low-pass filter module to obtain a digital baseband signal; A negative resistance amplifier module, used to reflect and amplify the downlink signal; A main control module is used to process the digital baseband signal and control the connection and disconnection between the signal receiving and matching module and the envelope detection module and the negative resistance amplification module respectively; The signal receiving and matching module includes an antenna, an SMA interface, a multiplexer, and a matching circuit; the input end of the antenna receives a downlink signal, the output end is connected to the input end of the SMA interface, and the output end of the SMA interface is connected to the first port of the multiplexer; the second port of the multiplexer is connected to the input end of the matching circuit, and the third port is connected to the negative resistance amplification module; the output end of the matching circuit is connected to the envelope detection module; The negative resistance amplifier module includes a DC blocking capacitor C5, a resonant circuit composed of a resonant inductor L3 and a resonant capacitor C7, a transistor Q1, an inductor L4, a DC bias circuit composed of a bias resistor R4 and a DC power supply, and a positive feedback circuit composed of a feedback inductor L5, a feedback capacitor C6 and a feedback capacitor C8; In which, the first end of the DC blocking capacitor C5 is connected to the third port of the multiplexer, and the second end is connected to the first end of the resonant inductor L3; the second end of the resonant inductor L3 is respectively connected to the first end of the resonant capacitor C7 and the collector of the transistor Q1; the second end of the resonant capacitor C7 is grounded; the emitter of the transistor Q1 is grounded, and the base is connected to the second end of the bias resistor R4; the first end of the bias resistor R4 is respectively connected to the positive electrode of the DC power supply and the first end of the inductor L4; the negative electrode of the DC power supply is grounded, and the second end of the inductor L4 is connected to the collector of the transistor Q1; the first end of the feedback inductor L5 is connected to the second end of the bias resistor R4, and the second end of the feedback inductor L5 is connected to the first end of the feedback capacitor C8; the first end of the feedback capacitor C6 is connected to the first end of the resonant inductor L3, and the second end is connected to the first end of the feedback capacitor C8; the second end of the feedback capacitor C8 is grounded.

2. The low-power backscatter communication tag according to claim 1, characterized in that: The envelope detection module includes a detection diode D1, a filter capacitor C2 and a load resistor R1; the anode of the detection diode is connected to the output end of the signal receiving and matching module; the filter capacitor C2 and the load resistor R1 are connected in parallel and then in series between the cathode of the detection diode D1 and the ground.

3. The low-power backscatter communication tag according to claim 1, characterized in that: The low-pass filtering module includes a primary low-pass filtering circuit and a secondary low-pass filtering circuit; the input end of the primary low-pass filtering circuit is connected to the output end of the envelope detection module, and the output end of the primary low-pass filtering circuit is connected to the input end of the secondary low-pass filtering circuit and the input end of the comparator module respectively; the output end of the secondary low-pass filtering circuit is connected to the input end of the comparator module; The cutoff frequency of the first-stage low-pass filter circuit is higher than the cutoff frequency of the second-stage low-pass filter circuit.

4. The low-power backscatter communication tag according to claim 3, characterized in that: In the comparator module, the positive input terminal of the comparator is connected to the output terminal of the first-level low-pass filter circuit, the negative input terminal is connected to the output terminal of the second-level low-pass filter circuit, and the output terminal of the comparator is connected to the input terminal of the main control module.

5. The low-power backscatter communication tag according to claim 1, characterized in that: The transistor Q1 is made to operate at a static operating point by the DC bias circuit, so that the negative resistance amplification module is in a negative resistance amplification state.

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