CN112801255A

CN112801255A - Passive label

Info

Publication number: CN112801255A
Application number: CN201911108903.0A
Authority: CN
Inventors: 易俊; 甘泉; 刘健
Original assignee: Zhejiang Johar Technology Co ltd
Current assignee: Zhejiang Johar Technology Co ltd
Priority date: 2019-11-13
Filing date: 2019-11-13
Publication date: 2021-05-14

Abstract

A passive tag comprising: a tag antenna; the power supply module is coupled with the tag antenna to obtain the energy of the reader; the command processing module is used for receiving a command signal and generating a feedback signal according to the command signal, and the power supply module is coupled with the command processing module to supply power to the command processing module; and the self-oscillation modulation module is coupled with the command processing module and is used for adjusting the reflection energy of the tag antenna according to the feedback signal so that the difference value between the first reflection energy and the second reflection energy is greater than a preset threshold value, wherein the reflection energy of the tag antenna when the feedback signal is at a first level is recorded as the first reflection energy, and the reflection energy of the tag antenna when the feedback signal is at a second level is recorded as the second reflection energy. The scheme provided by the invention can effectively increase the reverse communication distance, thereby increasing the working distance of the ultrahigh frequency RFID reader and the tag system.

Description

Passive label

Technical Field

The invention relates to the technical field of passive tags, in particular to a passive tag.

Background

The working distance between a Radio Frequency Identification (RFID) reader and a tag system depends on the smaller value of the forward communication distance and the reverse communication distance.

Normally, the forward downstream communication distance is a bottleneck. However, in the RFID tag with very high sensitivity, the communication distance of the backscatter becomes a bottleneck, which is determined by the backscatter, which is a special way of backward communication adopted by the uhf RFID tag.

The prior art can not solve the problem of limitation of the backscattering to the working distance between the ultrahigh frequency RFID tag and the reader.

Disclosure of Invention

The invention solves the technical problem of providing an improved passive tag which can effectively increase the reverse communication distance.

To solve the above technical problem, an embodiment of the present invention provides a passive tag, including: the tag antenna is used for receiving reader energy; a power module coupled to the tag antenna to obtain the reader energy; the command processing module is used for receiving a command signal and generating a feedback signal according to the command signal, and the power supply module is coupled with the command processing module to supply power to the command processing module; and the self-oscillation modulation module is coupled with the command processing module and is used for adjusting the reflection energy of the tag antenna according to the feedback signal so that the difference value between first reflection energy and second reflection energy is greater than a preset threshold value, wherein the first reflection energy is the reflection energy of the tag antenna when the feedback signal is at a first level, and the second reflection energy is the reflection energy of the tag antenna when the feedback signal is at a second level.

Optionally, the preset threshold is determined according to a receiving sensitivity of the reader.

Optionally, the marking a terminal voltage of the tag antenna corresponding to the first reflected energy as a first voltage, and marking a terminal voltage of the tag antenna corresponding to the second reflected energy as a second voltage, where a difference between the first reflected energy and the second reflected energy is greater than a preset threshold refers to: one of the first voltage and the second voltage is at least twice as large as the other.

Optionally, the power supply module is coupled to the self-oscillation modulation module to supply power to the self-oscillation modulation module.

Optionally, the passive tag further includes: a control switch switchable between an open state and a closed state to break or make an electrical connection between the self-oscillation modulation module and the power supply module.

Optionally, the command processing module is coupled to the control switch, and the control switch switches between the open state and the closed state according to the feedback signal; the self-oscillation modulation module adjusts the reflected energy of the tag antenna according to the feedback signal, and the adjusting comprises the following steps: when the feedback signal is at the first level, the control switch is switched to an on state, and the self-oscillation modulation module is in a non-working state; when the feedback signal is at the second level, the control switch is switched to a closed state, and the self-oscillation modulation module is in a working state and resonates with the tag antenna to amplify the reflected energy of the tag antenna.

Optionally, the oscillation frequency of the self-oscillation modulation module is determined according to a communication operating frequency.

Optionally, the oscillation amplitude of the self-oscillation modulation module is determined according to the input energy.

Optionally, the self-oscillation modulation module includes: the power supply module comprises a first PMOS (P-channel metal oxide semiconductor) tube, a second PMOS tube, a first NMOS (N-channel metal oxide semiconductor) tube and a second NMOS tube, wherein the source electrode of the first PMOS tube and the source electrode of the second PMOS tube are connected in parallel with the power supply module, the drain electrode of the first PMOS tube is connected in series with the drain electrode of the first NMOS tube, the drain electrode of the second PMOS tube is connected in series with the drain electrode of the second NMOS tube, the grid electrode of the first PMOS tube is coupled with the drain electrode of the second PMOS tube, the grid electrode of the second PMOS tube is coupled with the drain electrode of the first PMOS tube, the grid electrode of the first NMOS tube is coupled with the drain electrode of the second NMOS tube, the grid electrode of the second NMOS tube is coupled with the drain electrode of the first NMOS tube, the source electrode of the first NMOS tube is grounded, and the source electrode of the second NMOS; and a first end of the first capacitor is coupled to the drain electrode of the first PMOS tube, and a second end of the first capacitor is coupled to the drain electrode of the second PMOS tube.

Optionally, a first end of the tag antenna is coupled to the drain of the first PMOS transistor, and a second end of the tag antenna is coupled to the drain of the second PMOS transistor.

Optionally, the passive tag further includes: the first end of the control switch is coupled with the power module, the source electrode of the first PMOS tube and the source electrode of the second PMOS tube are connected with the second end of the control switch in parallel, and the control switch is switched between an open state and a closed state according to the feedback signal so as to disconnect or connect the electric connection between the self-oscillation modulation module and the power module.

Optionally, the adjusting, by the self-oscillation modulation module, the reflected energy of the tag antenna according to the feedback signal includes: when the feedback signal is at the first level, the control switch is switched to an on state, and the self-oscillation modulation module is in a non-working state; when the feedback signal is at the second level, the control switch is switched to a closed state, and the first capacitor resonates with the tag antenna to increase the terminal voltage of the tag antenna.

Optionally, the power module includes: the energy conversion module is used for converting the energy of the reader into direct current energy; a second capacitor coupled to the energy conversion module to store the DC energy.

Optionally, the power module further includes: an energy storage unit coupled with the energy conversion module to store the DC energy, the energy storage unit further coupled with the self-oscillation modulation module to supply power to the self-oscillation modulation module.

Optionally, the command processing module includes: a demodulator for demodulating the command signal; and the digital control unit is coupled with the demodulator and generates the feedback signal according to the demodulated command signal.

Compared with the prior art, the technical scheme of the embodiment of the invention has the following beneficial effects:

an embodiment of the present invention provides a passive tag, including: the tag antenna is used for receiving reader energy; a power module coupled to the tag antenna to obtain the reader energy; the command processing module is used for receiving a command signal and generating a feedback signal according to the command signal, and the power supply module is coupled with the command processing module to supply power to the command processing module; and the self-oscillation modulation module is coupled with the command processing module and is used for adjusting the reflection energy of the tag antenna according to the feedback signal so that the difference value between first reflection energy and second reflection energy is greater than a preset threshold value, wherein the first reflection energy is the reflection energy of the tag antenna when the feedback signal is at a first level, and the second reflection energy is the reflection energy of the tag antenna when the feedback signal is at a second level.

Compared with the existing passive tag, the passive tag has a longer reverse communication distance, and further the working distance between an ultrahigh frequency RFID reader and a tag system is increased. Specifically, because the reader identifies the feedback signal according to a difference between the first reflected energy and the second reflected energy, the passive tag of this embodiment adjusts the reflected energy through the additional self-oscillation modulation module, and ensures that a difference between the first reflected energy and the second reflected energy is greater than the preset threshold, so that the feedback signal can be accurately and effectively detected by the reader.

Further, the terminal voltage of the tag antenna corresponding to the first reflected energy is regarded as a first voltage, the terminal voltage of the tag antenna corresponding to the second reflected energy is regarded as a second voltage, and the difference value between the first reflected energy and the second reflected energy is greater than a preset threshold value: one of the first voltage and the second voltage is at least twice as large as the other. Thus, the difference in voltage value by at least two times facilitates ensuring that the difference between the first reflected energy and the second reflected energy is sufficiently large to ensure that the feedback signal can be accurately detected by the reader.

Drawings

FIG. 1 is a schematic diagram of a prior art UHF RFID reader and tag system;

FIG. 2 is a logic block diagram of a passive tag of the prior art;

FIG. 3 is a schematic diagram of the feedback signal and terminal voltage of the tag antenna in a prior art passive tag;

FIG. 4 is a logic block diagram of a passive tag of an embodiment of the present invention;

fig. 5 is a schematic diagram of a feedback signal and a terminal voltage of a tag antenna in the passive tag shown in fig. 4.

Detailed Description

As background art, the prior art cannot solve the problem of limitation of the backscatter on the working distance between the ultrahigh frequency RFID tag and the reader.

Specifically, as shown in fig. 1, an ultra high frequency RFID reader and tag system 1 includes: an ultra high frequency RFID reader (may be simply referred to as reader) 10, a reader antenna 11, an ultra high frequency RFID tag chip 12, and a tag antenna 13. Wherein, the uhf RFID reader 10 and the reader antenna 11 may be integrated as a reader device, and the uhf RFID tag chip 12 and the tag antenna 13 may be integrated as a passive tag 2.

In operation, the transmission power P1 of the reader 10 is reduced after path attenuation and reaches the tag antenna 13, and is recorded as the reception power P2 of the passive tag. The received power P2 is attenuated by the same path before returning to the reader 10.

When the modulation switch 120 inside the tag chip 12 is in an on state (which may be referred to as "on"), the strength of the reflected signal (i.e., the reflected power) of the passive tag 2 received by the reader 10 is P3A.

When the modulation switch 120 is in a closed state (which may be referred to as on), the intensity of the reflected signal received by the reader 10 is P3B.

The reader 10 needs to be able to detect the difference between P3A and P3B to determine whether the modulation switch 120 is on or off to extract the data transmitted by the passive tag 2.

For the ultra high frequency RFID tag chip 12 with high sensitivity, the high sensitivity tag enables the forward communication distance to be extended, but this also means that the energy emitted by the reader antenna 11 is more attenuated when it reaches the tag antenna 13. Therefore, since the received power P2 is already small, the difference between the reflected powers P3A and P3B becomes extremely small, even lower than the reception sensitivity of the reader 10.

In a common uhf RFID passive tag 2, as shown in fig. 2, a radio frequency front end is composed of a rectifier 20, a demodulator 21, and a modulator 22. The key core of the circuit of the modulator 22 is a switch 220 (i.e., the modulation switch 120 shown in fig. 1), which is usually implemented by a Negative channel Metal Oxide Semiconductor (NMOS) switch.

The digital control circuit 23 is supplied by the output voltage VC of the rectifier 20, receives the input command PIE from the demodulator 21, processes it and returns a feedback signal BS _ DATA.

Referring to fig. 3, when the feedback signal BS _ DATA is low, the switch 220 is turned on, and has no effect on the terminal voltage RFP-RFN of the tag antenna 13, the peak-to-peak value is V2, and the corresponding reader 10 receives a reflected power P3A.

When the feedback signal BS _ DATA is high, the switch 220 is closed, the peak-to-peak value of the terminal voltage RFP-RFN of the tag antenna 13 is pulled down to a small amplitude V1, and the reflected power received by the corresponding reader 10 is P3B.

Thereby, backscattering (Backscatter) of the passive tag 2 is achieved.

At the reader 10, the difference between the reflected powers P3A and P3B must be higher than the receiving sensitivity of the reader 10, and the feedback signal BS _ DATA of the passive tag 2 can be effectively detected by the reader 10.

However, according to the foregoing analysis, for the passive tag 2 with high sensitivity, since the received power P2 is already very small, the absolute values of the reflected powers P3A and P3B are both small, and the difference therebetween is smaller. When the difference between the reflected powers P3A and P3B is less than the receiving sensitivity of the reader 10, the reader will not recognize the feedback signal of the passive tag 2. This results in that although the high-sensitivity passive tag 2 can effectively increase the forward communication distance with the reader 10, due to the limitation of backscattering, the backward communication distance of the passive tag 2 cannot support the extension of the forward communication distance, and the working distance between the ultrahigh frequency RFID reader and the tag 1 is limited by the backward communication distance, and cannot be really and effectively extended.

To solve the above technical problem, an embodiment of the present invention provides a passive tag, including: the tag antenna is used for receiving reader energy; a power module coupled to the tag antenna to obtain the reader energy; the command processing module is used for receiving a command signal and generating a feedback signal according to the command signal, and the power supply module is coupled with the command processing module to supply power to the command processing module; and the self-oscillation modulation module is coupled with the command processing module and is used for adjusting the reflection energy of the tag antenna according to the feedback signal so that the difference value between first reflection energy and second reflection energy is greater than a preset threshold value, wherein the first reflection energy is the reflection energy of the tag antenna when the feedback signal is at a first level, and the second reflection energy is the reflection energy of the tag antenna when the feedback signal is at a second level. The reflected energy of the tag antenna refers to a portion of the reader energy received by the tag antenna that is radiated outward by the tag antenna, and may be radiated out by backscattering, for example.

The passive tag has a longer reverse communication distance, and therefore the working distance between an ultrahigh frequency RFID reader and a tag system is increased. Specifically, because the reader identifies the feedback signal according to a difference between the first reflected energy and the second reflected energy, the passive tag of this embodiment adjusts the reflected energy through the additional self-oscillation modulation module, and ensures that a difference between the first reflected energy and the second reflected energy is greater than the preset threshold, so that the feedback signal can be accurately and effectively detected by the reader.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

Fig. 4 is a logic block diagram of a passive tag of an embodiment of the present invention. The passive tag can be applied to ultrahigh frequency RFID scenes.

Specifically, referring to fig. 4, the passive tag 4 according to this embodiment may include: a tag antenna 40 for receiving reader energy; a power module 41 coupled to the tag antenna 40 to obtain the reader energy; a command processing module 42, configured to receive a command signal and generate a feedback signal BS _ DATA according to the command signal, where the power supply module 41 is coupled to the command processing module 42 to supply power to the command processing module 42; a self-oscillation modulation module 43 coupled to the command processing module 42, wherein the self-oscillation modulation module 43 is configured to adjust a reflection energy of the tag antenna 40 according to the feedback signal BS _ DATA, so that a difference between a first reflection energy and a second reflection energy is greater than a preset threshold, where the first reflection energy is a reflection energy of the tag antenna 40 when the feedback signal BS _ DATA is at a first level, and the second reflection energy is a reflection energy of the tag antenna 40 when the feedback signal BS _ DATA is at a second level.

In one implementation, the reader power and command signal are both transmitted by a reader (e.g., reader 10 shown in FIG. 1) to the tag antenna 40 via a reader antenna (e.g., reader antenna 11 shown in FIG. 1). The command signal sent by the reader may be carried in the transmission power transmitted by the reader antenna (e.g., the transmission power P1 shown in fig. 1), that is, the reception power (e.g., the reception power P2 shown in fig. 1) reaching and received by the tag antenna 40, transmitted to the power supply module 41 to convert the reader energy, and transmitted to the command processing module 42 to demodulate the command signal.

In one implementation, the preset threshold may be determined according to a reception sensitivity of the reader. For example, the preset threshold may be equal to a receiving sensitivity of the reader to ensure that the reader can accurately distinguish the first reflected energy from the second reflected energy to identify the feedback signal.

In one variation, the preset threshold may be greater than the receive sensitivity of the reader to reduce the effects of path fading.

In one embodiment, the terminal voltage RFP-RFN of the tag antenna 40 corresponding to the first reflected energy is denoted as a first voltage, and the terminal voltage RFP-RFN of the tag antenna 40 corresponding to the second reflected energy is denoted as a second voltage, where a difference between the first reflected energy and the second reflected energy is greater than a preset threshold value: one of the first voltage and the second voltage is at least twice as large as the other.

Specifically, the terminal voltage RFP-RFN of the tag antenna 40 refers to a peak-to-peak value of a voltage across the first terminal 40a and the second terminal 40b of the tag antenna 40 coupled to the tag chip. It should be noted that fig. 4 only shows the positions of the first end 40a and the second end 40b of the tag antenna 40 by way of example, and in practical applications, the two ends may be interchanged.

For convenience, the first level is assumed to be a low level in this embodiment, and accordingly, the first reflected energy may correspond to the reflected power P3A in fig. 1, and the first voltage is denoted as V2, as shown in fig. 5; assuming that the second level is a high level, correspondingly, the second reflected energy may correspond to the reflected power P3B in fig. 1, and the second voltage is denoted as V3, as shown in fig. 5.

With the passive tag 4 of this embodiment, when the feedback signal BS _ DATA is at a low level, the reflected power P3A of the tag antenna 40 and the reflected power P3A of the conventional passive tag 2 shown in fig. 1 to 3 remain substantially unchanged, and accordingly, the first voltage V2 is substantially equal to the voltage value V2 shown in fig. 3.

Further, when the feedback signal BS _ DATA is at a high level, the passive tag 4 designed according to this embodiment can amplify the reflected power P3B of the tag antenna 40, so that the second voltage V3 is significantly greater than the peak-to-peak value V1 shown in fig. 3 and is at least twice as large as the peak-to-peak value V2 shown in fig. 5, so as to ensure that the difference between the reflected power P3A corresponding to the first reflected energy and the reflected power P3B corresponding to the second reflected energy is sufficiently greater than the receiving sensitivity of the reader.

The reason why the second voltage V3 is at least twice the first voltage V2 can be derived based on the following formula: assuming that V2 ≈ 2 × V1 and V1 ≈ 0 in fig. 3, to satisfy (V2-V1) < (V3-V2), V3> (2 × V2) can be derived.

In practical applications, the proportional relationship between the second voltage V3 and the first voltage V2 can be adjusted as required. For example, the second voltage V3 may be three to four times the first voltage V2.

In one implementation, the power module 41 may be coupled to the self-oscillation modulation module 43 to supply power to the self-oscillation modulation module 43.

In one implementation, the passive tag 4 may further include: a control switch 44, said control switch 44 being switchable between an open state and a closed state to open or close an electrical connection between said self-oscillation modulation module 43 and said power supply module 41.

In one implementation, the command processing module 40 may be coupled to the control switch 44, and the control switch 44 may be switched between the open state and the closed state according to the feedback signal BS _ DATA.

For example, when the feedback signal BS _ DATA is at the first level, the control switch 44 may be switched to an on state, and the self-oscillation modulating module 43 may be in a non-operating state. At this time, the peak-to-peak value of the voltage across the tag antenna 40 is the first voltage V2, and the reflected power received by the corresponding reader end is P3A (i.e., the first reflected energy).

When the feedback signal is at the second level, the control switch 44 is switched to a closed state, the self-oscillation modulation module 43 is in an operating state, and resonates with the tag antenna 40 by using the energy of the power supply module 41, so as to increase the peak-to-peak value of the voltage across the tag antenna 40 to the second voltage V3, thereby amplifying the reflected energy of the tag antenna 40. At this time, the corresponding reader segment receives the reflected power P3B (i.e., the second reflected energy).

In one implementation, the oscillation frequency of the self-oscillation modulation module 43 may be determined according to the communication operating frequency. The communication operating frequency refers to a carrier center frequency specified by a communication protocol, and the communication protocol may be an existing communication protocol and also includes a related communication protocol specified in the future.

For example, the oscillation frequency of the self-oscillation modulation module 43 may be substantially equal to the communication operation frequency, so that the self-oscillation modulation module 43 can effectively excite the signal frequency to oscillate to generate resonance when operating. The resonance frequency may also be referred to as a signal frequency.

In one implementation, the oscillation amplitude of the self-oscillation modulation module 43 may be determined according to the input energy. In particular, the input energy may be provided by the power supply module 41.

In one implementation, the power module 41 may include: an energy conversion module 410, configured to convert the reader energy into direct current energy; a second capacitor 411 coupled to the energy conversion module 410 for storing the dc energy.

For example, the energy conversion module 410 may be a rectifier, the rectifier converts the rf energy received by the tag antenna 40 from the reader into dc energy and stores the dc energy into the second capacitor 411, and the command processing module 42 may be powered by the second capacitor 411 during operation.

In one implementation, the second capacitor 411 may be further coupled to the self-oscillation modulation module 43 through the control switch 44 to supply power to the self-oscillation modulation module 43 when the control switch 44 is closed.

In a variation, the power module 41 may further include: an energy storage unit 412 coupled to the energy conversion module 410 to store the dc energy, the energy storage unit 412 further coupled to the self-oscillation modulation module 43 to supply power to the self-oscillation modulation module 43.

Therefore, the second capacitor 411 can be dedicated to support the operation of the command processing module 42, so that the capacity of the second capacitor 411 can be reduced appropriately, which is beneficial to realizing the miniaturized design of the passive tag 4.

In one implementation, the energy storage unit 412 may be coupled to the self-oscillation modulation module 43 through the control switch 44 to supply power to the self-oscillation modulation module 43 when the control switch 44 is closed.

In one implementation, the energy storage unit 412 may be a large capacitor, a super capacitor, a battery, or the like.

In one implementation, the self-oscillation modulating module 43 may include: a first PMOS transistor 430, a second PMOS transistor 431, a first NMOS transistor 432, and a second NMOS transistor 433, wherein a source of the first PMOS transistor 430 and a source of the second PMOS transistor 431 are connected in parallel to the power module 41, a drain of the first PMOS transistor 430 and a drain of the first NMOS transistor 432 are connected in series, a drain of the second PMOS transistor 431 and a drain of the second NMOS transistor 433 are connected in series, a gate of the first PMOS transistor 430 is coupled to the drain of the second PMOS transistor 431, a gate of the second PMOS transistor 431 is coupled to the drain of the first PMOS transistor 430, a gate of the first NMOS transistor 432 is coupled to the drain of the second NMOS transistor 433, a gate of the second NMOS transistor 433 is coupled to the drain of the first NMOS transistor 432, a source of the first NMOS transistor 432 is grounded, and a source of the second NMOS transistor 433 is grounded.

Further, the self-oscillation modulating module 43 may further include: a first end 434a of the first capacitor 434 is coupled to the drain of the first PMOS transistor 430, and a second end 434b of the first capacitor 434 is coupled to the drain of the second PMOS transistor 431.

Further, the first end 40a of the tag antenna 40 may be coupled to the drain of the first PMOS transistor 430, and the second end 40b of the tag antenna 40 may be coupled to the drain of the second PMOS transistor 431.

In one embodiment, a first end of the control switch 44 may be coupled to the power module 41, a source of the first PMOS transistor 430 and a source of the second PMOS transistor 431 may be connected in parallel to a second end of the control switch 44, and the control switch 44 is switched between an open state and a closed state according to the feedback signal BS _ DATA to open or close an electrical connection between the self-oscillation modulation module 43 and the power module 41.

For example, when the feedback signal BS _ DATA may be at the first level, the control switch 44 is switched to an on state, and the self-oscillation modulation module 43 is in a non-operating state.

When the feedback signal BS _ DATA is at the second level, the control switch 44 may be switched to a closed state, the tag antenna 40 and the first capacitor 434 may equivalently form an LC oscillator, and the first capacitor 434 resonates with the tag antenna 40 to increase the terminal voltage of the tag antenna 40.

In one implementation, the command processing module 42 may include: a demodulator 420 for demodulating the command signal; a digital control unit 421 coupled to the demodulator 420 and generating the feedback signal BS _ DATA according to the demodulated command signal.

For example, the demodulator 420 may be coupled to the tag antenna 40 to convert the attenuation/non-attenuation variation of the radio frequency signal received by the tag antenna 40 into a high/low level variation, and transmit the conversion result as an input command PIE to the digital control unit 421. Wherein, the input command PIE includes the content of the command signal.

For another example, the demodulator 420 may operate directly based on the reader power, and the digital control unit 421 may be powered by the second capacitor 411.

In practical applications, the first level may be set to a high level, and the second level may be set to a low level.

Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A passive tag, comprising:

the tag antenna is used for receiving reader energy;

a power module coupled to the tag antenna to obtain the reader energy;

the command processing module is used for receiving a command signal and generating a feedback signal according to the command signal, and the power supply module is coupled with the command processing module to supply power to the command processing module;

and the self-oscillation modulation module is coupled with the command processing module and is used for adjusting the reflection energy of the tag antenna according to the feedback signal so that the difference value between first reflection energy and second reflection energy is greater than a preset threshold value, wherein the first reflection energy is the reflection energy of the tag antenna when the feedback signal is at a first level, and the second reflection energy is the reflection energy of the tag antenna when the feedback signal is at a second level.

2. The passive tag of claim 1, wherein the preset threshold is determined according to a receive sensitivity of a reader.

3. The passive tag of claim 1, wherein the terminal voltage of the tag antenna corresponding to the first reflected energy is denoted as a first voltage, and the terminal voltage of the tag antenna corresponding to the second reflected energy is denoted as a second voltage, and a difference between the first reflected energy and the second reflected energy is greater than a preset threshold value: one of the first voltage and the second voltage is at least twice as large as the other.

4. The passive tag of claim 1, wherein the power module is coupled with the self-oscillating modulation module to provide power to the self-oscillating modulation module.

5. The passive tag of claim 4, further comprising:

a control switch switchable between an open state and a closed state to break or make an electrical connection between the self-oscillation modulation module and the power supply module.

6. The passive tag of claim 5, wherein the command processing module is coupled to the control switch, the control switch switching between the open state and the closed state in accordance with the feedback signal;

the self-oscillation modulation module adjusts the reflected energy of the tag antenna according to the feedback signal, and the adjusting comprises the following steps:

when the feedback signal is at the first level, the control switch is switched to an on state, and the self-oscillation modulation module is in a non-working state;

when the feedback signal is at the second level, the control switch is switched to a closed state, and the self-oscillation modulation module is in a working state and resonates with the tag antenna to amplify the reflected energy of the tag antenna.

7. The passive tag of claim 1, wherein the oscillation frequency of the self-oscillating modulation module is determined from a communication operating frequency.

8. The passive tag of claim 1, wherein the amplitude of oscillation of the self-oscillating modulation module is determined from an input energy.

9. The passive tag of claim 1, wherein the self-oscillating modulation module comprises:

the power supply module comprises a first PMOS (P-channel metal oxide semiconductor) tube, a second PMOS tube, a first NMOS (N-channel metal oxide semiconductor) tube and a second NMOS tube, wherein the source electrode of the first PMOS tube and the source electrode of the second PMOS tube are connected in parallel with the power supply module, the drain electrode of the first PMOS tube is connected in series with the drain electrode of the first NMOS tube, the drain electrode of the second PMOS tube is connected in series with the drain electrode of the second NMOS tube, the grid electrode of the first PMOS tube is coupled with the drain electrode of the second PMOS tube, the grid electrode of the second PMOS tube is coupled with the drain electrode of the first PMOS tube, the grid electrode of the first NMOS tube is coupled with the drain electrode of the second NMOS tube, the grid electrode of the second NMOS tube is coupled with the drain electrode of the first NMOS tube, the source electrode of the first NMOS tube is grounded, and the source electrode of the second NMOS;

and a first end of the first capacitor is coupled to the drain electrode of the first PMOS tube, and a second end of the first capacitor is coupled to the drain electrode of the second PMOS tube.

10. The passive tag of claim 9, wherein a first end of the tag antenna is coupled to the drain of the first PMOS transistor and a second end of the tag antenna is coupled to the drain of the second PMOS transistor.

11. The passive tag of claim 10, further comprising:

the first end of the control switch is coupled with the power module, the source electrode of the first PMOS tube and the source electrode of the second PMOS tube are connected with the second end of the control switch in parallel, and the control switch is switched between an open state and a closed state according to the feedback signal so as to disconnect or connect the electric connection between the self-oscillation modulation module and the power module.

12. The passive tag of claim 11, wherein the self-oscillating modulation module adjusting the reflected energy of the tag antenna according to the feedback signal comprises:

when the feedback signal is at the second level, the control switch is switched to a closed state, and the first capacitor resonates with the tag antenna to increase the terminal voltage of the tag antenna.

13. A passive tag according to any of claims 1 to 12, wherein the power supply module comprises:

the energy conversion module is used for converting the energy of the reader into direct current energy;

a second capacitor coupled to the energy conversion module to store the DC energy.

14. The passive tag of claim 13, wherein the power module further comprises:

an energy storage unit coupled with the energy conversion module to store the DC energy, the energy storage unit further coupled with the self-oscillation modulation module to supply power to the self-oscillation modulation module.

15. A passive tag according to any of claims 1 to 12, wherein the command processing module comprises:

a demodulator for demodulating the command signal;

and the digital control unit is coupled with the demodulator and generates the feedback signal according to the demodulated command signal.