Carrier leakage elimination device and method for high-power ultra-high frequency radio frequency identification

Abstract

The present invention discloses a carrier leakage elimination device and method for high-power ultra-high frequency radio frequency identification. The device includes a power amplifier, a first directional coupler, a first 3dB bridge, a second 3dB bridge, a third 3dB bridge, two circulators, and an antenna. The output of the power amplifier is connected to the input of the first directional coupler, the output of the first directional coupler is connected to the first 3dB bridge, the first 3dB bridge is respectively connected to a circulator, and both circulators are connected to the second 3dB bridge, which is connected to the antenna. The two circulators are also connected to the third 3dB bridge, which is connected to the receiving signal terminal. The present invention can solve the carrier leakage problem of ultra-high frequency radio frequency identification readers or other microwave reflection communications when transmitting high-power signals.

Description

Technical Field

[0001] The present invention relates to the field of radio frequency technology, and in particular to a carrier leakage elimination device and method for high-power ultra-high frequency radio frequency identification. Background Art

[0002] RFID is an automatic identification technology that emerged in the 1990s. It uses radio frequency signals to achieve contactless information transmission through spatial coupling, and uses the transmitted information to achieve identification. The energy required for the operation of RFID's electronic data carrier, namely the electronic tag, can be obtained contactlessly through a card reader. Currently, the commonly used RFID frequency distribution internationally is as follows: low frequency 30-300KHz, with typical representative frequencies of 125KHz and 133KHz, typical applications such as animal identification and electronic locking and anti-theft; high frequency 3-30MHz, with a typical frequency of 13.56MHz, typical applications such as second-generation ID cards; ultra-high frequency 860-960MHz (including 433MHz frequency), with a typical frequency of 868MHz, typical applications such as ETC; microwave frequency bands are 2.45GHz and 5.8GHz.

[0003] RFID's low-frequency and high-frequency applications work using inductive coupling, with the distance between the electronic tag and the reader being a few centimeters or at most tens of centimeters. RFID's ultra-high-frequency and microwave applications use electromagnetic wave backscatter coupling, allowing the distance between the electronic tag and the reader to reach several meters or even tens of meters. However, since the reader integrates a transceiver antenna, i.e., the transmitting antenna and the receiving antenna share one, there must be a carrier signal leaked from the reader's transmitting circuit in the reader's receiving circuit. This carrier leakage forms a self-interference signal in the reader, which significantly deteriorates the reader's receiving sensitivity and thus affects the receiving distance. In severe cases, it can even block the reader, causing it to lose its communication capability. Therefore, the circuit must suppress the self-interference signal. For example, at a carrier leakage level of 0 to 5dBm, the receiver sensitivity of the integrated card reader is around -70dBm. However, at a carrier leakage level of -10dBm, the receiver sensitivity can reach -85dBm. The difference in receiving sensitivity between the two cases is 15dB, which will result in a communication distance that is at least twice as different. Therefore, this self-interference signal must be eliminated using a carrier leakage suppression circuit.

[0004] my country's UHF RFID standard stipulates that the reader's EIRP should be ≤ 2W. For example, ETC antennas typically have a gain of at least 6dBi, so the output power of the power amplifier in the reader is typically below 0.5W. Generally speaking, increasing transmit power is the most direct way to extend the communication range in wireless communications. However, in practice, certain UHF RFID applications require exceeding the conventional distance between the reader and the tag to meet actual communication requirements. This necessitates high-powered reader transmission signals, creating a need for carrier leakage cancellation devices that can withstand high power and effectively suppress carrier leakage.

[0005] Currently, there are two main types of carrier leakage cancellation technologies: active and passive devices, and analog and digital signal processing. Application-specific integrated circuits (ASICs) are also used. Their high level of integration allows for smaller circuits, but they also come with high development costs.

[0006] Passive devices, such as circulators and directional couplers, do not require power and do not introduce additional noise into the circuit, thus avoiding degrading the signal-to-noise ratio of the desired signal while eliminating leakage signals. Active devices, on the other hand, offer greater processing power and can amplify signals, thereby processing stronger leakage signals.

[0007] The difference between analog and digital circuits in eliminating carrier leakage lies in precision. Digital circuits can adjust the signal's amplitude and phase with greater accuracy. Currently, almost all carrier leakage cancellation technologies are based on generating a cancellation signal (sometimes called a reference signal) with the same amplitude but opposite phase as the leakage signal, and then adding the two together to cancel each other out. Therefore, the error between the two signals—the amplitude and phase errors of the cancellation and leakage signals—is a significant factor influencing the cancellation effect. Higher precision means smaller errors, ideally zero, completely canceling out the carrier leakage signal. While digital signals offer greater precision and allow for finer control over analog-to-digital conversion, they also introduce more quantization noise and digital spurious signals, which ultimately negatively impact the signal-to-noise ratio of the desired signal.

[0008] The transmission power of UHF RFID readers is relatively low, below 0.5W, and the general communication distance is within 10 meters. Increasing the transmission power to increase the communication distance, or increasing the transmission power of microwave reflection communication based on similar principles, will inevitably lead to an increase in the carrier leakage power. The current UHF RFID readers can generally withstand a leakage power below 10dBm, otherwise the reader's RF receiving channel will be blocked. Summary of the Invention

[0009] In view of the shortcomings of the prior art, the present invention aims to provide a carrier leakage elimination device and method for high-power ultra-high frequency radio frequency identification.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A carrier leakage elimination device for high-power ultra-high frequency radio frequency identification comprises a power amplifier, a first directional coupler, a first 3dB bridge, a second 3dB bridge, a third 3dB bridge, two circulators, and an antenna; the output end of the power amplifier is connected to the input end of the first directional coupler, the output end of the first directional coupler is connected to the first 3dB bridge, the first 3dB bridge is respectively connected to a circulator, both circulators are connected to the second 3dB bridge, and the second 3dB bridge is connected to the antenna; the two circulators are also connected to the third 3dB bridge, and the third 3dB bridge is connected to a receiving signal end.

[0012] Furthermore, the carrier leakage elimination device also includes a directional coupler three, a directional coupler four and a directional coupler five. The 3dB bridge three, the directional coupler three, the directional coupler four and the directional coupler five are connected in sequence, and the directional coupler five is connected to the receiving signal end.

[0013] Furthermore, the carrier leakage elimination device also includes a digitally controlled phase shifter, a second directional coupler, an attenuator 1, an attenuator 2, a microprocessor, and an amplitude and phase comparator; the input end of the digitally controlled phase shifter is connected to the output end of the first directional coupler, and the output end of the digitally controlled phase shifter is connected to the second directional coupler; the second directional coupler is connected to the fourth directional coupler; the second directional coupler and the third directional coupler are respectively connected to the first attenuator and the second attenuator, and the first attenuator and the second attenuator are both connected to the amplitude and phase comparator, the amplitude and phase comparator is connected to the microprocessor, and the microprocessor is connected to the digitally controlled phase shifter.

[0014] Furthermore, the directional coupler five is also connected to the attenuator three, the attenuator three is connected to a power detection module, and the power detection module is connected to the microprocessor.

[0015] Furthermore, in the digitally controlled phase shifter, 10 levels of phase shift are connected in series in the order of 0.5°, 1°, 2°, 4°, 8°, 16°, 19°, 45°, 90°, and 180°, and the 10th level of phase shift is also connected to the RF signal attenuator; each level of phase shift and RF signal attenuator are switched on and off by digital logic levels.

[0016] The present invention also provides a working method of the above-mentioned carrier leakage elimination device for high-power ultra-high frequency radio frequency identification, including a process of transmitting a signal to an antenna, wherein the process of transmitting a signal to an antenna is:

[0017] In the process of transmitting a signal to the antenna, the signal output by the signal source passes through the power amplifier PA to obtain the carrier transmission signal TX. The carrier transmission signal TX is first sent to the balanced circulator isolation circuit through directional coupler 1. In the balanced circulator isolation circuit, the transmission signal output by directional coupler 1 is divided into two parts with the same amplitude but a phase difference of 90 degrees through 3dB bridge 1. The two parts are respectively sent to 3dB bridge 2 through the circulators of the upper branch and lower branch. The phase of the upper branch signal, which was originally in phase with the transmission signal, is increased by 90 degrees at 3dB bridge 2, while the phase of the lower branch signal, which was originally 90 degrees out of phase with the transmission signal, remains unchanged at 3dB bridge 2. Therefore, the upper branch signal and the lower branch signal have the same amplitude and phase at 3dB bridge 2. They are superimposed to form a new transmission signal and sent to antenna ANT, which radiates into space.

[0018] In the process of transmitting the signal TX to the antenna ANT, the upper branch signal output by the 3dB bridge 1 has half the power of the transmitted signal and is in phase with the transmitted signal. When passing through the counterclockwise circulator, a part of the carrier will be leaked. This part of the carrier enters the 3dB bridge 3 and still maintains the phase unchanged when passing through the 3dB bridge 3. The power of the lower branch signal output by the 3dB bridge 1 is also half of the transmitted signal, but the phase lags behind the transmitted signal by 90 degrees. When passing through the circulator of the lower branch, a part of the carrier is also leaked. This part of the carrier enters the 3dB bridge 3 and lags the phase again by 90 degrees when passing through the 3dB bridge 3. The accumulated phase is 180 degrees different from the transmitted signal. In this way, two signals with the same amplitude but opposite phases are superimposed at the output port of the 3dB bridge 3. As a result, the two signals cancel each other out, thus eliminating the carrier leakage caused by the circulators of the upper and lower branches.

[0019] Furthermore, the method further includes a process of receiving a signal to a signal receiving end; the process of receiving a signal to a signal receiving end is:

[0020] The spatial electromagnetic waves returned by the electronic tag are received by the antenna and converted into weak electrical signals. The weak electrical signals must first pass through the balanced circulator isolation circuit; in the balanced circulator isolation circuit, 3dB bridge 2 divides the weak electrical signal into an upper branch signal and a lower branch signal with the same amplitude and a phase difference of 90 degrees. After the upper branch signal and the lower branch signal are circulated by the circulator, they are combined at the third point of the 3dB bridge. The lower branch signal, which was originally in phase with the received signal, has its phase increased by 90 degrees at the third point of the 3dB bridge, while the upper branch signal, which was originally 90 degrees out of phase with the received signal, maintains its phase at the third point of the 3dB bridge. Therefore, the upper branch signal and the lower branch signal have the same amplitude and phase at the third point of the 3dB bridge. They are superimposed to form a new received signal and sent to directional coupler 3. Then, they pass through directional couplers 4 and 5 in sequence and are output to the receiving signal end.

[0021] Furthermore, the method further includes a second-stage leakage signal elimination process, and the second-stage leakage signal elimination process is:

[0022] A reference signal is generated, which is taken from the output signal of the power amplifier and is generated by the coupling end of directional coupler 1. Directional coupler 2 couples out the reference signal, and directional coupler 3 couples out the leakage signal. The reference signal and leakage signal are adjusted in amplitude through attenuators 1 and 2, respectively, so that the reference signal and leakage signal have the same amplitude when they reach the amplitude and phase comparator.

[0023] The amplitude and phase comparator determines the amplitude difference and phase difference between the amplitude and phase comparators and sends them to the microprocessor. The microprocessor accurately quantifies the amplitude difference and phase difference between the reference signal and the leakage signal before addition, combining them with the coupling degrees of directional coupler two, directional coupler three, and directional coupler four, as well as the parameters of attenuator one and attenuator two. The microprocessor then changes the amplitude and phase of the reference signal by adjusting the numerically controlled phase shifter to obtain a reference signal and leakage signal with the same amplitude and opposite phase. The reference signal and leakage signal with the same amplitude and opposite phase are added at the four locations of the directional coupler and cancel each other out.

[0024] Furthermore, the signal obtained by adding the reference signal and the leakage signal is coupled out by directional coupler 5, and 1% is sent to the power detection module through attenuator 3. The power detection module detects the carrier leakage signal remaining after cancellation and sends the detection result to the microprocessor. If the expected value is reached, the microprocessor stops searching for the phase difference and amplitude difference. Otherwise, the amplitude difference and phase difference are corrected until the expected cancellation effect is achieved.

[0025] Furthermore, the process by which the microprocessor changes the amplitude and phase of the reference signal by adjusting the digitally controlled phase shifter is as follows:

[0026] First, based on the amplitude difference between the leakage signal and the reference signal, the amplitude of the reference signal is attenuated on a large scale.

[0027] Then, the optimal phase shift value is searched first: the phase shift accuracy is initialized to a coarser step. After the phase shift, the amplitude of the residual leakage signal is compared to see if it has decreased. If so, it is considered to be a valid phase shift value. The phase shift step accuracy is then increased, and so on, until the highest phase shift accuracy is achieved.

[0028] Next, determine the attenuation fine-tuning value of the CNC phase shifter: ensure that the amplitude of the reference signal sent to directional coupler 4 for addition is greater than the leakage signal. On this basis, search for the optimal attenuation value: initialize the attenuation value to a coarser step, and compare the amplitude of the residual leakage signal after attenuation to see if it has decreased. If so, it is considered an effective attenuation value. Then increase the attenuation step accuracy, and so on, until the highest attenuation accuracy is achieved.

[0029] The beneficial effects of the present invention are:

[0030] 1. High power handling capacity. The device of the present invention utilizes passive RF components such as circulators, directional couplers, and digitally controlled phase shifters, significantly improving its transmit signal power handling capacity. Theoretical calculations show that the device can function normally even with a transmit signal TX power of 100 watts. Experimental data demonstrates that the device maintains stable suppression of carrier leakage signals within a transmit power range of 1 watt to 20 watts. This power value is far greater than the 0.5 watt transmit power of typical UHF RFID systems.

[0031] Second, the device has a strong ability to eliminate carrier leakage. The device of the present invention adopts a two-stage cancellation strategy for the leaked carrier. The first stage of cancellation mainly eliminates the carrier leakage of the circulator in the circuit. It adopts a balanced circuit composed of two circulators and three 3dB bridges. This stage of cancellation mainly processes leakage signals with relatively large amplitudes. The second stage of cancellation targets the total carrier leakage signal remaining after the first stage of cancellation, such as antenna echo and directional coupler leakage. It adopts the method of first generating a reference signal, then sampling and comparing the phase difference and amplitude difference between the reference signal and the leakage signal, and then aligning the reference signal and the leakage signal through a digitally controlled phase shifter DCPS so that they are of equal amplitude and opposite direction. Finally, they are superimposed and cancel each other in the directional coupler. The second stage processes leakage signals with relatively small amplitudes. In general, through two-stage cancellation, the device of the present invention achieves a carrier leakage signal suppression ratio of over 70dB. When the transmit power TX is equal to 20 watts (43dBm), the amplitude of the carrier leakage signal leaking to the receiving link remains below -30dBm. This value is very safe for the receiving link and achieves the design goal of ensuring that the UHF RFID system can still operate normally even when the high-power signal is transmitted.

[0032] 3. The noise coefficient of the receiving link is small. The carrier leakage elimination device of the present invention is actually a transceiver isolation device. The impact of this type of device on the receiving link is mainly reflected in the insertion loss and the increase in the noise floor. In a unified way, it can be represented by the noise coefficient. The path loss from the antenna to the output end of the receiving signal in the device of the present invention is 1.45dB, and no amplifier is used in the device of the present invention, so the noise floor will hardly be increased. Therefore, it can be considered that the noise coefficient of the device of the present invention on the receiving path is 1.45dB. This value shows that connecting the device of the present invention to the ultra-high frequency radio frequency identification system will not have a significant impact on its receiving sensitivity. Compared with the significant increase in transmission power, this negative impact is completely acceptable.

[0033] In general, the present invention can solve the problem of carrier leakage in ultra-high frequency radio frequency identification readers or other microwave reflection communications when transmitting signals at high power, thereby expanding the distance between the reader and the electronic tag and enhancing the practicality of the system. It can also increase the communication distance between the rear equipment and the front reflection equipment in microwave reflection communication, thereby increasing the detection distance. Moreover, the device of the present invention uses existing electronic components on the market, and does not require the development of dedicated integrated circuits, so the circuit cost is relatively low. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the structure of the carrier leakage elimination device in embodiment 1 of the present invention;

[0035] Figure 2 Schematic diagram of the structure of the digital controlled phase shifter in Example 1 of the present invention;

[0036] Figure 3 This is a flow chart of the algorithm for the second-level elimination in Example 2 of the present invention;

[0037] Figure 4 Schematic diagram of the principle of the experiment in Example 3 of the present invention;

[0038] Figure 5 This is a schematic diagram of an attenuator with a resistor П-type connection;

[0039] Figure 6 This is a schematic diagram of the transmit-receive isolation results of the carrier leakage cancellation device obtained in the experiment in Example 3 of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with the accompanying drawings. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to this embodiment.

[0041] Example 1

[0042] If UHF RFID or similar microwave reflection communication systems want to increase the communication distance with electronic tags or front-end devices to meet the needs of certain practical application scenarios, increasing the transmit power is an effective and simple method. However, as the transmit power increases, the carrier leakage power also increases accordingly, and even deteriorates nonlinearity. UHF RFID and similar microwave reflection communication systems generally have low-noise amplifiers (LNAs) in the RF receive chain. When the carrier leakage signal power to the receive chain exceeds 0dBm (1mW), the LNA is prone to saturation distortion, which degrades the receiver sensitivity and can even block the receiver, causing the system to malfunction.

[0043] The device of this embodiment is proposed to meet such application requirements. Figure 1 As shown, directional couplers and circulators are used in the path through which large signals flow. These can withstand hundreds of watts of power, and the specially designed digitally controlled phase shifters in the path can also withstand nearly 10W of RF power. Moreover, these devices are basically passive, that is, they require almost no power and do not amplify the signal. Therefore, the carrier leakage elimination device proposed in this embodiment will not raise the noise floor level of the receiver, and the difference in the received signal is also controlled within 1.5dB, so it will not significantly affect the sensitivity of the receiver. At the same time, the carrier leakage elimination device proposed in this embodiment can suppress the carrier leakage to 70dB, so there is no risk of LNA saturation distortion for the transmission signal of tens of watts. Experimental test data shows that when the transmission and reception share the same antenna, the leakage generated by the 0.5-20W high-power carrier signal is eliminated, and the suppression ratio is above 70dB.

[0044] This embodiment provides a carrier leakage elimination device for high-power ultra-high frequency radio frequency identification, such as Figure 1 As shown, it includes a power amplifier, a directional coupler 1, a 3dB bridge 1, a 3dB bridge 2, a 3dB bridge 3, two circulators and an antenna ANT; the output end of the power amplifier is connected to the input end of the directional coupler 1, the output end of the directional coupler 1 is connected to the 3dB bridge 1, the 3dB bridge 1 is respectively connected to a circulator, both circulators are connected to the 3dB bridge 2, and the 3dB bridge 2 is connected to the antenna; the two circulators are also connected to the 3dB bridge 3, and the 3dB bridge 3 is connected to the receiving signal end (RX).

[0045] Furthermore, in this embodiment, the carrier leakage elimination device also includes a directional coupler three, a directional coupler four and a directional coupler five, the 3dB bridge three, the directional coupler three, the directional coupler four and the directional coupler five are connected in sequence, and the directional coupler five is connected to the receiving signal end.

[0046] Furthermore, in this embodiment, the carrier leakage elimination device also includes a digitally controlled phase shifter DCPS, a directional coupler 2, an attenuator 1, an attenuator 2, a microprocessor MPU, and an amplitude and phase comparator GPD; the input end of the digitally controlled phase shifter is connected to the output end of the directional coupler 1, and the output end of the digitally controlled phase shifter is connected to the directional coupler 2; the directional coupler 2 is connected to the directional coupler 4; the directional coupler 2 and the directional coupler 3 are respectively connected to the attenuator 1 (ПAttenuator 1) and the attenuator 2 (ПAttenuator 2), the attenuator 1 and the attenuator 2 are both connected to the amplitude and phase comparator, the amplitude and phase comparator is connected to the microprocessor, and the microprocessor is connected to the digitally controlled phase shifter.

[0047] Furthermore, in this embodiment, the directional coupler five is also connected to the attenuator three (Π attenuator three), the attenuator three is connected to the power detection module PD, and the power detection module is connected to the microprocessor.

[0048] In this embodiment, the attenuator 1, attenuator 2, and attenuator 3 are all resistor П-type attenuators.

[0049] Specifically, in this embodiment, the digitally controlled phase shifter DCPS plays a key role in the carrier leakage elimination circuit. This embodiment designs a 10-digital controlled phase shifter based on a transmission line, such as Figure 2 The digital controlled phase shifter DCPS designed in this embodiment has a phase shift accuracy of 0.5 degrees, which is better than most digital controlled phase shifters currently on the market with an accuracy of 5.625 degrees. Its phase shift range is 0-364.5 degrees. Whether each level of phase shift is determined by the closed state of the single-pole double-throw SPDT switch, and these switches are controlled by digital logic levels, such as Figure 2 As shown, 10 phase shifters are connected in series in the order of 0.5°, 1°, 2°, 4°, 8°, 16°, 19°, 45°, 90°, and 180°. The resulting total insertion loss is 6dB within the operating frequency band, with a 1dB input compression point of 39dBm and a 0.1dB input compression point of 36.5dBm. This is higher than the 20-0dBm input compression point of most commercially available digitally controlled phase shifters. This allows the device to handle the high-power transmit signals of UHF RFID readers. The digitally controlled phase shifter also includes a digitally controlled RF signal attenuator (ATT) with an attenuation accuracy of 0.25dB and an attenuation range of 31.75dB. It is controlled by a 7-bit logic level switch: 0.25dB, 0.5dB, 1dB, 2dB, 4dB, 8dB, and 16dB. For the parameters of the digitally controlled phase shifter with a phase accuracy of 0.5 degrees and an amplitude accuracy of 0.25dB, the cancellation ratio that can be achieved by applying the digitally controlled phase shifter DCPS can reach 25dB.

[0050] Example 2

[0051] This embodiment provides a method for operating the carrier leakage elimination device for high-power ultra-high frequency radio frequency identification described in Example 1. The method includes three parts:

[0052] (1) The process of transmitting signal TX to antenna ANT:

[0053] The signal output by the signal source passes through the power amplifier PA to obtain a +27~43dBm (0.5~20W) carrier transmission signal TX. The carrier transmission signal TX first passes through a directional coupler and is sent to the balanced circulator isolation circuit, that is, Figure 1 The dotted box portion in the figure. The balanced circulator isolation circuit is a core circuit specially designed for this embodiment. It consists of three 3dB bridges and two circulators. The transmission signal output by directional coupler one is divided into two parts with the same amplitude but a phase difference of 90 degrees through 3dB bridge one, and is sent to 3dB bridge two through the circulators of the upper and lower branches respectively. The upper branch signal, which was originally in phase with the transmission signal, has its phase increased by 90 degrees at 3dB bridge two, while the lower branch signal, which was originally 90 degrees out of phase with the transmission signal, has its phase maintained at 3dB bridge two. Therefore, the signals of the upper and lower branches have the same amplitude and phase at 3dB bridge two. They are superimposed into a new transmission signal and sent to antenna ANT, which radiates into space. The new transmission signal is 90 degrees out of phase with the original carrier transmission signal TX. The amplitude difference is the sum of the difference losses of directional coupler one and the balanced circulator isolation circuit. The coupling degree of directional coupler 1 is 10 dB, and the loss in the operating frequency band is 0.47 dB. The loss of the balanced circulator isolation circuit includes two 3 dB bridges, each with a loss of 0.16 dB, and two circulators, each with a loss of 0.2 dB. Therefore, the path loss from the transmitted signal TX to the antenna ANT is 0.47 + 0.16 x 2 + 0.2 x 2 = 1.19 dB. This value is relatively small and ensures that when the carrier leakage cancellation circuit of this embodiment is used in a UHF RFID system, most of the transmission power can still be delivered to the antenna.

[0054] (2) The process from antenna ANT to receiving output signal RX:

[0055] The electromagnetic waves returned by the electronic tag are received by the antenna ANT and converted into weak electrical signals, such as Figure 1As shown, the weak electric signal must first pass through the balanced circulator isolation circuit. The 3dB bridge 2 divides the weak electric signal into two upper and lower branches with the same amplitude and a phase difference of 90 degrees. After passing through the circulator respectively, they are merged at the third point of the 3dB bridge. The lower branch signal, which was originally in phase with the received signal, has its phase increased by 90 degrees at the third point of the 3dB bridge, while the upper branch signal, which was originally 90 degrees out of phase with the received signal, remains in phase at the third point of the 3dB bridge. Therefore, the signals of the upper and lower branches have the same amplitude and phase at the third point of the 3dB bridge. They are superimposed into a new received signal, sent to the directional coupler 3, and then pass through the directional couplers 4 and 5 in sequence to output the RX received signal. Directional couplers 3, 4, and 5 carry both weak received signals and larger carrier leakage signals, with the amplitudes differing by hundreds of millions of times. Therefore, the weak received signals coupled from these directional couplers are negligible. Therefore, the path loss from antenna ANT to the receive output signal RX is the difference between the balanced circulator isolation circuit and the direct loss through directional couplers 3, 4, and 5. The difference in loss in the balanced circulator isolation circuit is the sum of two 3dB bridges and two circulators. Directional couplers 3 and 5 both have a coupling factor of 20dB, resulting in an insertion loss of 0.13dB in the operating frequency band. Directional coupler 4 has a coupling factor of 10dB, resulting in an insertion loss of 0.47dB in the operating frequency band. Therefore, the path loss from antenna ANT to the receive output RX is 0.16x² + 0.2x² + 0.13 + 0.47 + 0.13 = 1.45dB. This value is very small for the carrier leakage cancellation circuit, which ensures that when the carrier leakage cancellation circuit of this embodiment is used in the UHF RFID system, the negative impact on the original received signal is very slight and the receiving sensitivity is basically not deteriorated.

[0056] (3) The process of leakage signal cancellation:

[0057] like Figure 1As shown, the leaked carrier mainly comes from two parts. One is the carrier leakage from the antenna ANT. Generally, the impedance of the antenna interface is designed according to a pure resistance of 50 ohms. However, in reality, the port impedance of the antenna cannot be exactly 50Ω, and there are reactance components. In addition, objects around the antenna, especially metal materials, will also cause changes in the antenna port impedance. Generally speaking, if the return loss of the antenna port can reach 20dB, it is already well matched. In this case, the carrier power sent to the antenna port will have a power of TX-20dB reflected back and enter the receiving link, forming a carrier leakage. This is the disadvantage of sharing a common antenna for transmission and reception. However, for ease of application, general UHF RFID systems use a shared antenna for transmission and reception. The other part of the carrier leakage comes from the circulator in the circuit. The circulator is a commonly used transceiver isolation device in UHF RFID. The signal is generally transmitted in the set circular direction for transmission and reception separation, but its isolation is also very limited. The isolation range of ferrite circulators is generally 20-30dB, and the median value can be 25dB, as shown in Figure 1. Figure 1 The dashed arrow next to the circulator in the balanced circulator isolation circuit shows that when the transmitted signal circulates normally through the circulator, a portion of it enters the receiving channel along this dashed line due to limited isolation. The sum of these two signals entering the receiving channel constitutes the main part of the carrier leakage.

[0058] To eliminate the leaked carrier, this embodiment adopts a two-stage cancellation scheme. The first stage is to use the designed balanced circulator isolation circuit, and the second stage is to use the digitally controlled phase shifter DCPS as the core to cancel the leakage signal in the directional coupler.

[0059] The process of first-level carrier leakage elimination is as follows: in the process of transmitting signal TX to antenna ANT, the upper branch signal output by 3dB bridge 1 has half the power of the transmitted signal and the same phase as the transmitted signal. When passing through the counterclockwise circulator, a part of the carrier is leaked. This part of the carrier enters 3dB bridge 3 and still maintains the phase unchanged when passing through bridge 3. The lower branch signal output by 3dB bridge 1 has half the power of the transmitted signal, but the phase lags 90 degrees than the transmitted signal. When passing through the clockwise circulator of the lower branch, a part of the carrier is also leaked. This portion of the carrier enters 3dB bridge three, where its phase lags again by 90 degrees. Its cumulative phase differs from the transmitted signal by 180 degrees. Thus, two signals with the same amplitude but opposite phases are superimposed at the output of 3dB bridge three. As a result, the two signals cancel each other out, eliminating carrier leakage caused by the circulators in the upper and lower branches (except for their opposite circulation directions, the electrical performance indicators of the two circulators are identical). This balanced circulator isolation circuit can improve the isolation of the transmit and receive signals by about 20dB compared to using a single circulator.

[0060] The second-stage carrier leakage elimination process is as follows: a reference signal is generated, and its amplitude and phase are adjusted to make it have the same amplitude but opposite phase as the final leaked carrier signal, and the two are added together in the directional coupler to cancel each other out, thereby achieving the purpose of further eliminating carrier leakage. Figure 1 As shown, the reference signal is taken from the signal output by the power amplifier PA and is generated by the coupling end of the directional coupler. Figure 1The GPD is an amplitude and phase comparator that compares the amplitude and phase differences between two input signals. In this embodiment, directional coupler 2 couples a reference signal, and directional coupler 3 couples a carrier leakage signal. Their amplitudes are adjusted through resistive attenuator 1 (P-type attenuator 1) and resistive attenuator 2 (P-type attenuator 2), respectively, so that their amplitudes are equivalent when they reach the GPD. This allows the amplitude and phase comparator GPD to more accurately determine the phase difference between them. The GPD sends the amplitude error A° and phase error β° of these two signals to the microprocessor MPU, which accurately quantifies them. Combining these values with the coupling degrees of directional couplers 2, 3, and 4, as well as parameters such as P-type attenuator 1 and P-type attenuator 2, the MPU can determine the amplitude and phase differences between the reference and leakage signals before addition. By adjusting the digitally controlled phase shifter DCPS to change the amplitude and phase of the reference signal, a reference signal and leakage signal with the same amplitude and opposite phase can be obtained. When added together at the four locations in the directional coupler, these signals cancel each other out. The added signal is coupled out by directional coupler 5 to obtain 1% and sent to the power detection PD module through resistor П-type attenuator 3 (П attenuator 3) to detect the residual carrier leakage signal after cancellation. If the expected value is reached, the search for phase difference and amplitude difference is stopped. Otherwise, it may be due to device and line errors, so the amplitude difference and phase difference are corrected in a small range until a satisfactory cancellation effect is achieved. The through-end output of directional coupler 5 is the receiving signal end, which is used to connect to the RF receiving link of the subsequent UHF RFID card reader.

[0061] In this embodiment, if Figure 3 As shown, the more specific second-level elimination process is:

[0062] Step 1, initialization:

[0063] Parameter reset: reset parameters including amplitude error A°, phase error β°, and carrier residual detection value;

[0064] Preset parameters: The parameters that need to be preset include the insertion loss, П attenuation 1, П attenuation 2, and П attenuation 3 of the digitally controlled phase shifter DCPS, as well as the confidence intervals of the amplitude-to-phase comparator GPD and the power detector PD.

[0065] The second step is to obtain the amplitude error A° and phase error β° between the final leakage signal and the reference signal: The GPD outputs the voltage corresponding to the amplitude error A° and the phase error β° to the MPU. After passing through the 12-bit ADC, A° and β° are calculated based on the coupling degree of directional couplers 2 and 3, and the first and second attenuators. This method can quickly determine the amplitude and phase differences between the leakage signal and the reference signal. Compared to methods that align the leakage signal by traversing the phase and amplitude of the reference signal, it can initially provide a relatively small phase error range, thereby shortening the search time for the optimal amplitude and phase of the reference signal.

[0066] The third step is to control the phase shift value and attenuation value of the digital controlled phase shifter DCPS: This step is the core of the method of this embodiment. Figure 3 The middle right half is a detailed breakdown of this step.

[0067] 3.1) First, based on the amplitude difference between the leakage signal and the reference signal, the amplitude of the reference signal is attenuated on a large scale;

[0068] 3.2) Then, search for the optimal phase shift value: Initialize the phase shift accuracy to a coarser step. After the phase shift, compare the amplitude of the residual signal to see if it has decreased. If so, consider it a valid phase shift value. Then increase the phase shift step accuracy, and so on, until the highest phase shift accuracy is achieved.

[0069] 3.3) Next, determine the DCPS attenuation fine-tuning value. Because the carrier leakage cancellation device in Example 1 lacks an amplifier, it does not introduce additional noise. However, there is a constraint: the reference signal amplitude must be greater than the leakage signal. The coupling degree of directional coupler 4 in the carrier leakage cancellation device is 10 dB, so the reference signal amplitude fed into directional coupler 4 for addition must be 10 dB greater than the leakage signal. The method for searching for the optimal attenuation value is the same as that for searching for the optimal phase shift value and will not be further elaborated.

[0070] Step 4: Detecting the residual carrier amplitude after cancellation: After achieving optimal phase shifting and optimal attenuation, directional coupler 5 couples out a small amount of the residual leakage signal. This is converted into a DC voltage by the power detection circuit PD and then fed into the microprocessor MPU for ADC processing. The actual output power of the receiving end (RX) is then calculated based on the coupling coefficient of directional coupler 5 and the threefold attenuation factor. Because the carrier leakage cancellation device formed in this embodiment is placed before the existing UHF RFID circuit, the amplitude of its carrier leakage output only needs to meet the UHF RFID reader's RX signal requirements. This requirement is the carrier leakage cancellation threshold to be achieved in this embodiment. When the calculated residual power is less than this threshold, the cancellation process is complete.

[0071] Step 5: Residual Signal Monitoring: Because the antenna is sensitive to changes in the surrounding environment, or changes in the operating conditions of the UHF RFID reader can affect the performance of the RF circuit, the method in this embodiment monitors the amplitude of the residual carrier in real time. Once it exceeds a threshold, a new round of carrier leakage cancellation is triggered.

[0072] Example 3

[0073] This embodiment provides a performance experiment of the carrier leakage elimination device described in Embodiment 1.

[0074] like Figure 4As shown, the DUT is the carrier leakage cancellation device under test. It has three interfaces: TX for connecting to a high-power transmit signal, ANT for connecting to a shared transmit and receive antenna, and RX for connecting to the subsequent receive circuitry. During the test, an RF signal source generates a carrier signal, which is then amplified and sent to the unit under test. The antenna then transmits it into space. Since the purpose of this embodiment is to test the effectiveness of carrier leakage cancellation, no electronic tags are used. Instead, a spectrum analyzer is used to directly measure the residual carrier in the RX signal output by the unit under test. The effectiveness of carrier leakage cancellation is characterized by Isolation = TX - RX.

[0075] Table 1 lists the main components of the carrier leakage cancellation device tested in this embodiment. The main printed circuit board uses FR4 material and has four layers: top layer, GND layer, power layer, and bottom layer. The module uses a DC 7.5V power supply with a current of ≤100mA.

[0076] Table 1

[0077]

[0078] Table 2 lists the attenuator configuration parameters of the carrier leakage elimination device tested in this embodiment. All three attenuators adopt the resistor П-type connection method, such as Figure 5 As shown, all resistors are 0603-chip thin-film resistors. Because the AD8302 amplitude-phase comparator and the ADL5513 RF power detector both have a confidence interval—the range of RF signal inputs where the detection error is relatively small—resistive I-type attenuators are used in the DUT to adjust the input signal levels of the AD8302 and ADL5513.

[0079] Table 2

[0080]

[0081] Table 3 lists the values of the carrier residual signal RX corresponding to different carrier input signals TX of the carrier leakage elimination device under test. The isolation of the DUT is defined as follows:

[0082] Isolation = TX - RX;

[0083] Table 3 also lists the optimal phase shift value and attenuation value corresponding to the isolation of the carrier leakage cancellation device. Figure 6This is a curve showing how the isolation of the carrier leakage cancellation device changes with the carrier input signal TX. Because it's difficult to test the carrier leakage at each stage of the carrier leakage cancellation device in real time using instruments, the isolation of the carrier leakage cancellation device actually represents the carrier signal leaked on the receiving link when the incoming carrier transmission signal is radiated into space through the antenna. Therefore, the isolation of the carrier leakage cancellation device can also be considered as the cancellation ratio of the carrier leakage cancellation device under high-power transmission conditions, that is:

[0084]

[0085] Table 3

[0086]

[0087]

[0088] Table 3 and Figure 6 It is noted that the carrier leakage elimination device described in Example 1 suppresses the carrier at the RX receiving end by more than 70 dB when the input transmit power TX is equal to 0.5 to 20 W, and the carrier signal actually leaked to the RX receiving end is less than -30 dBm. This level of carrier leakage is very safe for the low-noise amplifier (LNA) of the receiving link, and can ensure that the receiving link can operate normally when the transmitting and receiving antennas are shared.

[0089] Those skilled in the art can make various corresponding changes and modifications based on the above technical solutions and concepts, and all of these changes and modifications should be included in the scope of protection of the claims of the present invention.

Claims

1. A carrier leakage elimination device for high-power ultra-high frequency radio frequency identification, characterized in that: The invention comprises a power amplifier, a directional coupler 1, a 3dB bridge 1, a 3dB bridge 2, a 3dB bridge 3, two circulators and an antenna; the output end of the power amplifier is connected to the input end of the directional coupler 1, the output end of the directional coupler 1 is connected to the 3dB bridge 1, the 3dB bridge 1 is respectively connected to a circulator, and both circulators are connected to the 3dB bridge 2, and the 3dB bridge 2 is connected to the antenna; the two circulators are also connected to the 3dB bridge 3, and the 3dB bridge 3 is connected to the receiving signal end; It also includes a directional coupler three, a directional coupler four and a directional coupler five, wherein the 3dB bridge three, the directional coupler three, the directional coupler four and the directional coupler five are connected in sequence, and the directional coupler five is connected to the receiving signal end; The device further comprises a digitally controlled phase shifter, a second directional coupler, a first attenuator, a second attenuator, a microprocessor, and an amplitude and phase comparator; the input end of the digitally controlled phase shifter is connected to the output end of the first directional coupler, and the output end of the digitally controlled phase shifter is connected to the second directional coupler; the second directional coupler is connected to the fourth directional coupler; the second directional coupler and the third directional coupler are connected to the first attenuator and the second attenuator, respectively; the first attenuator and the second attenuator are both connected to the amplitude and phase comparator, the amplitude and phase comparator is connected to the microprocessor, and the microprocessor is connected to the digitally controlled phase shifter; In the digitally controlled phase shifter, 10 levels of phase shift are connected in series in the order of 0.5°, 1°, 2°, 4°, 8°, 16°, 19°, 45°, 90°, and 180°. The 10th level of phase shift is also connected to the RF signal attenuator; each level of phase shift and RF signal attenuator are switched on and off by digital logic levels.

2. The carrier leakage elimination device according to claim 1, wherein: The directional coupler five is also connected to the attenuator three, the attenuator three is connected to the power detection module, and the power detection module is connected to the microprocessor.

3. A method for operating a carrier leakage elimination device for high-power ultra-high frequency radio frequency identification according to any one of claims 1-2, characterized in that: The process of transmitting a signal to an antenna includes: In the process of transmitting a signal to the antenna, the signal output by the signal source passes through the power amplifier PA to obtain the carrier transmission signal TX. The carrier transmission signal TX is first sent to the balanced circulator isolation circuit through directional coupler 1. In the balanced circulator isolation circuit, the transmission signal output by directional coupler 1 is divided into two parts with the same amplitude but a phase difference of 90 degrees through 3dB bridge 1. The two parts are respectively sent to 3dB bridge 2 through the circulators of the upper branch and lower branch. The phase of the upper branch signal, which was originally in phase with the transmission signal, is increased by 90 degrees at 3dB bridge 2, while the phase of the lower branch signal, which was originally 90 degrees out of phase with the transmission signal, remains unchanged at 3dB bridge 2. Therefore, the upper branch signal and the lower branch signal have the same amplitude and phase at 3dB bridge 2. They are superimposed to form a new transmission signal and sent to antenna ANT, which radiates into space. In the process of transmitting the signal TX to the antenna ANT, the upper branch signal output by the 3dB bridge 1 has a power half of the transmitted signal and is in phase with the transmitted signal. When passing through the counterclockwise circulator, a part of the carrier will be leaked. This part of the carrier enters the 3dB bridge 3 and still maintains the phase unchanged when passing through the 3dB bridge 3. The power of the lower branch signal output by the 3dB bridge 1 is also half of the transmitted signal, but the phase lags 90 degrees behind the transmitted signal. When passing through the circulator of the lower branch, a part of the carrier is also leaked. This part of the carrier enters the 3dB bridge 3 and lags the phase again by 90 degrees when passing through the 3dB bridge 3. The accumulated phase is 180 degrees different from the transmitted signal. In this way, two signals with the same amplitude but opposite phases are superimposed at the output port of the 3dB bridge 3. As a result, the two signals cancel each other out, thus eliminating the carrier leakage caused by the circulators of the upper and lower branches. It also includes the second level leakage signal elimination process, specifically: A reference signal is generated, which is taken from the output signal of the power amplifier and is generated by the coupling end of directional coupler 1. Directional coupler 2 couples out the reference signal, and directional coupler 3 couples out the leakage signal. The reference signal and leakage signal are adjusted in amplitude through attenuators 1 and 2, respectively, so that the reference signal and leakage signal have the same amplitude when they reach the amplitude and phase comparator. The amplitude and phase comparator determines the amplitude difference and phase difference between the amplitude and phase comparators and sends them to the microprocessor. The microprocessor accurately quantifies the amplitude difference and phase difference between the reference signal and the leakage signal before addition, combining them with the coupling degrees of directional coupler two, directional coupler three, and directional coupler four, as well as the parameters of attenuator one and attenuator two. The microprocessor then changes the amplitude and phase of the reference signal by adjusting the numerically controlled phase shifter to obtain a reference signal and leakage signal with the same amplitude and opposite phase. The reference signal and leakage signal with the same amplitude and opposite phase are added at the four locations of the directional coupler and cancel each other out.

4. The method according to claim 3, characterized in that It also includes a process of receiving a signal to a signal receiving end; the process of receiving a signal to a signal receiving end is: The spatial electromagnetic waves returned by the electronic tag are received by the antenna and converted into weak electrical signals. The weak electrical signals must first pass through the balanced circulator isolation circuit; in the balanced circulator isolation circuit, 3dB bridge 2 divides the weak electrical signal into an upper branch signal and a lower branch signal with the same amplitude and a phase difference of 90 degrees. After the upper branch signal and the lower branch signal are circulated by the circulator, they are combined at the third point of the 3dB bridge. The lower branch signal, which was originally in phase with the received signal, has its phase increased by 90 degrees at the third point of the 3dB bridge, while the upper branch signal, which was originally 90 degrees out of phase with the received signal, maintains its phase at the third point of the 3dB bridge. Therefore, the upper branch signal and the lower branch signal have the same amplitude and phase at the third point of the 3dB bridge. They are superimposed to form a new received signal and sent to directional coupler 3. Then, they pass through directional couplers 4 and 5 in sequence and are output to the receiving signal end.

5. The method according to claim 3, characterized in that The signal obtained by adding the reference signal and the leakage signal is coupled out by directional coupler 5, and 1% is sent to the power detection module through attenuator 3. The power detection module detects the carrier leakage signal remaining after cancellation and sends the detection result to the microprocessor. If the expected value is reached, the microprocessor stops searching for the phase difference and amplitude difference. Otherwise, the amplitude difference and phase difference are corrected until the expected cancellation effect is achieved.

6. The method according to claim 3, characterized in that The process by which the microprocessor changes the amplitude and phase of the reference signal by adjusting the digitally controlled phase shifter is: First, based on the amplitude difference between the leakage signal and the reference signal, the amplitude of the reference signal is attenuated on a large scale. Then, the optimal phase shift value is searched first: the phase shift accuracy is initialized to a coarser step. After the phase shift, the amplitude of the residual leakage signal is compared to see if it has decreased. If so, it is considered to be a valid phase shift value. The phase shift step accuracy is then increased, and so on, until the highest phase shift accuracy is achieved. Next, determine the attenuation fine-tuning value of the CNC phase shifter: ensure that the amplitude of the reference signal sent to directional coupler 4 for addition is greater than the leakage signal. On this basis, search for the optimal attenuation value: initialize the attenuation value to a coarser step, and compare the amplitude of the residual leakage signal after attenuation to see if it has decreased. If so, it is considered an effective attenuation value. Then increase the attenuation step accuracy, and so on, until the highest attenuation accuracy is achieved.

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