Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
  • H04B1/40—Circuits
  • H04B1/50—Circuits using different frequencies for the two directions of communication
  • H04B1/52—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa
  • H04B1/525—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa with means for reducing leakage of transmitter signal into the receiver

Definitions

• the present invention relates to the field of carrier control in UHF passive radio frequency identification systems, and more particularly to a system and method for suppressing carrier leakage. Background technique
• UHF passive RFID systems when the tag communicates with the reader, the reader needs to always send a carrier to provide tag power, and the tag transmits the information to the reader by modulating backscatter. Therefore, when the reader receives the signal of the tag, the forwarded RF carrier of the reader leaks to the reverse receiving portion of the reader.
• the signal strength backscattered by the tag is very small compared to the strength of the forward transmitted carrier signal. In actual systems, the difference between the reverse signal and the forward signal will be more than 90 dB. Therefore, UHF readers typically use directional couplers to isolate the forward and reverse signals.
• the four-port directional couplers used in UHF readers are divided into input ports, output ports, coupled ports, and isolated ports.
• the RF signal output from the amplifier is input from the input port, the output port is output to the antenna, and part of the energy is output to the coupled port, and very little energy is output to the isolated port.
• the tag signal is input from the output port, partially coupled to the isolated port, and output to the opposite demodulator through the isolated port. Thereby the isolation of the forward signal and the reverse signal is achieved.
• the directional coupler can only provide about 20 to 30dB of isolation, and the isolation effect is not ideal.
• the present invention provides a system for suppressing carrier leakage, the system comprising: a directional coupler, a quadrature demodulator, and a reflected signal module, wherein
• the directional coupler is configured to output the leaked RF carrier signal from its own isolation port to the quadrature demodulator;
• the quadrature demodulator is configured to demodulate the leaked radio frequency carrier signal into an in-phase and quadrature signal, send the signal to the reflected signal, and suppress the leaked radio frequency carrier signal by using the reflected signal reflected by the reflected signal module ;
• the reflected signal module is configured to filter the in-phase and quadrature signals, phase rotation gain control, and integrate the opposite phase to obtain a control signal of the reflected signal, control the reflected signal by using the control signal, and send the reflected signal to the orthogonal solution. Tuner.
• the reflected signal module further includes:
• the reflected signal control sub-module is configured to filter the in-phase and quadrature signals, phase-rotate gain control, and integrate the opposite phase to obtain a control signal of the reflected signal, and send the signal to the phase-shifting reflective sub-module;
• the phase shifting reflection sub-module is configured to control a reflected signal of the directional coupler coupling port by using a control signal, and send the reflected signal to the orthogonal demodulator through the coupling port and the isolation port of the directional coupler.
• the filtering of the reflected signal module is low-pass filtering; the phase rotation gain control is to adjust the phase and amplitude of the in-phase and quadrature signals by changing the rotation angle and gain of the signal. After integrating with the opposite phase, four control signals are obtained, which are respectively used to control the intensity of the four tap points of the reflected signal on the transmission line.
• the reflected signal in the reflected signal module is a radio frequency carrier signal output by the coupled port of the directional coupler, and is reflected by the reflected signal module and reflected back to the coupled port of the directional coupler.
• the function of the reflected signal control sub-module is further implemented by an analog-to-digital conversion sub-module and a digital reflected signal control sub-module and a digital-to-analog conversion sub-module having the same operation function.
• the digitized reflected signal control sub-module further includes: a stop control sub-module, configured to determine the amplitude of the in-phase and quadrature signals after the detonation of the leakage signal, and when the value is less than the threshold, stop generating the control signal.
• the present invention also provides a method for suppressing carrier leakage, the method comprising:
• the leaked RF carrier signal When the leaked RF carrier signal is output from the isolated port of the directional coupler, the leaked RF carrier signal is demodulated to the in-phase and quadrature signals;
• the generating of the control signal and the carrier signal for suppressing leakage include:
• the filtering is low-pass filtering;
• the phase rotation gain control is to adjust the phase and amplitude of the in-phase and quadrature signals by changing the rotation angle and the gain of the signal; and integrating the opposite phases to obtain four-way control signals, respectively
• the reflected signal is a radio frequency carrier signal output by the coupling port of the directional coupler, and is reflected by the reflected signal module and reflected back to the coupled port of the directional coupler.
• the system and method for suppressing carrier leakage outputs a leaked RF carrier signal from an isolated port; demodulating a leaked RF carrier signal into an in-phase and quadrature signal by using a quadrature demodulator; After the signal is filtered, the phase rotation gain is controlled, and the opposite phase is integrated, a control signal is obtained, and the reflected signal is controlled by the control signal to suppress the leaked RF carrier signal. Since the reflected signal is used to cancel the leakage signal, the method of combining signals has a simple structure, high cancellation efficiency, and does not increase the insertion loss of the reverse signal, and can effectively suppress the leakage of the forward RF carrier signal, thereby improving the leakage. Sensitivity of UHF passive RFID systems. DRAWINGS
• FIG. 1 is a schematic structural diagram of a system for suppressing carrier leakage according to the present invention
• FIG. 2 is a schematic structural diagram of a reflected signal control sub-module of the present invention.
• FIG. 3 is a schematic structural view of a phase shifting reflection sub-module of the present invention.
• FIG. 4 is a schematic structural diagram of a digitally processed reflected signal control submodule
• FIG. 5 is a schematic flow chart of a method for suppressing carrier leakage according to the present invention.
• Figure 6 is a schematic diagram showing the isolation of the front reverse signal when the present invention is not used
• FIG. 7 is a schematic illustration of the front reverse signal isolation for use with the present invention. detailed description
• the leaked RF carrier signal is output from the isolated port; the quadrature demodulator is used to demodulate the leaked RF carrier signal out of the in-phase and quadrature signals; the in-phase and quadrature signals are filtered, and the phase-rotation gain is applied. After the control is integrated with the opposite phase, a control signal is obtained, and the reflected signal is controlled by the control signal to suppress the leaked RF carrier signal.
• FIG. 1 is a schematic structural diagram of a system for suppressing carrier leakage according to the present invention.
• the system includes: a directional coupler 11, a quadrature demodulator 12, and a reflected signal module 13, wherein the directional coupler 11 , for outputting the leaked RF carrier signal from the isolation port to the quadrature demodulator 12;
• the power amplifier module 14 in the UHF passive radio frequency identification system outputs a forward radio frequency carrier signal through an input port of the directional coupler 11 and then outputs the output signal to the antenna 15 from the output port.
• a combination of the standing wave of the antenna 15 and the isolation of the directional coupler 11 causes a portion of the RF carrier signal to leak to the isolated port of the directional coupler 11 and output from the isolated port.
• the power amplifier module 14, the directional coupler 11, and the antenna 15 do not need to be particularly limited, and a commonly used power amplifier device, directional coupler, and antenna can be used.
• the quadrature demodulator 12 is configured to demodulate the leaked radio frequency carrier signal into an in-phase and quadrature signal, and send the signal to the reflected signal module 13 to suppress the leakage by using the reflected signal reflected by the reflected signal module 13 RF carrier signal;
• the quadrature demodulator 12 is used to demodulate the in-phase signal and the quadrature signal (I signal and Q signal), respectively:
• ⁇ is the strength of the leaked RF carrier signal
• 6 is the phase difference between the leaked RF carrier signal and the local oscillator signal. Since the standing wave of the antenna is the main source of reverse leakage, it is mainly affected by the length of the feeder 15 of the antenna.
• the local oscillator signal is a basic signal that is input for demodulation when the quadrature demodulator 12 is used.
• the reflected signal is reflected by the reflected signal module 13 through the coupling port of the directional coupler 11 from the isolated port to the quadrature demodulator 12, and the reflected signal controlled by the control signal is leaked due to the phase rotation gain of the control signal.
• the phase of the RF carrier signal is opposite.
• the amplitude of the reflected signal is increased by the integration of the opposite phase with the opposite phase, which realizes the mutual cancellation of the original leakage RF carrier signal and achieves the purpose of suppressing the leakage of the RF carrier.
• the reflected signal module 13 is configured to filter the in-phase and quadrature signals, phase rotation gain control, and integrate the opposite phase to obtain a control signal of the reflected signal, and control the reflected signal of the coupled port of the directional coupler 11 by using the control signal.
• the reflected signal is sent to the quadrature demodulator 12 through the directional coupler 11.
• low-pass filtering is applied to the in-phase and quadrature signals to filter out high-frequency noise signals.
• the phase-rotation gain control of the in-phase and quadrature signals after filtering is to adjust the phase and amplitude of the in-phase and quadrature signals by changing the rotation angle and gain of the signal, and then integrating ⁇ + , ⁇ , Q by integrating with the opposite phase. + , Q-signal, used to control the reflected signal at the four tap points.
• the reflected signal refers to: when the directional coupler 11 forwards the RF carrier signal, the part of the RF carrier signal output by the coupled port is controlled by the reflected signal module 13 and then reflected back to the coupled port of the directional coupler 11, and the input directional coupler The reflected signal of the coupled port of 11 passes through the directional coupler 11 to the quadrature demodulator 12.
• the reflected signal module 13 includes: a reflected signal control sub-module 131 and a phase-shifted reflective sub-module 132, wherein
• the reflected signal control sub-module 131 is configured to filter the in-phase and quadrature signals, phase rotation gain control, and integrate the opposite phase to obtain a control signal of the reflected signal, and send the signal to the phase shifting reflection sub-module 132;
• FIG. 2 is a schematic structural diagram of a reflected signal control sub-module according to the present invention.
• the I signal and the Q signal are respectively filtered by the low-pass filter 201 and output. .
• the output I signal is input to the first multiplier 202 and the second multiplier 203, respectively multiplied by the phase adjustment coefficients A*cos ( ⁇ ), A*sin ( 6 );
• the Q signal is input to the third multiplier 204, the fourth multiplication method
• the unit 205 is multiplied by the phase adjustment coefficients A*cos ( ⁇ ) and A*sin ( ⁇ ), respectively.
• the results of four-way multiplication are obtained: A*I*cos ( ⁇ ), A*I*sin ( ⁇ ), A*Q*cos ( ⁇ ), A*Q*sin ( ⁇ ).
• ⁇ and Q are the in-phase and quadrature signals after the phase rotation gain.
• the phase ⁇ and amplitude gain A need to be adjusted. The specific adjustment settings should be made at the end of the overall system debugging. First set the low amplitude gain A, adjust ⁇ , select the phase with the smallest value when the signal is cancelled. ⁇ , then adjust the gain A to minimize the time for the ⁇ ⁇ .
• A*cos ( ⁇ ) and A*sin ( ⁇ ) signals to complete the operation can be realized by adjustable potentiometer.
• A*cos ( ⁇ ) and A*sin ( ⁇ ) can be directly input.
• Multipliers, adders, and subtractors can all be implemented using op amp circuits, which can be implemented in digital processing using addition, subtraction, and multiplication of software or digital circuits.
• the inverting integrator can use a typical operational amplification inverting integration circuit, in-phase integration circuit to invert the signal and then perform inverse integration.
• the chirp signal output by the adder 206 is output to the first in-phase integrator 208 and the first inverting integrator 209.
• the Q output signal from the subtracter 207 is output to the second in-phase integrator 210 and the second inverting integrator 211.
• the result of the in-phase integrator and the input signal are accumulated in phase, and the result of the inverting integrator and the input signal are inversely accumulated.
• the ⁇ ⁇ R , Q + , Q- signals are used to control the reflected signal strength of the phase-shifted reflection sub-module 132.
• the reflected signal is passed through the directional coupler 11 to the quadrature demodulator 12,
• the phase shift of the reflected signal during this process does not take into account the effect of the feed line length of the antenna 15, but the directional coupler 11, and the traces from the directional coupler 11 isolated port to the quadrature demodulator 12 on the board carry a reflected signal.
• a fixed phase shift ⁇ 2 in order to better suppress the RF carrier signal by the reflected signal, the preferred scheme is that the control signals ⁇ + , ⁇ , Q + , Q_ take into account ⁇ 2 , specifically, preferred
• the device 12 is opposite in phase to the original leakage signal. Since the phase shift ⁇ 2 is independent of the feed line length of the antenna 15, the phase adjustment coefficient ⁇ is not affected by the length of the feed line and has good adaptability.
• the phase shifting reflection sub-module 132 is configured to control the reflected signal of the coupling port of the directional coupler 11 by using a control signal, and send the reflected signal to the quadrature demodulator 12 through the coupling port and the isolation port of the directional coupler 11.
• FIG. 3 is a schematic structural diagram of a phase-shifting reflective sub-module according to the present invention.
• a first controllable reflective unit 301 in the phase-shifting reflective sub-module 132, a first controllable reflective unit 301, a second controllable reflective unit 302, and a second
• the three controllable reflection unit 303 and the fourth controllable reflection unit 304 respectively control the reflected signal strengths of the four reflection nodes by Q ⁇ , ⁇ , Q + , and 1 + .
• the four nodes are the four tap points on the transmission line, and the intrinsic diode (PIN tube) can change the impedance of the four nodes in a variable resistance manner.
• PIN tube the intrinsic diode
• the termination load 305 is a 50 ohm termination resistor.
• the first phase shifting unit 306, the second phase shifting unit 307, and the third phase shifting unit 308 implement a 45 degree phase shifting process for controlling the reflected signal, and transmit the reflected signal to the coupled port of the directional coupler 11.
• the input signal phase of the second controllable reflecting unit 302 The bit is delayed by 45 degrees from the input signal of the first controllable reflection unit 301. Therefore, the signal reflected by the second controllable reflective unit 302 to the coupled port of the directional coupler 11 is delayed by 90 degrees from the reflected signal of the first controllable reflective unit 301.
• the reflected signal of the third controllable reflective unit 303 is delayed by 90 degrees than the second controllable reflective unit 302; the reflected signal of the fourth controllable reflective unit 304 is delayed by 90 degrees than the third controllable reflective unit 303.
• the reflection signal of the first controllable reflection unit 301 is r ⁇ cos ⁇ t O
• the reflection signal of the second controllable reflection unit 302 is r 2 *cos (vt-180)
• the third controllable reflection unit The reflected signal of 303 is r 3 *cos t-90
• the reflected signal of the fourth controllable reflecting unit 304 is r 4 *cos .
• r ( ZL _ Z 0 ) / ( Z L + Z 0 ).
• Z 0 is the transmission line impedance, here is 50 ohms
• Z L is the load impedance
• Z L ZL / Z pin
• Z PIN is the PIN tube impedance.
• ⁇ 2 , ⁇ 3 , ⁇ 4 are respectively controlled by Q -, ⁇ , Q + , 1 + output from the reflected signal control module.
• the control voltage is less than or equal to 0, the reflected signal is 0.
• the control voltage is greater than 0, the reflected signal is controlled.
• the reflected signal at the coupled port of the directional coupler 11 is ( ⁇ 4 - ⁇ 2 ) *cos ( ⁇ ) + ( ⁇ 3 - ⁇ !) *sin t).
• FIG. 4 is a schematic structural diagram of a digital signal processing control sub-module. As shown in FIG. 4, the sub-module includes: a conversion submodule 401, a digital reflected signal control submodule 402, a digital to analog conversion submodule 403, and a stop control submodule 404, wherein
• the analog-to-digital conversion sub-module 401 converts the signal into a digital signal, and the input digital reflected signal control sub-module 402 processes. After completion, the digital-to-analog conversion sub-module 403 performs digital-to-analog conversion output.
• the function implemented by the digital reflected signal control sub-module 402 can be implemented by referring to the calculation performed by the reflected signal control sub-module 131 by applying a corresponding digital calculation module.
• FI finite-length unit impulse response
• CIC cascaded integrator comb
• the function of the stop control sub-module 404 is to determine the amplitude of the demodulated I and Q signals.
• I 2 + Q 2 is less than the threshold, the digital reflected signal control sub-module 402 is stopped.
• the threshold value may be set according to the target leakage power value, for example: the target leakage power is -20 dBm, and when the system is debugged, the test signal of -20 dBm is input by the RF signal input port of the quadrature demodulator 11 to detect The value of I 2 + Q 2 is calculated and used as the threshold of the stop control sub-module 404.
• FIG. 5 is a schematic flowchart of a method for suppressing carrier leakage according to the present invention. As shown in FIG. 5, the method specifically includes the following steps:
• Step 501 When the directional coupler outputs the forward RF carrier signal from the output port, the leaked RF carrier signal is output from the isolated port.
• the power amplifier module in the UHF passive radio frequency identification system outputs a forward RF carrier signal through an input port of the directional coupler, and then outputs the output port to the antenna.
• a combination of the standing wave of the antenna and the isolation of the directional coupler, a portion of the RF carrier signal leaks to the isolated port of the directional coupler and is output from the isolated port.
• the power amplifier module, the directional coupler, and the antenna do not need to be particularly limited, and a commonly used power amplifier device, directional coupler, and antenna can be used.
• Step 502 Demodulate the leaked RF carrier signal into an in-phase and quadrature signal by using a quadrature demodulator
• the demodulating the in-phase and quadrature signals by using the quadrature demodulator are respectively:
• ⁇ is the strength of the leaked RF carrier signal
• 6 is the phase difference between the leaked RF carrier signal and the local oscillator signal.
• the local oscillator signal is a basic signal input for understanding the modulation when the quadrature demodulator is used.
• Step 503 Filtering the in-phase and quadrature signals, phase rotation gain control, and integrating the opposite phase to obtain a control signal of the reflected signal of the directional coupler coupling port, and controlling the reflected signal by using the control signal to suppress the leaked RF carrier. signal.
• low-pass filtering is applied to the in-phase and quadrature signals to filter out high-frequency noise signals.
• the phase-rotation gain control of the in-phase and quadrature signals after filtering is to adjust the phase and amplitude of the in-phase and quadrature signals by changing the rotation angle and gain of the signal, and then integrating ⁇ + , ⁇ , Q by integrating with the opposite phase. + , Q-signal, used to control the reflected signal at the four tap points.
• the reflected signal refers to: a partial RF carrier signal output by the coupled port when the directional coupler forwards the RF carrier signal, which is reflected back to the coupled port.
• the ⁇ + , ⁇ , Q + , Q_ signals respectively control the intensity of the four tap points of the reflected signal on the transmission line.
• the reflected signal is output from the isolation port to the quadrature demodulator through the coupling port of the directional coupler.
• the control signal performs the phase rotation gain, the reflected signal controlled by the control signal is opposite to the phase of the original leakage RF carrier signal, and the control signal is further Under the action of the opposite phase integral, the amplitude of the reflected signal is increased, and the mutual leakage of the original leakage RF carrier signal is realized, and the purpose of suppressing the leakage of the RF carrier is achieved.
• step 503 further includes:
• Step 503a filtering the in-phase and quadrature signals
• the filtering may be an active low-pass filter composed of an operational amplifier, or a passive low-pass filter composed of a resistor-capacitor (RC) network and an inductor-capacitor (LC) network.
• the parameters of the low-pass filter must be balanced by two contradictions.
• the passband and stopband frequencies are as low as possible, and noise interference is filtered out as much as possible.
• the convergence speed of the automatic cancellation circuit is required to be fast, and the delay of the filter's passband and stopband frequency is increased. Will affect the speed of convergence.
• the passband -3dB cutoff frequency can be selected as ⁇
• the stopband cutoff frequency is 25KHz
• the stopband attenuation is -30dB.
• Step 503b performing phase rotation gain control
• ⁇ and Q are the in-phase and quadrature signals after the phase rotation gain.
• the phase ⁇ and amplitude gain A need to be adjusted. The specific adjustment settings should be made at the end of the overall system debugging. First, set the low amplitude gain A, adjust ⁇ , and select the signal to cancel the offset. Phase ⁇ , then adjust the gain A to minimize the time required for ⁇ ⁇ .
• Step 503c performing integral and opposite phase integration on the in-phase and quadrature signals after the phase rotation gain to obtain a control signal of the reflected signal of the directional coupler coupling port;
• Step 503d using a control signal to control a reflected signal of the coupled port
• the reflected signal of the coupled port has four tap points on the transmission line, that is, the aforementioned four tap points, and the four tap points are respectively separated by a phase difference of 90 degrees to ensure control of the complete period of the reflected signal.
• the four tap points can be controlled by the variable resistance method implemented by the PIN tube, specifically by changing the impedance of the four tap points to control the amplitude of the reflected signal.
• the voltage of the control signal is 0 or less than 0
• the bias current of the PIN tube is 0, and the impedance of the variable resistor is much larger than 50 ohms.
• the PIN tube is similar to a small capacitor, and the reflection is small.
• Step 503e suppressing the RF carrier signal by using a reflected signal of the coupled port.
• the reflected signal input to the coupled port of the directional coupler reaches the quadrature demodulator through the directional coupler, and the phase shift of the reflected signal in this process does not take into account the influence of the antenna feed length, but the directional coupler, and the single
• the trace from the directional coupler isolation port to the quadrature demodulator on the board will bring a fixed phase shift ⁇ 2 to the reflected signal.
• the preferred scheme is the control signal.
• phase to the quadrature demodulator is (6 ⁇ 180) and the phase of the original leak signal 6 is 180 degrees out of phase, so that the generated reflected signal reaches the orthogonal
• the demodulator 12 is opposite in phase to the original leakage signal. Since the phase shift ⁇ 2 is independent of the feed line length of the antenna 15, the phase adjustment coefficient ⁇ is not affected by the length of the feed line and has good adaptability.
• Fig. 6 is a schematic diagram showing the isolation of the front reverse signal when the present invention is not used.
• the directional coupler itself is used only for the isolation of the forward and reverse signals.
• the forward sum is The isolation of the reverse signal is approximately -28 dB.
• Fig. 7 is a view showing the isolation of the front reverse signal when the present invention is used. As shown in Fig. 7, after the method of suppressing carrier leakage by the present invention, the isolation of the forward and reverse signals is optimized to -55 dB. It can be seen that the present invention can significantly improve the isolation of the front reverse link signal.

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• Signal Processing (AREA)
• Transmitters (AREA)
• Radio Relay Systems (AREA)
• Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

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• 2010
  • 2010-08-20 CN CN201010265065.0A patent/CN102377450B/zh active Active
  • 2010-11-30 RU RU2013112157/07A patent/RU2542737C2/ru active
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