CN106209158B

CN106209158B - Carrier leakage eliminating system based on UHF RFID reader-writer

Info

Publication number: CN106209158B
Application number: CN201610710126.7A
Authority: CN
Inventors: 陈磊
Original assignee: Chizhou Richsemi Electronics Co ltd
Current assignee: Chizhou Richsemi Electronics Co ltd
Priority date: 2016-08-23
Filing date: 2016-08-23
Publication date: 2023-11-28
Anticipated expiration: 2036-08-23
Also published as: CN106209158A

Abstract

The application relates to a carrier leakage elimination system based on a UHF RFID reader-writer, and belongs to the technical field of carrier leakage elimination of reader-writers. The device comprises a directional coupler, a quadrature signal generator, a vector adder, a power detector, a multiplexer, a phase shifter, a circulator and a radio frequency balun, wherein the directional coupler is connected with the quadrature signal generator, the quadrature signal generator is respectively connected with the vector adder and the multiplexer, the vector adder is connected with the power detector, and the directional coupler, the phase shifter, the circulator, the radio frequency balun and the vector adder are sequentially connected. The application realizes a new carrier leakage elimination technology, and has high isolation and low production cost.

Description

Carrier leakage eliminating system based on UHF RFID reader-writer

Technical Field

The application relates to the technical field of carrier leakage elimination of readers, in particular to a carrier leakage elimination system based on a UHF RFID reader.

Background

For passive UHF RFID systems, communication between the reader and the tag is achieved in half duplex fashion. The reader transmits the modulated carrier wave to the tag, the tag in the identification area of the reader feeds back information to the reader in a back scattering mode, and the reader communicates with the tag according to the protocol specification. The reader-writer simultaneously emits carrier waves to provide energy for the passive tag through electromagnetic wave radiation in the process of reading the passive tag. Because the isolation between the reader-writer receiver and the transmitter is limited, the carrier signal of the transmitting end can leak to the receiving end and enter the reader-writer together with the tag modulation signal. The specific tag backscattering mechanism of the passive UHF RFID system ensures that the frequency of a tag modulation signal received by a reader-writer is 50-250 kHz different from the frequency of a transmission carrier signal, and an on-chip filter with a limited quality factor is difficult to filter carrier leakage signals in an ultra-high frequency band of about 900 MHz. For a reader-writer adopting a double-antenna structure, the isolation of a receiving and transmitting path can reach 30dB. In order to save cost, the main trend of the reader-writer is to use a single antenna to perform receiving and transmitting isolation through isolating devices such as a circulator, a directional coupler and the like. Although smaller signal transmission power can reduce carrier leakage, it also reduces the tag reading distance of the reader-writer.

Disclosure of Invention

Aiming at the defects and the shortcomings in the prior art, the application provides a carrier leakage elimination system based on a UHF RFID reader-writer, which realizes a novel carrier leakage elimination technology, and has high isolation and low production cost.

The technical scheme adopted for solving the technical problems is as follows:

the carrier leakage eliminating system based on UHF RFID reader-writer includes directional coupler, orthogonal signal generator, vector adder, power detector, multiplexer, phase shifter, circulator and RF balun.

Further, the directional coupler is connected with the transmitting end of the reader-writer transmitter.

Furthermore, the vector adder is a digital adjustable vector adder and consists of three transconductance stages and a shared load stage, and the transconductance stages adopt a differential source negative feedback structure.

Further, the quadrature signal generator generates quadrature signals using a single stage RC-CR network.

Further, the power detector is implemented by self-mixing.

Furthermore, the multiplexer realizes the function of selecting two paths of signal inputs by using control signals PHT and PHTN connected by an inverter.

Further, the circulator is connected with a receiving end of the reader-writer transmitter.

The application has the following beneficial effects: two transconductance stages of the vector adder can realize the equivalent transconductance adjustment by adjusting the negative feedback resistance of the transconductance stages; the single-stage RC-CR network is adopted to generate orthogonal signals, the amplitude of the I/Q two-path carrier cancellation reference signals is regulated through a vector adder, and the amplitude mismatch of the I/Q two-path signals output by the RC-CR network is provided with higher tolerance; the application can eliminate the deterioration of the sensitivity of the reader-writer receiver caused by shannon noise with higher carrier leakage signal.

Drawings

FIG. 1 is a schematic diagram of a system according to the present application;

FIG. 2 is a schematic diagram of a UHF RFID reader-writer receiving mechanism;

FIG. 3 is a schematic diagram of a vector adder circuit;

FIG. 4 is a schematic diagram of a quadrature signal generator circuit;

FIG. 5 is a schematic diagram of a power detector circuit;

fig. 6 is a schematic diagram of a multiplexer circuit.

Detailed Description

The application will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present application and are not intended to limit the scope of the present application. Furthermore, it should be understood that various changes and modifications can be made by one skilled in the art after reading the teachings of the present application, and such equivalents are intended to fall within the scope of the application as defined in the appended claims.

As shown in fig. 1, the carrier leakage elimination system based on the UHF RFID reader-writer comprises a directional coupler, a quadrature signal generator, a vector adder, a power detector, a multiplexer, a phase shifter, a circulator and a radio frequency balun, wherein the directional coupler is connected with the quadrature signal generator, the quadrature signal generator is respectively connected with the vector adder and the multiplexer, the vector adder is connected with the power detector, and the directional coupler, the phase shifter, the circulator, the radio frequency balun and the vector adder are sequentially connected.

Specifically, the application utilizes a directional coupler to obtain a reference signal source for carrier cancellation at the transmitting end of a reader-writer transmitter, the signal source generates I/Q two-path carrier cancellation reference signals through a quadrature signal generator, and the I/Q two-path carrier cancellation reference signals and a radio frequency tag signal containing carrier leakage are processed through a vector adder, so that carrier leakage cancellation is realized.

The vector adder is a digital adjustable vector adder and consists of three transconductance stages and a shared load stage, wherein the transconductance stages adopt a differential source negative feedback structure, and the equivalent transconductance of the two transconductance stages can be adjusted by adjusting the negative feedback resistance of the two transconductance stages. The signals are vector-added by a transconductance stage. The I/Q two-path carrier cancellation reference signal output by the quadrature signal generator is homologous to the carrier leakage signal and is used as a local oscillation signal of the down mixing. The signal is output by the multiplexer and is mixed with the carrier leakage signal to direct current, so that the deterioration of the sensitivity of the reader-writer receiver caused by the phase noise with higher carrier leakage signal is eliminated.

As shown in fig. 3, the load stage of the vector adder is composed of a differential inductance L, a blocking capacitance C0, and a capacitance C1 (the capacitive load contributed by the latter stage is small and negligible). The lc value is optimized to achieve maximum gain. The I/Q two-way quadrature carrier cancellation reference signal generated by the quadrature signal generator is input into the adjustable transconductance stage, the useful tag signal containing carrier leakage is input into the constant transconductance stage, and the useful signal is sent to the lower-stage circuit through the load stage and the output buffer stage.

As shown in fig. 4, the quadrature signal generator generates quadrature signals using a single stage RC-CR network. The single-stage RC-CR network can output two orthogonal I/Q signals for any frequency input signal, but only at one frequency point of omega=1/RC, the amplitude of the I/Q output signals is the same, and amplitude mismatch can be generated at other frequency points. Smaller I/Q amplitude mismatch can be achieved at wider frequencies through cascading of multi-stage RC-CR networks, but more losses are introduced. Because of the need of processing carrier leakage signals of 10dBm, carrier leakage reference signals of about 10dBm are needed, the signals are obtained by a transmitting end through a directional coupler, and then quadrature I/Q two-way signals are generated through a RC-CR network of the stage, in order to reduce the cost of the directional coupler and the power consumption of a post-stage circuit, the smaller the loss of the RC-CR network is, the better the loss of the RC-CR network is. The loss of the stage circuit and the amplitude mismatch of the output I/Q signal need to be considered in a compromise. The quadrature signals generated by the single-stage RC-CR network are used for adjusting the amplitude of the I/Q two-path carrier cancellation reference signals through the vector adder, and the tolerance to the amplitude mismatch of the I/Q two-path signals output by the RC-CR network is higher.

As shown in fig. 5, the power detector is implemented by self-mixing. The input RF signals VIN+, VIN-are coupled to the gates of the M2, M1 tubes via coupling capacitors C2, C3, respectively. The self-mixing function of the radio frequency signal input by the drain terminal and the radio frequency signal input by the gate terminal is realized by M1 and M2, and then the high frequency component is filtered by a low-pass filter consisting of M5, C5 and C4, so that the direct current level output is obtained.

C0 and C1 are blocking capacitors, C2 and C3 are coupling capacitors, R1, R2, R3 and R4 are bias resistors, drain voltages of M1 and M2 tubes are generated by a current mirror, the tubes work in a critical conduction state, and the drain and source potentials are almost equal, so that the drain bias voltage determines the direct current level of an output end. Since the tubes M1 and M2 in the critical on state are very sensitive to the change of the bias voltage, in order not to turn off the tubes, in the figure, the point B potential is equal to the point D potential, the point a potential is equal to the point C potential, the PMOS tubes M8 and M9 form a source follower structure, and M8 is a current source. When the current is constant, the potential difference between the two points C, D is constant, and thus the potential difference between the two points A, B is also constant. Namely, the voltage difference between the grid source ends of the M1 pipe and the M2 pipe is clamped by the stable grid source voltage difference of the M9 pipe. Thus stabilizing the dc bias of the tube in this way.

As shown in fig. 6, the multiplexer realizes a selection function for two signal inputs by using control signals PHT and PHTN connected by an inverter. When PHT is high level, PHTN is low level, M5 is conducted, M7 is turned off, DC bias voltage VBIAS is applied to grid electrode of M6 tube, M6 tube is conducted, signals PHASE0 and PHASE180 are output through drain ends of M1 tube and M2 tube; at this time, the M8 is turned off, the M10 tube is turned on, the M9 tube gate voltage is pulled to the ground potential, the M9 tube is turned off, and the signal DIVP and the DIVN path are turned off; similarly, when PHT is low level and PHTN is high level, signals DIVP and DIVN are output through the drain ends of the M3 pipe and the M4 pipe, and paths of signals PHASE0 and PHASE180 are cut off.

The circulator, the directional coupler and the radio frequency balun are all off-chip elements, wherein a simulation model of the circulator adopts an S2P file of the circulator with the MAFRIN series isolation degree of 20dB provided by M/A-COM company. The simulation model of the directional coupler uses the model XC 0900A-05S 4P file of the directional coupler provided by the Anara Xinger series.

In practical environments, the magnitude and phase of the carrier leakage signal will be greatly changed by the environment, so that the carrier leakage cancellation system needs to cancel carrier leakage signals with different magnitudes and different phases. The phase shifter is added at the input end to simulate carrier leakage signals with different phases, and the magnitude of the carrier leakage signals is adjusted by changing the isolation degree of the circulator. The phase shifter implementing the phase shift function is implemented by Verilog-a code.

The label signal and the carrier leakage signal are input from the left side, the carrier elimination reference signal obtained from the transmitting end through the coupling end of the directional coupler is input from the lower side, the local oscillation signal provided by the PLL is input from the lower side of the multiplexer, the carrier elimination signal of the multiplexer is output from the right side to the buffer stage, and the power detector and the carrier elimination signal are output from the right side.

Claims

1. The carrier leakage elimination system based on the UHF RFID reader-writer is characterized in that: the device comprises a directional coupler, an orthogonal signal generator, a vector adder, a power detector, a multiplexer, a phase shifter, a circulator and a radio frequency balun, wherein the directional coupler is connected with the orthogonal signal generator, the orthogonal signal generator is respectively connected with the vector adder and the multiplexer, the vector adder is connected with the power detector, the directional coupler, the phase shifter, the circulator, the radio frequency balun and the vector adder are sequentially connected, the vector adder is a digital adjustable vector adder and consists of three transconductance stages and a shared load stage, the transconductance stages adopt a differential source negative feedback structure, the orthogonal signal generator adopts a single-stage RC-CR network to generate orthogonal signals, the power detector is realized in a self-mixing mode, and the multiplexer realizes a selection function for two paths of signal input by using control signals PHT and PHTN connected by the inverter.

2. The UHF RFID reader-writer based carrier leakage cancellation system according to claim 1, wherein: the directional coupler is connected with the transmitting end of the reader-writer transmitter.

3. The UHF RFID reader-writer based carrier leakage cancellation system according to claim 1, wherein: the circulator is connected with a receiving end of a reader-writer transmitter.