It is applied to the echo cancellation system of remote UHF rfid interrogators
Technical field
The application is related to a kind of echo cancellation system for being applied to remote UHF rfid interrogators, more particularly to a kind of
The reader/writer module of long distance radio frequency identification.
Background technology
Ultrahigh frequency RFID (Radio Frequency Identification) is that one kind is operated in 840MHz~960MHz
Non-contact radio-frequency technology of identification.The rfid interrogator of its uhf band is to launch and receive radiofrequency signal by antenna, is realized
Automatic identification to label.
The freight detection of monitoring and the movement of transportation and communication, such as electronic license plate, goods identification need RFID read-write
Device all realizes that it is read come the RFID technique for realizing remote tag recognition, low frequency and high band by near field operation principle
Write region and distance is little, typically several centimetres to tens centimetres, remote tag recognition is generally by uhf band
Rfid interrogator is realizing.In order to realize remote tag recognition, uhf band rfid interrogator is by being constantly increasing power
The transmission power of amplifier, so that label can also be coupled to enough energy under larger distance, the response letter that it is returned
Number can pass to rfid interrogator.Read write line is in the state of receiving, it is still necessary to which power amplifier (PA) launches sufficiently high company
Continuous carrier signal provides energy to radio-frequency (RF) tag.But due to the transmitting and reception of the rfid interrogator of uhf band are to share day
Line, the continuous carrier signal of transmitting can leak into receiving terminal by bonder, and it is placed exactly in the middle of the frequency range for receiving signal,
Cannot be filtered using radio-frequency filter.DC component and interference are produced after the signal of leakage and the local oscillation signal mixing of frequency mixer
Signal, affects the sensitivity for receiving, so as to affect the reading distance of the rfid interrogator of uhf band.
Utility model content
The purpose of this utility model is to provide a kind of echo cancellation system for being applied to remote UHF rfid interrogators,
The system can have good receiving sensitivity in the case of higher continuous carrier is launched, it is achieved thereby that far Distance RFID read-write
Device.
For achieving the above object, this utility model provides following technical scheme:
The embodiment of the present application discloses a kind of echo cancellation system for being applied to remote UHF rfid interrogators, including day
Line, the power amplifier of transmitting chain, bonder, synthesizer, the low-noise amplifier of receives link and Echo Cancellation module, close
The outfan grown up to be a useful person is connected with the input of low-noise amplifier, and the Echo Cancellation module is taken out by the isolation end of bonder
Coupled signal during power amplifier transmitting continuous carrier signal, synthesizer obtains antenna transmitting and reveals from the coupled end of bonder
Signal, the Echo Cancellation module is processed the amplitude of coupled signal got and phase place so as to and leakage signal amplitude
Unanimously, opposite in phase, was synthesized before low-noise amplifier by synthesizer, so as to completely offset power amplifier
The signal of receiving terminal is leaked into during transmitting continuous carrier.
Preferably, it is applied in the echo cancellation system of remote UHF rfid interrogators in above-mentioned, the echo is supported
The module that disappears includes phase-shift network module, orthogonal mixer, variable gain amplifier and digital Echo Cancellation module,
The phase-shift network module is connected with the isolation end of bonder, and the isolation end of the bonder obtains continuous carrier
The coupled signal got is changed into coupled signal, phase-shift network module the orthogonal signalling on I roads and Q roads,
The output of the phase-shift network module is connected with the local oscillator end of orthogonal mixer, there is provided needed for orthogonal mixer just
Signal, the constant amount A and B that digital echo cancellation module is produced is handed over to be connected with the input of orthogonal mixer,
The output signal of the orthogonal mixer with can gain amplifier input be connected, digital echo cancellation module produce
Gain control amount C with can gain amplifier control end be connected, constantly change C values make at a high speed can gain amplifier output signal and
The amplitude of receiving terminal leakage signal is consistent,
The output of the variable gain amplifier is connected with the IN1 ends of synthesizer, coupled end and the synthesizer of bonder
IN2 ends are connected, and the given constant value of digital echo cancellation module makes the phase place of output signal and the letting out for receiving terminal of orthogonal mixer
The opposite in phase of leakage signal, while realizing the amplitude balance of two paths of signals in the case where variable gain amplifier is helped, synthesizer is combined
The two paths of signals.
Preferably, it is applied in the echo cancellation system of remote UHF rfid interrogators in above-mentioned, the numeral is returned
The constant amount A and B that ripple cancellation module is produced is to adjust the phase place of coupled signal, while changing the amplitude size of coupled signal.
Preferably, it is applied in the echo cancellation system of remote UHF rfid interrogators in above-mentioned, the echo is supported
The module that disappears also includes power detector, and the input of power detector is connected with the outfan of synthesizer, and power detector is real-time
The result of detection Echo Cancellation is simultaneously fed back to digital echo cancellation module.
Preferably, in above-mentioned rfid interrogator, the control method of the digital echo cancellation module includes:
(1) yield value of variable gain amplifier, is set first;
(2) the bit wide value for, assuming a, b is N, then a is a [N-1:0], b is b [N-1:, and a, b meet relation 0]:
a2+b2=2N-1-1
A is being adjusted from -2N-1- 1 to 2N-1- 1, b value also follows change;
(3) and then according to power detection value, Signal estimation amplitude Amp is obtained3, then A=Amp3× a, B=Amp3× b, it is defeated
Go out A, B value
(4) yield value of high speed variable gain amplifier, continuous repeat step (2) and (3), are adjusted;
(5) A, B value during power detector detection minimal power values, is retained.
Compared with prior art, the utility model has the advantage of:This utility model is sent out by using Echo Cancellation technology
Penetrating link can increase transmission power by power amplifier, and receives link improves what is received by low-noise amplifier (LNA)
Sensitivity, so that remote uhf band rfid interrogator is achieved.
Description of the drawings
In order to be illustrated more clearly that the embodiment of the present application or technical scheme of the prior art, below will be to embodiment or existing
The accompanying drawing to be used needed for having technology description is briefly described, it should be apparent that, drawings in the following description are only this
Some embodiments described in application, for those of ordinary skill in the art, on the premise of not paying creative work,
Can be with according to these other accompanying drawings of accompanying drawings acquisition.
Fig. 1 show uhf band rfid interrogator in this utility model specific embodiment and leaks when continuous carrier is launched
To receiving terminal schematic diagram;
The local oscillator end that Fig. 2 show the initial phase of continuous carrier and frequency mixer in this utility model specific embodiment is initial
The asynchronous interference signal of phase and the big logotype of DC component;
Fig. 3 show uhf band rfid interrogator principle schematic in this utility model specific embodiment;
Fig. 4 show uhf band rfid interrogator in this utility model specific embodiment and implements block diagram.
Specific embodiment
Below in conjunction with the accompanying drawing in this utility model embodiment, the technical scheme in this utility model embodiment is carried out
Detailed description, it is clear that described embodiment is only a part of embodiment of this utility model, rather than the enforcement of whole
Example.Based on the embodiment in this utility model, those of ordinary skill in the art institute on the premise of creative work is not made
The every other embodiment for obtaining, belongs to the scope of this utility model protection.
With reference to shown in Fig. 1, the signal of leakage is usedRepresent, whereinTransmitting continuous carrier
Initial phase, θ is that continuous carrier signal reveals the phase place change that process is produced through power amplifier (PA) amplification, bonder
Amount.The local oscillation signal of frequency mixer (mixer) is usedWhereinIt is local oscillation signal initial phase.
The post processing of frequency mixer is low frequency signal, and two frequency-doubled signals of local oscillator can be cut, and the phase of leakage signal
Position variable quantity very little, institute's above formula is reduced to
With reference to shown in Fig. 2, when continuous carrier signal initial phaseWith the initial phase of frequency mixer local oscillation signalDifference
When 0 °, than larger, interference signal is less, when continuous carrier signal initial phase for DC componentWith frequency mixer local oscillation signal
Initial phaseWhen differing 90 °, DC component is smaller, and jam-to-signal is larger.For far Distance RFID read write line, Ke Nengtian
The label return signal that line is received is less compared with interference signal, so as to affect follow-up demodulation and label judging process.Therefore
The signal of receiving terminal is leaked into when needing Echo Cancellation technology to eliminate power amplifier transmitting continuous carrier.
With reference to shown in Fig. 3, relative to the classical rfid interrogator structures of Fig. 1, far Distance RFID read write line increased echo
The structure of counteracting, including circuit realiration and the algorithm realization of Echo Cancellation of clawback counteracting.Mainly by the isolation end of bonder
(isolate) coupled signal when power amplifier launches continuous carrier signal is taken out, coupled signal is relative to receiving terminal
Leakage signal includes same information, and they are obtained by bonder.Echo Cancellation module is by digital algorithm to getting
Coupled signal amplitude and phase place processed so as to, opposite in phase, in low noise consistent with the leakage signal amplitude of receiving terminal
Being synthesized before acoustic amplifier (LNA), during so as to completely offsetting power amplifier transmitting continuous carrier reception is leaked into
The signal at end.
Using Echo Cancellation technology, the signal of low-noise amplifier process is entirely the signal returned by label, is not existed
The choking phenomenon of receiving terminal leakage signal.Simultaneously power amplifier can increase transmission power and understand due to launching work(without worry
Rate is larger and to leak into the leakage signal of receiving terminal also larger, so as to affect receiving sensitivity.In addition low-noise amplifier plus
Enter also to increase the gain of receives link front end, improve the sensitivity of receives link.In a word, with the help of Echo Cancellation, send out
Penetrating link can increase transmission power by power amplifier, and receives link improves what is received by low-noise amplifier (LNA)
Sensitivity, remote uhf band rfid interrogator is achieved.
Refering to Fig. 3, relative to classical uhf band rfid interrogator structure, remote uhf band rfid interrogator is also wrapped
Include orthogonal mixer (IQ mixer), high speed variable gain amplifier (VGA), synthesizer (combiner), low-noise amplifier
(LNA), the algorithm of power detector and numeral realizes module.
Rfid interrogator is under reception state, the output continuous carrier signal and the reflected signal of antenna of power amplifier
Receiving terminal will be leaked to by bonder, this is the signal eliminated required for us, is designated as:
TxSignal=Amp1cos(ωct+θ1)
Wherein Amp1 is the amplitude characteristic constant value of circuit.
Take out the local oscillator of the coupled signal as orthogonal mixer of continuous carrier signal by the isolation end of bonder simultaneously
Signal, local oscillation signal produces the orthogonal two paths of signals of IQ through 45 °/- 45 ° phase shifters, and the input of orthogonal mixer is by number
Word algorithm fits signal the constant A and B for coming, and its Main Function is the phase place for adjusting coupled signal, while can also change coupling
The amplitude size of signal.Principle is as follows:
Wherein:
The phase place of quadrature mixer output signal is that by determining, value changes with A and B changes again, therefore orthogonal mixer
Output phase is determined by A, B values.If A, B make the leakage signal opposite in phase of the output phase of orthogonal mixer and receiving terminal,
Orthogonal mixer output amplitude by a high speed can gain amplifier adjust so as to and the leakage signal amplitude of receiving terminal is equal, i.e.,
Eliminate Amp1And Amp2Difference.Two paths of signals can eliminate power amplifier transmitting after synthesizer (combiner) synthesis
The signal of receiving terminal is leaked into during continuous carrier.
Average power signal under the difference for ignoring amplitude, after the counteracting of calculating.
Wherein agree as follows:
C1=power1+power2 C2=2 × power3×cos(θ1) C3=2 × power4×sin(θ1) C4=θ2-ψ
Power above1~power4、C1~C4, for constant value, it can be seen that Feedback of Power value and constant value A,
Constant value B has a corresponding relation, mean power and information is passed to into digital back cancellation module after the counteracting of power detector detection,
Digital echo cancellation module constantly can adjust A and B values in the range of the digital signal bit wide of constant value A and constant value B, and remember
Record A, B value when power detector value of feedback is minimum and export, the following is the flow process that concrete Echo Cancellation digital algorithm is realized:
1) yield value of setting high-speed variable gain amplifier first;
2) the bit wide value for assuming a, b is N, then a is a [N-1:0], b is b [N-1:, and a, b meet relation 0]:
a2+b2=2N-1-1
A is being adjusted from -2N-1- 1 to 2N-1- 1, b value also follows change, N to refer to the sampling bit wide of ADC, and value is usually
It is specifically relevant by the ADC chips sampling bit wide for being adopted from 2,3,4.......
3) and then according to power detection value, Signal estimation amplitude Amp is obtained3, then A=Amp3× a, B=Amp3× b, output
A, B value;
4) yield value of high speed variable gain amplifier, continuous repeat step 2 are adjusted) and 3);
5) A, B value during power detector detection minimal power values is retained.
The signal cancellation of the higher-wattage that can would leak into receiving terminal using the mixed-media network modules mixed-media of Echo Cancellation is fallen, and so receives
Link can add low-noise amplifier (LNA), and the signal of the input of low noise is entirely the label return that antenna is received
Signal, will not enter saturation due to leakage signal.The sensitivity of receives link can well be increased in the case where LNA is helped, in addition
The transmission power of power amplifier can also constantly be improved and affected without worrying that continuous carrier signal can leak into receiving terminal
The sensitivity of reception, it is achieved thereby that the rfid interrogator of remote uhf band.
Finally, in addition it is also necessary to explanation, term " including ", "comprising" or its any other variant are intended to non-exclusive
Property include so that a series of process, method, article or equipment including key elements not only include those key elements, and
Also include other key elements being not expressly set out, or also include intrinsic for this process, method, article or equipment
Key element.