TWI470944B - Transceivers and noise cancellation methods for radio frequency identification - Google Patents

Description

Transceivers for radio frequency identification and noise cancellation methods /

The present invention relates to a wireless communication system and method, and more particularly to a transceiver and method for eliminating noise in radio frequency identification.

Radio frequency identification (RFID) is one of the most important top ten technologies in the 21st century. It usually requires a system consisting of a reader (Reader) and an RFID tag (Tag), like the first. The figure shows. The principle of RFID operation is to use the sensor 10 to emit radio waves, touch the RFID tag 12 in the sensing range, generate current by electromagnetic induction, supply the wafer on the RFID tag 12 to operate and emit a wireless signal backscatter sensor 10.

Different from the source of driving energy, RFID tags can be divided into active and passive. The passive tag itself has no battery device, and the required power is generated by the electromagnetic wave electromagnetic induction of the sensor, so the signal sent by the sensor will only passively respond to the sensor. The active tag has a built-in battery that can actively transmit signals for the sensor to read, and the signal transmission range is relatively more passive than passive.

When the RFID tag 12 responds to the sensor 10, it generally transmits the message by using the modulated carrier signal. At this time, the sensor 10 still sends a carrier signal without modulation to supply the power of the passive tag.

Figure 2 shows the architecture in sensor 10. Most of the transmitters 14 The transmitted carrier signal Cx will be transmitted through the antenna 18 to the environment. However, in reality there is a problem that the impedance does not match a little, and a small portion of the carrier signal Cx will be reflected back by the antenna 18, as shown by the reflected carrier signal CRx in FIG. The reflected carrier signal CRx will be received by the receiver 16 via a coupler 20, along with the wireless signal Rx received by the antenna 18. Compared with the desired wireless signal Rx, the reflected carrier signal CRx is equivalent to noise and should be suppressed or eliminated.

Figure 3 shows the spectrum of the reflected carrier signal CRx and the wireless signal Rx. It is difficult for the sensor 10 to transmit an absolutely clean (single tone only) carrier signal Cx, with some phase noise. Therefore, the spectrum of the reflected carrier signal CRx is spread around the carrier frequency f _Cx . As a result of the modulation, the wireless signal Rx is roughly composed of two tones whose frequency is the carrier frequency f _Cx of the carrier signal _Cx plus or minus Δf, as shown in FIG.

The presence of the reflected carrier signal CRx reduces the signal to noise ratio (SNR) of the receiver 16 at the receiving end. Once the reflected carrier signal CRx is too large, as shown in FIG. 3, the wireless signal Rx may be submerged under the reflected carrier signal CRx and cannot be recognized.

Therefore, how to eliminate or suppress the reflected carrier signal CRx is the goal of the industry. One of the most intuitive ways is to reduce the impedance mismatch and directly reduce the energy of the reflected carrier signal CRx. However, this method requires high-accuracy impedance matching, which will greatly increase the manufacturing cost of the inductor.

In view of this, the object of the present invention is to provide a wireless usable The radio frequency identification transceiver and the noise cancellation method generate a feedback current according to a part of the carrier signal to eliminate noise in the wireless signal.

An embodiment of the present invention provides a transceiver for use in radio frequency identification, including a transmitter, a receiver, and a noise canceller. The transmitter can be used to transmit a carrier signal to an antenna. The receiver can be used to receive a wireless signal from the antenna. According to a portion of the carrier signal, the noise canceller generates a feedback current that is fed to an input of the receiver to cancel noise in the wireless signal. The noise canceller adjusts the feedback current according to the signal strength of the noise in the wireless signal.

An embodiment of the present invention provides a method for eliminating noise, which is applied to a transceiver for radio frequency identification, comprising: transmitting a carrier signal to an antenna; receiving a wireless signal from the antenna; and using a portion of the carrier signal Generating a feedback current that is fed to an input of the receiver; and adjusting the feedback current according to the signal strength of the noise in the wireless signal to cancel noise in the wireless signal.

In order to better understand the above and other aspects of the present invention, the preferred embodiments are described below, and in conjunction with the drawings, the detailed description is as follows:

Figure 4 shows a block diagram of a transceiver that can be used in radio frequency identification (RFID) in accordance with the present invention. As shown in FIG. 4, transceiver 60 includes an inductor 62, an antenna 64, and a number of discrete elements.

The transmitter 66 can convert the digital information to be transmitted by the sensor 62 through the digital analog converter 68 and the mixer 70 to up-convert the transmission. The emitter TX, power amplifier 72, coupler 74, and antenna 64 are transmitted to the environment. The mixer 70 mixes the modulated signal output by the digital analog converter 68 with the carrier signal provided by the present oscillator.

The receiver 76 includes a low noise amplifier (LNA) 78, a mixer 80, and an analog digital converter 84. The wireless signal received by the antenna 64 from the RFID tag passes through the coupler 74, the balun 86 and the receiving end RX, and is received by the receiver 76. Following a process such as down-conversion, analog-to-digital conversion, etc., receiver 76 provides a corresponding digital signal to digital signal controller 88.

When the transmitter 66 transmits the carrier signal Cx through the transmitting terminal TX, the power amplifier 72, the coupler 74, and the antenna 64, part of the carrier signal Cx is reflected back by the antenna 64 to become the reflected carrier signal CRx for receiving the RFID signal. For the wireless signal of the tag, the reflected carrier signal CRx is a noise and should be suppressed or eliminated. If not properly processed, noise such as the reflected carrier signal CRx will be included in the wireless signal and received by the receiver 76 through the coupler 74, the balun 86 and the receiving terminal RX.

The sensor 62 further has a noise canceller 90 for eliminating or suppressing noise contained in the wireless signal received at the receiving end RX, that is, reflecting the carrier signal CRx, to increase the signal to noise ratio. The noise canceller 90 includes a plurality of sets of multiphase generators 92, a programmable current generator 94, a power detector 96, and an analog digital converter 98.

Part of the carrier signal Cx, through the coupler 74 and balance and imbalance The converter 100 will arrive at the carrier cancellation terminal CC and become the carrier cancellation signal CCx. Just because the carrier cancellation signal CCx and the reflected carrier signal CRx are both part of the carrier signal Cx and have only experienced different transmission paths, the carrier cancellation signal CCx differs from the reflected carrier signal CRx by only the signal phase and signal strength. Figure 5 illustrates the phase and intensity relationship of some of the signals in Figure 4 to each other. In Fig. 5, it is assumed that the carrier cancellation signal CCx is located in the fourth quadrant, and the reflected carrier signal CRx is located in the first quadrant.

Based on the carrier cancellation signal CCx, the plurality of sets of phase generators 92 can provide one of a pair of base signals. Taking Figure 5 as an example, multiple sets of phase generators 92 can generate base signal pairs (2LO ₀ , 2LO ₉₀ ), (-2LO ₀ , 2LO ₉₀ ), (-2LO ₀ , -2LO ₉₀ ), and (2LO ₀ , -2LO ₉₀ ), respectively located in the first quadrant, the second quadrant, the third quadrant, and the fourth quadrant of Figure 5. Here, 2LO ₀ is the first basic signal of the backward carrier cancellation signal CCx, 2LO ₉₀ is π/2 radians behind 2LO ₀ , and so on.

The four pairs of base signals represent the four phase relationships of the base signal and the carrier cancellation signal CCx. Based on the polarity signals IS and QS, the plurality of sets of phase generators 92 can select a pair of outputs from the four pairs of base signals to the programmable current generator 94. For example, at a certain point in time, the polarity signals IS and QS provided by the digital signal controller 88 are both logically 1, so that the plurality of sets of phase generators 92 provide the base signal pair (-2LO ₀ , -2LO ₉₀ ). Program current generator 94.

In one embodiment, the programmable current generator 94 is a transconductor that converts the received base signal pair into a relative compensation current pair II _FB according to two amplification factors gm _I and gm _Q . With the IQ _FB , it is fed back into the feedback current I _FB and fed to the input of the receiver 76, that is, the receiving end RX. The digital signal controller 88 provides the override control signals IGM and QGM to determine the amplification factors gm _I and gm _Q .

Taking Figure 5 as an example, the programmable current generator 94 linearly converts the base signal pair (-2LO ₀ , -2LO ₉₀ ) to the corresponding compensation current pair II _FB and IQ _{FB , respectively} . The feedback current I _FB is the vector sum of the compensation current pair II _FB and IQ _FB . In Fig. 5, the feedback current I _{FB is} approximately the inverse of the reflected carrier signal CRx, so the feedback current I _FB can almost completely cancel the reflected carrier signal CRx, and the noise is eliminated.

The power detector 96 detects the signal strength of the noise in the wireless signal on the receiving end RX, that is, the intensity of the reflected carrier signal CRx, to generate a received signal strength index (RSSI). Based on the received signal strength indicator, the digital signal controller 88 can update the override control signals IGM and QGM, as well as the polarity signals IS and QS, thereby adjusting the feedback current I _FB . The digital signal controller 88 can be internally built with an optimization operation to find the optimum override control signal and polarity signal such that the received signal strength indicator is at a minimum.

For example, the digital signal controller 88 can combine all possible magnification control signals IGM and QGM, and the arrangement of the polarity signals IS and QS once, generate all corresponding feedback currents I _FB , and record all corresponding receptions. Signal strength indicator.

Among them, the magnification control signal and the polarity signal corresponding to the lowest received signal strength index are the optimum magnification control signal and the polarity signal. The optimum override control signal and the polarity signal allow the reflected carrier signal CRx of the noise to be substantially offset by the feedback current I _FB . The digital signal controller 88 can memorize the optimal multiplying control signal and the polarity signal as the normal operation, eliminating the reflected carrier signal CRx to increase the signal to noise ratio at the receiving end RX.

FIG. 6 illustrates a plurality of sets of phase generators 92 including a polyphase filter 102 and a polarity selector 104. Based on the carrier cancellation signal CCx (consisting of balanced carrier cancellation signals CCx_P and CCx_N), the polyphase filter 102 generates four local signals LO ₀ , LO ₉₀ , LO ₁₈₀ , and LO ₂₇₀ , each before the local signal A local signal is approximately π/2 radians. Polarity selector 104 has two identical circuits 104I and 104Q.

Taking the circuit 104I as an example, when the polarity signal IS is 0, the base signal CC_IB is equal to the local signal LO ₀ minus the local signal LO ₁₈₀ , so it is equal to 2*LO ₀ . Conversely, when the polarity signal IS is 1, the base signal CC_IB is equal to the local signal LO ₁₈₀ minus the local signal LO ₀ , so it is equal to -2*LO ₀ . Similarly, in this embodiment, the base signal CC_QB will be equal to 2*LO ₉₀ or -2*LO ₉₀ depending on the polarity signal QS.

Therefore, depending on the polarity signals IS and QS, the base signal pairs (CC_IB, CC_QB) provided by the plurality of sets of phase generators 92 will be four basic signal pairs (2LO ₀ , 2LO ₉₀ ), (-2LO ₀ , 2LO ₉₀ ), (-2LO ₀ , -2LO ₉₀ ), and (2LO ₀ , -2LO ₉₀ ) one of them. Although in the embodiment of Fig. 6, each pair of base signals are orthogonal to each other, the present invention is not limited thereto. In other embodiments, each pair of base signals may not be orthogonal to each other.

Figure 7 illustrates a programmable current generator 94 having the same transducers 106I and 106Q. Taking the transducer 106I as an example, it receives the base signal CC_IB, generates a compensation current II _FB , and the magnification control signal IGM determines the amplification factor gm _I (=II _FB /CC_IB). Similarly, the magnification control signal QGM determines the amplification factor gmQ. After the compensation current II _FB and the compensation current IQ _{FB are} integrated, it becomes the feedback current I _FB and is fed to the positive terminal RX_P of the receiving end RX. Conversely, the feedback current I _{FB is} fed out of the negative terminal RX_N of the receiving terminal RX. For the feeding and feeding of current, as long as the output of the transducers 106I and 106Q is directly connected to the receiving end RX, the circuit is very simple.

It can be seen from the fifth, sixth and seventh graphs that the polarity signals IS and QS select one of several phase relationships corresponding to the carrier cancellation signal CCx, which roughly determines that the feedback current I _FB is located in FIG. Which quadrant of the magnification; the override control signals IGM and QGM roughly determine the angle (phase) and length (intensity) of the feedback current I _FB within the quadrant selected by the polarity signal. The digital signal controller 88 in Fig. 4 can find the optimum magnification control signal and the polarity signal such that the received signal strength index is the lowest, so that the feedback current I _FB substantially cancels the reflected carrier signal CRx.

It will also be apparent from the embodiment of Fig. 4 that regardless of whether the impedance of the antenna 64 is accurately matched, the digital signal controller 88 can adaptively generate an appropriate feedback current I _FB to offset the reflected carrier signal CRx that may be generated.

In conclusion, the present invention has been disclosed in the above preferred embodiments, and is not intended to limit the present invention. A person skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

10, 62‧‧‧ sensor

12‧‧‧RFID tags

14, 66‧‧‧transmitters

16, 76‧‧‧ Receiver

18, 64‧‧‧ antenna

20, 74‧‧‧ coupler

60‧‧‧ transceiver

68‧‧‧Digital Analog Converter

70, 80‧‧‧ Mixer

72‧‧‧Power Amplifier

78‧‧‧Low noise amplifier

84, 98‧‧‧ analog digital converter

86, 100‧‧‧Balance and Unbalance Converter

88‧‧‧Digital Signal Controller

90‧‧‧ Noise Canceller

92‧‧‧Multiple phase generators

94‧‧‧Programmable current generator

96‧‧‧Power Detector

102‧‧‧Multiphase Filter

104‧‧‧Polar selector

104I, 104Q‧‧‧ circuits

106I, 106Q‧‧‧Transducer

CC‧‧‧ Carrier Elimination

CCx, CCx_P, CCx_N‧‧‧ carrier cancellation signal

CC_IB, CC_QB‧‧‧ basic signal

CRx‧‧‧ reflected carrier signal

Cx‧‧‧ carrier signal

f _Cx ‧‧‧carrier frequency

I _FB ‧‧‧feedback current

IGM, QGM‧‧‧ rate control signal

II _FB , IQ _FB ‧‧‧Compensation current

IS, QS‧‧‧ polar signals

LO ₀ , LO ₉₀ , LO ₁₈₀ , LO ₂₇₀ ‧‧‧ local signal

RSSI‧‧‧ Received Signal Strength Indicators

RX‧‧‧ Receiver

RX_P‧‧‧ Positive

RX_N‧‧‧ negative end

TX‧‧‧transmitter

Figure 1 shows a conventional radio frequency identification system.

Figure 2 shows the architecture of the sensor in Figure 1.

Figure 3 shows the spectrum of the reflected carrier signal CRx and the wireless signal Rx.

Figure 4 shows a block diagram of a transceiver that can be used for radio frequency identification in accordance with the present invention.

Figure 5 illustrates the phase and intensity relationship of some of the signals in Figure 4 to each other.

Figure 6 illustrates a plurality of sets of phase generators.

Figure 7 illustrates a programmable current generator.

60‧‧‧ transceiver

62‧‧‧ sensor

64‧‧‧Antenna

66‧‧‧transmitter

68‧‧‧Digital Analog Converter

70‧‧‧ Mixer

72‧‧‧Power Amplifier

74‧‧‧ Coupler

76‧‧‧ Receiver

78‧‧‧Low noise amplifier

80‧‧‧ Mixer

84‧‧‧ analog digital converter

86‧‧‧Balance and Unbalance Converter

88‧‧‧Digital Signal Controller

90‧‧‧ Noise Canceller

92‧‧‧Multiple phase generators

94‧‧‧Programmable current generator

96‧‧‧Power Detector

98‧‧‧ Analog Digital Converter

100‧‧‧Balance and Unbalance Converter

CC‧‧‧ Carrier Elimination

I _FB ‧‧‧feedback current

IGM, QGM‧‧‧ rate control signal

IS, QS‧‧‧ polar signals

RSSI‧‧‧ Received Signal Strength Indicators

RX‧‧‧ Receiver

TX‧‧‧transmitter

Claims (11)

A transceiver for radio frequency identification, comprising: a transmitter for transmitting a carrier signal to an antenna; a receiver having an input for receiving a wireless signal from the antenna via the input And a noise canceller, comprising: a plurality of sets of phase generators, according to the part of the carrier signal, generating a pair of base signals having a predetermined phase relationship, wherein the preset phase relationship is a complex phase One of the relationships; and a programmable current generator that generates a feedback current according to the pair of base signals, feeds the input of the receiver, and adjusts the signal according to the signal strength of the noise in the wireless signal The current is fed back to cancel the noise in the wireless signal. The transceiver of claim 1, wherein the plurality of sets of phase generators comprise: a multi-phase filter that generates a multi-phase local signal based on the portion of the carrier signal; and a selection According to a first polarity signal, the difference between the two local signals of the multi-phase local signal is used as one of the two basic signals, and according to a second polarity signal, the other of the multi-phase local signals The difference between the two local signals is the other of the two basic signals. The transceiver of claim 1, wherein the programmable current generator converts the pair of basic signals into a pair of compensation currents at two amplification rates, and feeds the input terminals together, and The programmable current generator receives a double rate control signal to determine the second amplification rate. The transceiver of claim 1, wherein the pair of base signals have a phase difference of about π/2 radians from each other. A transceiver for radio frequency identification, comprising: a transmitter for transmitting a carrier signal to an antenna; a receiver having an input for receiving a wireless signal from the antenna via the input And a noise canceller, according to the part of the carrier signal, generating a feedback current, feeding the input end of the receiver, and adjusting the feedback current according to the signal strength of the noise in the wireless signal to eliminate The noise in the wireless signal; and a digital signal controller providing an optimization operation to control the noise canceller to minimize the noise in the wireless signal, wherein the digital signal controller The magnification control signal and the polarity signal obtained by the optimization operation are memorized as used in normal operation. A method for eliminating noise is applied to a transceiver for radio frequency identification, comprising: transmitting a carrier signal to an antenna; receiving a wireless signal from the antenna; providing a complex phase relationship; generating a signal according to the portion of the carrier signal And a pair of base signals, wherein the pair of base signals conform to one of the phase relationships; according to the pair of base signals, the feedback current is generated, fed to the input end of the receiver; and the signal according to the noise in the wireless signal Intensity to adjust the feedback Streaming to eliminate noise in the wireless signal. The method for eliminating noise according to claim 6 of the patent application, comprising: generating a multi-phase local signal according to the portion of the carrier signal; and using a difference between two local signals of the multi-phase local signal as One of the two base signals; and the difference between the other two of the local signals of the multi-phase as the other of the two base signals. The method for eliminating noise according to claim 6 of the patent application includes: providing a bipolar signal for selecting one of the phase relationships. The method for eliminating noise according to claim 6 of the patent application, comprising: generating a pair of basic signals according to the portion of the carrier signal; and converting the pair of base signals to become a pair of compensation currents, and feeding the same Input. The method for canceling noise according to claim 9 includes: providing two amplification factors to convert the pair of base signals to become the pair of compensation currents; and optimizing the ones according to an optimization operation Magnification to minimize noise in the wireless signal. The noise cancellation method according to claim 10, comprising: a rate control signal and a polarity signal obtained by memorizing the optimization operation. No., used as normal operation.