JP5120225B2 - RFID reader / writer device and RFID reader / writer system - Google Patents

Description

The present invention relates to an RFID reader / writer device that performs radio communication with an RFID and performs reading and writing, and an RFID reader / writer system.

An RFID (Radio Frequency IDentification) system includes an RFID for registering ID and information data, and an RFID reader / writer device for recognizing and controlling the RFID. An RFID tag (passive tag) that does not contain a battery includes an internal antenna and an IC chip. The RFID reader / writer device transmits a modulation signal (command) to the RFID tag, and then the RFID tag returns a response. When the RFID tag responds, the RFID reader / writer device transmits a non-modulated signal and supplies power to the RFID tag. At the same time, the RFID tag performs data modulation by controlling the non-modulated signal by reflection / termination (on / off), and performs RFID modulation. Data is sent to the reader / writer device.

The spectrum of the modulated signal transmitted by the RFID tag spreads around the non-modulated signal transmitted by the RFID reader / writer device, and the receiving unit of the RFID reader / writer device receives the modulated signal from the RFID tag and the transmitting unit of the RFID reader / writer device. An unmodulated signal is received simultaneously. A carrier canceller may be used to cancel the wraparound of the unmodulated signal from the transmission unit of the RFID reader / writer device.

In general, a carrier canceller adjusts the amplitude and phase of an unmodulated signal extracted from a transmission unit with a quadrature modulator to generate a cancel signal having the same amplitude as that of the wraparound signal, and adding the cancel signal. Cancel the sneak signal. Patent Document 1 discloses a wireless tag communication device using a cancel signal. Patent Document 2 discloses a response wraparound canceller for an RFID reader.
JP 2006-217427 A 2005 IEICE Communication Society "Applicable wraparound canceller for UHF band RFID reader"

For example, in transmission modulation PR-ASK (Phase-Reverse ASK) used in RFID, the phase state of an unmodulated carrier wave transmitted at the time of reception from the RFID reader / writer device is 0 ° and 180 °. However, the transmission unit and the carrier canceller have a slight error between the phase state 0 ° and the phase state 180 °. Due to this minute error, the carrier reproduction accuracy differs between the phase state 0 ° and the phase state 180 °. I will make it. If the suppression effect required for the carrier canceller is 40 dB and 50 dB so that the transmission output can be increased and at the same time a weak signal from the RFID tag can be received in order to enable communication with a long-distance RFID, this small error becomes a problem. The sneak signal cannot be canceled at the required level. That is, in the prior art, due to a phase error of 0 ° in the transmission unit, a minute error in the phase state of 180 °, a DC offset generated at the time of band limitation in the phase state of 0 °, phase state of 180 ° in the carrier canceller, etc. The suppression effect required by the carrier canceller may not be obtained.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an RFID reader capable of canceling a sneak signal using a carrier canceller regardless of the phase state of an unmodulated carrier wave. A writer device and an RFID reader / writer system are provided.

In order to achieve the above object, according to the first aspect of the present invention, a predetermined transmission signal is transmitted from the antenna 34 toward the RFID at the time of transmission, and an unmodulated carrier wave for power supply is transmitted via the antenna 34 at the time of reception. The RFID reader / writer device 10 communicates with the RFID by receiving a reply signal returned from the RFID according to the transmission signal by the receiver 52 via the antenna 34, and
A carrier canceller 40 that cancels wraparound of the unmodulated carrier for power supply transmitted at the time of reception to the receiver by adding a cancel signal having the same amplitude and opposite phase as the wraparound signal;
Amplitude correction means 48 for correcting the amplitude of the cancellation signal;
Phase correction means 46 for correcting the phase of the cancellation signal;
A correction value holding means 12 for holding an amplitude correction value and a phase correction value for each phase state of the unmodulated carrier wave, and outputting to each of the amplitude correction means and the phase correction means;
Phase predicting means 20 for predicting the phase state of the unmodulated carrier wave for power supply,
Based on the phase state predicted by the phase prediction unit 20, the correction value holding unit 12 converts the amplitude correction value ΔA and the phase correction value Δφ generated by the phase state into the amplitude correction unit 48 and the phase correction unit 46. It is a technical feature to output each of the above.

Even when the carrier canceller cancels by adding a cancel signal having the same amplitude and opposite phase as the sneak signal to the sneak signal, there is no power supply due to the amplitude error or phase error generated in the modulator 24 or the carrier canceller 40. Depending on the phase state of the modulated carrier wave, the amplitude and phase of the cancel signal that can suitably cancel the sneak signal differ. For this reason, the sneak signal cannot be sufficiently suppressed using the cancel signal corrected with the same amplitude correction value and phase correction value regardless of the phase state of the unmodulated carrier wave.

Therefore, in the RFID reader / writer device of claim 1 and the RFID reader / writer system of claim 4, the amplitude correction value and the phase correction value are held for each phase state, and the phase state of the unmodulated carrier wave is predicted and predicted. Based on the phase state, the cancel signal is corrected by the amplitude correction value and the phase correction value generated by the phase state and added to the wraparound signal. For this reason, the sneak signal whose amplitude and phase differ depending on the phase state of the unmodulated carrier wave can be sufficiently suppressed by the carrier canceller having different errors depending on the phase state of the unmodulated carrier wave.

According to the RFID reader / writer device of the second aspect, the phase state of the unmodulated carrier wave for power supply is predicted by counting the transmission signal to obtain the phase of the final bit, so that the phase state of the unmodulated carrier wave can be obtained accurately. .

The RFID reader / writer device according to claim 3 holds the amplitude correction value and the phase correction value for each phase state of 0 ° and 180 °, predicts the phase state of the unmodulated carrier wave, and predicts the predicted 0 ° or 180 °. Based on the phase state, the cancel signal is corrected with the amplitude correction value and the phase correction value generated by the phase state of 0 ° or 180 ° and added to the wraparound signal. For this reason, it is possible to sufficiently suppress the sneak signal whose amplitude and phase differ depending on the phase states of 0 ° and 180 ° of the unmodulated carrier wave.

The RFID reader / writer apparatus according to the embodiment transmits a PR-ASK (Phase-Reverse ASK) modulation signal. Therefore, prior to the description of the configuration of the RFID reader / writer device of the embodiment, the PR-ASK modulation method in the embodiment will be described with reference to the waveform diagram of FIG. FIG. 6A shows a 010-bit waveform in the baseband of PR-ASK. With respect to 0 bit, with 1 bit, the rise (high level) time is doubled, and the fall (low level) time is the same. FIG. 6B shows a modulation waveform of PR-ASK. FIG. 6C shows an RF waveform modulated by PR-ASK. Here, in PR-ASK, the phase is inverted bit by bit, here, for each bit of 010, with phase φ at the first 0 bit, phase −φ at the next 1 bit, and phase φ at the next 0 bit. Have returned to. In the embodiment, the phase φ is set to the phase state 0 °, and the phase −φ is set to the phase state 180 °. FIG. 6D shows the detected PR-ASK waveform.

FIG. 2 is an explanatory diagram illustrating a bit configuration in a transmission section in the RFID reader / writer apparatus according to the embodiment.
The RFID reader / writer device 10 transmits data consisting of 0 and 1 bits described above with reference to FIG. 6A, which constitutes a preamble, a frame sync, a transmission command, and a CRC in a transmission section in which a signal is transmitted to the RFID tag. In a receiving section in which a modulated signal (command) modulated with (bit) is transmitted to the RFID tag and the RFID tag side responds thereafter, the RFID reader / writer device 10 transmits an unmodulated signal to supply power to the RFID tag. .

FIG. 3 shows an RF waveform in which the bit configuration shown in FIG. 2 is modulated by PR-ASK in the RFID reader / writer device of the embodiment. In the transmission interval, a preamble, frame sync, transmission command, and a 0-bit and 1-bit modulation signal constituting the CRC in FIG. 2 are transmitted, and in the reception interval (next non-modulation interval), the final modulation signal in the transmission interval is transmitted. (The phase φ [phase state 0 °] or phase −φ [phase state 180 °] described above) is continued and output as an unmodulated carrier wave.

A configuration of an RFID reader / writer device 10 according to the embodiment and an RFID reader / writer system using the RFID reader / writer device will be described with reference to FIG.
FIG. 1 is a block diagram illustrating a configuration of an RFID reader / writer device according to an embodiment. As described above, the RFID reader / writer device 10 transmits a modulation signal (command) to the RFID tag in the transmission section in which the signal is transmitted to the RFID tag, and the RFID tag returns a response in the subsequent reception section. . When the RFID tag responds, the RFID reader / writer device 10 transmits a non-modulated signal and supplies power to the RFID tag. At the same time, the RFID tag performs data modulation by controlling the non-modulated signal by reflection / termination (on / off), Data is sent to the RFID reader / writer device 10.

In the transmission section for transmitting the signal to the RFID tag described above, the CPU 12 outputs a transmission command to the RFID. The framer 14 generates a preamble, a frame sync, a transmission command, and a CRC (cyclic redundancy check) frame shown in FIG. 2 based on the transmission command. The band limit 16 includes a digital filter, and prevents the band from being widened by limiting the band. The D / A converter 18 converts the digital signal output from the band limiter 16 into an analog signal, thereby generating a PR-ASK baseband signal. The band limit 22 is composed of an analog filter, and controls the band of the PR-ASK baseband signal. The modulator 24 modulates the PR-ASK baseband signal with the oscillation signal from the local oscillator 54 to obtain an RF signal in the transmission section shown in FIG. The distributor 26 is composed of a coupler, and distributes the modulated signal to the variable attenuator 28 side and the carrier canceller 40. The variable attenuator 28 varies the transmission output according to the distance from the RFID reader / writer device to the RFID. For a long-distance RFID, the attenuation amount is reduced and a high transmission signal is output, and the short-distance RFID is output. In contrast, the attenuation is increased and a low transmission signal is output. The power amplifier 30 amplifies the output of the transmission signal. The transmission signal is transmitted from the antenna 34 via the antenna duplexer 32 composed of a circulator.

In the reception section for receiving the signal from the RFID tag described above, the modulator 24 generates an unmodulated carrier wave in the reception section shown in FIG. 3 with the oscillation signal from the local oscillator 54. The distributor 26 outputs the unmodulated carrier wave to the variable attenuator 28 side, and distributes the unmodulated carrier wave to the carrier canceller 40 as a reference signal. The output unmodulated carrier wave is attenuated by the variable attenuator 28, amplified by the power amplifier 30, and transmitted from the antenna 34 via the antenna duplexer 32.

On the other hand, the received signal received via the antenna 34 is applied to the carrier canceller 40 and the adder 50 on the receiver 52 side via the antenna duplexer 32. The demodulator 42 of the carrier canceller 40 includes an i-orthogonal q demodulator, and performs amplitude detection by orthogonally detecting the unmodulated carrier wave (reference signal) distributed from the distributor 26 together with the reception signal supplied from the antenna duplexer 32. And phase information. The band limiter 44 drops the RF signal into a baseband signal, extracts the DC component, and cancels the response from the RFID. The modulator 49 modulates the reception signal dropped to the baseband to generate an RF signal. The phase corrector (phase correction means) 46 corrects the phase of the RF signal. The amplitude corrector (amplitude correction means) 48 corrects the amplitude of the RF signal subjected to phase correction. That is, the carrier canceller 40 adjusts the amplitude and phase of the unmodulated carrier wave distributed from the distributor 26 and the received signal by the demodulator (orthogonal modulator) 42 and cancels the cancellation signal having the same amplitude as that of the sneak signal and the opposite phase. And the cancel signal is added to the adder 50 on the receiver 52 side, thereby canceling the wraparound signal that wraps around the received signal. The reception signal with the wraparound signal canceled is output from the adder 50 to the receiver and sent to the CPU 12 as reception data.

Here, as described above, the phase state of the unmodulated carrier wave is 0 ° and 180 °, but the transmitter unit including the modulator 24, the divider 26, the variable attenuator 28, the power amplifier 30, and the carrier canceller. No. 40 has a slight error in each of the phase state 0 ° and the phase state 180 °. Due to this minute error, the generation accuracy of the cancel signal differs in the phase state 0 ° and the phase state 180 °.

For this reason, in the RFID reader / writer device 10 of the embodiment, as shown in FIG. 4, the phase correction value Δφ (φa) and the amplitude correction value ΔA when the phase state is 0 ° are displayed on the map in the ROM (not shown) in the CPU 12. (Aa), and the phase correction value Δφ (φb) and the amplitude correction value ΔA (Ab) when the phase state is 180 ° are held. Then, the phase state (phase state 0 ° or phase state 180 °) of the unmodulated carrier wave is predicted, and based on the predicted phase state, the cancel signal is corrected with the amplitude correction value and the phase correction value generated by the phase state. Added to the sneak signal. The phase correction value Δφ (φa) and the amplitude correction value ΔA (Aa) when the phase state is 0 °, the phase correction value Δφ (φb) and the amplitude correction value ΔA (Ab) when the phase state is 180 °, A correction value of a value measured at the time of shipment adjustment of the RFID reader / writer device is written in a map in the ROM.

As described above with reference to FIG. 2, FIG. 3, and FIG. 6, the prediction of the phase state of the unmodulated carrier wave (phase state 0 ° or phase state 180 °) is performed in the transmission interval in the reception interval (next unmodulation interval). Since the final phase of the modulated signal at (in the above-described phase φ [phase state 0 °] or phase −φ [phase state 180 °]) is continued and output as an unmodulated carrier wave, modulation in the transmission section is performed. As the final phase of the signal, the number of bits of data in the transmission section (frame sync, transmission command, CRC) is counted, and the final phase is determined depending on whether it is odd or even. That is, when the number is odd, the phase of the previous reception period is continued, and when the number is even, the phase is different from the previous reception period.

The process of obtaining the final phase of the modulated signal in the transmission section and determining the correction value will be described with reference to the flowchart of FIG. 5 showing the process and the block diagram of FIG.
The phase of the unmodulated phase (unmodulated carrier wave) in the previous reception section is set to θ (either phase φ [phase state 0 °] or phase −φ [phase state 180 °]) (S12). As described above with reference to FIG. 1, the CPU 12 generates a transmission command (S14). Then, the framer 14 performs transmission frame processing for creating a transmission frame (S16). Next, the next reception interval start phase is predicted by the next reception interval start phase prediction 20. First, it is determined whether or not there is a preamble in the transmission frame (S18). If there is a preamble (S18: Yes), the number of commands in the transmission frame is set to an odd number, and the phase of the next modulation section (reception section) does not change, so θ ′ = θ is set (S22). On the other hand, when there is no preamble (S18: No), it is determined whether or not the number of transmission commands (frame sync, transmission command and CRC bits) of the transmission frame is an even number (S20). When the number is an odd number (S20: No), the phase of the next modulation section (reception section) does not change as in S22 described above, so θ ′ = θ is set (S26). On the other hand, when it is an even number (S20: Yes), the phase of the next modulation section (reception section) changes, so that θ ′ = θ + 180 ° (S24). That is, when θ is 0 ° in the phase state, it is 180 °, and when θ is 180 °, it is 0 °. Then, the CPU 12 sets a carrier canceller adjustment value from the ROM table described above with reference to FIG. 4 based on the phase of θ ′ (S28). Specifically, when θ ′ is 0 °, the phase correction value φa is set in the phase corrector 46 and the amplitude correction value Aa is set in the amplitude corrector 48. When θ ′ is 180 °, the phase correction value φb is set in the phase corrector 46 and the amplitude correction value Ab is set in the amplitude corrector 48. Thereafter, the CPU 12 replaces the non-modulation phase θ with θ ′ (S30) and ends the process.

In the RFID reader / writer device 10 and the RFID reader / writer system of the embodiment, the amplitude correction value ΔA and the phase correction value Δφ are held for each phase state of 0 ° and 180 °, and the phase state of the unmodulated carrier wave is 0 ° or 180 °. Based on the predicted phase state, the cancel signal is corrected with the amplitude correction value and the phase correction value generated by the phase state and added to the wraparound signal. Therefore, a sneak signal whose amplitude and phase differ depending on the phase state of the unmodulated carrier wave can be sufficiently suppressed by the carrier canceller 40 having different errors depending on the phase state of the unmodulated carrier wave.

In the RFID reader / writer device 10 of the embodiment, the phase state of the unmodulated carrier wave for power supply is predicted by counting the transmission signal to obtain the phase of the final bit, so that the phase state of the unmodulated carrier wave can be obtained accurately. .

In the RFID reader / writer device of the embodiment, the amplitude correction value and the phase correction value are held for each phase state of 0 ° and 180 °, the phase state of the unmodulated carrier wave is predicted, and the predicted 0 ° or 180 ° Based on the phase state, the cancel signal is corrected by the amplitude correction value and the phase correction value generated by the phase state of 0 ° or 180 ° and added to the wraparound signal. For this reason, it is possible to sufficiently suppress the sneak signal whose amplitude and phase differ depending on the phase states of 0 ° and 180 ° of the unmodulated carrier wave.

1 is a block diagram illustrating a configuration of an RFID reader / writer device according to an embodiment of the present invention. It is explanatory drawing which shows the bit structure of the signal in the RFID reader / writer apparatus which concerns on embodiment. FIG. 3 is a waveform diagram showing an RF waveform in which the bit configuration shown in FIG. 2 is modulated by PR-ASK in the RFID reader / writer device of the embodiment. The phase correction value Δφ (φa) and amplitude correction value ΔA (Aa) when the phase state is 0 ° held in the ROM map, and the phase correction value Δφ (φb) and amplitude correction value ΔA when the phase state is 180 ° It is explanatory drawing which shows (Ab). It is a flowchart which shows the process which calculates | requires the final value of the modulation signal in a transmission area, and determines a correction value. FIG. 6A shows a 010-bit waveform in the baseband of PR-ASK. FIG. 6B shows a modulation waveform of PR-ASK. FIG. 6C shows an RF waveform modulated by PR-ASK. FIG. 6D shows the detected PR-ASK waveform.

Explanation of symbols

10 RFID reader / writer device 12 CPU (correction value holding means)
20th reception interval start phase prediction (phase prediction means)
24 Modulator (Transmitter)
30 Power amplifier (transmitter)
34 Antenna 40 Carrier canceller 46 Phase corrector (phase correction means)
48 Amplitude corrector (Amplitude correction means)
52 Receiver Δφ Phase correction value ΔA Amplitude correction value

Claims (4)

At the time of transmission, a predetermined transmission signal is transmitted from the antenna toward the RFID. At the time of reception, an unmodulated carrier wave for supplying power is supplied to the RFID via the antenna, and the RFID returns a response according to the transmission signal. An RFID reader / writer device that communicates with the RFID by receiving a reply signal via an antenna through a receiver,
A carrier canceller that cancels wraparound of the unmodulated carrier wave for power supply transmitted at the time of reception to the receiver by adding a cancel signal having the same amplitude and opposite phase as the wraparound signal;
Amplitude correction means for correcting the amplitude of the cancellation signal;
Phase correction means for correcting the phase of the cancellation signal;
A correction value holding means for holding an amplitude correction value and a phase correction value for each phase state of the unmodulated carrier wave, and outputting to the amplitude correction means and the phase correction means, respectively.
Phase predicting means for predicting the phase state of the unmodulated carrier wave for power supply,
The correction value holding unit outputs the amplitude correction value and the phase correction value generated by the phase state to the amplitude correction unit and the phase correction unit, respectively, based on the phase state predicted by the phase prediction unit. An RFID reader / writer device. The phase of the unmodulated carrier for supplying power is the phase of the last bit of the transmission signal,
2. The RFID reader / writer device according to claim 1, wherein the phase predicting unit counts the transmission signal to obtain a phase of a final bit to predict a phase state of the unmodulated carrier wave for supplying power. The transmission signal is PR-ASK (Phase-Reverse ASK) modulation,
The RFID reader / writer device according to claim 1 or 2, wherein the phase state of the unmodulated carrier wave is 0 ° and 180 °. At the time of transmission, a predetermined transmission signal is transmitted from the antenna toward the RFID. At the time of reception, an unmodulated carrier wave for supplying power is supplied to the RFID via the antenna, and the RFID returns a response according to the transmission signal. An RFID reader / writer system that communicates with the RFID by receiving a reply signal via an antenna through a receiver,
A carrier canceller that cancels wraparound of the unmodulated carrier wave for power supply transmitted at the time of reception to the receiver by adding a cancel signal having the same amplitude and opposite phase as the wraparound signal;
Amplitude correction means for correcting the amplitude of the cancellation signal;
Phase correction means for correcting the phase of the cancellation signal;
A correction value holding means for holding an amplitude correction value and a phase correction value for each phase state of the unmodulated carrier wave, and outputting to the amplitude correction means and the phase correction means, respectively.
Phase predicting means for predicting the phase state of the unmodulated carrier wave for power supply,
The correction value holding unit outputs the amplitude correction value and the phase correction value generated by the phase state to the amplitude correction unit and the phase correction unit, respectively, based on the phase state predicted by the phase prediction unit. RFID reader / writer system.

Images