RFID system and reader writer

Abstract

A technology for detecting an RFID by a reader writer and transmitting harmonics for reading and writing the RFID timely without using an object detection sensor is provided. Using a nonlinearity of a rectifier or a demodulator in an IC chip of the RFID, a continuous wave or a modulated wave of two or more different frequencies is output from the reader writer. The RFID receives the continuous wave or the modulated wave of two or more different frequencies and the reader writer receives harmonics intermodulation generated by the rectifier or the demodulator in the IC chip. Therefore, the RFID can be detected without any special object detection sensor, and a modulated wave for reading or writing the RFID can be transmitted.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1A is a diagram showing a structure of an ordinary RFID system;

FIG. 1B is a diagram showing a structure of an ordinary RFID system;

FIG. 2 is a diagram showing an RFID system in which a reader writer reads and writes an RFID when the RFID attached to an item is carried by a forklift truck;

FIG. 3 is a diagram showing an RFID system in which a reader writer reads and writes an RFID when the RFID attached to an item is moving by a belt conveyor;

FIG. 4A is a diagram showing a timing at which a reader writer reads and writes an RFID moving a the belt conveyor;

FIG. 4B is a diagram showing the timing at which the reader writer reads and writes the RFID moving by the belt conveyor;

FIG. 4C is a diagram showing the timing at which the reader writer reads and writes the RFID moving by the belt conveyor;

FIG. 5A is a diagram showing a timing at which, using an object detection sensor, a reader writer reads and writes an RFID moving by a belt conveyor;

FIG. 5B is a diagram showing the timing at which, using the object detection sensor, the reader writer reads and writes the RFID moving by the belt conveyor;

FIG. 6 is a block diagram showing a structure of an RFID according to a first embodiment of the present invention;

FIG. 7 is a diagram showing a rectifier in a circuit of an IC chip of the RFID according to the first embodiment of the present invention;

FIG. 8 is a diagram showing frequency characteristics obtained when the RFID receives continuous wave having two different frequencies from a reader writer to generate an intermodulation product, according to the first embodiment of the present invention;

FIG. 9 is a block diagram showing a structure of the reader writer according to the first embodiment of the present invention;

FIG. 10 is a flowchart showing processings performed by the reader writer according to the first embodiment of the present invention;

FIG. 11A is a diagram showing timings of a detection, a read, and a write of the RFID using the reader writer according to the first embodiment of the present invention;

FIG. 11B is a diagram showing the timings of a detection, a read, and a write of the RFID using the reader writer according to the first embodiment of the present invention;

FIG. 12 is a diagram showing frequency characteristics obtained when an RFID receives a single frequency wave from a reader writer to generate an intermodulation product, according to a second embodiment of the present invention;

FIG. 13 is a block diagram showing a structure of the reader writer according to the second embodiment of the present invention; and

FIG. 14 is a flowchart showing processings performed by the reader writer according to the second embodiment of the present invention.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be explained in detail with reference to the accompanying drawings. In all of the drawings for explaining the embodiments, the same members are denoted by the same reference symbols in principle and repetitive descriptions thereof will be omitted.

First Embodiment

FIG. 6 shows a block diagram of an RFID according to a first embodiment of the present invention. The RFID is composed of an IC chip 210 and an antenna 220. The IC chip 210 includes a rectifier/modulator 211, a demodulator (for data generation) 212, a clock generator 213, a receive logic 214, a transmit logic 215, a control logic 216, a memory 217 and the like. Depending on a type of the RFID, a battery may be included in addition to these components.

Since a so-called passive RFID including no battery operates using electromagnetic waves output from a reader writer as operating power, a voltage Vdd is supplied to each block of the IC chip 210 through the rectifier of the IC chip.

FIG. 7 shows an ordinary circuit of the rectifier. The rectifier is comprised of a diode and a capacitance, and boosts a voltage from a weak level to an operational level. In this case, since the diode is a nonlinear element, if a voltage input to the nonlinear element is assumed to be Vi and an output voltage therefrom is assumed to be Vout, the Vi and Vout can be expressed by a following formula (1).

In addition, in a so-called active RFID including a battery, although a case in which no rectifier is included exists sometimes, a demodulator also includes a nonlinear element equivalent to that in a rectifier. Therefore, the formula (1) shows characteristics common among all types of RFIDs.

Vout=α₀+α₁Vin+α₂Vin²+α₃Vin³+  (1)

(α₀,α₁,α₂,α₃, . . . :proportional constants determined by characteristics of a nonlinear element)

Here, when the reader writer transmits a continuous or modulated wave having two different frequencies (ω₁, ω₂) and the RFID receives the continuous or modulated wave having the two frequencies, since the continuous or modulated wave having two different frequencies is input to the rectifier/modulator 211 or the demodulator 212 in the IC chip 210 via the antenna 220, an output voltage Vout of the diode, which is a nonlinear element is expressed by a following formula (2).

Vout=α₀+α₁(A₁ cos ω₁t+A₂ cos ω₂t)+α₂(A₁ cos ω₁t+A² cos ω₂t)²+α₃(A₁ cos ω₁t+A₂ cos ω₂t)³+  (2)

By expanding a right side of the formula (2), and removing a DC component and fundamental frequency components ω₁ and ω₂, respective frequency components are obtained as shown in formulas (3) to (9).

Vout[ω₁±ω₂]=α₂A₁A₂ cos(ω₁+ω₂)t+α₂A₁A₂ cos(ω₁−ω₂)t   (3)

Vout[2ω₁±ω₂]=(¾)α₃A₁²A₂ cos(2ω₁+ω₂)t+(¾)α₃A₁²A₂ cos(2ω₁−ω₂)t   (4)

Vout[2ω₂±ω₁]=(¾)α₃A₂²A₁ cos(2ω₂+ω₁)t+(¾)α₃A₂²A₁ cos(2ω₂−ω₁)t   (5)

Vout[2ω₁]=(½)α₂A₁² cos(2ω₁)t   (6)

Vout[2ω₂]=(½)α₂A₂² cos(2ω₂)t   (7)

Vout[3ω₁]=(¼)α₃A₁³ cos(3ω₁)t   (8)

Vout[3ω₂]=(¼)α₃A₂³ cos(3ω₂)t   (9)

FIG. 8 is a diagram representing the formulas (3) to (9) with reference to a frequency axis. Note that, FIG. 8 is a concept diagram and does not precisely show a level of each frequency. As shown, it can be understood that the RFID receives the continuous or modulated waves having two different frequencies (ω₁, ω₂) output from the reader writer and various intermodulation products according to a nonlinearity of the IC chip circuit are generated to transmitted through the antenna.

The reader writer can detect the RFID by receiving the intermodulation products transmitted from the RFID along with transmitting continuously the continuous or modulated waves having the two different frequencies (ω₁, ω₂).

Usually, it seems to be general to receive 2ω₁−ω₂ and 2ω₂−ω₁, which are third-order intermodulation components near a transmission frequency, because the receive circuit of the reader writer thereof is simple. However, other intermodulation products may be received. Furthermore, although the present embodiment employs the example in which the reader writer transmits the continuous or modulated waves having two different frequencies, the invention is not restricted thereto. Because the RFID can generate intermodulation products even in the case of three or more different frequencies.

Thus, the reader writer can detect the RFID without any special object detection sensor.

FIG. 9 is a block diagram of a structural example of the reader writer and FIG. 10 is a flowchart of processings performed by the reader writer. In a state A of FIG. 10, since the reader writer simultaneously transmits continuous or modulated waves having two different frequencies (ω₁, ω₂), the frequencies ω₁ and ω₂ are output from an oscillator 113 to two transmit blocks 111 by control from a control block 114. And the transmit blocks 111 execute an output processing using the two different frequencies as carrier frequencies through transmit antennas 1 and 2.

In a reception by the reader writer, a frequency 2ω₁−ω₂ received by a receive antenna is amplified by an amplifier in a receive block 112. Then, a frequency 2ω₁−ω₂+ω_IF is output from the oscillator 113 by control from the control block 114. A mixer executes a frequency transform for the output from the amplifier into an intermediate frequency (ω_IF), then, the output from the mixer is input to a demodulator and a receive signal level detector through a filter and an amplifier. If a level of the ω_IF is equal to or higher than X dBm, the reader writer transits to a state B and communicates with the RFID. If the level is lower than X dBm, the reader writer remains in the state A and continues to transmit the ω₁, ω₂ and receive the 2ω₁−ω₂.

In the state B, the reader writer performs normal communication with the RFID. Here is shown an example of communication with the RFID using the frequency ω₁. When the reader writer transits to the state B, the frequency ω₁ is output from ports 1, 2 of the oscillator 113 by control from the control block. Then, an operation of modulation or non-modulation for the output is executed and a modulated wave or a continuous wave of the ω₁ is output from the transmit antennas 1 and 2. In a reception of the RFID, since the ω₁ is received from the receive antenna, ω₁+ω_IF is output from a port 3 of the oscillator 113, the received wave ω₁ and the ω₁+ω_IF are mixed, and a frequency transform into ω_IF is executed. Thereafter, the output is input to the demodulator and the receive signal level detector through the filter and the amplifier. The demodulator performs a data detection and the communication with the RFID is performed.

Hereinabove, it has been shown that the reader writer can detect the RFID. Now, an operational example of the reader writer after detecting the RFID is shown in FIG. 11.

The reader writer 101 is adapted to receive 2ω₁−ω₂ simultaneously with transmitting the frequencies ω₁ and ω₁ continuously. When the RFID 201 enters the read/write area of the reader writer 101, the RFID 201 transmits a third-order intermodulation wave 2ω₁−ω₂. Therefore, the reader writer 101 receives the 2ω₁−ω₂ and detects that the RFID 201 is located in the read/write area. Accordingly, the reader writer 101 transmits a command to the RFID 201 and receives a response to the command from the RFID 201. Thereafter, the reader writer 101 transmits continuously the frequencies ω₁ and ω₂ to detect another RFID 201 subsequently.

The example in which the reader writer transmits the two different frequencies and receives the third-order intermodulation product 2ω₁−ω₂ to detect the RFID is shown here. However, the reader writer may receive another intermodulation product (for example, 2ω₂−ω₁, 2ω₁+ω₂, 2ω₂+ω₁ or the like) to detect the RFID. In addition, the reader writer may output two or more frequencies or a single frequency and receive an intermodulation product or harmonics transmitted from the RFID to detect the RFID.

An example in which a single frequency is transmitted by a reader writer is shown in a following second embodiment of the invention.

Second Embodiment

In the first embodiment described above, the example in which the reader writer outputs the two different frequencies to detect the RFID is employed. However, if the reader writer can outputs only a single frequency, due to a nonlinearity of the IC chip of the RFID, an output voltage Vout is expressed as shown in a formula (10).

Vout=α₀+α₁A₁ cos ω₁t+α₂(A₁ cos ω₁t)²+α₃(A₁ cos ω₁t)³   (10)

By expanding a right side of the formula (10) and removing a DC component and a fundamental frequency component ω₁, frequency components with a two or three times frequency of the fundamental frequency are output, as shown in formulas (11) and (12).

Vout[2ω₁]=(½)α₂A₁²cos(2ω₁)t   (11)

Vout[3ω₁]=(¼)α₃A₁³cos(3ω₁)t   (12)

FIG. 12 is a diagram representing the formulas (11) and (12) with reference to a frequency axis.

As shown, even if the reader writer outputs the single frequency, harmonics with two or three times frequency of the fundamental frequency is output due to the nonlinearity of the RFID. And, the reader writer can detect the RFID by receiving the harmonics.

FIG. 13 shows a block diagram of a structural example of the reader writer, and FIG. 14 shows a flowchart of processings performed by the reader writer. In a state A of FIG. 14, the reader writer outputs a continuous wave with the frequency ω₁ from an oscillator 113 to a transmit block 111 by control from a control block 114, and the transmit block 111 executes an output operation through a transmit antenna 1 using ω₁ as a carrier frequency.

In a reception by the reader writer, a frequency 2ω₁ received by a receive antenna is amplified by an amplifier in a receive block 112. Then, a frequency 2ω₁+ω_IF is output from the oscillator 113 by control from the control block 114. A mixer executes a frequency transform for the output into the intermediate frequency (ω_IF), then, the output is input to a demodulator and a receive signal level detector through a filter and an amplifier. If a level of the ω_IF is equal to or higher than X dBm, the reader writer transits to a state B and communicates with the RFID. If the level is lower than X dBm, the reader writer remains in the state A and continues to transmit the ω₁ and receive the 2ω₁.

In the state B, the reader writer performs normal communication with the RFID. Here is shown an example of communication with the RFID using frequency ω₁. When the reader writer transits to the state B, the frequency ω₁ is output from a port 1 of the oscillator by control from the control block 114. Then, an operation of modulation or non-modulation for the output is executed and the modulated wave or the continuous wave of the ω₁ is output from the transmit antenna 1. In a reception of the RFID, since the ω₁ is received from the receive antenna, ω₁+ω_IF is output from a port 2 of the oscillator, the received wave ω₁ and ω₁+ω_IF are mixed, and a frequency transform into ω_IF is executed. Thereafter, the output is output to the demodulator and the receive signal level detector through the filter and the amplifier. The demodulator performs a data detection and the communication with the RFID is performed.

Hereinabove, the present invention achieved by the inventors has been explained specifically based on the embodiments thereof. However, the invention is not restricted to those embodiments. It is obvious that various changes and modifications may be made in a scope of the invention without departing from a gist of the invention.

Claims

1. An RFID system, comprising: an RFID; anda reader writer communicating with the RFID,wherein the reader writer outputs a continuous wave or a modulated wave with two or more different frequencies,wherein the RFID receives the continuous wave or the modulated wave with two or more different frequencies and outputs an intermodulation product having a frequency component of a frequency different from the two or more different frequencies, andwherein the reader writer receives the intermodulation product.

2. The RFID system according to claim 1, wherein the reader writer receives the intermodulation product output from the RFID, detects presence of the RFID, and performs normal communication with the RFID.

3. The RFID system according to claim 1, wherein the RFID receives the continuous wave or the modulated wave with two or more different frequencies from the reader writer and generates a third-order intermodulation product according to a nonlinearity of an internal rectifier or an internal receive logic.

4. An RFID system, comprising: an RFID; anda reader writer communicating with the RFID,wherein the reader writer outputs a continuous wave or a modulated wave with single frequency,wherein the RFID receives the continuous wave or the modulated wave with single frequency and outputs harmonics with a two or three times frequency of the single frequency, andwherein the reader writer receives the harmonics with frequency two or three times the single frequency.

5. The RFID system according to claim 4, wherein the reader writer receives the harmonics with a two or three times frequency of the single frequency output from the RFID, detects presence of the RFID, and performs normal communication with the RFID.

6. The RFID system according to claim 4, wherein the RFID receives the continuous wave or the modulated wave with single frequency and generates harmonics with a two or three times frequency of the single frequency according to a nonlinearity of an internal rectifier or an internal receive logic.

7. A reader writer communicating with an RFID, comprising: a transmit unit outputting a continuous wave or a modulated wave with two or more different frequencies; anda receive unit receiving an intermodulation product having a frequency component of a frequency different from the two or more frequencies output from the RFID receiving the continuous wave or the modulated wave with two or more different frequencies.

8. The reader writer according to claim 7, wherein the reader writer receives the intermodulation product output from the RFID, detects presence of the RFID, and performs normal communication with the RFID.