KR100726549B1 - Radio Frequency IDentification reader - Google Patents

Abstract

The present invention relates to an RFID reader for adjusting output power of a transmission signal according to a position of an electronic tag. The RFID reader according to the present invention comprises: an RF unit for processing a transmission / reception signal transmitted through an antenna; A baseband unit which converts the signal processed by the RF unit into a digital signal, processes the signal, and measures an electric field strength of the RF received signal; And a controller configured to determine a distance to the electronic tag from the electric field strength measurement value of the RF received signal transmitted from the baseband unit and to adjust the output power of the RF transmitted signal of the RF unit. The RF unit may include a power gain amplifier, and the controller may generate a control voltage by comparing a reference output power corresponding to the electric field strength measurement with a current output power of the RF unit, and convert the generated control voltage into the power gain. The output power of the RF unit is adjusted by transferring to an amplifier.

According to the RFID reader according to the present invention, it is possible to improve the reading distance, the energy supply environment, and the data recognition rate of the electronic tag by differentially controlling the transmission power of the transmission signal according to the position of the electronic tag without discriminating the handle type reader or the fixed reader. There is an effect that can reduce the power loss because it is possible to increase and decrease the transmission power as needed to break away from the conventional method of maintaining the constant transmission power irrespective of the position of the electronic tag.

Description

RFID reader {Radio Frequency IDentification reader}

1 is a view schematically illustrating a general RFID reader communicating with an electronic tag.

Figure 2 is a block diagram schematically showing the components of the RFID reader according to an embodiment of the present invention.

3 is a diagram illustrating a data table of reference transmission power that an RFID reader has for power control according to an embodiment of the present invention.

4 is a diagram illustrating a data table of the control voltage provided by the RFID reader for power control according to an embodiment of the present invention.

5 is a flowchart illustrating a method in which an RFID reader controls transmission power according to a position of an electronic tag according to an embodiment of the present invention.

6 is a block diagram schematically illustrating the components of an electronic tag that communicates with an RFID reader according to an embodiment of the present invention.

<Explanation of symbols for main parts of drawing>

210: RFID reader 211a, 211b: antenna

212a: first switching part 212b: second switching part

212c: RF reception processing unit 212d: RF transmission processing unit

213: baseband processing stage 214: Q-RSSI circuit

215: I-RSSI circuit 216: control circuit

220: electronic tag

The present invention relates to an RFID reader, and more particularly, to an RFID reader that adjusts output power of a transmission signal according to a position of an RFID tag.

Currently, ubiquitous network technology has attracted the attention of many people, ubiquitous network technology means a technology that allows to naturally connect to various networks regardless of time and place.

As the next generation technology of the ubiquitous network technology, RFID technology may be cited. Among them, RFID technology introduced in commerce is representative. The commercial RFID system includes an electronic tag attached to a product and embedded with detailed information, and an RFID reader that reads the information of the electronic tag using RF communication, and the electronic tag attached to the product is an area where the RFID reader is located. It passes through and transmits information using RF communication, thus providing a foundation for efficiently managing logistics / distribution such as distribution, assembly, price change, and sales of goods.

On the other hand, the receiving end of the conventional RFID reader is generally implemented by envelope detection using an amplitude shift keying (ASK) modulation scheme. According to the conventional design scheme, the data recognition rate is lowered because the bit error rate is lowered. There are disadvantages.

Therefore, the radio wave environment varies greatly depending on factors such as the position and speed at which the electronic tag passes through the antenna area of the RFID reader, and the packaging material (for example, pallet load) of the product with the electronic tag. According to the change, an error rate, stability, recognition distance, etc. of data received by the RFID reader may be different.

FIG. 1 is a diagram schematically illustrating a form in which a general RFID reader 30 communicates with the electronic tags 10 and 20. The general RFID reader 30 includes two antennas as transmission bands and reception bands. Perform RFID communication with.

The RFID communication method has a structure in which transmit / receive signals use the same frequency band. Therefore, the transmit / receive signals are separated and processed at the baseband stage instead of the RF stage, so that the antenna is separated into the transmit / receive band.

In addition, the electronic tags 10 and 20 form various shapes such as an electronic tag 10 that is individually moved or an electronic tag 20 that is fixed at the same position as shown in FIG. Alternatively, since it has a fixed structure, the communication environment of the electronic tags 10 and 20 and the RFID reader 30 can be considered to be very flexible.

For this reason, the RFID reader 30 transmits and receives data with the electronic tags 10 and 20 positioned within a predetermined distance range according to various radio standards (130 KHz band, 13.56 Mhz band, UHF band, 2.45 GHz band, etc.). Maintain minimal transmit signal power to ensure stable exchange.

That is, the reading distance of the electronic tags 10 and 20, the energy supply distance to the electronic tag, and the recognition rate vary considerably according to the transmission power of the RFID reader 30, and in order to satisfy the minimum standard, the RFID reader 30 ) Usually transmits a high power signal of 1W (EIRP; 4W for Effective lsotropic radiated power).

Therefore, the conventional RFID reader 30 has a problem in that it wastes more power than necessary to maintain a high transmission power on a plurality of antennas.

The present invention breaks down the conventional method of maintaining a constant transmission power according to the characteristics of the RFID communication environment to identify the location of the electronic tag and to perform wireless data communication by differentiating the transmission power when communicating with individual electronic tags. It is an object to provide an RFID reader.

In order to achieve the above object, the RFID reader according to the present invention, in transmitting and receiving at least one electronic tag and the RFID signal, RF unit for processing the transmission and reception signal transmitted through the antenna; A baseband unit which converts the signal processed by the RF unit into a digital signal, processes the signal, and measures an electric field strength of the RF received signal; And a controller for determining a distance from the electronic tag from the electric field strength measurement value of the RF received signal transmitted from the baseband unit and adjusting the output power of the RF transmitted signal of the RF unit.

The RF unit of the RFID reader according to the present invention includes a power gain amplifier, and the controller generates a control voltage by comparing the current output power of the RF unit with a reference output power corresponding to the electric field strength measurement value, and generating the generated voltage. The output power of the RF unit is adjusted by transferring the controlled voltage to the power gain amplifier.

In addition, the baseband portion of the RFID reader according to the present invention includes a RSSI (Received Signal Strength Indicator) circuit for measuring the electric field strength of the RF received signal.

In addition, the RSSI circuit of the RFID reader according to the present invention uses the I-RSSI circuit for measuring the electric field strength of the RF received signal from the I (in-phase) signal and the electric field strength of the RF received signal from the quadrature-phase (Q) signal. It is equipped with Q-RSSI circuit to measure.

Hereinafter, an RFID reader according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram schematically showing the components of the RFID reader 210 according to an embodiment of the present invention.

2, the RFID reader 210 according to the embodiment of the present invention is the RF processing stage 212, the baseband processing stage 213, Q-RSSI circuit 214, I-RSSI circuit 215 and control It includes a circuit 216, the RF processing stage 212 is a first switching unit (212a), the second connected to the plurality of antennas (211a, 211b) for transmitting and receiving signals to and from the electronic tag 220 It consists of a switching unit 212b, an RF transmission processing unit 212d, and an RF reception processing unit 212c.

The first switching unit 212a of the RF processing stage performs a switching operation so that two antennas 211a and 211b may be sequentially connected to the second switching unit 212b.

When the second switching unit 212b is connected to any one of the two antennas 211a and 211b, the second switching unit 212b transmits and receives a transmission signal from the RF transmission processing unit 212d to the antennas 211a and 211b. When the signal is transmitted from the antennas 211a and 211b to the RF receiving processor 212c, the transmission and reception signals are separated and transmitted by performing a switching operation.

As such, the first switching unit 212a and the second switching unit 212b interlock with each other to allow the antennas 211a and 211b to simultaneously monitor the moving area of the electronic tag 220 while processing the transmission and reception signals. .

The first switching unit 212a and the second switching unit 212b may be implemented in various forms, for example, a single-pole quadruple-throw (SP1), a 4: 1 mux / demux (SPDT), a single pole (SPDT). Dual throw), the second switching unit 212b is preferably provided with an isolator (Isolator) at the connection end with the RF transmission processing unit (212d).

The RF receiving processor 212c suppresses and amplifies the noise component of the received signal transmitted from the second switching unit 212b and transmits the amplified signal to the baseband processor 213.

In addition, the RF transmitter 212d includes a voltage gain amplifier (VGA) to amplify the transmitted signal transmitted from the baseband processor 213 and to filter the mixed signal in the processing of the received signal. To the second switching unit 212b.

The baseband processing stage 213 is connected to the RF transmission processing unit 212d and the RF reception processing unit 212c, respectively, and is composed of two parts for processing a transmission signal and a reception signal (components of the baseband processing unit 213). (Not shown), the part processing the received signal includes a mixer, a low pass filter (LPF), an amplifier, a modulator, an A / D converter, etc. to separate and filter the I and Q signals of the received signal. , Amplification / modulation and AD conversion.

The baseband processing stage 213 may include a D / A converter, a low pass filter, a demodulator, a gain amplifier, a filter, and the like to convert a digital signal into an RF signal and gain power. The control is transmitted to the RF transmission processing unit 212d.

The digital signal transmitted from the baseband processing stage 213 is transferred to the control circuit 216, the I-RSSI circuit 215, and the Q-RSSI circuit 214.

The I-RSSI circuit 215 is a circuit for measuring the reception strength of an in-phase (I) signal. Usually, the I-RSSI circuit 215 detects and corrects that the signal strength increases and becomes irregular due to interference or mixed noise components. Means a circuit used for the purpose.

The Q-RSSI circuit 214 measures a reception strength of a quadrature (Q) signal and performs a function similar to that of the I-RSSI circuit 215.

The I-RSSI circuit 215 and the Q-RSSI circuit 214 measure electric field strengths of the I and Q signals, respectively, and transmit the measured values to the control circuit 216.

The control circuit 216 is provided with a communication protocol to control wireless communication with the electronic tag 220, and periodically sends an information request signal to determine the position of the electronic tag 220.

In addition, the control circuit 216 analyzes the code of the tag identification information received from the electronic tag 220 and demodulated by the baseband processing stage 213, in which the data format is converted and filtering is performed to extract necessary information. Process.

Here, the control circuit 216 may be a field programmable gate array (FPGA) circuit or a digital signal processing (DSP) circuit.

The FPGA circuit refers to a gate array circuit (logical integrated circuit) that can be added to the programming if necessary to implement the function of the RFID reader 210 outside the production process of the chip, the gate array and PLD (Programmable Logic Devices) ) Is implemented.

These FPGA circuits have the advantages of being able to use multiple I / Os like a gate array, programmable at a time, and increasing the utility of the gate by 95%.

The DSP (Digital Signal Processing) circuit processes algebraic operations on digital data obtained by converting analog signals to analog / digital (A / D) conversion and performs signal processing such as filtering and spectral analysis.

3 is a diagram illustrating a data table of reference transmission power provided by the RFID reader 210 according to an embodiment of the present invention for power control, and FIG. 4 is an RFID reader according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a data table of control voltages provided by 210 for power control. 5 is a flowchart illustrating a method in which the RFID reader 210 controls transmission power according to the position of the electronic tag 220 according to an embodiment of the present invention.

Referring to FIG. 3, the data table included in the control circuit 216 includes data on an Rx (receive) I-RSSI value, an Rx Q-RSSI value (unit: dBm / FA), and a reference transmit power (unit: dBm). 4, the control voltage (unit: V) and the attenuation value (unit: dBm) are recorded. The operation of the control circuit 216 is described based on the numerical values in the data table. do.

First, when the received signal is processed as a high frequency (RF) signal in the RF processing stage, the baseband processing stage 213 converts it into a digital signal and processes it (S100).

At this time, the I-RSSI circuit 215 and the Q-RSSI circuit 214 couple the RF reception signal to convert the DC voltage, and transfer the converted voltage signal to the control circuit 216 (S105).

The voltage signal transmitted from the I-RSSI circuit 215 and the Q-RSSI circuit 214 means the electric field strength value of the received signal, the control circuit 216 is a value of the electric field strength value of the Q signal and I signal The power of the transmission signal is sensed by the RF processor in order to compare the reference transmission power set according to the combination with the current transmission signal power.

When the power of the current transmission signal is sensed, the control circuit 216 compares the reference transmission power corresponding to the electric field strength combination of the Q signal and the I signal (S110) to determine the current transmission signal power of the electronic tag 220. Whether it is stronger or weaker than necessary compared to the position is determined (S115).

When the current transmission signal power is detected corresponding to the position of the electronic tag 220, the control circuit 216 determines the attenuation value or amplification value of the transmission signal (S120, S125) to generate a control voltage corresponding thereto. (S130, S135).

The control circuit 216 transfers the control voltage to the power gain amplifier of the RF processing stage (S140), and the power gain amplifier adjusts the power of the transmission signal by controlling the gain of the transmission signal according to the control voltage. (S145).

For example, the current value of the Rx I-RSSI and Rx Q-RSSI is in the state that the electronic tag 220 is located 4m away from the RFID reader 210 and the RFID reader 210 maintains a transmission power of about 30 dBm. If measured at " -50 dBm " and " -52 dBm, " respectively, the control circuit 216 determines the reference transmit power as 24 dBm.

The control circuit 216 determines that the current transmission power is 30 dBm, and generates a control voltage of 4.5 V corresponding to the attenuation value "-5 dBm" by referring to the control voltage data table shown in FIG. Pass it to the gain amplifier.

6 is a block diagram schematically illustrating the components of the electronic tag 220 for communicating with the RFID reader 210 according to an embodiment of the present invention.

Referring to FIG. 6, the electronic tag 220 includes a tag antenna 221, a reception demodulator 222, a transmission modulator 224, a power supply unit 223, a control unit 225, and a memory 226. do.

The tag antenna 221 receives an information request signal through a wireless channel or transmits processed tag identification information. Usually, a dipole antenna is used.

The power supply unit 223 is a device for supplying power to the reception demodulation unit 222, the control unit 225 and the transmission modulator 224. The electronic tag 220 is classified into an active method and a passive method according to the driving method of the tag antenna 221 and the power supply unit 223. For example, the electronic tag 220 and the RFID reader 210 In the active mode, UHF signals with a frequency band of 400 MHz to 900 MHz are used.

The reception demodulation unit 222 demodulates the incoming information request signal into digital data and transmits the received information request signal to the control unit 225. The control unit 225 analyzes a code of the demodulated information request signal to provide tag identification information. Create

In addition, the control unit 225 has a communication protocol to control wireless communication with the RFID reader 210. In this case, the memory 226 stores the information code system, and the control unit 225 generates the tag identification information using the same.

The transmission modulator 224 modulates the generated tag identification information into an RF signal, and the modulated tag identification information is transmitted to the RFID reader 210 through a tag antenna 221.

The present invention has been described above with reference to the preferred embodiments, which are merely examples and are not intended to limit the present invention, and those skilled in the art to which the present invention pertains do not depart from the essential characteristics of the present invention. It will be appreciated that various modifications and applications are not possible that are not illustrated above. For example, each component specifically shown in the embodiment of the present invention can be modified. And differences relating to such modifications and applications will have to be construed as being included in the scope of the invention defined in the appended claims.

According to the RFID reader according to the present invention, it is possible to improve the reading distance, the energy supply environment, and the data recognition rate of the electronic tag by differentially controlling the transmission power of the transmission signal according to the position of the electronic tag without discriminating the handle type reader or the fixed reader. There is an effect that can be, and regardless of the position of the electronic tag, it is possible to increase and decrease the transmission power as needed to escape the conventional way to maintain a constant transmission power, there is an effect that can reduce the power loss.

Claims (7)

In the RFID reader for transmitting and receiving RFID tags and at least one electronic tag, RF unit for processing the transmission and reception signal transmitted through the antenna; A baseband unit which converts the signal processed by the RF unit into a digital signal, processes the signal, and measures an electric field strength of the RF received signal; And And a controller for determining a distance from the electronic tag from the electric field strength measurement value of the RF received signal transmitted from the baseband unit and adjusting the output power of the RF transmitted signal of the RF unit. The method of claim 1, The RF unit includes a power gain amplifier, The controller generates a control voltage by comparing a reference output power corresponding to the electric field strength measurement with a current output power of the RF unit, and transmits the generated control voltage to the power gain amplifier to adjust the output power of the RF unit. RFID reader, characterized in that. The method of claim 1, wherein the base band portion RFID reader, characterized in that it comprises a RSSI (Received Signal Strength Indicator) circuit for measuring the electric field strength of the RF received signal. The method of claim 3, wherein the RSSI circuit is RFID reader characterized in that it is provided with an I-RSSI circuit for measuring the electric field strength of the RF received signal from the I (In-phase) signal and a Q-RSSI circuit for measuring the electric field strength of the RF received signal from the Q (Quadrature) signal . The method of claim 1, wherein the control unit RFID reader, characterized in that implemented on a field programmable gate array (FPGA) chip or a digital signal processing (DSP) chip. The method of claim 1, wherein the control unit And a class of the electric field strength measurement value and a reference output power corresponding to the class in a data table. The method of claim 6, wherein the data table is And at least one of distance information according to the grade of the electric field strength measurement value, the control voltage, and an adjustment value of the output power.

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