Abstract:
The present invention discloses an RFID (Radio Frequency Identification) system for reading and writing an identification information of an RFID tag in a non-contacting manner using a radio frequency. In accordance with RFID system of the present invention, a peak value of a response signal dynamically generated according to an environmental condition including a distance between a reader and the tag is detected, and an identification information provided from the tag is accurately read base on the peak value.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an RFID (Radio Frequency Identification) system for reading and writing an identification information of an RFID tag in a non-contacting manner using a radio frequency, and in particular to an RFID system including a peak detector wherein a peak value of a response signal dynamically generated according to an environmental condition including a distance between a reader and the tag is detected, and an identification information provided from the tag is accurately read base on the peak value.  
         [0003]     2. Description of Prior Art  
         [0004]     An RFID refers to a technology wherein a unique identification information is inputted in a small IC chip and an object or an animal having the IC chip attached thereto is recognized, traced or managed using the radio frequency. The RFID system comprises an RFID tag or an RFID transponder having the unique identification information stored therein and being attached to the object or the animal, and a reader or an interrogator reading or writing the identification information stored in the tag. An information processing apparatus such as a computer is connected to the reader to process a data collected from the tag.  
         [0005]      FIG. 1  is a configuration diagram illustrating a basic structure of a conventional RFID system.  
         [0006]     As shown, a tag  5  is a passive tag that does not have an internal power supply, and comprises a small semiconductor IC chip and an antenna. The IC chip includes an RF circuit, a logic circuit and a memory. The tag  5  has various sizes and shapes. A reader  1  comprises a transmitter for transmitting an RF signal of a predetermined frequency band to the tag  5 , and a receiver for receiving a signal transmitted from the tag  5 , and an antenna for transceiving the signals.  
         [0007]      FIG. 2  is a configuration diagram illustrating a basic operation of the conventional RFID system of  FIG. 1 .  
         [0008]     As shown, the reader  1  transmits the RF signal of the predetermined frequency band including a high frequency carrier signal and a certain inquiry signal. When the tag  5  is placed in a magnetic field of the reader  1  formed by the RF signal, the tag  5  is supplied with an operating power supply required for operating the IC chip from the high frequency carrier signal. That is, the high frequency carrier signal transmitted from the reader  1  generates an AC in the antenna of the tag, and the generated AC is rectified to be used as an electrical energy for the IC chip. In addition, the tag  5  modulates the received RF signal, and the data stored in the tag  5  is subjected to a backscattered modulation based on the modulated RF signal to be transmitted to the reader  1  as a response signal. As described above, in accordance with the conventional RFID system, a power transmission for activating the passive tag is carried out as well as a data transmission between the reader  1  and the tag  5 .  
         [0009]     Generally, since the passive tag that does not have the internal power supply has a short recognition distance of less than one meter, a short range RFID system of a low frequency (125 kHz, 12.56 MHz) is mainly used. The short range RFID system transmits the power and the signal by a winding coil of the reader, and the tag generates a power supply energy and receives the signal via a magnetic coupling by the magnetic field of AC flowing in the coil. Therefore, the conventional low frequency RFID system using the passive tag having the short recognition distance is used for a limited purpose such as entrance management and a traffic card.  
         [0010]     On the other hand, an active tag having a long recognition distance that allows reading/writing and includes a sensor to allow a history management and an environmental information sensing has a large power consumption so that the active tag should include a battery. Therefore, the active tag is disadvantageous in that the active tag may hardly be miniaturized, has a high price and a limited usable span according to a span of the battery.  
         [0011]     Recently, a standardization of the passive RFID technology using the magnetic field and the backscattered modulation in a UHF band of 860-960 KHz and 2.4 Ghz is in progress. Accordingly, the recognition distance of the passive tag is expected to be increased to five meters. In addition, a communication distance between the tag and the reader may be increased when a transmission output of the reader is increased and the antenna of the tag is enlarged.  
         [0012]     Moreover, the RFID tag is expected to progress from the passive type that merely transmits the identification information according to a request of the reader to a ubiquitous sensor having a sensing function to actively sense the environmental information such as a temperature, humidity, a pollution information and a crack information to be transmitted to a network. In addition, in accordance with a USN (Ubiquitous Sensor Network), a subminiature tag is attached to the animal or a human as well as the objects such as a telephone pole, a sidewalk, a wall or a floor of a building to collect the information in real time using wireless readers installed in various places or a mobile wireless reader carried by a user and to transmit the collected information to the network.  
         [0013]     Therefore, in order to build the USN, a development of a low price, high performance and subminiature tag should be preceded. The tag suitable for the USN (uSensor) should have the low price as well as a small size so as to be installed anywhere, and have the sensing function, the high performance to process a large amount of information and a sufficient long recognition distance.  
         [0014]      FIG. 3  is a diagram illustrating a detailed configuration of the reader  10  shown in  FIG. 1 .  
         [0015]     As shown, the reader  1  in accordance with the present invention, comprises a first frequency synthesizer  13  for mixing I and Q signals generated by modulating a data of a digital processor  14 , a forward signal processor  10  including a transmitter  15  for transmitting an output signal of the first frequency synthesizer  13  to a tag  50  through a coupler  16  an RF antenna  17  after amplifying the same to a predetermined level.  
         [0016]     In addition, the reader  1  comprises a receiver  31  for adjusting a gain after amplifying a response signal of the tag  50  received through the RF antenna  17  and the coupler  16 , and a reverse signal processor  30  including a second frequency synthesizer  33  for providing a demodulated signal (I signal and Q signal) to the digital processor  14  by generating a predetermined frequency in order to receive a response signal of the tag  50  through a frequency channel identical to a frequency provided to the tag  50  through the transmitter  15  and mixing the output signal of the receiver  31 .  
         [0017]     An RF signal f 1  including the inquiry signal is transmitted to the tag  50  through the RF antenna  17 .  
         [0018]     The RF signal received through the receiver  31  is demodulated through the frequency channel coherent with the frequency channel transmitted through the transmitter  15  by the second frequency synthesizer  33  to output the I and Q signals.  
         [0019]     In accordance with the conventional RFID system, a magnitude of the RF signal provided from the tag varies dynamically according to a communication environment including the distance between the reader and the tag. It is difficult to interpret the received RF signal of the tag due to a peak value varying dynamically and a noise of an actual RF signal. Therefore, an apparatus for separately setting a threshold corresponding to the response signal is required in order to accurately detect the receive response signal of the tag.  
       SUMMARY OF THE INVENTION  
       [0020]     It is an object of the present invention to provide an RFID system wherein a response characteristic is improved by detecting the peak value of the response signal dynamically generated according to an external environment condition including the distance between the reader and the tag and processing the response signal of the tag corresponding to the detected peak value.  
         [0021]     In order to achieve the above-described objects of the present invention, there is provided an RFID system for reading an information stored in a tag according to a signal transmitted by a reader, the system comprising: an peak detector detecting a peak value of an information signal demodulated from the response signal received from the tag; and a digital processor for determining a validity of the response signal according to the output signal based on an output signal being outputted from the peak detector.  
         [0022]     It is preferable that the peak detector comprises a peak value detector for detecting the peak value and outputting a reference level corresponding to the peak value.  
         [0023]     It is also preferable that the peak detector further comprises a comparator for comparing the reference level corresponding to the peak value to the information signal. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  is a configuration diagram illustrating a basic structure of a conventional RFID system.  
         [0025]      FIG. 2  is a configuration diagram illustrating a basic operation of the conventional RFID system of  FIG. 1 .  
         [0026]      FIG. 3  is a diagram illustrating a detailed configuration of a reader shown in  FIG. 1 .  
         [0027]      FIG. 4  is a diagram illustrating a configuration of a RFID system in accordance with the present invention.  
         [0028]      FIG. 5  is a diagram illustrating an example of a configuration of a peak detector shown in  FIG. 4 .  
         [0029]      FIG. 6  is a diagram illustrating another example of a configuration of the peak detector shown in  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     The present invention will now be described in detail with reference to the accompanied drawings.  
         [0031]      FIG. 4  is a diagram illustrating a configuration of a RFID system in accordance with the present invention.  
         [0032]     Referring to  FIG. 4 , the RFID system in accordance with the present invention comprises a reader  100  for tranceiving an RF signal, and a tag (not shown) transmitting an information stored therein to the reader  100  using the RF signal in a predetermined frequency band transmitted by the reader  100  via a backscattered modulation. The reader  100  comprises a digital processor  110  for processing a received or a transmitted signal, a peak detector  157  for detecting a peak value of a response signal being outputted from a second frequency synthesizer  153 , a forward signal processor  130  for providing a modulated signal outputted by the digital processor  110  to the tag through an RF antenna ANT, and a reverse signal processor  150  for receiving the RF signal provided by the tag and transmitting the same to the digital processor  110 .  
         [0033]     The forward signal processor  130  comprises a first frequency synthesizer  132  for mixing I and Q signals generated from a data in the digital processor  110  with a carrier signal of a communication channel, a transmitter  133  for amplifying an output signal of the first frequency synthesizer  132  to a predetermined level so as to be transmitted to the tag through the RF antenna ANT, and a coupler  135  for selecting a reception or a transmission of the signal.  
         [0034]     The reverse signal processor  150  comprises a receiver  151  for receiving and amplifying a response signal from the tag through the RF antenna ANT to a predetermined level, and a second frequency synthesizer  153  demodulating the information signal including an information stored in the tag from the response signal received through a frequency channel identical to an output frequency channel of the first frequency synthesizer  13  to be output as a demodulated signal (I and Q signals).  
         [0035]     The RF antenna ANT is a dipole antenna, and it is preferable that the RF antenna ANT is a rectanna having a rectifier (not shown) combined. The RF antenna ANT may comprise a ½ wavelength dipole antenna having a rectifying diode connected to a center thereof.  
         [0036]     The peak detector  157  detects the peak value of the information signal demodulated from the response signal.  
         [0037]     The digital processor  110  receives the output signal being outputted from the peak detector  157  to determine a validity of the response signal received from the tag. The digital processor  110  may comprise a universal digital signal processor (DSP), a microprocessor, a dedicated digital signal processor or combinations thereof.  
         [0038]      FIG. 5  is a diagram illustrating an example of the configuration of the peak detector  157  shown in  FIG. 4 .  
         [0039]     Referring to  FIG. 5 , the peak detector  157  comprises a peak value detecting unit  157   a  comprises a peak value detector  157   a.  The peak value detector  157   a  detects the peak value of the demodulated response signal and generates a reference level based on the peak value. For instance, a level corresponding to 55% of a magnitude of the packaging structure of a MEMS microphone may be generated as the reference level to be transmitted to the digital processor  110 . It is possible that different levels other than 55% may be generated as the reference level.  
         [0040]     The digital processor  110  determines the validity by comparing the reference level to the information signal.  
         [0041]      FIG. 6  is a diagram illustrating another example of a configuration of the peak detector  157  shown in  FIG. 4 .  
         [0042]     Referring to  FIG. 6 , the peak detector  157  comprises the peak value detector  157   a  for detecting the peak value of the information signal of the tag and a comparator  157   d  for comparing the reference level corresponding to the peak value and the information signal.  
         [0043]     The peak value detector  157   a  detects the peak value of the demodulated information signal, and generates the reference level based on the peak value.  
         [0044]     The comparator  157   d  compares the reference level and the information signal to output a logic value of “H” or “L”. That is, the logic value of “H” is output when the information signal is larger than the reference level and the logic value of “L” is output when the information signal is smaller than the reference level.  
         [0045]     The digital processor  110  determines whether the output signal of the comparator has a correct frame and a correct CRC value. That is, the frame is determined to be incorrect or invalid when a duration of the frame is out of a certain range. In addition, the CRC value is determined to be incorrect when an error exist in the CRC value. When the frame has the invalid frame or CRC value, the output signal is determined to be invalid.  
         [0046]     When the output signal is valid, the corresponding reference level is a proper reference level. When the output signal is invalid, other reference level is compared to the information signal by varying the reference level.  
         [0047]     The digital processor  110  may provide the collected information to a computer (not shown) or a host server (not shown) via a network (not shown).  
         [0048]     An operation process of the RFID system in accordance with the present invention is described below in detail.  
         [0049]     The first frequency synthesizer  132  generates the carrier signal having a frequency in use in order to transmit the inquiry signal. The generated carrier signal and the inquiry signal are mixed (modulated) to be transmitted to the transmitter  133 . The transmitter  133  amplifies the mixed signal and transmits the amplified signal to the tag via the coupler  135  and the RF antennal ANT.  
         [0050]     The tag that has received the inquiry signal generates the response signal to be transmitted to the reader  100 .  
         [0051]     The response signal of the tag is transmitted to the receiver  151  of the reverse signal processor  150  through the RF antenna ANT and the coupler  135 . The receiver  151  amplifies the response signal to a predetermined level through a bandpass filter (not shown), a low noise amplifier (not shown) and a automatic gain controller (not shown). The amplified response signal is outputted through the frequency channel identical to the output frequency channel of the second frequency synthesizer  153  by the second frequency synthesizer  153 . That is, the response signal is demodulated to the information signal (I and Q signals) including the information stored in the tag by the second frequency synthesizer  153 .  
         [0052]     The response signal demodulated by the second frequency synthesizer  153  is inputted to the peak detector  157 , and the peak detector  157  detects the peak value and generates the reference level based on the detected the peak value.  
         [0053]     The generated reference level is compared to the information signal, thereby generating an output signal including the comparison result.  
         [0054]     The output signal of the peak detector  157  is inputted to the digital processor  110 .  
         [0055]     Since the response signal dynamically varies according to the distance between the reader and the tag, the peak detector varies the reference level according to the peak value, and outputs different comparison result according to the varying reference level.  
         [0056]     Accordingly, the digital processor  110  determines the validity of the signal by checking the frame and the CRC value. When the signal is valid, the corresponding threshold value is the proper threshold value. When the signal is invalid, the signal is ignored. The digital processor  110  may provide the collected information to the computer or the host server through the network.  
         [0057]     As described above, the RFID system in accordance with the present invention is advantageous in that a response characteristic is improved by detecting the peak value of the response signal dynamically generated according to an external environment condition including the distance between the reader and the tag and processing the response signal of the tag corresponding to the detected peak value.  
         [0058]     While the present invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be effected therein without departing from the spirit and scope of the invention.