Abstract:
A radio frequency identification (RFID) device includes: a first amplifier configured to amplify a level of a first radio signal applied through a first antenna, and output an amplified signal; a second amplifier configured to amplify the amplified signal to a predetermined level, and output a power signal; a demodulator configured to demodulate the amplified signal and generate a command signal; a transmission switch configured to selectively output the power signal according to a response signal corresponding to the command signal; and a modulator configured to output a second radio signal, which is generated by modulating the power signal, to a second antenna.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The priority based on Korean patent application No. 10-2009-129395, filed on Dec. 23, 2009, the disclosure of which is hereby incorporated in its entirety by reference, is claimed. 
     BACKGROUND OF THE INVENTION 
     Embodiment in accordance with the present invention relates to a radio frequency identification (RFID) device which is capable of automatically identifying an object by communicating with an external reader. 
     An RFID is a contactless identification technology which can automatically identifies an object by using a radio signal. Specifically, an RFID tag is attached to an object to be identified, and the RFID tag communicates with an RFID reader through transmission/reception of a radio signal. In this manner, the identification of the object is achieved. The use of the RFID can overcome the shortcomings of a conventional automatic identification technology, such as a barcode and an optical character recognition technology. 
     In recent years, RFID tags have been used in various fields, such as a distribution management system, a user authentication system, an electronic cash system, a traffic system, and so on. 
     For example, a distribution management system performs a commodity classification or an inventory management by using integrated circuit (IC) tags (in which data are recorded) instead of a delivery statement or tag. In another example, a user authentication system performs a room management by using IC cards in which personal information is recorded. 
     Meanwhile, a memory used in the RFID tag may be implemented with a nonvolatile ferroelectric memory. 
     In general, a nonvolatile ferroelectric memory (i.e., a ferroelectric random access memory (FeRAM)) is considered by many as a next generation storage device because it has a data processing speed similar to that of a dynamic random access memory (DRAM) and data is retained even when power is interrupted. 
     The FeRAM has a structure substantially similar to that of the DRAM but uses a ferroelectric capacitor as a storage element. Ferroelectric has a high remnant polarization characteristic. As a result, data is not erased even though an electric field is removed. 
       FIG. 1  illustrates an overall structure of a general RFID device. 
     The RFID device includes an antenna unit  1 , an analog unit  10 , a digital unit  20 , and a memory unit  30 . 
     The antenna unit  1  receives a radio signal transmitted from an external RFID reader. The radio signal received through the antenna unit  1  is inputted to the analog unit  10  through antenna pads  11  and  12 . 
     The analog unit  10  amplifies the inputted radio signal and generates a power supply voltage VDD which can then be used as a driving voltage of an RFID tag. The analog unit  10  detects an operation command signal CMD from the inputted radio signal, and outputs the command signal CMD to the digital unit  20 . In addition, the analog unit  10  detects the output voltage VDD and outputs a power on reset signal POR and a clock CLK to the digital unit  20 . The power on reset signal POR is a signal which controls a reset operation. 
     The digital unit  20  receives the power supply voltage VDD, the power on reset signal POR, the clock CLK, and the command signal CMD from the analog unit  10 , and outputs a response signal RP to the analog unit  10 . In addition, the digital unit  20  outputs an address ADD, an input/output data I/O, a control signal CTR, and the clock CLK to the memory unit  30 . 
     The memory unit  30  reads, writes and stores data by using a memory device. 
     The RFID device uses several frequency bands, and the device characteristics vary depending on the frequency bands. In general, as the frequency band is lowered, the recognition speed of the RFID device becomes slower, and the RFID device operates with a shorter distance and is less influenced by the environment. On the other hand, as the frequency band becomes higher, the recognition speed of the RFID device becomes faster, and the RFID device operates at a longer distance and is greatly influenced by the environment. 
     When a distance between the external reader and the RFID device is far, a weak radio signal is inputted to the RFID device. The inputted weak radio signal may not reach a level at which a Schottky diode or the like provided inside a demodulator can be driven. In this case, the long-distance recognition performance of the RFID device is deteriorated. 
     Furthermore, when the conventional RFID device outputs a response signal RP through the antenna unit  1  to the external reader, a radio signal RF is generated by using an internal oscillator provided in the RFID device. In this case, due to the power requirements of the separate internal oscillator, power consumption increases and the circuit of the RFID device becomes complicated. 
     BRIEF SUMMARY OF THE INVENTION 
     Various embodiments of the present invention are directed to improving the long-distance recognition performance of an RFID through the detection of a weak input signal by amplifying a radio signal received in an RFID device through a low noise amplifier (LNA) and outputting the amplified radio signal to a demodulator. 
     Various embodiments of the present invention are directed to providing an RFID device which does not include a separate internal oscillator by generating a radio signal outputted from the RFID device by using a radio signal applied from an external reader to the RFID device. 
     Various embodiments of the present invention are directed to providing an RFID device capable of controlling display devices such as light emitting diodes (LEDs). 
     In an embodiment of the present invention, a radio frequency identification (RFID) device includes: an amplifying unit configured to amplify a first radio signal applied through a first antenna, and output a first amplified signal and a second amplified signal; a demodulator configured to demodulate the first amplified signal and provide a command signal; a switch configured to receive the second amplified signal and transmit the second amplified signal according to a response signal corresponding to the command signal; and a modulator configured to receive the second amplified signal from the switch and output a second radio signal to a second antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a conventional RFID device. 
         FIG. 2  is a block diagram of an RFID system according to an embodiment of the present invention. 
         FIGS. 3 and 4  are waveform diagrams showing an operation of the RFID device according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Description of the embodiments of the present invention will now be made in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like elements. 
       FIG. 2  is a block diagram of an RFID device according to an embodiment of the present invention. 
     The RFID device  100  according to the embodiment of the present invention includes dual antennas ANT_TX and ANT_RX, a low noise amplifier (LNA)  110 , a power amplifier (PA)  120 , a modulator  130 , a demodulator  140 , a power on reset unit  150 , a clock generator  160 , a digital unit  170 , a driving controller  180 , a memory unit  190 , and a plurality of pads PAD 1  to PADn. The low noise amplifier  110  and the power amplifier  120  define an amplifying unit that may include other components. 
     The plurality of pads PAD 1  to PADn are coupled to an external driving device  200 . Two independent antennas ANT_RX and ANT_TX are provided for reception and transmission of a radio signal. 
     The antenna ANT_RX receives a radio signal RF_RX transmitted from an external RFID reader. The radio signal RF_RX received in the RFID device  100  through the antenna ANT_RX is inputted to the LNA  110  through an antenna pad. 
     The antenna ANT_TX transmits a radio signal RF_TX received from the RFID device  100  to the external RFID reader. The radio signal RF_TX applied from the modulator  130  to the antenna ANT_TX is transmitted to the external RFID reader. 
     The LNA  110  amplifies the radio signal RF_RX while minimizing added noise. That is, the LNA  110  amplifies a signal while minimizing noise added to the radio signal RF_RX applied through the antenna ANT_RX, and outputs the amplified signal RF_LNA to the PA  120  and the demodulator  140 . 
     The PA  120  amplifies the amplified signal RF_LNA applied from the LNA  110 , and outputs the power signal RF_PA to a transmission switch TX_SW. 
     The transmission switch TX_SW selectively outputs the power signal RF_PA (i.e., modified power signal RF_MOD) to the modulator  130  under the control of a response signal TX applied from the digital unit  170 . That is, when the response signal TX is activated, the transmission switch TX_SW outputs the power signal RF_PA (i.e., modified power signal RF_MOD) to the modulator  130 . On the other hand, when the response signal TX is deactivated, the transmission switch TX_SW is disconnected from the modulator  130  and thus does not output the power signal RF_PA (i.e., modified power signal RF_MOD) to the modulator  130 . By controlling the on/off timing of the response signal TX a desired transmission signal can be generated. 
     When the response signal TX applied from the digital unit  170  is activated, the modulator  130  outputs the radio signal RF_TX, which is generated by modulating the modified power signal RF_MOD, to the antenna ANT_TX. 
     The demodulator  140  demodulates the amplified signal RF_LNA from the LNA  110  and outputs a command signal RX to the digital unit  170 . 
     Also, the power on reset unit  150  detects a power supply voltage VDD generated at a power supply voltage pad P 1 , and outputs a power on reset signal POR to the digital unit  170 . The power on reset signal POR is a signal which controls a reset operation. 
     The power on reset signal POR rises with the power supply voltage while the power supply voltage goes from a low level to a high level. The power on reset signal POR then changes from a high level to a low level at the moment that the power supply voltage reaches the power supply voltage level VDD, thereby resetting an internal circuit of the RFID device  100 . 
     The clock generator  160  supplies the digital unit  170  with a clock CLK which controls an operation of the digital unit  170 . 
     In this embodiment, the RFID device  100  is driven by the external power supply voltage pad P 1  and an external ground voltage pad P 2 . In a conventional RFID device, an RFID tag receives a radio signal through communication with the RFID reader. The radio signal then supplies the power supply voltage through a voltage amplification unit provided inside the RFID tag. 
     In this embodiment, however, a large amount of power is consumed because the RFID device  100  is coupled to the external driving device  200 . Accordingly, in this embodiment, the power supply voltage VDD and a ground voltage GND are supplied to the RFID device  100  through the additional external power supply voltage pad P 1  and the additional ground voltage pad P 2 . 
     The digital unit  170  receives the power supply voltage VDD, the power on reset signal POR, the clock CLK, and the command signal RX, interprets the command signal RX, and generates a control signal and processing signals. The digital unit  170  outputs the response signal RP corresponding to the control signal and the processing signals to the transmission switch TX_SW. Also, the digital unit  170  outputs an address ADD, data I/O, the control signal CTR, and the clock CLK to the memory unit  190 . 
     The driving controller  180  is coupled between the digital unit  170  and the plurality of pads PAD 1  to PADn. The driving controller  180  outputs driving signals, which control an operation of the driving device  200  provided outside the RFID device  100 , to the plurality of pads PAD 1  to PADn according to the command signal applied from the digital unit  170 . The driving device  200  is coupled to the driving controller  180  of the RFID device  100  through the plurality pads PAD 1  to PADn. 
     The plurality of pads PAD 1  to PADn are coupled to the external driving device  200  through connection pins, and correspond to a coupling unit which couples the RFID device  100  and the driving device  200  to each other. The driving device  200  corresponds to a driving control device which controls an operation of a display device such as an LED, a motor, or a speaker. 
     The memory unit  190  may be implemented with a nonvolatile ferroelectric memory (FeRAM). The FeRAM has a data processing speed similar to that of a DRAM. Also, the FeRAM has a structure substantially similar to that of the DRAM. The FeRAM uses a ferroelectric material as a capacitor, so that it has a high remnant polarization characteristic which is a characteristic of the ferroelectric material. Due to the remnant polarization characteristic, data is not erased even though an electric field is removed. 
       FIGS. 3 and 4  are waveform diagrams showing the operation of the RFID device  100  according to an embodiment of the present invention. Specifically,  FIG. 3  is a waveform diagram showing a case in which the command signal RX is applied to the RFID device  100 . 
     As seen in  FIG. 3 , the radio signal RF_RX is received through the antenna ANT_RX. The radio signal RF_RX received in the RFID device  100  through the antenna ANT_RX is applied to the LNA  110 . 
     Subsequently, the LNA  110  amplifies the radio signal RF_RX from the antenna ANT_RX, and outputs the amplified signal RF_LNA to the PA  120  and the demodulator  140 . 
     The radio signal RF_RX from the antenna ANT_RX is very weak. At this point it may be impossible to drive a Schottky diode included in the demodulator  140 . Accordingly, the LNA  110  amplifies the radio signal RF_RX and generates the amplified signal RF_LNA having a voltage level at which the Schottky diode included in the demodulator  140  can be driven. 
     The demodulator  140  demodulates the amplified signal RF_LNA applied from the LNA  110 , and outputs the command signal RX to the digital unit  170 . That is, the demodulator  140  detects the command signal RX by using an envelope detector implemented with the Schottky diode. 
       FIG. 4  is a waveform diagram showing a case in which the response signal TX is outputted from the RFID device  100 . As seen in  FIG. 4 , the radio signal RF_RX is received through the antenna ANT_RX. At this time, the radio signal RF_RX may have a constant frequency, regardless of a change in the input signal. The radio signal RF_RX received in the RFID device  100  from the antenna ANT_RX is applied to the LNA  110 . 
     Subsequently, the LNA  110  amplifies the radio signal RF_RX from the antenna ANT_RX, and outputs the amplified signal RF_LNA to the PA  120  and the demodulator  140 . The PA  120  amplifies the amplified signal RF_LNA from the LNA  120 , and outputs the amplified power signal RF_PA to the transmission switch TX_SW. 
     The transmission switch TX_SW selectively outputs the power signal RF_PA (i.e., modified power signal RF_MOD) to the modulator  130  under the control of the response signal TX applied from the digital unit  170 . That is, when the response signal TX is activated to a high level, the transmission switch TX_SW is turned on to output the power signal RF_PA (i.e., modified power signal RF_MOD) to the modulator  130 . 
     On the other hand, when the response signal TX is deactivated to a low level, the transmission switch TX_SW is disconnected from the modulator  130  and thus does not output the power signal RF_PA to the modulator  130  (i.e., modified power signal RF_MOD is low). 
     The modulator  130  modulates the modified power signal RF_MOD and outputs the modulated modified power signal as the radio signal RF_TX. The antenna ANT_TX transmits the radio signal RF_TX applied from the modulator  130  to the external RFID reader. 
     As described above, when outputting the response signal TX to the antenna ANT_TX, the radio signal RF_TX is generated by using the radio signal RF_RX applied through the antenna ANT_RX, without using an internal oscillator of the RFID device  100 . 
     That is, the radio signal RF_RX sent from the external RFID reader is amplified by using the LNA  110  and the PA  120 , and transmitted to the external RFID reader by using the separate antenna ANT_TX. 
     In this case, the radio signal RF_RX applied from the external RFID reader and the radio signal RF_TX outputted to the external RFID reader through the modulator  130  may have the same frequency. The radio signal RF_TX is a signal which is generated by amplifying the voltage level of the radio signal RF_RX through the LNA  110  and the PA  120 . 
     In recent years, lighting installed in buildings are using a plurality of LEDs. In this case, a specific light pattern can be provided by individually controlling on/off operations of the LEDs. Furthermore, a desired brightness can be provided by controlling individual LEDs among the plurality of lights, or lights positioned at desired locations can be separately controlled. 
     In the above-described lighting controlling method, the lighting can be remotely controlled through the RFID device. Specifically, an RFID tag is attached to an LED device, and a desired signal is transmitted over a radio frequency through an external reader. The RFID tag attached to the LED device recognizes the transmitted signal and receives a separate command according to a unique ID. In this way, the number and brightness of the LEDs can be controlled as desired. 
     Such an RFID tag is relatively cheaper than a general wireless remote controller. Hence, in a case where the RFID tag is applied to the lightings or the like, the implementation costs can be reduced and more options can be provided to users. 
     The embodiments of the present invention provide the following effects. 
     The long-distance recognition performance of the RFID can be improved through the detection of the weak input signal by amplifying the radio signal received in the RFID device through the LNA and outputting the amplified radio signal to the demodulator. 
     Moreover, since the radio signal outputted from the RFID device is generated by using the radio signal applied from the external RFID reader to the RFID device, a separate internal oscillator may be omitted from the RFID device. 
     In this case, the configuration of the RFID device can be simplified and the operating voltage can be reduced. Also, the operating characteristics can be improved. 
     The above embodiments of the present invention are illustrative and not limitative. Various alternatives and equivalents are possible. Other additions, subtractions, or modifications are obvious in view of the present disclosure and are intended to fall within the scope of the appended claims.