Abstract:
In the conventional non-contact passive (power-source-less) IC card system method, a self-oscillator is built in a responder. The self-oscillator changes its oscillation frequency by the fluctuation of the power source voltage. Accordingly, it has been difficult to perform time management in the circuit in the responder. In order to solve this problem, in a carrier signal (micro wave) transmitted from an interrogator, the information to be transmitted is multiplexed by a clock frequency component reproduced by the responder. Upon reception of this, the responder extracts the clock frequency component from the modulated wave multiplexed and oscillates a stable frequency clock according to that component. Thus, it is possible to eliminate the problem that the information transfer rate of the circuit signal from the responder to the interrogator fluctuates according to the distance between the interrogator and the responder.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an IC (integrated circuit) card system comprising an interrogator and a responder. 
         [0003]    2. Description of the Prior Art 
         [0004]    In recent years automatic-identification technology for objects has been widely used. The widely used bar-code system is a leading technology of the automatic-identification technologies for objects. However, this bar-code system does now allow information to be rewritten; thus, the non-contact IC card system, in which it is possible to rewrite and read information by utilizing electronic circuitry via wireless communication, has emerged. 
         [0005]    The above non-contact IC card system, has focused on the RFID (Radio Frequency Identification) system, which is a non-contact passive IC card system utilizing a carrier signal providing a responder without a battery. In a typical embodiment of the above system, the carrier signal is transmitted to the passive IC card in another place, and the power source for operating a circuit of the responder is provided by the carrier signal. Moreover, in the system, information transmitted from the interrogator is written via the carrier signal, and stored in the responder, or information stored in an IC card is generated by the interrogator via the carrier signal. The construction thereof comprises, for example as shown in  FIG. 6 , the responder  0601  corresponding to the IC card, and the interrogator  0602 . 
         [0006]    Conventionally, there are three methods for generating a clock signal used in a processing circuit of the responder. 
         [0007]    The first method is a method for generating the clock signal by separating the carrier from the interrogator. In this method, the clock signal is generated by the separating carrier, and a low-frequency such as LF band (30 kHz˜300 KHz) or HF band (3 MHz˜30 MHz) is used for the carrier. 
         [0008]    Next, in the case that a comparatively high-frequency is used as a carrier, it is difficult to generate a clock signal by the first method. Because the frequency of the carrier is high and it is not suitable for an RFID system to separate the high-frequency signal, which requires a measurable amount of power. Accordingly, a method for generating the clock signal by arranging a local self-oscillation apparatus in the responder has been utilized as the second method. In a method for self-oscillation by a crystal oscillator etc. it is possible to generate a clock signal having a stable frequency. However, since the crystal oscillator circuit is required large space on the printed-circuit board, it is difficult to miniaturize the local self-oscillation apparatus, and to apply this method to a small IC chip utilizing microwave as a carrier, of which the size is typically 1 mm square. Because it requires use of a crystal oscillator, of which physical size is relative to wavelength, and there is a theoretical limit based on the wavelength in miniaturizing a crystal oscillator. 
         [0009]    Finally, another method, in cases where the carrier signal has a comparatively short wavelength, will be described. In this method, a local self-oscillation apparatus is arranged in the responder, and the self-oscillation is performed by a combination of a capacitor, a resistor, and an inductor. This method is suitable for miniaturization and enables high-speed communication in the RFID system utilizing a microwave frequency as a carrier. However, the voltage generated in the responder fluctuates according to the communication distance between the responder and the interrogator, which influences the oscillator made up of a capacitor, a resistor, and an inductor. As a result, the unstable oscillation frequency ensued, which was indeed problematic. 
         [0010]      FIG. 5  is a block diagram of the conventional non-contact passive (battery-less) IC card system, in which the self-oscillation type local oscillation unit is utilized in the responder. The responder  0501  comprises the oscillator unit of carrier signal  0502 , the oscillator unit of transmitting signal  0503 , and the transmitter unit of interrogator  0504 . The responder comprises the receiver unit of the responder  0505 , the signal processing unit  0506 , the power recovery circuit unit  0507 , the self-oscillation unit  0508 , and the logic circuit  0509 . 
         [0011]    The carrier signal  0510  is transmitted between the interrogator  0501  and the responder. (Japanese Patent Publication No. H09-233611) 
         [0012]    Next, the operation of the conventional non-contact passive IC card system will be described. 
         [0013]    The carrier signal  0510  (e.g. microwave) modulated by the information in the interrogator  0501  or a non-modulated wave is transmitted from the transmitter unit of interrogator  0504  (e.g. transmitting antenna) to the responder as the carrier signal  0510 . In the responder, the carrier signal  0510  received by the receiver unit of the responder  0505  (e.g. reception antenna) is distributed, and one portion thereof is inputted to the signal processing unit  0506  (e.g. microwave circuit) and another portion thereof is inputted to the power recovery circuit unit  0507 . The power generated by the power recovery circuit unit  0507  is supplied to the signal processing unit  0506 , the self-oscillation unit  0508 , and the logic circuit  0509  etc. Here, the self-oscillation unit  0508  (e.g. CR type oscillation apparatus using a capacitor and a resistor, or LC type oscillation apparatus using an inductor and a capacitor) performs as a clock generator performing all time management in the responder, and the clock is inputted to the logic circuit  0509 . As the communication distance between the interrogator and the responder becomes long, energy attenuation increases. Therefore, the power voltage recovered by the power recovery circuit unit  0507  fluctuates depending on the distance between the interrogator and the responder. However, in case of the non-contact passive IC card system utilizing a microwave frequency, it is difficult to provide a voltage stabilization circuit etc. for operation at the power voltage limit. Therefore, the oscillation frequency of the self-oscillation unit  0508  changes depending on the fluctuation of the recovered power supply voltage, and the information transmission rate of the response signal from the responder to the interrogator  0501  fluctuates depending on the distance between the responder and the interrogator  0501 . 
         [0014]    In the conventional non-contact passive IC card system, wherein high-frequency, such as microwave, is used as a carrier; and a self-oscillation apparatus is used in the responder. This self-oscillation apparatus changes the oscillation frequency thereof depending on the power supply voltage. Meanwhile, in cases where the power is generated by the carrier signal (e.g. microwave) transmitted from the interrogator, the recovered power supply voltage thereof significantly depends on the distance between the interrogator and the responder, and the frequency of the self-oscillation unit becomes unstable, thereby causing fluctuation in the information transmission rate of the communication. Moreover, in the passive IC card system operated at extreme low-voltage, the voltage stabilization circuit is unable to be provided. Accordingly, since the self-oscillation apparatus fluctuates the oscillation frequency thereof, it is difficult to perform time management of the circuit in the responder. 
       SUMMARY 
       [0015]    The present invention resolves the above deficiency, wherein the clock frequency component reproduced in the responder is multiplexed the carrier signal (e.g. microwave) transmitted from the interrogator other than essential information to be transmitted, and the responder receives the modulated signal, which is multiplexed, and extracts clock frequency component there from, and a stable frequency clock is oscillated based on the component. 
         [0016]    The invention of Claim  1  for achieving the above objective is a non-contact passive IC card system comprising an interrogator, and a responder; wherein said interrogator comprises a generation unit for generating a carrier signal by utilizing microwave as a carrier, a generation unit for generating a clock signal for time management of a circuit in said responder, a generation unit for generating a transmitting signal by multiplexing the carrier signal generated by said generation unit for generating a carrier signal and the clock signal generated by said generation unit for generating a transmitting signal, and a transmitter unit for transmitting a transmitting wave generated by said generation unit for generating a transmitting signal; and said responder comprises a receiver unit of the responder for receiving the transmitting signal from the transmitter unit of said interrogator, a signal processing unit for processing the transmitting signal received from said receiver unit of the responder, a power recovery circuit unit for generating power supply by the transmitting signal received from said receiver unit of the responder, an extraction unit of clock frequency component for extracting a frequency component of said clock signal by the transmitting signal received from said receiver unit of the responder, and a clock generation unit for time management of a circuit in said responder by the clock frequency component extracted by said extraction unit of clock frequency component; thereby resolving the deficiency that a clock frequency in the responder fluctuates and the information transmission rate of the circuit signal from the responder to the interrogator fluctuates depending on the distance between the responder and the interrogator. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0017]      FIG. 1  is the first functional block diagram of the non-contact passive IC card system of the present invention. 
           [0018]      FIG. 2  is the first functional block diagram of the power recovery circuit and the clock-frequency extraction unit of the present invention. 
           [0019]      FIG. 3  is the second functional block diagram of the non-contact passive IC card system of the present invention. 
           [0020]      FIG. 4  is the second functional block diagram of the power recovery circuit and the clock-frequency extraction unit of the present invention. 
           [0021]      FIG. 5  is a functional block diagram of the conventional non-contact passive IC card system. 
           [0022]      FIG. 6  is a block diagram of the non-contact passive IC card system. 
           [0023]      FIG. 7  is a functional block diagram of the non-contact passive IC card system of the third embodiment. 
           [0024]      FIG. 8  is a view of explanation for the third embodiment. 
       
    
    
     DETAILED DESCRIPTION  
     The First Embodiment 
       [0025]    As shown in  FIG. 1 , the interrogator  0101  comprises the generation unit of carrier signal  0102 , the generation unit of clock signal  0103 , the generation unit of transmitting signal  0104 , and the transmitter unit of interrogator  0105 . The responder comprises the receiver unit of the responder  0106 , the signal processing unit  0107 , the power recovery circuit unit  0108 , the extraction unit of clock frequency component  0109 , the clock oscillation unit  0110 . The common system comprises the above configuration and the logic circuit unit  0111  in the responder. 
         [0026]    The generation unit of carrier signal  0102  generates information signal modulates the carrier utilizing microwave. Here, “microwave” corresponds to wave of frequencies such as the wave in VHF-band (30 MHz˜300 MHz), UHF-band (300 MHz˜3 GHz), and SHF-band (3 GHz˜30 GHz). Moreover, “carrier signal” corresponds to carrier signal, which is modulated by a carrier utilizing microwave. 
         [0027]    The generation unit of clock signal  0103  generates the clock signal supplied to the clock oscillation unit  0110 , which performs time management of the circuit in the responder. 
         [0028]    The generation unit of transmitting signal  0104  generates a transmitting signal by multiplexing the carrier signal generated by the generation unit of carrier signal  0102  and the clock signal generated by the generation unit of clock signal  0103 . 
         [0029]    The transmitter unit of interrogator  0105  transmits the multiplexed carrier signal  0112 . 
         [0030]    The receiver unit of the responder  0106  receives the carrier signal  0112 . 
         [0031]    The signal processing unit  0107  processes the signal of the transmitting signal from the interrogator  0101 , which has been received by the receiver unit of the responder  0106 . The signal processing unit  0107  comprised a microwave circuit. Here, “microwave circuit” corresponds to a circuit for processing microwave frequency, and typically includes expensive high-frequency components. 
         [0032]    The power recovery circuit unit  0108  generates power by the transmitting signal from the interrogator  0101 , which has been received by the receiver unit of the responder  0106 , and distributes the transmitting signal to the extraction unit of clock frequency component  0109 . For example, as shown in  FIG. 2 , the power recovery circuit unit  0201  comprises the rectification unit  0202 , the power-supplying unit  0203 , and the clock frequency distribution unit  0204 . The rectification unit  0202  rectifies the transmitting signal from the interrogator, which has been received by the receiver unit of the responder. The power-supplying unit  0203  supplies power to the responder. The clock frequency distribution unit  0204  distributes the clock frequency to the extraction unit of clock frequency component  0205 . The power-supplying unit  0203  comprises an integrator etc. By increasing the integral time constant, the direct-current component may be extracted from the output of the rectification unit  0202 . 
         [0033]    Moreover, the clock frequency distribution unit  0204  distributes output from the rectification unit  0202  to the extraction unit of clock frequency component  0205 . 
         [0034]    The extraction unit of clock frequency component  0109  extracts the clock frequency component from the transmitting signal from the interrogator, which has been distributed from the power recovery circuit unit  0108 . For example, as shown in  FIG. 2 , the extraction unit of clock frequency component  0205  comprises an integrator etc. By shortening the integral time constant, the clock oscillation frequency component may be extracted from the output of the clock frequency distribution unit  0204  in the power recovery circuit unit  0201 . 
         [0035]    The clock oscillation unit  0110  generates by utilizing the clock frequency component, which has been extracted by the extraction unit of clock frequency component  0109 , and performs time management of the circuit in the responder. 
         [0036]    Hereinafter, the operation of the present invention will be described. 
         [0037]    The carrier signal (e.g. microwave), which is modulated by the information in the responder  0101  or non-modulated wave, and the frequency component for selecting frequency of the clock oscillation unit  0110  in the responder are multiplexed and modulated. The carrier signal  0112 , which is multiplexed, is transmitted from the transmitter unit of the interrogator  0105  (e.g. transmitting antenna) to the responder. In responder, the carrier signal received by the receiver unit of the responder  0106  (e.g. reception antenna) is distributed, and one portion thereof is inputted to the signal processor unit  0107  and another portion thereof is inputted to the power recovery circuit unit  0108 . The power generated in the power recovery circuit unit  0108  is supplied to the signal processing unit  0107  (e.g. microwave circuit), the clock oscillation unit  0110 , and the logic circuit unit  0111  etc. 
         [0038]    The extraction unit of clock frequency component  0109  is connected to the power recovery circuit unit  0108 . The power recovery circuit unit  0108  distributes the carrier signal received from the receiver unit of responder  0106  to the extraction unit of clock frequency component  0109 , and the extraction unit of clock frequency component  0109  extracts the clock frequency component of the circuit of the entire responder. The extraction unit of clock frequency component  0109  extracts the clock frequency component by utilizing, for example, ASK (Amplitude Shift Keying) reception circuit etc., and supplies information of the clock frequency to the clock oscillation unit  0110 . 
         [0039]    Thus, the frequency information for the operation in stable oscillation frequency is supplied to the clock oscillation unit  0110 . 
         [0040]    The clock oscillation unit  0110  performs as a clock generator performing all time management in the responder, and the clock is inputted to the logic circuit unit  0111 . Then, energy of the carrier signal attenuates depending on the communication distance, thereby causing fluctuation in the supply voltage. Even in the above case, according to the method of the present invention, it is able to manage the frequency of the clock oscillation unit  0110  by the clock frequency transmitted from the responder  0101 , thereby resolving the deficiency that the clock frequency in the responder fluctuates and the information transmission rate of the circuit signal from the responder to the interrogator fluctuates depending on the distance between the responder and the interrogator. 
         [0041]    Note that, in the above description, the extraction unit of clock frequency component  0109  is connected to the power recovery circuit unit  0108 , and receives the carrier signal, which has been received from the receiver unit of responder  0106 , from the power recovery circuit unit  0108 ; however, the present invention is not limited to the above embodiment. 
         [0042]    As shown in  FIG. 3 , the extraction unit of clock frequency component  0309  is able to receive the carrier signal directly from the receiver unit of responder  0106 . 
         [0043]    In the above case, the interrogator  0301  of the non-contact passive IC card system comprises the generation unit of carrier signal  0302 , the generation unit of clock signal  0303 , the generation unit of transmitting signal  0304 , and the transmitter unit of interrogator  0305 . The responder comprises the receiver unit of the responder  0306 , the signal processing unit  0307 , the power recovery circuit unit  0308 , the extraction unit of clock frequency component  0309 , and the clock oscillation unit  0310 . As in the first embodiment, the common system comprises the above embodiment and the logic circuit unit  0311  in the responder. 
         [0044]    The logic circuit unit  0111  in the responder is comprised therewith. 
         [0045]    In the embodiment of  FIG. 3 , the power recovery circuit unit  0308  recovers the power by the transmitting signal from interrogator  0301  received by the receiver unit of the responder  0306 . 
         [0046]    For example, as shown in  FIG. 4 , the power recovery circuit unit  0401  comprises the rectification unit  0402 , and the power supply unit  0403 . The rectification unit  0402  rectifies the transmitting signal from the interrogator, which has been received by the receiver unit of the responder. The power-supplying unit  0403  supplies power to the responder. The power supply unit  0403  comprises an integrator etc. By increasing the integral time constant, the direct-current component may be extracted from the output of the rectification unit  0402 . 
         [0047]    Moreover, the extraction unit of clock frequency component  0309  extracts the clock frequency component from the transmitting signal from interrogator  0301  received by the receiver unit of the responder  0306 . For example as shown in  FIG. 4 , the extraction unit of clock frequency component  0404  comprises the rectification unit  0406  and the extraction unit  0406 . The rectification unit  0406  rectifies the transmitting signal from the interrogator, which has been received by the receiver unit of the responder. The extraction unit  0406  comprises the integrator etc. By shortening the integral time constant, the clock oscillation frequency component may be extracted from the transmitting signal of the interrogator, which has been received by the receiver unit of the responder. 
       The Second Embodiment 
       [0048]    The IC card system of the second embodiment of the present invention is characterized in that a carrier frequency at 2.45 GHz, and clock frequency from several hundred kHz to several dozen MHz are used. 
       The Third Embodiment 
       [0049]    The third embodiment of the present invention relates to the responder or to the non-contact passive IC card system according to the first embodiment, wherein the signal processing unit comprises a demodulation means for sampling and demodulating the transmitting signal received from the interrogator according to the clock frequency component oscillated by the clock oscillation unit. 
         [0050]    As shown in  FIG. 7 , the interrogator  0701  of the non-contact passive IC card system of the third embodiment comprises the generation unit of carrier signal  0702 , the generation unit of clock signal  0703 , the generation unit of transmitting signal  0704 , and the transmitter unit of interrogator  0705 . The responder comprises the receiver unit of the responder  0706 , the signal processing unit  0707 , the power recovery circuit unit  0708 , the extraction unit of clock frequency component  0709 , and the clock oscillation unit  0710 . Moreover, the signal processing unit  0707  comprises the demodulation means  0713 . The common system comprises the above embodiment and the logic circuit unit  0711  in the responder. Furthermore, The carrier signal  0712  is transmitted from the interrogator  0701 . 
         [0051]    Hereinafter, the third embodiment of the present invention includes a signal processing unit that comprises the demodulation means for sampling and demodulating the transmitting signal received from the interrogator by the clock frequency component oscillated by the clock oscillation unit will be described. Otherwise, the third embodiment is substantially the same as that of the first and the second embodiments. 
       Demodulation Means 
       [0052]    The demodulation means performs sampling and demodulation of the transmitting signal received from the interrogator by the clock frequency component oscillated by the clock oscillation unit. 
         [0053]    In wireless communication, in order to reduce noise, a limitation is generally set on the passband of the transmitting signal by a circuit, however, the transmitting signal (square wave) becomes distorted. 
         [0054]      FIG. 8(   a ) is an illustration of an undistorted wave pattern of the transmitting signal (square wave).  FIG. 8(   b ) is an illustration of a wave pattern of the transmitting signal distorted by the band-limiting upon passage of the transmitting signal of  FIG. 8(   a ) through the transmission path. In order to demodulate “0 ” and “1” from the distorted wave pattern in  FIG. 8(   b ), by sampling on the leading edge (or trailing edge) of the clock signal pattern oscillated by the clock oscillation unit in  FIG. 8(   c ), it becomes able to regenerate data with a low code error rate. 
         [0055]    As described hereinabove, by utilizing the clock frequency component oscillated by the clock oscillation unit, the demodulation means becomes able to perform accurate sampling of the transmitting signal received from the interrogator, and demodulation of the information with a low code error rate. 
         [0056]    In the non-contact passive IC card system utilizing microwave, which is able to implement miniaturization, high-speed and high-capacity, it is difficult to generate the clock signal by receiving and directly separating the carrier transmitted from the interrogator in the responder. Accordingly, in the system utilizing microwave as a carrier, a self-oscillation unit is utilized as a clock oscillation unit for performing time management of circuit in the responder. Meanwhile, the power voltage recovered in the power recovery circuit unit in the responder depends on the distance between the interrogator and the responder. In the non-contact passive system utilizing microwave, it is difficult to provide a voltage stabilization circuit etc. for an operation at low voltage during power recovery because of the limitations on both the size of the circuit in the responder and the energy of the carrier signal. Accordingly, the circuit in the responder is directly affected by the fluctuation of power voltage. Therefore, it is difficult for a self-oscillation unit, in which the fluctuation of power voltage changes the oscillation frequency, to perform stable time management in the responder. 
         [0057]    According to the method of the present invention, the energy of the carrier signal (e.g. microwave) attenuates depending on the communication distance between the interrogator and the responder, so that, even when the power voltage in the responder fluctuates, it is able to control frequency of the clock oscillation unit in the responder by the clock frequency component transmitted from the interrogator, thereby resolving the deficiency of fluctuation of the clock frequency in the responder. 
         [0058]    As described hereinabove, according to the present invention, by the construction of  FIGS. 1 and 3 , it becomes able to avoid the fluctuation of the clock oscillation frequency in the responder in the conventional method, thereby enabling stability, high-speed and high-capacity of communication, simplification of the demodulation circuit in the interrogator, simplification and miniaturization of the circuit of the responder, an increase of communication distance, and an increase in the number of responders such as multi-reader.