KR20030091356A - Passive transponder - Google Patents

Abstract

PURPOSE: A manual transponder device is provided to improve the restrictive usage of an RF-ID system by recording and erasing ID data. CONSTITUTION: A manual transponder device includes a detector/rectifier(100), a charger tank(120), a chip power shunt portion(140), a modulation shunt portion(200), a storage portion(160), a detection/input buffer(240), a controller, and a modulator(220). The detector/rectifier(100) is coupled to an antenna through the second and the third antenna connection terminals to convert an RF signal to the first and the second voltage signals. The charger tank(120) is coupled between the first voltage signal output portion of the detector/rectifier(100) and the first antenna connection terminal to transmit the first voltage signal as the driving power. The chip power shunt portion(140) is coupled between the first voltage signal output portion of the detector/rectifier(100) and the first antenna connection terminal to restrain the intensity of the first voltage signal. The modulation shunt portion(200) is coupled between the second voltage signal output portion of the detector/rectifier(100) and the first antenna connection terminal to restrain the intensity of the second voltage signal. The storage portion(160) stores initial data and transmission data. The detection/input buffer(240) is coupled between the second voltage signal output portion of the detector/rectifier(100) and the controller. The controller is used for controlling all operations of the manual transponder device. The modulator(220) is coupled between the second voltage signal output portion of the detector/rectifier(100) and the first antenna connection terminal to modulate the amplitude of the transmission data.

Description

Passive Transponder Device {PASSIVE TRANSPONDER}

The present invention relates to a radio frequency identification (RF-ID) passive transponder. More specifically, it relates to an RF-ID passive transponder capable of recording / erasing data and operating in the 900 MHz and 2.4 GHz bands.

Radio frequency identification (RF-ID) by RF-ID tag is regarded as an important technology in the information technology industry. Conventional recognition technology has been a simple touch-type recognition technology using magnetic barcode technology in the fields of logistics, distribution barcodes, identification cards, and access control, but recently, more advanced non-contact high-frequency identification technology has become popular. Until now, high frequency identification technology has been limitedly used for access control, traffic card, vehicle recognition, expressway tolling system (ETC), logistics, and factory automation. However, recently, high-performance RF-ID tag technology using ultra-thin ID chip has been developed. It is expected to be used for identification cards such as high-speed, high-sensitivity wireless smart cards, wireless electronic money, and passports, and in the future, printable ultra-thin RF tags will emerge, creating a distribution revolution that will gradually replace existing barcodes. In the chip design of the above-mentioned RF-ID field, the chip power source used in the RF-ID tag rectifies the high frequency power radiated from the transceiver through a high efficiency Schottky diode and stores it in a capacitor inside the chip, which is sufficient for the operation of the internal circuit. To provide current. The research in this field has been actively conducted along with the development of high efficiency diode, impedance matching method and high efficiency antenna with the aim of improving chip rectification efficiency. This allows the transceiver not only to verify the existence of the RF-ID tag, but to exchange information between the transceiver and the RF-ID tag or to receive a command from the transceiver. A highly functional, high-efficiency RF-ID system has been developed to perform the operation. However, such an RF-ID system requires a complicated configuration to receive a command from a transceiver, and there is a problem in that an input buffer malfunctions due to a floating signal generated when modulating an incident high frequency signal. In addition, since identification (ID) data for distinguishing each RF-ID tag is recorded at the time of manufacture of the RF-ID tag and cannot be erased and rewritten, there is a problem that the application of the RF-ID system has many limitations.

On the other hand, in the conventional RF-ID system, nonlinear devices such as Schottky diodes used for detection and rectification in RF-ID tags generate harmonics other than selected high frequency signals due to their nonlinear impedance characteristics. For this reason, in the RF-ID system operating a single high frequency as a communication signal, there is a problem in that a reading error frequently occurs due to the generation of unnecessary harmonics.

Referring to US Patent Registration No. 6060815 proposed to solve a problem caused by using a high frequency of a single frequency as a communication signal, RF- which operates a plurality of high frequency signals having different frequencies as an interrogation signal. An ID system is disclosed. The method using a plurality of high frequency signals proposed in the patent has the effect of reducing the transmission frequency drift effect and increasing the bandwidth in the reflection of the high frequency signal incident on the RF-ID tag. A plurality of high frequency signals incident on the RF-ID tag by the above-described method are converted into signals of the driving frequency band of the RF-ID tag by a Schottky diode or a frequency mixing element which is a nonlinear impedance element, and the converted signals are RF- It is used as a driving power source for ID tags.

Accordingly, it is an object of the present invention to provide a passive transponder device that solves the limitation of the application of the RF-ID system by enabling recording and erasing of ID data.

Another object of the present invention is to provide a passive transponder device capable of effectively preventing a malfunction of an input buffer buffering a command received from a transceiver.

It is still another object of the present invention to provide a passive transponder device which eliminates an overcurrent phenomenon occurring irregularly inside a passive transponder implemented in a CMOS type.

Yet another object of the present invention is to provide a passive transponder device coupled to the logic of an RF-ID chip operating in the 900 MHz band and the 2.45 GHz band to increase detection and rectification efficiency, stabilize internal drive power, and protect the input buffer. It is.

1 is a block diagram showing the internal configuration of a passive transponder according to a preferred embodiment of the present invention.

2A-2B are circuit diagrams showing a detection / rectification circuit according to a preferred embodiment of the present invention.

3 is a circuit diagram showing a chip power shunt circuit according to a preferred embodiment of the present invention.

4 is a circuit diagram showing a modulation shunt circuit according to a preferred embodiment of the present invention.

5 is a circuit diagram showing a modulation circuit according to a preferred embodiment of the present invention.

6 is a circuit diagram showing a command detection / input buffer according to a preferred embodiment of the present invention.

Figure 7 is a block diagram showing the configuration of a passive transponder system according to a preferred embodiment of the present invention.

According to a preferred embodiment of the present invention, a passive transformer coupled through a plurality of antennas and first to third antenna connection terminals for receiving a plurality of RF signals having different frequencies transmitted from an interrogator A fond device, comprising: a detector / rectifier coupled to the antenna through the second antenna connection terminal and the third antenna connection terminal, converting the RF signal into a first voltage signal and a second voltage signal, and outputting the first and second voltage signals; A charger tank coupled between the first voltage signal output side of the detector / rectifier and the first antenna connection terminal and receiving the first voltage signal and supplying the first voltage signal to a driving power supply of the passive transponder device; A chip power shunt unit coupled between the first voltage signal output side and the first antenna connection terminal and limiting the magnitude of the first voltage signal; Coupled between the second voltage signal output side of the wave / rectifier and the first antenna connection terminal, storing initial data and transmission data related to the operation of the passive transponder and a modulation shunt for limiting the magnitude of the second voltage signal. A command detection / input buffer coupled between a storage unit, a second voltage signal output side of the detection / modulation unit, and a control unit, and detecting a command from the second voltage signal, and a command input from the command detection / input buffer. The transmission data is coupled between the control unit for controlling the overall operation of the passive transponder and the second voltage signal output side of the detector / rectifier and the first antenna connection terminal, and the transmission data recorded in the storage unit under control of the control unit. A passive transponder device is provided that includes a modulation circuit that amplitude modulates a.

According to another embodiment of the present invention, in a passive transponder system, a first RF signal having a selected frequency and at least one first modulated tone modulated by narrowband frequency modulation such that the selected frequency and the mean center frequency coincide. A transmitter for transmitting a 2 RF signal, and using the plurality of RF signals as driving power in synchronization with an average center frequency of the first RF signal and the second RF signal, using the unique ID data included therein; And a passive transponder device for low frequency modulating and transmitting the received plurality of RF signals, and a receiver for detecting the ID data from the low frequency modulated RF signal received from the passive transponder device.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification, for convenience of description, an embodiment implemented with an NMOS transistor will be described. However, this does not limit the scope of the present invention to a device implemented with an NMOS transistor, and those skilled in the art may configure the same circuit using a PMOS transistor. to be.

Figure 1a is a block diagram showing the internal configuration of a passive transponder according to a preferred embodiment of the present invention, Figure 1b is a view showing the shape of a flat antenna.

Referring to FIG. 1A, a passive transponder includes a detection / rectification circuit 100, a charge tank 120, a chip power shunt (SHUNT) circuit 140, an EEP ROM 160, an MCU 180, and a modulation shunt circuit ( 200, modulation circuit 220 and command detection / input buffer 240. The passive transponder according to the present invention is composed of one chip including the above-described components, and as shown in FIG. 1, the first antenna connection terminal, the second antenna connection terminal, and the first antenna connection terminal of the flat antenna 10. 3 are connected to each antenna connection terminal. However, an impedance matching circuit coupled between the passive transponder and the planar antenna 10 is not shown in FIG. 1A.

The detection / rectification circuit 100 converts the RF signal of the 915 MHz band or the 2.45 GHz band transmitted from the RF-IF interrogator into a DC voltage signal, and multiplies it to be the minimum voltage required for driving the passive transponder. The rectifier circuit 100 has two output nodes, an E node and an M node, the E node being an output node of the first voltage signal secondary rectified and voltage-multiplied by a second Schottky diode, and the M node being detected Output node of the first voltage rectified by the first Schottky diode of the rectifier circuit. The internal configuration of the detection / rectification circuit 100 will be described with reference to Figs. 2A to 2B.

The charger tank 120 is coupled to the E node, and is included in one semiconductor chip constituting the passive transponder, and the first voltage signal output from the rectifier circuit 100 is connected to the passive transponder through the charger tank 120. Used as a driving power source. In the present invention, a flat plate capacitor is used as a charger tank, and the capacitance of the flat plate capacitor is preferably 1 nF or more. In a preferred embodiment of the present invention, a basic type charger pump is implemented by using a flat plate capacitor having a capacitance of 1800 pF. However, the charger pump can also be implemented using an NMOS transistor or a PMOS transistor.

The chip power shunt circuit 140 limits the magnitude of the voltage signal applied to each component coupled to the E node. In particular, in the RF circuit as in the present invention, both ends of the Schottky Diod of the rectifier circuit are provided. Limit the magnitude of the voltage across the An internal configuration of the chip power shunt circuit 140 will be described with reference to FIG. 3.

The EEP ROM 160 is a recording element capable of recording and erasing information through electrical means. The EEP ROM 160 is included in one semiconductor chip constituting a passive transponder and applies a driving power supply VDD from the detection / rectification circuit 100. And transmit initial data and transmission data related to the operation of the passive transponder to the control circuit 180. In the EEP ROM 160, transmission data including an operation mode required for an application purpose of the passive transponder and initial data necessary for internal operation control (INITIALIZE DATA) and ID data of the passive transponder are recorded. Here, when the radio wave signal of the interrogator is applied, the operation mode waits for the next operation command by (1) the continuous mode which immediately transmits a data frame without the standby operation, and (2) the command pulse included in the radio wave signal. Command mode is included. In the command mode, a delay time of a data frame to be sent is set separately. Herein, the data frame is 156-bit Bi-Phase encoded data and is transmitted at 64 Kbps.

The control circuit 180 starts the passive transponder operation by at least one radio signal transmitted from the interrogator, and when a command included in the radio signal is input through the command detection / input buffer 240, the EEP ROM The operation of the internal component is controlled to modulate and transmit the ID information recorded in the 160. The control circuit 180 includes at least one oscillator, a power supply control circuit, control logic, and a bi-phase modulator.

The modulation shunt circuit 200 limits the magnitude of the second voltage signal applied to each component coupled to the M node. In particular, in the high frequency circuit as in the present invention, the Schottky Diod of the rectifying circuit The magnitude of the voltage across both ends is limited. An internal configuration of the modulated shunt circuit 200 will be described with reference to FIG.

The modulation circuit 220 is coupled to the M node, and amplitude modulation modulates the transmission data recorded in the EEP ROM 160 by the control signal PMOD of the control circuit 180 through the planar antenna 10. Send to the interrogator. An internal configuration of the modulation circuit 220 will be described with reference to FIG. 5.

The command detection / input buffer 240 is coupled to an M node, and is composed of an NMOS transistor connected in a silicon diode structure as data detection means, an NMOS transistor acting as a switch as a buffer protection means, and an input buffer. The command detection / input buffer 240 detects a command pulse included in the signal first rectified by the detection / rectification circuit 160 in the non-modulation mode, temporarily stores the command pulse in the buffer, and then controls the control circuit 180. ). The internal configuration of the command detection / input buffer 240 will be described with reference to FIG. 6.

The flat antenna 10 shown in FIG. 1B receives a plurality of RF signals having different frequencies transmitted from the interrogator and inputs them to the passive transponder through the first to third antenna connection terminals.

2A to 2B are circuit diagrams showing a detection / rectification circuit according to a preferred embodiment of the present invention.

The rectifier circuit 100 shown in FIG. 2A is a voltage multiplier circuit (VOLTAGE DOUBLER CIRCUIT) and is composed of a first Schottky diode 102, a second Schottky diode 104, and a coupling capacitor 106. The N node (cathode) of the first Schottky diode 102 and the P node (anode) of the second Schottky diode 104 are coupled, and the first Schottky diode 102 and the second One terminal of the coupling capacitor 106 is coupled to the coupling point of the Schottky diode 104. Here, the coupling capacitor 106 has a capacitance of 5 pF and is preferably composed of a flat capacitor. The P node of the first Schottky diode 102 is coupled to the third antenna connection terminal, and the N node of the second Schottky diode 104 is coupled to the E node. In addition, a coupling point of the first Schottky diode 102 and the second Schottky diode 104 is coupled to the M node, and the other terminal of the coupling capacitor 106 is coupled to the second antenna connection terminal.

As shown in FIG. 2A, by configuring the rectifier circuit 100 using two Schottky diodes operating in the RF band (915 MHz band or 2.45 GHz band), the detection efficiency is increased, the impedance is reduced by half, and thus Due to this, there is an advantage in that impedance matching between the planar antenna 10 and the rectifier circuit 100 is facilitated.

The rectifier circuit 100 shown in FIG. 2B is composed of one Schottky diode 108 and a coupling capacitor 110. The P node of the Schottky diode 108 is coupled with one terminal, the M node, and the third antenna connection terminal of the coupling capacitor 110, and the N node of the Schottky diode 108 is coupled with the E node. The other terminal of the coupling capacitor 110 is coupled to the second antenna connection terminal. The rectifier circuit 100 shown in FIG. 2B has an advantage that it can be implemented at a low cost in general, but it is inevitable to obtain an output voltage lower than that of the voltage multiplier circuit shown in FIG. 2A for the same input signal.

3 is a circuit diagram illustrating a chip power shunt circuit according to a preferred embodiment of the present invention.

The chip power shunt circuit 140 shown in FIG. 3 is composed of a plurality of NMOS transistors 142 to 148 coupled in series. The NMOS transistors 142 to 148 are load transistors each operating as a load resistor, and have a diode structure in which a gate and a drain are connected. The gate and drain of the NMOS transistor 142 are coupled to the E node, and the source is coupled to the gate and drain of the NMOS transistor 144. The remaining NMOS transistors 144-148 are also coupled in the same manner. Preferably, the voltage across the drain-source of the plurality of NMOS transistors 142 to 148 is approximately 1V. Although not shown, the base of the plurality of NMOS transistors 142 to 148 is coupled to the first antenna connection terminal.

4 is a circuit diagram illustrating a modulation shunt circuit according to a preferred embodiment of the present invention.

The modulation shunt circuit 200 shown in FIG. 4 is composed of a plurality of NMOS transistors 202 to 208 coupled in series. The plurality of NMOS transistors 202 to 208 are load transistors each operating as a load resistor, and have a diode structure to which a gate and a drain are connected. The gate and drain of the NMOS transistor 202 are coupled to the M node, and the source is coupled to the gate and drain of the NMOS transistor 204. The remaining NMOS transistors 204-208 are also coupled in the same manner. The voltage applied between the drain and the source of the plurality of NMOS transistors 202 to 208 is preferably within 0.6V to 1V. Although not shown, the base of the plurality of NMOS transistors 202 to 208 is coupled to the first antenna connection terminal.

5 is a circuit diagram showing a modulation circuit according to a preferred embodiment of the present invention.

In the modulation circuit 220 illustrated in FIG. 5, one terminal is coupled to an M node, and the other terminal acts as a switch and a first resistor 222 coupled to the drain of the NMOS transistor 224, and the source is a first antenna. NMOS transistor 224 coupled to the connection terminal. The resistance value of the first resistor 222 determines the time constant and reflectance of the frequency of the reflected RF signal transmitted from the planar antenna 10 of the passive transponder. Therefore, the resistance value of the first resistor 222 is preferably several KOhm since the interrogator should not affect the detection efficiency of the interrogator. In the preferred embodiment of the present invention, the resistance of 2 KOhm is used.

The NMOS transistor 224 repeats the ON / OFF operation by the PMOD signal applied from the control circuit 180 to the gate to amplitude modulate the transmission data. That is, when the PMOD signal is LOW, the transistor 224 is switched off and the impedance of the planar antenna 10 is unchanged. When the PMOD signal is HIGH, when the NMOS transistor 224 is switched on, the impedance of the planar antenna 10 is changed due to the resistance 222 connected between the M node and the first antenna. This modulates the amplitude of the RF signal reflected from the passive transponder. Thus, by the modulation circuit 220, the RF signal sent out of the interrogator and reflected from the passive transponder will comprise differentially-phased (Pi-Phase) encoded data frames, and the modulated data frames are transmitted at 64 Kbps. do.

6 is a circuit diagram illustrating a command detection / input buffer according to a preferred embodiment of the present invention.

In the command detection / input buffer 240 shown in FIG. 6, an NMOS transistor 242, an NMOS transistor 242, and a buffer 248 having a gate and a drain coupled to an M node and a source coupled to an input terminal of the buffer 248 are illustrated. One terminal is coupled to the coupling point of), and the other terminal is composed of a resistor 244 coupled to the drain of the NMOS transistor 246, an NMOS transistor 246 and a buffer 248 to which a driving power is applied as a gate. have.

The NMOS transistor 242 is a silicon diode in which a gate and a drain are combined as data detection means. The NMOS transistor 242 detects a command pulse included in the second voltage signal rectified primarily by the detection / rectification circuit 160 and inputs the buffer to the buffer during unmodulation. In another embodiment, the data detection means may also be implemented with a PIN diode, so that the NMOS transistor 242 is collectively referred to herein as data detection means.

The NMOS transistor 246 is a switch operating as a buffer protection means together with the resistor 244, and performs switching on / switching off operations at the time of non-modulation and modulation to prevent malfunction of the buffer 248. do. Hereinafter, the operation of the buffer protection means composed of the resistor 244 and the NMOS transistor 246 will be described with reference to the modulation circuit 220.

When the passive transponder is modulated by the modulation circuit 220, the NMOS transistor 224 is switched on so that the M node has a potential value of approximately 0 V, which causes a floating signal to be applied to the input of the buffer 248. Will occur. At this time, when driving power is applied to the gate of the NMOS transistor 246, the NMOS transistor 246 is switched on, and an input terminal of the buffer 248 is connected to a first antenna connection terminal (first ground). The resistor 244 connected in series with the NMOS transistor 246 is a resistor for impedance matching during modulation / unmodulation similarly to the resistor 222 and is used to increase the impedance of the NMOS transistor 246.

On the other hand, during the non-modulation operation of the passive transponder, the NMOS transistor 246 is input so that the data detected by the NMOS transistor 242 from the signal first rectified by the detection / rectification circuit 100 is input to the buffer 248. ) Is switched off. In this case, the impedance of the resistor 244 and the NMOS transistor 246 should be relatively larger than the input end impedance of the buffer 248 so that loss of data does not occur. Here, if the impedance of the buffer protection means is small, not only the loss of data detected by the NMOS transistor 242 may occur, but also the efficiency of the detection / rectification circuit 100 may be reduced, so that the resistance value of the resistor 244 is reduced. It is preferable that the number is several KOhm to several tens of KOhm, and in the preferred embodiment of the present invention, a resistance of 14 KOhm is used.

7 is a block diagram showing the configuration of a passive transponder system according to a preferred embodiment of the present invention.

Referring to FIG. 7, an interrogator is composed of a transmitter for transmitting RF signals having different frequencies and a receiver for receiving RF signals reflected from a passive transponder device. For example, a personal computer (PC) is connected. For convenience of description, only the case of operating in the 915MHz band will be described. However, those skilled in the art can easily implement a passive transponder system operating in the 2.45 GHz band by appropriately changing the contents disclosed in the present invention.

The crystal oscillator 305 generates a fixed frequency signal of 915 MHz, F2, which is a continuous signal generated at the fixed frequency, is multiplied by the frequency multiplier 310 and then the first antenna 320 via the amplifier 315. Is sent. In addition, the 915 MHz frequency signal generated from the crystal oscillator 305 is mixed in the mixer 335 with the tone modulated signal in the range of 1-25 KHz generated from the voltage controlled oscillator 330 and multiplied by the frequency in the frequency multiplier 340. After that, it is transmitted from the second antenna 350 via the amplifier 345. The RF signals transmitted from the first antenna 320 and the second antenna 350 described above are uniformly shifted from the selected center frequency (915 MHz), and therefore, the average center frequency of the two RF signals is equal to the selected center frequency. . Here, the tone modulated high frequency signal suppresses generation of standing waves that cause an undetected area in the passive transponder sensing area.

The passive transponder device 400 includes a plurality of antennas tuned to the selected center frequency. The passive transponder device 400 receives driving power from the above-described F1 and F2 RF signals, and amplitude modulates the ID data included therein. Send to the receiver of the gator. Since the internal configuration and operation of the passive transponder device 400 have been described above, a detailed description thereof will be omitted.

The receiver of the interrogator receives the modulated RF signal from the passive transponder device 400 through the third antenna 355, and the received signal passes through the amplifier 360 and the band filter 365 and then the passive oscillator ( Mixed with the high frequency signal generated from 370. Thereafter, the signal processor 380 detects the preamble or ID data received from the passive transponder device 400, and transmits the preamble or ID data to the combined control device 385. That is, the receiver detects the presence of the passive transponder when the strength and duration of the low frequency modulated RF signal by the passive transponder device is greater than or equal to a preset value, and detects the ID data in the low frequency modulated RF signal. do.

The present invention is not limited to the above embodiments, and many variations are possible by those skilled in the art within the spirit of the present invention. In addition, the scope of the present invention can be interpreted only by the claims described below.

As described above, the present invention solves the limitation of the application of the RF-ID system by enabling the recording and erasing of ID data.

In addition, it is possible to effectively prevent malfunction of an input buffer buffering a command received from a transceiver, and to protect an internal circuit from an overcurrent phenomenon that occurs irregularly inside a passive transponder implemented in a CMOS type.

Claims (15)

In the passive transponder device coupled through a plurality of antennas and first to third antenna connection terminals for receiving a plurality of RF signals having different frequencies transmitted from the interrogator, A detector / rectifier coupled to the antenna through the second antenna connection terminal and the third antenna connection terminal, and converting the RF signal into a first voltage signal and a second voltage signal and outputting the first and second voltage signals; A charger tank coupled between the first voltage signal output side of the detector / rectifier and the first antenna connection terminal and receiving the first voltage signal and supplying the first voltage signal to a driving power of the passive transponder device; A chip power shunt unit coupled between the first voltage signal output side of the detector / rectifier and the first antenna connection terminal and limiting the magnitude of the first voltage signal; A modulation shunt unit coupled between the second voltage signal output side of the detector / rectifier and the first antenna connection terminal and configured to limit the magnitude of the second voltage signal; A storage unit for storing initial data and transmission data related to the operation of the passive transponder; A command detection / input buffer coupled between the second voltage signal output side of the detector / modulator and a control unit and detecting a command from the second voltage signal; A control unit controlling the overall operation of the passive transponder by a command input from the command detection / input buffer; And And a modulation circuit coupled between the second voltage signal output side of the detector / rectifier and the first antenna connection terminal, the modulation circuit configured to amplitude modulate the transmission data recorded in the storage unit under control of the controller. . The method of claim 1, The charger tank is a passive transponder device, characterized in that the flat capacitor. The method of claim 1, The chip power shunt unit includes a plurality of MOS transistors coupled between the first voltage signal output side of the detector / rectifier unit and the first antenna connection terminal and having a diode coupling structure connected in series. Device. The method of claim 1, The modulation shunt unit includes a plurality of MOS transistors coupled between the second voltage signal output side of the detector / rectifier and the first antenna connection terminal and having a diode coupling structure connected in series. . The method of claim 1, The storage unit is an EEP ROM, and the storage unit includes an operation mode required for an application purpose of the passive transponder and initial data necessary for internal operation control (INITIALIZE DATA) and an ID data of the passive transponder. Passive transponder device, characterized in that data is recorded. The method of claim 1, The modulator is coupled between the second voltage signal output side of the detector / rectifier and the first antenna connection terminal, A resistor coupled to the second voltage signal output side and one terminal thereof, for changing the impedance of the antenna to amplitude modulate the RF signal; And The other terminal of the first resistor and the drain is coupled, the source is coupled to the first antenna connection terminal, and includes a MOS transistor that is switched by receiving the modulation control signal PMOD of the control unit through a gate, The MOS transistor is switched on / switched off by the PMOD signal to set / release a current path between the resistor and the antenna, thereby changing the impedance of the antenna, thereby amplitude of the RF signal reflected from the transponder. Passive transponder device, characterized in that for modulating. The method of claim 1, The command detection / input buffer, Coupled between the second voltage signal output side of the detector / modulator and the controller, A first MOS transistor having a diode structure in which a gate and a drain are coupled, and detecting a command from the second voltage signal input to the drain; An input buffer coupled to a source of the first MOS transistor and outputting a command input from the first MOS transistor to the controller; A resistor having one terminal coupled to a source of the first MOS transistor; And And a second MOS transistor having a drain coupled to the other terminal of the resistor, a source coupled to the first antenna connection terminal, and switched to receive driving power through a gate. The method of claim 7, wherein And the first MOS transistor is turned off and the second MOS transistor is switched on to establish a current path between the resistor and the antenna during a modulation operation of the passive transponder device. The method of claim 7, wherein In an unmodulated operation of the passive transponder device, the first MOS transistor operates as a diode to detect a command included in a second voltage signal, and the second MOS transistor is switched off to prevent the loss of the detected command. Characterized by a passive transponder device. The method of claim 1, The detection / rectification unit, A Schottky diode coupled to the third antenna connection terminal and outputting a first voltage signal to an N node; And a coupling capacitor coupled between the third antenna connection terminal and the second antenna connection terminal and outputting a second voltage signal to a coupling point with the third antenna connection terminal. The method of claim 1, The detection / rectification unit, A first Schottky diode coupled to the third antenna connection terminal and outputting a second voltage signal to an N node; A second Schottky diode coupled to an N node of the first Schottky diode and outputting a first voltage signal to the N node; And And a coupling capacitor coupled between the coupling point of the first Schottky diode and the second Schottky diode and the second antenna connection terminal. The method according to claim 10 or 11, wherein And the coupling capacitor is a flat capacitor. In a passive transponder system for detecting a plurality of passive transponders located within a certain detection area, A transmitter for transmitting a first RF signal having a selection frequency and at least one second RF signal tone modulated by narrowband frequency modulation such that the selection frequency and the average center frequency coincide; The plurality of RF signals are used as a driving power source in synchronization with the average center frequency of the first RF signal and the second RF signal, and low frequency modulation is performed on the received plurality of RF signals by using unique ID data included therein. Passive transponder device for transmitting by; And And a receiver for detecting the ID data from a low frequency modulated RF signal received from the passive transponder device. The method of claim 13, The receiver detects the presence of the passive transponder when the strength and duration of the low frequency modulated RF signal by the passive transponder device is greater than or equal to a preset value, and detects the ID data in the low frequency modulated RF signal. Passive transponder system, characterized in that. The method of claim 13, And the receiver further comprises a band pass filter for removing the plurality of RF signals and their harmonics from the low frequency modulated RF signal.