JP2008283637A - Wireless communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless communication device capable of making the rapid transition from carrier sensing to data communication. <P>SOLUTION: The wireless communication device 50 is equipped with: a transmitting circuit 100 including a local oscillator for transmission 1 and generating a transmitting signal which uses an output signal from the local oscillator for transmission 1 as its carrier; a receiving circuit 200 with receiving mixers 9I, 9Q which demodulate a received signal by using the output signal from the local oscillator for transmission 1; and a carrier sensing circuit 300 including a local oscillator 20 for the carrier sensing and a mixer for carrier sensing 14 generating a differential frequency component between an output signal from the local oscillator 20 for the carrier sensing and a received signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wireless communication apparatus having a carrier sense function.

  Some wireless communication devices have a carrier sense function (for example, Patent Documents 1 and 2). The carrier sense function is a function for confirming whether or not a channel to be used is unused before transmitting a transmission signal in order to prevent a plurality of carriers having the same frequency from being generated at the same time. It is. For example, this type of wireless communication device includes a carrier sense circuit that receives an output signal of a receiving mixer in a receiving circuit, receives the communication signal when another wireless communication device is communicating, and receives this communication signal. Confirms whether it is a channel to be used.

  For example, when the frequency of the channel to be used by the wireless communication apparatus is fc, a local signal having a frequency fc + Δf shifted by the frequency Δf is generated by the local oscillator. Here, when another wireless communication device is communicating using the channel of frequency fc, the wireless communication device receives the carrier wave of frequency fc emitted from the other wireless communication device, and the carrier mixer receives the carrier wave of frequency fc. A difference frequency component Δf and a sum frequency component 2fc + Δf between the frequency fc and the frequency fc + Δf of the local signal are generated. In the carrier sense circuit, only the difference frequency component Δf is extracted through the filter, and when the difference frequency component Δf is detected, it is determined that the channel to be used is already used, and the difference frequency component Δf is not detected. If it is determined that the channel to be used is unused.

When the channel to be used is unused, the wireless communication apparatus switches to the data communication after switching the oscillation frequency of the local oscillator from fc + Δf to the frequency fc of the channel.
JP 2006-42246 A JP 2003-347946 A

  For example, in the communication standard in the RFID system, since the communication period is provided immediately after the carrier sense period without providing the setup period of the local oscillator, the reader / writer apparatus as the wireless communication apparatus is configured with the PLL as the local oscillator. It is necessary to switch the oscillation frequency at high speed. However, in the PLL, it is difficult to switch the oscillation frequency at high speed, and as a result, it is difficult for the wireless communication device to shift from carrier sense to data communication at high speed.

  Accordingly, an object of the present invention is to provide a wireless communication apparatus that can shift from carrier sense to data communication at high speed.

  The wireless communication device of the present invention includes a transmission local oscillator, a transmission circuit that generates a transmission signal using the output signal from the transmission local oscillator as a carrier wave, and a reception signal using the output signal from the transmission local oscillator. Carrier sense having a receiving circuit having a receiving mixer to demodulate, a carrier sensing local oscillator, and a carrier sensing mixer for generating a difference frequency component between the output signal from the carrier sensing local oscillator and the received signal Circuit.

  According to this wireless communication apparatus, since the carrier sense circuit has the local oscillator for carrier sense separately from the local oscillator for transmission for the transmission circuit, before the transition from carrier sense to data communication, The oscillation frequency of the local oscillator can be set. Therefore, according to this wireless communication apparatus, it is possible to shift from carrier sense to data communication at high speed.

  The transmission circuit described above includes a distributor that distributes an output signal from the transmission local oscillator to the output side and the reception mixer side, and a first switch provided between the distributor and the transmission local oscillator. Furthermore, it is preferable to have it.

  According to this configuration, when shifting from carrier sense to data communication, it is possible to shift from carrier sense to data communication at high speed and easily simply by switching the first switch from OFF to ON. Further, by turning off the first switch at the time of carrier sense, it is possible to prevent erroneous detection that the output signal from the transmitting local oscillator is radiated and there is a channel in communication. Further, it is possible to prevent erroneous detection due to the in-device sneaking of the output signal from the transmitting local oscillator.

  Moreover, it is preferable that the above-described transmission circuit further includes a variable attenuation type attenuator between the output side and the distributor. According to this configuration, the isolation between the carrier sense circuit and the transmission circuit can be further improved during carrier sense. Further, according to this configuration, it is possible to control the output power of the transmission circuit during data communication.

  In addition, the above-described wireless communication device includes an antenna duplexer that guides a transmission signal from the transmission circuit to the antenna and a reception signal from the antenna to the reception circuit, and a second antenna provided between the antenna duplexer and the transmission circuit. And a third switch that switches between connecting the antenna duplexer and the reception circuit or switching between the antenna duplexer and the carrier sense circuit.

  According to this configuration, since the second switch can be turned off during carrier sensing, it is possible to further improve the isolation between the carrier sensing circuit and the transmission circuit. Further, according to this configuration, since the third switch can connect the antenna duplexer and the carrier sense circuit during carrier sense, it is possible to reduce the influence of the carrier sense circuit on the receiving circuit. It is. On the other hand, in data communication, since the third switch can connect the antenna duplexer and the receiving circuit, it is possible to increase the isolation between the carrier sense circuit and the transmitting circuit. Can reduce the influence on the carrier sense circuit.

  Another wireless communication apparatus of the present invention includes a transmission local oscillator having a transmission local oscillator, generating a transmission signal using the output signal from the transmission local oscillator as a carrier wave, and receiving the output signal from the transmission local oscillator A receiving circuit having a receiving mixer for demodulating a signal, a carrier sensing local oscillator, and a carrier sensing mixer for generating a difference frequency component between an output signal from the carrier sensing local oscillator and a received signal. A carrier sense circuit also serving as a mixer, and a first switch for switching between a local oscillator for transmission and a local oscillator for carrier sense are provided.

  According to this wireless communication apparatus, since the carrier sense circuit has the local oscillator for carrier sense separately from the local oscillator for transmission for the transmission circuit, before the transition from carrier sense to data communication, The oscillation frequency of the local oscillator can be set. Therefore, according to this wireless communication apparatus, it is possible to shift from carrier sense to data communication at high speed.

  Further, according to this wireless communication apparatus, when shifting from carrier sense to data communication, simply switching the first switch from the carrier sense local oscillator to the transmission local oscillator, the carrier sense to the data communication at high speed, And it can be easily transferred. In addition, when the carrier sense is performed, the first switch is switched from the local oscillator for transmission to the local oscillator for carrier sense, and the output signal from the local oscillator for transmission is radiated, so that there is a miscommunication channel. Can be prevented. Further, it is possible to prevent erroneous detection due to the in-device sneaking of the output signal from the transmitting local oscillator.

  Another wireless communication apparatus described above includes an antenna duplexer that guides a transmission signal from a transmission circuit to an antenna and a reception signal from the antenna to a reception circuit, and a second antenna provided between the antenna duplexer and the transmission circuit. It is preferable to further include this switch.

  According to this configuration, since the second switch can be turned off at the time of carrier sensing, it is possible to suppress unnecessary radiation that is radiated from the local oscillator of the carrier sensing circuit. .

  The another wireless communication device described above preferably further includes a third switch for switching whether the output signal of the reception mixer is guided to the reception circuit side or the carrier sense circuit side.

  According to this configuration, since the third switch can guide the output signal of the reception mixer to the carrier sense circuit side during carrier sense, the isolation between the carrier sense circuit and the reception circuit can be improved. Is possible. On the other hand, in data communication, the third switch can guide the output signal of the receiving mixer to the receiving circuit side, so that the influence of the carrier sense circuit on the receiving circuit can be reduced.

  The carrier sense circuit described above uses a heterodyne system, and the oscillation frequency of the carrier sense local oscillator is preferably a value obtained by adding 10.7 MHz to a desired channel.

  According to this configuration, the carrier sense circuit detects a difference frequency component having a frequency of 10.7 MHz. The frequency 10.7 MHz band is a frequency band used for FM radios, card-type PHS modules, and the like, and many discrete parts have already been manufactured. Therefore, it is possible to reduce the price.

  ADVANTAGE OF THE INVENTION According to this invention, the radio | wireless communication apparatus which can transfer to carrier communication from data communication at high speed is obtained.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

In this embodiment, a reader / writer device (wireless communication device) used in an RFID system will be described. Before describing the reader / writer device according to the present embodiment, an overview of the RFID system and an overview of carrier sense will be described.
[Outline of RFID system]

  The RFID system includes an RFID tag (also referred to as an electronic tag) and a reader / writer device. The RFID tag has a memory, and data such as ID data, product code, management code, and visitor management number can be stored in the memory. These data are read or written by the reader / writer device. Specifically, first, the reader / writer device wirelessly transmits a command command to the RFID tag, and the RFID tag returns a response command to the command command. Upon receiving this response command, the reader / writer device performs processing for the response command (for example, data reading and data writing described above).

Note that the RFID tag includes an active type having a driving power source such as a battery and a passive type having no driving power source such as a battery. A passive RFID tag generates drive power from a carrier wave from a reader / writer device.
[Overview of career sense]

  In UHF band RFID systems in Japan, it is necessary to transmit radio waves within the frequency range defined by the Radio Law. For this reason, in the case where a plurality of reader / writer devices are installed adjacent to each other, a situation occurs in which the same frequency must be used. As a result, a plurality of reader / writer devices may interfere with each other. In order to avoid mutual interference among a plurality of reader / writer devices, it is necessary for the plurality of reader / writer devices to use radio channels in a time-sharing manner. As a specific solution, there is a carrier sense function stipulated in the Japanese Radio Law.

  The carrier sense function is a function in which the reader / writer device confirms whether or not a radio channel to be used is unused before transmitting a command command to the RFID tag. The reader / writer device transmits a command command to the RFID tag only when the radio channel of the frequency is not in use, thereby shifting the transmission timing with respect to a plurality of adjacent reader / writer devices and causing mutual interference. It can be avoided.

  Here, the carrier sense will be described in more detail with reference to FIG. FIG. 1 is a diagram illustrating a configuration of an RFID system. Prior to data transmission, the reader / writer device RW2 preparing for transmission transmits / receives the presence / absence of another reader / writer device RW1 that is already communicating with the RFID tag Tag between the other reader / writer device RW1 and the RFID tag Tag. It is determined by detecting the presence or absence of a carrier signal.

  FIG. 2 is a diagram illustrating an example of a radio channel in the RFID system. As shown in FIG. 2, in the RFID system, for example, there are a plurality of channels in a frequency band within 2 MHz. The reader / writer device selects one channel from these channels and oscillates the carrier frequency from the local oscillator. In order to oscillate this carrier, the reader / writer device first performs carrier sense, and transmits the carrier only when the desired frequency is available, that is, when the other reader / writer device is not using the desired frequency. it can.

  FIG. 3 is a diagram illustrating an example of a wireless communication method in the RFID system. As shown in FIG. 3A, for example, in the UHF band high-power RFID system, the carrier sense period is defined as 5 ms or more (5 ms + random backoff), and a transmission period of maximum 4 s is provided immediately thereafter. Yes. Therefore, the reader / writer device must immediately shift to data transmission when a desired carrier is vacant due to carrier sense.

  FIG. 4 is a circuit diagram showing a part of the configuration of a reader / writer device according to a conventional example. A reader / writer device 50X shown in FIG. 4 includes a transmission circuit having a PLL (local oscillator) 1, a modulation unit 2, a driver amplifier (Driver Amp) 3, a distributor 5 and a power amplifier (Power Amp) 6, and a receiving mixer 9I. , 9Q, filters 10I, 10Q, amplifiers (Amp) 11I, 11Q and a direct conversion type receiving circuit having a phase shifter 21, and a carrier sense circuit having PLL1, a receiving mixer 9Q, a filter 10C and an amplifier (Amp) 11C And an antenna duplexer 7 and an antenna 8.

  In order to establish communication with the RFID tag, the reader / writer device 50X shown in FIG. 4 first needs to search for a free channel and secure a channel (carrier sense). When the power is turned on, the reader / writer device 50X sets up the amplifiers 11I, 11Q, 11C, PLL1, and the like, and starts searching for an empty channel after the setup is completed.

  With reference to FIG. 5, the carrier sense by the reader / writer device 50X shown in FIG. 4 will be described in detail. FIG. 5 is a diagram illustrating the frequency of each signal of the carrier sense circuit. If the frequency of the carrier wave received by the reader / writer device 50X from the other reader / writer device is fc, the carrier sense local signal (carrier sense Lo signal) of frequency fc + Δf can be used to detect this carrier wave. In the channel where the carrier wave is radiated from the reader / writer device, the frequency component of Δf is detected by the carrier sense circuit. Note that Δf represents a frequency shift, and the designer may arbitrarily determine the frequency of Δf.

  Specifically, the carrier wave of frequency fc and the local signal for carrier sensing of frequency fc + Δf are combined by the receiver mixer 9Q, and the difference frequency component of frequency Δf and the sum frequency component of frequency 2fc + Δf are generated. Since the sum frequency component is an unnecessary component, it is removed by the low-pass filter 10C, and only the difference frequency component of the frequency Δf is extracted. When the difference frequency component of the frequency Δf is detected, it is determined that the desired channel is already used, and when the difference frequency component of the frequency Δf is not detected, the desired channel is unused. To be judged. If it is determined by carrier sense that the desired channel is unused, the frequency of PLL1 is switched from fc + Δf to fc, and the process proceeds to data transmission to the RFID tag.

  As shown in FIG. 3A, in the communication standard of the RFID system, since the communication period is provided immediately after the carrier sense period without providing the setup period of PLL1, it is necessary to switch the oscillation frequency of PLL1 at high speed. There is. However, since it takes time to lock the frequency in the PLL1, as shown in FIG. 3B, a set time for locking the frequency of the PLL1 occurs. As described above, it is difficult for the PLL 1 to switch the oscillation frequency at high speed. As a result, it is difficult to shift from carrier sense to data transmission at high speed.

  Therefore, in order to shorten the frequency switching time of the PLL1, it is conceivable to use a local signal having the same frequency as that during data transmission at the time of carrier sensing.

  FIG. 6 is a circuit diagram showing a part of the configuration of a reader / writer device according to a modification of the conventional example. A reader / writer device 50Y shown in FIG. 6 is different from the conventional example in that the carrier sense circuit receives a carrier sense local signal from the distributor 5 in the reader / writer device 50X. With this configuration, the same local signal as that used during transmission is used during carrier sensing.

  FIG. 7 is a diagram illustrating the frequency of each signal of the carrier sense circuit. In consideration of the lock time of PLL1, if the oscillation frequencies fc and fcs of PLL1 are the same for carrier sensing and data transmission, the sum frequency component of frequency fc + fcs appears, but the difference frequency component cannot be extracted. For this reason, the direct current component is monitored, it is recognized that a large direct current component has flowed into the carrier sense circuit, and the carrier sense is determined. However, since the carrier sense circuit is distributed from the receiving mixer 9Q, a large DC component flows to the receiving circuit. In the receiving circuit, it is conceivable to remove the DC component by AC coupling or the like. However, when the frequency is close, the direct current component is large, and thus the DC component may not be reliably removed. For this reason, there arises a problem that an amplifier or the like in the receiving circuit is saturated.

Therefore, the present invention proposes a reader / writer device that can shift from carrier sense to data communication at high speed.
[First Embodiment]

  FIG. 8 is a circuit diagram showing the reader / writer device according to the first embodiment of the present invention. The reader / writer device 50 shown in FIG. 8 includes an antenna 8, an antenna duplexer 7, a transmission circuit 100, a reception circuit 200, a carrier sense circuit 300, and a control circuit 400.

  The antenna duplexer 7 is, for example, a circulator. The antenna duplexer 7 guides the reception signal from the antenna 8 to the reception circuit 200 and the carrier sense circuit 300, and guides the transmission signal from the transmission circuit 100 to the antenna 8.

  The transmission circuit 100 modulates the carrier wave with the baseband signal from the control circuit 400 to generate a transmission signal, and transmits it to the antenna 8. The transmission circuit 100 includes a transmission PLL (local oscillator) 1, a modulation unit 2, a driver amplifier (Driver Amp) 3, a first switch (SW) 4, a distributor 5, and a power amplifier (Power Amp). 6.

  The transmission PLL 1 sets an oscillation frequency according to a frequency setting signal from the control circuit 400 and supplies a carrier wave to the modulation unit 2.

  The modulation unit 2 generates a modulated wave obtained by modulating the carrier wave from the transmission PLL 1 with the baseband signal (modulation signal) from the control circuit 400. This modulated wave is also used as a local signal for transmission. The modulation unit 2 outputs this modulated wave to the first switch 4 via the driver amplifier 3.

  The first switch 4 switches on / off based on a switching signal from the control circuit 400. Specifically, the first switch 4 is turned on only during data transmission and data reception. If the modulated wave from the transmission PLL 1 is output from the transmission circuit 100, for example, a carrier exists due to unnecessary radiation of the reader / writer device 50 itself, wraparound in the reader / writer device 50, or the like during carrier sensing. May be erroneously detected. Therefore, such unnecessary radiation and sneak power need to be lower than the carrier sense level defined in the standard. For example, the sneak power to the carrier sense circuit 300 needs to be −74 dBm or less for the high output type and −64 dBm or less for the low output type. Note that all components are operating during carrier sense. In this way, the first switch 4 suppresses, for example, the modulation wave from the transmission PLL 1 from entering the carrier sense circuit 300 during carrier sensing.

  The distributor 5 distributes the modulated wave to the power amplifier 6 and the receiving circuit 200. The modulated wave amplified through the power amplifier 6 is output as a transmission signal from the antenna 8 through the antenna duplexer 7. The modulated wave distributed to the receiving circuit 200 side is used as a local signal for transmission.

  Here, in an RFID system using a passive RFID tag, the transmission circuit 100 needs to continuously generate a carrier wave during transmission in order to supply power to the RFID tag. That is, there are times when it is necessary to operate the transmission circuit 100 and the reception circuit 200 simultaneously. That is, in the passive RFID system, a non-modulated wave is continuously sent to the RFID tag at the time of reception. The RFID tag generates a power source from an unmodulated wave from the reader / writer device, and performs load modulation on the unmodulated wave of the reader / writer device. Therefore, an unmodulated wave is supplied to the local signal for transmission at the time of reception.

  The reception circuit 200 generates a baseband signal obtained by demodulating the reception signal and outputs the baseband signal to the control circuit 400. The reception circuit 200 employs a direct conversion method, and includes reception mixers 9I and 9Q, filters 10I and 10Q, amplifiers (Amp) 11I and 11Q, and a phase shifter 21.

  The reception mixer 9I multiplies the reception signal and the transmission local signal to generate an I-phase baseband signal (demodulation signal), and outputs it to the control circuit 400 via the filter 10I and the amplifier 11I. Similarly, the receiving mixer 9Q generates a Q-phase baseband signal (demodulated signal) by multiplying the received signal by the transmission local signal delayed by π / 2 by the phase shifter, and generates the filter 10Q and the amplifier 11Q. To the control circuit 400.

  The carrier sense circuit 300 performs carrier sense according to the control circuit 400. The carrier sense circuit 300 includes a filter 12, an amplifier (Amp) 13, a carrier sense mixer 14, a filter 15, an amplifier (Amp) 16, an RSSI unit 17, a determination unit 18, a driver amplifier (Driver Amp). ) 19 and a carrier sense PLL (local oscillator) 20.

  The filter 12 is provided for image removal, and it is only necessary to pass only a frequency to be carrier sensed, which is a desired frequency. For example, a SAW filter is used as the filter 12. The amplifier 13 is a low noise amplifier.

  The carrier sense mixer 14 synthesizes the received signal from the amplifier 13 and the carrier sense local signal from the driver amplifier 19, generates a difference frequency component and a sum frequency component of these signals, and outputs them to the filter 15. To do. In order to extract these difference frequency components and sum frequency components, the carrier sense circuit 300 of this embodiment employs a superheterodyne method, and the carrier sense mixer 14 sets the frequency of the received signal to an intermediate frequency. It is provided for switching. The intermediate frequency is preferably 10.7 MHz. Since the 10.7 MHz band is a frequency band widely used for FM radios, card-type PHS modules, and the like, many discrete parts have already been manufactured. As a result, the parts price is low and the price of the reader / writer device 50 can be reduced.

  The filter 15 is a low-pass filter and blocks the sum frequency component from the carrier sense mixer 14. That is, the filter 15 outputs the difference frequency component from the carrier sense mixer 14 to the RSSI unit 17 via the amplifier 16. For example, a ceramic filter (FFE1070MA11UXL) manufactured by TDK Corporation can be applied to the filter 15.

  RSSI (Receiver Signal Strength Indicator) is a DC voltage output representing the electric field strength of the receiver. The RSSI output level is used for measuring the electric field strength and monitoring the carrier sense level. In the present embodiment, the RSSI unit 17 monitors the carrier sense level with RSSI corresponding to 10.7 MHz. For example, the carrier sense level needs to realize the sensitivity defined in the Japanese Radio Law. For example, in Japan, the carrier sense level defined for UHF band RFID reader / writer devices is -74 dBm for the high output type and -64 dBm for the low output type.

  The determination unit 18 determines the presence or absence of a carrier from the carrier sense level from the RSSI unit 17. The determination unit 18 outputs the determination result to the control circuit 400.

  The carrier sense PLL 20 generates a carrier sense local signal having a frequency obtained by adding 10.7 MHz to a desired frequency in accordance with the frequency setting signal from the control circuit 400, and the carrier sense mixer 14 via the driver amplifier 19. Output to.

  The control circuit 400 controls carrier sense and transmission of a transmission signal and analyzes a reception signal from the RFID tag. Therefore, the control circuit 400 outputs a channel frequency setting signal, a baseband signal (modulation signal), and a switch switching signal to the transmission circuit 100 during data transmission, and receives the demodulated response signal from the reception circuit 200 during reception. To analyze. At the time of carrier sense, the control circuit 400 outputs a frequency setting signal to the carrier sense circuit 300 and determines a channel at the time of transmission based on the determination result from the carrier sense circuit 300.

  Next, the operation of the reader / writer device 50 according to the first embodiment will be described with reference to FIG. FIG. 9 is a flowchart showing the operation of the reader / writer device of the first embodiment. FIG. 9 shows an operation based on the Japanese radio law.

  First, when the reader / writer device 50 is powered on (step S01), setup of each circuit is started. At this time, the oscillation frequency of the transmission PLL 1 is set to a desired channel frequency based on the frequency setting signal from the control circuit 400, and the oscillation frequency of the carrier sense PLL 20 is set to the frequency setting signal from the control circuit 400. Is set up to a frequency obtained by adding 10.7 MHz to a desired channel (step S02).

  After the setup is completed, for example, after a predetermined time, the mode shifts to the carrier sense mode. Then, the carrier sense mixer 14 in the carrier sense circuit 300 generates a difference frequency component and a sum frequency component between the carrier frequency of the received signal and the frequency of the carrier sense local signal from the carrier sense PLL 20. Only the components pass through the filter 15. The RSSI unit 17 monitors the carrier sense level of the difference frequency component, and the determination unit 18 determines the presence or absence of a carrier from the carrier sense level. The determination result is output to the control circuit 400.

  When shifting to the carrier sense mode, the first switch 4 is turned off based on a switching signal from the control circuit 400. Thereby, it is possible to suppress the transmission local signal from the transmission PLL 1 from entering the carrier sense circuit 300 during the carrier sense (step S03).

  Next, based on the determination result from the carrier sense circuit 300, the control circuit 400 determines whether or not the desired channel is an empty channel (step S04). If the desired channel is being used by another reader / writer device, the desired channel is changed (step S05), the process returns to step S03, and carrier sense is executed again. Specifically, the control circuit 400 resets the oscillation frequency of the transmission PLL 1 and the oscillation frequency of the carrier sense PLL 20 and performs carrier sense again (step S05).

  As described above, the reader / writer device 50 starts carrier sense. When another reader / writer device oscillates a carrier wave within a specified time, that is, within the carrier sense period shown in FIG. Abandon transmission, select another channel or a channel at random, and perform carrier sense again. That is, the reader / writer device 50 repeats carrier sense until an empty channel exists.

  On the other hand, when the desired channel is an empty channel, the reader / writer device 50 shifts to the data transmission mode and starts data transmission to the RFID tag. Specifically, the first switch 4 is turned on based on a switching signal from the control circuit 400, and a baseband signal is output from the control circuit 400 to the transmission circuit 100. Then, the modulation unit 2 modulates the carrier wave with the baseband signal, and the transmission signal is output from the transmission circuit 100.

  Here, since the transmission PLL 1 has already performed the frequency lock in step S02 or S05, the transition time from the carrier sense to the data transmission mode depends on the switching time of the first switch 4. Since the switching time of the first switch 4 is very fast compared to the frequency lock time of the transmission PLL 1, almost no set time shown in FIG.

  Thereafter, a response signal is received from the RFID tag, and the received signal is demodulated by the receiving circuit 200 and analyzed by the control circuit 400 (step S06). The reader / writer device 50 may issue a plurality of commands as long as it is within a maximum of 4 seconds within the transmission time defined in FIG. The reader / writer device 50 can communicate with the RFID tag only within the maximum 4 s.

  After the data transmission is completed, the first switch 4 is turned off based on a switching signal from the control circuit 400. As shown in FIG. 3, a stop period is set after the transmission period, and carrier sense and transmission are stopped for a period of 50 ms after the end of communication (step S07).

  Note that, at the time of data transmission / reception, the carrier sense circuit 300 is preferably operated as it is without turning off the power. However, the reader / writer device 50 can turn off the power of the circuit only for 50 ms in the stop period shown in FIG. 3, so that the circuit operates stably until the power is turned off and carrier sensing is performed again. The power may be turned on. This again reduces the set time (see FIG. 3B) during the carrier sense operation.

  Thus, according to the reader / writer device 50 of the first embodiment, the carrier sense circuit 300 includes the carrier sense PLL 20 in addition to the transmission PLL 1 for the transmission circuit 100. Before shifting to data transmission, the oscillation frequency of the transmission PLL 1 can be set. Furthermore, the shift from carrier sense to data transmission is switched only by switching the first switch 4. Therefore, according to the reader / writer device 50 of the first embodiment, it is possible to shift from carrier sense to data transmission at high speed.

  Further, according to the reader / writer device 50 of the first embodiment, when the first switch 4 is turned off at the time of carrier sense, the output signal from the transmission PLL 1 is radiated and there is a channel in communication. It is possible to prevent erroneous detection. In addition, it is possible to prevent erroneous detection due to the output signal from the transmission PLL 1 sneaking into the apparatus.

  Further, according to the reader / writer device 50 of the first embodiment, since the carrier sense circuit 300 is distributed from the front stage of the receiving mixers 9I and 9Q, the power amplifier 6, the antenna duplexer 7, and the carrier sense circuit 300 The front end part can be modularized. As a result, the carrier sense circuit 300 and the antenna duplexer 7 exist as components of the front end unit, and the carrier sense circuit 300 can be combined with these front end modules. These front end portions can be integrated with high-frequency components and devices using LTCC (low temperature co-fired ceramics) or the like.

  Further, by making the carrier sense circuit 300 into a module, the carrier sense circuit 300 can be created as an additional circuit of the reader / writer device. Thus, the design can be made by adding the carrier sense circuit 300 to the conventional reader / writer device.

Further, according to the reader / writer device 50 of the first embodiment, the transmission PLL 1 and the carrier sense PLL 20 are operated, and the carrier sense PLL 20 is set to a frequency obtained by adding 10.7 MHz to a desired carrier. Therefore, the difference between the carrier frequency and the local oscillation frequency does not approach “0”, and the carrier sense detection signal does not disappear.
[Second Embodiment]

  FIG. 10 is a circuit diagram showing a reader / writer device according to the second embodiment of the present invention. A reader / writer device 50A shown in FIG. 10 is different from the first embodiment in that the reader / writer device 50 includes a transmission circuit 100A instead of the transmission circuit 100. The other configuration of the reader / writer device 50A is the same as that of the reader / writer device 50.

  The transmission circuit 100 </ b> A is different from the transmission circuit 100 in the configuration further including the variable attenuator 22. The other configuration of the transmission circuit 100A is the same as that of the transmission circuit 100.

  The variable attenuator 22 is connected between the distributor 5 and the power amplifier 6 and adjusts the amount of attenuation according to the adjustment signal from the control circuit 400.

  At the time of carrier sense, the first switch 4 is turned off. However, it may be difficult to suppress the wraparound of the carrier wave from the transmission circuit 100 with only the first switch 4. In the reader / writer device 50A, it is necessary to obtain an isolation from a maximum output of +30 dBm to a carrier sense level of -74 dBm. That is, it is necessary to realize an isolation of 104 dBm. Therefore, when isolation cannot be obtained only by the first switch 4, the attenuation amount of the variable attenuator 22 is maximized only at the time of carrier sense. At the time of transmission in the reader / writer device 50A, the attenuation amount of the variable attenuator 22 is set in accordance with minimization or an adjustment signal from the control circuit 400.

  Next, the operation of the reader / writer device 50A of the second embodiment will be described with reference to FIG. FIG. 11 is a flowchart illustrating the operation of the reader / writer device according to the second embodiment. The reader / writer device 50A is different from the first embodiment in that, in the operation of the reader / writer device 50, steps S03A and S06A are performed instead of steps S03 and S06, respectively.

  That is, the reader / writer device 50A turns off the first switch 4 in step S03 and simultaneously sets the attenuation amount of the variable attenuator 22 to, for example, the maximum (step S03A). At this time, the set value of the attenuation amount of the variable attenuator 22 is preferably the maximum, but may not necessarily be the maximum as long as the effects described later can be obtained. Other operations in step S03A are the same as those in step S03.

  The reader / writer device 50A turns on the first switch 4 in step S06 and simultaneously adjusts the attenuation amount of the variable attenuator 22 in accordance with the adjustment signal from the control circuit 400 (step S06A). Other operations in step S06A are the same as those in step S03.

  As described above, the reader / writer device 50A of the second embodiment can obtain the same advantages as those of the reader / writer device 50 of the first embodiment.

Further, according to the reader / writer device 50A of the second embodiment, the attenuation of the variable attenuator 22 is maximized at the time of carrier sensing, so that the isolation between the carrier sense circuit 300 and the transmission circuit 100 can be further expanded. Can do. Further, according to the reader / writer device 50A of the second embodiment, the attenuation of the variable attenuator 22 in the data transmission mode can be adjusted, so that the transmission power of the transmission circuit 100 can be controlled.
[Third Embodiment]

  FIG. 12 is a circuit diagram showing a reader / writer device according to the third embodiment of the present invention. A reader / writer device 50B shown in FIG. 12 is different from the second embodiment in that the reader / writer device 50A further includes second and third switches 23 and 24. Other configurations of the reader / writer device 50B are the same as those of the reader / writer device 50A.

  The second switch 23 is connected between the transmission circuit 100 </ b> A and the antenna duplexer 7, and switches on / off according to a switching signal from the control circuit 400. Specifically, the second switch 23 is turned off at the time of carrier sense and turned on at the time of data transmission. The second switch 23 is provided in order to increase the isolation between the carrier sense circuit 300 and the transmission circuit 100 during carrier sense.

  The third switch 24 is connected between the antenna duplexer 7, the reception circuit 200, and the carrier sense circuit 300, and connects the antenna duplexer 7 and the reception circuit 200 according to a switching signal from the control circuit 400. Or switching between connecting the antenna duplexer 7 and the carrier sense circuit 300. Specifically, the third switch 24 connects the antenna duplexer 7 and the carrier sense circuit 300 during carrier sense, and connects the antenna duplexer 7 and the reception circuit 200 during data transmission.

  The third switch 24 is provided in order to reduce the influence of the carrier sense circuit 300 on the receiving circuit 200 during carrier sensing. The third switch 24 is used to increase the isolation between the carrier sense circuit 300 and the transmission circuit 100 during data transmission, and to reduce the influence of the reception circuit 200 on the carrier sense circuit 300. Is provided.

  Next, the operation of the reader / writer device 50B of the third embodiment will be described with reference to FIG. FIG. 13 is a flowchart illustrating the operation of the reader / writer device according to the third embodiment. The reader / writer device 50B is different from the second embodiment in that steps S03B, S06B, and S07B are performed in place of steps S03A, S06A, and S07 in the operation of the reader / writer device 50A.

  That is, the reader / writer device 50B turns off the first switch 4 in step S03A, and at the same time, the second switch 23 turns off, and the third switch 24 connects the antenna duplexer 7 and the carrier sense circuit 300. (Step S03B). Other operations in step S03B are the same as those in step S03A.

  The reader / writer device 50B turns on the first switch 4 in step S06A, and at the same time, the second switch 23 turns on, and the third switch 24 connects the antenna duplexer 7 and the receiving circuit 200. (Step S06B). Other operations in step S06B are the same as in step S06A.

  The reader / writer device 50B further turns off the second switch 23 at the same time as turning off the first switch 4 in step S07 (step S07B). Other operations in step S07B are the same as those in step S07.

  As described above, the reader / writer device 50B of the third embodiment can obtain the same advantages as the reader / writer device 50A of the second embodiment.

  Further, according to the reader / writer device 50B of the third embodiment, since the second switch 23 is turned off during carrier sensing, the isolation between the carrier sensing circuit 300 and the transmission circuit 100 can be further expanded. Can do.

Also, according to the reader / writer device 50B of the third embodiment, since the second switch 24 connects the antenna duplexer 7 and the carrier sense circuit 300 at the time of carrier sense, the carrier sense circuit 300 is a receiving circuit. The influence on 200 can be reduced. On the other hand, at the time of data transmission, the second switch 24 connects the antenna duplexer 7 and the reception circuit 200, so that the isolation between the carrier sense circuit 300 and the transmission circuit 100 can be enhanced, and the reception circuit The influence of 200 on the carrier sense circuit 300 can be reduced.
[Fourth Embodiment]

  FIG. 14 is a circuit diagram showing a reader / writer device according to the fourth embodiment of the present invention. A reader / writer device 50C illustrated in FIG. 14 includes an antenna 8, an antenna duplexer 7, a transmission circuit 100C, a reception circuit 200C, a carrier sense circuit 300C, and a control circuit 400.

  The antenna duplexer 7 is, for example, a circulator. The antenna duplexer 7 guides the reception signal from the antenna 8 to the reception circuit 200C and the carrier sense circuit 300C, and guides the transmission signal from the transmission circuit 100C to the antenna 8.

  The transmission circuit 100 </ b> C modulates the carrier wave with the baseband signal from the control circuit 400 to generate a transmission signal, and transmits it from the antenna 8. The transmission circuit 100 </ b> C includes a transmission PLL (local oscillator) 1, a modulation unit 2, a first switch 4 </ b> C, a driver amplifier 3, a distributor 5, and a power amplifier 6.

  The transmission PLL 1 sets an oscillation frequency according to a frequency setting signal from the control circuit 400 and supplies a carrier wave to the modulation unit 2.

  The modulation unit 2 generates a modulated wave modulated by the carrier wave from the transmission PLL 1 and the baseband signal from the control circuit 400. The modulation unit 2 outputs this modulated wave to the first switch 4C.

  The first switch 4 </ b> C switches between the carrier sense PLL 20 and the transmission PLL 1 based on a switching signal from the control circuit 400. Specifically, the first switch 4C connects the transmission PLL 1 and the driver amplifier 3 only at the time of data transmission and data reception, and connects to the carrier sense PLL 20 and the driver amplifier 3 at the time of carrier sensing. By switching the first switch 4C, the carrier sense mode and the transmission mode can be switched. The driver amplifier 3 is connected to the distributor 5.

  The distributor 5 distributes the modulated wave to the power amplifier 6 and the receiving circuit 200 </ b> C, and the power amplifier 6 amplifies the modulated wave and transmits it to the antenna duplexer 7.

  Here, in an RFID system using a passive RFID tag, the transmission circuit 100C needs to continuously generate a carrier wave during transmission in order to supply power to the RFID tag. That is, there are times when it is necessary to operate the transmission circuit 100C and the reception circuit 200C simultaneously. That is, in the passive RFID system, unmodulated waves are continuously sent to the RFID tag during reception. The RFID tag creates a power source from an unmodulated wave from the reader / writer device 50C, and performs load modulation on the unmodulated wave of the reader / writer device 50C. Therefore, an unmodulated wave is supplied as a local signal for transmission at the time of reception.

  The reception circuit 200C generates a baseband signal obtained by demodulating the reception signal and outputs the baseband signal to the control circuit 400. The reception circuit 200C employs a direct conversion system, and includes a reception mixer 9I, a reception / carrier sense combined mixer 9QC, filters 10I and 10Q, amplifiers (Amp) 11I and 11Q, and a phase shifter 21. Have.

  The reception mixer 9I multiplies the reception signal and the transmission local signal to generate an I-phase baseband signal (demodulation signal), and outputs it to the control circuit 400 via the filter 10I and the amplifier 11I.

  The reception / carrier sense mixer 9QC generates a Q-phase baseband signal (demodulation signal) by multiplying the reception signal and the transmission local signal delayed by π / 2 by the phase shifter, and generates the filter 10Q and the amplifier 11Q. To the control circuit 400.

  The carrier sense circuit 300C performs carrier sense according to the control circuit 400. The carrier sense circuit 300C shares the reception / carrier sense combined mixer 9QC and the phase shifter 21 with the reception circuit 200C, and shares the first switch 4C, the driver amplifier 3, and the distributor 5 with the transmission circuit 100C. Furthermore, the carrier sense circuit 300C includes a filter 15, an amplifier (Amp) 16, an RSSI unit 17, a determination unit 18, and a carrier sense PLL 20.

  The reception / carrier sense combined mixer 9QC multiplies the received signal (carrier wave radiated by another reader / writer device) by the carrier sense local signal from the driver amplifier 3, thereby obtaining the difference frequency component of these signals. The sum frequency component is generated and output to the filter 15. In order to extract these difference frequency component and sum frequency component, the carrier sense circuit of this embodiment adopts a superheterodyne system, and the reception / carrier sense combined mixer 9QC converts the frequency of the received signal to an intermediate frequency. Provided to convert to. The intermediate frequency is preferably 10.7 MHz. Since the 10.7 MHz band is a frequency band widely used for FM radios, card-type PHS modules, and the like, many discrete parts have already been manufactured. As a result, the parts price is low, and the price of the reader / writer device can be reduced.

  The filter 15 is a band pass filter, and blocks the sum frequency component from the reception / carrier sense combined mixer 9QC. That is, the filter 15 outputs the difference frequency component from the reception / carrier sense combined mixer 9QC to the RSSI unit 17 via the amplifier 16. For example, a ceramic filter (FFE1070MA11UXL) manufactured by TDK Corporation can be applied to the filter 15.

  RSSI (Receiver Signal Strength Indicator) is a DC voltage output representing the electric field strength of the receiver. The RSSI output level is used for measuring the electric field strength and monitoring the carrier sense level. In the present embodiment, the RSSI unit 17 monitors the carrier sense level with RSSI corresponding to 10.7 MHz. For example, the carrier sense level needs to realize the sensitivity defined in the Japanese Radio Law. For example, in Japan, the carrier sense level defined for UHF band RFID reader / writer devices is -74 dBm for the high output type and -64 dBm for the low output type.

  The determination unit 18 determines the presence or absence of a carrier from the carrier sense level from the RSSI unit 17. The determination unit 18 outputs the determination result to the control circuit 400.

  The carrier sense PLL 20 generates a carrier sense local signal having a frequency obtained by adding 10.7 MHz to a desired frequency in accordance with the frequency setting signal from the control circuit 400, and is also used for reception / carrier sense via the driver amplifier 3. Output to mixer 9QC.

  The control circuit 400 controls carrier sense and transmission of a transmission signal and analyzes a reception signal from the RFID tag. Therefore, the control circuit 400 outputs a channel frequency setting signal, a baseband signal (modulation signal), and a switch switching signal to the transmission circuit at the time of data transmission, and analyzes the demodulated response signal from the reception circuit 200C at the time of reception. To do. Further, at the time of carrier sensing, the control circuit 400 outputs a frequency setting signal to the carrier sensing local oscillator, and determines a channel at the time of transmission based on the determination result from the carrier sensing circuit 300C.

  Next, the operation of the reader / writer device 50C of the fourth embodiment will be described with reference to FIG. FIG. 15 is a flowchart illustrating the operation of the reader / writer device according to the fourth embodiment. FIG. 15 shows an operation based on the Japanese radio law.

  First, when the reader / writer device 50C is powered on (step S01), the setup of each circuit is started. At this time, the oscillation frequency of the transmission PLL 1 is set to a desired channel frequency based on the frequency setting signal from the control circuit 400, and the oscillation frequency of the carrier sense PLL 20 is set to the frequency setting signal from the control circuit 400. Is set up to a frequency obtained by adding 10.7 MHz to a desired channel (step S02).

  After the setup is completed, for example, after a predetermined time, the mode shifts to the carrier sense mode. Then, the difference frequency component and the sum frequency component between the frequency of the carrier wave of the received signal and the frequency of the carrier sense local signal from the carrier sense PLL 20 are generated by the reception / carrier sense combined mixer 9QC in the carrier sense circuit 300C. Only the difference frequency component passes through the filter 15. The RSSI unit 17 monitors the carrier sense level of the difference frequency component, and the determination unit 18 determines the presence or absence of a carrier from this carrier sense level. The determination result is output to the control circuit 400.

  When shifting to the carrier sense mode, the first switch 4C is connected to the carrier sense PLL 20 based on a switching signal from the control circuit 400 (step S03C). Note that the first switch 4C may be connected to the carrier sense PLL 20 at the time of setup after power-on (step S02). Since the reader / writer device 50C must not output a transmission signal to the RFID tag unless there is an empty channel, it is necessary to perform carrier sense after the power is turned on. Therefore, the reader / writer device 50C may connect the first switch 4C to the carrier sense PLL 20 in step S02.

  Next, the control circuit 400 determines whether or not the desired channel is an empty channel based on the determination result from the carrier sense circuit 300C (step S04). If the desired channel is being used by another reader / writer device, the desired channel is changed (step S05), the process returns to step S03C, and carrier sense is executed again. Specifically, the control circuit 400 resets the oscillation frequency of the transmission PLL 1 and the oscillation frequency of the carrier sense PLL 20 (step S05), and carrier sense is executed again.

  As described above, the reader / writer device 50C starts carrier sense, and when another reader / writer device oscillates a carrier wave within a specified time, that is, within the carrier sense period shown in FIG. The other channel or a channel is selected at random, and carrier sense is performed again. That is, the reader / writer device 50C repeats the carrier sense until an empty channel exists.

  On the other hand, when the desired channel is an empty channel, the reader / writer device 50C shifts to the data transmission mode and starts data transmission to the RFID tag. Specifically, the first switch 4C is connected to the transmission PLL 1 based on the switching signal from the control circuit 400, and the baseband signal is output from the control circuit 400 to the transmission circuit 100C. Then, the modulation unit 2 modulates the carrier wave with the baseband signal, and a transmission signal is output from the transmission circuit 100C (step S06C).

  Here, since the transmission PLL 1 has already performed the frequency lock in step S02 or S05, the transition time from the carrier sense to the data transmission mode depends on the switching time of the first switch 4C. Since the switching time of the first switch 4C is much faster than the frequency lock time of the transmission PLL 1, almost no set time shown in FIG.

  Thereafter, a response signal is received from the RFID tag, and the received signal is demodulated by the receiving circuit 200C and analyzed by the control circuit 400 (step S06C). Note that the reader / writer device 50C may issue a plurality of commands as long as it is within a maximum of 4 seconds within the transmission time defined in FIG. The reader / writer device 50C can communicate with the RFID tag only within the maximum 4s.

  After the data transmission is completed, the first switch 4C is connected to the carrier sense PLL 20 based on a switching signal from the control circuit 400. As shown in FIG. 3, a stop period is set after the transmission period, and carrier sense and transmission are stopped for a period of 50 ms after the end of communication (step S07C).

  Note that the carrier sense circuit is preferably operated as it is without turning off the power supply during data transmission / reception. However, the reader / writer device 50C can turn off the power of the circuit only for 50 ms during the stop period shown in FIG. 3, so that the circuit operates stably until the power is turned off and carrier sensing is performed again. The power may be turned on. This again reduces the set time (see FIG. 3B) during the carrier sense operation.

  As described above, according to the reader / writer device 50C of the fourth embodiment, the carrier sense circuit 300C includes the carrier sense PLL 20 in addition to the transmission PLL 1 for the transmission circuit 100C. Before shifting to data transmission, the oscillation frequency of the transmission PLL 1 can be set. Furthermore, the transition from carrier sense to data transmission is switched only by switching the first switch 4C. Therefore, according to the reader / writer device 50C of the fourth embodiment, it is possible to shift from carrier sense to data transmission at high speed.

Also, according to the reader / writer device 50C of the fourth embodiment, the transmission PLL 1 and the carrier sense PLL 20 are operated, and the carrier sense PLL is set to a frequency obtained by adding 10.7 MHz to a desired carrier. Therefore, the difference between the carrier frequency and the local oscillation frequency does not approach “0”, and the carrier sense detection signal does not disappear.
[Fifth Embodiment]

  FIG. 16 is a circuit diagram showing the reader / writer device according to the first embodiment of the present invention. A reader / writer device 50D shown in FIG. 16 is different from the fourth embodiment in that the reader / writer device 50C further includes second and third switches 23 and 24. Specifically, the reader / writer device 50D includes a transmitter circuit 100D, a receiver circuit 200D, and a carrier sense circuit 300D instead of the transmitter circuit 100C, the receiver circuit 200C, and the carrier sense circuit 300C in the reader / writer device 50C. Other configurations of the reader / writer device 50D are the same as those of the reader / writer device 50C.

  The transmission circuit 100D is different from the fourth embodiment in the configuration further including the second switch 23 in the transmission circuit 100C, and the reception circuit 200D is the fourth in the configuration further including the third switch 24 in the reception circuit 200C. This is different from the embodiment. The carrier sense circuit 300D is different from the fourth embodiment in that the carrier sense circuit 300C further shares the second and third switches 23 and 24. Other configurations of the transmission circuit 100D, the reception circuit 200D, and the carrier sense circuit 300D are the same as those of the transmission circuit 100C, the reception circuit 200C, and the carrier sense circuit 300C, respectively.

  The second switch 23 is connected between the transmission circuit 100 </ b> C and the antenna duplexer 7, and switches on / off according to a switching signal from the control circuit 400. Specifically, the second switch 23 is turned off at the time of carrier sense and turned on at the time of data transmission. The second switch 23 is provided in order to suppress unnecessary radiation that is radiated from the carrier sensing PLL 20 during carrier sensing.

  The third switch 24 is between the reception / carrier sense combined mixer 9QC and the Q channel filter 10Q of the reception circuit 200D, and between the reception / carrier sense combined mixer 9QC and the circuit after the filter 15 of the carrier sense circuit 300D. It is connected to the. In response to the switching signal from the control circuit 400, the third switch 24 switches whether to guide the output signal of the reception / carrier sense / mixer 9QC to the reception circuit 200D side or to the carrier sense circuit 300D side. Specifically, the third switch 24 connects the reception / carrier sense combined mixer 9QC and the Q channel filter 10Q of the reception circuit 200D during data transmission, and receives / carrier sense combined mixer 9QC and the carrier sense during carrier sense. The circuit after the filter 15 of the circuit 300D is connected.

  The third switch 24 is provided to reduce the influence of the carrier sense circuit 300D on the Q channel side of the receiving circuit during carrier sensing. The third switch 24 is used to increase the isolation between the circuit after the filter 15 of the carrier sense circuit 300D and the Q channel side of the reception circuit 200D during data transmission, and also to the Q channel of the reception circuit 200D. This side is provided to reduce the influence of the carrier sense circuit 300D on the circuits after the filter 15.

  Next, the operation of the reader / writer device 50D of the fifth embodiment will be described with reference to FIG. FIG. 17 is a flowchart illustrating the operation of the reader / writer device according to the fifth embodiment. The reader / writer device 50D is different from the fourth embodiment in that steps S03D, S06D, and S07D are performed in place of steps S03C, S06C, and S07C in the operation of the reader / writer device 50C, respectively.

  That is, in step S03D, the reader / writer device 50D connects the first switch 4C to the carrier sense PLL 20, further turns off the second switch 23, and moves the third switch 25 to the carrier sense circuit 300D side. Connecting. Other operations in step S03D are the same as those in step S03C.

  In step S06D, the reader / writer device 50D connects the first switch 4C to the transmitting PLL 1, further turns on the second switch 23, and connects the third switch 24 to the receiving circuit 200D side. . Other operations in step S06D are the same as those in step S06C.

  Further, the reader / writer device 50D turns off the second switch 23 in step S07D. Other operations in step S07D are the same as those in step S07C.

  The reader / writer device 50D of the fifth embodiment can obtain the same advantages as the reader / writer device of the fourth embodiment.

  Further, according to the reader / writer device 50D of the fifth embodiment, since the second switch 23 is turned off at the time of carrier sense, unnecessary radiation that is emitted secondarily can be reduced.

  Further, according to the reader / writer device 50D of the fifth embodiment, at the time of carrier sense, the third switch 24 connects the reception / carrier sense combined mixer 9QC and the carrier sense circuit 300D side. It is possible to reduce the influence of 300D on the receiving circuit 200D. On the other hand, at the time of data transmission, the third switch 24 connects the reception / carrier sense combined mixer 9QC and the reception circuit 200D side, so that the influence of the carrier sense circuit 300D on the reception circuit 200D can be reduced. It is.

  The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the switching function of the first switches 4 and 4C can be realized in various forms. For example, the control circuit 400 functions as a first switch, and can switch between the transmission PLL 1 and the carrier sense PLL 20 by controlling the output on / off of the transmission PLL 1 and the carrier sense PLL 20. It becomes.

It is a figure which shows the structure of an RFID system. It is a figure which shows an example of the radio channel in a RFID system. It is a figure which shows an example of the radio | wireless communication system in a RFID system. It is a circuit diagram which shows a part of structure of the reader / writer apparatus concerning a prior art example. FIG. 5 is a diagram showing the frequency of each signal of the carrier sense circuit shown in FIG. 4. It is a circuit diagram which shows a part of structure of the reader / writer apparatus which concerns on the modification of a prior art example. It is a figure which shows the frequency of each part signal of the carrier sense circuit shown in FIG. 1 is a circuit diagram showing a reader / writer device according to a first embodiment of the present invention. It is a flowchart which shows operation | movement of the reader / writer apparatus of 1st Embodiment. It is a circuit diagram which shows the reader / writer apparatus which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the reader / writer apparatus of 2nd Embodiment. It is a circuit diagram which shows the reader / writer apparatus which concerns on the 3rd Embodiment of this invention. It is a flowchart which shows operation | movement of the reader / writer apparatus of 3rd Embodiment. FIG. 6 is a circuit diagram showing a reader / writer device according to a fourth embodiment of the present invention. It is a flowchart which shows operation | movement of the reader / writer apparatus of 4th Embodiment. It is a circuit diagram which shows the reader / writer apparatus which concerns on the 5th Embodiment of this invention. It is a flowchart which shows operation | movement of the reader / writer apparatus of 5th Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Transmission PLL (transmission local oscillator), 2 ... Modulation part, 3 ... Driver amplifier, 4, 4C ... 1st switch, 5 ... Distributor, 6 ... Power amplifier, 7 ... Antenna sharing device, 8 ... Antenna , 9I, 9Q, 9QC ... reception mixer, 9QC ... reception / carrier sense combined mixer (reception mixer), 10I, 10Q, 10C ... filter, 11I, 11Q, 11C ... amplifier, 12 ... filter, 13 ... amplifier, 14 ... Carrier sense mixer, 15 ... Filter, 16 ... Amplifier, 17 ... RSSI section, 18 ... Determination section, 19 ... Driver amplifier, 20 ... Local oscillator for carrier sense, 21 ... Phase shifter, 22 ... Variable attenuator, 23 ... 2nd switch, 24 ... 3rd switch, 50, 50A, 50B, 50C, 50D ... Reader / writer device (wireless communication device), 100, 100A, 00C, 100D ... transmission circuit, 200,200C, 200D ... reception circuit, 300,300C, 300D ... carrier sense circuit, 400 ... control circuit.

Claims (7)

A transmission circuit having a local oscillator for transmission, and generating a transmission signal using the output signal from the local oscillator for transmission as a carrier;
A receiving circuit having a receiving mixer for demodulating a received signal with an output signal from the transmitting local oscillator;
A carrier sense circuit having a carrier sense local oscillator and a carrier sense mixer for generating a difference frequency component between an output signal from the carrier sense local oscillator and the received signal;
A wireless communication device. The transmission circuit includes:
A distributor for distributing an output signal from the transmitting local oscillator to an output side and the receiving mixer side;
A first switch provided between the distributor and the transmitting local oscillator;
The wireless communication apparatus according to claim 1, further comprising:   The radio communication apparatus according to claim 2, wherein the transmission circuit further includes a variable attenuation type attenuator between an output side and the distributor. An antenna duplexer for guiding a transmission signal from the transmission circuit to an antenna and guiding a reception signal from the antenna to the reception circuit;
A second switch provided between the antenna duplexer and the transmission circuit;
A third switch for switching between connecting the antenna duplexer and the receiving circuit or connecting the antenna duplexer and the carrier sense circuit;
The wireless communication device according to claim 2, further comprising: A transmission circuit having a local oscillator for transmission, and generating a transmission signal using the output signal from the local oscillator for transmission as a carrier;
A receiving circuit having a receiving mixer for demodulating a received signal with an output signal from the transmitting local oscillator;
A carrier sense circuit having a carrier sense local oscillator and also serving as the mixer for carrier sense as a carrier sense mixer for generating a difference frequency component between an output signal from the local oscillator for carrier sense and the received signal;
A first switch that switches between the local oscillator for transmission and the local oscillator for carrier sense;
A wireless communication device. An antenna duplexer for guiding a transmission signal from the transmission circuit to an antenna and guiding a reception signal from the antenna to the reception circuit;
A second switch provided between the antenna duplexer and the transmission circuit;
The wireless communication device according to claim 5, further comprising:   The wireless communication apparatus according to claim 5 or 6, further comprising a third switch for switching whether the output signal of the reception mixer is guided to the reception circuit side or the carrier sense circuit side.

Images