Communication terminal device and communication system

Abstract

To provide a communication terminal device that performs wireless communication with an interrogator by backscatter communication, and that maintains a power supply voltage level and prevents intentional state transition from becoming impossible even when radio waves received from the interrogator become unstable.SOLUTION: A communication terminal device includes: a wireless chip that can wirelessly communicate with an interrogator by backscatter communication and generates a power supply voltage from radio waves transmitted from the interrogator; a sensor that is connected to a power supply line to which the power supply voltage output from the wireless chip is supplied and is communicatively connected to the wireless chip; a switch circuit including a first switch whose one end is connected to the power supply line; and a capacitor connected to the other end of the first switch.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The disclosed technology relates to a communication terminal device and a communication system.

Background Art

[0002] As technologies related to wireless tags, the following technologies are known. For example, Patent Document 1 describes a wireless tag having a wireless communication circuit that performs wireless communication with a transceiver via an antenna and whose power is turned on by an electromagnetic wave transmitted from the transceiver. The wireless communication circuit includes a capacitor that charges a charge when the power is turned on, a circuit section that causes a discharge current based on the charge charged in the capacitor to flow through a current path including the antenna when the power is turned off, a monitor circuit that operates by power based on the charge when the power is turned off and determines the presence or absence of degradation based on the potential of a node in the current path, and a storage circuit section that stores the determination result in the monitor circuit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Backscatter communication is a communication method that uses radio wave reflection. When a terminal that has received the radio wave transmitted by an interrogator reflects the radio wave and carries information thereon, it enables information transmission from the terminal to the interrogator. A typical application form of backscatter communication is a passive RFID (Radio Frequency Identification) system. In passive RFID, by obtaining power for driving a terminal (wireless tag) from the radio wave transmitted from the interrogator, it is possible to obtain information from a terminal not equipped with a power source at a distance of about 10 m from the interrogator. Also, a wireless tag with a sensor mounted on the terminal and transmitting sensor information to the interrogator has been put into practical use. In recent years, by also obtaining power for driving the sensor from the radio wave transmitted from the interrogator, sensing without a power source has also been realized.

[0005] In a wireless tag with a sensor, when the radio wave received by the terminal from the interrogator becomes unstable due to fading or the like during the transmission of sensor information to the interrogator, the level of the internal power supply voltage decreases, and an event in which the transmission of sensor information is interrupted often occurs. In order to avoid this problem, it is conceivable to suppress fluctuations in the power supply voltage accompanying radio wave fluctuations by connecting a capacitor to the power supply line to which the power supply voltage is supplied. In the communication protocol of a wireless tag system, the state of the terminal is intentionally transitioned by cutting off the power supply from the interrogator to the terminal. If a capacitor is fixedly connected to the power supply line, there is a possibility that the level of the power supply voltage does not decrease and the intentional state transition of the terminal becomes impossible. Depending on the natural discharge of the capacitor, the level of the power supply voltage may stagnate near the power-on reset level of the terminal, and the terminal may stop responding to commands.

[0006] The disclosed technology has been made in view of the above points, and in a communication terminal device that performs wireless communication with an interrogator by backscatter communication, even when the radio wave received from the interrogator becomes unstable, the level of the power supply voltage is maintained, and an intentional state transition is prevented. The purpose is to avoid becoming impossible.

Means for Solving the Problem

[0007] The communication terminal device according to the disclosed technology is capable of wireless communication with an interrogator by backscatter communication, and includes a wireless chip that generates a power supply voltage from radio waves transmitted from the interrogator, a sensor connected to a power supply line to which the power supply voltage output from the wireless chip is supplied and communicably connected to the wireless chip, a switch circuit including a first switch having one end connected to the power supply line, and a capacitor connected to the other end of the first switch.

[0008] The wireless chip may control the on / off of the first switch based on a command from the interrogator. The wireless chip may control the first switch to be in an on state during a period from the start of sensing by the sensor to the completion of transmission of sensor information acquired by the sensing to the interrogator, and control the first switch to be in an off state during other periods.

[0009] The communication terminal device may further include a discharge circuit including a second switch connected in parallel with the capacitor. When the second switch is in an on state, the charge stored in the capacitor is discharged. The communication terminal device may be configured such that when the first switch is in an on state, the second switch is in an off state, and when the first switch is in an off state, the second switch is in an off state.

[0010] The communication terminal device may further include a soft start circuit including a third switch and a resistance element connected in series to the third switch and connected in parallel with the first switch. When the third switch is in an on state, the capacitor is charged with a charging current smaller than the charging current that flows when the first switch is in an on state.

[0011] The communication terminal device may further include a discharge circuit including a second switch connected in parallel with the capacitor, a third switch, and a resistor element connected in series with the third switch, and a soft start circuit connected in parallel with the first switch. When the second switch is turned on, the charge accumulated in the capacitor is discharged. When the third switch is turned on, the capacitor is charged with a charging current smaller than the charging current that flows when the first switch is turned on.

[0012] The communication terminal device may be configured such that the second switch is turned off when the third switch is turned on, and the second switch is turned on when the third switch is turned off. The wireless chip may control the on / off states of the first switch, the second switch, and the third switch based on a command from the interrogator. The wireless chip may control the third switch to be turned on before controlling the first switch to be turned on.

[0013] The communication system according to the disclosed technology includes an interrogator and a communication terminal device. The communication terminal device is capable of wireless communication with the interrogator by backscatter communication, includes a wireless chip that generates a power supply voltage from radio waves transmitted from the interrogator, a sensor connected to a power supply line to which the power supply voltage output from the wireless chip is supplied and communicably connected to the wireless chip, a switch circuit including a first switch having one end connected to the power supply line, and a capacitor connected to the other end of the first switch.

Effects of the Invention

[0014] According to the disclosed technology, in a communication terminal device that performs wireless communication with an interrogator by backscatter communication, even when the radio waves received from the interrogator become unstable, it is possible to maintain the level of the power supply voltage and avoid the inability to perform an intentional state transition.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8A

Figure 8B

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0016] Hereinafter, an example of an embodiment of the disclosed technology will be described with reference to the drawings. In each drawing, the same or equivalent components and parts are given the same reference numerals, and duplicate descriptions are omitted.

[0017] [First Embodiment] FIG. 1 is a block diagram showing an example of the configuration of a communication system 1 according to a first embodiment of the disclosed technology. The communication system 1 includes an interrogator 20 and a communication terminal device 10. The communication system 1 constitutes a radio tag system in which the interrogator 20 and the communication terminal device 10 can communicate with each other by backscatter communication.

[0018] The communication terminal device 10 includes a wireless chip 11, a sensor 12, a switch circuit 14, and a capacitor 13. The wireless chip 11 is an RFIC (radio frequency integrated circuit) capable of wireless communication with the interrogator 20 by backscatter communication. The wireless chip 11 generates a power supply voltage VDD for driving the wireless chip 11 and the sensor 12 from the radio wave transmitted from the interrogator 20. The power supply voltage VDD is supplied to the sensor 12 via the power supply line L P .

[0019] The sensor 12 is connected to the wireless chip 11 via the signal line L S1 and the power supply line L P . The type of the sensor 12 is not particularly limited, and the sensor 12 may be, for example, an acceleration sensor, a speed sensor, an angle sensor, a pressure sensor, a displacement sensor, a temperature sensor, a magnetic sensor, or an optical sensor. The sensor 12 is driven by the power supply voltage VDD supplied via the power supply line L P . The sensor 12 transmits the information (hereinafter referred to as sensor information I S ) acquired by sensing to the wireless chip 11 via the signal line L S1It is transmitted to the wireless chip 11 via. The communication interface between the sensor 12 and the wireless chip 11 is not particularly limited, but for example, SPI (Serial Peripheral Interface) can be used. The wireless chip 11, based on a command from the interrogator 20, obtains sensor information I S from the sensor 12 and transmits this to the interrogator 20.

[0020] The switch circuit 14 has a first switch SW1 with one end connected to the power line L P and the other end connected to one end of the capacitor 13. The first switch SW1 turns on and off based on a control signal S S2 supplied via a signal line L from the wireless chip 11. The wireless chip 11 controls the on and off of the first switch SW1 by generating a control signal S C1 based on a command from the interrogator 20. C1

[0021] One end of the capacitor 13 is connected to the other end of the first switch SW1 and the other end is connected to the ground line. When the first switch SW1 is in the on state, one end of the capacitor 13 is connected to the power line L P . When the capacitor 13 is connected to the power line L P , fluctuations in the power supply voltage VDD are suppressed. The capacitance of the capacitor 13 is not particularly limited, but is set to an appropriate value that can obtain the effect of suppressing fluctuations in the power supply voltage VDD. For example, by setting the capacitance of the capacitor 13 to 44 μF, it is possible to maintain the operation of the sensor 12 even when the power supply from the interrogator 20 is interrupted for 2 seconds.

[0022] FIG. 2 is a circuit diagram showing an example of the specific configuration of the switch circuit 14. The switch circuit 14 includes P-channel type MOSFETs (hereinafter referred to as P-MOS) 31, 32, an N-channel type MOSFET (hereinafter referred to as N-MOS) 34, and a resistive element 33. The drain of the P-MOS 31 is connected to the power line L Pis connected, the source is connected to the source of P-MOS32, and the gate is connected to the gate of P-MOS32 and the drain of N-MOS34. The drain of P-MOS32 is connected to one end of the capacitor 13. P-MOS31 and 32 constitute the first switch SW1.

[0023] One end of the resistor element 33 is connected to the power supply line L P and the other end is connected to the drain of N-MOS34. The source of N-MOS34 is connected to the ground line, and the gate is connected to the signal line L S2 . A control signal S C1 for controlling the on / off of the first switch SW1 is supplied to the gate of N-MOS34.

[0024] The operation of the communication terminal device 10 will be described below. The wireless chip 11 generates a power supply voltage VDD from the radio wave transmitted from the interrogator 20 and outputs it to the power supply line L P . The wireless chip 11 and the sensor 12 are driven by the power supply voltage VDD.

[0025] When the wireless chip 11 receives a transmission command for sensor information from the interrogator 20, it outputs a high-level control signal S C1 to the signal line L S2 . As a result, N-MOS34, P-MOS31, and 32 are turned on. That is, the first switch SW1 constituting the switch circuit 14 is turned on. As a result, one end of the capacitor 13 is connected to the power supply line L P . The sensor 12 performs sensing based on a command from the wireless chip 11 and transmits the sensor information I S obtained by the sensing to the wireless chip 11 via the signal line L S1 . The wireless chip 11 transmits the sensor information I S acquired by the sensor 12 to the interrogator 20 by backscatter communication.

[0026] Sensor information I SWhen a series of transmissions to the interrogator 20 is completed, the wireless chip 11 outputs a low-level control signal S C1 to the signal line L S2 . As a result, the N-MOS 34 and the P-MOS 31, 32 are turned off. That is, the first switch SW1 is turned off. Thereby, the capacitor 13 is disconnected from the power supply line L P . In this way, from the start of sensing by the sensor 12 to the completion of transmission of the sensor information I S to the interrogator 20, the first switch SW1 is controlled to be in the on state, so that the capacitor 13 is connected to the power supply line L P . In other periods, the first switch SW1 is controlled to be in the off state, so that the capacitor 13 is disconnected from the power supply line L P .

[0027] In a communication terminal device, when the radio wave received from the interrogator becomes unstable due to fading or the like while the sensor information is being transmitted to the interrogator, the level of the internal power supply voltage decreases, and an event in which the transmission of the sensor information is interrupted often occurs. According to the communication terminal device 10 according to the embodiment of the disclosed technology, since the on state of the first switch SW1 is maintained during the period from the acquisition of the sensor information I S to the completion of transmission to the interrogator 20, the capacitor 13 is maintained in a state of being connected to the power supply line L P during this period. Since the capacitor 13 is connected to the power supply line L P , fluctuations in the power supply voltage VDD are suppressed. Therefore, even when the radio wave received by the communication terminal device 10 from the interrogator 20 becomes unstable due to fading or the like, the level of the power supply voltage VDD can be maintained for a certain period. As a result, it is possible to maintain the power supply to the wireless chip 11 and the sensor 12 for a certain period, and the risk of interruption of the transmission of the sensor information I S can be suppressed.

[0028] FIG. 3A and FIG. 3B are voltage waveform diagrams showing an example of the transition of the power supply voltage VDD when the transmission of radio waves from the interrogator 20 is stopped at time t1. FIG. 3A shows the case where the capacitor 13 is not connected to the power supply line L P and FIG. 3B shows the case where the capacitor 13 is connected to the power supply line L P . When the capacitor 13 is not connected to the power supply line L P , when the transmission of radio waves from the interrogator 20 stops, the power supply voltage VDD drops rapidly. In this case, the time from when the transmission of radio waves from the interrogator 20 stops until the power supply voltage VDD reaches the minimum operating voltage of the wireless chip 11 is several hundred milliseconds. On the other hand, when the capacitor 13 is connected to the power supply line L P , when the transmission of radio waves from the interrogator 20 stops, the power supply voltage VDD drops gradually. In this case, by appropriately setting the capacitance of the capacitor 13, the time from when the transmission of radio waves from the interrogator 20 stops until the power supply voltage VDD reaches the minimum operating voltage of the wireless chip 11 can be made about several seconds. Thus, by connecting the capacitor 13 to the power supply line L P , even when the radio waves from the interrogator 20 are interrupted, it is possible to maintain the level of the power supply voltage VDD for a certain period.

[0029] On the other hand, in the communication protocol of the wireless tag system, the state of the communication terminal device 10 is intentionally transitioned by cutting off the power supply from the interrogator 20 to the communication terminal device 10. If the capacitor 13 is fixedly connected to the power supply line L P , there is a possibility that the voltage level of the power supply line L P will not drop, and the intentional state transition of the communication terminal device 10 may become impossible. Depending on the natural discharge of the capacitor 13, the voltage level of the power supply line L P may stagnate near the power-on reset level of the communication terminal device 10, and there is a possibility that the communication terminal device 10 will stop responding to commands.

[0030] According to the communication terminal device 10 according to the embodiment of the disclosed technology, the first switch SW1 connects the capacitor 13 to the power supply line LP It is possible to switch between connection and disconnection. For example, during the period from the acquisition of sensor information I S to the completion of transmission to the interrogator 20, the first switch SW1 is turned on, and in other periods, the first switch SW1 is turned off. Thus, at the timing when an intentional state transition of the communication terminal device 10 occurs, the capacitor 13 can be in a state disconnected from the power line L P This makes it possible to avoid the situation where an intentional state transition of the communication terminal device 10 becomes impossible.

[0031] As described above, according to the communication terminal device 10 according to the embodiment of the disclosed technology, even when the radio wave received from the interrogator 20 becomes unstable, it is possible to maintain the level of the power supply voltage and avoid the situation where an intentional state transition becomes impossible.

[0032] [Second Embodiment] FIG. 4 is a block diagram showing an example of the configuration of a communication terminal device 10A according to a second embodiment of the disclosed technology. The communication terminal device 10A is different from the communication terminal device 10 (see FIG. 1) according to the above-described first embodiment in that it further includes a discharge circuit 15. The discharge circuit 15 has a second switch SW2 connected in parallel with the capacitor 13. When the second switch SW2 is turned on, the charge accumulated in the capacitor 13 is discharged. The second switch SW2 is turned off when the first switch SW1 is turned on, and is turned on when the first switch SW1 is turned off. That is, the first switch SW1 and the second switch SW2 operate with inverse logic.

[0033] FIG. 5 is a circuit diagram showing an example of the specific configuration of the switch circuit 14 and the discharge circuit 15. Since the configuration of the switch circuit 14 is the same as that of the communication terminal device 10 according to the first embodiment (see FIG. 2), the description thereof will be omitted. The discharge circuit 15 includes a resistance element 41 and an N-MOS 42. One end of the resistance element 41 is connected to one end of the capacitor 13, and the other end is connected to the drain of the N-MOS 42. The resistance element 41 functions as a discharge resistor for limiting the discharge current. The source of the N-MOS 42 is connected to the ground line, and the gate is connected to the drain of the N-MOS 34. The second switch SW2 is constituted by the N-MOS 42.

[0034] The operation of the communication terminal device 10A will be described below. When the wireless chip 11 receives a transmission command for sensor information from the interrogator 20, it outputs a high-level control signal S C1 to the signal line L S2 . As a result, the N-MOS 34, P-MOS 31, and 32 are turned on, and the N-MOS 42 is turned off. That is, the first switch SW1 constituting the switch circuit 14 is turned on, and the second switch SW2 constituting the discharge circuit 15 is turned off. When the first switch SW1 is turned on, one end of the capacitor 13 is connected to the power supply line L P . When the second switch SW2 is turned off, the capacitor 13 becomes in a chargeable state. The sensor 12 performs sensing based on a command from the wireless chip 11, and transmits the sensor information I S obtained by the sensing to the wireless chip 11 via the signal line L S1 . The wireless chip 11 transmits the sensor information I S acquired by the sensor 12 to the interrogator 20 by backscatter communication.

[0035] When a series of transmissions of the sensor information I S to the interrogator 20 is completed, the wireless chip 11 outputs a low-level control signal S C1 to the signal line L S2Output to this. As a result, N-MOS 34 and P-MOS 31, 32 are in the off state, and N-MOS 42 is in the on state. That is, the first switch SW1 constituting the switch circuit 14 is in the off state, and the second switch SW2 constituting the discharge circuit 15 is in the on state. When the first switch SW1 is in the off state, the capacitor 13 is disconnected from the power supply line L P Therefrom. When the second switch SW2 is in the on state, the charge accumulated in the capacitor 13 is discharged.

[0036] According to the communication terminal device 10A according to the second embodiment of the disclosed technology, similar to the communication terminal device 10 according to the first embodiment, even when the radio wave received from the interrogator 20 becomes unstable, it is possible to maintain the level of the power supply voltage and avoid the inability of intentional state transition.

[0037] Here, when the capacitor 13 is disconnected from the power supply line L P If there is residual charge in the capacitor 13 when it is disconnected, the power supply voltage VDD may be affected by the residual voltage of the capacitor 13 due to the leakage of the first switch SW1. According to the communication terminal device 10A according to the present embodiment, when the first switch SW1 is in the off state, the second switch SW2 is in the on state, so when the capacitor 13 is disconnected from the power supply line L P Therefrom, the capacitor 13 is discharged. As a result, it is possible to avoid the power supply voltage VDD being affected by the residual voltage of the capacitor 13 when the capacitor 13 is disconnected from the power supply line L P Therefrom. In the present embodiment, a configuration in which both the first switch SW1 and the second switch SW2 are controlled using one control signal S C1 Has been illustrated, but the switch SW1 and the second switch SW2 may be individually controlled using two control signals.

[0038] [Third Embodiment] FIG. 6 is a block diagram showing an example of the configuration of the communication terminal device 10B according to the third embodiment of the disclosed technology. The communication terminal device 10B is different from the communication terminal device 10 (see FIG. 1) according to the first embodiment described above in that it further includes a soft start circuit 16. The soft start circuit 16 is connected in parallel to the first switch SW1. The soft start circuit 16 includes a third switch SW3 and a resistor element R connected in series to the third switch SW3.

[0039] The third switch SW3 turns on and off based on the control signal S C2 supplied from the wireless chip 11. The wireless chip 11 controls the on and off of the third switch SW3 by generating the control signal S C2 based on a command from the interrogator 20. The charging current of the capacitor 13 when the third switch SW3 is on is limited by the resistor element R. Therefore, when the third switch SW3 is turned on, the capacitor 13 is charged with a charging current smaller than the charging current that flows when the first switch SW1 is turned on.

[0040] FIG. 7 is a circuit diagram showing an example of the specific configuration of the switch circuit 14 and the soft start circuit 16. Since the configuration of the switch circuit 14 is the same as that of the communication terminal device 10 according to the first embodiment (see FIG. 2), the description thereof is omitted. The soft start circuit 16 includes a diode 51, a P-MOS 52, resistor elements 53, 54, and an N-MOS 55.

[0041] The diode 51 has its anode connected to the power supply line L P and its cathode connected to the source of the P-MOS 52. The diode 51 functions as a rectifying element that blocks the current flowing from the capacitor 13 to the power supply line L P via the third switch SW3.

[0042] The drain of P-MOS52 is connected to one end of resistor element 53, and the gate is connected to the drain of N-MOS55. P-MOS52 constitutes the third switch SW3. The other end of resistor element 53 is connected to one end of capacitor 13. Resistor element 53 constitutes a resistor R for restricting the charging current. One end of resistor element 54 is connected to the power supply line L P and the other end is connected to the drain of N-MOS55. The source of N-MOS55 is connected to the ground line, and the gate is connected to the signal line L S3 . A control signal S C2 for controlling the on / off of the third switch SW3 is supplied to the gate of N-MOS55.

[0043] The operation of the communication terminal device 10B will be described below. When the wireless chip 11 receives a transmission command for sensor information from the interrogator 20, it outputs a low-level control signal S C1 to the signal line L S2 and a high-level control signal S C2 to the signal line L S3 . The low-level control signal S C1 turns off N-MOS34 and P-MOS31, 32, and the high-level control signal S C2 turns on N-MOS55 and P-MOS52. That is, the first switch SW1 constituting the switch circuit 14 is turned off, and the third switch SW3 constituting the soft start circuit 16 is turned on. As a result, one end of capacitor 13 is connected to the power supply line L P via the resistor R (resistor element 53), and the charging of capacitor 13 is started. Since the charging current at this time is restricted by the resistor R (resistor element 53), it is smaller than the charging current that flows when the first switch SW1 is in the on state.

[0044] When the charging of capacitor 13 is completed, the wireless chip 11 outputs the control signal S C1Transition to a high level. As a result, N-MOS 34 and P-MOS 31, 32 turn on. That is, the first switch SW1 constituting the switch circuit 14 turns on. As a result, one end of the capacitor 13 is connected to the power supply line L P Thereby, the sensor 12 performs sensing based on a command from the wireless chip 11, and transmits sensor information I S obtained by the sensing to the wireless chip 11 via the signal line L S1 . The wireless chip 11 transmits the sensor information I S acquired by the sensor 12 to the interrogator 20 by backscatter communication.

[0045] According to the communication terminal device 10B according to the third embodiment of the disclosed technology, similar to the communication terminal device 10 according to the first embodiment, even when the radio wave received from the interrogator 20 becomes unstable, it is possible to maintain the level of the power supply voltage and avoid the inability to perform an intentional state transition.

[0046] Here, when the capacitor 13 is connected to the power supply line L P , the charging current of the capacitor 13 may become excessive, and as a result, the power supply voltage VDD may decrease and the operation of the wireless chip 11 may become unstable. According to the communication terminal device 10B according to the third embodiment of the disclosed technology, by turning on the third switch SW3 before turning on the first switch SW1, a so-called "soft start" for gently charging the capacitor 13 is realized. Thereby, it is possible to suppress a decrease in the power supply voltage VDD caused by the rush current (charging current) flowing when the capacitor 13 is connected to the power supply line L P .

[0047] FIG. 8A is a voltage waveform diagram showing an example of the transition of the power supply voltage VDD during charging of the capacitor 13 when soft start is not performed. That is, FIG. 8A shows that by turning on the first switch SW1 constituting the switch circuit 14, the capacitor 13 is connected to the power supply line L PIt is the waveform of the power supply voltage VDD when connected to . In this case, at time t2 when the first switch SW1 is in the on state, an excessive charging current flows through the capacitor 13, and the power supply voltage VDD decreases.

[0048] On the other hand, FIG. 8B is a voltage waveform diagram showing an example of the transition of the power supply voltage VDD during charging of the capacitor 13 when soft start is performed. That is, FIG. 8B shows that by turning on the third switch SW3 constituting the soft start circuit 16, the capacitor 13 is connected to the power supply line L P It is the waveform of the power supply voltage VDD when connected to . In this case, the charging current flowing through the capacitor 13 at time t3 when the third switch SW3 is in the on state is smaller than the charging current flowing when the first switch SW1 is in the on state. By suppressing the charging current of the capacitor 13, the decrease in the power supply voltage VDD is suppressed.

[0049] [Fourth Embodiment] FIG. 9 is a block diagram showing an example of the configuration of the communication terminal device 10C according to the fourth embodiment of the disclosed technology. The communication terminal device 10C is different from the communication terminal device 10 (see FIG. 1) according to the first embodiment described above in that it further includes a discharge circuit 15 and a soft start circuit 16. The discharge circuit 15 has a second switch SW2 connected in parallel to the capacitor 13. The soft start circuit 16 is connected in parallel to the first switch SW1. The soft start circuit 16 includes a third switch SW3 and a resistance element R connected in series to the third switch SW.

[0050] The second switch SW2 and the third switch SW3 are turned on and off based on the control signal S C2 supplied from the wireless chip 11. The wireless chip 11, based on a command from the interrogator 20, the control signal S C2By generating, the on / off states of the second switch SW2 and the third switch SW3 are controlled. When the third switch SW3 is in the on state, the second switch SW2 is in the off state, and when the third switch SW3 is in the off state, the second switch SW2 is in the off state. When the second switch SW2 is in the on state, the charge accumulated in the capacitor 13 is discharged. When the third switch SW3 is in the on state, the capacitor 13 is charged with a charging current smaller than the charging current that flows when the first switch SW1 is in the on state.

[0051] FIG. 10 is a circuit diagram showing an example of a specific configuration of the switch circuit 14, the discharge circuit 15, and the soft start circuit 16. Since the configurations of these circuits are the same as those of the communication terminal devices 10, 10A, and 10B according to the above-described first to third embodiments, the description thereof is omitted. In the communication terminal device 10C according to the present embodiment, the gate of the N-MOS 42 constituting the discharge circuit 15 is connected to the gate of the P-MOS 52 and the drain of the N-MOS 55 constituting the soft start circuit 16.

[0052] Hereinafter, the operation of the communication terminal device 10C will be described with reference to FIG. 11. FIG. 11 is a table showing the control signals S C1 , S C2 and the state of the capacitor 13.

[0053] When the communication terminal device 10C is activated, the state of the communication terminal device 10C is set to "standby". In this state, the radio chip 11 outputs a low-level control signal S C1 and outputs a low-level control signal S C2 . Due to the low-level control signal S C1 , the N-MOS 34, the P-MOS 31, and 32 are in the off state, and due to the low-level control signal S C2As a result, N-MOS55 and P-MOS52 are in the off state, and N-MOS42 is in the on state. That is, the first switch SW1 that constitutes the switch circuit 14 is in the off state, the second switch SW2 that constitutes the discharge circuit 15 is in the on state, and the third switch SW3 that constitutes the soft start circuit 16 is in the off state. Thereby, the capacitor 13 is disconnected from the power line L P and the capacitor 13 is discharged. The "standby" state is a state in which an intentional state transition of the communication terminal device 10C is possible.

[0054] When the communication terminal device 10C receives a sensor information transmission command from the interrogator 20, the state of the communication terminal device 10C transitions to "sensor information transmission preparation". In this state, the wireless chip 11 transitions the control signal S C2 to a high level. As a result, N-MOS55 and P-MOS52 are in the on state, and N-MOS42 is in the off state. That is, the second switch SW2 that constitutes the discharge circuit 15 is in the off state, and the third switch SW3 that constitutes the soft start circuit 16 is in the on state. Thereby, charging of the capacitor 13 by the soft start circuit 16 is started. That is, the capacitor 13 is charged with a charging current smaller than the charging current that flows when the first switch SW1 is in the on state.

[0055] When the charging of the capacitor 13 is completed, the state of the communication terminal device 10C transitions to "during sensor information transmission". In this state, the wireless chip 11 transitions the control signal S C1 to a high level. As a result, N-MOS34 and P-MOS31, 32 are in the on state. That is, the first switch SW1 that constitutes the switch circuit 14 is in the on state. Thereby, the capacitor 13 is connected to the power line L P via the first switch SW1. The sensor 12 performs sensing based on a command from the wireless chip 11, and transmits the sensor information I S acquired by the sensing to the wireless chip 11 via the signal line L S1 . The wireless chip 11 receives the sensor information I Sis transmitted to the interrogator 20 by backscatter communication. Since the capacitor 13 is connected to the power line L P fluctuations in the power supply voltage VDD are suppressed. Therefore, even when the radio wave received from the interrogator 20 becomes unstable due to fading or the like, the level of the power supply voltage VDD can be maintained for a certain period, and the risk of interruption of the transmission of the sensor information I S is suppressed.

[0056] When a series of transmissions of the sensor information I S to the interrogator 20 is completed, the state of the communication terminal device 10C transitions to "sensor information transmission completed". In this state, the wireless chip 11 transitions the control signal S C1 to a low level. As a result, N-MOS34, P-MOS31, and 32 are turned off. That is, the first switch SW1 constituting the switch circuit 14 is turned off. This state is the same as the above-described "sensor information transmission preparation" state.

[0057] Thereafter, the state of the communication terminal device 10C transitions to "standby". In this state, the wireless chip 11 transitions the control signal S C2 to a low level. As a result, N-MOS55 and P-MOS52 are turned off, and N-MOS42 is turned on. That is, the second switch SW2 constituting the discharge circuit 15 is turned on, and the third switch SW3 constituting the soft start circuit 16 is turned off. As a result, the capacitor 13 is disconnected from the power line L P and the capacitor 13 is discharged.

[0058] According to the communication terminal device 10C according to the fourth embodiment of the disclosed technology, similar to the communication terminal device 10 according to the first embodiment, even when the radio wave received from the interrogator 20 becomes unstable, the level of the power supply voltage is maintained, and it is possible to avoid the inability to perform an intentional state transition. Further, due to the action of the discharge circuit 15, the capacitor 13 is disconnected from the power line L PWhen disconnected, it is possible to avoid the power supply voltage VDD being affected by the residual voltage of the capacitor 13. Further, due to the action of the soft start circuit 16, when connecting the capacitor 13 to the power supply line L P the charging current of the capacitor 13 is suppressed, and a decrease in the power supply voltage VDD due to the rush current is suppressed.

[0059] Regarding the above first to fourth embodiments, the following supplementary notes are further disclosed. (Supplementary Note 1) A wireless chip capable of wireless communication with an interrogator by backscatter communication and generating a power supply voltage from radio waves transmitted from the interrogator, a sensor connected to a power supply line to which the power supply voltage output from the wireless chip is supplied and communicably connected to the wireless chip, a switch circuit including a first switch having one end connected to the power supply line, a capacitor connected to the other end of the first switch, and a communication terminal device having the same.

[0060] (Supplementary Note 2) The wireless chip controls the on / off of the first switch based on a command from the interrogator The communication terminal device according to Supplementary Note 1.

[0061] (Supplementary Note 3) The wireless chip controls the first switch to be in the on state during the period from the start of sensing by the sensor to the completion of a series of transmissions of sensor information obtained by the sensing to the interrogator, and controls the first switch to be in the off state during other periods The communication terminal device according to Supplementary Note 1 or Supplementary Note 2.

[0062] (Supplementary Note 4) The device further includes a discharge circuit including a second switch connected in parallel with the capacitor, and when the second switch is in the on state, the charge stored in the capacitor is discharged The communication terminal device according to any one of Appendices 1 to 3.

[0063] (Appendix 5) When the first switch is in the on state, the second switch is in the off state, and when the first switch is in the off state, the second switch is in the off state The communication terminal device according to Appendix 4.

[0064] (Appendix 6) Including a third switch and a resistance element connected in series to the third switch, and further having a soft start circuit connected in parallel to the first switch, When the third switch is in the on state, the capacitor is charged with a charging current smaller than the charging current that flows when the first switch is in the on state The communication terminal device according to any one of Appendices 1 to 5.

[0065] (Appendix 7) A discharge circuit including a second switch connected in parallel to the capacitor, Including a third switch and a resistance element connected in series to the third switch, and further having a soft start circuit connected in parallel to the first switch, When the second switch is in the on state, the charge stored in the capacitor is discharged, When the third switch is in the on state, the capacitor is charged with a charging current smaller than the charging current that flows when the first switch is in the on state The communication terminal device according to any one of Appendices 1 to 3.

[0066] (Appendix 8) When the third switch is in the on state, the second switch is in the off state, and when the third switch is in the off state, the second switch is in the on state The communication terminal device according to Appendix 7.

[0067] (Appendix 9) The wireless chip controls the on / off states of the first switch, the second switch, and the third switch based on a command from the interrogator. The communication terminal device according to appendix 7 or appendix 8.

[0068] (Appendix 10) Before controlling the first switch to the on state, the wireless chip controls the third switch to the on state. The communication terminal device according to any one of appendices 7 to 9.

[0069] (Appendix 11) A communication system including an interrogator and a communication terminal device, wherein the communication terminal device is capable of wireless communication with the interrogator by backscatter communication, and includes a wireless chip that generates a power supply voltage from radio waves transmitted from the interrogator, a sensor connected to a power supply line supplied with the power supply voltage output from the wireless chip and communicably connected to the wireless chip, a switch circuit including a first switch having one end connected to the power supply line, a capacitor connected to the other end of the first switch, and having a communication system.

Explanation of symbols

[0070] 1 Communication system 10, 10A, 10B, 10C Communication terminal device 11 Wireless chip 12 Sensor 13 Capacitor 14 Switch circuit 15 Discharge circuit 16 Soft start circuit 20 Interrogator

Claims

1. A communication terminal device having a wireless chip capable of wireless communication with an interrogator by backscatter communication and generating a power supply voltage from radio waves transmitted from the interrogator, a sensor connected to a power supply line to which the power supply voltage output from the wireless chip is supplied and communicably connected to the wireless chip, a switch circuit including a first switch having one end connected to the power supply line, a capacitor connected to the other end of the first switch, and having the above components.

2. The wireless chip controls the on / off of the first switch based on a command from the interrogator. The communication terminal device according to Claim 1.

3. The wireless chip controls the first switch to be in the on state during a period from the start of sensing by the sensor to the completion of a series of transmissions of sensor information obtained by the sensing to the interrogator, and controls the first switch to be in the off state during other periods. The communication terminal device according to Claim 1.

4. The communication terminal device further includes a discharge circuit including a second switch connected in parallel with the capacitor, and when the second switch is turned on, the charge accumulated in the capacitor is discharged. The communication terminal device according to Claim 1.

5. When the first switch is in the on state, the second switch is in the off state, and when the first switch is in the off state, the second switch is in the off state. The communication terminal device according to Claim 4.

6. The communication terminal device further includes a soft start circuit including a third switch and a resistance element connected in series to the third switch and connected in parallel with the first switch, and when the third switch is turned on, the capacitor is charged with a charging current smaller than the charging current that flows when the first switch is turned on. The communication terminal device according to Claim 1.

7. a discharge circuit including a second switch connected in parallel with the capacitor, a soft start circuit including a third switch and a resistance element connected in series to the third switch and connected in parallel with the first switch, when the second switch is turned on, the charge accumulated in the capacitor is discharged, when the third switch is turned on, the capacitor is charged with a charging current smaller than the charging current that flows when the first switch is turned on. The communication terminal device according to Claim 1.

8. When the third switch is in the on state, the second switch is in the off state, and when the third switch is in the off state, the second switch is in the on state. The communication terminal device according to claim 7.

9. The wireless chip controls the on / off states of the first switch, the second switch, and the third switch based on a command from the interrogator. The communication terminal device according to claim 7.

10. Before controlling the first switch to the on state, the wireless chip controls the third switch to the on state. The communication terminal device according to claim 7.

11. A communication system including an interrogator and a communication terminal device, wherein the communication terminal device is capable of wireless communication with the interrogator by backscatter communication, and includes a wireless chip that generates a power supply voltage from radio waves transmitted from the interrogator, a sensor connected to a power supply line to which the power supply voltage output from the wireless chip is supplied and communicably connected to the wireless chip, a switch circuit including a first switch having one end connected to the power supply line, a capacitor connected to the other end of the first switch, and has a communication system.

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