Non-contact data carrier system

Abstract: A non-contact data carrier includes a battery (29), an electric-supply circuit (4) for rectifying a received carrier signal and generating power, and an electric-supply switching circuit (9) for comparing the voltage of the battery and the voltage generated by the electric-supply circuit and selecting either one of the voltages. When the battery (29) can supply power, long-distance communication can be performed by supplying power from the battery. In case of battery exhaustion, power is supplied from the electric-supply circuit (4) which receives a stronger carrier signal by using the non-contact IC card in the proximity of a question unit and rectifies the carrier signal, so that the function of the non-contact data carrier is maintained.

Description: BACKGROUND OF THE INVENTION The present invention relates to a non-contact data carrier system, for communicating by use of a radio wave, for uses for verification of various IDs, financial trading and control of a door lock of a car, and a non-contact data carrier used for the same. A non-contact IC card as an example of the non-contact data carrier has a convenience that it is unnecessary to insert the non-contact IC card into a slot of a reader/writer as well as features of normal IC cards having a large storage capacity and a high-degree security function. Therefore, the non-contact IC card is a product of which a great market can be expected not only as a commuter ticket of public transportation and a ticket for a ski lift but also as a room entry/exit card for opening or closing a door and a card for electronic money. Such a non-contact IC card performs information transmission and reception with a question unit by use of a medium such as a radio wave. Power necessary for operation of a control circuit and a memory of the non-contact IC card is obtained from a battery incorporated in the card or by rectifying, by a radio wave transmitted from the question unit, an induced current generated due to mutual induction of a coil provided in the non-contact IC card. Fig. 4 is a block diagram showing the configuration of a conventional non-contact IC card which operates on power supplied from a battery 29. A main circuit unit 13 of the non-contact IC card comprises a reset circuit 5, a demodulation circuit 6, a modulation circuit 7 and a memory 12. The main circuit unit 13 further comprises a control circuit 11 for controlling the above-mentioned circuits and performing reading from and writing to the memory 12 in accordance with the contents of a signal transmitted from a question unit (not shown). A transmitter-receiver 1 comprising an antenna and a tuning circuit (both are not shown) receives a radio signal transmitted from the question unit. A carrier signal detection circuit 3 compares the level of the received signal and a reference level preset in the carrier signal detection circuit 3. When the level of the received signal is higher than the reference level, a switching circuit 8 goes into on state, so that power is supplied from a battery 29 to the main circuit unit 13. As a result, the non-contact IC card operates. When the level of the received signal is not higher than the reference level, the non-contact IC card does not operate and goes into sleep state which is the state only to receive and detect a signal which will be again transmitted from the question unit. In the non-contact IC card having the switching circuit 8, power is supplied to the circuit components only when a carrier signal from the question unit is detected. Therefore, when no carrier signal is transmitted from the question unit, that is, when information transmission and reception is not performed between the non-contact IC card and the question unit, only the carrier signal detection circuit 3 consumes power, so that power consumption is reduced. The above-mentioned non-contact IC card uses an internal battery 29 as the power source and the power necessary for operation of the non-contact IC card is supplied from the battery 29. On the other hand, in a non-contact IC card which uses induced electromotive force generated at a coil incorporated in the non-contact IC card, rectified induced-electromotive-force is stored and the stored force is used for operation of the non-contact IC card. Therefore, the induced electromotive force generated in the coil decreases corresponding to increase of the distance between the non-contact IC card and the question unit. In order to prevent the induced electromotive force from decreasing, it is necessary to use the non-contact IC card in the proximity of the question unit at the time of communication. That is, in the latter non-contact IC card, the longer the distance between the question unit and the non-contact card is, the lower the value of the induced electromotive force is, so that it is difficult to ensure the power necessary for operation. On the contrary, in the former non-contact IC card, since stable power is supplied from the battery 29, long-distance communication can be performed. Generally, the convenience of the non-contact IC card is influenced by a communication-possible distance between the question unit and the non-contact IC card. By increasing the communication distance between the non-contact IC card and the question unit, the non-contact IC card can be used at a position remote from the question unit, and thus the convenience is improved. The non-contact IC card in which power is supplied from a battery is excellent in convenience because a long communication distance can be ensured compared with the non-contact IC card using the induced electromotive force. However, since the battery is required for operation, the non-contact IC card becomes inoperable when the capacity of the battery is low, that is, when the battery is exhausted. As described above, when the non-contact IC card is in sleep state, only the carrier signal detection circuit 3 is actuated for detecting a signal from the question unit. Therefore the power consumption is reduced. However, slight power is still consumed. Consequently, the battery is exhausted when the non-contact IC card is used for a long time. Normally, the non-contact IC card does not have means for displaying the remaining capacity of the internal battery, so that it is impossible for the user of the non-contact IC card to predict battery exhaustion. For this reason, the non-contact IC card is hardly used for important work or for recording important data. When the battery is exhausted, the use of the non-contact IC card cannot be continued unless a replacement battery is at hand. Even if a battery is available, a tool such as a screwdriver is necessary for battery replacement, so that it is very difficult to replace the battery in a short time to use again the non-contact IC card. GB-A- 2 292 866 discloses the features in the preamble of the claim. In this prior art a card is usually in a standby state or a low-power state in which the operation of a clock is stopped and thus the operation of a CPU is also stopped thereby reducing the consumption of a primary battery. These standby state and low-power state are set by an end command which is included in a received signal. Both the standby state and low-power state are not set by decrease of a received signal level. Therefore, both the standby state and low-power state are different from a sleep state. When the card receives a signal via the antenna from an external device such as a reader/writer, the card starts its operation. At the same time, the voltage of the electromagnetic wave carrying the signal is rectified by the rectifier circuit and stored in the storage capacitor. The voltage across the storage capacitor is compared with the voltage of the primary battery, and a voltage higher than the other is used to supply electric power to the internal circuits. In the card, the built-in primary battery is used only for backup of data stored in the RAM composed of SRAM during the standby state, as long as the electromagnetic wave is sufficiently strong. Therefore, only little power consumption occurs in the standby state. Furthermore, even in the case where the electromagnetic wave is weak, the card can operate using the primary battery. When the card is remote outside a communication range from the reader/writer which sends the end command to the card, the card cannot receive the end command. Consequently, the card does not turn to the standby state and futile power consumption of the battery is continued. In EP-A-0 697 680 there is taught a start-up signal of a prescribed time interval sent periodically from a fixed transceiver. The signal received from an antenna is detected and amplified in a mobile transceiver and then compared with a reference value of a prescribed level to allow discrimination. A pulse signal is generated with a pulse width corresponding to the level of the received signal. The pulse signal is converted into a start discriminator pulse signal of fixed pulse width and integrated. When the integrated value exceeds a prescribed reference start-up value, the mobile transceiver is determined to have entered an area where communication is possible with the fixed transceiver, and the internal circuitry of the mobile transceiver is started. US patents 5,317,309 and 5,519,386 disclose a non-contact data carrier where the battery voltage is compared with the voltage of an electric supply means to conserve the battery. US 5,519,386 also suggests the use of such a card in a car (opening the doors of a vehicle). A non-contact hand-held carrier with a question unit in the car and control means connected to lock control means for switching a door lock condition is known from US - A - 4,737,784. This patent also suggests to include a sensor in the door handle. An object of the present invention is to prevent trouble caused by battery exhaustion of the non-contact IC card while maintaining the convenience that long-distance communication can be performed. BRIEF SUMMARY OF THE INVENTION This problem is solved by the invention as defined in the claim. According to the above-described configuration, when the battery is capable of supplying-power, power is supplied from the battery, so that long-distance communication is realizable. In case of battery exhaustion, power is supplied by induced electromotive force from the question unit by using the non-contact data carrier in the proximity of the question unit, so that the function of the non-contact data carrier can be maintained. Moreover, in the non-contact data carrier the level of the carrier signal and a predetermined reference level are compared with each other by the carrier signal detection means. When the level of the carrier signal is higher than the reference level, the switching means goes into on state. When the switching means is in on state, the voltage value of the battery and the value of the voltage generated by the electric-supply means are compared. When the voltage value of the battery is higher than the value of the generated voltage, power of the battery is output to the main circuit unit by the electric-supply switching means. Moreover, the voltage of the electric-supply means obtained by the received signal and the battery voltage are compared with each other. When the voltage obtained by the received signal is higher than the battery voltage, the power supply from the battery is stopped. When the voltage obtained by the received signal is lower, power is supplied from the battery. Thereby, the power consumption of the battery of the non-contact data carrier is reduced, the battery life is increased. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING FIG. 1 is a block diagram showing a circuit configuration of a non-contact IC card according to a first embodiment of a non-contact data carrier system of the present invention; FIG. 2 is a circuit diagram showing a concrete example of the non-contact IC card according to the first embodiment of the present invention; FIG. 3 is a flowchart showing an operation of the non-contact IC card according to the first embodiment of the present invention; FIG. 4 is the block diagram showing the circuit configuration of the conventional non-contact IC card. DETAILED DESCRIPTION OF THE INVENTION A non-contact IC card according to an embodiment of the non-contact data carrier system of the present invention will be described with reference to FIG. 1 to FIG. 3. FIG. 1 is a block diagram of the non-contact IC card according to this embodiment. In FIG. 1, the non-contact IC card comprises a transmitter-receiver 1 for receiving a carrier signal from a question unit (not shown) provided in a fixed apparatus of the non-contact data carrier system and for returning to the question unit a result of processing performed by the non-contact IC card side on the information transmitted from the question unit. The transmitter-receiver 1 has, for example, an antenna and a tuning circuit (not shown). The non-contact IC card further comprises a rectifier 2 connected to terminals 101, 102 of the transmitter-receiver 1 for rectifying the received carrier signal, and a carrier signal detection circuit 3 for comparing the output signal level of the transmitter-receiver 1 with a predetermined reference level. The non-contact IC card further comprises a switching circuit 8 for supplying power from a battery 29 to a main circuit unit 13 in accordance with a result of the comparison, and an electric-supply circuit 4 connected to the rectifier 2 for storing the rectified direct-current power, converting it into a voltage to be supplied to the main circuit unit 13 and outputting the voltage. The non-contact IC card comprises an electric-supply switching circuit 9 for comparing the output voltage of the electric-supply circuit 4 and the output voltage of the battery 29 supplied by way of the switching circuit 8, and for switching in accordance with the comparison result the power source which supplies power to the main circuit unit 13. The main circuit unit 13 comprises a reset circuit 5 for initializing the circuit by resetting it when a voltage supplied from the electric-supply switching circuit 9 reaches a predetermined value at the time of rise of the voltage. The main circuit unit 13 further comprises a demodulation circuit 6 for demodulating a received signal, a modulation circuit 7 for modulating transmission data, and a memory 12 for holding data. These circuit blocks are connected to a control circuit 11. Subsequently, an operation of the non-contact IC card will be described in detail in accordance with the flow of the signal transmitted from the question unit. The carrier signal from the question unit is received by the transmitter-receiver 1 comprising the antenna. The received carrier signal is input to the carrier signal detection circuit 3, and the level of the carrier signal is compared with a reference level that is preset in the detection circuit 3. When the level of the carrier signal is higher than the reference level, the switching circuit 8 goes into on state, so that the voltage of the battery 29 is supplied to the main circuit unit 13. When the supplied voltage reaches a predetermined level, the reset circuit 5 is actuated, so that the non-contact IC card is initialized. The received carrier signal is rectified by the rectifier 2, and is inputted to the electric supply circuit 4. A direct-current voltage is output from the electric supply circuit 4. The electric-supply switching circuit 9 compares the value of the voltage of the battery 29 supplied by way of the switching circuit 8 and the value of the voltage supplied from the electric-supply circuit 4. When the voltage applied from the battery 29 is higher than the voltage supplied from the electric-supply circuit 4, power is supplied from the battery 29 to the main circuit unit 13 like in the conventional non-contact IC card incorporating a battery. Since the battery 29 outputs a stable voltage, the non-contact IC card can operate even when the question unit is away from the non-contact IC card. When the voltage of the battery 29 lowers and the value of the voltage input from the electric-supply circuit 4 is higher than the value of the voltage of the battery 29, power is supplied from the electric-supply circuit 4 to the main circuit unit 13 through the electric supply switching circuit 9. According to this configuration, the power supplied from the electric-supply circuit 4 is used to operate the non-contact IC card in the proximity of the question unit so that a strong radio wave is received. Therefore, operation of the use of the non-contact IC card can be continued even when the battery voltage is low, for example, when the power of the battery is exhausted. The received signal is also supplied to the demodulation circuit 6, so that the data included in the signal are demodulated. The demodulated data are analyzed at the control circuit 11. In accordance with the data, the control circuit 11 performs data-reading from the memory 12 and data-writing to the memory 12. Further, the control circuit 11 produces data to be returned to the question unit and inputs the data to the modulation circuit 7. At the modulation circuit 7, the return data are modulated. The modulated data are transmitted from the transmitter-receiver 1 to the question unit. Communication between the question unit and the non-contact IC card is performed through such a signal flow. The output voltage of the electric-supply circuit 4 varies according to the distance between the non-contact IC card and the question unit. When the non-contact IC card is close to the question unit, the transmitter-receiver 1 receives a strong radio wave, and therefore the output voltage of the electric-supply circuit 4 is high. When the output voltage of the electric-supply circuit 4 becomes much higher than the voltage of the battery 29, a very high output voltage is applied to the main circuit unit 13 through the electric-supply switching circuit 9, so that there is a possibility that devices in the main circuit unit 13 are damaged. To prevent such damage, the electric-supply circuit 4 has a part for safely controlling the voltage output to the electric-supply switching circuit 9. In the case that the voltage supplied from the electric-supply circuit 4 reaches a voltage value necessary for driving the non-contact IC card, power from the electric-supply circuit 4 may be supplied to the main circuit unit 13 instead of power from the battery 29. When the non-contact IC card is close to the question unit, the output voltage of the electric-supply circuit 4 is high. In this case, the electric-supply switching circuit 9 switches the power source from the battery 29 to the electric-supply circuit 4. According to this configuration, the internal battery can be effectively used, so that the power consumption of the battery can be saved. Further, in a writing operation to the memory 12 at which the power consumption increases and in transitional state where the power source is switched between the electric-supply circuit 4 and the battery 29, power is immediately supplied from the battery 29 when the output voltage of the electric-supply circuit 4 lowers. Therefore, reliability is improved in important processing such as writing to a memory. The carrier signal detection circuit 3, switching circuit 8 and electric-supply switching circuit 9 included in the non-contact IC card of the present invention may be formed on a semiconductor chip constituting the main circuit unit 13. Operation of these circuits can be realized by control by a microcomputer. FIG. 2 shows a concrete example for realizing the carrier signal detection circuit 3, the switching circuit 8 and the electric-supply switching circuit 9 in simpler circuit configurations in order to reduce the cost and the size of the circuit components incorporated in the non-contact IC card. This example will hereinafter be described in comparison with FIG. 1. In FIG. 2, the carrier signal detection circuit 3 of FIG. 1 comprises a low-power-consumption comparator 23. The switching circuit 8 of FIG. 1 comprises a FET (field effect transistor) 21, and the electric-supply switching circuit 9 comprises a diode 28. To the two input terminals of the comparator 23, the voltage of the signal rectified by the rectifier 2 and the voltage from the battery 29 are input. These voltages are compared by the comparator 23. By adjusting the value of a resistor 22 connected across the positive output of the battery 29 and the noninverting input terminal of the comparator 23, the level of the voltage inverted by the comparator 23 is set, so that a signal level to activate the non-contact IC card is decided. The output terminal of the comparator 23 is connected to the gate of the FET 21. When the output terminal is at high level, the FET 21 turns ON. At this time, power of the battery 29 is supplied to a main circuit unit 13 which is similar to that of FIG. 1. In the case that the electric-supply switching circuit 9 of FIG. 1 comprises the diode 28 like in FIG. 2, the set voltage for switching is a value obtained by subtracting the forward voltage of the diode 28 from the voltage of the battery 29. FIG. 3 is a flowchart of signal level comparison operation performed in the non-contact IC card of the present invention shown in FIG. 1. The signal received at step 41 is converted into a direct-current voltage at step 42 and compared with the preset reference level by the carrier signal detection circuit 3 (step 43). When the level of the received signal is higher than the reference level, the switching circuit 8 turns ON at step 44 and the process proceeds to the next step 46. When the level of the signal is lower than the reference level, the switching circuit 8 stays in OFF state as shown at step 45, so that the non-contact IC card goes into sleep state. Thereafter, the power is supplied only when there is a call from the question unit. Then, at step 46, the power source for operation of the non-contact IC card is decided. The direct-current voltage obtained by rectifying the received signal is compared with the output voltage of the battery 29. When the output voltage of the battery 29 is higher, the electric-supply path is switched to that of the battery 29, so that power from the battery 29 is supplied to the main circuit unit 13 (step 47). When the output voltage from the electric-supply circuit 4 is equal to or higher than the output voltage of the battery 29, the electric-supply switching circuit 9 switches the power supply path to that of the electric-supply circuit 4. This stops the power supply from the battery 29, so that the non-contact IC card is operated by the power supplied from the electric-supply circuit 4 (step 48). Although a transmitter and a receiver are integrated into the transmitter-receiver 1 in the above description, it is needless to say that similar effects are obtained when a transmitter and a receiver are separately provided. As described above, according to the non-contact IC card of the present invention, since stable power is supplied from the internal battery, communication can be performed even when the IC card is away from the question unit. Thus, the non-contact IC card of the present invention is convenient. Furthermore, even when the power of the battery is exhausted, the non-contact IC card is still usable by receiving the power in electromagnetic wave from the question unit by bringing the non-contact IC card close to the question unit. Further, when the non-contact IC card is used at a location close to the question unit, an advantageous effect extending the battery life is obtained, because the power of the battery is not used.

Claims: A non-contact data carrier comprising: transmission-reception means (1) for performing data transmission and data reception with a question unit (20); carrier signal detection means (3) for detecting a carrier signal included in the data transmitted from said question unit (20); a demodulation circuit (6) for demodulating said carrier signal; a modulation circuit (7) for modulating transmission data to be transmitted to said question unit (20); a memory (12) for holding data; an internal battery (29); a control circuit (11) for controlling said modulation circuit (7) and said memory (12), said control circuit (11) receiving an output of said demodulation circuit (6); electric-supply means (2, 4) for rectifying said carrier signal and generating a voltage; and electric-supply switching means (9) to which an output of said electric-supply means (2, 4) and an output of a further switching means (8) are input, said electric-supply switching means (9) comparing a voltage value of said battery (29) and a voltage value of said electric-supply means (2, 4), and switching said electric-supply switching means (9) to said electric-supply means (2, 4) when the voltage value of said electric-supply means (2, 4) is higher than the voltage value of said battery (29), characterized in that said further switching said means (8) supplies the power of said internal battery (29) to the non-contact data carrier when said carrier signal is detected; and said carrier signal detection means (3) compares the level of said carrier signal with a predetermined level and the non-contact data carrier is brought into a sleep state in which, when the level of said carrier signal is lower than said predetermined level, an electric power is only supplied to said carrier signal detection means (3) and the further switching means (8).

Inventors: ASAKA NOBUYOSHI, IIYAMA KEIICHI, ASAKA, NOBUYOSHI, IIYAMA, KEIICHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1998
Main classification: G06K7
IPC codes: G06K19, G07C9, B60R25