Noncontact integrated circuit card.

BACKGROUND OF THE INVENTION

Field of the Invention

0001The present invention relates to a noncontact integrated circuit (IC) card, and more particularly to a noncontact IC card which is capable of restricting the amount of electric power consumed while waiting to receive signals.

Description of the Related Art

0002In recent years, a noncontact IC card, which does not have an external electrode on the surface thereof, has been the most remarkable among the many kinds of IC cards produced. Though the noncontact IC card transmits and receives signals to and from an external device in the same manner as a normal IC card which has an external electrode, the transmission and receiving are performed by using a space transmission medium, such as electromagnetic wave, light, magnetism and so on.

0003A structure of a conventional noncontact IC card is shown in Fig.5. A ROM 2 and a RAM 3 are connected through a bus 8 to a CPU 1 which controls operations of the IC card. Connected to the bus 8 is an input-output control circuit 4 which controls input and output of data to and from an external device and connected to the input-output control circuit 4 through a modem circuit 5 is an antenna 6.

0004Furthermore, a battery 7 is contained in the IC card so as to supply electric power to each electric circuit.

0005In such an IC card, if the antenna 6 receives a request signal in the form of electromagnetic wave from the external device, the request signal is input to the CPU 1 through the input-output control circuit 4 after being demodulated in the modem circuit 5. The CPU 1 decodes the request signal and produces a predetermined response signal. The response signal is input to the modem circuit 5 through the input-output control circuit 4, modulated, and then transmitted to the external device from the antenna 6.

0006However, it is required that the CPU 1, the modem circuit 5 and so on always be operated on standby so that the IC card receives and processes the request signal from the external device. Therefore, electric power is always being consumed in order to operate the CPU 1, the modem circuit 5 and so on, and this causes a problem in that the electric power supplied by the contained battery 7 is rapidly consumed.

0007French patent specification FR-A-2 604 808 discloses a noncontact IC card comprising data transmit-receive means, detection means for detecting a trigger signal from a receive signal, data process means connected to the data transmit-receive means and a battery. The power is supplied to the main circuit only after the detection means have detected an external trigger signal. This measure is carried out for power saving means.

0008European patent specification EP-A-256594 concerns portable equipment comprising data processing means, clock generating means, data transmit-receive means, and detection means. The clock generating means are actuated when the detection means detects a trigger signal.

SUMMARY OF THE INVENTION

0009The present invention is intended to solve the above problem and an object of the present invention is to provide a noncontact IC card which can with certainty receive and process a request signal from an external device while restricting the consumption of the electric power supplied by the battery contained in the IC card.

0010According to the present invention there is provided a noncontact IC card, comprising: data transmit-receive means for transmitting and receiving data to and from outside in a noncontact manner; detection means for detecting a trigger signal from a signal received by said data transmit-receive means; data process means connected to said data transmit-receive means for processing data and transmitting a response signal when said data transmit-receive means receives a trigger signal; clock generating means for supplying a clock signal to said data process means; actuating means for actuating said clock generating means when said detection means detects said trigger signal; first stop means for stopping said clock generating means after said data process means input a clock signal from said clock generating means actuated by said actuating means and executes a predetermined process; and a battery for supplying electric power; characterised in that it further comprises measuring means for measuring the time lapsed from when said data process means transmits said response signal through said data transmit-receiving means until said data transmit-receive means receives subsequent data; and second stop means for stopping said clock generating means when the time measured by said measuring means exceeds a predetermined value.

0011In the noncontact IC card of the present invention, when the detection means detects the trigger signal from the received signal, the clock generating means is actuated by the actuating means and the clock signal is supplied to the data process means.

0012In the noncontact IC card of an embodiment of the invention, in addition, after the data process means executes a predetermined process, the first stop means stops the clock generating means.

0013Furthermore, in the noncontact IC card of still another embodiment, after the data process means executes a predetermined process, the first stop means stops the clock generating means, and if the time required from when the data process means transmits a response signal till the data transmit-receive means receives subsequent data exceeds a predetermined value, the second stop means stops the clock generating means.

BRIEF DESCRIPTION OF THE DRAWINGS

0014<ul id="ul0001" list-style="none"><li>Fig.1 is a block diagram showing a structure of a noncontact IC card according to an embodiment of the present invention;</li><li>Fig.2 is a block diagram showing an internal structure of a demodulation circuit;</li><li>Fig.3 is a block diagram showing an internal structure of a clock generating circuit;</li><li>Fig.4 is a flowchart showing operations of the embodiment; and</li><li>Fig.5 is a block diagram showing a structure of a conventional noncontact IC card.</li></ul>

DESCRIPTION OF THE PREFERRED EMBODIMENTS

0015Referring to the accompanying drawings, preferred embodiments of the present invention will be hereinafter described.

0016As shown in Fig.1, a noncontact IC card according to an embodiment of the present invention contains an IC 10, and connected to the IC 10 are an antenna circuit 16, a battery 17 and a crystal oscillator 19. The IC 10 comprises a CPU 11 connected to a bus 18. Connected to the bus 18 are a ROM 12 for storing a program for controlling operations of the CPU 11, a RAM 13 for storing data and an input-output control circuit 14 for controlling input and output of data from and to an unillustrated external device. Furthermore, a timer 20, for dividing and counting an internal clock, and a prescaler 21, for setting an initial value of the timer 20, are connected to the bus 18.

0017The input-output control circuit 14 comprises a UART 22 for executing serial asynchronous data transmission, a baud rate generator 23 for setting transmission rate of the UART 22, and a carrier generator 24 for generating a carrier. A modem circuit 15 is connected to the input-output control circuit 14 and the antenna circuit 16 is connected to the modem circuit 15. The modem circuit 15 comprises a modulation circuit 25 for modulating output of the UART 22 by a carrier, a demodulation circuit 26 for demodulating an input signal from the antenna circuit 16, and output transistors 27 and 28 for driving the antenna circuit 16.

0018Furthermore, a clock generating circuit 29 for supplying a clock signal to each circuit in the IC 10 is connected to the CPU 11 and the demodulation circuit 26 in the modem circuit 15. The clock generating circuit 29 is connected to the crystal oscillator 19 outside of the IC 10. 30 denotes a monitor timer for monitoring runaway of the CPU 11.

0019The modem circuit 15 and the antenna circuit 16 constitute a data transmit-receive means, the CPU 11 constitutes a data process means, the crystal oscillator 19 and the clock generating circuit 29 constitute a clock generating means, and the timer 20 and the prescaler 21 constitute a measuring means.

0020Fig.2 shows an internal structure of the demodulation circuit 26 in the modem circuit 15. A first comparator 31 and a second comparator 32, for comparing the amplitude of a detection signal, are respectively connected to an input signal demodulation circuit 33 and a waveform shaping circuit 34. A threshold value Vt₁ for detecting a request signal is set in the first comparator 31 and a threshold value Vt₂ for detecting a trigger signal is set in the second comparator 32. These threshold values Vt₁ and Vt₂ are designed so that the following relation stands up for a level Vs₁ of a request signal and a level Vs₂ of a trigger signal:<maths id="math0001" num="[1]"><math display="block"><mrow><mtext>Vt₁ &lt; Vs₁ &lt; Vt₁ &lt; Vs₂</mtext></mrow></math><img file="EP0446519B1_D0001.tif" /></maths>

0021Furthermore, the input signal demodulation circuit 33 is connected to the UART 22 and the waveform shaping circuit 34 is connected to the clock generating circuit 29.

0022The second comparator 32 and the waveform shaping circuit 34 constitute a detection means for detecting a trigger signal.

0023The internal structure of the clock generating circuit 29 is shown in Fig.3. A set terminal S of a second flip flop 37 is connected to an output terminal Q of a first flip flop 35 through an OR circuit 36. The output terminal Q of the second flip flop 37 is connected to a reset terminal R of the first flip flop 35 through a NOR circuit 38 while connected to each circuit, such as the CPU 11, in the IC 10 through a NAND circuit 39, 1/2 dividers 40 and 41 and a NAND circuit 42. An output of the 1/2 divider 40 is connected to a set terminal S of a third flip flop 46 through a 1/8 divider 43, prescaler 44 and a timer 45, and an output terminal Q of the flip flop 46 is connected to the NAND circuit 42. Furthermore, connected to the NAND circuit 39 is the crystal oscillator 19.

0024The first and second flip flops 35 and 37, the OR circuit 36, the NOR circuit 38 and the NAND circuit 39 constitute an actuating means and first and second stop means.

0025Next, operations of the embodiment will be explained. First, as shown in Fig.1, while waiting to receive a trigger signal from an unillustrated external device, the CPU 11 outputs a STP instruction to the clock generating circuit 29 so that generation of an internal clock is stopped.

0026When the external device transmits a trigger signal and a subsequent request signal, it is judged in the demodulation circuit 26 in the modem circuit 15 whether the signal received through the antenna circuit 16 is a trigger signal or a request signal. The received trigger and request signals respectively have the levels Vs₂ and Vs₁ shown in the above equation [1]. If a trigger signal is first received, since the level Vs₂ of the trigger signal is higher than the threshold value Vt₂ of the second comparator 32 shown in Fig.2, a trigger signal pulse is output from the second comparator 32 to the clock generating circuit 29 through the waveform shaping circuit 34.

0027The trigger signal pulse is input to a trigger terminal T of the first flip flop 35 shown in Fig.3. The flip flop 35 detects a leading edge of the trigger signal pulse and outputs a "H"-level signal from the output terminal Q to the set terminal S of the second flip flop 37 through the OR circuit 36, and then the second flip flop 37 outputs a "H"-level oscillation control signal from the output terminal Q to the NAND circuit 39. This causes an oscillation of the crystal oscillator 19 to start and an output of the NAND circuit 39 is divided into 1/4 by the 1/2 dividers 40 and 41 and output as an internal clock from the NAND circuit 42 to each circuit in the IC 10. In actuality, the 1/8 divider 43, the prescaler 44, the timer 45 and the third flip flop 46 operate in order to cause a delay until an oscillation waveform becomes stable, and after a predetermined time has passed since the crystal oscillator 19 started oscillating, the internal clock is output.

0028When the internal clock is thus actuated, the CPU 11 reads a program from the ROM 12 shown in Fig.1 and executes a data process according to a flowchart shown in Fig.4. The timer 20 for monitoring receiving of a request signal and the prescaler 21 are initialized in Step S1. Then, a response signal to the trigger signal is transmitted to the external device through the input-output control circuit 14, the modem circuit 15 and the antenna circuit 16 in Step S2.

0029After that, the timer 20 and the prescaler 21 is set in an enabled state and the counting of the timer 20 is started in Step S3. It is determined, based on the state of the UART 22, whether or not the data is input through the demodulation circuit 26 in Step S4. If the input of data is confirmed, the content of the received data is read out from the UART 22 and it is judged whether or not the data is a request signal in Step S5. The request signal should be at least an 8-bit data string and it is required to be read out for a predetermined length.

0030If it is judged in Step 5 that the data is a request signal, after an internal process in accordance with the request signal is executed in Step S6, a response signal is transmitted to the external device in Step S7. When the transmission is completed, a STP instruction is output to the clock generating circuit 29 in Step S8. The STP instruction is input to reset terminals R of the second and third flip flops 37 and 46 shown in Fig.3 so as to make the output terminals Q of the flip flops 37 and 46 at "L"-level. This closes the NAND circuits 39 and 42 and stops the oscillation of the crystal oscillator 19 and the output of the internal clock.

0031On the other hand, if it is not confirmed in Step S4 that the data is input to the UART 22, or if it is judged in Step S5 that the data is not a request signal, overflow of the timer 20 is checked in Step S9. If the timer 20 does not overflow, Step S4 is repeated and it is judged again whether the data is input to the UART 22. However, if the timer 20 overflows, it is judged that something wrong has happened because the time from when the trigger signal is received until the request signal is received is too long, and the counting of the timer 20 is stopped in Step S10. Then, an STP instruction is executed in Step S8 and the internal clock is stopped.

0032After this, in order to actuate again the internal clock and operate the CPU 11, it is necessary to receive a trigger signal from the external device or input a reset signal from the reset terminal 47 of the IC 10 shown in Fig.1 to the clock generating circuit 29 through the OR circuit 48.

0033When a reset signal is input from the reset terminal 47, the reset signal is input to the reset terminal R of the first flip flop 35 through the NOR circuit 38 shown in Fig.3 and to the set terminal S of the second flip flop 37 through the OR circuit 36.

0034Furthermore, besides a reset signal and an oscillation control signal which is an output of the output terminal Q of the second flip flop 37, a trigger prohibition flag signal for prohibiting a trigger can also be input to the NOR circuit 38. When the reset input to the first flip flop 35 through the NOR circuit 38 is at the "L"-level, the trigger signal pulse is not available.

0035The first flip flop 35 detects a leading edge of the trigger signal pulse and outputs an "H"-level signal from the output terminal Q, and therefore, if an extremely long trigger signal pulse is received, that is, a trigger signal is not in a pulse form, but remains at "H"-level, after the CPU 11 executes a STP instruction in response to the overflow of the timer 20, the first flip flop 35 is not set until the trigger signal once reaches the "L"-level. Therefore, it is possible to certainly stop the oscillation of the internal clock.