Card reader/writer for non-contact IC card

Abstract: The invention proposes a card reader/writer comprising a UART ( 13 ), which converts serial data into parallel data and vice versa; a send circuit ( 14 ), which modulates a digital signal of the serial data from said UART and converts it into a send electrical signal; a transmitting antenna ( 15B ), which transmits said send electrical signal as a radio wave; a receiving antenna ( 16 ), which converts a received radio wave into a receive electrical signal; a receive circuit ( 17 ), which demodulates said receive electrical signal and converts it into a digital signal; and a control unit, which controls said card reader/writer, wherein said transmitting antenna ( 15B ) comprises a series resonance circuit and said receiving antenna ( 16 ) comprises a parallel resonance circuit.

Description: The present invention relates to a card reader/writer which employs radio waves as communication media thereof. Description of the Related Art Fig. 6 shows a card apparatus (card system), which is disclosed in AIM JAPAN ┌Data carrier Technic and Application┘ 1990 Nikkan Kogyo Shinbun. This card system includes a conventional card reader/writer 1 and a noncontact IC card 2. Fig. 7 shows a receive circuit 17 of the conventional card reader/writer 1. In Fig. 6, the card reader/writer 1 includes an input/output circuit 11, which is connected to a host computer (HOST) to communicate with the host computer, a control unit 12, which controls the whole system and processes data, a UART (universal asynchronous receiver transmitter) 13, which converts serial data to parallel data or vice versa, a send circuit 14, which modulates the digital signals of serial data received from the UART 13 and converts them to electrical signals, a transmitting antenna 15, which includes a parallel resonance circuit and transmits the electrical signals as radio waves, a receiving antenna 16, which includes a parallel resonance circuit and converts received radio waves into electrical signals, a receive circuit 17, which demodulates the electrical signals and converts into digital signals, and a power circuit 18, which supplies a power source of, for example, 5 VDC, to the foregoing constituents and a power source of, for example, 24 VDC, to the transmitting antenna 15 and the receiving antenna 16. The control unit 12 includes a CPU, ROM, RAM, etc. Further in Fig. 6, the noncontact IC card 2 is equipped with a transmit-receive antenna 21, which converts received radio waves into electrical signals and vice versa, a receive circuit 22, which demodulates the electrical signals and converts them into digital signals, a UART (universal asynchronous receiver transmitter) 23, which converts serial data to parallel data or vice versa, a control unit 24, which controls the whole system and processes data, a send circuit 25, which modulates the digital signals of the serial data received from the UART 23 and converts them into electrical signals, and a power circuit 26, which includes a battery. The control unit 24 is equipped with a CPU, ROM, RAM, etc. In Fig. 7, the receive circuit 17 is provided with a receiving buffer 171 connected to the receiving antenna 16, an AGC (automatic gain control) 172, which automatically controls the gain of the receiving buffer 171, and a demodulator 173 connected between the receiving buffer 171 and the UART 13. The operation of the conventional card reader/writer 1 and the noncontact IC card 2 will now be described with reference to Figs. 8, 9, 10 and 11. Figs. 8 and 9 show the forms of the signals sent from the card reader/writer 1 to the noncontact IC card 2. Fig. 10 shows a flowchart, which gives a brief overview of the operation of the noncontact IC card 2. Fig. 11 shows a flowchart, which gives the details of the operation corresponding to steps 33 and 34 in Fig. 10. As a basic operation, the card reader/writer 1 sends a command to the noncontact IC card 2 and the noncontact IC card 2 executes the command and sends the result back to the card reader/writer 1. For instance, when the system is applied to a security system, the card reader/writer 1 is installed on a door of a room, while the noncontact IC card 2 is carried by an inhabitant of the room. The card reader/writer 1 continually sends a command, requesting for an ID to be returned, and when the noncontact IC card 2 receives the command, it returns the ID. The card reader/writer 1 checks the ID and unlocks the door if it accepts the ID. There are some cases where the host computer connected to the card reader/writer 1 checks the ID. As shown in (a) of Fig. 8, the signal sent from the card reader/writer 1 to the noncontact IC card 2 is configured so that a trigger signal is sent out first, then a start flag is sent out following a 2-bit interval, and the data shown in Fig. 9 follow. A frame, which is a unit of data, includes a 1-bit start bit, 8-bit data, a 1-bit parity bit, and a 2-bit stop bit as shown in Fig. 9. The start flag of Fig. 8 indicates the data, which have the same configuration as that of the single frame of Fig. 9, the 8-bit data in the single frame having a predetermined bit pattern. First, upon receipt of the trigger signal shown in (a) of Fig. 8, the noncontact IC card 2 is switched from a sleep state to an active state and enables the UART 23 to receive signals (refer to steps 30 through 32 of Fig. 10. Then, when the noncontact IC card receives the start flag shown in (a) of Fig. 8, it begins receiving a data block shown in Fig. 9 (refer steps 33 and 34), implements the processing in response to the command, sends the result back to the card reader/writer 1 or carries out other appropriate processing, then moves back into the sleep state (refer to a step 35). The UART 23 of the noncontact IC card 2 starts receiving the data when it detects the 1-bit start bit and receives the following 8 bits as data (refer to a step 40 of Fig. 11). The 2-bit stop bit indicates the break between frames; if this break cannot be detected, it is determined as a framing error and the data received this time is not taken in, and the system waits until it detects the next start bit (1 bit indicating the change from the high level to the low level as shown in Fig. 9), i.e., until synchronization is achieved before it goes back to the step 40 (refer to steps 41 and 42). If no framing error occurs, then the system accepts the next data (refer to a step 43). In other words, if the start bit is not properly detected, it is very likely that the next start bit cannot be properly detected until the framing error takes place. As shown in (a) of Fig. 8, after the trigger signal is received, the start flag, which is the data block having a particular bit pattern, is received. The noncontact IC card 2 enables the UART 23 to receive signals only after the end of the trigger signal; therefore, the start flag can be securely received if the trigger signal is properly received. If, however, the trigger signal 1 is left out as indicated by the dotted line shown in (b) of Fig. 8, resulting in a failure to properly receive the trigger signal (e.g., if the distance between the card reader/writer 1 and the noncontact IC card 2 is just barely within the communication range), then the noncontact IC card 2 is actuated to make the UART 23 ready for receiving, causing a portion of A to be erroneously received as the start bit in the start flag. The UART 23 processed data on an 8-bit basis; therefore, the following start flag cannot be properly received, skipping the whole data block. The operation of the receive circuit 17 of the card reader/writer 1 will now be described. The intensity of a radio wave greatly varies depending on the distance between the card reader/writer 1 and the noncontact IC card 2. For this reason, the gain of the receive circuit 17 needs to be adjusted. This is why the receive circuit incorporates an AGC 172. The AGC 172, however, requires some time to restore its original gain once the gain decreases. The card reader/writer 1 has the transmitting antenna 15 and the receiving antenna 16, which share the same frequency; therefore, it receives the radio waves (extremely intensive), which the card reader/writer itself sends out, through its own receiving antenna 16. This causes the gain of the AGC 172 to decrease for a while after transmission. As a result, the communication distance between the card reader/writer 1 and the noncontact IC card 2 is shortened. This means that there was a problem with the conventional noncontact IC card 2 in that, if it fails to properly receive the trigger signal from the card reader/writer 1, then it cannot securely receive the start flag and skips the whole data block, resulting in an increased communication error rate with consequent damaged communication reliability. There was also a problem with the conventional card reader/writer 1 in that, since it uses the same frequency for transmitting and receiving, it receives its own transmitted radio waves through the receiving antenna 16. This intensive radio waves decrease the gain of the AGC 172 of the receive circuit 17, which in turn deteriorates the receiving sensitivity and shortens the communication distance. This led to a higher communication error rate with consequent deteriorated communication reliability. There was still another problem with the conventional card reader/writer 1 in that, since it uses the same frequency for transmitting and receiving, the transmitting antenna 15 and the receiving antenna 16 thereof interfere with each other. This destroys the waveforms of transmitted and received signals, leading to a higher communication error rate and poor communication reliability. Accordingly, it is an object of the present invention to provide a card reader/writer, which is capable of preventing the interference between the transmitting antenna and the receiving antenna, thus decreasing the communication error rate and improving the communication reliability. This object is solved by a card reader/writer as set out in the independent claim 1. Avantageous development of the invention is defined in dependent claim 2. Brief description of the drawings: Fig. 1 is a block diagram showing the configuration of the card reader/writer according to an unclaimed example; Fig. 2 is a block diagram showing the configuration of the card reader/writer according to a further unclaimed example; Fig. 3 shows the operation of the card reader/writer of Fig. 16; Fig. 4 is a block diagram showing the configuration of the card reader/writer according to an embodiment of the present invention; Fig. 5 is a block diagram showing the configuration of the card reader/writer according to another embodiment of the present invention; Fig. 6 is a block diagram showing a card apparatus, which includes a conventional card reader/writer and noncontact IC card; Fig. 7 shows the configuration of a receive circuit of the card reader/writer of Fig. 6; Fig. 8 shows a form of the signal transmitted from the card reader/writer to the noncontact IC card of Fig. 6; Fig. 9 shows a form of the signal transmitted from the card reader/writer to the noncontact IC card of Fig. 6; Fig. 10 is a flowchart showing the operation of the noncontact IC card of Fig. 6; and Fig. 11 is a flowchart showing the operation of the noncontact IC card of Fig. 6. An example not forming part of the present invention will be described with reference to the attached drawings. Fig. 1 shows the configuration of a card reader/writer 1E according to this example, the input/output circuit 11, the UART 13 through the transmitting antenna 15, the receive circuit 17, and the power circuit 18 being the same as those of the conventional card reader/writer 1. In Fig. 1, the card reader/writer 1E includes a control unit 12E which differs from the conventional control unit 12 in function, and a receiving antenna 16A, which has a switching circuit 161 having analog switches or relays. The control unit 12E is equipped with a CPU, ROM, RAM, etc.. During transmission, the switching circuit 161 is controlled by a transmission status signal from the control unit 12E to prevent the receiving antenna 16A from resonating. The control unit 12E sets the switching circuit 161 to ON during transmission to prevent the receiving antenna 16A from resonating, while it sets the switching circuit 161 to OFF during receiving to receive radio waves. This prevents the transmitting antenna 15 and the receiving antenna 16A from interfering with each other, resulting in a reduced communication error rate, thus contributing to higher communication reliability. A further example not forming part of the present invention will be described with reference to the attached drawings. Fig. 2 shows the configuration of a card reader/writer 1F according to this example, the input/output circuit 11, the UART 13, the send circuit 14, and the receiving antenna 16 through the power circuit 18 being the same as those of the conventional card reader/writer 1. Fig. 3 shows the waveforms of the receive signals of the card reader/writer 1F. In Fig. 2, the card reader/writer 1F includes a control unit 12F, which differs from the conventional control unit 12 in function, and a transmitting antenna 15A, which has a switching circuit 151 having analog switches or relays. The control unit 12F is equipped with a CPU, ROM, RAM, etc.. In the card reader/writer 1E, both the transmitting antenna 15A and the receiving antenna 16 include parallel resonance circuits, and the transmitting antenna 15A also receives radio waves during receiving. For this reason, the two antennas resonate, and a slight difference in the resonance frequency disturbs the phase, causing the receiving antenna 16 to receive a waveform, which combines the waveform obtained through the transmitting antenna 15A and that through the receiving antenna 16 as shown in (c) of Fig. 3. Hence, as shown by the arrowhead in (c) of the drawing, the received waveform is distorted, preventing the receiving antenna 16 from producing an intact received waveform. Accordingly, the control unit 12F of the card reader/writer 1F sets the switching circuit 151 to ON by the receiving status signal during receiving in order to prevent the resonance of the transmitting antenna 15A. This allows the receiving antenna 16 to receive a signal with an intact waveform as shown in (b) of Fig. 2. During transmission, the control unit 12F sets the switching circuit 151 to OFF. Fig. 2 (a) shows the waveform of the signal sent from the noncontact IC card 2 to the card reader/writer 1F. Hence, the interference between the transmitting antenna 15A and the receiving antenna 16 can be prevented. This enables a reduced communication error rate, resulting in enhanced communication reliability. An embodiment of the present invention will be described with reference to the attached drawings. Fig. 4 shows the configuration of a card reader/writer 1G according to this embodiment of the present invention, the input/output circuit 11 through the send circuit 14, and the receiving antenna 16 through the power circuit 18 being the same as those of the conventional card reader/writer 1. In Fig. 4, the card reader/writer 1G is equipped with a transmitting antenna 15B, which has a series resonance circuit. Configuring the transmitting antenna 15B with the series resonance circuit does not form the loop as in the parallel resonance circuit, thus preventing radio waves from being received. This makes it possible to protect the waveform of the signal received through the receiving antenna 16 from being distorted, leading to a reduced communication error rate with resultant higher communication reliability. The series resonance circuit requires larger electric currents for driving than in the parallel resonance circuit; therefore, it is necessary to increase the capacity of the power circuit 18 of the card reader/writer 1G when using the series resonance circuit. The series resonance circuit, however, can be driven at a lower voltage and therefore, it is not necessary to use two power supplies as in a case where the parallel resonance circuit is used; a single power supply of, for example, 5 VDC may be used for the card reader/writer 1G (the voltage depends on Q in the case of the series resonance). A further embodiment of the present invention will be described with reference to the attached drawings. Fig. 5 shows the configuration of a card reader/writer 1J according to this embodiment of the present invention, the input/output circuit 11, the UART 13, the send circuit 14, the receive circuit 17, and the power circuit 18 being the same as those of the conventional card reader/writer 1. In Fig. 5, the card reader/writer 1J includes a control unit 12J, which differs from the conventional control unit 12 in function, and the transmitting antenna 15B, which includes a series resonance circuit, and the receiving antenna 16A, which has the foregoing switching circuit 161. The control unit 12J provided with a CPU, ROM, RAM, etc.. The card reader/writer 1J is equipped with the transmitting antenna 15B and the receiving antenna 16A, which have already been explained. Hence, it permits extension of the receiving distance and prevents the transmitting antenna 15B from affecting the receiving antenna 16A, making it possible to achieve a card reader/writer, which is capable of reducing the communication error rate with resultant higher communication reliability.

Claims: A card reader/writer comprising: a UART ( 13 ), which converts serial data into parallel data and vice versa; a send circuit ( 14 ), which modulates a digital signal of the serial data from said UART and converts it into a send electrical signal; a transmitting antenna ( 15B ), which transmits said send electrical signal as a radio wave; a receiving antenna ( 16 ), which converts a received radio wave into a receive electrical signal; a receive circuit ( 17 ), which demodulates said receive electrical signal and converts it into a digital signal; and a control unit, which controls said card reader/writer, characterized in that said transmitting antenna ( 15B ) comprises a series resonance circuit and said receiving antenna ( 16 ) comprises a parallel resonance circuit. The card reader/writer according to claim 1, characterized in that said receiving antenna ( 16A ) comprises a switching circuit ( 161 ), which is adapted to prevent said parallel resonance circuit from resonating during transmission when switched on.

Inventors: FUJIOKA SHUZO, FUJIOKA, SHUZO
Applicants: MITSUBISHI ELEC SEMICONDUCTOR, MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA, MITSUBISHI ELECTRIC SEMICONDUCTOR SOFTWARE CO., LTD.
Application year: 1995
Main classification: G06K7
IPC codes: G06K19, G06K7