Reader/writer for performing efficient transmission/reception with no-battery information storage medium

Abstract: A reader/writer (100) transmits power and modulated data to a no-battery information storage medium (200) having a communication function in a noncontact state, and receives modulated data from the no-battery information storage medium (200). The reader/writer (100) has a driver (104), a loop antenna (105), and a current detection unit (106). The driver (104) transmits the power and the modulated data. The loop antenna (105) is connected to the output line of the driver (104). The current detection unit (106) is arranged between the loop antenna (105) and the output line of the driver (104). While the reader/writer (100) supplies a transmission carrier current from the driver (104) to the loop antenna (105), if it receives the modulated data from the no-battery information storage medium (200), it uses the current detection unit (106) to extract, as a reception signal, a change in transmission carrier current of the loop antenna (105) caused by the modulated data signal received by the loop antenna.

Description: The present invention relates to a reader/writer and, more particularly, to a reader/writer which serves as, e.g., one kind of information processing system to perform radio communication with a no-battery information storage medium such as a battery-less radio card or radio tag. Recently, in the field of information processing apparatuses, information processing systems including an information processing apparatus such as a reader/writer for performing, in a noncontact state, radio communication with a no-battery information storage medium such as a battery-less radio card or radio tag applied as, e.g., an access control system have been developed. In this case, while receiving the power by a radio wave transmitted from the transmission antenna on the information processing apparatus side such as the reader/writer, the no-battery information storage medium side such as the battery-less radio card or radio tag transmits data as an amplitude-modulated signal with a low degree of modulation to the reader/writer side. The reader/writer side which receives a radio wave transmitted from the battery-less radio card or radio tag side receives it by using a reception The reader/writer side amplitudes the received signal to a sufficient magnitude, and then performs detection processing and information processing for demodulating the received signal. In this radio information processing system, however, when communication is to be performed between the reader/writer and the no-battery information storage medium such as the battery-less radio card or radio tag at a relatively short distance, the influence of the interfere between the transmission and reception systems caused by near arrangement of the transmission and reception antennas is great on the reader/writer side, failing efficient transmission/reception. In conventional signal processing in which the amplitude-modulated signal with a low degree of modulation received on the reader/writer side is directly amplified to perform detection for modulation, saturation easily occurs at a low power supply voltage, posing a problem in signal processing. EP 0 525 642 A2 discloses a reader/writer according to the preamble of claim 1. The present invention, therefore, has been made in consideration of the above problems in the prior art, and has as its object to provide a reader/writer in which, in an information processing system for transmitting power and modulated data to a no-battery information storage medium having a communication function in a noncontact state, and receiving modulated data from the no-battery information storage medium, the influence of the interfere between transmission and reception systems is eliminated to allow efficient transmission/reception, and saturation is avoided to perform satisfactory signal processing even when the power supply voltage is low. This object is achieved by a reader/writer according to claim 1. Further developments of the invention are given in the dependent claims. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a block diagram for explaining the general background to which the present invention relates; FIG. 2 is a block diagram showing the arrangement of main part according to a background, embodiment; FIG. 3 is a view showing a detailed example of a current detection transformer used in the embodiment of FIG. 2; FIGS. 4A to 4E are waveform charts, respectively, for explaining the operation of the embodiment of FIG. 2; FIG. 5 is a block diagram showing the arrangement of main part according to a preferred embodiment of the present invention; FIG. 6 is a block diagram showing the arrangement of main part according a more preferred embodiment of she present invention; and FIGS. 7A to 7F are timing charts, respectively, for explaining the operation of the embodiment of FIG. 6. Reference will now be made in detail to the presently preferred embodiments of the invention as illustrated in the accompanying drawings, in which like reference characters designate like or corresponding parts throughout the several drawings. The general description of the present invention will be described prior to the description of embodiments of the present invention. FIG. 1 shows the schematic arrangement of an information processing system constituted by a reader/writer 100 serving as an information processing apparatus for performing mutual radio communication, and a no-battery information storage medium 200 such as a no-battery radio card. The present invention particularly relates to an improvement in, of the two, the reader/writer 100 portion. The schematic arrangement of the reader/writer 100 will be first described with reference to FIG. 1. The reader/writer 100 transmits power and data from a loop transmission antenna coil 105 to the no-battery radio card 200 via a modulation circuit 103 and a driver 104. The no-battery radio card 200 receives the power and the data via a transmission/reception antenna coil 201, and supplies an output 207 from a full-wave rectification circuit 206 as a DC-power supply output 209 stabilized by a smoothing/stabilization circuit 208 to the respective portions of a circuit inside the card 200. The present invention is directed to provide the new reader/writer 100. That is, on the reader/writer 100 side of the information processing system, a current detection transformer 106 receives transmission data from the no-battery radio card 200 side without arranging any reception antenna, and a signal processing circuit 107 and a demodulation circuit 108 perform predetermined processing. In FIG. 1, the reader/writer 100 comprises, in addition to the above arrangement, an interface circuit 101 for communicating with an external host device (not shown), and a control circuit 102 for transmission/reception control which is connected to the interface circuit 101 and also to the modulation and demodulation circuits 103 and 108. The no-battery radio card 200 comprises, in addition to the above arrangement, demodulation and modulation circuits 203 and 210 connected to the transmission/reception coil 201, a control logic circuit 204 connected to the demodulation and modulation circuits 203 and 210, and a nonvolatile memory 205 connected to the control logic circuit 204. These circuits 203, 210, 204, and 205 receive the DC-power supply output 209 from the smoothing/stabilization circuit 208, as described above. FIG. 2 shows the arrangement, extracted from FIG. 1, of the main part of an information processing apparatus according to a background embodiment. As shown in FIG. 2, the driver 104 of the reader/writer 100 is constituted by a positive-phase constant-voltage driver 110 and a negative-phase constant-voltage driver 111. The driver 104 performs a push-pull operation to supply a transmission current including power and transmission data to the transmission antenna coil 105 by effectively using a low power supply voltage. After the power and the transmission data transmitted from the transmission antenna coil 105 of the reader/writer 100 are received by the transmission/reception antenna coil 201 of the no-battery radio card 200, they are rectified by the full-wave rectification circuit 206 constituted by a diode bridge circuit, and used to generate the above-described DC-power supply output. On the no-battery radio card 200 side, transmission data 211 from the modulation circuit 210 (see FIG. 1) is input to the gate of a transistor 221 while the transmission of the power from the reader/writer 100 is received. The transistor 221 is turned on/off in accordance with the transmission data 211 to apply load variations to the transmission/reception antenna coil 201, thereby transmitting data from the no-battery radio card 200 to the reader/writer 100 side. The transmission antenna coil 105 of the reader/writer 100 is constituted by a loop coil to generate an electromotive force in response to the transmission data from the transmission/reception antenna coil 201 of the no-battery radio card 200. As a result, a reception data signal current from the no-battery radio card 200 side which is superposed on the transmission current from the reader/writer 100 side flows through a line which is connected to the transmission antenna coil 105 via a line extending from the output of the constant-voltage driver 110, and extended from the transmission antenna coil 105 to the output of the constant-voltage driver 111. Since the current detection transformer 106 is interposed in the line 120 between the output of the constant-voltage driver 111 and the transmission antenna coil 105, the reception data signal from the no-battery radio card 200 side which is superposed on the transmission current from the reader/writer 100 side can be obtained as a reception signal 123 across the two terminals of a load resistor 112 of a secondary coil 122 of the current detection transformer 106. FIG. 3 shows a detailed arrangement of the current detection transformer 106. , More specifically, in FIG. 3, a line 120 is wound on a toroidal core 121, and the secondary coil 122 having a predetermined number of turns, i.e., N turns is arranged on the toroidal core 121. Assuming that i 0 is an AC current flowing through the line 120, a current i 0 X (1/N) flows through the secondary coil 122. This current can be extracted as the reception signal 123. If the number N of turns of the secondary coil 122 is set large (e.g., N > 10), the influence on the transmission current of the transmission antenna coil 105 can be satisfactorily decreased. For example, if the number N of turns is set to 20, only 1/20, i.e., 5% the transmission current is extracted from the secondary coil 122 of the current detection coil 106, and can be ignored as the load on the transmission current. In this manner, while transmitting the power to the no-battery radio card 200, the reader/writer 100 can extract the reception signal 123 from the no-battery radio card 200 which is superposed on the transmission current, as an amplitude-modulated signal with a low degree of modulation, as shown in FIG. 4A. When the reception signal 123 from the current detection transformer 106 is detected by an envelope detection circuit 113, a detection output 124 like the one shown in FIG. 4B is obtained. The detection output 124 is amplified by an amplifier 114 to obtain an output 125 like the one shown in FIG. 4C. The output 125 is binarized by a comparator 115 to obtain a binarized output 109 like the one shown in FIG. 4D. The binarized output 109 is demodulated by the demodulation circuit 108 to obtain a demodulated output 511 like the one shown in FIG. 4E. An information processing apparatus according to the preferred embodiment of the present invention will be described below. FIG. 5 shows the arrangement, extracted from FIG. 1, of the main part of the information processing apparatus according to the preferred embodiment of the present invention. As one of contact-less IC card schemes which are going to be internationally standardized recently, there is a scheme in which power and data are transmitted/received between two transmission coils 105 and 401 of a reader/writer 100, and two transmission/reception coils 201 and 301 of a contact-less IC card 200A side, as shown in FIG. 5. In this case, on the contact-less IC card 200A side, a data transmission modulation circuit 210 is constituted by a resistor 220, a MOS transistor 221, and the like. Data is transmitted by applying load variations to one of the transmission/reception antenna coils 201 and 301. Another modulation circuit 210 having this arrangement must be arranged in the antenna coil 301. However, the contact-less IC card 200A is desirably constituted by an LSI as small as possible in order to bury it in a card having a thickness of 0.76 mm as an ISO credit card size. Therefore, as for the modulation circuit 210, one circuit is more preferable than two circuits. In this embodiment, the number of circuits of the contact-less IC card 200A is decreased, and a simple circuit is added to the reader/writer 100 side to allow satisfactory reception. More specifically, as shown in FIG. 5, a first current detection transformer 106 is arranged on a line connecting the output of a constant-voltage driver 104 of the reader/writer 100 with the first transmission antenna coil 105. A second current detection transformer 406 is arranged on a line connecting the output of a constant-voltage driver 404 with the second transmission antenna coil 401. Outputs from first and second envelope detection circuits 113 and 413 are input to a summing-amplifier 414. Upon detection of these reception signals, they are summed and amplified by the summing-amplifier 414. An output from the summing-amplifier 414 is binarized into a binary output 109 by a comparator 115, and then demodulated by a demodulation circuit 108. As for a reception signal 123 shown in FIG. 4A, a signal having undergone binary phase modulation with a sub-carrier having a synchronous frequency 1/n ( n is an integer) the transmission carrier frequency used for transmission serves as a modulated signal transmitted from the no-battery radio card or the contact-less IC card. In this manner, according to this embodiment, the current detection transformers 106 and 406 are respectively arranged on lines connecting the drivers 104 and 404 of the reader/writer 100 with the transmission antenna coils 105 and 401. Accordingly, data can be stably transmitted by arranging the modulation circuit 210 in only one of the two transmission/reception antenna coils 201 and 301 inside the contact-less IC card 200A. FIG. 6 and FIGS. 7A to 7F respectively show the arrangement of a new preferred demodulation circuit 108 for the above-described binary-phase-modulated binary signal 109, and the timing charts of its operation. More specifically, in FIG. 6, a transmission carrier frequency pulse 550 is input to a central position detection circuit 501 for detecting the central position of the pulse of a binary-phase-modulated binary signal 109, and a frequency division counter 502 for generating a demodulation clock. In this embodiment, a signal having undergone binary phase modulation with a sub-carrier having a 1/16 frequency in synchronism with the transmission carrier frequency used for transmission is transmitted from a no-battery radio card 200 or a contact-less IC card 200A. This signal serves as a reception signal 123 of a reader/writer 100 (see FIGS. 2 and 5), is subjected to detection, amplification, and binarization, and input to the demodulation circuit 108. The central position detection circuit 501 starts counting on the basis of the transmission carrier frequency pulse 550 (FIG. 7A) every ON period of the pulse of the binary-phase-modulated binary signal 109 (FIG. 7B). If the pulse of the binary signal 109 still exists after 4 pulses have been counted, a central position detection pulse 508 appearing after this timing (FIG. 7C) is output. At the timing when central position detection pulses 508 corresponding to n 1 pulses are continuously counted, the 16-frequency division counter 502 starts operation to generate a demodulation clock 510 (FIG. 7D) obtained by frequency-dividing the transmission carrier frequency pulse 550 into 16 pulses. Since the rise timing of the demodulation clock 510 is adjusted to substantially the central position of the binary-phase-modulated binary signal 109, a synchronous demodulated signal 511A (FIG. 7E) of the binary-phase-modulated signal 109 stabilized by a D flip-flop 503 can be attained. When the central position of the pulse of the binary-phase-modulated signal 109 is detected, and the n 1 pulses are continuously detected, a flip-flop 506 is set. At the same time, the binary-phase-modulated signal 109 is input to a pulse omission detection circuit 505. Upon detection of a state wherein n 2 or more pulses do not continuously exist, the flip-flop 506 is reset. With this operation, a gate pulse 512 (FIG. 7F) corresponding to the ON period of the binary-phase-modulated signal 109 can be generated. The gate pulse 512 and the synchronous demodulated signal 511A of the binary-phase-modulated signal 109 can be gated through an AND circuit 507 to enable a demodulated output within the period of the gate pulse 512. As described in detail above, when communication is performed between the reader/writer and the battery-less radio card at a relatively short distance, the influence of the interfere between the transmission and reception antenna coils caused by their proximity arrangement is conventionally great on the reader/writer side to fail efficient transmission/reception. In the present invention, since the current detection transformer is arranged on the line connecting the transmission driver with the transmission antenna coil, a reception signal can be obtained from an output from the current detection transformer without arranging any reception antenna on the reader/writer side. With this arrangement, efficient transmission/reception can be performed without causing any interfere between the antennas, unlike the prior art. Preferably, the turn ratio is so set as to sufficiently decrease a current on the secondary side of the current detection transformer. In this case, the current detection transformer does not act as a load on the drive current of the transmission antenna coil. In the present invention, a low-modulation-degree signal of a reception signal obtained from the current detection transformer is subjected to envelope detection before amplification. Even if the signal is greatly amplified, it can be amplified without any distortion to allow stable signal processing. Preferably, the central position of a signal having undergone binary phase modulation with a 1/n sub-carrier frequency in synchronism with the transmission carrier frequency is detected using the transmission carrier frequency, and a demodulation clock is generated at this timing. As a result, stable demodulation can be performed. In the present invention, since the present period of the reception signal is detected to enable a demodulated output for only this period, only a correct demodulated output can be output. As has been described in detail above, according to the present invention, an information processing apparatus which transmits power and modulated data to a no-battery information storage medium having a communication function in a noncontact state, and receives modulated data from the no-battery information storage medium, wherein the influence of the interfere between the transmission and reception systems is removed to allow efficient transmission/reception, and saturation is avoided to perform satisfactory signal processing even when the power supply voltage is low can be provided.

Claims: A reader/writer (100) adapted to transmit power and modulated data to a no-battery information storage medium (200A) having a communication function in a non-contact state, and to receive modulated data from said no-battery information storage medium, comprising: a driver (104) adapted to transmit the power and the modulated data; a loop antenna (105) connected to an output line of said driver and being adapted to receive a transmission carrier current from said driver; and current detection means (106) for extracting, as a reception signal, a change in transmission carrier current of said loop antenna caused by a signal of the modulated data received by said loop antenna while the transmission carrier current is supplied from said driver upon reception of the modulated data from said no-battery information storage medium, wherein, when an amplitude-modulated signal with a low degree of modulation is received as the modulated data from said no-battery information storage medium, said reader/writer uses said current detection means to extract, as the reception signal, the change in transmission carrier current of said loop antenna caused by the modulated data signal received by said loop antenna, and an amplifier (414) for amplifying the signal extracted by said current detection means, characterized in that : said driver includes first and second drivers (104, 404), said loop antenna includes first and second loop antennas (105, 401), said current detection means includes first and second current detection means (106, 406), wherein each current detection means is arranged between its respective loop antenna and the output line of its driver, and each current detection means comprises a transformer (122, 422) adapted to detect the transmission carrier current flowing through the loop antenna, and an envelope detection circuit (113, 413) adapted to detect an envelope of an output from the transformer to extract the signal received by the loop antenna, and said amplifier (414) comprises an addition means (414) for adding signal currents of demodulated data extracted from the respective outputs of said first and second current detection means. A reader/writer according to claim 1, wherein, when a binary-phase-modulated signal has undergone binary phase modulation with a sub-carrier having a frequency 1/n ( n is an integer), a transmission carrier frequency used for transmission is received as the modulated data from said no-battery information storage medium (200A), said reader/writer is adapted to use said current detection means (106, 406) to extract, as the modulated data received by the respective loop antennas (105, 401), a signal current of the binary-phase-modulated signal having undergone binary phase modulation with the sub-carrier having the frequency 1/n of the transmission carrier frequency used for transmission, and further comprises signal processing means (115) for changing the binary-phase-modulated signal extracted by said current detection means into a binary signal; and demodulation means (108) for starting counting from an edge of a pulse for an ON period of the pulse of the binary signal from said signal processing means on the basis of the transmission carrier frequency to detect a timing of substantially a center of a width of the pulse, and starting dividing the transmission carrier frequency from a detection timing to generate a clock having the same frequency as that of the sub-carrier, and to use the clock as a demodulation clock for the binary-phase-modulated signal. A reader/writer according to claim 1, wherein, when a binary-phase-modulated signal has undergone binary phase modulation with a sub-carrier having a frequency 1/n ( n is an integer) a transmission carrier frequency used for transmission is received as the modulated data from said no-battery information storage medium (200A), said reader/writer is adapted to use said current detection means (106, 406) to extract, as the modulated data received by the respective loop antennas (105, 401), a signal current of the binary-phase-modulated signal having undergone binary phase modulation with the sub-carrier having the frequency 1/n of the transmission carrier frequency used for transmission, and further comprises signal processing means (115) for changing the binary-phase-modulated signal extracted by said current detection means into a binary signal; and demodulation means (108) for starting counting from an edge of a pulse for an ON period of the pulse of the binary signal from said signal processing means on the basis of the transmission carrier frequency to detect a timing of substantially a center of a width of the pulse, and when the timing is continuously detected a predetermined number of times, turning on a gate for the demodulated output of the binary-phase-modulated signal to enable the demodulated output, or when the timing cannot be detected the predetermined number of times within a predetermined time, turning off said gate to disable the demodulated output. A reader/writer according to any one of claims 1 to 3, wherein said drivers (104, 404) are adapted to perform constant-voltage driving. A reader/writer according to any one of claims 1 to 4, wherein said loop antennas (105, 401) each include a loop antenna coil (105). A reader/writer according to claim 5, wherein a current extracted from the respectiver outputs from said current detection transformers (122, 422) is not more than 1/10th of the current flowing through said loop antenna coils (105, 401).

Inventors: IWATA KAZUKI, SUDO KIYOHITO, YOKOTA TSUNESHI, IWATA, KAZUKI, SUDO, KIYOHITO, YOKOTA, TSUNESHI
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1997
Main classification: G06K7
IPC codes: G06K7, G06K17, G01S13