Data communication device

This application claims priority from the Japanese Patent Application No. 2009-090881, the content of which is incorporated therein by reference in its entirety.

1. Field of Invention

This invention is related to the data communication device, especially to the date communication device used for the data communication between an IC card and an IC Card read and write device.

2. Description of the Related Art

An antenna is formed on an IC card side when data communication is held between a non-contact type IC card and a read and write device of the IC card in the conventional designs. The antenna is configured from a conduction line loop and data communication is held by using induced electromotive force generated by applying an electric current to the loop. This type of data communication device is disclosed in Japanese Patent Application No. Hei 11-234164.

However, the application of an electric current to the conduction loop is required in the data communication device described above, which leads to a large consumption of electric power. The large consumption of the electric power is a serious problem especially for small scale devices which require low power consumption.

The shape of the antenna, which is made of the conduction loop, should be optimized depending on the frequency to obtain the maximum efficiency in the gain and radiation power. It leads to a problem of increased surface area of the antenna on the IC card as well as an increase of manufacturing cost.

The invention provides a data communication device that includes a first electrostatic induction electrode, a second electrostatic induction electrode facing the first electrostatic induction electrode so as to promote electrostatic induction between the first and second electrostatic induction electrodes, a reception and amplification circuit connected to the first electrostatic induction electrode, and a wiring connecting the reception and amplification circuit and the first electrostatic induction electrode. The reception and amplification circuit receives and amplifies an electrostatic induction signal generated at the first electrostatic induction electrode in response to a data signal applied to the second induction electrode.

FIGS. 1A and 1B show the configuration of the data communication device of an embodiment of the invention.

FIG. 2 is a circuit diagram of the data communication device of an embodiment of the invention.

FIGS. 3A , 3 B, 3 C and 3 D are wave form charts for the operation of the data communication device of an embodiment of the invention.

The data communication device of an embodiment of this invention executes the dual direction data communication between an IC card and a read and write device using electrostatic induction. The IC card and the read and write device are either in contact or located close to each other. However, the electrodes of these devices are not contacted. Therefore, the data communication is essentially a non-contact communication. First, the basic configuration of the data communication device of this invention will be explained. The detailed explanation of the circuits of the device will follow.

FIGS. 1A and 1B show the IC card mounted on the read and write device. FIG. 1A is the side view (see through view), and FIG. 1B is the plan view (see through view) of the device.

As it is shown in the figure, a first electrostatic induction electrode 11 , a first feedback electrode 12 and a first transmission and reception circuit 20 are buried in an IC card made from a resin. A second electrostatic induction electrode 101 , a second feedback electrode 102 and a second transmission and reception circuit 120 are also buried in a read and write device 100 made from a resin. Therefore, these electrodes are buried in the resin, a dielectric material, and are not exposed.

The IC card 10 is mounted on the read and write device 100 , where the first electrostatic induction electrode 11 and the second electrostatic induction electrode 101 are facing each other with the resin in between and where the feedback electrode 12 and the second feedback electrode 102 are facing each other with the resin in between. The first feedback electrode 12 is disposed close to the first electrostatic induction electrode 11 and the second feedback electrode 102 is disposed close to the second electrostatic induction electrode 101 . The IC card 10 is mounted on the read and write device 100 , as shown in FIGS. 1A and 1B . However, it is also possible that the IC card 10 is inserted into a slit formed in the read and write device 100 .

A data signal is sent from a first transmission and reception circuit 20 to the first electrostatic induction electrode 11 when the data signal is sent from the IC card 10 to the read and write device 100 . Then, the first electrostatic induction electrode 11 is charged according to the data signal and electric charges of the opposite polarity are induced by the electrostatic induction at the first electrostatic induction electrode 11 and the second electrostatic induction electrode 101 facing the first electrostatic induction electrode 11 . When the data signal is a serial data signal, where H level and L level signals repeat themselves, the data signal with H level and L level signals repeating reversely appears at the second electrostatic induction electrode 101 . The second transmission and reception circuit 120 of the read and write device 100 receives and amplifies this reversed data signal.

A data signal is sent from a second transmission and reception circuit 120 to the second electrostatic induction electrode 101 when the data signal is sent from the read and write device 100 to the IC card 10 . Then, the second electrostatic induction electrode 101 is charged according to the data signal and electric charges of the opposite polarity are induced by the electrostatic induction at the second electrostatic induction electrode 101 and the first electrostatic induction electrode 11 facing the second electrostatic induction electrode 101 . When the data signal is a serial data signal, where H level and L level signals repeat themselves, the data signal with H level and L level signals repeating reversely appears at the first electrostatic induction electrode 11 . The first transmission and reception circuit 20 of the read and write device 100 receives and amplifies this reversed data signal.

The dual directional communication between the IC card and the read and write device 100 is possible in this way.

The ground potential of the IC card 10 and read and write device 100 are not necessarily the same because the IC card 10 and the read and write device 100 are electrically insulated from each other. The data reception error can take place when the ground potential of the IC card 10 and the read and write device 100 are not the same.

The first feedback electrode 12 and the second feedback electrode 102 are formed in order to avoid the date reception error. The data signal received and amplified by the first transmission and reception circuit 20 is applied to the first feedback electrode 12 through feedback. And the data signal received and amplified by the second transmission and reception circuit 120 is applied to the second feedback electrode 102 through feedback.

The data signal received and amplified by the second transmission and reception circuit 120 of the read and write device 100 is applied to the second feedback electrode 102 when the data signal is sent from the IC card 10 to the read and write device 100 . In this case, the signal with the same polarity as that of the original data signal reappears at the first electrostatic induction electrode 11 of the IC card 10 due to the electrostatic induction.

Then, an inverted signal of the reappeared signal appears at the second electrostatic induction electrode 101 of the read and write device 100 because of the further electrostatic induction caused by the reappeared signal. That is, the amplitude of the data signal at the second electrostatic induction electrode 101 is strengthened. This can prevent the reception error even if there is a difference more or less between the ground potential of the IC card 10 and the ground potential of the read and write device 100 .

The date signal is sent from the read and write device 100 to the IC card 10 in the same way. It is preferable to dispose the first feedback electrode 12 in such a way that it surrounds the first electrostatic induction electrode 11 in the plan view as shown in FIG. 1B for strengthening the capacity coupling between the first feedback electrode 12 and the second electrostatic induction electrode 101 located in diagonal direction so that the electrostatic induction between the two can easily take place, in order to enhance the feedback effect described above. Likewise, it is preferable to dispose the second feedback electrode 102 in such a way that it surrounds the second electrostatic induction electrode 101 for strengthening the capacity coupling between the second feedback electrode 102 and the first electrostatic induction electrode 11 located in diagonal direction so that the electrostatic induction between the two can easily takes place.

FIG. 2 is a circuit diagram of a data communication device of this embodiment. The first transmission and reception circuit 20 of the IC card 10 has a first reception and amplification circuit 21 , a first input threshold adjusting circuit 22 , a first signal generating circuit 23 , and a first feedback circuit 24 . Also, the second transmission and reception circuit 120 of the read and write device 100 has a second reception and amplification circuit 121 , a second input threshold adjusting circuit 122 , a second signal generating circuit 123 , and a second feedback circuit 124 . The first and second transmission and reception circuits 20 , 120 have basically the same configuration. The configuration of the first transmission and reception circuit 20 will be explained below.

The first reception and amplification circuit 21 is connected to the first electrostatic induction electrode 11 through a wiring 25 . The first reception and amplification circuit 21 receives and amplifies the electrostatic induction signal that is generated at the electrostatic induction electrode 11 in response to a data signal applied to the second electrostatic induction electrode 101 located at the read and write device side. The first reception and amplification circuit 21 is configured from an input capacitor C 1 , an inverter INV 1 and a feedback resistor R 1 .

The input capacitor C 1 has first and second electrodes, and the first electrode is connected to the first electrostatic induction electrode 11 through the wiring 25 . Therefore, the electrostatic induction signal described above is inputted to the first electrode of the input capacitor C 1 through the wiring 25 .

The inverter INV 1 has an input terminal and an output terminal. The second electrode of the input capacitor C 1 is connected to the input terminal. It is preferable that the inverter INV 1 is configured from the CMOS inverter so as to lower the power consumption. The feedback resistor R 1 is connected between the input terminal and the output terminal of the inverter INV 1 . Therefore, the voltage of the input terminal INV 1 is set around the input threshold value of the inverter INV 1 . The output signal of the inverter INV 1 is outputted through a buffer circuit 26 .

The first input threshold adjusting circuit 22 has a function to make the input threshold of the inverter INV 1 changeable. The first input threshold adjusting circuit 22 has a by-pass resistor R 2 , a switching control circuit 27 , which controls the switching elements of MOS transistors M 1 -M 4 , and a capacitor isolation resistor R 3 .

The by-pass resistor R 2 connects the input terminal of the inverter INV 1 and the wiring 25 , forming the electricity flow from the output terminal of the inverter INV 1 to the wiring 25 . Each source of the MOS transistors M 1 -M 4 is connected to the first ground potential VSS 1 through the source resistors R 11 -R 14 and each drain is connected to the wiring 25 through capacitor isolation resistor R 3 . The capacitor isolation resistor R 3 is formed to prevent the parasitic capacitance CP 2 attached to the drains of the MOS transistor M 1 -M 4 to apply to the wiring 25 .

The wiring 25 has own parasitic capacitance CP 1 . If the drains of the MOS transistors M 1 -M 4 are directly connected to the wiring 25 , the capacitance value of the parasitic capacitance CP 2 is added to the capacitance value of the parasitic capacitance CP 1 , increasing the total capacitance value of the parasitic capacitance of the wiring 25 . Therefore, the electrostatic induction signal from the first electrostatic induction electrode 11 is decreased. The influence from the parasitic capacitance CP 2 on the wiring 25 is minimized by forming the capacitance isolation resistor R 3 .

A switching control circuit 27 controls on/off of the MOS transistors M 1 -M 4 and the control signals SA-SD are applied to the gates of the MOS transistors M 1 -M 4 . When the control signals SA-SD are at high level, the corresponding MOS transistors M 1 -M 4 are on and when the control signals SA-SD are at low level, the corresponding MOS transistors M 1 -M 4 are off That is, the control signals SA-SD determine the number of the transistors, that are turned on among the MOS transistors M 1 -M 4 .

When all the MOS transistors M 1 -M 4 are off, an electric current path is not formed from the output terminal of the inverter INV 1 to the first ground potential VSS 1 , and therefore, the threshold of the inverter INV 1 does not change. However, when one of the MOS transistors M 1 -M 4 is turned on, an electric current path is formed from the output terminal of the inverter INV 1 to the first ground potential VSS 1 through the transistor that has been turned on. Therefore, the threshold of the inverter INV 1 decreases. As the number of MOS transistors that are tuned on increases among the MOS transistors M 1 -M 4 , the electric current going through this electric current path goes up, leading to the further reduction of the threshold of the inverter INV 1 .

The input threshold of the inverter INV 1 can be adjusted by forming the first input threshold adjusting circuit 22 , keeping the electric current consumption of the first reception and amplification circuit 21 minimum. The electric current going through the inverter INV 1 increases, making the electric current consumption larger, when the signal around the input threshold of the inverter INV 1 is constantly inputted. The electric current going through the inverter INV 1 can be reduced by adjusting the input threshold of the inverter INV 1 using the first input threshold adjusting circuit 22 , namely, by differentiating the level of the input signal and the input threshold.

The first input threshold adjusting circuit 22 is formed at the side where the ground potential VSS 1 is disposed and it makes the input threshold of the inverter INV 1 adjustable towards the reduction of the threshold. It is also possible to form the first input threshold adjusting circuit 22 at the side where the source voltage VDD 1 is disposed and to make the input threshold of the inverter INV 1 adjustable towards the increase of the threshold. As for the switching controlling circuit 27 , switching can also be controlled through a program using a microcomputer built in the IC card 10 .

The first feedback circuit 24 has a configuration where the output signal of the inverter INV 2 is sent back to the feedback electrode 12 . That is the output signal of the inverter INV 1 of the first reception and amplification circuit 21 is inputted to the feedback inverter INV 2 through a buffer circuit 26 . The output signal of the feedback inverter INV 2 is applied to the first feedback electrode 12 .

Suppose the data signal is transmitted from read and write device 100 to the IC card 10 . The data signal which has been inverted and amplified by the reception and amplification circuit 21 of the IC card 10 is further inverted by the feedback inverter INV 2 and applied to the first feedback electrode 12 . Therefore, the induction charges of opposite polarity appear at the second electrostatic induction electrode 101 of the read and write device 100 . That is, a signal that has the same polarity as that of the original data signal from the read and write device 100 reappears.

Then, an inverted signal of the reappeared signal appears at the first electrostatic induction electrode 11 of the IC card 10 because of the further electrostatic induction caused by the reappeared signal. That is, the amplitude of the data signal at the first electrostatic induction electrode 11 is strengthened. This can prevent the reception error even if there is a difference more or less between the first ground potential VSS 1 of the IC card 10 and the second ground potential VSS 2 of the read and write device 100 .

The detailed operation of the device when the data signal is sent from the IC card 10 to the read and write device 100 is explained below based on FIGS. 3A , 3 B and 3 C. The same operation will take place when data is sent from the read and write device 100 to the IC card 10 .

The data signal that repeats H level and L level signals is applied to the first electrostatic induction electrode 11 from the first signal generation circuit 23 of the IC card 10 as shown in FIG. 3A . H level is the source voltage VDD 1 of the IC card 10 and the L level is the first ground potential VSS 1 .

The induction charges of the opposite polarity appear at the second electrostatic induction electrode 101 of the read and write device 100 due to the electrostatic induction. The electrostatic induction signal caused by the electrostatic charges becomes the signal inverted from the data signal and is transmitted to the wiring 125 connected to the second electrostatic induction electrode 101 . The electrostatic induction signal on the wiring 125 is the signal inverted from the original data signal as shown in FIG. 3B . The amplitude of the signal is reduced because of the influence from the parasitic capacitance CP 1 of the wiring 125 .

The electrostatic induction signal at the wiring 125 is inverted and amplified by the second reception and amplification circuit 121 . That is, the electrostatic induction signal is changed to a differential wave form by going through the input capacitor C 1 . This differential wave form gets smoother, as shown in FIG. 3C , by increasing the capacitance value of the input capacitor C 1 and it can be inputted to the inverter INV 1 .

The symbol Vt in FIG. 3C signifies the input threshold of the inverter INV 1 . That is, as it is showed in FIG. 3C and FIG. 3D , the output signal of the inverter INV 1 is at H level, when the input signal is lower than the threshold Vt and the output signal of the inverter INV 1 is at L level, when the input signal is higher than the threshold. In this case, the H level is the second source voltage VDD 2 of the read and write device 100 and the L level is the second ground potential VSS 2 . The electrostatic induction signal is inverted and amplified by the inverter INV 1 in this way and the data signal sent from the IC card reappears. Accordingly, the data communication device of this embodiment enables the date communication with low power consumption and low manufacturing cost.

The data transmissions are done in dual directions between the IC card 10 and the read and write device 100 in the embodiment described above. This invention is, however, not limited to this embodiment. It can be widely used in the non-contact data transmission.

It is also possible to use only the necessary circuit configurations among various circuit configurations described in the embodiment above. For example, both the IC card 10 and the read and write device 100 have the first and second transmission and reception circuits 20 and 120 of the same configurations respectively. However, when this embodiment is applied to the data transmission of single direction, only the circuit configurations required for the single direction data transmission (for example, the first signal generating circuit 23 formed at the side the IC card and the reception and amplification circuit 121 formed at the side of the read and write device 100 ) are necessary to be formed.