JP2001211108A - Non-contact communication medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent impedance variation from becoming small owing to the on/off switching of an FET and to eliminate loss due to a reactive current. SOLUTION: This medium is equipped with an antenna coil L, a resonant capacitor C which is connected across the antenna coil L, a diode D which has its anode connected to one terminal of the antenna coil L, and an N-channel FET (switch element SW) which has its drain connected to the cathode of the diode D and its source connected to the other terminal of the antenna coil L, and the reactive current is not caused to flow through a parasitic diode PD generated between the source and drain of the H-channel FET.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contactless communication medium used for a contactless automatic ticket gate, various contactless identification devices, and the like.

[0002]

2. Description of the Related Art A non-contact communication medium is a medium for transmitting and receiving data by electromagnetically coupling with a main unit. For example, there is a non-contact IC card using a non-contact automatic ticket gate as a main unit. This contactless IC card
An antenna coil, a resonance capacitor connected in parallel to both ends of this antenna coil, and an N-channel FET connected in parallel to this resonance capacitor. Transmission data is given to the gate of this FET to change the impedance at both ends of the antenna coil. Then, transmission is performed. Also,
The signal is received by demodulating the change in the voltage of the resonance capacitor. Further, in a non-contact type IC card without a built-in battery, a power supply voltage is taken out by rectifying a voltage between both ends of a capacitor, and this is supplied to a control circuit and a storage circuit.

FIG. 3 shows a configuration diagram of a conventional non-contact IC card having the above configuration.

[0004] The antenna coil L is electromagnetically inductively coupled by approaching the antenna coil provided on the main unit, and the resonance capacitor C forms a parallel resonance circuit with the antenna coil L and is connected to the antenna coil of the main unit. At the time of electromagnetic induction coupling. The resonance capacitor C is connected to a switch element SW composed of an N-channel FET, and the switch element SW is turned on / off by transmission data from the transmission / reception circuit 1 during transmission. During reception, the transmission / reception circuit 1 demodulates the voltage generated at both terminals of the capacitor C to obtain reception data. The received data is stored in the storage circuit 3 by the control circuit 2, or the received data is stored in the control circuit 2 based on the data stored in the storage circuit 3.
Creates transmission data. Further, the voltage between both ends of the capacitor C is rectified by the power supply circuit 4 and taken out as the power supply voltage of the transmission / reception circuit 1, the control circuit 2, and the storage circuit 3.

[0005] A non-contact communication medium having the above configuration is disclosed in, for example, Japanese Patent Publication No. 62-43238.

[0006]

However, in the non-contact communication medium conventionally proposed as described above, a parasitic diode PD having a drain as a cathode between a drain and a source is usually used as a switching element (see FIG. 1).
In order to use a FET that can be used, when the drain and source of this FET are connected to both terminals of the antenna coil L,
An invalid current flows from the source to the drain irrespective of the on / off state of the FET, thereby reducing the impedance change due to the on / off state of the FET, deteriorating the noise resistance of transmission data, and increasing the loss due to the reactive current. There was a problem of becoming.

Accordingly, an object of the present invention is to prevent a change in impedance due to the on / off of the FET from becoming small and to eliminate a loss due to a reactive current.

[0008]

The present invention is configured as follows to solve the above-mentioned problems.

That is, an antenna coil, a resonance capacitor connected in parallel to both ends of the antenna coil, a diode having an anode connected to one terminal of the antenna coil, and a drain connected to a cathode of the diode and the other terminal of the antenna coil. And an N-channel FET having a source connected thereto, and transmission is performed by giving transmission data to the gate of the FET and changing the impedance at both ends of the antenna coil.

According to the above configuration, when the FET is off, an invalid current does not flow through the FET even if the antenna terminal connected to the anode of the diode becomes a negative voltage.
For this reason, there is an effect that the impedance change due to ON / OFF does not become small and the loss can be reduced.

Further, by connecting a resistor in series with the diode, the current flowing from the drain to the source can be adjusted to an appropriate magnitude.

By connecting the anode of the diode to the connection point between the antenna coil and the power supply circuit and connecting the cathode to the drain of the FET, the voltage generated in the resonance circuit is directly input to the power supply circuit.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a configuration diagram of a contactless IC card according to an embodiment of the present invention.

This non-contact IC card has an antenna coil L and a resonance capacitor C connected in parallel to both ends of the antenna coil L, as in the conventional card shown in FIG.
N channel F connected in parallel to antenna coil L
A switch element SW made of ET, a power supply circuit 4 for rectifying a voltage generated in the resonance circuit to extract a power supply voltage, a demodulation of a voltage generated in the resonance circuit to create reception data, and a switch based on transmission data. The transmission / reception circuit 1 includes a transmission / reception circuit 1 for controlling the switching of the element SW, a control circuit 2 for processing transmission / reception data, and a storage circuit 3 for storing transmission / reception data.

An electromagnetic wave for constantly transmitting power is output from a reader / writer (not shown), and when the non-contact IC card enters a predetermined area near the reader / writer, the non-contact IC card is output.
An induced power due to the electromagnetic wave is generated in the antenna coil L of the card, and a voltage Q times the induced power is generated in a resonance circuit including the antenna coil L and the resonance capacitor C. Here, Q is the quality factor of the resonance circuit.
tor is the ratio of the load impedance of the resonance circuit to the reactance of the antenna coil L. Then, the power supply circuit 4 of the non-contact IC card rectifies the voltage generated in the resonance circuit and converts it to a substantially constant DC voltage. This DC voltage is used as a power source for all operations of the contactless IC card.

Transmission of a command from the reader / writer to the non-contact IC card is performed by applying ASK modulation to the electromagnetic wave with a command data string. At this time, the voltage generated in the resonance circuit changes in accordance with the command data, so that the transmission / reception circuit detects and amplifies the voltage and outputs it to the control circuit 2 as a command data string. The control circuit 2 analyzes the command, executes commands such as authentication, read, and write, and outputs response data to the transmission / reception circuit 1.

The transmission / reception circuit 1 encodes a response data string output from the control circuit 2 and outputs a signal for turning on / off the switch element SW. When the switch element is turned ON / OFF, a response is transmitted to the reader / writer.

The configuration differs from the non-contact IC card shown in FIG.
The point is that a diode D is connected between the drains of the channel FETs. The connection direction of the diode D is a direction in which the cathode is connected to the drain of the N-channel FET. The anode of the diode D is connected to a connection point between the antenna coil L and the power supply circuit 4.

With the above configuration, it is possible to prevent the diode D from flowing an invalid current to the parasitic diode PD having the drain as a cathode. For this reason, it is possible to prevent a change in impedance due to ON / OFF of the FET from being reduced, and to suppress power consumption due to a flow of a reactive current.

Since the diode D is connected in series with the switch element SW, only a half-wave rectified current flows through the switch element SW. Transmission can be performed without any problem. On the other hand, since the anode of the diode D is connected to the connection point between the antenna coil L and the power supply circuit 4, the output of the resonance circuit is directly input to the power supply circuit 4. Therefore, there is no influence of the rectification of the diode D on the extraction of power.

FIG. 2 shows another embodiment of the present invention.
In this embodiment, a resistor R for adjusting current is connected in series to a diode D. By connecting the resistor R in series, the current flowing into the FET can be easily adjusted.

[0022]

According to the present invention, transmission data is stored in the FET.
When the transmission is performed by changing the impedance of both ends of the antenna coil by giving it to the gate of the FET, it is possible to prevent an invalid current from flowing through the parasitic diode having the drain as a cathode between the drain and the source of the FET. , The change in impedance due to ON / OFF of the power supply can be prevented from becoming small, and invalid power consumption can be suppressed. Therefore, in particular, a small non-contact IC without a battery
Very useful for cards and the like. In addition, by connecting a resistor in series with the diode, the current flowing through the FET can be adjusted, which makes it easy to set an appropriate current according to the characteristics of the FET used.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a non-contact IC card according to an embodiment of the present invention;

FIG. 2 is a main part configuration diagram of a non-contact IC card according to another embodiment of the present invention;

FIG. 3 is a configuration diagram of a conventional non-contact IC card.

[Explanation of symbols]

 L-antenna coil C-resonant capacitor R-resistance D-diode SW-switch element (N-channel FET)

Claims (2)

[Claims] An antenna coil, a resonance capacitor connected in parallel to both ends of the antenna coil, a diode having an anode connected to one terminal of the antenna coil,
N-channel FET with drain connected to the cathode of this diode and source connected to the other terminal of the antenna coil
A non-contact communication medium comprising: transmitting transmission data to a gate of the FET and changing impedance at both ends of the antenna coil to perform transmission. 2. The non-contact communication medium according to claim 1, wherein a resistor is connected in series to said diode.