JP2571490Y2 - Data carrier modulation circuit - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a data transmission circuit of a non-power-supply electromagnetic coupling type data carrier which is supplied with electric power by an alternating magnetic field generated from a fixed facility and performs data communication with the fixed facility. This includes non-contact type IC cards, industrial data tags, and the like. .

[0002]

2. Description of the Related Art In a conventional electromagnetic coupling type data carrier, as shown in FIG. 2, an LC resonance circuit is formed by connecting a resonance capacitor (2) in parallel with a coil (1) for receiving electric power. A capacitor (1
0), the load is connected or disconnected by the switching means (5) to modulate the current flowing through the coil, and a change in the current generates a response signal.

FIG. 3 is also an example of a conventional electromagnetic coupling type data carrier, in which a capacitor (10) shown in FIG.
1).

[0004]

In order to increase the communicable distance of an electromagnetically coupled data carrier, the output of an antenna coil in a fixed facility must be increased.
However, if the data carrier is brought near the fixed facility, an excessive voltage is induced in the LC resonance circuit including the coil and the capacitor of the data carrier.
The risk that the data carrier IC is destroyed increases. To avoid this IC destruction, it is necessary to connect a voltage limiting circuit equivalently in parallel with the coil. However, when the voltage induced in the LC resonance circuit is clamped by the voltage limiting circuit and when the voltage is not clamped, the increase and decrease of the current when the load is turned on and off in the LC resonance circuit is reversed.
This means that the polarity of the communication data is inverted between when the data carrier is near the fixed facility and when it is far away. As shown in FIGS. 2 and 3, many conventional electromagnetic coupling type data carriers do not have a voltage limiting circuit connected in parallel to the LC resonance circuit.
The withstand voltage of C was increased. Also, even those having a voltage limiting circuit have to increase the withstand voltage of the IC because the limiting voltage is high. However, in order to increase the withstand voltage of the IC, it is necessary to make the manufacturing process of the IC special, or to increase the chip size of the IC, which causes a problem that the manufacturing cost of the IC increases. The problem of the present invention overcomes such conventional disadvantages,
It is an object of the present invention to realize a new signal transmission circuit in order to realize an electromagnetically coupled data carrier having a large communicable range using an IC having ordinary withstand voltage characteristics.

[0005]

According to the present invention, a series circuit of a resonance capacitor and a resistor and a voltage limiting circuit are connected equivalently in parallel with a coil of a data carrier, and switching means is provided. Thus, both ends of the resistor are short-circuited or opened.

[0006]

In the above arrangement, when the switching means is turned on and both ends of the resistor are short-circuited, the Q value of the LC resonance circuit including the coil and the resonance capacitor becomes large, and the current flowing through the coil becomes extremely large. Further, when the switching means is turned off and a resistor is inserted in the LC resonance circuit, the Q value decreases and the current flowing through the coil decreases. That is, data can be transmitted by increasing or decreasing the current flowing through the coil by turning on / off the switching means. This current modulation has the same polarity regardless of whether the terminal voltage of the coil is clamped by the voltage limiting circuit, and the current increases when the resistance is short-circuited. Therefore, regardless of whether the data carrier is near or far from the fixed facility, the data polarity does not change and stable data communication can be performed.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a circuit diagram showing one of the embodiments of the electromagnetic coupling type data carrier of the present invention and showing a principle configuration of the present invention. As shown in the drawing, a series circuit of a resonance capacitor (2) and a resistor (3) and a voltage limiting circuit (4) in which two zener diodes are connected in opposite directions are provided in parallel at both ends of the coil (1). It is connected. One end of the parallel circuit forms a reference potential line Vdd, and the other end has a diode (6).
Connected to the cathode. The anode of the diode (6) forms a negative power supply line Vss. A filtering capacitor (7) and a data carrier main circuit (8) are connected between the reference potential line Vdd and the negative power supply line Vss. Both ends of the resistor (3) are respectively connected to two terminals of a switching means (5), and the switching means (5) is supplied with a switch control signal (9) from the data carrier main circuit. In the above configuration, an induced voltage is generated in the coil (1) by an AC electromagnetic field supplied from a fixed facility. The induced voltage is detected and rectified by a diode (6) and a filtering capacitor (7), and is supplied as a power source for a data carrier main circuit (8). In the normal state, the switching means (5) is kept on by the switch control signal (9), and the Q value of the LC resonance circuit including the coil (1) and the resonance capacitor (2) is large. Considering now an alternating magnetic field emitted from a fixed facility located relatively far away, no current flows through the voltage limiting circuit (4) because the voltage induced in the coil (1) is not excessive. Therefore, the LC resonance circuit is in a resonance state, and a resonance current flows through the coil (1). In such a state, when the switching means (5) is turned off by the switch control signal (9), the resistor (3) is inserted into the LC resonance circuit, so that the Q value becomes small and the current flowing through the coil (1) becomes Become smaller. Thus, the current of the coil (1) can be modulated by the switch control signal (9). Next, consider the case where the data carrier is near a fixed facility. At this time, very large power is induced in the coil (1), but the terminal voltage of the coil (1) is clamped to a constant value by flowing a current through the voltage limiting circuit (4), and the LC resonance circuit is brought into a resonance state. Not be. However, the switching means (5) is switched by the switch control signal (9).
Is turned on, the resistor (3) is short-circuited, so that a large current flows through the coil (1) and the resonance capacitor (2). It is obvious that the current decreases when the switching means (5) is turned off. From the above, it is apparent that the relationship between the increase and decrease of the current and the polarity of the switch control signal (9) is constant irrespective of the magnitude of the electric power induced in the coil (1). Therefore, stable data communication is realized regardless of the distance between the data carrier and the fixed facility.

FIG. 4 is another embodiment of the present invention.
It is a more specific circuit diagram. In this embodiment, one end of the coil (1) is connected to a level shifter circuit including a capacitor (12) and a Zener diode (13). The potential of the output line of the level shifter circuit is always negative, is double-rectified by the diode (6) and the filtering capacitor (7), and is supplied to the power supply line Vs of the data carrier main circuit.
make s. One end of the resonance capacitor (2) is connected to an output line of the level shifter circuit. Therefore, both terminals of the resonance capacitor (2) are at a potential lower than the reference potential line Vdd. Therefore, a MOS transistor (15) can be used as the switching means. The series circuit of the resonance capacitor (2) and the resistor (3) is directly connected in terms of AC with respect to the coil (1), and is equivalently connected in parallel. The Zener diode (13) operates not only as a diode for the level shifter but also as a voltage limiting circuit. When excessive power is induced in the coil (1), a current flows to limit the voltage of the power supply line Vss. Work to do. The drain and source of the MOS transistor (15) are connected to both ends of the resistor (3), and the gate is supplied with a switch control signal (9) output from the data carrier main circuit to control the Q value of the LC resonance circuit. It has become. MOS transistor (1
The resistor (14) pulling down the gate of (5) to the power supply line Vss is used when the data carrier is far from the fixed facility and there is no sufficient power supply and the output signal of the data carrier main circuit (8) is weak. It works to turn on the transistor and increases the Q value of the LC resonance circuit. Thus, the terminal voltage of the coil (1) can be amplified, so that the operation range of the data carrier can be expanded. In such a configuration, when the MOS transistor (15) is turned on and off, the current of the coil (1) increases and decreases. The operation is the same as that of FIG. Can be.

[0009]

According to the present invention, even if an electromagnetically coupled data carrier is placed near an antenna coil of a fixed facility and excessive power is induced in the coil of the data carrier, the function of the voltage limiting circuit allows the data carrier to be driven. No voltage exceeding the withstand voltage of the component is generated. Moreover, at this time, the current flowing through the coil can be modulated so that the polarity of the data transmitted from the data carrier does not change. As a result, it is no longer necessary to unnecessarily increase the withstand voltage of the IC or the capacitor used for the data carrier, so that the cost of parts can be saved and a low-cost electromagnetically coupled data carrier can be manufactured. In addition, since the intensity of the AC electromagnetic field generated from the antenna coil of the fixed facility can be increased, the communicable distance of the data carrier can be increased, and the usefulness of the electromagnetic coupling type data carrier can be increased.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an electromagnetic coupling type data carrier according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional electromagnetic coupling type data carrier.

FIG. 3 is a circuit diagram of a conventional electromagnetic coupling type data carrier.

FIG. 4 is a circuit diagram of an electromagnetic coupling type data carrier according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coil 2 Resonant capacitor 3 Resistance 4 Voltage limiting circuit 5 Switching means 6 Diode 7, 10, 12 Capacitor 9 Switch control signal 11, 14 Resistance 15 MOS transistor

Claims (1)

(57) [Scope of request for utility model registration] 1. A power supply-free electromagnetic coupling type data carrier, wherein a series circuit of a resonance capacitor and a resistor and a voltage limiting circuit are connected equivalently in parallel with a coil for receiving power, and switching means is provided to connect both ends of the resistor. A modulation circuit for a data carrier, wherein a current flowing through the coil is modulated by being short-circuited or opened, and a response signal is generated by a change in the current.