JPH0559557U - Data carrier modulation circuit - Google Patents

Abstract

(57) [Summary] [Object] The present invention improves that the modulation polarity of an AC electromagnetic field modulation circuit for data transmission is inverted due to the withstand voltage characteristics of components of an electromagnetic coupling type data carrier. [Configuration] A coil for receiving electric power, a series circuit of a resonance capacitor and a resistor, and a voltage limiting circuit are connected in parallel, and both ends of the resistor are short-circuited or opened by a switching means to determine the Q value of the LC resonance circuit. It is varied, which modulates the current through the coil. [Effect] The polarity of the data transmitted from the data carrier is maintained constant regardless of whether the power induced in the coil is small or excessive.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to improvement of a data transmission circuit of a powerless electromagnetically coupled data carrier which is supplied with power by an alternating magnetic field generated from a fixed facility and communicates data with the fixed facility. Non-contact type IC cards, industrial data tags, etc. are also included in the scope. .

[0002]

[Prior Art]

 In the conventional electromagnetic coupling type data carrier, as shown in FIG. 2, a resonance capacitor (2) is connected in parallel with a coil (1) for receiving electric power to form an LC resonance circuit, and a capacitor is used as a load of the LC resonance circuit. (10) is provided, and the load is connected or disconnected by the switching means (5) to modulate the current flowing through the coil, and a response signal is generated according to the change in the current.

FIG. 3 is also an example of a conventional electromagnetic coupling type data carrier, in which the capacitor (10) in FIG. 2 is replaced with a resistor (11).

[0004]

[Problems to be solved by the device]

 In order to increase the communicable distance of the electromagnetic coupling type data carrier, the output of the antenna coil of the fixed facility must be increased. However, if this is done, if the data carrier is brought near a fixed facility, an excessive voltage will be induced in the LC resonant circuit consisting of the data carrier coil and capacitor, increasing the risk of the IC of the data carrier being destroyed. .. In order to avoid this IC destruction, it is necessary to connect a voltage limiting circuit in parallel with the coil. However, the increase / decrease in the current when the load is turned on / off in the LC resonant circuit is reversed depending on whether the voltage induced in the LC resonant circuit is clamped by the voltage limiting circuit or not. This means that the polarity of the communication data is reversed when the data carrier is near the fixed facility and when it is far away. In many cases, the conventional electromagnetic coupling type data carrier does not have a voltage limiting circuit connected in parallel with the LC resonance circuit as shown in FIGS. 2 and 3, and therefore the withstand voltage of the IC is increased. Further, even if the device has a voltage limiting circuit, the withstanding voltage of the IC must be increased because the limiting voltage is high. However, in order to increase the withstand voltage of the IC, it is necessary to specialize the manufacturing process of the IC or increase the chip size of the IC, which causes a problem that the manufacturing cost of the IC increases. The object of the present invention is to overcome the conventional drawbacks and to realize a new signal transmission circuit in order to realize an electromagnetic coupling type data carrier having a wide communicable range by using an IC having an ordinary withstand voltage characteristic. Is.

[0005]

[Means for Solving the Problems]

 In order to solve the above problems, in the present invention, a series circuit of a resonant capacitor and a resistor and a voltage limiting circuit are connected in parallel to a coil of a data carrier, and switching means is provided to short-circuit both ends of the resistor. It was configured to open.

[0006]

[Action]

 When the switching means is turned on and both ends of the resistor are short-circuited in the above configuration, the Q value of the LC resonant circuit including the coil and the resonant capacitor becomes large, and the current flowing through the coil becomes extremely large. When the switching means is turned off and a resistor is inserted in the LC resonance circuit, the Q value becomes small and the current flowing through the coil becomes small. That is, by turning the switching means on and off, the current flowing through the coil can be increased or decreased to send data. This current modulation has the same polarity regardless of whether the coil terminal voltage is clamped by the voltage limiting circuit, and the current increases when the resistor is short-circuited. Therefore, regardless of whether the data carrier is near or far from the fixed facility, the polarity of the data does not change and stable data communication is possible.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the electromagnetic coupling type data carrier of the present invention and showing the theoretical 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 at both ends of the coil (1). It is connected in parallel. One end of the parallel circuit forms the reference potential line Vdd, and the other end is connected to the cathode of the diode (6). The anode of the diode (6) forms the 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 source 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 the alternating electromagnetic field supplied from the fixed facility. The induced voltage is detected and rectified by the diode (6) and the filtering capacitor (7) and supplied as a power source for the data carrier main circuit (8). In the normal state, the switching means (5) is kept in the ON state 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. Now, considering an AC magnetic field emitted from a fixed facility located relatively far away, the voltage induced in the coil (1) is not excessive, so that no current flows in the voltage limiting circuit (4). Therefore, the LC resonance circuit enters a resonance state and a resonance current flows through the coil (1). When the switching means (5) is turned off by the switch control signal (9) in such a state, the resistor (3) is inserted in the LC resonance circuit, so that the Q value becomes small and the current flowing through the coil (1). Becomes 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, an extremely large amount of power is induced in the coil (1), but the terminal voltage of the coil (1) is clamped to a constant value by passing a current through the voltage limiting circuit (4), and the LC resonance circuit is brought into resonance. Don't However, when the switching means (5) is turned on by the switch control signal (9), the resistor (3) is short-circuited, so that a large current flows through the coil (1) and the resonance capacitor (2). It is self-evident that the current is reduced when the switching means (5) is turned off. From the above, it is clear that the relationship between the increase / decrease in current and the polarity of the switch control signal (9) is constant regardless of the amount of 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 also one of the embodiments of the present invention and 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 and is double-voltage rectified by the diode (6) and the filtering capacitor (7) to form the power supply line Vss of the data carrier main circuit. One end of the resonance capacitor (2) is connected to the 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, the MOS transistor (15) can be used as the switching means. Further, the series circuit of the resonance capacitor (2) and the resistor (3) is directly connected to the coil (1) in an alternating manner, and is equivalently connected in parallel. The Zener diode (13) operates as a diode for the level shifter and also has a function as a voltage limiting circuit. When excessive power is induced in the coil (1), a current is caused to flow so that the voltage of the power supply line Vss is reduced. Work to limit. The drain and source of the MOS transistor (15) are connected to both ends of the resistor (3), and the gate is given a switch control signal (9) output from the data carrier main circuit to control the Q value of the LC resonance circuit. It is like this. The resistor (14) that pulls down the gate of the MOS transistor (15) to the power supply line Vss is the output signal of the data carrier main circuit (8) because the data carrier is far from the fixed facility and sufficient power is not supplied. When it is weak, it works to turn on the transistor, increasing the Q value of the LC resonant circuit. As a result, the terminal voltage of the coil (1) can be amplified, so that the operating range of the data carrier can be expanded. In such a configuration, when the MOS transistor (15) is turned on and off, the current in the coil (1) increases and decreases, but the operation is the same as in the case of FIG. 1 described above, and the polarity is constant over a wide operating range. Can communicate data.

[0009]

[Effect of the device]

 According to the present invention, even if the electromagnetically coupled data carrier is placed near the antenna coil of a fixed facility and excessive power is induced in the coil of the data carrier, the voltage limiting circuit works to withstand the components of the data carrier. No voltage that exceeds the voltage 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 ICs and capacitors used in data carriers, and it is possible to save component costs and manufacture low-cost electromagnetic coupling type data carriers. Also, since the strength of the alternating 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 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 resonance 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)

[Scope of utility model registration request] 1. In a non-power-supply electromagnetically coupled data carrier, a series circuit of a resonant capacitor and a resistor and a voltage limiting circuit are connected 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, characterized in that a current flowing through the coil is modulated by short-circuiting or opening, and a response signal is generated by a change in the current.