JPH0625949U - Data carrier signal demodulation circuit - Google Patents

Abstract

(57) [Summary] [Objective] The present invention realizes a circuit means that efficiently reflects the change in the amplitude of the AC magnetic field for power supply generated from a fixed facility to the change in the AC voltage inside the electromagnetic coupling type data carrier. The purpose is to do. A resonance circuit is configured by connecting a power receiving coil and a resonance capacitor in parallel, and a detection circuit for detecting a voltage change of the power induced in the resonance circuit, and a DC power supply for rectifying and filtering the voltage. The current-voltage conversion element was inserted in series with the rectifier of the rectifier circuit. [Effect] By passing the electric power induced in the coil through the current-voltage conversion element, the voltage between the terminals of the coil changes according to the change of the alternating magnetic field. By detecting this voltage change by the detection circuit, the data superimposed on the AC magnetic field can be efficiently separated and demodulated.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention is an electromagnetically coupled data carrier that operates with electric power induced in a coil by an AC magnetic field emitted from a fixed facility and generates a clock from the frequency of the AC magnetic field, particularly for two-way communication with a fixed facility. However, although it is possible to rewrite and read the data in the built-in electrically rewritable non-volatile memory, this is related to the improvement of the signal demodulation circuit, including non-contact type IC cards and industrial data tags. Contains inside.

[0002]

[Prior art]

 Conventionally, among electromagnetically coupled data carriers that do not have a built-in power supply, there has been no one that can rewrite the contents of memory by bidirectional wireless communication. We have installed a non-volatile memory called MONOS on a C-MOS-IC that has extremely low power consumption and high performance, and has made various modifications including the present invention to create an electromagnetically coupled data carrier that allows memory rewriting. developed.

[0003]

[Problems to be solved by the device]

 In a data carrier that performs bidirectional communication with a fixed facility, data is transmitted by binary modulation of an AC magnetic field, which is a means of supplying electric power and clock frequency. Frequency modulation, phase modulation, amplitude modulation, etc. are conceivable as the binary modulation method, but the binary amplitude modulation method is the best in terms of the simplicity of the demodulation circuit and the stability of the clock frequency. Is. However, in this amplitude modulation, the modulation depth has certain restrictions. In other words, the amplitude modulation depth should be as small as possible in order to reliably extract the clock frequency even when the data carrier is far from the fixed facility and the strength of the AC magnetic field is weak. On the other hand, the detection circuit as the demodulation circuit can accurately demodulate the data if the ratio of the two amplitudes is large. In designing a data carrier, the balance between these two characteristics must be well chosen. However, in an electromagnetic coupling type data carrier, a capacitor is connected in parallel with the power receiving coil to form a resonant circuit in order to increase the voltage amplitude of the inductive power, so the output impedance of the power receiving circuit is large. Has become. Therefore, when the electromotive force induced in the coil is large, the current supplied to the load circuit by the coil also becomes large, so the voltage drop due to the output impedance is large, and the voltage actually generated between the terminals of the coil is as high as expected. Does not grow to Further, when the power induced in the coil is temporarily reduced by the amplitude modulation of the AC magnetic field, the circuit current of the data carrier is supplied from the filtering capacitor of the power supply circuit, and the current is not supplied from the resonance circuit. Therefore, there is no voltage drop due to the output impedance of the resonant circuit. Therefore, the voltage across the terminals of the coil does not drop as expected. Thus, even if amplitude modulation is applied to the AC magnetic field for power supply, the voltage generated between the terminals of the coil of the data carrier cannot be amplitude-modulated to a sufficient depth. The problem to be solved by this proposal is to efficiently convert the amplitude change of the AC magnetic field generated from the fixed facility into the amplitude change of the terminal voltage of the power receiving coil of the data carrier.

[0004]

[Means for Solving the Problems]

 In order to solve the above problems, in the present invention, a current-voltage conversion element is inserted in series with the rectifier of the power supply circuit.

[0005]

[Action]

 The current-voltage conversion element described above converts part of the power supplied from the resonance circuit of the power receiving coil and the capacitor to the circuit load of the data carrier into a voltage, which is added to the voltage between the terminals of the coil. did. As a result, the voltage between the terminals of the coil can be increased when the AC magnetic field is large and the power induced in the coil is large.

[0006]

【Example】

 FIG. 1 is a circuit diagram showing an embodiment of the present invention. Referring to the drawing, the coil 1 constitutes a parallel resonance circuit together with the capacitor 2. One end of the resonance circuit forms the reference potential line Vss, and the other end is connected to the voltage doubler line Vac via the level shift capacitor 3. Between the voltage doubler line Vac and the reference potential line Vss, a level shift diode 4, an output modulation circuit composed of a capacitor 5 and an N-channel MOS transistor 6, a diode 7, a capacitor 8 and a resistor. A detection circuit composed of 9 and a rectification circuit composed of a resistor 11 for current-voltage conversion, a rectification diode 12 and a filtering capacitor 13 are provided.

The output modulation circuit changes the circuit impedance according to the output signal DATAout of the data carrier main circuit 10, thereby amplitude-modulating the alternating current flowing through the coil 1 and changing it into an alternating magnetic field around the coil 1. And send the data to the fixed facility. The detection circuit detects the change in the AC voltage induced in the coil 1 due to the change in the amplitude of the AC magnetic field emitted from the fixed facility, separates the input data DATAin and transmits it to the data carrier main circuit 10. The operation description will be given later.

The DC output voltage Vs0 of the rectifier circuit is stabilized by the constant voltage circuit 14 and becomes a power source Vs1. The power supply Vs1 supplies power to the voltage detection circuit 15 and the clock generation inverter 19 (not shown), and serves as the source voltage of the P-channel MOS transistor 16. A resistor 20 is connected between the input and output of the inverter 19 to form a self-biased amplifier. The AC voltage component of the voltage doubler line Vac is transmitted to the amplifier via the capacitor 18, is saturated and amplified into a rectangular wave, and becomes a clock signal Cl, which is used as a timing signal of the data carrier main circuit 10.

The gate of the transistor 16 is pulled up to the power supply Vs1 by the resistor 17 and at the same time controlled by the output signal Ss of the voltage detection circuit 15. That is, when the voltage detection circuit 15 determines that the voltage of the power supply Vs1 is higher than the minimum operating voltage of the logic circuit and the logic value of the signal Ss becomes L level, the transistor 16 is turned on. The power supply Vs2 of the data carrier main circuit 10 connected to the drain of the transistor 16 starts to be supplied with power. As a result, the data carrier main circuit 10 starts to operate, but the initialization circuit incorporated at the beginning of the data carrier restricts the logic circuit to the communication standby state. In the data carrier having the above-mentioned structure, the method of detecting the data transmitted from the fixed facility by the amplitude modulation method will be described in detail.

FIG. 2 is a circuit diagram showing the impedance arrangement and voltage distribution inside the data carrier. As shown in the figure, the AC voltage of the electromotive force induced in the resonance circuit consisting of the coil 1 and the capacitor 2 is vo (PP value), the parallel impedance of the resonance circuit is Zo, and the impedance of the load circuit of the data carrier is If Zl, the peak value of the voltage doubler line Vac for supplying power to the load circuit of the data carrier is given by the formula 1. However, the voltage loss of the level shift circuit is assumed to be negligible.

[0011]

[Equation 1] Vac = vo · Zl / (Zo + Zl)

Now, assuming that the impedance Zl of the load circuit is sufficiently larger than the impedance Zo of the resonance circuit, Vac = vo from Formula 1. At this time, the relationship between the two becomes like the straight line (a) shown in the graph of FIG. 3, and the crest values of the voltage doubler line Vac are Vh1 and Vl1 with respect to the two values vh and vl of the AC voltage vo, respectively. Become. The waveform (a) in FIG. 4 represents the change of the AC voltage vo, and the waveform (b) represents the voltage waveform of the voltage doubler line Vac corresponding to it. Since the detection circuit detects the crest value envelope of the voltage doubler line Vac, the amplitude of the output signal of the detection circuit becomes the difference between Vh1 and Vl1 and a sufficiently large detection output can be obtained.

However, since most of the data carrier circuit is composed of semiconductors, the impedance Zl of the load circuit rapidly decreases with an increase in the power supply voltage. Further, since the power supply voltage can be regarded as the same as the peak value of the voltage doubler line Vac, in the actual data carrier, the equation 1 becomes as shown by the curve (b) in the graph of FIG. That is, the increase in the peak value of the voltage doubler line Vac becomes slower as the AC voltage vo increases. For the sake of explanation, considering the case where the resistor 11 is short-circuited in the embodiment of FIG. 1, as shown in the graph of FIG. 3, when the AC voltage vo has a value of vh, the voltage doubler line V ac The peak value is Vh2. From this state, it is assumed that the AC voltage vo decreases rapidly and reaches a value of v 1. At this time, since a DC voltage of Vh2 is stored in the filtering capacitor 13 of the rectifying circuit, a reverse bias voltage is applied to the rectifying diode 12 of the rectifying circuit. Therefore, the output modulation circuit and the load circuit other than the detection circuit are disconnected from the voltage doubler line Vac. Therefore, the peak value of the voltage doubler line Vac is substantially determined by the condition of the straight line (a) in the graph of FIG. However, since the peak value does not become larger than Vh2, the peak value eventually becomes a value close to Vh2 even with respect to the AC voltage value vl. That is, even if the alternating voltage vo is amplitude-modulated as shown in the waveform (a) of FIG. 4 by the amplitude modulation of the AC magnetic field, the peak value of the voltage doubler line Vac becomes almost constant, and the voltage of FIG. Since the waveform becomes like (c), signal detection becomes impossible.

When the resistor 11 is inserted in the rectifier circuit, the relationship between the AC voltage vo and the peak value of the voltage doubler line Vac is as shown by the curve (c) in the graph of FIG. As a result, the peak values Vh3 and Vl1 determined by the curve (c) and the straight line (a) are determined for the two values vh and vl of the AC voltage v o, respectively. The waveform (d) in FIG. 4 represents the voltage waveform of the voltage doubler line Vac at this time. The detection circuit detects such a binary voltage level and transmits the detection output whose amplitude is given by the difference between Vh3 and Vl1 to the data carrier main circuit as the input signal DATAin.

The embodiment of FIG. 1 has been described above. In the present invention, the resistor provided in series with the rectifier has a function of converting current into voltage. As long as it has a current-voltage conversion function in this way, for example, an inductance can also achieve the object of the present invention. Further, a plurality of rectifying diodes may be connected in series and the parasitic resistance thereof may be used. Of course, the method of utilizing the Zener voltage of the Zener diode is the best current-voltage converting means and is included in the scope of the present invention.

[0016]

[Effect of device]

 According to the present invention, in the data carrier of the electromagnetic coupling type with no power supply, the change of the amplitude of the alternating magnetic field generated from the fixed facility for supplying power and transmitting data is reflected in the change of the alternating voltage inside the data carrier. I can do it now. As a result, it has become possible to transmit binary data superimposed on an AC magnetic field to a data carrier by the amplitude modulation method. Further, at this time, since the depth of amplitude modulation can be suppressed within a certain range, the frequency of the alternating magnetic field can be continuously supplied to the data carrier. As a result, the clock signal of the data carrier becomes stable and the operation of the logic circuit becomes accurate. When it becomes possible to send data and clock signals from the fixed facility to the data carrier in this way, it is necessary not only to be able to send the data to the data carrier but also to send a control command to the data carrier to start the operation. Since the selection becomes possible, the function of the data carrier is dramatically increased.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a data carrier showing an embodiment of the present invention.

FIG. 2 is a block circuit diagram for explaining the embodiment of FIG.

FIG. 3 is a graph for explaining the operation principle of the present invention, showing a relationship between two voltages vo and Vac.

FIG. 4 is a voltage waveform diagram for explaining the operation principle of the present invention.

[Explanation of symbols]

 1 Coil 2 Resonance Capacitor 5 Modulation Capacitor 6 N-Channel MOS Transistor 7 Detection Diode 8 Detection Capacitor 9 Detection Resistor 10 Data Carrier Main Circuit 11 Current Voltage Conversion Resistor 12 Rectification Diode 13 Filtering Capacitor 14 constant voltage circuit 15 voltage detection circuit

Claims (1)

[Scope of utility model registration request] A non-power-supply electromagnetically coupled data carrier that operates by electric power induced in a coil by an AC magnetic field emitted from a fixed facility, generates a clock signal from the frequency of the AC magnetic field, and has an electrically rewritable nonvolatile memory. In at least a power supply circuit for rectifying and filtering the AC power induced in the coil into a DC power supply, and a detection circuit for detecting a signal superimposed on the AC power by an amplitude modulation method, and the power supply circuit A signal demodulation circuit for a data carrier, characterized in that a current-voltage conversion element is inserted in series with the rectifier constituting the above.