JPH04256226A - Non-contact medium communication circuit provided with resonance circuit - Google Patents

Abstract

PURPOSE:To always set a resonance circuit in a resonance state and to transmit data at high speed for a long distance with high reliability by means of supplying small apparent power even with a low frequency. CONSTITUTION:Switch elements SW1 and SW2 change over two coils L1 and L2 connected to a capacitor C. The timing of switching is that when an input current I for the coils becomes '0'. A zero crossing detection circuit 1 detects the timing of zero crossing. A switching circuit is provided so that a system is switched to the switch elements SW1 and SW2 based on transmission data at timing when the coil input current (i) is '0'.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention uses an LC resonant circuit to perform data communication with a non-contact medium having a power receiving section and a data communication section, and to supply power to the medium. Relating to contact media communication circuits.

0002

BACKGROUND OF THE INVENTION As an alternative to conventional systems for exchanging information with contact media such as magnetic cards, contactless media communication systems equipped with resonant circuits are currently being proposed.

[0003] A contactless media communication circuit with a resonant circuit is
AC power (
carrier) and modulates this carrier with communication data. At this time, the LC resonant circuit acts as an antenna and outputs the modulated electromagnetic waves to the outside. Non-contact media such as commuter passes are internally equipped with a data processing unit including a register. By coupling this non-contact medium and the above-mentioned non-contact medium communication circuit by electromagnetic waves, power supply and data transmission are performed simultaneously, and information is exchanged between the two.

0004

However, since the above-mentioned conventional non-contact medium communication circuit uses a simple LC circuit as a resonant circuit, it has the following drawbacks.

(1) In a configuration in which power supply and data transmission are performed at different frequencies, the strong electromagnetic waves of the power supply affect the transmitted data, reducing the reliability of the data.

(2) If power supply and data transmission are performed at the same frequency, the data transmission speed is limited by the frequency, so high-speed data transmission cannot be achieved.

(3) In (2) above, if the frequency is increased, the electric field strength at the position λ/2π is 15 mV, which is legally regulated.
(below), the output cannot be increased and the transmission distance will decrease.

(4) Furthermore, if high-speed data transmission is attempted while the frequency is low, the period of transient phenomena occurring at the falling and rising edges of data becomes longer, making it almost impossible to utilize the resonance state. That is, it becomes necessary to supply extremely large apparent power to the coil.

An object of the present invention is to provide a contactless media communication circuit equipped with a resonant circuit that can solve the above problems by switching two coils or capacitors so that a resonant state can always be maintained. do.

0010

[Means for solving the problem] Two devices with the same impedance
an LC resonant circuit in which a capacitor is connected in parallel or in series to a circuit in which two coils are connected in parallel via switch elements; a power supply section that supplies alternating current power to the LC resonant circuit; and a coil input current of the LC resonant circuit. The present invention is characterized in that it includes a zero cross detection circuit that detects the timing when the current is zero, and a switching circuit that switches the switch element at the timing when the coil input current is zero based on transmission data.

[0011] The winding directions of the two coils can be reversed.

[0012] Further, the resonance frequency when each of the two coils and the capacitor are connected is f1.
, f2, and the power supply section is a frequency variable type capable of outputting at either frequency f1 or f2, and the switching circuit switches the switch element at the timing when the coil input current is zero, and the power supply section It is characterized by switching the output frequency from the resonant frequency to the same frequency as the resonance frequency at that time.

Furthermore, the two coils may be replaced by two capacitors having the same impedance, the capacitors may be replaced with coils, and the zero-cross detection circuit may detect the timing when the input voltage is zero.

[0014]

[Operation] Assume that one of the two coils (this coil is used as an antenna coil) is connected to a capacitor and is in a resonant state at a certain timing. This L
When the zero-crossing timing of the coil input current is detected while power is being supplied to the C resonance circuit, the switching circuit switches the switching element. In other words,
The antenna coil is removed from the capacitor and the other coils are connected to the capacitor to form an LC resonant circuit. Since the switching of the switch element occurs at a timing when the coil input current is zero, the resonance conditions of the entire circuit remain unchanged. Therefore, electromagnetic waves are output from the antenna coil with the highest efficiency.

Furthermore, if the winding directions of the two coils are reversed, power can be supplied in both phases when the transmission data is 0 and 1. In other words, power can be supplied at 100% duty. In this case, the data is P
It is transmitted using SK (Phase Shift Keying).

[0016] Furthermore, if the resonance frequency between the first coil and the capacitor is f1, and the resonance frequency between the second coil and the capacitor is f2, the power supply section can output either frequency f1 or f2. In this case, the frequency is switched between f1 and f2 each time the switch element is switched. In this case as well, power can be supplied at 100% duty, and data will be output using frequency modulation (FSK).

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of the present invention. This embodiment has two coils L1 and L2 and a capacitor C.
A parallel resonant circuit is constituted by one of the coils and the capacitor. In this embodiment, coil L2 is used as a dummy coil, and coil L1 is used as an antenna coil. A switch element SW1 is connected in series to the antenna coil L1, and a switch element SW2 is connected in series to the dummy coil L2. Only one of the switch elements SW1 and SW2 is turned on. A power supply section e is connected to this LC parallel resonant circuit. This power supply part e has an output frequency f0
It is.

The input current I to the coil is detected by a current zero-cross detection circuit 1. This zero cross detection circuit 1 can be constructed from a known circuit. The output of zero cross detection circuit 1 is led to hold circuit 2. This hold circuit 2 is triggered by the output from the zero-cross detection circuit 1, holds input data (transmission data), and outputs a switching signal to the switch elements SW1 and SW2. When a switching signal is output, the switching elements SW1 and SW2 are switched. In addition, 1
A signal is output at the timing when the coil input current I becomes 0 every bit-equivalent time.

[0019] Furthermore, the data is the carrier frequency (f0)
The data is synchronized with the carrier by the synchronization circuit 2 based on the ratio of the data baud rate and is output to the hold circuit 2. For example, when the baud rate is f0/2, data is output from the synchronization circuit 2 to the hold circuit every T=2/f0 while being synchronized with f0.

FIG. 2 shows a timing chart when the parallel resonant circuit of FIG. 1 is used. The timing at which the switching element switches is when the data changes from “1” to “0”
and when it switches from "0" to "1". At this switching timing, the input current I to the coil is zero. Further, since the antenna coil L1 and the dummy coil L2 have the same impedance, the resonance condition is maintained even after switching of the switch element. Therefore, in the example shown in the figure, the data is “
1'', an electromagnetic wave is output from the antenna coil L2, but as shown in the figure, since switching is performed while the resonance state is maintained, there is no waveform distortion of the input current.

In the above embodiment, the antenna coil L1
Although the dummy coil L2 and L2 have the same winding structure, they may have a reverse winding structure. In this case, the dummy coil also serves as an antenna coil, and an electromagnetic wave whose phase is reversed is output from the dummy coil L2 during the period when the data is "0". That is, PSK (phase shift keying)
Can send. In this PSK transmission, power can be transmitted at 100% duty, so the transmission power is doubled compared to the embodiment shown in FIG.

FIG. 3 shows another embodiment of the invention. In this embodiment, the power supply unit is composed of e1 and e2, which are switched by switch elements SW3 and SW4. The frequencies of each power supply unit e1, e2 are f1, f2. Moreover, the resonance frequency of the coil L1 and the capacitor C is f
1, and the resonance frequency between the coil L2 and the capacitor C is f2. When the zero-cross detection circuit 1 detects the zero-cross timing of the input current i to the coil, the hold circuit 2 switches the switch elements SW1 and SW2 and simultaneously switches the switch elements SW3 and SW4. When switch element SW2 is on, switch element SW4 is on. When switch element SW1 is on, switch element SW3
is on.

With the above configuration, when the data is "1", an electromagnetic wave is output from the coil L1 at the frequency f1, and when the data is "0", the electromagnetic wave is output from the coil L2 at the frequency f2.
Electromagnetic waves are output from. That is, FSK(freq
(shift keying) transmission. In this case as well, 100%
Power can be supplied according to duty.

FIG. 4 shows yet another embodiment of the present invention. In this embodiment, a series resonant circuit is used as the resonant circuit. Other points are the same as in FIG.

FIG. 5 shows yet another embodiment of the invention. In this embodiment, the capacitor and coil in FIG. 1 are interchanged. In other words, the capacitors C1 and C2 are switched by a switch element. In this case, the zero-cross detection circuit 1 is made into a voltage zero-cross detection circuit. Even in this case, power supply and data transmission can be performed while maintaining the resonance condition in exactly the same way.

Note that in FIG. 1, the zero cross detection circuit 1
may be configured to be detected using the input voltage e, each coil current IL1, IL2, etc. Further, it can also be used as a rising or falling detection circuit.

[0027]

[Effects of the Invention] A large coil current can be caused to flow by supplying a small apparent power. This allows long-distance transmission. Furthermore, high-speed data transmission is possible even if the frequency of the power supply section is low. Furthermore, the reliability of the data is improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 shows a timing chart.

FIG. 3 is a circuit diagram of another embodiment of the present invention.

FIG. 4 is a circuit diagram of still another embodiment of the present invention.

FIG. 5 is a circuit diagram of still another embodiment of the present invention.

[Explanation of symbols]

L1, L2 - coil C-capacitor e-Power supply section 1-Zero cross detection circuit 2-Hold circuit

Claims (4)

[Claims] 1. An LC resonant circuit in which a capacitor is connected in parallel or in series to a circuit in which two coils of the same impedance are each connected in parallel via a switch element, and a power supply unit that supplies alternating current power to the LC resonant circuit. , a resonant circuit comprising: a zero cross detection circuit that detects the timing when the coil input current of the LC resonant circuit is zero; and a switching circuit that switches the switch element at the timing when the coil input current is zero based on transmission data. contactless media communication circuit. 2. A non-contact medium communication circuit according to claim 1, comprising a resonant circuit, wherein the two coils are wound in opposite directions. 3. In claim 1, resonance frequencies when each of the two coils and the capacitor are connected are f1 and f2, respectively, and the power supply section is f1.
. A contactless media communication circuit with a resonant circuit characterized by switching to the same frequency. 4. An LC resonant circuit in which a coil is connected in parallel or in series to a circuit in which two capacitors having the same impedance are connected in parallel via switch elements, and a power supply section that supplies alternating current power to the LC resonant circuit. , a resonant circuit comprising: a zero cross detection circuit that detects the timing when the coil input voltage of the LC resonant circuit is zero; and a switching circuit that switches the switch element at the timing when the coil input voltage is zero based on transmission data. contactless media communication circuit.