JPH10224275A - Antenna for reader/writer for non-contact ic card - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce electric resistance value in an inputting part by connecting ends with each other which are opposite to an end that is connected to an intermediate tap through a condenser and making the connection point between either of coils and the condenser ground electric potential. SOLUTION: An amplifier amplifies an input signal fo into an output signal, that has amplitude between positive voltage VCC and negative voltage VEE and supplies it to a tap between coils L10 and L20 through a resistance R1. An oscillator circuit is an LC-type Hartley oscillator circuit that uses the coils and a condenser, and a parallel resonant circuit that uses an intermediate tap between the coils having a broad resonance Q, so that the adjustment of the circuit may be easy. Here, resistances R2 and R3 are resistance parts that are contained by the coils L10 and L20. An inputted signal fo is oscillated after it passes through the amplifier and the resistance R1. Thus, an oscillated output signal is oscillated from here to a non-contact IC card with the coils L10 and L20 as antennas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reader / writer antenna for performing power transmission and data communication with a non-contact type IC card having no battery.

[0002]

2. Description of the Related Art As an example of the technique of the antenna of the reader / writer, there is one implemented by an induction radio system using a magnetic field. This technique generally uses an antenna coil having a function of both power transmission and data transmission from a reader / writer, and utilizes a series resonance of the antenna coil and a capacitor. FIG. 2 shows an example of the circuit. In the figure, the amplifier is the input signal f
0 is amplified to a signal having an amplitude swinging between the positive voltage Vcc and the negative voltage VEE. R4 is a resistor for adjusting the Q of the antenna, C2 is a resonance capacitor, L30 is a coil, and R5 is an internal resistance of the coil L30.

In FIG. 2, under the condition of series resonance of L30 and C2: ω0 = 1 / L30 · C2 (1) In equation (1), if the current flowing through this circuit is i, then V0 = i · ( R4 + R5) (Equation 2) On the other hand, when data transmission has a speed of P (bps), the Q required by the antennas
Assuming W, it is general that Q = f0 / BW (Equation 3) BW ≒ 2 · P (Equation 4)

Here, the above-mentioned Q is also expressed as: Q = ω0 · L / (R4 + R5) (Equation 5), and Q can be adjusted by an external resistor R4. Therefore, V0 = i · 4π · L30 · P (6) Here, the generated magnetic field corresponding to the required power transmission distance is uniquely determined by the current x the number of turns, that is, the current if the coil area and the number of turns are determined by AT (ampere turn). As a result, the output voltage of the antenna driving circuit is uniquely determined as shown in the above equation (6).

[0005]

In the above conventional example, the heat generated by the external resistor that determines the Q of the antenna circuit is W _R4 =
I ² × R ₄ . Therefore, in order to further extend the power transmission distance while keeping Q constant, it is necessary to increase the current i. Thus, heat generation in R ₄ increases in proportion to the square of the I, there is a problem that a problem such as increase in temperature comes to occur. The present invention has been made in view of such circumstances,
It is an object of the present invention to provide an antenna capable of reducing a term of R4 of R2 + R5 in Expression 2 while keeping Q constant for a required bandwidth without using Expression 5.

[0006]

According to the first aspect of the present invention,
Using a middle tap, one coil is electrically divided into a first coil and a second coil for input at an arbitrary position, and in the first coil and the second coil,
A circuit configuration in which respective ends opposite to the end connected to the intermediate tap are connected to each other via a capacitor, and a connection point between one of the first and second coils and the capacitor is set to a ground potential. Non-contact type I characterized by having
This is a C card reader / writer antenna.

According to a second aspect of the present invention, in the reader / writer antenna for a non-contact type IC card according to the first aspect, the intermediate tap is slidable.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an antenna for a reader / writer of a non-contact type IC card according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of the antenna according to the first embodiment. In FIG. 1, R1 is an external resistor that adjusts the resonance Q of the circuit by changing its value. By using an intermediate tap for a single coil, two coils L10 and L20 are made. L
10 is a first tapped antenna coil, L20 is a second tapped antenna coil, and by moving the position of the tap, the range of the first and second antenna coils is changed. , L1
The ratio of the values of 0 and L20 can be changed. R2 is the internal resistance of the antenna coil L10, and R3 is the internal resistance of the antenna coil L20. Therefore, this resistance R
2 and R3 may be replaced by the resistance of the coils L10 and L20, or independent resistance elements may be used. C1 is a capacitor for resonance. The amplifier amplifies the input signal f0 to an output signal having an amplitude between the positive voltage Vcc and the negative voltage VEE, passes through the resistor R1, and supplies it to the tap between L10 and L20.

Next, the operation of this circuit will be described. The circuit shown in FIG. 1 is a so-called LC-type Hartley oscillation circuit using a coil and a capacitor. Here, the resistors R2 and R3 are actually connected to the coils L10 and L2.
0 and the resistance components included in each. In FIG.
The input signal f0 passes through the amplifier and oscillates after passing through the resistor R1. As for the oscillation frequency fa, the values of the coils L1 and L2 are La and Lb, respectively, and the capacitor C1
Is represented by the following equation: Fa ≒ 1 / 2π ｛(La + Lb) Ca｝ ^1/2 . The output signal oscillated in this manner is transmitted from this coil L10 and L20 to the non-contact type IC card using the antenna as an antenna.

In general, as is well known in high frequency intermediate frequency filter circuits and the like, a parallel resonance circuit using an intermediate tap of a coil is better than a simple parallel resonance circuit using a coil and a capacitor. The resonance Q is wide, and the circuit adjustment is easy. FIG. 3 is a circuit diagram showing a simple parallel resonance circuit using the above-mentioned fixed coil and capacitor, and a graph showing the relationship between input frequency and output current by this circuit. On the other hand, FIG. 4 shows an example of the parallel resonance circuit using the above-described intermediate tap and a graph showing the relationship between the input frequency and the output current similarly to FIG. 3. Comparing FIG. 3 with FIG. 4, it can be seen that Q is gentler in the circuit of FIG. 4 using the intermediate tap. The present invention utilizes this principle for an antenna coil, and has an effect of setting Q by adding a small external resistor as compared with the series resonance system. In other words, the coiled parallel resonance antenna with the tap itself uses the action having Q having a wider width than the series resonance antenna.

Here, the output current and Q are measured and compared with those according to the prior art and those according to the present invention by simulation on a computer. FIG.
Is a circuit for simulating a serial antenna circuit according to the prior art, and in correspondence with FIG. 2, the resistors R4 and R4 in FIG.
R5, capacitor C2, and coil L30 correspond to R6, R11, C2, and L12 in FIG. 5, respectively. 6 and 7
Is a circuit for simulation of the circuit according to the present invention, and when this is taken into correspondence with FIG. 1 described above, the resistor R1 in FIG. 1 corresponds to R63 in FIG. 7, but there is no corresponding one in FIG. I have. The coils L10 and L20 in FIG. 1 correspond to L1 and L2 in FIGS. 6 and 7, respectively, and the resistance components R2 and R3 in FIG. 1 correspond to R66 and R65 in FIGS. Compared with FIG. 1, both L2 and R65 in FIG. 6 / FIG.
Are reversed, but this is for the convenience of simulation, and is actually equivalent without any difference. The capacitor C1 in FIG. 1 corresponds to C60 in FIGS.

As an input, instead of the amplified input signal f0 in FIGS. 1 and 2, VSIN9,
6 and 7, VSIN 54 is used in the simulation as a waveform generation source. Both of these waveform sources
An input having a voltage value of 1 V and a frequency of 153 kHz is provided.
A graph obtained as a result of performing the simulation in this manner is shown in FIG. 8 using the circuit of FIG. 5, FIG. 9 using the circuit of FIG. 6, and FIG. 1 using the circuit of FIG.
0, respectively.

First, when R6 = 100Ω is inserted as an external adjustment resistor in the circuit example of FIG. 5 and simulation is performed, FIG. is there. Further, as an index indicating the sharpness of Q, when the input frequency at which the current value of the maximum value of the curve becomes half the maximum value is fa, the lower input frequency is defined as fa, and the higher input frequency is defined as fb.
Define fb / fa. The value of r approaches 1 when Q is high, that is, when the curve is sharp, and greatly approaches Ｑ when Q is low, that is, when the curve is gentle. This FIG.
Indicates that r = 3.2. On the other hand, in FIG. 9 of the simulation result using FIG. 6 which is an embodiment of the present invention, when the above r is obtained, both L1 and L2 sides are 1.1, and Q is too high from the sharpness of the curve. FIG. 7 shows a circuit in which an external resistor 3Ω is inserted so as to have a Q value substantially the same as that in FIG. 8, and the result of simulation using the circuit is shown in FIG. Here, the curve is gentler than that of FIG. 9, and when the above r is obtained, L1, L
It is 2.5 on both sides.

[0014]

As described above, according to the reader / writer antenna of the non-contact IC card according to the present invention,
Since the middle tap is used in the parallel resonance circuit,
The electrical resistance of the input section can be reduced, and the heat generation of the resistor can be suppressed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an antenna for a reader / writer of a non-contact IC card according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional antenna.

FIG. 3 is a series resonance filter circuit and a characteristic graph thereof.

FIG. 4 is a parallel resonance filter circuit using taps and a characteristic graph thereof.

FIG. 5 is a circuit diagram for simulation to which FIG. 2 is applied.

FIG. 6 is a circuit diagram for simulation to which FIG. 1 is applied.

FIG. 7 is a circuit diagram for simulation to which FIG. 1 is applied.

8 is a graph showing a simulation result of FIG.

FIG. 9 is a graph showing a simulation result of FIG. 6;

FIG. 10 is a graph showing a simulation result of FIG. 7;

[Explanation of symbols]

 R1, R2, R3: resistor, L10, L20: coil, C1: capacitor

Claims (2)

[Claims] 1. An intermediate tap is used to electrically divide one coil into a first coil and a second coil with respect to an input at an arbitrary position. In the coil, the respective ends opposite to the end connected to the intermediate tap are connected to each other via a capacitor, and the connection point between one of the first and second coils and the capacitor is grounded. An antenna for a reader / writer of a non-contact type IC card, which has a circuit configuration for setting a potential. 2. The reader / writer antenna for a non-contact type IC card according to claim 1, wherein the intermediate tap is slidable.