KR20080040512A - A radio frequency identification device and an impedance matching method for the radio frequency identification device - Google Patents

Abstract

A radio frequency identification device and an impedance matching method for the same are provided to rapidly control impedance matching between a tag chip and an antenna by adjusting reactance of impedance through length control of the antenna and a stub unit. A radio frequency identification device includes an antenna(1), a tag chip(3), a conductor pattern unit(2), and a variable conductor bar(4). The antenna transmits a radio frequency identification signal. The tag chip generates the radio frequency identification signal by being separated from the antenna at a predetermined distance. The conductor pattern unit is separated from the antenna at a predetermined distance, has an end electrically connected to the tag chip, and forms one extended antenna together with the antenna. The variable conductor bar variably adjusts a connection position between the conductor pattern unit and the antenna to match impedance between the tag chip and the antenna.

Description

A RADIO FREQUENCY IDENTIFICATION DEVICE AND AN IMPEDANCE MATCHING METHOD FOR THE RADIO FREQUENCY IDENTIFICATION DEVICE}

1 is a block diagram showing a configuration of a radio frequency identification device according to the prior art,

2 is a block diagram showing the configuration of a radio frequency identification device according to the present invention,

3 is a waveform diagram showing a change in an impedance imaginary value with respect to an operating frequency of an antenna according to a moving distance of a variable conductor bar in a radio frequency identification device according to the present invention;

4 is a waveform diagram showing the relationship between the return loss and the operating frequency of the antenna according to the moving distance of the variable conductor bar in the radio frequency identification device according to the present invention,

5 is a block diagram showing an embodiment of a radio frequency identification device according to the present invention.

* Explanation of symbols on the main parts of the drawings

1: antenna 2: conductor pattern part (CONDUCTOR PATTERN PORTION)

3: TAG CHIP 4: MOVABLE CONDUCTOR BAR

S: STUB

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to radio frequency identification, and in particular, to identify an impedance between an antenna and a tag chip so that return loss can be minimized. Device and an impedance matching method for such a radio frequency identification device.

A radio frequency identification tag (hereinafter, simply referred to as a tag) is generally composed of an antenna and a tag chip, and impedance matching between these antennas and the tag chip is a radio frequency between the antenna and the tag chip according to such impedance matching. Since the return loss is determined when transmitting and receiving a signal, it greatly affects the performance of the radio frequency identification tag.

Specifically, since the rectifier circuits configured in the tag chip have a capacitance component, the input impedance of the tag chip has a negative imaginary value. Therefore, in order to realize the optimal impedance matching between the antenna and the tag chip, it is necessary to easily adjust the characteristic impedance of the antenna itself so that the antenna has a positive equivalent imaginary value so as to cancel the negative imaginary value of the tag chip.

Here, if the impedance is expressed as a complex value, that is, the sum of a real value and an imaginary value, the following equation (1) is obtained.

In Equation (1), Z is impedance, R is a real value, and X is an imaginary value (also called reactance).

Matching the impedance of the tag chip and the antenna is basically the same as the real value in the impedance of the tag chip and the antenna, and the X value and the absolute value of the tag chip so that the negative X value of the tag chip is canceled in Equation (1) This means that the characteristic impedance of the antenna is adjusted to have the same amount of X value.

In addition, since the characteristic impedance of the antenna is changed depending on the utilization environment to which the tag is attached, that is, the material of the object to which the tag is attached, such as wood, paper, glass, plastic, metal, and a mixture thereof, the antenna accordingly Means for adjusting the characteristic impedance of are devised.

That is, when the center frequency (characteristic impedance) of the tag changes according to the material of the object to which the tag is attached, the following equation (2) is given.

Is the wavelength (length) of the antenna, C is the speed of light, f is the center frequency, and e is the permittivity.

If the dielectric constant of the object to which the tag is attached is increased by the characteristic shown in Eq. Therefore, the antenna tunes the center frequency by impedance matching to the antenna having a high center frequency as the dielectric constant is increased.

  On the other hand, with reference to Figure 1 showing an example of the prior art for adjusting the characteristic impedance of such an antenna as follows.

1 is a block diagram showing the configuration of a radio frequency identification device according to the prior art.

In Fig. 1, the tag according to the prior art has a radiation body 1a, a rectangular feed loop 1b, and both ends 1b-1, 1b- of the feed loop 1b. 2) a tag chip 3 connected therebetween.

The feed loop 1b and the radiator 1a serve as antennas by mutual coupling. The impedance of this antenna is adjusted by the length la and width lb and thickness W of the feed loop 1b and the distance d between the feed loop 1b and the radiator 1a.

However, the radio frequency identification device according to the related art has a length la, a width lb and a thickness W, and a feed loop 1b and a radiator 1a of a feed loop 1b for adjusting impedance characteristics of an antenna. Adjusting all the distances d results in a larger tag. Therefore, there is a problem in that miniaturization of the tag has disadvantages or limits in impedance adjustment.

In addition, the radio frequency identification device according to the prior art has a variety of antennas such as the length (la) and width (lb) and thickness (W) of the feed loop (1b) and the distance (d) between the feed loop (1b) and the radiator (1a) Since there is an impedance characteristic adjustment factor, a complicated impedance adjustment process must be performed, which may adversely affect radio frequency signal emission characteristics of the antenna.

Accordingly, the present invention is to solve the problems of the prior art, to provide a radio frequency identification device that is simple to adjust the antenna impedance characteristics, which does not interfere with the miniaturization of the tag and does not adversely affect the radio frequency signal radiation characteristics of the antenna. There is a purpose.

Another object of the present invention is to provide a simple impedance matching method for a radio frequency identification device.

One object of the present invention, in the radio frequency identification device,

An antenna for transmitting a radio frequency identification signal;

A tag chip spaced apart from the antenna by a predetermined distance and generating a radio frequency identification signal;

A conductor pattern unit installed at a predetermined distance from the antenna and having an end portion electrically connected to the tag chip, and configured to form an extended antenna together with the antenna; And

An entire antenna which is mechanically and electrically connected to the conductor pattern portion and the antenna to form one extended antenna to which the radio frequency identification signal moves, and extends according to the connection position of the conductor pattern portion and the antenna; It is to determine the impedance characteristics of the antenna by determining the length, and a variable conductor bar that can be variably adjusted the connection pattern with the conductor pattern portion and the antenna for impedance matching with the tag chip; It can be achieved by providing a radio frequency identification device according to the present invention.

Another object of the present invention is an antenna for transmitting a radio frequency identification signal, a tag chip which is installed at a predetermined distance apart from the antenna to generate a radio frequency identification signal, a tag chip which is installed at a predetermined distance apart from the antenna and installed on the tag chip. An impedance matching method of a radio frequency identification element comprising a conductor pattern portion having an end portion connected thereto,

A variable conductor bar is provided to electrically connect the conductor pattern portion and the antenna to form a single antenna by the conductor pattern portion, the antenna, and the variable conductor bar, and the conductor pattern portion and the antenna of the variable conductor bar. By adjusting the impedance position of the antenna by adjusting the length of the antenna by adjusting the connection position with the antenna, it can be achieved by providing an impedance matching method of the radio frequency identification device, characterized in that impedance matching of the tag chip and the antenna.

The object of the present invention, the configuration of the present invention to achieve this and its working effects will be more clearly understood from the following description of the embodiments of the present invention with reference to the accompanying drawings.

First, referring to Figure 2 showing the configuration of the radio frequency identification device according to the present invention.

In Fig. 2, reference numeral 1 is included in the radio frequency identification element according to the present invention, and is an antenna for transmitting radio frequency identification signals. Preferably, the antenna 1 is composed of a half-wavelength dipole antenna that is symmetrical left and right about its symmetric center axis 1a.

The tag chip 3 included in the radio frequency identification element according to the present invention is installed to be spaced apart from the antenna 1 by a predetermined distance to generate a radio frequency identification signal. That is, the tag chip 3 is a signal source for generating a radio frequency identification signal for wirelessly communicating the identity of the object to which the tag chip is attached.

The conductor pattern portion 2 included in the radio frequency identification element according to the present invention is provided to be spaced apart from the antenna 1 by a predetermined distance, and has an end portion electrically connected to the tag chip 3. 2) is a transmission path of a signal for transmitting the radio frequency identification signal from the tag chip 3 to the antenna 1 side and together with the antenna 1 forms one extended antenna.

The variable conductor bar 4 included in the radio frequency identification element according to the present invention is one extended by which the radio frequency identification signal is moved by mechanically and electrically connecting the conductor pattern portion 2 and the antenna 1. Form an antenna. In addition, the variable conductor bar 4 determines a moving path that moves until the radio frequency identification signal emitted from the tag chip 3 is transmitted to the air, that is, the length L of the entire extended antenna. Therefore, the impedance characteristics of the entire extended antenna are determined by adjusting the connection pattern between the conductor pattern portion 2 of the variable conductor bar 4 and the antenna 1, and between the tag chip 3 and the entire extended antenna Impedance matching can be adjusted.

 According to the connection position between the conductor pattern portion 2 and the antenna 1 of the variable conductor bar 4, the STUB portions S are independent of the movement path of the radio frequency identification signal. (2) and the end length of the antenna (1), when the length of the stub portion increases, the total length (L) of the extended antenna is reduced.

Accordingly, the connection position between the conductor pattern portion 2 and the antenna 1 of the variable conductor bar 4 is limited to the vertical dotted line between the conductor pattern portion 2 and the antenna 1. When the phase 2 moves toward the virtual symmetry center line 1c of the antenna 1 and decreases the total length L of the extending antenna, the imaginary value of the impedance component of the antenna, that is, the reactance is REACTANCE. Decreases, and the connection position between the conductor pattern portion 2 and the antenna 1 of the variable conductor bar 4 moves in a direction away from the virtual symmetric centerline 1c of the antenna 1 in FIG. If the total length L of the antenna to be extended is increased, the imaginary value, or reactance, of the impedance component of the antenna increases.

On the other hand, with reference to Figure 5 showing an embodiment of a radio frequency identification device according to the present invention as follows. 5 illustrates an example in which the idea of the present invention described above with reference to FIG. 2 is applied to a radio frequency identification tag as a circuit pattern.

Since the embodiment of FIG. 5 is the same as that described with reference to FIG. 2 in the basic concept, repeated descriptions will be avoided, and only the configuration and operation effects that are differentiated in the embodiment of FIG.

As shown in FIG. 5, the antenna 1, the conductor pattern part 2, and the variable conductor bar 4 may be embodied in a conductor pattern, which is mechanically and electrically connected to each other. That is, the conductor pattern portion 2 and the antenna of the optimal variable conductor bar 4 whose impedance between the antenna portion and the tag chip 3 is matched according to the material of the object on which the radio frequency identification element according to the present invention is installed. Since the connection position with (1) can be determined, it is the embodiment shown in FIG. 5 that the variable conductor bar 4 is formed in the conductor pattern at this position. Therefore, the radio frequency identification device according to the present invention can exhibit characteristics suitable for miniaturization and mass production.

Meanwhile, the impedance imaginary value and the return loss characteristic of the radio frequency identification device according to the present invention will be described with reference to FIGS.

In FIG. 3, the vertical axis of the illustrated waveform diagram represents an impedance imaginary value of an antenna among the radio frequency identification elements according to the present invention, and the horizontal axis represents an operating frequency of the antenna. In FIG. 3, the right legend in FIG. 2 is X from 9 millimeters (mm) to 21 millimeters (mm) when the moving distance of the variable conductor bar 4 toward the vertical dotted line, that is, toward the virtual symmetry centerline 1c in FIG. mm), that is, as the length of the spur portion S increases and the length L of the entire antenna decreases, the impedance imaginary value also decreases.

In FIG. 4, the vertical axis of the illustrated waveform diagram represents the return loss of the antenna among the radio frequency identification elements according to the present invention, and the horizontal axis represents the operating frequency of the antenna. In FIG. 4, the right legend shows that X is 9 millimeters (mm) to 21 millimeters (mm) when the moving distance of approaching the variable conductor bar 4 toward the vertical dotted line in FIG. 2 toward the virtual symmetry center line 1c, respectively. mm), that is, as the length of the spur portion S increases and the length L of the entire antenna decreases, the return loss decreases to a negative value when viewed at one operating frequency, that is, 0.95 GHz. Show characteristics. Overall, it shows that relatively good return loss can be obtained due to the characteristics of the antenna below -35 dB at each operating frequency (resonant frequency).

Therefore, as confirmed by the experimental data, by adjusting the position of the variable conductor bar 4, impedance matching between the tag chip of the radio frequency identification element and the antenna can be adjusted, and the return loss can be adjusted.

In addition, the impedance matching method of the radio frequency identification device according to the present invention, as shown in FIGS. 2 and 5 is an antenna (1) for transmitting a radio frequency identification signal, and is installed at a predetermined distance apart from the antenna (1) A tag chip (3) for generating a frequency identification signal, and a conductor pattern portion (2) having an end portion provided to be spaced apart from the antenna (1) by a predetermined distance and connected to the tag chip (3) In the impedance matching method,

A variable conductor bar 4 is provided to electrically connect the conductor pattern portion 2 and the antenna 1 to the conductor pattern portion 2, the antenna 1, and the variable conductor bar 4. By forming one antenna by adjusting the connection position between the conductor pattern portion 2 and the antenna 1 of the variable conductor bar 94 by adjusting the impedance characteristics of the entire antenna by adjusting the length of the antenna 1 The tag chip 3 and the entire antenna may be impedance matched.

As described above, by providing the radio frequency identification device according to the present invention, the impedance characteristics of the antenna can be adjusted by moving the position of the variable conductor bar, so that the impedance matching between the tag chip and the antenna can be adjusted.

In addition, according to the present invention, the imaginary value of the impedance can be adjusted by adjusting the length of the antenna and the length of the stub part by moving the position of the variable conductor bar, thereby quickly matching impedance between the tag chip and the antenna. There is an adjustable effect.

In addition, according to the present invention, an optimum variable variable of an impedance between an antenna part and a tag chip according to the material of an object on which the radio frequency identification element according to the present invention is installed by moving the position of the variable conductor bar is provided. Since the connection position with the conductor pattern portion of the conductor bar and the antenna can be determined, a variable conductor bar can be formed in the conductor pattern at this position, thereby miniaturizing the radio frequency identification element and producing the mass.

Claims (5)

In the radio frequency identification device, An antenna for transmitting a radio frequency identification signal; A tag chip spaced apart from the antenna by a predetermined distance and generating a radio frequency identification signal; A conductor pattern unit installed at a predetermined distance from the antenna and having an end portion electrically connected to the tag chip, and configured to form an extended antenna together with the antenna; And An entire antenna which is mechanically and electrically connected to the conductor pattern portion and the antenna to form one extended antenna to which the radio frequency identification signal moves, and extends according to the connection position of the conductor pattern portion and the antenna; It is to determine the impedance characteristics of the antenna by determining the length, and a variable conductor bar that can be variably adjusted the connection pattern with the conductor pattern portion and the antenna for impedance matching with the tag chip; A radio frequency identification element. The method of claim 1, A stub (STUB) that is independent of the movement path of the radio frequency identification signal is formed at the end of the conductor pattern portion and the antenna according to the connection pattern portion of the variable conductor bar and the antenna, and the stub And the total length of the extended antenna is reduced when the length of the unit is increased. The method of claim 1, When the total length of the extended antenna is reduced by moving the connection pattern between the conductor pattern portion and the antenna of the variable conductor bar, the reactance of the impedance component of the antenna is reduced. Identification element. The method of claim 1, And said antenna is a half-wavelength dipole antenna. A conductor pattern unit having an antenna for transmitting a radio frequency identification signal, a tag chip installed at a predetermined distance apart from the antenna to generate a radio frequency identification signal, and an end portion installed at a predetermined distance apart from the antenna and connected to the tag chip; In the impedance matching method of the radio frequency identification device comprising: A variable conductor bar is provided to electrically connect between the conductor pattern portion and the antenna to form one antenna by the conductor pattern portion, the antenna and the variable conductor bar, and the conductor pattern portion of the variable conductor bar and the antenna And impedance matching of the tag chip and the antenna by adjusting an impedance characteristic of the antenna by adjusting the length of the antenna by adjusting a connection position with the antenna.

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