# Patent

## Title
Optical disc

## Abstract

An optical disc includes an electromagnetic coupling module mounted therein. The electromagnetic coupling module includes a wireless IC chip and a feeder circuit substrate in which a feeder circuit including a resonant circuit having a predetermined resonant frequency is disposed. The electromagnetic coupling module is electromagnetically coupled to a reflective film defining a metal thin film of the optical disc, and the reflective film defines an antenna or radiation pattern of the electromagnetic coupling module.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical discs and in particular, to an optical disc in which an electromagnetic coupling module having a wireless integrated circuit (IC) chip for use in a radio frequency identification (RFID) system is disposed.
2. Description of the Related Art
Recently, digital versatile discs (DVDs) have become very popular as media capable of recording a large amount of data, such as video and audio data. With the desire to record longer video data having higher image quality, the development of optical discs whose light source is a blue semiconductor laser is rapidly advancing, and one example of this type of optical discs is a Blu-ray disc (BD) that is currently commercially available.
When a portable recording media is capable of easily storing high-quality digital contents, the protection of the copyright of the digital contents becomes very important. BDs perform control so as to prevent unauthorized discs from being played by causing a player to read a unique ID recorded in the innermost area of a signal recordable region, called a burst cutting area, for each disc as a bar-code pattern. However, techniques for creating unauthorized discs are rapidly advancing, such that more robust measures for copyright protection are desired.
To address this issue, a DVD having a structure in which an RFID tag is incorporated to prevent unauthorized duplication is disclosed in Japanese Unexamined Patent Application Publication No. 9-245381 and Japanese Unexamined Patent Application Publication No. 2006-92630. In Japanese Unexamined Patent Application Publication No. 9-245381, an antenna pattern is provided in an area that is adjacent to the central hole and that does not include a reflective film provided therein. This limits the size of the antenna pattern, such that a relatively large gain cannot be obtained and the reading distance by an RFID reader/writer is undesirably small. One possible solution is to provide the antenna pattern on the back surface of a signal recordable region at which a reflective film is provided. However, with this approach, if the antenna pattern and the reflective film overlap, communications are adversely affected.
In Japanese Unexamined Patent Application Publication No. 2006-92630, an RFID tag is provided which has a slot antenna structure in which a slit is provided on each of an inner portion and an outer portion of a reflective film that are not disposed in a signal recordable region. However, because slot antennas have relatively high impedances, it is difficult to perform matching to the impedance of a wireless IC chip of the RFID. As a result, a problem occurs in which a sufficient antenna gain cannot be obtained.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide an optical disc that includes an electromagnetic coupling module having high electromagnetic-wave radiation efficiency in a wide band and that is suitable for copyright protection.
A preferred embodiment of the present invention provides an optical disc in which an electromagnetic coupling module is mounted, wherein the electromagnetic coupling module includes a wireless IC chip and a feeder circuit substrate in which a feeder circuit including a resonant circuit having a predetermined resonant frequency is disposed, and the electromagnetic coupling module is electromagnetically coupled to a reflective film defining a metal thin film of the optical disc, and the reflective film is used as an antenna radiator of the electromagnetic coupling module.
In the optical disc according to this preferred embodiment of the present invention, the electromagnetic coupling module including the wireless IC chip and the feeder circuit substrate is electromagnetically coupled to the reflective film defining the metal thin film of the optical disc. An excitation of the reflective film improves the electromagnetic-wave radiation efficiency. An improved antenna gain increases the acceptable distance to an RFID reader/writer.
In the optical disc according to this preferred embodiment of the present invention, the wireless IC chip may preferably be disposed on the feeder circuit substrate, and the reflective film may preferably face a surface of the feeder circuit substrate on which the wireless IC chip is not disposed. With this arrangement, the electromagnetic coupling between the electromagnetic coupling module and the reflective film is improved.
The electromagnetic coupling module may preferably be disposed in a region other than a signal recordable region of the optical disc. The effects on the reading of the recorded information from the optical disc that is caused by mounting the electromagnetic coupling module in the optical disc can be avoided.
The resonant circuit disposed in the feeder circuit substrate may include an inductance element defined by a linear electrode. The linear electrode defining the inductance element improves the electromagnetic coupling to the reflective film.
When a plurality of resonant circuits defines the resonant circuit disposed in the feeder circuit substrate, impedance matching between the wireless IC chip and the feeder circuit and impedance matching between the feeder circuit and the reflective film can be preferably performed in a wide frequency band.
The optical disc may be a digital versatile disc (DVD) or a compact disc (CD), a soft key for playback may be provided in a recording surface of the DVD or the CD, and the soft key for playback may be stored in the wireless IC chip. This enables effective protection of a copyright against unauthorized duplication and other piracy.
According to various preferred embodiments of the present invention, because the reflective film disposed in the optical disc is used as the antenna radiator of the electromagnetic coupling module in which the wireless IC chip is disposed, an electromagnetic-wave radiation efficiency is improved in a wide band. In addition, information stored in the wireless IC chip can be obtained using an RFID system, and the obtained information can be effectively utilized for copyright protection.
Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view that illustrates an optical disc according to a preferred embodiment of the present invention.
FIG. 2 is a cross-sectional view that illustrates an enlarged main portion of the optical disc shown in FIG. 1.
FIG. 3 is a cross-sectional view that illustrates a feeder circuit substrate according to a first preferred embodiment of the present invention.
FIGS. 4A and 4B are perspective views that illustrate connection states between a wireless IC chip and the feeder circuit substrate.
FIG. 5 is an equivalent circuit diagram of the feeder circuit substrate according to the first preferred embodiment of the present invention.
FIG. 6 is an exploded perspective view of the feeder circuit substrate according to the first preferred embodiment of the present invention.
FIG. 7 is an equivalent circuit diagram that illustrates a feeder circuit substrate according to a second preferred embodiment of the present invention.
FIG. 8 is an exploded plan view of the feeder circuit substrate according to the second preferred embodiment of the present invention.
FIG. 9 is a graph that illustrates a reflection characteristic of an electromagnetic coupling module that uses the second preferred embodiment of the present invention.
FIG. 10 is a chart in the XY plane that illustrates directivity of the electromagnetic coupling module using the second preferred embodiment of the present invention.



DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Preferred embodiments of an optical disc according to the present invention will be described below with reference to the accompanying drawings.
General Configuration of Optical Disc and Electromagnetic Coupling Module
A plan view of an optical disc 50 according to a preferred embodiment of the present invention is shown in FIG. 1, and a cross-sectional view that illustrates an enlarged main portion thereof is shown in FIG. 2. The optical disc 50 is a CD, a DVD, or a BD for example. As illustrated in FIG. 2, the optical disc 50 has a three-layer structure in which a reflective film 51 preferably made of an aluminum-deposited film, for example, is disposed between polycarbonate resin layers 52 and 53 arranged on the upper and lower surfaces thereof. The reflective film 51 defines an antenna or radiation pattern. The diagonally shaded portion in FIG. 1 is the portion in which the reflective film 51 is provided. In the reflective film 51, a portion surrounding a central hole 54 is a non-recordable region 55, and the remaining portion thereof is a recordable region. Information recorded in the reflective film 51 is read by an optical pickup 65.
An electromagnetic coupling module 1, which will be described below, is embedded in the non-recordable region 55. The location of attachment of the electromagnetic coupling module 1 to the optical disc 50 may be in the outer portion of the reflective film 51, as opposed to the inner portion, or may be on the back surface side of the recordable region.
As illustrated in the cross-sectional view of FIG. 3, the electromagnetic coupling module 1 includes a known wireless IC chip 5 used in an RFID system and a feeder circuit substrate 10 in which a feeder circuit 16 having a predetermined resonant frequency is disposed. The wireless IC chip 5 is mounted on the front side of the feeder circuit substrate 10. The back side (i.e., the surface on which the wireless IC chip 5 is not disposed) of the feeder circuit substrate 10 faces the reflective film 51.
The wireless IC chip 5 includes a clock circuit, a logic circuit, and a memory circuit, stores necessary information, and is DC-connected directly to the feeder circuit 16 included in the feeder circuit substrate 10.
The feeder circuit 16 is a circuit arranged to supply the reflective film 51 with a transmission signal having a predetermined frequency and also to select a reception signal having a predetermined frequency from signals received at the reflective film 51 and supply the reception signal to the wireless IC chip 5. The feeder circuit 16 includes a resonant circuit that resonates at the frequency of each of the transmission and reception signals.
The perspective views of FIGS. 4A and 4B illustrate connection structures between the wireless IC chip 5 and the feeder circuit substrate 10. FIG. 4A illustrates a connection structure in which pairs of antenna (balance) terminals 7a and 17a are disposed on the back surface side of the wireless IC chip 5 and the front surface side of the feeder circuit substrate 10, respectively. FIG. 4B illustrates another connection structure in which, in addition to the pairs of antenna (balance) terminals 7a and 17a, pairs of ground terminals 7b and 17b are disposed on the back surface side of the wireless IC chip 5 and the front surface side of the feeder circuit substrate 10, respectively. The ground terminals 17b of the feeder circuit substrate 10 are terminated, such that they are not connected to another terminal of the feeder circuit substrate 10.
First Preferred Embodiment of Feeder Circuit Substrate According to the Present Invention
As illustrated in FIGS. 3 and 5, as equivalent circuits, the feeder circuit substrate 10 includes the feeder circuit 16 including a series LC lumped-constant resonant circuit including a helical inductance element L and a capacitance element C. As illustrated in FIG. 5, a coil electrode pattern defining the inductance element L is arranged such that its winding axis is substantially perpendicular to the reflective film 51, and the feeder circuit 16 is primarily magnetically coupled to the reflective film 51.
Specifically, as illustrated in FIG. 6, the feeder circuit substrate 10 is constructed by laminating, pressing and bonding, and sintering of dielectric ceramic sheets 31A to 31F. The sheet 31A includes a connection electrode 32 and a via-hole conductor 33a. The sheet 31B includes a capacitor electrode 34a and a via-hole conductor 33b. The ceramic sheet 31C includes a capacitor electrode 34b and via-hole conductors 33c and 33b. The sheet 31C includes a capacitor electrode 34b and via-hole conductors 33c and 33b. The sheet or sheets 31D include a conductor pattern 35a and via-hole conductors 33d and 33b. The sheet or sheets 31E include a conductor pattern 35b and via-hole conductors 33e and 33b. The sheet 31F includes a conductor pattern 35c. Each of the sheets 31A to 31F may also be a sheet made of a magnetic ceramic material. The feeder circuit substrate 10 can be easily obtained by a known process of manufacturing a multilayer substrate, such as sheet laminating method or thick-film printing method, for example.
By laminating the sheets 31A to 31F, the feeder circuit 16 is provided, which includes the series LC resonant circuit in which the inductance element L whose winding axis of the helical coil is substantially perpendicular to the reflective film 51 and the capacitance element C are connected in series to each other. The capacitor electrode 34a is connected to the connection electrode 32 through the via-hole conductor 33a and is further connected to the wireless IC chip 5 with a solder bump 6 disposed therebetween. An end of the inductance element L is connected to the connection electrode 32 through the via-hole conductor 33b and is further connected to the wireless IC chip 5 with a solder bump 6 disposed therebetween.
That is, among the components defining the feeder circuit 16, the inductance element L defined by the coil electrode pattern supplies the reflective film 51 with a transmission signal through a magnetic field, and a reception signal from the reflective film 51 is supplied to the inductance element L through a magnetic field. Accordingly, it is preferable that, of the inductance element L and the capacitance element C defining the resonant circuit in the feeder circuit substrate 10, the inductance element L be arranged closer to the reflective film 51.
The electromagnetic coupling module 1 having the above-described configuration receives a high-frequency signal (e.g., in the ultrahigh frequency (UHF) band) emitted from a reader/writer 60 (see FIG. 2) at the reflective film 51, resonates the feeder circuit 16 (the series LC resonant circuit including the inductance element L and the capacitance element C) primarily magnetically coupled to the reflective film 51, and supplies the wireless IC chip 5 with only a reception signal in a predetermined frequency band. The electromagnetic coupling module 1 extracts a predetermined energy from this reception signal, matches information stored in the wireless IC chip 5 to a predetermined frequency with the feeder circuit 16 using the extracted energy as a driving source, then conveys a transmission signal from the inductance element L of the feeder circuit 16 to the reflective film 51 through magnetic field coupling, and transmits it from the reflective film 51 to the reader/writer 60.
The function of the reader/writer 60 can preferably be installed in a DVD/CD playback drive device, for example. To prevent unauthorized discs from being played, a soft key (i.e., encryption key) for playback corresponding to a recorded content is recorded on a recording surface of the optical disc 50, and the soft key recorded on the recording surface is also stored in the wireless IC chip 5. In playback of the optical disc 50, the reader/writer 60, and the optical pickup 65 read the respective soft keys, and the content is played only when the read soft keys match each other. Alternatively, a key to permit playback may be stored in the wireless IC chip 5. The wireless IC chip 5 can store various types of information regarding the optical disc 50, other than information preventing unauthorized duplication, and the stored information can be updated, instead of being read by the reader/writer 60. The information can also be used to detect theft from a store.
In the optical disc 50, the electromagnetic coupling module 1 is electromagnetically coupled to the reflective film 51 made of an aluminum-deposited film, for example. An excitation of the reflective film 51 improves the electromagnetic-wave radiation efficiency. As compared to when the reflective film 51 is not used, an increase of an approximately 20-dB gain is obtained, and the communication distance to the reader/writer 60 increases by approximately 10 times. The feeder circuit 16 and the reflective film 51 are coupled primarily through a magnetic field. However, coupling through an electric field may also be present.
In the electromagnetic coupling module 1, the wireless IC chip 5 is DC connected directly on the feeder circuit substrate 10 including the feeder circuit 16. The feeder circuit substrate 10 has substantially the same size as the wireless IC chip 5 and is rigid. Due to this arrangement, the wireless IC chip 5 can be precisely positioned on the feeder circuit substrate 10. Additionally, because the feeder circuit substrate 10 is made of a ceramic material and is resistant to heat, the wireless IC chip 5 can be attached to the feeder circuit substrate 10 by soldering. That is, because ultrasonic bonding is not used, the wireless IC chip 5 can be inexpensively attached, there is no risk of breaking the wireless IC chip 5 by pressure applied in ultrasonic bonding, and the self-alignment achieved by reflow soldering can also be utilized.
In the feeder circuit 16, the resonant-frequency characteristic is determined by the resonant circuit including the inductance element L and the capacitance element C. The resonant frequency of a signal emitted from the reflective film 51 is substantially equivalent to the self-resonant frequency of the feeder circuit 16, and the maximum gain of the signal is substantially determined by at least one of the size of the feeder circuit 16, the shape thereof, the distance between the feeder circuit 16 and the reflective film 51, and the medium. That is, in preferred embodiments of the present invention, because the frequency of a signal emitted from the reflective film 51 is substantially determined by the resonant frequency of the resonant circuit (i.e., the feeder circuit 16), the frequency characteristic is substantially independent of the electrical length and shape of the reflective film 51.
In the feeder circuit 16, the coil electrode pattern is arranged such that its winding axis is substantially perpendicular to the reflective film 51. Thus, advantages are obtained in which the magnetic-flux component to the reflective film 51 is increased, the transmission efficiency of the signal energy is improved, and the gain is increased.
In preferred embodiments of the present invention, the resonant circuit may also function as a matching circuit to match the impedance of the wireless IC chip 5 and that of the reflective film 51. Alternatively, the feeder circuit substrate 10 may further include a matching circuit that includes an inductance element and a capacitance element and that is provided separately from the resonant circuit. To add the function of the matching circuit to the resonant circuit, the design of the resonant circuit is relatively complicated. If the matching circuit is provided separately from the resonant circuit, the resonant circuit and the matching circuit can be designed independently.
Second Preferred of Feeder Circuit Substrate According to the Present Invention
In the feeder circuit substrate 10 according to the second preferred embodiment, as illustrated in the equivalent circuit diagram of FIG. 7, the feeder circuit 16 includes magnetically coupled inductance elements L1 and L2. The inductance element L1 is connected to feed terminals 19a and 19b connected to the wireless IC chip 5 through capacitance elements C1a and C1b. The inductance element L1 is also connected in parallel to the inductance element L2 through capacitance elements C2a and C2b. In other words, the feeder circuit 16 includes a series LC resonant circuit including the inductance element L1 and the capacitance elements C1a and C1b and a series LC resonant circuit including the inductance element L2 and the capacitance elements C2a and C2b. The resonant circuits are connected by magnetic field coupling M illustrated in FIG. 7. Both of the inductance elements L1 and L2 are magnetically coupled to the reflective film 51 of the optical disc 50, which is illustrated in FIGS. 1 and 2.
Specifically, as illustrated in FIG. 8, the feeder circuit substrate 10 is constructed by laminating, pressing and bonding, and sintering of dielectric ceramic sheets 41a to 41i. More specifically, the sheet 41a includes the feed terminals 19a and 19b and via-hole conductors 49a and 49b. The sheet 41b includes capacitor electrodes 42a and 42b. The sheet 41c includes capacitor electrodes 43a and 43b and via-hole conductors 49c and 49d. The sheet 41d includes capacitor electrodes 44a and 44b and via-hole conductors 49c, 49d, 49e, and 49f. 
The sheet 41e includes connection conductor patterns 45a, 45b, and 45c and via-hole conductors 49d, 49g, 49h, and 49i. The sheet 41f includes conductor patterns 46a and 47a and via-hole conductors 49g, 49i, 49j, and 49k. The sheet 41g includes conductor patterns 46b and 47b and via-hole conductors 49g, 49i, 49j, and 49k. The sheet 41h includes conductor patterns 46c and 47c and via-hole conductors 49g, 49i, 49j, and 49k. Moreover, the sheet 41i includes conductor patterns 46d and 47d. 
By laminating the sheets 41a to 41i, the conductor patterns 46a to 46d are connected together through the via-hole conductor 49j, thus defining the inductance element L1, and the conductor patterns 47a to 47d are connected together through the via-hole conductor 49k, thus defining the inductance element L2. The capacitance element C1a includes the electrodes 42a and 43a. The capacitance element C1b includes the electrodes 42b and 43b. The capacitance element C2a includes the electrodes 43a and 44a. The capacitance element C2b includes the electrodes 43b and 44b. 
The inductance element L1 includes one end connected to the capacitor electrode 43a through the via-hole conductor 49g, the connection conductor pattern 45c, and the via-hole conductor 49c and another end connected to the capacitor electrode 43b through the via-hole conductor 49d. The inductance element L2 includes one end connected to the capacitor electrode 44a through the via-hole conductor 49i, the connection conductor pattern 45a, and the via-hole conductor 49e and another end connected to the capacitor electrode 44b through the via-hole conductor 49h, the connection conductor pattern 45b, and the via-hole conductor 49f. 
The feed terminal 19a is connected to the capacitor electrode 42a through the via-hole conductor 49a. The feed terminal 19b is connected to the capacitor electrode 42b through the via-hole conductor 49b. 
In the feeder circuit substrate 10 having the above-described configuration, the series LC resonant circuits including the magnetically coupled inductance elements L1 and L2 resonate, and the inductance elements L1 and L2 function as a radiating element. Coupling the inductance elements L1 and L2 through the capacitance elements C2a and C2b enables the resonant circuits to function as a matching circuit to match the impedance of the wireless IC chip 5 (typically about 50Ω) connected to the feed terminals 19a and 19b and that of air (about 377Ω).
The coupling coefficient k for the adjacent inductance elements L1 and L2 is represented by k2=M/(L1×L2), and is preferably at least about 0.1, and in the second preferred embodiment, is approximately 0.8975, for example. Because each of the series LC resonant circuits including the capacitance elements C1a, C1b, C2a, and C2b and the inductance elements L1 and L2 is a lumped-constant resonant circuit, the series LC resonant circuits can be miniaturized as a laminated type. In addition, because the capacitance elements C1a and C1b are disposed between the feed terminals 19a and 19b and the inductance elements, a low-frequency surge can be cut off, so the wireless IC chip 5 can be protected against the surge.
From results of a simulation performed by the inventors of the present invention based on the equivalent circuit illustrated in FIG. 7, the reflection characteristic illustrated in FIG. 9 for the feeder circuit substrate 10 was obtained. As shown in FIG. 9, the center frequency is about 915 MHz, a reflection characteristic of about −10 dB or less in a wide band of about 850 MHz to about 970 MHz was obtained.
FIG. 10 illustrates the directivity (i.e., the magnetic field strength) in the XY plane of the feeder circuit substrate 10. The x-axis, y-axis, and z-axis correspond to the arrows X, Y, and Z illustrated in FIG. 2, respectively.
The operational advantage of the second preferred embodiment is substantially the same as that of the first preferred embodiment, and the second preferred embodiment can effectively prevent playback of an unauthorized duplication of the optical disc. That is, the electromagnetic coupling module 1 receives a high-frequency signal (e.g., in the UHF band) emitted from the reader/writer 60 at the reflective film 51, resonates the feeder circuit 16 (the series LC resonant circuit including the inductance element L1 and the capacitance elements C1a and C1b and the series LC resonant circuit including the inductance element L2 and the capacitance elements C2a and C2b) primarily magnetically coupled to the reflective film 51, and supplies the wireless IC chip 5 with only a reception signal in a predetermined frequency band. The electromagnetic coupling module 1 extracts a predetermined energy from this reception signal, matches information retained in the wireless IC chip 5 to a predetermined frequency with the feeder circuit 16 using the extracted energy as a driving source, then conveys a transmission signal from the inductance elements L1 and L2 of the feeder circuit 16 to the reflective film 51 through magnetic field coupling, and transmits it from the reflective film 51 to the reader/writer 60.
In particular, in the second preferred embodiment, the reflection characteristic has a wide frequency band, as illustrated in FIG. 9. This results from the feeder circuit 16 being defined by the plurality of LC resonant circuits including the magnetically coupled inductance elements L1 and L2 with a high degree of coupling.
The optical disc according to preferred embodiments of the present invention is not limited to the above-described preferred embodiments. Various modifications can be made without departing from the scope of the invention.
For example, the resonant circuit(s) defining the feeder circuit may have various circuit configurations, such as a series LC resonant circuit or a parallel LC resonant circuit, and may be either a lumped-constant type or a distributed-constant type. Information stored in the wireless IC chip and the use of the information by using the reader/writer may have any form.
As described above, preferred embodiments of the present invention are useful for an optical disc. In particular, preferred embodiments of the present invention are advantageous in that they include an electromagnetic coupling module having high electromagnetic-wave radiation efficiency in a wide band and are suitable for copyright protection.
While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.

## Claims

1. An optical disc comprising:
an electromagnetic coupling module provided adjacent to a reflective film defining a metal thin film of the optical disc; wherein
the electromagnetic coupling module includes a wireless IC chip and a feeder circuit substrate;
the feeder circuit substrate includes a feeder circuit including a matching circuit; and
the electromagnetic coupling module is electromagnetically coupled to the reflective film defining the metal thin film of the optical disc, and the reflective film defines an antenna or radiation pattern of the electromagnetic coupling module.

2. The optical disc according to claim 1, wherein the wireless IC chip is disposed on the feeder circuit substrate, and the reflective film faces a surface of the feeder circuit substrate on which the wireless IC chip is not disposed.

3. The optical disc according to claim 1, wherein the electromagnetic coupling module is disposed in a region of the optical disc other than a signal recordable region of the optical disc.

4. The optical disc according to claim 1, wherein the feeder circuit substrate includes a resonant circuit having a predetermined resonant frequency disposed therein; and
the resonant circuit includes an inductance element defined by a linear electrode.

5. The optical disc according to claim 4, wherein the resonant circuit disposed in the feeder circuit substrate includes a plurality of resonant circuits.

6. The optical disc according to claim 1, wherein the optical disc is one of a digital versatile disc and a compact disc, a soft key for playback is set in a recording surface of the one of the digital versatile disc and the compact disc, and the soft key for playback is stored in the wireless IC chip.