Patent Application
20090273418
1. Field of the Invention
The present invention relates to a communication system which performs non-contact proximity data transmission using near-field electromagnetic coupling effect produced between a transmission antenna and a receiving antenna disposed close to each other, and to an antenna apparatus used for such non-contact proximity data transmission. More particularly, the present invention relates to a communication system and an antenna apparatus which perform high-speed digital data transmission using near-field electromagnetic coupling effect.
2. Description of the Related Art
In recent years, in order to provide interfaces for processing a high-speed digital signal, there are standards, such as LVDS (Low Voltage Differential Signaling), XAUI (10 Giga bit Attachment Unit Interface), PCI (Peripheral Component Interconnect)-Express, etc. Some of the interfaces have a data rate of as high as over 6 Gbps. In these interface standards, a small voltage amplitude is employed in order to achieve high-speed signal transmission. However, there is a problem in that the interfaces are more subject to noise as the amplitude of voltage decreases. To overcome this problem, differential transmission is employed in place of single-ended transmission.
Among these, LVDS has been developed for the purpose of reducing the number of signal lines, etc. For example, the number of signal lines necessary for transmitting a video signal having 6 bits to 10 bits for expressing individual gray scales of RGB is 20 to 40 by CMOS/TTL. Whereas by LVDS, the number can be reduced to 4 pairs (three pairs for data, and one pair for clock) to 6 pairs (five pairs for data, and one pair for clock). Main applications of LVDS include communication devices, PDPs (Plasma Display Panels), digital interfaces for liquid crystal panels, etc.
A differential transmission line controlled to have characteristic impedance of 100Ω is often used for a transmission line of a high-speed digital interface of this kind. A specific transmission line, which is employed in this case, includes a microstrip transmission line made of a dielectric substrate (printed-circuit board, etc.) having a conductor layer on a back side and a conductor pattern drawn by a line on a front side, a coaxial cable with a harness, etc. A transmitter IC (Integrated Circuit) and a receiver circuit are connected by a transmission line having a physical connection and an electrical connection as a matter of course.
As opposed to this, the present inventors think that it is possible to apply a method of high-speed digital signal transmission using a non-contact data communication technique. Non-contact communication has advantages that while data transmission is performed by radio, a transmitter and a receiver are disposed in proximity, and thus an illegal device for interception is not allowed to lie therebetween. Accordingly, it is not necessary to prevent hacking on the transmission line, and to consider how to maintain secrecy.
For example, two IC chips are mounted on one printed circuit board by flip chip attach, and it becomes possible to perform data transmission using near-field electromagnetic coupling through transmission of 5.6 cm between these IC chips (for example, refer to Co-authored by Wilson J, Lei Luo, Jian Xu, Mick S., Erickson E., Hsuan-Jung Su, Chan B., How Lin, Franzon P., “AC coupled interconnect using buried bumps for laminated organic packages” (Electronic Components and Technology Conference, 2006. Proceedings. 56th, 30 May-2 Jun. 2006 Page(s):8pp.); Co-authored by Lei Luo, John Wilson, Stephen Mick, Jian Xu, Liang Zhang, Evan Erickson, Paul Franzon, “A 36 Gb/s ACCI Multi-Channel Bus using a Fully Differential Pulse Receiver” (IEEE 2006 Custom Integrated Circuits Conference (CICC)). It is possible to achieve 2.5-Gbps data transfer by disposing an antenna electrode on the IC chip and an antenna electrode on the printed circuit board with being opposed, and connecting the IC chip with a transmission line on the printed circuit board using capacitive coupling between these electrodes. The sizes of antenna electrodes used here are 200 μm×200 μm for both the IC chip and the printed circuit board, and a communication distance is very short, namely 1 μm. Also, a bump is used for mounting the IC chip. That is to say, a bump formed on an IC chip is embedded in the gutter formed on the printed circuit board, and thus both of the antenna electrodes are disposed in close proximity, which is very complicated. The IC chip is mounted by flip chip attach, and thus it is unrealistic to detach or to replace the IC chip after the mounting.
Also, as another example of a non-contact data transmission technique, a proposal has been made of a technique of transferring data between chips produced by a laminated plurality of IC chips, which are polished as thin as tens of micrometers in consideration of SIP (System In Package) implementation (for example, refer to Japanese Unexamined Patent Application Publication No. 2005-228981; Co-authored by Miura N., Mizoguchi D., Inoue M., Sakurai T., Kuroda T., “A 195-gb/s 1.2-W inductive inter-chip wireless superconnect with transmit power control scheme for 3-D-stacked system in a package” (Solid-State Circuits, IEEE Journal of Volume 41, Issue 1, January 2006 Page(s):23-34); and Co-authored by Jian Xu, John Wilson, Stephen Mick, Lei Luo, Paul Franzon, “2.8 Gb/s Inductively Coupled Interconnect for 3-D ICs” (2005 Symposium on VLSI Circuits Digest of Technical Papers)). For example, a plurality of channels including a transmission and receiving circuit, and an antenna coil are laid out on an IC chip at 50-μm intervals in proximity using a semiconductor process. When an antenna coil having a diameter of 48 μm is used, it is possible to achieve 1.0-Gbps data transfer between antennas that are 43 μm apart.
Here, non-contact data transmission techniques using near-field electromagnetic coupling can be roughly divided into techniques of using capacitive coupling between two antenna electrodes provided at a transmitter and a receiver, respectively, and techniques of using inductive coupling between two antenna coils in the same manner. Also, the above techniques can be divided into two kinds of techniques from another viewpoint. One of the techniques does not necessitate impedance matching in accordance with a length of a wire connecting a transmission and receiving circuit, and an antenna. The other techniques necessitate impedance matching.
When an antenna is disposed very near to a transmission circuit or a receiving circuit, an input/output terminal of the circuit and an input/output terminal of the antenna operate in a substantially same phase, and thus the influence of reflection can be disregarded. Accordingly, impedance matching is not necessarily necessitated. In contrast, if an antenna is disposed apart from a transmission and receiving circuit, a length of a wiring line between them (transmission line) can not be disregarded, and thus impedance matching becomes necessary between an input/output terminal of the circuit and an input/output terminal of the antenna. In particular, in the case of high-speed data transfer exceeding 1 Gbps, if there is an impedance mismatch in a system including a transmission and receiving circuit and an antenna, reflection is caused by the mismatch. Accordingly, unnecessary ringing occurs on a receive signal, which causes an increase in jitter and deteriorates an error rate. Thus, high-speed data transfer is hindered.
In the case of capacitive coupling, if an antenna electrode has a length not less than ⅛ times a signal wavelength k (in consideration of a wavelength contraction ratio), it is necessary to consider a resonance frequency depending on the length. Also, if a parasitic inductive component (L) of a feed line is not disregarded, the parasitic inductive component and a self-capacity (C) of an antenna electrode form a series resonant circuit, and there is a self-resonant frequency fr to be determined by 1/2π√LC. In contrast, only in the case where the antenna size is sufficiently smaller than λ/8, and the above-described parasitic inductive component can be disregarded, the circuit can be regarded to have a pure capacity. Accordingly, the coupling of the transmission and receiving antennas can be regarded as a so-called AC coupling.
On the other hand, in the case of inductive coupling, an inductive component (L) of a coil and a parasitic capacitive component (C) of a wiring line forming the coil and with respect to GND form a parallel resonant circuit, and there is also a self-resonant frequency fr to be determined by 1/2π√LC in this case.
In a frequency band not less than the self-resonant frequency fr, the capacitive coupling antenna does not function as a capacitor, and the inductive coupling antenna does not function as an inductor. Also, resonance occurs at a signal component near fr both in the capacitive coupling antenna and in the inductive coupling antenna, and thus a frequency band that can be used for data transfer is restricted by the self-resonant frequency fr.
To date, for a non-contact data transfer antenna, a so-called lumped-parameter antenna structure has often been employed. In general, a large-sized antenna tends to have a low self-resonant frequency fr. Thus, in order to allow the use of a high frequency band and to increase a data transfer rate, it is necessary to set the size of the antenna small. However, in the case of non-contact communication using near-field electromagnetic coupling, a communication distance thereof becomes the same level as the antenna size. Accordingly, if a small-sized antenna is used, there is a restriction that a transfer distance also becomes short.
In this manner, in a related-art non-contact communication, there is a drawback in that the transfer distance becomes short when data is transferred at a high speed. Thus, applications of non-contact communication is limited to an ultra short distance, such as data transfer between laminated IC chips, etc. Also, if an antenna is disposed apart from a transmission/receiving circuit, and is connected to the circuit by a transmission line, a data transfer rate is limited to about ½ times an antenna band in the case of a resonant narrow-band antenna. Accordingly, there is a drawback in that it is difficult to achieve high speed.
It is desirable to provide an excellent communication system capable of performing high-speed digital data transmission using near-field electromagnetic coupling effect, and an antenna apparatus to be used for such non-contact proximity data transmission.
It is further desirable to provide an excellent communication system and an antenna apparatus which are capable of performing high-speed digital data transmission by near-field electromagnetic coupling effect using an antenna enabling use of a high-frequency band.
According to an embodiment of the present invention, there is provided a communication system including: a transmission slot antenna having a ring-shaped slot transmission line between an antenna electrode and a grounded conductor surface at a transmitter side; and a receiving slot antenna having a ring-shaped slot transmission line between an antenna electrode and a grounded conductor surface at a receiver side, wherein the transmission antenna and the receiving antenna are disposed with being opposed in proximity, and data transmission is performed using near-field electromagnetic coupling effect produced between the slot transmission lines of the transmission antenna and the receiving antenna.
However, here, a “system” means a logical set of a plurality of apparatuses (or functional modules for achieving a specific function), and is not limited to the case where individual apparatuses and functional modules are contained in a single casing.
Non-contact proximity data communication is a communication technique for performing data transmission using near-field electromagnetic coupling effect produced between a transmission antenna and a receiving antenna disposed close to each other. There are two types of techniques, capacitive coupling and inductive coupling, depending on the difference in a coupling effect to be used. Also, it is possible to classify the communication techniques depending on whether impedance matching is necessary in accordance with the length of a wiring line connecting the transmission and receiving circuit, and the antenna.
In the case of capacitive coupling, if an antenna electrode has a length not less than ⅛ times a signal wavelength λ, when a parasitic inductive component of a feed line is not disregarded, the parasitic inductive component and a self-capacity of an antenna electrode form a series resonant circuit, and there is a self-resonant frequency. On the other hand, in the case of inductive coupling, an inductive component of a coil and a parasitic capacitive component of a wiring line forming the coil and with respect to GND form a parallel resonant circuit, and there is also a self-resonant frequency. Resonance occurs near the resonance frequencies. The capacitive coupling or the inductive coupling does not operate at a frequency band of the resonance frequencies or higher, and thus there is a problem in that a frequency band that can be used for data transfer is restricted.
Also, the larger the size of an antenna becomes, the lower the self-resonant frequency tends to be. Thus, in order to allow the use of a high frequency band and to increase a data transfer rate, it is necessary to set the size of the antenna small. However, in the case of non-contact communication using near-field electromagnetic coupling, a communication distance thereof becomes the same level as the antenna size. Accordingly, if a small-sized antenna is used, the transfer distance also becomes short. That is to say, the transfer distance becomes short when data is transferred at a high speed. Also, if an antenna is disposed apart from a transmission and receiving circuit, and is connected to the circuit by a transmission line, a data transfer rate is limited to about ½ times an antenna band in the case of a resonant narrow-band antenna. Accordingly, it is difficult to achieve high speed.
In contrast, in a communication system according to the present invention, non-contact data communication is performed between a transmitter and a receiver whose antennas are disposed close to each other. As a data transfer principle, the communication system uses coupling of transmission lines originally having a small frequency variance, and employs non-resonant configuration. Specifically, two slot antennas are disposed with being opposed in proximity, and coupling is directly performed between a near-field electric field component or a near-field magnetic field component of a TE10 wave traveling along the slot transmission line of the transmission antenna. This is different from a resonant antenna.
The slot antenna has a ring-shaped slot transmission line between the antenna electrode and grounded conductor surface. Here, regarding the shape of the slot antenna having a ring-shaped slot, a shape of the electrode surrounded with the grounded conductor surface is preferably a regular polygon, such as a regular octagon, a regular hexagon, etc. In such a case, the ring-shaped slot between the antenna electrode and a grounded conductor surface is suitably considered to be a slot transmission line. Also, two feed points are disposed sandwiching the center of the ring-shaped slot. A length of the slot line between the two feed points is substantially equal in the clockwise direction and in the counterclockwise direction, and thus the slot line plays an equal role for signal transmission between the transmission antenna and the receiving antenna.
The slot transmission line goes to the other of the surfaces of the substrate through a through hole at each of the feed points, and is connected to a microstrip transmission line connected to a transmission IC or a receiving IC. It becomes possible to make reflection little and to prevent the occurrence of a stationary wave by reducing an impedance mismatch at connection time between the slot transmission line and the microstrip transmission line through the through hole. Thus, it is possible to have a broadband characteristic. It is possible to obtain impedance matching by setting a ratio between a characteristic impedance of two slot transmission lines connected in parallel between the two feed points and a characteristic impedance of a microstrip transmission line is set to about 2:1.
Also, the slot transmission line has a large frequency variance of the characteristic impedance compared with the microstrip transmission line. However, it is possible to obtain good transmission characteristic having little reflection in a broad frequency band by designing to match the characteristic impedance individually in the vicinity of center frequencies of the frequency band necessary for digital baseband signal transmission.
When a transmission antenna and a receiving antenna are disposed close to each other, and a high-speed digital baseband signal is directly supplied to the transmission antenna as a transmission signal, an electromotive force occurs between the transmission antenna and the receiving antenna by near-field electromagnetic coupling effect. Thus, it is possible to perform non-contact data transfer using this effect. As described above, a transmission line having a broadband characteristic itself is used as an antenna, it is possible to directly transmit a broadband AC component included in a digital baseband as a pulse signal from the transmission antenna to the receiving antenna. Accordingly, the communication system is suitable for increasing speed of the system and reducing power consumption without necessitating complicated modulation and demodulation circuits by directly transmitting the digital baseband signal. Thus, it is possible to easily achieve a communication system having a transmission rate exceeding Gbps.
If a length of slot transmission line is less than a wavelength of a progressive wave, compared with the amplitude of the progressive wave traveling in a forward direction, the amplitude of a progressive wave (so-called return current) traveling in a backward direction becomes large and dominant. Thus, if an antenna is manufactured to have a small size, etc., the receiving circuit ought to obtain, on the slot transmission line of the receiving antenna, a receive signal flowing in the opposite direction to the direction of the progressive wave input into the slot transmission line of the transmission antenna.
Also, an antenna used in a communication system according to the present invention is a non-resonant antenna. Thus, the antenna is not restricted by the self-resonant frequency fr. Accordingly, a broad band can be kept even if the size of the antenna is increased, and thus a communication distance in the non-contact communication system can be extended.
Here, it is possible to configure a transmission antenna and a receiving antenna not by a double-sided substrate, but by a three-layer or a four-layer (that is to say, not less than two-layer) substrate individually. However, in this case, it is necessary not to dispose an inner pattern on a portion overlapping the antenna structure so that the inner pattern does not electrically influence on the antenna electrode and the slot transmission line. For example, an inner pattern ought to be used for a grounded conductor surface, a portion overlapping the antenna electrode and the microstrip transmission line ought to be largely cut away, or an opening which is slightly larger than the antenna electrode ought to be formed on a portion overlapping the antenna electrode.
Also, the concept of the present invention, in which a transmission line having a substantially broadband characteristic itself is used as a non-contact data transfer antenna, and a digital baseband signal is directly transmitted, can be applied not only to single-ended transmission, but also to differential signal transmission. When a small amplitude voltage is used in order to achieve high-speed signal transmission, it is advantageously possible to restrain influence of noise by differential signal transmission.
When differential signal transmission is performed, the antenna electrode of the slot antenna at the transmitter side is divided into two substantially along a line perpendicular to a line connecting the two feed points, and a differential signal, such as LVDS or CML, etc., is supplied to the individual two feed points. Also, each antenna electrode is properly terminated at two points of both end parts of a divided gap, and thus it is possible to obtain good transmission characteristic with little reflection. Then, a differential signal can be obtained from the two feed points disposed at the antenna electrode at the receiver side.
In general, good impedance matching is not necessarily obtained at an output stage of a digital signal with a transmission line. For example, in the case of an open drain configuration, such as CML (Common Mode Logic), etc., the output impedance changes between a low impedance (a few Ω) to a high impedance (hundreds of Ω) in accordance with output data (0, 1). In such a case, a reflective wave occurred by an impedance mismatch at a transmission antenna returns to a transmission IC, and is reflected by the output stage thereof, and then enters into the transmission antenna again. Then, a large intersymbol interference occurs, and there is a fear that an adverse effects, such as an increase in jitter, deterioration of bit error rate (BER) might be caused at a receiving IC side.
In contrast, an antenna apparatus according to present invention has a characteristic having little reflection in a wide frequency range. Accordingly, the antenna apparatus does not request good impedance matching at an output stage with a transmission line, and has advantages in that cost and consumption power can be reduced. In particular, the antenna apparatus has an affinity to a differential digital signal, and thus has an advantage in that a high-speed serial transfer technique, which is currently widespread, can be applied.
Also, an antenna apparatus according to present invention has a configuration in which an antenna electrode to which a digital signal is supplied and the surrounding grounded conductor surface are separated by a ring-shaped slot, and thus electromagnetic field distribution is limited to a local range. Accordingly, it is possible to ensure isolation even if a plurality of antennas are disposed on a same substrate. Thus, it is possible to increase the number of channels, and to expand a data transfer band of the system. Further, it is possible to fabricate an antenna and an IC on a same multi-layer printed circuit board. Thereby, it is possible to miniaturize the system and to reduce cost.
Of course, in a communication system according to the present invention, a transmitter and a receiver are disposed in proximity, and thus an illegal device for interception is not allowed to lie therebetween. Accordingly, it is not necessary to prevent hacking on the transmission line, and to consider how to maintain secrecy.
By the present invention, it is possible to provide an excellent communication system and antenna apparatus which are capable of performing high-speed digital data transmission by near-field electromagnetic coupling effect using an antenna enabling use of a high-frequency band.
Also, by the present invention, it is possible to provide an excellent communication system and antenna apparatus which are capable of directly transferring a digital baseband signal without contact using a pulse signal including broadband frequency components.
By the present invention, it is possible to ensure impedance matching over a very broad band, and to employ a communication system having a good transmission characteristic by employing a transmission line having a substantially broadband characteristic itself as a non-contact data transfer antenna, and, in particular, using a slot antenna having a ring-shaped slot. For example, it becomes possible to easily achieve a non-contact transfer distance of about 5 mm at a transfer rate of 5 Gbps or more. Also, it is possible to directly transmit a broadband AC components included in a digital baseband as a pulse signal. Accordingly, the communication system is suitable for a high speed and for reduction of power consumption without necessitating complicated modulation and demodulation circuits.
Other and further objects, features and advantages of the present invention will become apparent by the detailed description based on the following embodiments of the present invention and the accompanying drawings.
In the following, detailed descriptions will be given of embodiments of the present invention with reference to the drawings.
In a communication system according to the present invention, non-contact data transmission is performed using a near electromagnetic field. The communication system directly transmits a broadband AC component included in a digital baseband as a pulse signal from a transmission antenna to a receiving antenna using a transmission line having a substantially broadband characteristic itself as a non-contact data transfer antenna. The communication system directly transmits a digital baseband signal, and thus is suitable for increasing speed of the system and reducing power consumption without necessitating complicated modulation and demodulation circuits.
Both the transmission substrate 100 and the receiving substrate 120 include a dielectric substrate having one of surfaces on which a conductor layer is formed, and the other of the surfaces on which a circuit component is mounted.
One 101 of surfaces of the transmission substrate 100, which faces the receiving substrate 120, is made of a conductor layer, and has a slot antenna 103 having a ring-shaped slot transmission line, namely, a ring-shaped slot 102 formed between a central antenna electrode on the surface 101 and the surrounding grounded conductor. Regarding the shape of the slot antenna 103, the shape of the electrode surrounded with the grounded conductor is preferably a regular polygon, such as a regular octagon, a regular hexagon, etc., in addition to a circle as shown in the figure (described later).
On the slot antenna 103 including the ring-shaped slot 102, two feed points 107 and 108 are disposed sandwiching the center of the ring-shaped slot 102.
One 107 of feed points is connected to a feed line 105 comes out from a transmission IC 106 on the other 104 of the surfaces of the transmission substrate 100 through a through hole. The feed line 105 is configured as a microstrip transmission line made of a linear conductor pattern formed on the other 104 of the surfaces of the transmission substrate 100. The characteristic impedance of the microstrip transmission line can be adjusted by a line width thereof and a thickness of the transmission substrate 100 (for example, refer to Written by Arai Hiroyuki, “New Antenna Engineering—Antenna Technology for Mobile Communication Era—” Sogo Denshi Shuppan Sha, Sep. 10 2001, Third Edition, Pages: 30-31). Here, it is possible to make reflection little and to prevent the occurrence of a stationary wave by reducing a connection impedance mismatch between the slot transmission line and the microstrip transmission line through the through hole. Thus, it is possible to have a broadband characteristic.
Also, the other 108 of the feed points is disposed at a position substantially opposite to the feed point 107 sandwiching the center of the slot antenna 103, and is connected to a terminating resistor 109 on the other surface 104 of the transmission substrate 100 through a through hole. As shown in the figure, a length of the slot line between the feed points 107 and 108 is substantially equal in the clockwise direction and in the counterclockwise direction, and thus the slot line plays an equal role for signal transmission between the transmission antenna and the receiving antenna.
In the same manner, one 124 of surfaces of the receiving substrate 120, which faces the transmission substrate 100, is made of a conductor layer, and has a slot antenna 123 having a ring-shaped slot 122 formed between an antenna electrode and grounded conductor. Two feed points 127 and 128 are disposed sandwiching the center of the ring-shaped slot 122.
One 127 of the feed points is connected to a feed line 125 including a microstrip transmission line connected to a receiving IC 126 on the other 121 of the surfaces of the receiving substrate 120 through a through hole. Note that an impedance mismatch between the slot transmission line and the microstrip transmission line through the through hole at connection time is kept small (the same as above).
Also, the other 128 of the feed points is disposed at a position substantially opposite to the feed point 127 sandwiching the center of the slot antenna 123, and is connected to a terminating resistor 129 on the other surface 121 of the receiving substrate 120 through a through hole. As shown in the figure, a length of the slot line between the feed points 127 and 128 is substantially equal in the clockwise direction and in the counterclockwise direction, and thus the slot line plays an equal role for signal transmission between the transmission antenna and the receiving antenna (the same as above).
In this regard, at the receiving antenna side, the terminating resistor 129 can be set to 0 Ω. In this case, as shown in
A description will be given of an operation principle of the antenna shown in
Regarding the shape of the slot antenna having a ring-shaped slot, the shape of the electrode surrounded with the grounded conductor is preferably a regular polygon, such as a regular octagon, a regular hexagon, etc. In such a case, the ring-shaped slot between the antenna electrode and a grounded conductor surface is suitably considered to be a slot transmission line. On the other hand, if an antenna electrode is rectangular-shaped, and the direction connecting two feed points (a height of the rectangle) is sufficiently large with respect to the perpendicular direction (a width of the rectangle) thereof, the antenna electrode is suitably considered to be a coplanar transmission line. In the following, a description will be limitedly given of the case where the ring-shaped slot is considered to be the former slot transmission line.
In the structure of the transmission antenna shown in
A quasi-TEM (Transverse Electric Magnetic) wave 201 flowing in from the microstrip transmission line 200 is subjected to line transition as described above, and then as shown in
The two progressive waves 204a and 204b traveling on the slot transmission line 203 in the opposite directions with each other are synthesized at the other 206 of the feed points of the ring-shaped slot as two progressive waves 205a and 205b, individually, and are connected to a microstrip transmission line 207 through a through hole to be converted into a quasi-TEM wave 208 again.
As described later, when near electric field and near magnetic field leaked out from individual progressive waves, which branch into two directions and travel on the slot transmission line at a transmission antenna side, reach the slot transmission line of the receiving antenna, progressive waves traveling in a forward direction and in the opposite direction are induced by electromagnetic coupling effect.
As described above, a length of the slot line between the two feed points is substantially equal in the clockwise direction and in the counterclockwise direction, and thus the slot line plays an equal role for signal transmission between the transmission antenna and the receiving antenna. Here, if the slot transmission line 203, to which the microstrip transmission lines 200 and 207 are connected at the individual feed points 202 and 206, is interpreted from circuitry view, the circuit has a configuration in which two slot transmission lines on which the two progressive waves 204a (205a) and 204b (205b) of TE10-mode are traveling in the opposite directions with each other, are connected in parallel with one microstrip transmission line. Accordingly, it is possible to obtain impedance matching by setting a ratio between a characteristic impedance of the two slot transmission lines connected in parallel and a characteristic impedance of the microstrip transmission line is set to about 2:1.
The slot transmission line has a large frequency variance of the characteristic impedance compared with a transmission line of the microstrip. However, it is possible to obtain good transmission characteristic having little reflection in a broad frequency band by designing to match characteristic impedance individually in the vicinity of center frequencies of the frequency band necessary for digital baseband signal transmission.
In particular, an electric-field analysis made by the present inventors shows that if a length of slot transmission line is less than a wavelength of a progressive wave, compared with the amplitude of the progressive wave traveling in the forward direction, the amplitude of a progressive wave (a so-called return current) traveling in a backward direction becomes large and dominant. Accordingly, in a small-sized system, if an antenna area is requested to be reduced, it is advantageous to have a configuration in which a receiver obtains a receive signal in the opposite direction to a traveling direction of the progressive wave input into the transmission antenna. Measurement results shown in
As described with reference to
A description will be given of a principle of non-contact digital data transfer in the communication system shown in
In a transmission antenna and a receiving antenna according to the present embodiment, it is possible to restrain a return loss at very low over a frequency of 10 GHz or more from a direct current (DC) component, and thus to directly input a digital baseband signal without performing modulation (as already described, it is possible to make reflection little and to prevent the occurrence of a stationary wave by reducing impedance mismatch at connection time between the slot transmission line and the microstrip transmission line through a through hole).
As described with reference to
The present inventors test-manufactured a slot antenna having a ring-shaped slot transmission line between an antenna electrode and a grounded conductor. A description will be given of that result with reference to
In
As shown in
An output from the receiving substrate 710 was taken out from one of the ports by single end, and a terminating resistor of 50Ω was connected to the other of the ports. As described with reference to
Also,
These results proves that the antenna has a sufficiently good characteristic for achieving a transfer rate of about 5 Gbps both in the case of using a double-sided substrate and in the case of multi-layer substrate of three layers or more, and thus demonstrates the operation of an antenna provided by the present invention.
In a communication system according to the present invention, a transmission line having a substantially broadband characteristic itself is used as a non-contact data transfer antenna, and a digital baseband signal is directly transmitted. Such a concept of the present invention can be applied not only to a single-ended transmission, but also to a differential signal transmission. When a small amplitude voltage is used in order to achieve high-speed signal transmission, it is advantageously possible to restrain influence of noise by the differential signal transmission.
First, a description will be given of a transmitter. In the communication system shown in
In this regard, a method of terminating the individual electrodes 503a and 503b is not limited to that shown in
Also, the circuit component, such as the transmission IC 501 is mounted on the other of the surfaces of the transmission substrate 500. The transmission IC 501 outputs the digital baseband signal on two-branched differential transmission lines 502a and 502b as a differential electronic signal, such as LVDS, CML, etc. The individual differential transmission lines 502a and 502b are made of microstrip transmission lines, and are connected to individual antenna electrodes 503a and 503b at the feed points 504 and 505, respectively, through through holes.
The electronic signal output from the transmission IC 501 goes through impedance-matched microstrip transmission lines (502a, 502b), through holes, and slot transmission lines, and is mostly converted into heat at the terminating resistor. Thus, it is possible to obtain good transmission characteristic with little reflection.
Next, a description will be given of a receiver. The receiving substrate 520 includes a slot antenna 521 having a ring-shaped slot transmission line formed between an antenna electrode and the grounded conductor. Two feed points 522 and 523 are disposed sandwiching the center of the ring-shaped slot 521, and are connected to microstrip transmission lines 525a and 525b on the other of the surfaces through through holes, respectively. The two microstrip transmission lines 525a and 525b meet near the antenna, and are connected to the receiving IC 526 as a differential transmission line 525.
The individual differential transmission lines 502a and 502b, which are made of microstrip transmission lines, are connected to individual antenna electrodes 503a and 503b at the feed points 504 and 505, respectively, through through holes. Accordingly, a quasi-TEM wave flowing into the differential transmission line 502a is converted into two progressive waves of TE10-mode which are traveling in the opposite directions with each other, at the feed point 504. In the same manner, a quasi-TEM wave flowing into the differential transmission line 502b is converted into two progressive waves of TE10-mode which are traveling in the opposite directions with each other, at the feed point 505. After that, two pairs of the progressive waves traveling in the opposite directions with each other with the individual feed points 504 and 505 as respective branch points are terminated at individual ends of the antenna electrodes 503a and 503b through terminating resistors 506a, 506b or terminating resistors 507a, 507b. That is to say, the electronic signal output from the transmission IC 501 goes through impedance-matched microstrip transmission lines (502a, 502b), through holes, and slot transmission lines, and is mostly converted into heat at the terminating resistor. Thus, it is possible to obtain good transmission characteristic with little reflection (described above).
The progressive waves that flowed from the individual differential transmission lines 502a and 502b to the feed points 504 and 505 branch and travel toward the terminating resistors 506a, 506b or 507a, 507b, 507c, and 507d. In this manner, as shown in
As shown in
In the communication system according to the present invention, an antenna apparatus having a ring-shaped slot transmission line between an antenna electrode and a grounded conductor is used as a transmission and a receiving antennas. There is an advantage in that a digital baseband signal can be directly transmitted using a transmission line itself having a broadband characteristic as a non-contact data transfer antenna. On the other hand, the slot antenna itself is common knowledge for those skilled in the art. Finally, a description will be given of the difference between the slot antenna and the antenna apparatus used in the present invention.
In general, an infinite conducting plate which is provided with a cutaway having a length L and a width of W (L>>W) and of which smaller-width sides of the slot are connected to a high-frequency power source is referred to a slot antenna, which has a complementary relationship with a dipole antenna. Such a slot antenna resonates at a certain specific frequency which is determined by the length L, and operates so as to send out a plane wave or receive the wave (for example, refer to Written by Arai Hiroyuki, “New Antenna Engineering—Antenna Technology for Mobile Communication Era—” Sogo Denshi Shuppan Sha, Sep. 10 2001, Third Edition, Pages: 55-57).
Also, several proposals have been already made of a slot antenna produced by providing a conductor plate with a ring-shaped slot. The slot antenna is mainly used for sending out and receiving a circularly polarized wave of a specific frequency (narrow band) (for example, refer to Japanese Patent Nos. 2646273 and 3247140). In these antennas, a circular slot line is provided with a feed point and a perturbation element, a stationary wave is produced with respect to a TE10 wave having a frequency such that a half wavelength is equal to the slot line length from the feed point to the perturbation element in the clock-wise or the counter-clock wise direction as viewed from the feed point. The electric field component of the stationary wave and the electric field component of a counter-clockwise circularly polarized wave or a clockwise circularly polarized wave are converted into a plane wave to be transmitted or received as a radio wave. Accordingly, a ring-shaped slot antenna of this kind has a resonant narrow-band characteristic.
In contrast, in a communication system according to the present invention, two slot antennas are disposed with being opposed in proximity, and coupling is directly performed between a near electric field component and a near magnetic field component of a TE10 wave traveling along the slot transmission line of the transmission antenna. This is different from a resonant antenna. Here, two feed points are disposed sandwiching the center of the ring-shaped slot. A length of the slot line between the feed points is substantially equal in the clockwise direction and in the counterclockwise direction, and thus the slot line plays an equal role for signal transmission between the transmission antenna and the receiving antenna. Also, there is little impedance mismatch in the connection of the slot transmission line with the microstrip transmission line through a through hole, and thus resulting in little reflection. Accordingly, it is possible to prevent the occurrence of a stationary wave, and thus it is possible to have a broadband characteristic.
Accordingly, by a communication system according to the present invention, it becomes possible to directly transfer a digital baseband signal in proximity without contact using a pulse signal including broadband frequency components. Thus, it becomes possible to easily provide overwhelmingly faster transmission compared with related-art communication methods using modulation and demodulation.
The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP filed in the Japan Patent Office on Apr. 30, 2008, the entire content of which is hereby incorporated by reference.
It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-118412 | Apr 2008 | JP | national |
