JP2006020303A - Interconnection circuit between two loop antennas embedded in wristband of wrist-carried wireless instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wristwatch type wireless apparatus having two loop antennas. <P>SOLUTION: A wireless instrument according to the present invention comprises: a wristband (2) having a first portion (2a) and a second band portion (2b) connected to opposite edges of a casing (3); and a first loop antenna (4a) and a second loop antenna (4b) embedded in the first band portion (2a) and the second band portion (2b) respectively and extending between corresponding upper and lower surfaces. The first band portion (2a) and the second band portion (2b) have upper and lower surfaces, both the loop antennas are connected to a first tuning circuit (5a) and a second tuning circuit (5b) via the opposite edges of the casing, respectively, and the first tuning circuit (5a) and the second tuning circuit (5b) are connected to an antenna receiver (6) arranged in said casing (3) and together in a hybrid manner via an interconnection circuit (7), both tuning circuits being connected partially in parallel and partially in series. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

      The present invention relates to a wireless device worn on a wrist, and more particularly, to a wristwatch-type receiver having a magnetic loop antenna incorporated in a wristband thereof.

      In this specification, the loop antenna is described as a single loop conductor disposed on substantially the same plane, and its operating frequency is such that a substantially uniform current flows along the conductor.

      In recent years, wireless devices that receive radio frequency signals with an antenna system incorporated in a wristband have become common. The prior art discloses an example in which an antenna device embedded in a wristband and having a variable length in the circumferential direction is used together with a wireless device that is carried around a person's arm. Thus, the antenna is formed to have a length sufficient to receive a radio signal in the VHF band (30-300 MHz) or higher. As shown in FIG. 3, the loop antenna 101 is integrally formed in the wristband 102. The wristband 102 is connected to the case 103 of the wireless device 100 worn on the wrist, and when the band is fastened, a continuous loop is formed via the wristband central fixing structure 104 (eg, fastener). Is done.

      However, in such a configuration, the connection / coupling of the loop in the central fixed structure 104 has a great influence on the reception capability. Therefore, it is difficult to design a mechanism for performing a preferable operation. The reason is that this part is easily damaged. Furthermore, the wristband 102 usually has a wristband length adjustment structure, and the length of the wristband is adjusted to the thickness of the wearer's arm. By this length adjustment, the loop length of the antenna changes for each wearer, and the receivable frequency band varies for each wearer.

      Such a solution is complicated and bulky in that the wireless device 100 includes an accessory device that compensates for variations in antenna gain and resonant frequency resulting from differences in antenna loop length. This solution is not preferred for such wireless devices.

      Patent Document 1 discloses a solution to this problem in FIG. 4, which prevents connection failure and / or breakage due to the attachment and detachment of the above-mentioned type of loop antenna, and has a reception frequency band on the thickness of the wearer's arm. We are proposing a wireless device that can be worn on the wrist without being affected.

US Pat. No. 5,986,566

      The wireless device 110 to be worn on the wrist has a case 113 and a center fixed wristband 112. The wristband 112 has a front surface 121, a back surface 122, and a fixing structure 114 disposed at the center thereof. The wristband 112 is composed of a pair of wristband parts 112a and 112b. These portions are attached to the end of the case 113. The reception antenna 111 is mounted in at least one end 112a of the wristband and receives a signal. The antenna 111 is connected to a receiving circuit in the case 113 via a terminal. According to the above-mentioned document, the loop antenna 111 extends between the front surface 121 and the rear surface 122 of the wristband 112, but does not penetrate (extend beyond) the central fixing structure 114. Reception is possible without the attached wristband 112 and without forming a loop, but this is also true when worn.

      However, the solution according to Patent Document 1 has several drawbacks. The measures taken with the antenna structure described above do not exhibit optimal antenna efficiency and optimal noise matching. The non-negligible part of antenna loss is due to the human wrist interfering with the antenna and the wristband dielectric material. Improvement in antenna efficiency can be achieved by reducing the ratio of antenna loss to antenna radiation resistance. Therefore, the efficiency of the antenna can be improved by either reducing the antenna loss or increasing the antenna radiation resistance.

      It is an object of the present invention to improve antenna efficiency by reducing antenna ohmic and dielectric losses and increasing antenna radiation resistance.

      The main object of the present invention is to implement a wrist-worn wireless device that receives two radio frequency signals by mounting two loop antennas in the wristband so as to improve antenna efficiency. On the other hand, a reduction in antenna loss can be achieved by connecting two loop antennas in parallel, while an increase in antenna radiation resistance can be achieved by connecting two loop antennas in series.

      In order to achieve the above main object, a wireless device according to an embodiment of the present invention includes a wristband having a first band portion and a second band portion connected to opposite ends of a case, and the first band portion. A first loop antenna and a second loop antenna respectively embedded in the second band portion and extending between the front surface and the back surface, wherein the first band portion and the second band portion have the front surface and the back surface The loop antennas are respectively connected to a first tuning circuit and a second tuning circuit through opposite ends of the case, and the first tuning circuit and the second tuning circuit are arranged in the case. The antenna receiver is connected to the antenna receiver through an interconnect circuit in a hybrid system that is partially connected in parallel and partially in series.

      As described above, the present invention relates to a wireless device attached to a wrist that receives a radio frequency signal in a frequency band of 30 to 300 MHz (preferably 88 to 108 MHz) using a wireless data transmission system. The present invention particularly relates to an antenna structure with optimized antenna efficiency.

      In FIG. 1, the wireless device 1 has a wristband 2. The wristband 2 has a first band portion 2 a and a second band portion 2 b connected to the opposite end of the case 3. Each band portion has an upper (front) surface and a lower (back) surface. The first loop antenna 4a and the second loop antenna 4b are embedded in the first band portion 2a and the second band portion 2b, respectively, and extend between corresponding front and back surfaces. Both the first loop antenna 4a and the second loop antenna 4b are connected to the first tuning circuit 5a and the second tuning circuit 5b through the opposite ends of the case 3, respectively. Both tuning circuits are connected to an antenna receiver 6 arranged in the case 3. Furthermore, both tuning circuits are connected to each other in a hybrid manner via the interconnection circuit 7. This will be described in detail with reference to FIG.

      The same reference numerals in FIG. 2 and FIG. 1 represent common parts.

      Both the first loop antenna 4a and the second loop antenna 4b are shown in the form of coils, which are connected to the antenna receiver 6 via a first tuning circuit 5a and a second tuning circuit 5b. Furthermore, an interconnection circuit 7 is provided for interconnecting both the first tuning circuit 5a and the second tuning circuit 5b, and also both the first loop antenna 4a and the second loop antenna 4b.

      As mentioned above, the object of the present invention is to optimize antenna efficiency. In order to achieve this goal, it is important to reduce the ratio of antenna loss to radiation resistance, and therefore reduce antenna loss and increase radiation resistance. In the present invention, reduction of the ohmic loss and dielectric loss of the antenna is achieved by connecting the first loop antenna 4a and the second loop antenna 4b in parallel. By connecting both the loop antennas in parallel, the loss is reduced by about 50%, and the radiation resistance can be maintained at the level of a single loop antenna. Further, an increase in radiation resistance can be achieved by connecting both the first loop antenna 4a and the second loop antenna 4b in series. By connecting both loop antennas in series, the radiation resistance is increased by a factor of about 4, but the loss is only increased by a factor of 2 or more. As a result, the ratio of the antenna loss to the radiation resistance is reduced to about ½.

In order to achieve this purpose, an interconnection circuit 7 is used to interconnect both the first tuning circuit 5a and the second tuning circuit 5b, and both the first loop antenna 4a and the second loop antenna 4b. Provided. This is done in a hybrid manner between two “extream” connections, i.e. partly in parallel and partly in series. According to one embodiment of the present invention shown in FIG. 2, the interconnection circuit 7 includes a first capacitor C _P1 and a second capacitor C _P2 and a third capacitor C _S. The first capacitor C _P1 and the second capacitor C _P2 respectively partially (partially) connect the first tuning circuit 5a and the second tuning circuit 5b in parallel. The third capacitor _{C S} is the first tuning circuit 5a and the second tuning circuit 5b partially (partially) connected in series.

In the embodiment shown here, each of the first loop antenna 4a and the second loop antenna 4b has two connection points (respectively 8a, 9a and 8b, 9b), and the corresponding first tuning circuit 5a and second loop antenna respectively. Connected to the tuning circuit 5b. The first capacitor _CP1 has one end connected to the connection point 8a and the other end connected to the connection point 8b. The second capacitor _CP2 has one end connected to the connection point 9a and the other end connected to the connection point 9b. Thus, the first tuning circuit 5a and the second tuning circuit 5b are partially connected in parallel via the capacitor _CP1 and the capacitor _CP2 . The third capacitor _CS has one end connected to the connection point 8b and the other end connected to the connection point 9a. Both circuits are partially connected in series via a third capacitor C _S. Finally, the antenna receiver 6 is connected to the connection point 8a and the connection point 9b.

Alternatively, the same result can be achieved by connecting the third capacitor _CS to the connection point 8a and the connection point 9b and the antenna receiver 6 to the connection point 8b and the connection point 9a.

      In the hybrid connection, both loop antennas are connected partially in parallel and partially in series. Thereby, the ratio of the antenna loss to the radiation resistance can be greatly reduced, and the antenna efficiency is also greatly increased.

      To further increase antenna efficiency, attention must be paid to the components of the tuning circuit. In fact, loop antenna tuning is necessary because of the narrow bandwidth of this type of antenna. This tuning can be achieved using a varactor.

      According to the embodiment of the present invention shown in FIG. 2, each of the first tuning circuit 5a and the second tuning circuit 5b introduces a minimum conductive loss by connecting varactors in parallel.

Therefore, the first tuning circuit 5a includes a capacitor 52a and a varactor 51a connected in series, and a resistor 53a having one end connected between the capacitor 52a and the varactor 51a and the other end connected to a predetermined potential _VA. Have. The resistor 53a applies a constant tuning voltage to the varactor 51a during reception of the radiation signal. The capacitance of the varactor varies with this tuning voltage. Therefore, reception of any particular frequency of the antenna requires various varactor capacitances that vary with this tuning voltage. The voltage _VA is determined by conventional means, for example with a binary search algorithm.

The second tuning circuit 5b is the same type as the first tuning circuit 5a. The second tuning circuit 5b includes a capacitor 52b and a varactor 51b connected in series, one end is connected between the capacitor 52b and varactor 51b, and a resistor 53b which other end is connected to a predetermined potential _{V B.} The resistor 53b gives a constant tuning voltage to the varactor 51b during reception of the radiation signal, and the capacitance of the varactor changes according to this tuning voltage. Therefore, reception of any particular frequency of the antenna requires various varactor capacitances that are tuned by this tuning voltage. The voltage V _B is determined by conventional means, for example with a binary search algorithm.

      As another example, in order to optimize the operating characteristics of these tuning circuits, each tuning circuit has two varactors connected in series and of opposite polarity instead of one varactor and one capacitor. You may have.

      In order to greatly improve the signal response of the first tuning circuit 5a and the second tuning circuit 5b, both varactors 51a and 51b are connected in “anti” parallel and with opposite polarities. This method is the preferred solution even when both tuning circuits are asymmetric. The reason is that this method has less insertion loss and can be constructed with fewer parts than a symmetrical tuning circuit that includes two varactors connected in series and of opposite polarity.

Furthermore, the first tuning circuit 5a and the second tuning circuit 5b, it is preferable to include a capacitor C _T for adjusting the tuning range. The capacitor _{C T} has one end between the capacitor 52a and varactor 51a of first tuning circuit 5a, and the other end is connected between the varactor 51b and capacitor 52b of second tuning circuit 5b.

      The shape of the loop antenna is preferably rectangular or so-called open O-shaped. Preferably, both loop antennas have the same shape in order to maintain symmetry. However, other loop shapes can be used as long as it can fit within a portion of the wristband. Both antennas preferably operate in the 88-108 MHz frequency band using a wireless data transmission system.

      The wireless device of the present invention is preferably a wristwatch.

      The above description relates to one embodiment of the present invention, and those skilled in the art can consider various modifications of the present invention, all of which are included in the technical scope of the present invention. The The numbers in parentheses described after the constituent elements of the claims correspond to the part numbers in the drawings, are attached for easy understanding of the invention, and are used for limiting the invention. Must not. In addition, the part numbers in the description and the claims are not necessarily the same even with the same number. This is for the reason described above.

1 is a cross-sectional view of a wireless device attached to a wrist according to an embodiment of the present invention. The figure showing the antenna circuit inside the case of the radio | wireless apparatus by one Example of this invention. The perspective view of the wristwatch type pager (pager) which concerns on a prior art. The perspective view of another wristwatch type pager which concerns on a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radio equipment 2 Wrist band 2a 1st band part 2b 2nd band part 3 Case 4a 1st loop antenna 4b 2nd loop antenna 5a 1st tuning circuit 5b 2nd tuning circuit 6 Antenna receiver 7 Interconnection circuit 8a, 9a Connection Point 8b, 9b Connection point 51a, 51b Varactor 52a, 52b Capacitor 53a, 53b Resistance 100 Radio equipment 101 Loop antenna 102 Wristband 103 Case 104 Center fixed structure

Claims (8)

(A) a wristband (2) having a first band portion (2a) and a second band portion (2b) connected to opposite ends of the case (3);
The first band portion (2a) and the second band portion (2b) have a front surface and a back surface,
(B) a first loop antenna (4a) and a second loop antenna (4b) embedded in the first band portion (2a) and the second band portion (2b), respectively, and extending between the front surface and the back surface; ,
Have
The loop antennas are connected to the first tuning circuit (5a) and the second tuning circuit (5b) through opposite ends of the case, respectively.
The first tuned circuit (5a) and the second tuned circuit (5b) are partially parallel and connected to the antenna receiver (6) arranged in the case (3) via an interconnect circuit (7). A wireless device connected in a hybrid system connected in series. The interconnect circuit (7) is a capacitor network;
The capacitor network is:
A first capacitor (C _P1 ) and a second capacitor (C _P2 ) that connect the first tuning circuit (5a) and the second tuning circuit (5b) in part,
The wireless device according to claim 1, comprising a third capacitor (C _S ) for connecting the first tuning circuit (5a) and the second tuning circuit (5b) in part. Each of the first tuning circuit (5a) and the second tuning circuit (5b) has a first connection point (8a, 8b) and a second connection point (9a, 9b),
The first and second capacitors are respectively connected to a first connection point (8a, 8b) and a second connection point (9a, 9b) of the both tuning circuits;
The third capacitor is connected to a second connection point (9a) of the first tuning circuit and a first connection point (8b) of the second tuning circuit;
The antenna receiver (6) is connected between a first connection point (8a) of the first tuning circuit and a second connection point (9b) of the second tuning circuit. The wireless device according to 1. The first tuning circuit (5a) and the second tuning circuit (5b) include a capacitor (52a, 52b) and a varactor (51a, 51b) connected in series, respectively, and one end between the capacitor and the varactor. The wireless device according to claim 1, wherein the wireless device is configured by resistors (53a, 53b) connected to each other and connected to predetermined potentials (V _A , V _B ). One end of the capacitor (C _T ) for adjusting the tuning range of the first tuning circuit (5a) and the second tuning circuit (5b) is between the capacitor of the first tuning circuit (5a) and the varactor, and the other end is The wireless device according to claim 1, wherein the wireless device is connected between a varactor and a capacitor of the second tuning circuit (5b). The wireless device according to claim 1, wherein both of the loop antennas have a rectangular shape or an open O shape. The wireless device according to claim 1, wherein both of the loop antennas operate in a frequency band of 88 to 108 MHz. The wireless device according to claim 1, wherein the wireless device is a wristwatch.

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