JP2002368512A - Power loss suppression antenna circuit and portable terminal provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna circuit which suppresses the increase of a power loss in a transmission/reception changeover part even when radiation resistance is falling down in an antenna by receiving influence from a circumferential environment. SOLUTION: A power loss suppression antenna circuit which comprises the transmission/reception changeover part connected to the antenna is provided with an adjusting circuit 4 which is inserted between the antenna 1 and the transmission/reception changeover part 3. The adjusting circuit 4 adjusts the real number part of impedance when the antenna 1 is viewed from the antenna side connection terminal c of a device 3 to be larger than the real number part of impedance when the antenna 1 is viewed from the power feeding point d of the antenna.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cellular phone, a PDA, and the like.
The present invention relates to a power loss suppressing antenna circuit used for a portable terminal such as a portable terminal and a portable terminal including the power loss suppressing antenna circuit. Specifically, even if a metal object comes close to the antenna of the mobile terminal and the radiation resistance of the antenna decreases,
The present invention relates to a power loss suppression antenna circuit capable of suppressing an increase in power loss in an antenna circuit, and a mobile terminal including the power loss suppression antenna circuit.

[0002]

2. Description of the Related Art FIG. 5 is an external view of a foldable portable telephone. In a mobile phone 19 shown in the figure, a lower housing 16 having a key 15 and an upper lid 18 having a display unit 17 are foldably connected, and the antenna 1 is provided at an upper end of the lower housing 16.

FIG. 6 shows a conventional general antenna circuit used for a portable telephone or the like. As shown in FIG. 1, the antenna circuit includes an antenna 1 and a transmission / reception switching unit 3.
A matching circuit 2 for matching the impedance of the antenna 1 with the impedance of the transmission / reception switching unit 3 is inserted between the two. The other side of the transmission / reception switching unit 3 is connected to the transmission unit 5 via the terminal a1.
To the receiving unit 6 via the terminal a2.

FIG. 7 is a modified view of the antenna circuit disclosed in Japanese Patent Application Laid-Open No. 11-145852. In the figure, 1 is an antenna, 2A, 2B and 2C are matching circuits, 3 is a transmission / reception switching unit, 5 is a transmission unit, 6 is a reception unit, 9a,
9b is a selection switch for selecting the matching circuits 2A to 2C, 7 is a level detection unit, and 8 is a control unit.

Hereinafter, the operation of FIG. 7 will be described. For example, at the time of transmission, the level detection unit 7 measures the power supplied to the antenna at the feeding point d, controls the selection switches 9a and 9b under the control of the control unit 8, and the power output from the antenna 1 is maximized. Thus, the optimum matching circuit is selected from the plurality of matching circuits 2A to 2C having different impedances. As a result, the power output from the antenna 1 can be maximized.

In this antenna circuit, the selection switch 9 selects an appropriate matching circuit 2 so that the antenna 1
The impedance mismatch of the transmission / reception switching unit 3 at the subsequent stage is improved, and the best antenna gain is obtained.

[0007]

However, in a portable terminal such as a foldable portable telephone or a PDA, an antenna is generally provided in a lower housing provided with a key, and an upper lid provided with a display unit is provided. When the cover is opened, the radiation resistance of the antenna decreases due to the approach of the upper lid to the antenna, thereby increasing the power loss in the transmission / reception switching unit, leading to a reduction in reception sensitivity.

The antenna circuit disclosed in Japanese Patent Application Laid-Open No. H11-145852 includes an antenna 1 and a transmission / reception switching unit 3 at a subsequent stage.
A matching circuit 2 is provided between the two.
Focuses on impedance matching between the antenna 1 and the transmission / reception switching unit 3, and the antenna 1 and the transmission unit 5 or the reception unit 6
No consideration is given to the power loss in the transmission / reception switching unit 3 inserted between the two.

The present invention has been made in order to solve the above-mentioned problem, and the real part of the impedance when the antenna direction is viewed from the antenna side connection terminal of the transmission / reception switching unit 3 connected to the antenna is supplied to the antenna. An antenna that suppresses power loss in the transmission / reception switching unit 3 that occurs when the radiation resistance of the antenna is reduced due to the surrounding environment by making the impedance larger than the real part of the impedance when the antenna is viewed from a point. It is intended to provide a circuit.

[0010]

In order to achieve the above object, a power loss suppressing antenna circuit according to the present invention including a device connected to an antenna includes an adjustment circuit inserted between the antenna and the device. The adjustment circuit has means for adjusting the real part of the impedance as seen from the antenna-side connection terminal of the device to be larger than the real part of the impedance as seen from the feeding point of the antenna. And

The device of the present invention is characterized in that a plurality of devices are connected to the antenna. Further, the adjustment circuit of the present invention is characterized in that it is constituted by a lumped constant circuit or a distributed constant circuit. Further, the present invention is characterized in that a matching circuit is provided at a subsequent stage of the device.

Further, the device of the present invention is characterized in that it comprises a transmission / reception switching unit for switching between transmission and reception signals.

Further, the present invention is a portable terminal having a power loss suppressing antenna circuit having an adjustment circuit inserted between an antenna and a device connected to the antenna, wherein the adjustment circuit is an antenna of the device. There is provided a means for adjusting the real part of the impedance as viewed from the side connection terminal so as to be larger than the real part of the impedance as viewed from the feeding point of the antenna.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an antenna circuit according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an antenna circuit according to one embodiment of the present invention. The antenna circuit shown in FIG.
And a matching circuit 2 is provided between the transmission / reception switching unit 3 and the transmission / reception unit 5. The matching circuit 2 may not be provided when the matching between the transmission / reception switching unit 3 and the transmission unit 5 or the reception unit 6 is good. In FIG. 1, the same members or those having the same functions as those in FIGS. 6 and 7 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 1, the adjustment circuit 4 is arranged such that the real part R ′ of the impedance Z ′ as viewed from the antenna side connection terminal c of the transmission / reception switching unit 3 when viewed from the antenna 1 direction is shifted from the feeding point d of the antenna 1 toward the antenna 1. This is for adjusting the impedance Z so as to be larger than the real part R of the impedance Z.

The matching circuit 2a includes a transmission / reception switching unit 3 and a transmission unit 5
A circuit provided between the transmission and reception switching unit 3 and the transmission unit 5 for matching impedance. The matching circuit 2b
This circuit is provided between the transmission / reception switching unit 3 and the reception unit 6 and matches the impedance between the transmission / reception switching unit 3 and the reception unit 6. By inserting these matching circuits 2a and 2b, the transmission / reception switching unit 3 and the transmission unit 5 or the transmission / reception switching unit 3 are inserted.
And the reception unit 6 can prevent signal reflection. Therefore, the transmission signal from the transmission unit 5 is transmitted to the antenna 1 through the matching circuit 2a, the transmission / reception switching unit 3 and the adjustment circuit 4, and the reception signal from the antenna 1 is transmitted to the adjustment circuit 4, the transmission / reception switching unit 3
And transmitted to the receiving unit 6 via the matching circuit 2b. As will be described later, the matching circuits 2a and 2b and the adjustment circuit 4 can be realized by a lumped constant using an inductor or a capacitor or a distributed constant circuit using a microstrip line, for example.

FIG. 2 shows an equivalent circuit for explaining the principle of power loss in the transmission / reception switching unit 3 in the antenna circuit.
FIG. 2A is an equivalent circuit of a conventional antenna circuit without the adjustment circuit 4 inserted therein, and FIG. 2B is an equivalent circuit of the antenna circuit of the present invention with the adjustment circuit 4 inserted therein. . First, the power loss in the transmission / reception switching unit 3 in FIG. In FIG. 2A, r
Represents the internal resistance of the transmission / reception switching unit 3, R represents the radiation resistance of the antenna 1, Pin represents the power input from the transmission unit 5 to the transmission / reception switching unit 3, and Pr represents the power loss due to the internal resistance r. The relationship between the power loss Pr and the input power Pin is represented by Expression (1). Pr = Pin · r / (r + R) (1)

As can be seen from equation (1), the transmission / reception switching unit 3
Has an internal resistance r, a part of the power Pin input from the transmission unit 5 to the transmission / reception switching unit 3 is consumed as power loss Pr by the internal resistance r of the transmission / reception switching unit 3.

The power loss Pr depends on the real part (radiation resistance) R of the impedance Z as viewed from the antenna side connection terminal c of the transmission / reception switching unit 3 toward the antenna 1, and the power loss decreases as the real part R decreases. It turns out that it becomes large. In the antenna circuit, when the surrounding environment, for example, a metal piece approaches, the radiation resistance R of the antenna decreases.
The power loss Pr of the antenna circuit increases.

On the other hand, in order to reduce or suppress the power loss Pr, in the present invention, as shown in FIG.
An adjustment circuit 4 is provided between the antenna 1 and the transmission / reception switching unit 3,
The real part R ′ of the impedance Z ′ when viewing the antenna 1 side from the antenna side connection terminal c of the transmission / reception switching unit 3 is the antenna 1
By adjusting the impedance Z to be larger than the real part R of the impedance Z when the antenna 1 is viewed from the feeding point d, the power loss at the internal resistance r of the transmission / reception switching unit 3 can be reduced. The principle will be described below.

In FIG. 2B, the impedance Z when the antenna 1 is viewed from the feeding point d of the antenna 1 is represented by Z = R
+ JX (R: real part, X: imaginary part), and the impedance Z ′ viewed from the terminal c is Z ′ = R ′ + jX ′ (R ′:
(Real part, X ′: imaginary part), the relationship between the power loss Pr ′ and the input power Pin is expressed by the equation (2). Pr ′ = Pin · r / (r + R ′) (2)

From the equations (1) and (2), to make the power loss Pr 'when the adjusting circuit 4 is inserted smaller than the power loss Pr when the adjusting circuit 4 is not inserted, the adjusting circuit 4
It can be easily understood that the real part R 'of the impedance Z' of the above may be adjusted so that R <R '.

FIG. 3 shows a specific circuit configuration example of the adjustment circuit 4 and the matching circuit 2 of the present invention. In FIG. 3A, the adjustment circuit 4 includes, for example, inductors L1 and L
2 and a capacitor C1. In FIG. 3B, the matching circuit 2 is formed of, for example, an L-type lumped constant circuit including an inductor L3 connected in parallel and a capacitor C2 connected in series. The adjusting circuit 4 and the matching circuit 2 can be configured by distributed constant circuits. Of course, the adjustment circuit 4 and the matching circuit 2 are merely examples, and may be constituted by other known circuits.

As described above, the real part R ′ of the impedance Z ′ viewed from the antenna side connection terminal of the transmission / reception switching unit 3 is larger than the real part R of the impedance Z viewed from the feeding point d of the antenna 1. By adjusting so that the radiation resistance R of the antenna 1 is reduced by the influence of the surrounding environment, an increase in power loss in the transmission / reception switching unit 3 is suppressed.

FIG. 4 is a diagram showing a system configuration of a portable terminal having a power loss suppressing antenna circuit. In FIG. 4, 1 is an antenna for receiving radio waves from a base station, 4 is an adjustment circuit, 3 is a transmission / reception switching unit, 2a and 2b are matching circuits, and demodulates radio waves received by the antennas and converts them into baseband signals. A receiving unit 5, a transmitting unit that modulates a transmission voice signal and a control signal into a radio wave and transmits the signal from the antenna 1, a system control unit 21 that processes a voice signal and a control signal, and the like, 26 denotes an incoming telephone number and its telephone number. A display unit (LCD) 22 composed of a liquid crystal display or the like for displaying an image related to the number outputs voice information from a speaker 23, generates a ringing sound from a ringer 24, or voice information input from a microphone 25. , An input device such as a numeric keypad or a function button,
Is an image processing unit that processes an image input through the camera 30 or the USB port 29 and the like, and processes the image so that it can be stored in a memory (not shown) in the system control unit 21.

When the upper lid of the portable terminal is opened, the upper lid comes close to the antenna 1 and the radiation resistance of the antenna decreases. In the embodiment of the present invention, the antenna 1 of the portable terminal and the transmission / reception switching unit 3 are used. By providing the adjustment circuit 4 between them, an increase in power loss in the transmission / reception switching unit can be suppressed.

[0027]

As described above in detail, according to the present invention, the real part of the impedance seen from the antenna side connection terminal of the transmission / reception switching unit is the impedance part seen from the feeding point of the antenna. By inserting an adjustment circuit that can be adjusted to be larger than the real part between the antenna and the transmission / reception switching unit, even if the radiation resistance of the antenna decreases due to the surrounding environment, the power in the antenna circuit can be reduced. The effect is that the loss can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an antenna circuit having an adjustment circuit and a matching circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing an equivalent circuit of the antenna circuit.

FIG. 3 is a diagram illustrating a specific circuit configuration example of a matching circuit and an adjustment circuit of the present invention.

FIG. 4 is a diagram illustrating a system configuration of a portable terminal including a power loss suppression antenna circuit.

FIG. 5 is an external view of a foldable mobile phone having an antenna.

FIG. 6 is a block diagram showing a conventional general antenna circuit.

FIG. 7 is a block diagram showing a conventional antenna circuit having a selection switch.

[Explanation of symbols]

 Reference Signs List 1 antenna 2 matching circuit 3 transmission / reception switching unit 4 adjustment circuit 5 transmission unit 6 reception unit 15 key 16 top cover 17 display unit 18 top cover 19 portable terminal

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J047 AA02 AA04 AB06 FA12 FD01 5K011 BA04 DA02 DA21 JA01 KA03 5K027 AA11 BB17 CC08

Claims (8)

[Claims] 1. An antenna circuit including a device connected to an antenna, comprising: an adjustment circuit inserted between the antenna and the device, wherein the adjustment circuit views the antenna from an antenna-side connection terminal of the device. A means for adjusting the real part of the impedance to be larger than the real part of the impedance when the antenna is viewed from the feeding point of the antenna. 2. The power loss suppressing antenna circuit according to claim 1, wherein a plurality of said devices are connected to an antenna. 3. The power loss suppressing antenna circuit according to claim 1, wherein said adjustment circuit is constituted by a lumped constant circuit. 4. The power loss suppressing antenna circuit according to claim 1, wherein said adjustment circuit is constituted by a distributed constant circuit. 5. The power loss suppressing antenna circuit according to claim 1, wherein a matching circuit is provided at a stage subsequent to said device. 6. The power loss suppressing antenna circuit according to claim 1, wherein the device is a transmission / reception switching unit that switches transmission / reception signals. 7. A portable terminal comprising a power loss suppression antenna circuit having an adjustment circuit inserted between an antenna and a device connected to the antenna, wherein the adjustment circuit is an antenna-side connection terminal of the device. A portable terminal having means for adjusting the real part of the impedance as viewed from above from the antenna to be larger than the real part of the impedance as viewed from the feeding point of the antenna. 8. The mobile terminal according to claim 7, wherein the device is configured by a transmission / reception switching unit that switches a transmission / reception signal.