WO2012070826A2

WO2012070826A2 - Antenna matching device and method for multi-band mobile communication terminal

Info

Publication number: WO2012070826A2
Application number: PCT/KR2011/008897
Authority: WO
Inventors: Maeng-Youl Lee; Sung Jin Kim; Yong Goo Lee
Original assignee: Gigalane Co. Ltd
Priority date: 2010-11-26
Filing date: 2011-11-22
Publication date: 2012-05-31
Also published as: KR20120056953A; KR101311729B1; WO2012070826A3

Abstract

An antenna matching device, and more particularly, an antenna matching device and method for a multi-band mobile communication terminal are provided. The antenna matching device uses in a combined manner a tunable matching element (e.g., an RF MEMS variable capacitor) that operates mechanically in accordance with a mobile communication service area and a communication system (operating mode) with an electrically operable tunable matching element. Accordingly, a lifetime of the mechanically operable tunable matching element can be lengthened as long as possible.

Description

ANTENNA MATCHING DEVICE AND METHOD FOR MULTI-BAND MOBILE COMMUNICATION TERMINAL

The following description relates to an antenna matching device, and more particularly, to an antenna matching device and method for a multi-band mobile communication terminal.

With the recent development of information communication technologies, communication devices become smaller, lighter, and multifunctional. In particular, next generation mobile communication terminals have evolved to multi-band phones incorporating personal communication service (PCS), code division multiple access (CDMA), global system for mobile communication (GSM), and wideband CDMA (WCDMA) technologies, and simultaneously being equipped with multi-functions, such as Bluetooth and global positioning system (GPS).

To implement multi-band in a mobile communication terminal, a number of antennas may be used. However, this may lead to an increase in size and cost of the terminal. Thus, technologies for multi-band implementation with a single compact antenna have been researched. To implement multi-band with a single antenna, it has been suggested to design an antenna having a wide bandwidth which can avoid an additional tuning process and to connect a number of antennas having a single band. However, the above configurations have difficulties in increasing efficiency of an antenna while implementing multi-band. Thus, to achieve a high-efficient single antenna for multi-band, a method of tuning a resonance frequency of the antenna according to an applied frequency has been introduced. This method can implement a multi-band mobile communication terminal with a single antenna, and can design an antenna having a high efficiency with respect to resonance frequency.

FIG. 1 is a diagram illustrating an equivalent circuit of an antenna matching unit of a multi-band antenna implemented as a prior art radio frequency (RF) switch. Referring to FIG. 1, the antenna matching unit includes a plurality of

capacitors

21, 22, and 23. The

capacitors

21, 22, and 23 are electrically connected to an antenna 10 according to operation of

RF switches

31, 32 and 33, respectively. Accordingly, values of the capacitors loaded to the antenna 10 are varied by operation of the

RF switches

31, 32, and 33, resulting in tuning a resonance frequency of the antenna 10.

Generally, a field effect transistor or a positive intrinsic negative diode is used as the RF switch, and when a tuning capacitor implemented using such transistor or diode, a quality factor of the capacitor is deteriorated in ON state, leading to degrading the matching properties of a tuning circuit. Moreover, power loss increases for driving a switch, and the overall performance of a system is degraded due to nonlinearity of components and signal distortion. Furthermore, an electric switch to be employed to the antenna has disadvantages in inferior linearity and a complicated and difficult design of a bias circuit for driving the switch.

To solve the above drawbacks caused by the antenna matching unit utilizing the electric RF switch, researches on an RF micro electro mechanical system (MEMS) variable capacitor have increasingly drawn attention.

RF MEMS variable capacitor can be operated in an electrostatic, an electromagnetic, or a piezoelectric driving scheme. In electromagnetic and piezoelectric driving schemes, a driving speed of mechanical displacement components is slow and a significant amount of power is consumed due to the driving current. On the other hand, in an electrostatic driving scheme, a driving speed of mechanical displacement components is fast, power consumption is small, and it is easy to fabricate the components, and due to such advantages, many researches on the electrostatic capacitor have been conducted.

U.S. Patent No. 6,355,534 disclosed a variable tunable range MEMS capacitor. In the U.S. Patent, the tunable capacitor includes a fixed charge plate and a movable charge plate. The movable charge plate is disposed above the fixed charge plate and can move up and down by an electrostatic force. In addition, a stiffener is superimposed over the movable charge plate. The stiffener is to prevent the movable charge plate from being bent when moving downward.

The tunable capacitor in the U.S. Patent has advantages in accomplishment of a much larger tuning range and increase in the tunable range using the stiffener over the varactor diode. In addition, the tunable capacitor can move the movable charge plate upward and downward based on an electrostatic force. Accordingly, a distance between the fixed charge plate and the movable charge plate changes, and thereby capacitance can change.

However, since the prior art MEMS variable capacitor makes use of mechanical displacement, a problem has arisen that the reliability of lifetime of a capacitor may not be ensured.

More specifically, a multi-band mobile communication terminal should be compatible with a time division multiplex access (TDMA) system and a CDMA system. Since the TDMA system transmits and receives a downlink and an uplink through a single shared wireless frequency band, the uplink and the downlink should be transmitted and received within their allocated time slots, and if failing in transmission or reception within the allocated time slots, it is not possible to establish a communication.

That is, since the mobile communication terminal supporting TDMA scheme can process transmission and reception only during an allocated time slot, the terminal needs to be continuously switched between call transmission mode and calk reception mode repeatedly during the time slot so as to normally process output of a transmission signal and input of a reception signal. Hence, an RF MEMS variable capacitor in a mobile communication terminal supporting TDMA scheme should repeatedly move its movable charge plate continuously to vary the capacitance according to the transmission mode and the reception mode. As such, due to the nature of the TDMA communication system, the movable charge plate of the RF MEMS variable capacitor should be mechanically moved constantly. Thus, if the RF MEMS variable capacitor is employed by a communication terminal without solution to compensate for mechanical deterioration due to the continuous movement or to minimize the movement itself, limitation of lifetime of components inevitably causes deterioration in the reliability of the terminal.

The present invention is to provide an antenna matching device and method for increasing a lifetime of tunable matching component element such as a radio frequency micro electro mechanical system (RF MEMS) variable capacitor that has impedances changing according to mechanical displacement.

Further, the present invention is to provide an antenna matching device and method for maximizing a lifetime of a tunable matching component element that mechanically operates by using, in a combined manner, a tunable matching component element operating mechanically in accordance with a mobile communication service area and a communication system with a tunable matching component element that operates electrically.

The present invention provides an antenna matching device for a multi-band mobile communication terminal, the antenna matching device including: a first antenna matching unit configured to vary an impedance required for antenna matching to an impedance in mechanical operating mode; a second antenna matching unit configured to vary an impedance required for antenna matching to an impedance in electrical operating mode; and a control unit configured to selectively control the first and second antenna matching units in accordance with a communication environment and a signal transmission and reception cycle.

The control unit may be further configured to control the first antenna matching unit to vary the impedance each time a change in frequency band and channel is requested.

The first antenna matching unit may be a radio frequency micro electro mechanical system (RF MEMS) variable capacitor that operates in one of driving schemes including electrostatic, electromagnetic, and piezoelectric driving schemes to vary the impedance.

Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention.

According to the exemplary embodiment of the present invention, an antenna matching device varies an antenna matching impedance by controlling a radio frequency micro electro mechanical system (RF MEMS) variable capacitor only when a change to a particular frequency band or a particular channel among various frequency bands is requested. In addition, in time division multiplex access (TDMA) mode, the antenna matching device varies an antenna matching impedance by controlling electric RF switches of second antenna matching units in accordance with a signal transmission and reception cycle.

Hence, the antenna matching device uses, in a combined manner, the RF MEMS variable capacitor as a first antenna matching unit with the RF switches as the second antenna matching units in accordance with a mobile communication service area and a communication system, thereby increasing a lifetime of the RF MEMS variable capacitor, compared to a prior art communication terminal that only uses an RF MEMS variable capacitor to match an impedance of an antenna to an impedance of an internal circuit even in TDMA mode.

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the principles of the invention.

FIG. 1 is a diagram illustrating an equivalent circuit of a radio frequency (RF) switch as a prior art multi-band antenna matching unit.

FIG. 2 is a block diagram illustrating an example of an antenna matching device.

FIG. 3 is an equivalent circuit diagram of the antenna matching device illustrated in FIG. 2.

The following description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be suggested to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions of a radio frequency (RF) transmitter and receiver for a mobile communication terminal may be omitted for increased clarity and conciseness.

FIG. 2 is a block diagram illustrating an example of an antenna matching device, and FIG. 3 is an equivalent circuit diagram of the antenna matching device illustrated in FIG. 2.

The antenna matching device as shown in the example illustrated in FIG. 2 may be equipped in a multi-band mobile communication terminal. A multi-band mobile communication terminal refers to a mobile communication terminal capable of using various mobile communication services from all countries that adopt different types of communication systems, and all frequency bands for the services. The multi-band mobile communication terminal supports multiple mode. Multiple mode includes code division multiple access (CDMA) mode based on wideband CDMA (WCDMA) and time division multiple access (TDMA) mode based on global system for mobile communications (GSM). Thus, hereinafter, for convenience of explanation, examples assume that a multi-band mobile communication terminal is a mobile communication terminal supporting multiple modes.

In addition, the multi-band mobile communication terminal as set forth herein may support three service bands including WCDMA 2000, CDMA 1900, and WCDMA 850 in CDMA mode, and supports four service bands including personal communication service (PCS) 1900, digital cellular system (DCS) 1800, GSM 900, and GSM 850 in TDMA mode. In WCDMA 2000, WCDMA 1900, WCDMA 850, PCS 1900, DCS 1800, GSM 900, and GSM 850, numbers 2000, 1900, 1800, and 850 indicate frequency bands, respectively, 2000 MHz, 1900 MHz, 1800 MHz, and 850 MHz. Thus, WCDMA 2000, WCDMA 1900, and WCDMA 850 refer to WCDMA schemes having a frequency band of 2000 MHz, 900 MHz, and 850MHz, respectively. In the same manner, PCS 1900, DCS 1800, GSM 900, and GSM 850 refer to GSM type schemes having a frequency band of 1900 MHz, 1800 MHz, 900 MHz, and 850 MHz, respectively.

The multi-band mobile communication terminal capable of supporting the above all frequency bands may be equipped with an antenna matching device according to exemplary embodiments of the present invention.

FIG. 2 is a diagram illustrating an antenna matching device according to an exemplary embodiment of the present invention. Referring to FIG. 2, antenna matching device includes a first antenna matching unit 70 to vary an impedance required for antenna matching to an impedance in a mechanical operating scheme. The first antenna matching unit 70 may be implemented as a radio frequency micro electro mechanical system (RF MEMS) variable capacitor. In addition, any capacitor that operates in one of driving schemes including an electrostatic driving scheme, an electromagnetic driving scheme, and a piezoelectric driving scheme to vary an impedance may be used. The RF MEMS variable capacitor of any driving scheme may be an equivalent circuit that includes an inductor L and variable capacitors C_B, C_D, C_E and C_G, as shown in FIG. 3. The inductor L is connected in series with and between an antenna terminal ANT and a transmission signal input terminal PA, and the variable capacitors C_B, C_D, C_E and C_G are connected in parallel with and between both ends of the inductor L and a ground. Values of the variable capacitors C_B, C_D, C_E, and C_G are varied by a control unit 100 which will be described later. For example, in response to a request for changing a frequency band or a channel in a mobile communication service area, the control unit 100 varies the values of the capacitors to vary matching impedances to frequency bands suitable to the service area or the communication environment. A different type of a mechanical RF switch, other than the MEMS RF variable capacitor, may be employed, as long as the mechanical RF switch has more advanced characteristics in terms of insertion loss and signal isolation, as compared to an existing switch.

Referring to FIG. 2, the antenna matching device may further include second

antenna matching units

80 and 90 to vary an impedance required for antenna matching to an electrical impedance. The second

antenna matching units

80 and 90 are connected to one end of the antenna ANT. As shown in FIG. 3, the second

antenna matching units

80 and 90 includes, respectively, a first electric switching element SW1 and a second electric switching element SW2 (for example, semiconductor switch elements), and variable capacitors C_A and C_F being connected to ground ends of the respective first electric switching element SW1 and the second electric switching element SW2, respectively. The electric switching elements SW1 and SW2 are switched on or off under the control of the control unit 100.

The variable capacitors C_A and C_F change in their values in response to the control unit 100 controlling the switching elements, resulting in matching the impedance of the antenna to an impedance of an internal circuit. The variable capacitors C_A and C_Fmay be modified to a RF MEMS variable capacitor shown in FIG. 3.

The control unit 100 of the antenna matching device may selectively control the matching

units

70, 80, and 90 in accordance with a communication environment and a signal transmission and reception cycle to match the impedance of the antenna to the impedance of the internal circuit of the terminal. More specifically, the control unit 100 may control an impedance of the first antenna matching unit 70 to be varied only when a change in a frequency band (a frequency band of CDMA mode and a frequency band of TDMA mode) and a channel is requested. In TDMA mode, the control unit 100 controls impedances of the second

antenna matching units

80 and 90 to be varied in accordance with a predetermined signal transmission and reception cycle. Consequently, the impedance of the antenna is matched to the impedance of the internal circuit of the terminal. To this end, the control unit 100 may include inside a memory that stores impedances required for controlling the first antenna matching unit 70 and the

second matching units

80 and 90 in accordance with the frequency band, the channel and the signal transmission and reception cycle in TDMA mode.

Hereinafter, an antenna matching method of an antenna matching device illustrated in the above examples will be described in detail.

The control unit 100 of the multi-band mobile communication terminal receives a pilot signal provided from a base station through a control channel. The control unit 100 checks a channel status based on the reception intensity of the pilot signal. Then, the control unit 100 reports the reception intensity of the pilot signal and location information of itself to the base station. The base station determines a communication channel for the mobile communication terminal based on the reported reception intensity of the pilot signal and the location information. Once a determination on the communication channel has been made, the determined channel is allocated to the mobile communication terminal. Accordingly, the control unit 100 of the mobile communication terminal is allowed to vary a capacitance of the first antenna matching unit 70 to be suitable to the allocated frequency band or channel only when the terminal requests a change to a particular frequency band or a particular channel allocated by the base station among a number of frequency bands, and thereby an impedance of the antenna can be matched to an impedance of an internal circuit of the terminal, resulting in shifting an operating mode or a channel to another.

In TDMA mode, a signal should be transmitted and received in different wireless frequency bands having a difference of several MHz between down link and up link frequency. That is, since antenna impedance is required to be varied in accordance with the regular changes in bandwidth for signal transmission and reception, the control unit 100 varies capacitances C_A and C_F to transmission and reception bands by controlling the first and second switching elements SW1 and SW2 of the second

antenna matching units

80 and 90, which are switched on or off in accordance with a signal transmission and reception cycle in TDMA mode. Hence, the impedance of the antenna is matched to the signal transmission and reception band of TDMA mode, so that a signal can be transmitted or received normally.

As illustrated in the above examples, the antenna matching device uses an RF MEMS variable capacitor as a first antenna matching unit and RF switches as second antenna matching units in a combined manner in accordance with a mobile communication service area and a communication system (operating mode), thereby matching an impedance of an antenna to an impedance of an internal circuit. Accordingly, it is possible to lengthen a lifetime of the RF MEMS variable capacitor, compared to a system only employing an RF MEMS variable capacitor.

A number of examples have been described above. Nevertheless, it should be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.

this invention can be applied to the manufacturing of antenna matching device.

Claims

An antenna matching device for a multi-band mobile communication terminal, the antenna matching device comprising:

a first antenna matching unit configured to vary an impedance required for antenna matching to an impedance in mechanical operating mode;

a second antenna matching unit configured to vary an impedance required for antenna matching to an impedance in electrical operating mode; and

a control unit configured to selectively control the first and second antenna matching units in accordance with a communication environment and a signal transmission and reception cycle.
The antenna matching device of claim 1, wherein the control unit is further configured to control the first antenna matching unit to vary the impedance each time a change in frequency band and channel is requested.
The antenna matching device of one of claims 1 and 2, wherein the control unit is further configured to only control the second antenna matching unit to vary the impedance in accordance with a signal transmission and reception cycle in Time Division Multiple Access (TDMA) mode.
The antenna matching device of claim 1, wherein the first antenna matching unit is a radio frequency micro electro mechanical system (RF MEMS) variable capacitor that operates in one of driving schemes including electrostatic, electromagnetic, and piezoelectric driving schemes to vary the impedance.
The antenna matching device of claim 1, wherein the second antenna matching unit is further configured to be connected to and between an antenna terminal and a ground terminal and comprise an impedance element and a switching element to be switched on or off in response to an electrical signal.
The antenna matching device of claim 1, wherein the control unit is further configured to comprise an inner memory to store impedances required to control the first antenna matching unit and the second antenna matching unit in accordance with a frequency band, a channel and a transmission and reception cycle of TDMA mode.
An antenna matching method for a multi-band mobile communication terminal which comprises a first antenna matching unit to vary an impedance required for antenna matching to an impedance in mechanical operating mode and a second antenna matching unit to vary an impedance required for antenna matching to an impedance in electrical operating mode, the antenna matching method comprising:

controlling the first antenna matching unit to vary a matching impedance only when there is a request for a change to a particular frequency band or a particular channel among a number of frequency bands; and

controlling the second antenna matching unit to vary a matching impedance in accordance with a signal transmission and reception cycle when a communication service mode is TDMA mode.
The antenna matching method of claim 7, wherein the particular frequency band is one of service bands including wideband code division multiple access (WCDMA) 2000, WCDMA 1900, and WCDMA 850 in CDMA mode and is one of service bands including personal communication service (PCS) 1900, Digital Cellular System (DCS) 1800, global system for mobile communications (GSM) 900 and GSM 850 in TDMA mode.