WO2011000438A1

WO2011000438A1 - Antenna device and portable electronic device comprising such an antenna device

Info

Publication number: WO2011000438A1
Application number: PCT/EP2009/058454
Authority: WO
Inventors: Yongjian Han (Frank)
Original assignee: Laird Technologies Ab
Priority date: 2009-07-03
Filing date: 2009-07-03
Publication date: 2011-01-06
Also published as: CN102473998A

Abstract

An antenna device (18) for a portable electronic device, preferably for the FM frequency range, comprises a radiator element (16) provided with a first antenna connection point (23), a matching element (26) connected between the radiator element (16) and ground, and an amplifier stage (24) connected to the first antenna connection point (23), where an output of the amplifier stage (24) is connectable to a radio circuit (22). The radiator element is at least a part of the cover of the portable radio communication device.

Description

ANTENNA DEVICE AND PORTABLE ELECTRONIC

DEVICE COMPRISING SUCH AN ANTENNA DEVICE FIELD OF INVENTION

The present invention relates generally to antenna devices and more particularly to an antenna device for use in a portable electronic device, such as a mobile phone, which is adapted for radio signals having a relatively low frequency, such as radio signals in the FM band.

BACKGROUND

Internal antennas have been used for some time in portable radio communication devices and then also in relation to the FM band. The FM band is defined as frequencies between 88-108 MHz in Europe or between 76-110 MHz in the USA. One internal antenna operable in the FM band is a so-called active antenna, where a half-loop radiating element in the interior of a portable radio communication device is used together with a high-impedance low-noise amplifier. Such an antenna device is for instance known from WO

2009/061267. It is also known to replace the half-loop element with a monopole element in such an active antenna. Another active antenna device is described in EP 1915775, where the cover is used as a radiator element.

However, it would be advantageous if the cover could be put to further use. SUMMARY OF THE INVENTION

An object of the present invention is to provide an antenna device for use in a portable electronic device, which occupies less space and that can be combined with other functionality.

The invention is based on the realization that the cover of a portable electronic device can be used as a radiator element of an active antenna as well as for electrostatic discharge protection. According to the present invention there is provided an antenna device for receiving radio signals in at least one operating frequency band and for being provided in a portable electronic device equipped with a cover. The antenna device comprises a radiator element provided with a first antenna connection point, a matching element connected between the radiator element and ground at least one electrostatic discharge protection unit connected between the radiator element and ground and an amplifier stage connected to the first antenna connection point, where an output of the amplifier stage is connectable to a radio circuit. As the radiator element at least a part of the cover of the portable radio communication device is used. According to the invention a portable electronic device comprises a cover, a radiator element provided with a first antenna connection point, a matching element connected between the radiator element and ground, at least one electrostatic discharge

protection unit connected between the radiator element and ground, an amplifier stage with an input connected to the first antenna connection point and a radio circuit connected to an output of the amplifier stage. According to the invention at least a part of the cover of the portable electronic device is used as the radiator element.

The antenna device according to the invention provides operation with sufficient performance throughout a frequency band having a relatively low frequency, such as the FM radio band. Through using a part of the cover as the radiator element space is saved within the portable electronic device. No extra space is required for the radiator element. As a part of the cover is used, reception is also enhanced as compared with placing a radiator element inside the cover, as the cover might otherwise slightly block radiation. The antenna device furthermore uses the cover for two functions simultaneously, Electrostatic discharge (ESD) protection and radiator element. This combines space saving with cost saving.

Further preferred embodiments are defined in the dependent claims.

BRIEF DESCRIPTION OF DRAWINGS

The invention is now described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 shows a front view of a portable electronic device according to the present invention;

Fig. 2 shows a back view of the portable electronic device according to the present invention; Fig. 3 shows a sectional view of the portable

electronic device according to the present invention;

Fig. 4 shows a schematic diagram of an antenna device according to a first embodiment of the invention connected to a radio circuit;

FIG. 5 shows a schematic diagram of an antenna device according to a second embodiment of the invention;

FIG. 6 shows a schematic diagram of an antenna device according to a third embodiment of the invention; FIG. 7 shows a schematic diagram of an antenna device according to a fourth embodiment of the invention;

FIG. 8 shows a schematic diagram of an antenna device according to a fifth embodiment of the invention; and

FIG. 9 shows a schematic diagram of an exemplifying electrostatic discharge protection unit.

DETAILED DESCRIPTION OF THE INVENTION

In the following, a detailed description of a

preferred embodiment of an antenna device and a portable electronic device according to the invention will be given. In the description, for purposes of explanation and not limitation, specific details are set forth, in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be utilized in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known units, entities and circuits are omitted so as not to obscure the description of the present invention with unnecessary details.

Fig. 1 shows a front view of the cover of a portable electronic device 10, such as a portable radio

communication device, like a mobile phone. The

portable electronic device can however be another type of device, such as a lap top computer, a palm top computer, an electronic organizer such as a personal digital assistant (PDA), a game console, a small clock, such as a travel alarm clock, a TV receiver, an FM radio receiver or a media player such as an MP3 or a CD player. The device 10 is, as an example, provided with a display 12 placed close to an upper end of the device and a keypad 14 placed close to a lower end of the device. These are here provided via openings in the cover of the device 10. It should however be realized that the device may just as well be provided without a display and/or without a keypad. The device 10 is also provided with at least one antenna. Fig. 2 shows a back view of the cover of the portable electronic device 10. The cover of the device here includes a lid 16, which is a battery lid. This battery lid 16, which is of an electrically conductive material is a radiator element. According to the invention the whole or a part of the cover, like the battery lid, is thus used as a radiator element.

Fig. 3 shows a schematic side view of the portable electronic device 10, which is a cross section through the cover. In order to clarify the description of the present invention only a few elements of the portable electronic device are included. Thus a number of units in the portable electronic device have here been omitted, like for instance the display and the keypad shown in fig. 1. The portable electronic device 10 here includes a circuit board 20 on which an amplifier stage 24 as well as a radio circuit 22 is provided. The radio circuit 22 is here in the form of an FM receiver circuit, which may for instance be used to demodulate radio signals. The circuit board 20, which may be a multi-layer PCB (printed circuit board), furthermore includes a ground plane (not shown), which is used for providing ground for various elements of the device including the antenna device of the present invention. In the portable electronic device 10 there is furthermore a battery compartment in which a battery 18 is placed. Above this battery is the battery lid 16, which is used as a radiator element in an antenna device of the invention. The battery lid is flush with the rest of the cover of the portable electronic device. This lid is suitable for providing a radiator element, since it can easily be made of an electrically conducting material like metal and insulated from the rest of the cover. It should here be realized that a battery lid is just one example of a part of the cover that can be used in an antenna device of the present invention.

With reference to fig. 4, the general configuration of an antenna device 30 according to a first embodiment of the present invention being connected to the radio circuit 22 is shown. The antenna device 30, which is indicated as a dashed box, here includes the radiator element 16, i.e. the battery lid, which in this embodiment is an electric radiator element, and more particularly a monopole element.

The monopole element 16 is provided with a first antenna connection point 23, which leads to a matching element 26 connected between the radiator element and ground. In this first embodiment the matching element is a shunt inductor 26 being connected between the first antenna connection point 23 and ground. This shunt inductor 26 may be physically connected

relatively close to the antenna connection point 23. There is also a first electrostatic discharge

protection unit 28 connected between the radiator element 16 and ground and in this first embodiment furthermore with one end connected to the first antenna connection point 23 and with an opposite end connected to ground. There is furthermore the

amplifier stage 24 in the antenna device 30, the input of which is also connected to the antenna connection point 23 and the output of which is connected to the FM receiver circuit 22, which could be a conventional circuit manufactured by Philips Semiconductors and sold under the name HVQFN40. The amplifier stage 24 amplifies signals received by the monopole element 16 and provides them to the FM receiver circuit 22. The amplifier stage 24, which has an input impedance

Z_1n, may comprise a field effect transistor (FET) with the gate connected to the shunt inductor 26, the source connected directly to ground and the drain connectable to the input of the FM receiver circuit 22 (not shown). There may also be a load resistor

connected between the drain of the transistor and a feed voltage Vdd. The amplifier stage 24 may here be a GaAs amplifier stage, which means that the FET

transistor would here be a GaAS FET transistor, which may be a GaAS pHEMT transistor. The monopole element 16 and the inductor 26 are here co-designed with the amplifier stage 24. This means that none of them are adapted to the 50 Ω impedance normally used when connecting various elements. The reason for this is that it is very hard to adapt the impedance of a small radiator element to this type of impedance. Therefore the amplifier stage 24 is

designed to have a high input impedance Z_1n, which is typically ten times or more higher than 50 Ω.

The monopole element 16 and inductor 26 are here thus adapted to match the input impedance Z_1n of the amplifier stage 24. These are thus selected to

provide, perhaps together with a parasitic capacitance provided between the input of the amplifier stage 24 and ground, an impedance at the antenna connection point 23 that matches the input impedance Z_1n of the amplifier stage 26. Such a parasitic capacitance typically occurs because of the non-ideal properties of wires, connection points and the gate-source connection of the transistor in the amplifier stage 24.

The antenna device according to the described

embodiment receives radio signals in at least one operating frequency band that is here the FM radio frequency band. The matching element 26 furthermore matches the radiator element 16 for operation in the FM band, the signals in which the amplifier stage amplifies for better handling in the radio

communication unit 22. In the case of operation in the FM band, the pass band is between 88-108 MHz in Europe or between 76-110 MHz in the USA. In relation to this reception the matching element 26 thus assists in matching the radiator element 16 for operation in this frequency band. The antenna device including monopole element, inductor and amplifier stage is here a so- called active antenna.

Through the use of a monopole element being matched to an amplifier stage using an inductor there is obtained an antenna that has a good isolation in relation to magnetic interference, especially as compared with magnetic dipole antennas. This is important if the portable electronic device is a cellular phone where there may exist a number of different antennas, such as GSM antennas, Bluetooth antennas and GPS antennas. In this way the noise factor of the amplifier is minimized.

The first electrostatic discharge protection unit 28 here together with the battery lid 16 protects the electrical components of the portable electronic device including the amplifier stage 24 of the antenna device 30. This means that in this first embodiment at least a part of the cover, and here the battery lid 16, is used as FM antenna while at the same time providing ESD protection of the whole portable

electronic device 10. Because the first electrostatic discharge protection unit 28 is connected to the first antenna connection point 23 ESD protection is also given to the amplifier stage 24. The metal battery lid 16 is thus here used for both ESD protection and as the radiator element of the antenna device. Through using a part of the cover as the radiator element space is saved within the portable electronic device. No extra space is thus required for the radiator element. As a part of the cover is used, reception is also enhanced as compared with placing a radiator element inside the cover, as the cover might otherwise slightly block radiation. Through combining functions, i.e. using the battery lid both for ESD protection and as a radiator element, costs are furthermore saved.

It may be preferred that the shunt inductor 26 and amplifier stage 24 are provided relatively close to the monopole element 16 in order to minimize parasitic effects and interference from external sources.

In order for the antenna device to operate, the transistor of the amplifier stage may preferably have a minimum noise figure below 1 dB and a gain above 15 dB in the operating frequency band. Also, the transistor may have a noise resistance Rn of less than 10 Ohms in order to achieve the highest possible signal reception quality for arbitrary antenna configurations. A further characteristic of the transistor may be that the input capacitance is low, preferably less than 3 pF, in order to obtain high input impedance.

Furthermore, the amplifier stage can in a variation of the present invention also be a so-called cascode amplifier stage. Such a cascode amplifier stage comprises a first field effect transistor with the gate connected to the monopole element and shunt inductor, the source connected directly to ground and the drain connected to the source of a second field effect transistor. The gate of the second transistor is connected to ground via a capacitor. The drain of the second transistor is then connectable to the input of the FM receiver circuit. There is here also a load resistor connected between the drain of the second transistor and the feed voltage. An FM transmitter circuit can furthermore be connected to the monopole element via a switch. This switch is necessary if the input impedance of the transmitter circuit is much lower, such as ten times lower than the input impedance Z_1n of the amplifier in front of the FM receiver circuit. However, this switch can be omitted if the input impedance of the transmitter circuit is in the same order as the input impedance Z_1n of the amplifier.

By providing a transmitter circuit connected to the monopole element, this monopole element can be shared and thus function for both transmission and reception. The transmitter circuit should preferably be connected to the monopole element approximately at the first antenna connection point. It should here be realised that there are a number of further variations that can be made to the present invention.

The radiator element may for instance be a

substantially magnetic radiator element, like a magnetic half-loop element, where the first antenna connection point would be provided at one end of the lid and a second antenna connection provided at an opposite side of the lid. In this way the radiator element would in essence be a half-loop radiator element. A magnetic radiator element has some

characteristics that are of interest. It can for instance be shorter than a corresponding electric radiator element, which is of interest for small portable electronic devices operating at a fairly low frequency, such as in the FM range.

A schematic diagram showing an antenna device 30 according to a second embodiment that uses such a half-loop element is shown in fig. 5. Here there is the radiator element 16 together with the first electrostatic discharge protection unit 28 and

amplifier stage 24 connected to one end of the

radiator element 16 via the first antenna connection point 23 as in the first embodiment. However the opposite end of the radiator element 16 is provided with a second antenna connection point 32. To this second antenna connection point 32 there is connected a first end of a second electrostatic discharge protection unit 34, the second en of which is

connected to ground via a matching element 36, which matching element is also here an inductive matching element.

The matching element also here matches the radiator element 16 for operation in the FM band. Here the first electrostatic discharge protection unit 28 essentially protects the amplifier stage 24, while the second electrostatic discharge protection unit 34 protects the rest of the portable electronic device.

Fig. 6 shows a schematic diagram of an antenna device 30 according to a third embodiment of the invention, which is also based on a half-loop radiator element. Here there is the radiator element 16, first and second antenna connection points 23 and 32, first electrostatic discharge protection unit 28 and

amplifier stage 24 as in the second embodiment.

However, here the second antenna connection point 32 is connected directly to ground and the matching element 38 is provided as a capacitor connected between ground and the first antenna connection point 23 of the radiator element 16. This embodiment

combines the use of a single electrostatic discharge protection unit protecting both the amplifier stage and the rest of the portable electronic device from the first embodiment with an alternative matching arrangement for the half-loop radiator element. Fig. 7 shows a schematic diagram of an antenna device

30 according to a fourth embodiment of the invention, which is also based on a half-loop radiator element. Here there is the radiator element 16, first and second antenna connection points 23 and 32, matching unit 38, first electrostatic discharge protection unit 28 and amplifier stage 24 as in the fourth embodiment. However, here the second antenna connection point 32 is connected to ground via a second electrostatic discharge protection unit 34. This embodiment combines the matching arrangement of the third embodiment with the electrostatic discharge protection arrangement of the second embodiment.

Fig. 8 shows a schematic diagram of an antenna device 30 according to a fifth embodiment of the invention, which is also based on a half-loop radiator element. Here there is the radiator element 16, first and second antenna connection points 23 and 32, first electrostatic discharge protection unit 28 and

amplifier stage 24 as in the second embodiment.

However, here the second antenna connection point 32 is connected to ground only via the matching unit 36. There is no second electrostatic discharge protection unit. This embodiment combines the matching

arrangement of the second embodiment with the

electrostatic discharge protection arrangement of the third embodiment .

As can be understood from the above-described

embodiments, the use of a second electrostatic

discharge protection unit is optional. Electrostatic discharge protection units may be provided in a multitude of ways, for instance through solely using an inductor connected between battery lid and ground. One exemplifying realization is shown in fig. 9. Here the electrostatic discharge protection unit 28 is realized through a pair of parallel diodes, a first Dl oriented towards the radiator element and a second D2 oriented towards ground. This means that the anode of the second diode D2 is connected to the radiator element while the cathode is connected to ground. Consequently the anode of the first diode Dl is connected to ground while the cathode is connected to the radiator element.

The antenna device was above being described as including the radiator element, the matching element, electrostatic discharge protection unit and the amplifier stage. It is possible that the antenna device does not include the electrostatic discharge protection unit, in which case it would thus only include the radiator element, the amplifier stage and the matching element.

Preferred embodiments of an antenna device according to the invention have been described. However, the person skilled in the art realizes that these can be varied within the scope of the appended claims without departing from the inventive idea.

It should for instance be realized that also the antenna device according to the second, third and fourth embodiments can be combined with the amplifier stage variations and/or transmitter circuit described in relation to the first embodiment.

It is realized that the shape and size of the antenna device according to the invention can be varied within the scope defined by the appended claims. More or less of the cover than the battery lid may be used as antenna. Thus, the exact antenna configurations can be varied depending on how much of the cover that is being made of an electrically conducting material.

The above-described embodiments of an antenna device according to the invention have been described as antenna devices adapted for reception of radio signals in the FM frequency band. However, other applications are also possible, such as use for digital video broad-casting (DVB) signals in the frequency range of about 400-800 MHz.

A FET has been described as the preferred transistor type. It will be realized that other types of transistors, such as hetero-junction bipolar transistors (HBT), can be used as well.

Claims

1. An antenna device (30) for receiving radio signals in at least one operating frequency band and for being provided in a portable electronic device (10) equipped with a cover, said antenna device (30) comprising a radiator element (16) provided with a first antenna connection point (23), a matching element (26; 36; 38) connected between the radiator element (16) and ground, at least one electrostatic discharge protection unit (28; 28, 34) connected between the radiator element and ground, and an amplifier stage (24) connected to said first antenna connection point (23), where an output of the amplifier stage (24) is connectable to a radio circuit (22), - wherein the radiator element is at least a part of the cover of the portable radio communication device.

2. The antenna device according to claim 1, wherein the electrical properties of the matching element (26; 38) has been selected together with the electrical properties of the radiator element to match the input impedance (Z_1n) of the amplifier stage (24).

3. The antenna device (30) according to any previous claim, wherein the radiator element (20) is co-designed with the amplifier stage (24).

4. The antenna device (30) according to any previous claim, wherein the radiator element is a monopole element.

5. The antenna device (30) according to claim 4, wherein the matching element (26) is inductive and connected to the first antenna connection point.

6. The antenna device (30) according to any of claims 1 - 3, further comprising a second antenna connection point (32) at the opposite end of the radiator element in relation to the first antenna connection point via which second antenna connection point the radiator element is connected to ground.

7. The antenna device (30) according to claim 6, wherein the matching element (36) is inductive and connected to the second antenna connection point.

8. The antenna device (30) according to claim 6, wherein the matching element (38) is capacitive and connected to the first antenna connection point.

9. The antenna device (30) according to any of claims 6 — 8, wherein one electrostatic discharge protection unit (34) is connected to the second antenna connection point.

10. The antenna device (30) according to any previous claim, wherein one electrostatic discharge protection unit (28) is connected to the first antenna connection point.

11. The antenna device (30) according to any previous claim, wherein the operating frequency band is the FM band.

12. The antenna device (30) according to any previous claim, wherein the amplifier stage (26) has an input impedance (Z_1n) that is ten times or more higher than 50 Ω.

13. The antenna device (30) according to any previous claim, wherein the amplifier stage (26) includes one or more GaAS FET transistors.

14. The antenna device (30) according to claim

13. wherein said GaAS FET transistors include one or more GaAS pHEMT transistors.

15. A portable electronic device (10) comprising a cover, a radiator element (16) provided with a first antenna connection point (23), - a matching element (26; 36; 38) connected between the radiator element (16) and ground, at least one electrostatic discharge protection unit (28; 28, 34) connected between the radiator element and ground, - an amplifier stage (24) with an input connected to the first antenna connection point, and a radio circuit (22) connected to an output of the amplifier stage, wherein the radiator element is at least a part of the cover of the portable electronic device.

16. The portable electronic device (10) according to claim 15, wherein the electrical properties of the matching element (26; 38) has been selected together with the electrical properties of the radiator element to match the input impedance (Z_1n) of the amplifier stage (24).

17. The portable electronic device (10) according to claim 15 or 16, wherein the operating frequency band is the FM band.