GB2467325A - Radio-antenna modules for connection to external matching circuits - Google Patents

Abstract

A radio-antenna module (14) comprising a circuit board substrate (15) bearing a radio circuit and an antenna. The radio circuit and antenna are not electrically connected to each other on the module itself, but are provided with terminals (17, 19) for connection to an external matching circuit (21). By moving the matching circuit off the circuit board substrate of the module itself, a number of manufacturing advantages are obtained.

Description

RADIO-ANTENNA MODULES FOR CONNECTION TO EXTERNAL MATCHING CIRCUITS

[0001] This invention relates to a radio-antenna module, which is a modular component used when combining a radio circuit with an integrated antenna.

BACKGROUND

[0002] Most radio systems have an input or output impedance of typically 50 ohms although ohms is occasionally used. Transmission lines, such as co-axial cables, are also generally only available in a limited number of characteristic impedances such as 50 ohms. Efficient antenna configurations often have an impedance other than 50 ohms; in this case some sort of impedance matching circuit is then required to transform the antenna impedance to 50 ohms. The matching circuit is usually just a network of capacitors and inductors although other circuit components may be used.

[0003] The effect of the matching network is to optimize the transfer of power from a source (e.g. antenna) to a load (e.g. radio receiver integrated circuit) by maximizing the power delivered to the load while meeting certain other performance specifications. Other such specifications include the noise performance, stability, linearity and minimizing the insertion loss of the matching circuit itself.

[0004] The normal configuration for the radio circuit on a mobile device such as a cellular radio handset is to surface mount the radio on the main Printed Circuit Board (PCB) or Printed Wiring Board (PWB). The radio device is often a radio frequency integrated circuit (RFIC).

There is then a transmission line between the RFIC and the antenna. The transmission line is usually printed, on the main PCB, as a microstrip, coplanar waveguide and the like, but sometimes co-axial cables are used. The standard characteristic impedance of the transmission line is 50 ohms. At the end of the transmission line, just before the antenna, the matching circuit components are surface mounted. The antenna is usually supplied as an external component. The radio, transmission line and matching circuit are thus part of the bill of materials for the host device (e.g. a handset) and the antenna is costed and supplied separately.

[0005] It is less common, but known prior art, to mount the matching circuit on the antenna itself. This is most easily achieved if the antenna is manufactured from a small PCB or has a flexible printed circuit onto which the matching components may be reflowed. In this configuration the matching circuit is supplied as part of the antenna and becomes an antenna cost rather than a PCB cost. Examples of this prior art are WO 92/05602 (Burrel et al.) and GB2434037 (lellici et al.).

[0006] Recently, the present Applicant has been developing radio-antenna modules in which the RFIC and associated radio circuits have been moved onto the small antenna PCB from the main PCB of the host application device. This has many advantages for the designer of the host device because all the radio frequency (RF) design work has been done. This arrangement saves both cost and space on the main PCB and can greatly reduce the time to market. Examples of this prior art are UK patent application GBO81 1426.6 and GB2450786.

[0007] The present Applicant has marketed a number of radio-antenna modules, several of which have been designed to add Global Positioning System (GPS) functionality to mobile devices not previously having this capability. A typical GPS module includes a small PCB having mounted upon it a connector, an antenna, a matching circuit and a radio circuit including the RFIC. In some versions the RFIC includes a baseband processor and so if the module is supplied with a suitable DC power source, it can give out positional information such as latitude and longitude. The host platform need only have the mating half of the connector and a complete GPS RF solution may be added.

[0008] Figures 1 and 2 show two versions of this concept, a vertical blade' design and a planar design. Although a connector is one method of attaching a radio-antenna module to the host PCB, other connection methods are possible and in some applications the preferred method of connection is to reflow the module PCB onto the main host PCB because this can shorten the connecting tracks.

[0009] A problem particular to modules containing antennas is that the antenna must be re-matched for every application. Antennas are sensitive to their surroundings and so their matching circuit must be customized if anything on the host platform is changed or if the antenna is moved to a new host device. In particular, any changes to the length of the host PCB or to the position of anything metallic, such as a battery, near the antenna can cause the antenna to resonate at a different frequency and need re-tuning through the use of a matching circuit.

[0010] In the modules shown in Figures 1 and 2, the printed circuit layout for the matching circuit contains pads on which surface mount components such as capacitors and inductors may be placed. If allowance is made for a sufficiently complex matching circuit then the PCB layout need not be changed from one application to another. However, the number of components, their electrical value and the cost will change from one application to another.

This is a significant disadvantage because for each application: i) There will be a different set of components to be sourced.

ii) The bill of materials will be different.

iii) A new module part number must be issued.

iv) The pick and place machine mounting the components must be re-programmed.

v) The surface mount reflow process may need re-programming.

The cost and logistical overhead of these operations are not negligible.

BRIEF SUMMARY OF THE DISCLOSURE

[0011] In accordance with a first aspect of the present invention there is provided a module comprising a circuit board substrate comprising first means for electrical attachment to a radio circuit and second means for electrical attachment to an antenna, the first means including a first electrical port or terminal and the second means including a second electrical port or terminal, wherein the first and second electrical ports or terminals are configured as connection points for a matching circuit that is located off the circuit board substrate.

[0012] The radio circuit in preferred embodiments is a radio frequency integrated circuit, although other radio circuits are not excluded.

[0013] The first means may comprise surface mount technology (SMT) components, or may comprise a socket or through holes or the like adapted to receive leads or pins from an integrated circuit. The second means may comprise an electrically-conductive antenna feed pad mounted on the circuit board substrate, or may alternatively comprise a socket or through hole or the like adapted to receive a signal terminal of an antenna.

[0014] The first and second means are electrically isolated from each other on the circuit board substrate, but are each provided with an electrical port or terminal adapted to receive a connection from a matching circuit that is located off the circuit board substrate (for example, on a main PCB substrate on which the module circuit board substrate is itself mounted). The matching circuit, when connected, provides the electrical RF link between the antenna and the radio circuit for proper operation.

[0015] The module may be provided complete with a radio circuit and an antenna.

Alternatively, the module may be provided with just one or other of these components, or may be provided without either component, thereby allowing customers to use their own radio circuit and/or antenna components.

[0016] By way of embodiments of the present invention, a solution has been found to the problem of customizing the matching circuit needed on a radio-antenna module. The solution is based on the fact that components on a host board (e.g. main PCB or PWB) can be easily changed during the customer's product development. This is in fact normally done for the matching circuits of conventional stand-alone antennas. The present invention routes the antenna signal outside the module to a matching circuit on the host board; the signal is then routed back into the module to the radio circuit front-end. This idea is most easily implemented when the module is surface mounted onto the host PCB because this makes it possible to keep the RF tracks very short, and so with a negligible loss in the antenna performance. If a connector were used there would be rather more loss resulting in worse antenna performance.

[0017] External module matching offers several major advantages: i) It is no longer necessary to change any part of the module to fit different customers. Having no custom builds is a big cost saving.

ii) The same module can be manufactured in very large quantities and sold to different customers. The economies of scale mean the module can be made and sold at lower cost.

iii) It is feasible to use more complex methods of manufacturing, such as 3D-MID (Molded Interconnect Devices) because now only one set of tooling is required.

iv) The same module without the antenna can be sold to customers as it does have a separate RF connection.

v) The same module without the radio can be sold to customers as it does have a separate antenna connection.

vi) The risk for the customers is lower because they could buy the same module and use it on several products without the module requiring any changes.

[0018] Embodiments of the present invention may also be used where the matching circuit comprises one or more active elements, such as variable capacitors, PIN diodes, and MEMS devices. The control signal for the active components can come from the module itself or from an external circuit. The inclusion of active elements is advantageous for compensating the detuning of the antenna causes by the changeable external environment. An algorithm would monitor some specific parameter (e.g. Bit Error Rate, signal strength, signal to noise ratio, current consumption) and adjust the control signal in order to maximize/minimize such parameter. Alternatively, a simple look-up table could be used to tune the antenna for a certain condition. Typical examples of such changeable conditions are the presences of the user hand/head or the relative position of the device with respect to a table of various materials.

[0019] When the module includes a transmitter, such as a WLAN, Bluetooth� or cellular radio module, some of the transmitted signal may be detected by forward and reverse directional couplers and used to actively tune the antenna. Even for receive-only systems, such as GPS, an artificial signal from an oscillator may be injected for a short time to aid active tuning.

[0020] Embodiments of the present invention have the greatest advantage if the antenna can be re-tuned by a matching circuit alone and no modifications to the antenna itself are required.

Fortunately, this is often the case.

[0021] The present invention is applicable to modules operating in a single frequency band such as GPS, BluetoothTM, etc. Dual band matching is also possible for protocols such as WLAN where 2.4 and 5GHz bands may be used. There is an increasing trend for combination' radios where BluetoothTM and GPS functions are combined in a single RFIC to save space on a compact device such as a handset. These combination RFICs have two separate ports for the antennas and embodiments of the present invention may be simply implemented on a combination radio-antenna module by having two external matching circuits.

[0022] The present invention is applicable to cellular radio-antenna modules and to many other types of radio where it is advantageous to combine the radio and antenna together into a module separate from a host device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which: Figure 1 shows a blade' style GPS module mounted on a PCB; Figure 2 shows a planar' style GPS module mounted on a PCB; Figure 3 shows the module of Figure 2 with the screening can removed; Figure 4 shows a schematic outline of an embodiment of the present invention; and Figure 5 is a plot of antenna simulation results for the embodiment of Figure 4.

DETAILED DESCRIPTION

[0024] Figure 1 shows a blade' style GPS radio module 1 comprising a radio circuit 2 and a pair of antennas 3, all mounted and connected to each other on a daughterboard PCB 4. The PCB 4 is mounted edgewise (hence blade' style) on a main motherboard PCB 5. The module 1 is shown without its metal screening can so as to show its components more clearly.

[0025] Figure 2 shows a planar' style GPS radio module 6 which is similar to the module 1 of Figure 1, but differently configured for planar mounting on a main motherboard PCB 7. In this radio module 6, the antenna 8 is formed on the exposed surface of the daughterboard PCB 9, with the radio circuit 10 being located on the other surface, facing the main motherboard PCB 7.

[0026] Figure 3 shows the module 6 of Figure 2 when separated from the main motherboard PCB 7 and turned over. The screening can 11 is shown removed for clarity. The radio circuit or RFIC 12 and various matching components 13 are also visible. As can be seen, there is great scope for adjusting and changing the matching circuits 13 on the daughterboard PCB 9, thereby to form a ready-to-use' radio and antenna module, but such a module cannot easily and cheaply be customized for different applications.

[0027] Figure 4 shows a schematic outline of a currently preferred embodiment of the present invention in the form of a module 14 comprising a circuit board substrate 15 on which can be mounted an RFIC (not shown) and other optional components, which are here shown covered by a shielding or screening can 16. A conductive antenna feed pad 17 is provided on the substrate 15 outside the boundary of the screening can 16. A terminal of an antenna (not shown) can be attached, for example by soldering, to the feed pad 17. The substrate 15 may be provided with surface mount technology (SMT) soldering pads 18 around its perimeter and/or on its underside. The antenna feed pad 17 and the RFIC are electrically isolated from each other on the substrate 15 of the module 14. However, the RFIC is provided with an RF front-end port connection 19, and the feed pad 17 with an antenna port connection 20, optionally by way of associated SMT soldering pads. These port connections 19, 20 and configured to allow an external matching circuit 21 to form an electrical RF connection between the antenna and the RFIC. The matching circuit 21 is not formed on the substrate 15 of the module, but instead is formed on a host motherboard substrate 22 on which the module 14 is mounted.

[0028] Figure 5 shows simulation results where a matching circuit has been used to retune a GPS antenna both up and down in frequency. The tuning range is more than 200MHz using just two matching components: one inductor and one capacitor. This should be more than enough to compensate for all the possible de-tuning caused by the plastics and other objects close to the module. Re-tuning of a greater frequency range is possible with more complex matching networks.

[0029] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0030] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0031] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims (16)

1. CLAIMS1. A module comprising a circuit board substrate comprising first means for electrical attachment to a radio circuit and second means for electrical attachment to an antenna, the first means including a first electrical port or terminal and the second means including a second electrical port or terminal, wherein the first and second electrical ports or terminals are configured as connection points for a matching circuit that is located off the circuit board substrate.
2. 2. A module as claimed in claim 1, wherein the first means comprises surface mount technology (SMT) components.
3. 3. A module as claimed in claim 1, wherein the first means comprises a socket or through-holes.
4. 4. A module as claimed in any preceding claim, wherein the second means comprises an electrically-conductive antenna feed pad mounted or formed on the circuit board substrate.
5. 5. A module as claimed in any one of claims 1 to 3, wherein the second means comprises a socket or through-hole.
6. 6. A module as claimed in any preceding claim, wherein each of the first and the second means is provided with or comprises an electrical port or terminal adapted to receive a connection from respective terminals of the matching circuit.
7. 7. A module as claimed in any preceding claim, in combination with a radio circuit connected to the first means.
8. 8. A module as claimed in claim 7, wherein the radio circuit is a radio frequency integrated circuit (RFIC).
9. 9. A module as claimed in any preceding claim, in combination with an antenna connected to the second means.
10. 10. A module as claimed in any preceding claim, further comprising means for generating a control signal adapted to control an active element provided in the matching circuit.
11. 11. A module as claimed in any preceding claim, further comprising a transmitter, and wherein a part of a signal from the transmitter is fed to the first electrical port or terminal.
12. 12. A module as claimed in any preceding claims, further comprising an oscillator adapted to feed a tuning signal to the first electrical port or terminal.
13. 13. A module as claimed in any preceding claim, wherein the second means is configured to allow connection of a plurality of antennas, with one second electrical port or terminal for each of said plurality of antennas.
14. 14. A module as claimed in any preceding claim, in combination with a matching circuit that is not located on the circuit board substrate.
15. 15. A module as claimed in claim 14, wherein the matching circuit is formed on a separate circuit board substrate on which the module is mounted.
16. 16. A module substantially as hereinbefore described with reference to or as shown in Figures 4 and 5 of the accompanying drawings.