GB2490145A

GB2490145A - A DAB (RTM) receiver module, including tuneable impedance matching circuitry, for retrofitting DAB radio to a car

Info

Publication number: GB2490145A
Application number: GB1106641.2A
Authority: GB
Inventors: Kenneth Robert Hattersley
Original assignee: Frontier Silicon Ltd
Current assignee: Frontier Silicon Ltd
Priority date: 2011-04-20
Filing date: 2011-04-20
Publication date: 2012-10-24
Also published as: GB201106641D0; CN102752064A

Abstract

The present invention provides a digital audio broadcast (DAB) receiver module 100 which can be used in conjunction with additional apparatus 110 to retrofit a DAB radio to a vehicle. The module includes an antenna interface unit / port suitable for coupling to an antenna 102 such as a legacy FM antenna, a â receiver unitâ 106 for down-converting RF signals received by the antenna to baseband or an IF, and a tuneable impedance matching circuit 104 between the antenna interface unit and the input of the â receiver unitâ . An output from the receiver unit is adapted for connection to an external unit 110 including a DAB baseband decoder and optionally a display. The impedance matching unit can be tuned by adjusting capacitance or inductance, manually or automatically.

Description

t V.' INTELLECTUAL ..* PROPERTY OFFICE Application No. GB 1106641.2 RTM Date:12 August 2011 The following term "DAB" is a registered trademark and should be read as such wherever it occurs in this document.

Intellectual Properly Office is an operating name of the Patent Office www.ipo.gov.uk A DAB Receiver

FIELD OF THE INVENTION

The present invention relates to a DAB receiver, in particular to a DAB receiver module for retrofitting DAB radio to a vehicle, for example a car.

BACKGROUND OF THE INVENTION

Many of the vehicles on the road today are fitted with FM radio receivers, which are not capable of receiving DAB (Digital Audio Broadcasting) radio signals. Whilst retrofitting kits are available, many have integrated or internal antennas and either retransmit the received and decoded DAB radio signals over the FM band (so that the car head unit can receive the audio), or an audio output may be connected to a suitable auxiliary input on the car head unit.

It is known that short integrated or internal and retrofit antennas may not offer satisfactory performance when compared to external antennas because the impedance match of the internal antenna and its so called "aperture" are degraded because of their size and proximity to nearby body metal work may cause variabilities leading to bad performance at installation time. Furthermore, once installed, internal antennas may suffer ongoing performance issues due to changes in proximity effects for example if an object is placed near to the antenna.

It is also known that to achieve an attractively priced retrofitting kit requires a cost effective design with reduced material cost of the components of the kit, commensurate with good performance.

We have therefore appreciated the need for an improved DAB receiver module for retrofitting DAB radio to a vehicle, for example a car, using an external antenna or preferably one of a variety of antennas. Whilst this document describes the invention with reference to a car, it will be appreciated that it can be equally applied to other types of vehicle with similar characteristics to a car.

SUMMARY OF THE INVENTION

The present invention provides a DAB receiver module for retrofitting DAB radio to a vehicle, comprising: an antenna interface unit having an input coupleable to an antenna for receiving DAB radio signals and an output for outputting received DAB radio signals; a tuneable matching circuit between the output of the antenna interface port and the input of a receiver unit for matching the output impedance of the antenna with an input impedance of the receiver unit; the receiver unit having an input for receiving a DAB radio signal from the tuneable matching circuit and having an output for outputting an interface signal of the DAB radio signal; and a controller coupled to the tuneable matching unit, the controller being configured to adjust one or both of a capacitance or inductance of the matching unit to substantially match the output impedance of the antenna interface and the input impedance of the receiver unit.

Advantageously, by using a tuneable matching unit, it means that any number of antenna options are available to the end user: there is no requirement for a retrofitting kit to incorporate a matched antenna, which gives the end user a larger degree of freedom in choosing which antenna option to use in their car and this assists to reduce material costs of the retrofitting kit.

In embodiments, the antenna interface unit input comprises a RF connector for coupling the antenna interface to a remotely-located antenna. Alternatively, the antenna interface unit input comprises contact pads for coupling with a co-located antenna.

In some embodiments, the DAB receiver module further comprises an input for receiving power and/or an input for receiving control signals for control of the receiver unit.

In further embodiments, the DAB receiver module may be decoupled from variable and degrading noise and cable effects by incorporating a balun or common mode choke at the interface to the non-antenna interface cables.

In further embodiments, the DAB receiver module further comprises a baseband decoder module having an input coupleable to the receiver unit output for receiving an interface signal from the receiver unit, the baseband decoder being configured to process a received interface signal of the DAB radio signal to generate an audio and/or a data output from the interface signal.

In one embodiment, the baseband decoder is located remote from the receiver unit.

In the one embodiment, either or both of the audio and data outputs of the baseband decoder are coupleable to respective inputs of a control unit for displaying data extracted from the DAB radio signal and for outputting audio extracted from the DAB radio signal.

In a different embodiment, the baseband decoder is co-located with the receiver unit.

In this different embodiment, either or both of the audio and data outputs of the baseband decoder are coupleable to respective inputs of a control unit located remote from the baseband decoder, the control unit for displaying data extracted from the DAB radio signal and for outputting audio extracted from the DAB radio signal.

Preferably, in this different embodiment, the baseband decoder and control unit are coupleable via a USB link, a CAN-bus link or a fibre optic cable.

In embodiments, the control unit audio output is coupleable to a head unit of a vehicle, the head unit for playing received audio over a vehicle music system. Preferably, the control unit audio output is coupleable to a head unit of a vehicle over a wired or wireless connection.

In embodiments, the interface signal is an intermediate frequency (IF) signal, or a baseband interface signal.

The present invention also provides a DAB car radio system for retrofitting in a vehicle, comprising: an antenna for receiving DAB signals; a DAB receiver module according to the above embodiments; a baseband decoder module having an input coupled to the receiver unit output for receiving an interface signal from the receiver unit, the baseband decoder being configured to process a received interface signal of the DAB radio signal to generate an audio and/or a data output from the interface signal; and a control unit having one or more inputs coupled to the audio and/or data outputs of the baseband decoder, the control unit for displaying data extracted from the DAB radio signal and for outputting audio extracted from the DAB radio signal.

In embodiments of the DAB car radio system, the control unit audio output is coupleable to a head unit in a vehicle, the head unit for playing received audio over a vehicle music system.

Preferably, the control unit audio output is coupleable to a head unit of a vehicle over a wired or wireless connection.

In embodiments of the DAB car radio system, the system further comprises a balun or common mode choke between the output of the receiver unit and the input of the baseband decoder module.

In embodiments of the DAB car radio system, the interface signal is an intermediate frequency (IF) signal, or a baseband interface signal.

LIST OF FIGURES

The present invention will now be described, by way of example only, and with reference to the accompanying figures, in which: Figure 1 shows a DAB receiver module and associated components for retrofitting DAB radio to a car; Figure 2 shows example antenna connections; Figure 3 shows further example antenna connections.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows a block diagram of the DAB receiver module 100 for retrofitting DAB radio to a car. In its basic form, the DAB receiver module 100 comprises a tuneable matching unit 104 and a radio receiver unit 106. An antenna 102 suitable for receiving DAB radio signals is coupled to an antenna interface (not shown), which is coupled to the input of the tuneable matching unit 104. The output of the tuneable matching unit 104 is coupled to the input of the receiver unit 106.

The receiver unit 106 amplifies, filters with controllable characteristics the DAB radio signals received by the antenna and provides an intermediate frequency (IF) output or other baseband interface signal output for further processing by a baseband decoder (not shown). The receiver unit may comprise a single simple integrated circuit and the controllability of its characteristics include gain and filter bandwidths.

The tuneable matching unit 104 is controlled by a controller (not shown) to substantially match the impedance of the antenna to the impedance at the input of the receiver unit 106, by adaptive variation of circuit inductance and I or circuit capacitance. The circuit capacitance may be controlled by the use of varactor diodes which have a capacitance which is inverse proportion to the DC voltage applied, by electronic circuit means, whereas the inductance can be varied by manual adjustment. The controller determines the signal level input to the receiver unit 106 and itself adjusts the capacitance of the tuneable matching unit 104, or a user manually adjusts the inductance until a suitable peak in the input signal is obtained. By using a tuneable matching unit 104, it means that any number of antenna options are available to the end user: there is no requirement for a retrofitting kit to incorporate a matched antenna, which gives the end user a larger degree of freedom in choosing which antenna option to use in their car (see later) and this assists to reduce material costs of the retrofitting kit.

The controller (not shown) function for the characteristics of the of the receiver unit (106) and the tuneable matching unit (104) may be accommodated within the receiver module (100) or within a head unit (110).

In a first embodiment of the invention, a baseband decoder (not shown) is located remote from the DAB receiver module 100, and the IF signals, or other baseband interface signals, power and control signals are passed between the baseband decoder and DAB receiver module 100 via a suitable physical interface (108). This interface may be a metallic cable such as a shielded copper cable, or part fibre optic cable.

Many cable alternatives would be apparent to the skilled reader.

Optionally a balun or common mode choke will be placed in any metallic paths such as cables leading away from the receiver module body 100, at a point as close to the antenna interface as possible, one realisation of this may simply be a single ferrite ring which is placed around all cables.

The baseband decoder then processes the IF signal or other baseband interface signals and extracts the DAB audio stream and any data stream in the DAB radio signal. These audio and data streams are then fed into a suitable control unit 110, which may comprise a display and a user interface to control the receiver unit 100 (for example tuning to different stations) and display the data embedded in the DAB radio signal. The control unit 110 may form part of the car head unit that enables the audio to be played on the car audio system. Alternatively, the control unit 110 may be formed of a separate unit coupled to the car head unit (for example via an auxiliary audio output connector 111, or over an FM broadcast radio link from an auxiliary FM transmitter module 112).

In a second embodiment of the invention, the baseband decoder (not shown) forms part of, and is co-located with, the DAB receiver module 100. In this embodiment, the IF signals or other baseband interface signal are processed locally by the baseband decoder, and the audio and/or data streams extracted from the DAB radio signal are passed to the control unit 110 via a suitable connection. Examples of suitable connections include a USB link, or a CAN-bus link, or a fibre optic cable.

An advantage of this embodiment is that all processing of the radio signal is carried out local to the receiver prior to transmission to the head unit. As such, there is less likelihood of the IF signal or other baseband interface signal being affected by electrical noise and interference, which would degrade the decoded DAB signal.

A first example antenna tuning algorithm is discussed below: At installation time: 1. Fit an antenna of choice 2. Put control unit into an automatic setup mode 3. Tune to a DAB signal 4. Monitor received signal strength voltage 5. Controller varies matching unit capacitance using varactor diode.

a. Increase DC tuning voltage, (thereby decrease capacitance) i. If signal increases, store value of DC tuning voltage when peak found ii. If signal decreases, b. decrease voltage i. When peak found store value of DC tuning voltage.

A second example of an antenna tuning method uses the above-mentioned first method, but on a continuous basis to mitigate the effects of post-installation variabilities in the car.

A third example antenna tuning algorithm for use at installation time is given below: 1. Fit an antenna of choice with a predetermined matching inductance 2. Put unit into a "manual" set up mode.

3. Tune to a DAB signal 4. Head unit indicates received signal strength voltage on display.

5. Manually adjust the inductance to obtain a maximum received signal strength voltage Figure 2 shows example antenna connections.

The physical embodiment of the module is such that a single mechanical structure can be deployed in at least 4 different end applications, options 1 to 4 below. This allows for a low cost to be achieved through economies of scale by a single design The physical embodiment permits the antenna input coupling to be achieved in three key ways, 1) using an RF connector 220 on a cable, 2) by an unbalanced signal input contact pad 222 or 3) by balanced antenna connections using the pad 224 and a ground pad 225. A ferrite ring common mode choke 250 is shown placed around the output cables; other methods to achieve a balun may be possible.

Option 1 shows the DAB receiver module 100 having an antenna interface that comprises a RF connector 220 for connecting to a suitable antenna having an RF connector output such as a roof mounted whip (which has been known to have a good radio signal reception and good match to the receiver input impedance). Using this coupling, the module may be placed anywhere in the car so long as a connection to the antenna can be made and may be remote from the antenna.

Option 2 shows the DAB receiver module 100 having an antenna interface that comprises a signal input metal pad 222 coupling to an external glass mounted antenna element 240 on the glass windshield or other window 230 where the antenna has a metal pad 223 which is a counterpart to 222. Using this coupling, the module should be placed in close proximity to the antenna so that pads 222 and 223 are aligned. For example, the DAB receiver module 100 may be mounted on the opposite side of the glass to the antenna. This type of antenna is easier to fit or more permanent than type 1, even though its signal reception may be reduced by comparison.

Option 3 shows the DAB receiver module 100 having an antenna interface that comprises the signal input metal pad 224 with a ground pad 225 coupling for direct coupling to an internal glass mounted antenna elements 242 and 243 on the glass windshield or other window 230. Using this coupling, the module should be placed near the antenna. For example, the DAB receiver module 100 may be mounted on the glass on the same side as the antenna. This antenna is entirely internal to the vehicle and is thus protected and avoids unsightly external whips. However, it may have less signal reception than 1 or 2 above.

It is to be noted that options 2 and 3 above can achieve increased radio performance by using the variable antenna impedance matching network and the tuning algorithm examples above which mitigate the effects of the mismatch presented by the element 240 in option 2 and 242 and 243 in option 3.

Figure 3 shows a fourth option of antenna choice.

In figure 3, the DAB receiver module 100 is housed in an externally mounted shark-fin type housing 350 (similar to those seen on cars with DAB radios fitted by the manufacturer) together with an antenna 358, which may be a straight or helical whip.

The shark-fin housing 350 is mounted to the roof of the car by means of an adhesive layer 352 and a capacitive ground to the car roof is provided via a metal base 354.

Cables to power the module and to pass signals to the baseband decoder (depending on the embodiment) and control and display unit pass through a cable guide 356, which is flexible enough to be mounted between the roof and the boot lid of a car.

In an alternative embodiment of the option shown in figure 3, the DAB receiver module 100 is mounted internal to the car in a region close to the shark-fin housing 350.

Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments and modifications will be apparent to a skilled person in the art which lie within the scope of the present invention. Any of the embodiments described hereinabove can be used in any combination.

Claims

CLAIMS: 1. A DAB receiver module for retrofitting DAB radio to a vehicle, comprising: an antenna interface unit having an input coupleable to an antenna for receiving DAB radio signals, and an output for outputting received DAB radio signals; a receiver unit having an input for receiving a DAB radio signal from the antenna interface and having an output for outputting an interface signal of the DAB radio signal; a tuneable matching unit coupled between the output of the antenna interface and the input of the receiver unit for matching an output impedance of the antenna interface with an input impedance of the receiver unit; and a controller coupled to the tuneable matching unit, the controller being configured to adjust one or both of a capacitance or inductance of the matching unit to substantially match the output impedance of the antenna interface and the input impedance of the receiver unit.
2. A DAB receiver module according to claim 1, wherein the antenna interface unit input comprises a RF connector for coupling the antenna interface to a remotely-located antenna.
3. A DAB receiver module according to claim 1, wherein the antenna interface unit input comprises contact pads for coupling with a co-located antenna.
4. A DAB receiver module according to claims 1, 2 or 3, further comprising an input for receiving power and/or an input for receiving control signals for control of the receiver unit.
5. A DAB receiver module according to any preceding claim, further comprising a baseband decoder module having an input coupleable to the receiver unit output for receiving an interface signal from the receiver unit, the baseband decoder being configured to process a received interface signal of the DAB radio signal to generate an audio and/or a data output from the intermediate frequency signal.
6. A DAB receiver module according to claim 5, wherein the baseband decoder is located remote from the receiver unit.
7. A DAB receiver module according to claim 6, wherein either or both of the audio and data outputs of the baseband decoder are coupleable to respective inputs of a control unit for displaying data extracted from the DAB radio signal and for outputting audio extracted from the DAB radio signal.
8. A DAB receiver module according to claim 5, wherein the baseband decoder is co-located with the receiver unit.
9. A DAB receiver module according to claim 8, wherein either or both of the audio and data outputs of the baseband decoder are coupleable to respective inputs of a control unit located remote from the baseband decoder, the control unit for displaying data extracted from the DAB radio signal and for outputting audio extracted from the DAB radio signal.
10. A DAB receiver module according to claim 9, wherein the baseband decoder and control unit are coupleable via a USB link, a CAN-bus link or a fibre optic cable.
11. A DAB receiver module according to any one of claims 7 to 10, wherein the control unit audio output is coupleable to a head unit of a vehicle, the head unit for playing received audio over a vehicle music system.
12. A DAB receiver module according to claim 11, wherein the control unit audio output is coupleable to a head unit of a vehicle over a wired or wireless connection.
13. A DAB receiver module according to any one of claims 5 to 12, further comprising a balun or common mode choke between the output of the receiver unit and the input of the baseband decoder module.
14. A DAB receiver module according to any preceding claim, wherein the interface signal is an intermediate frequency (IF) signal, or a baseband interface signal.
15. A DAB car radio system for retrofitting in a vehicle, comprising: an antenna for receiving DAB signals; a DAB receiver module according to any one of claims 1 to 4; a baseband decoder module having an input coupled to the receiver unit output for receiving an interface signal from the receiver unit, the baseband decoder being configured to process a received interface signal of the DAB radio signal to generate an audio and/or a data output from the intermediate frequency signal; and a control unit having one or more inputs coupled to the audio and/or data outputs of the baseband decoder, the control unit for displaying data extracted from the DAB radio signal and for outputting audio extracted from the DAB radio signal.
16. A DAB car radio system according to claim 15, wherein the control unit audio output is coupleable to a head unit in a vehicle, the head unit for playing received audio over a vehicle music system.
17. A DAB car radio system according to claim 16, wherein the control unit audio output is coupleable to a head unit of a vehicle over a wired or wireless connection.
18. A DAB car radio system according to claim 15, 16 or 17, further comprising a balun or common mode choke between the output of the receiver unit and the input of the baseband decoder module.
19. A DAB car radio system according to any one of claims 15 to 18, wherein the interface signal is an intermediate frequency (IF) signal, or a baseband interface signal.
20. A DAB receiver module for retrofitting DAB radio to a vehicle substantially as herein described with reference to the accompanying figures.