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Design a Bluetooth mono headset

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					BLUETOOTH


Design a Bluetooth mono
headset in 60mins
By Karen Parnell                         mize the time it takes to bring a                        tions can reduce the BOM and the              main difference among head-
Product Marketing Manager                new product to market. Growth in                         design’s size and weight. Design-             sets in the market is the headset
for Wireless Audio Products              Bluetooth headsets has increased                         ers ideally want to place more                application code flexibility, and
CSR plc                                  the expectations of consumers,                           blocks inside the device itself, but          the level and extensiveness of
E-mail: karen.parnell@csr.com            requiring designers to imple-                            this would require multiple dies              their interoperability testing.
                                         ment features such as DSPs, echo                         in one package, which would                   Some device-level features such
The Bluetooth headset market has         cancellation, noise reduction,                           increase costs. The most practical            as battery-charge circuits and
experienced impressive growth in         on-chip battery charge circuits                          solution would be to integrate the            SMPS are specific to headsets.
the past five years, with total ship-    and a switch mode power sup-                             RF, memory, interfaces, microcon-             However, most of the headset-
ments rising from 7 million units in     ply (SMPS). In addition, designers                       troller, battery-charge circuit, clock        specific features are software-
2003 to over 60 million headsets         still have to consider the choice                        generator, DAC and SMPS into one              defined. Generally, the two types
in 2005. This uptrend is expected        of Bluetooth chip, Bluetooth                             device. The only external elements            of headsets are flash-based,
to continue this year and beyond.        stack, headset profile software,                         required should be the balun, fil-            where the Bluetooth software is
This, together with the massive          hardware/software (HW/SW) de-                            ter, speaker, microphone, battery,            stored in the flash memory; and
adoption in mobile handsets, is          velopment kit, reference design,                         pushbuttons and LEDs.                         ROM-based, where the headset
turning Bluetooth technology             interoperability testing and the                             The package type should be                software is stored in on-chip
into a globally accepted means           eventual Bluetooth Qualification                         as small as possible, lead-free to            ROM with user-configurable keys
of communication.                        Body testing. This process can be                        meet global RoHS legislation, and             being stored in off-chip EEPROM.
    Advances in Bluetooth tech-          lengthy and leaves designers with                        easy to handle in production to               These keys can be programmed
nology, performance, battery             little or no time to concentrate                         keep costs to a minimum. The                  to define the exact headset hu-
consumption and NFC, as well             on differentiation. Designers                            main factor in overall size of the            man-machine interface (HMI)
as changes in driving legisla-           who are increasingly concerned                           headset is the battery. A typical             requirements.
tion have contributed to the             with practical, easy-to-use and                          Li-ion battery designed for a                    Flash-based headsets offer
phenomenal success that the              aesthetic designs appealing to                           headset is about 5mm x 12mm                   software upgrades, allowing them
market has enjoyed. However,             a wide audience are challenged                           x 45mm, which is much larger                  to operate with new phones. Ex-
headset designers are now faced          to meet these additional require-                        than a typical 8mm x 8mm device               tensive interoperability testing
with a number of challenges to           ments quickly and at a low cost.                         package.                                      means that for high-volume
succeed.                                                                                              The Bluetooth lower-layer                 production, ROM-based devices
    Due to increasing competition        Cost reduction                                           hardware and firmware are es-                 are far more common, translating
in this market, Bluetooth headset        In a typical mono headset design,                        sentially predetermined by the                into lower production costs.
designers are pressured to mini-         a large amount of on-chip func-                          Bluetooth specification. The
                                                                                                                                                Industry solution
                                                                                                                                     Speaker
                                                                                                                                                Both the Bluetooth special interest
                                                                                             Interfaces
                                           Clock                          Baseband                                                              group (SIG) and individual com-
                                            gen                            and logic
 Antenna                                                                                                                                        panies involved in wireless con-
                            Crystal                                                              Audio
                           oscillator                                         Flash              codec                                          nectivity recognize the challenges
                                                                                                                          MIC
                                                                                                                        bias gen                that designers face. Companies
           Filter       Balun
                                                                                                                                                are starting to incorporate all the
                                                                              RAM                 USB                              Microphone   necessary hardware, software,
                                                          RF                                Synchronous                                         design notes and support for ad-
                                                         radio                                  serial
                                                                              MMU
                                                                                              interface                                         vanced Bluetooth headset design,
                                          DAC
                                                                                                                                                allowing designers to concentrate
                                                                                                 UART                                           on customizing new products
                                                                            PHY
                                                                            layer                                                               and getting them to market in
                        Lithium                                           HW engine
                    polymer/ion cell
                                            Power control                                          Audio
                                                                                                   PCM
                                                                                                                                                the quickest time possible. One
                                            and regulation
                                                                                                 interface
                                                                                                                                      User
                                                                                                                                                such rapid design approach has
                                              VREG                                                                                 pushbutton   come from U.K.-based wireless
                                                             Microcontroller
                                                                                                     Programmable I/O




                                                                                                                                    and LEDs
                                               Battery
                                                                                  RISC                                                          connectivity provider CSR. CSR’s
                                               charger           Interrupt
                                                                 controller    Microcontroller                                                  BlueVOX1 solution allows custom-
                                              Switch
                                               mode
                                                                  Event
                                                                                                                                                ers to create a high-performance,
                                             regulator
                                                                  timer                                                                         low-cost Bluetooth mono headset
                                                                                       Integrated into the device                               in as little as 60mins by meeting
                                                                                                                                                the cost, quality, time and tech-
Figure 1: The reference design is constructed around a specific Bluetooth IC, and the designer must evaluate the suit-                          nological requirements of headset
ability of the design for the required headset application.                                                                                     designers.

                                                                                             Electronic Engineering Times-Asia | September 1-15, 2006 | eetasia.com             
Design process                         Both are based on BlueCore4-             However, a designer can reduce               two sets of PS keys. The first set
Hardware development—The first         headset ROM, which features              development time considerably                relates to non-standard value
step in designing a Bluetooth          the switch mode regulator and            by using the fully tested standard           and the second set for particular
mono headset is PCB and Blue-          audio codec on-chip, and is fully        software.                                    application specifications.
tooth IC hardware development.         tested. The Bluetooth single-chip            Designers must decide on
The reference board design is          provides a fully qualified Bluetooth     other specifications like Blue-              Applications testing, Bluetooth
the most important tool in the         system v2.0 + EDR with 6Mbit in-         tooth profiles such as HFP 1.5 for           qualifications—After the HW/SW
design process because it defines      ternal ROM and is pre-loaded with        EDR and eSCO, Headset Profile                development, the final stage is
the recommended PCB layout; it         CSR’s Headset v4 application soft-       1.1, HFP 1.0 and HMI configura-              test and qualification of the overall
indicates where the device and         ware, which includes headset and         tion, and application policy.                reference design, including the
discrete components can be po-         hands-free profiles, HMI configura-      Headset v4 software is a Blue-               HW/SW intended for mass produc-
sitioned and how to implement a        tions and application policy. Both       tooth software solution that                 tion. Designers have to perform a
low-cost PCB antenna. The place-       reference designs conform to the         requires very little modification.           number of tests, including signal
ment and position of components        Bluetooth specification and come         Headset v4 features a wind noise-            output, BER performance relative
are extremely important because        with a full list of interoperability-    reduction filter with treble boost           to received signal strength indica-
they affect RF performance. Start-     tested devices. Designers who            for improved audio quality and               tor, and channel interference.
ing with a hardware reference          have specific headset operational        fully configurable HMI with the                  Bluetooth qualification re-
design that has passed all Blue-       requirements with certain mobile         use of BlueVOX Configurator. By              quires certain testing standards
tooth qualification tests takes the                                                                                          for all products using Bluetooth
                                            Antenna
pain out of the layout process. The                                                       Module-specific PS key:
                                                                                                                             wireless technology. Bluetooth
reference design is also instrumen-                                                                                          devices need to have the right
                                                                                          ∗ Unique Bluetooth address
tal in determining interference                                                           ∗ Crystal trim                     qualification to use the Bluetooth
                                          External RF                                     ∗ Power settings
between board components and                                                                                                 trademark. Qualification also
                                          components
EMI issues on the device.                                                                 Set during production. Different
                                                                                          for each individual headset.
                                                                                                                             ensures that the devices achieve
    Typically, a designer will start                                                                                         a level of interoperability as it
with a hardware development                Headset                                        HMI configuration PS keys:         requires standard specification
                                           Bluetooth              EEPROM
kit for headset applications that             chip                                        ∗ Ringtone
                                                                                                                             conformity for radio links, pro-
includes a fully tested and func-                                                         ∗ PIOs used
                                                                                          ∗ LED flashing pattern
                                                                                                                             tocols, profiles and information
tional reference design. Figure                       Speaker                             ∗ Power management                 requirements. Designers must
 features a generic headset                                                              Set once during development.       also submit compliance decla-
                                                                                          Identical for every headset
reference design. The reference                                                           of the same type.
                                                                                                                             rations and seek approval from
                                                 Microphone
design is constructed around a                                                                                               regulating bodies.
specific Bluetooth IC, and the                                                                                                   The testing and qualification
designer must evaluate the suit-                                                                                             process can take several weeks,
ability of the design for the re-      Figure 2: The function of the EEPROM is to store two sets of PS keys.                 especially if modifications have
quired headset application. A                                                                                                been made and many third-party
designer will typically test to see    phones may wish to undertake             connecting the reference design              components were used. How-
if the standard chip running the       specific interoperability tests to       to a Windows-based PC through                ever, the new Qualified Product
application layer code meets           ensure that the standard chip            the supplied SPI/UART cables,                Listing (QPL) scheme soon to be
the required HMI specification.        meets requirements. In addition,         designers can fully evaluate                 finalized by the Bluetooth SIG
These requirements might be            if the designer wishes to change         the Bluetooth application code               will allow designers to save time
LED operation and quantity, how        the antenna type or layout of the        and modify it to suit additional             and cost by referencing the QPL
many buttons and what the but-         reference design, re-testing is          hardware specifications and HMI              number in their Bluetooth End
ton presses mean, power down           highly recommended.                      configuration.                               Product Listing. Designers using
and up times, ringtones and LED                                                    Should a designer use the                 solutions such as BlueVOX will
color support. The development         Software development—Once the            standard Headset v4 software,                benefit from reference designs
board should have numerous             hardware reference design has            they can move straight to con-               that have been taken through
configurable parameters to allow       been established, designers must         figuring the device’s HMI. In a              the full Bluetooth Qualification
the designer to establish design       evaluate if the standard software        ROM-based headset, an exter-                 process, including the application
requirements. Designers can also       solution integrated into the ROM         nal I 2 C serial EEPROM next to              software, firmware and device
measure power consumption              is suitable. Bluetooth software is       the Bluetooth IC on the circuit              level testing. If the final design
under certain conditions such          subject to certain Bluetooth stan-       board is required to store the               is based on the reference design
as Hands-Free Profile (HFP 1.5)        dards, hence, it remains similar for     Persistent Store values (PS keys)            from the development kit when
plus Enhanced Data Rate (EDR)          most Bluetooth devices. Designers        that configure the HMI. A size of            this new scheme is in place, the
and extended SCO (eSCO) with           can modify the BlueVOX Software          32Kbits is usually sufficient for            designer doesn’t need to apply
different package types.               Development Kit to customize the         most applications in a TSSOP or              for qualification. The final design
    Designers using BlueVOX have       device to implement a proprietary        MLP package. Figure 2 shows                  needs to be submitted with the
the choice of two reference de-        feature, such as a specific switch       the headset software architecture            CSR QPL number, and to the FCC
signs for a Lithium battery or a       type that may need specific code         (ROM plus external EEPROM). The              and CE if worldwide approval is
primary cell-based (AAA) design.       support and hardware interface.          function of the EEPROM is to store           required.




2   Electronic Engineering Times-Asia | September 1-15, 2006 | eetasia.com

				
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