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Testing and qualifying a Bluetooth design

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Testing and qualifying a Bluetooth design Powered By Docstoc
					Testing and qualifying
a Bluetooth design
By James Kraemer                                        mum power, with a range limit
Director of Product Development                         of approximately 20m) and
and Engineering                                         Class 3 (0dBm maximum                               Antenna
Smart Modular Technologies Inc.                         power, with a range limit of
E-mail: james.kraemer                                   approximately 10m).
@smartm.com                                                In November 2003, the Blue-
                                                        tooth SIG adopted Bluetooth ver                     RF filter
Bluetooth is widely acknow-                             1.2. Components meeting this
ledged as finally coming into its                       specification offer better inter-                                                                  I/O
own as consumers begin to un-                           ference protection and im-                           Balun                                        Power
derstand its functionality. This                        proved coexistence with other                                           RF      Baseband
                                                                                                                                                        USB/UART
short-range wireless technology                         2.4GHz products, such as
is well-suited for cable replace-                       WLANs, some cordless tele-
                                                                                                                                                                      12-pin
ment across a wide range of ap-                         phones and microwave ovens, as                                                                              interface
plications. The Bluetooth Spe-                          well as improved voice connec-                                        Flash           16MHz                connector
cial Interest Group (SIG) has ex-                       tions compared to previous ver-                                      memory           crystal
panded to include more 3000+                            sions. These advances are due
members across industries such                          partly to the addition of adaptive            Figure 2: The latest module solutions offer designers the means to
as communications, medical                              frequency-hopping technology,                 implement Bluetooth technology with reduced design risk.
and personal computing.                                 enhanced voice processing and
   For product managers and                             faster connection setups. Blue-               aging design allow for an em-         with moderate performance
design engineers, the question                          tooth ver 1.2 products are also               bedded or external antenna?           characteristics might initially
has changed from “When will                             backward-compatible with ver                  What is the product life cycle        cut costs, but will likely require
we implement Bluetooth?”                                1.1 products.                                 and how many variants are             a complete redesign in the next
to “How will we implement                                  Once designers have chosen                 planned?                              generation.
Bluetooth in our designs?”                              to integrate Bluetooth techno-                                                          In addition to the expected
What are the pitfalls? What is                          logy into their products, there               How can I be most efficient?          RF and baseband functionality,
the most efficient, cost-effec-                         are many issues that should be                The original Bluetooth design         some Bluetooth modules offer
tive way forward? For designers                         considered beyond simple per-                 had a number of discrete ICs          a dedicated microcontroller,
with limited wireless experi-                           formance figures in a vendor’s                with supporting circuitry. It         antenna and connector integra-
ence, the road ahead could look                         datasheet. For instance, what                 eventually evolved into a mo-         tion, as well as on-board flash
very intimidating.                                      are the usage scenarios for the               dule (Figure 1).                      memory, voltage regulators, fil-
   Bluetooth is a short-range                           product? Is the product embed-                   Since then, the level of inte-     ters and crystals. These features
wireless networking techno-                             ded or an external add-on?                    gration has increased and the         offer simplified designs, lower
logy that operates in one of                            What operating systems need to                number of external parts has          development costs and im-
three power classes: Class 1                            be supported? What profiles/                  decreased as the technology           proved time-to-market.
(20dBm maximum power, with                              services will satisfy the require-            progressed. As a result, the lat-         If they are not using one of
a range limit of approximately                          ments of the product applica-                 est module solutions offer de-        these highly integrated mo-
100m), Class 2 (4dBm maxi-                              tions? Does the product pack-                 signers the means to imple-           dules, designers must pay care-
                                                                                                      ment Bluetooth technology             ful attention to the layout of the
                                                                                                      with reduced design risk, mak-        Bluetooth PCB. Component
             Crystal                                                                                  ing the reality of a drop-in          placement, tracking, decoup-
  Antenna
                                                                                                      “complete Bluetooth solution”         ling, grounding, shielding and
                                                                         PCU         Serial parllel   even more possible (Figure 2).        board material are crucial
                                                   Memory-                           interface
                                     RAM
                                                   mapped                                                A major consideration when         to ensuring good RF perfor-
                                                    control
              Clock                                 status                                            adding Bluetooth functionality        mance. When using a pre-
            generation
                                                                         LMR                          to a design is if the module or       designed, pre-certified mo-
    RPF
                                                                                                      chipset meets the current             dule, designers avoid the need
                                                                         LMR         UART             Bluetooth standard and/or if it       to worry about these factors in
                   RF
                 receiver             Baseband and logic
                                                                                                      is upgradable. A good way to          their final design.
    Balun                            memory management
                                                                         USB         USB              avoid delayed design cycles is to
                    RF
                transmitter
                                                                        Memory
                                                                                                      select a product that does not        Product development issues
                                                                         driver                       require additional Bluetooth          Once a designer understands
                    RF
                                                                                                      certification or FCC/CE regu-         the basic application needs of
                synthesizer
                                          RISC
                                                                      Flash/memory                    latory certification.                 the product, it is important to
                                      Microcontroller
                                                               Programmable
                                                                                                         Designers should also con-         keep a watchful eye on power
                                                                                     Input/output
                                                                    I/O                               sider choosing a Bluetooth so-        dissipation (battery life), physi-
                                                                                                      lution that has leading-edge          cal limitations of the Bluetooth
                          Voltage                                                                     performance and on-board              circuitry in the existing product
                         regulator
                                                                                                      memory. This will make the            design (how much real estate is
                                                                                                      product more likely to last           available) and transmission-rate
Figure 1: The original Bluetooth design was a number of discrete ICs                                  through a few generations of          limitations or needs. For in-
with supporting circuitry before evolving into a module.                                              designs. Selecting a module           stance, most Bluetooth Internet
                                                                                      ference in the Rx path.              considerations given to fil-
                                                                Bias voltage
                                                                                       A shield helps reduce inter-        tering requirements, match-
                                                        L2                            nal and external interfe-            ing and layout.
                                      C2                                              rence from radiating into the     4. Connectors—Many Blue-
                              L1                                                      module and other RF-sensi-           tooth modules do not have
                  TxA/RxA                                           Antenna
                                                                                      tive components. RF coup-            connectors, but have leaded
          Bluetooth                   C1
                              L1                Balun                                 ling also needs to be con-           BGA or SMD packages. Re-
          radio chip
                  TxB/RxB                                    Bandpass                 sidered, and components              work on any products that
                                      C1                       filter                 should be carefully oriented         feature these leaded mo-
                                                                                      on the PCB.                          dules requires the use of a
                                                                                         For example, the RF per-          BGA or SMD rework station.
Figure 3: A matching network formed by L1 and C1 is used to transform
                                                                                      formance of a Bluetooth de-          These stations are costly,
between the impedances of the Tx differential port and that of the balun.
                                                                                      vice with an antenna was             and the process can be time-
                                                                                      measured. In case 1, a 0Ω            consuming when these com-
                                                                                      matching network was used            ponents need to be extracted
connections are limited to               selected, this matching                      to measure the initial an-           from the PCB for test, debug
732.2Kbps, which can affect              needs to be done by the de-                  tenna state (Figure 4); in           or repair. In such cases, the
audio quality.                           signer and then the solution                 case 2, an optimum match-            main PCB could easily be
   Here are five considerations          needs to be recertified by                   ing network was imple-               damaged and reworking the
that are critical to the develop-        the Bluetooth Qualification                  mented to enhance antenna            leaded module back onto the
ment process:                            Review Board (BQRB).                         performance (Figure 5).              PCB could be challenging.
1. Module vs. chipset—Taking          3. Antenna matching—Most                           In the cases above, mea-          (For instance, a BGA X-ray
   chips and designing them              Bluetooth radio chipsets (and                surements performed in-              machine may be needed to
   directly on the PCB saves on          modules) have an on-chip                     cluded 3D radiation pattern,         verify whether the pins have
   footprint. But the advantage          Tx/Rx switch in the front-end                return loss and antenna effi-        connected properly to th
   pretty much ends there.               architecture to allow both the               ciency. For this analysis, the        PCB.) Working with a mo
   Single-chip/chipset ap-               Tx and Rx paths to use the                   return loss and antenna effi-        -dule that has the appropriat
   proaches require RF design            same differential port. Typi-                ciency will be considered.             signals brought out on
   resources to provide filters,         cally, the output transceiver                In these examples, initial            connector can save time fo
   amplifiers, matching net-             architecture is a single com-                measurements showed that              a designer
   works, oscillators, clocks and        bined Tx/Rx chain.                           the antenna was detuned                When a module is equippe
   antenna for both the transmit                                                                                           with standard connectors of-
   (Tx) and receive (Rx) paths.                                                                                            fering USB or UART inter-
                                                                                                        Standard
   It also requires extensive test                                                                      50Ω cable
                                                                                                                           faces, the designer essen-
   equipment suites to verify                                                                                              tially has a plug-and-pla
   and synthesize the design.                                                                                               module to insert into the ex-
   The design will also have                                                    R1                                         isting design without th
   to be certified for use in                                                  (0Ω)                                         need to redesign the PCB t
   Bluetooth products.                                                                                                      integrate BGA- or SMT-typ
2. Antennas—Most Bluetooth                                                                                                  components. An on-modul
   handheld devices require            Figure 4: 0Ω matching network was used to measure initial antenna state.             connector can also help de-
   antennas that radiate in a                                                                                              bugging and testing withou
   spherical pattern so they can                                                                                            needing special equipment.
                                                                                                       Standard
   connect in any direction.                                                                           50Ω cable        5. Crystal—Some modules do
   Good antenna design for                                                                                                 not have an on-board crystal,
   Bluetooth products is impor-                                                                                            while others have, but with
   tant and designers selecting                                               L1                                           the module not fully tested
   an external antenna need                                                (4.7nH)                                         and certified. In either of
   to consider space, cost and                                                                                             these scenarios, some spe-
   antenna patterns. The sur-                                                                                              cial design considerations
   rounding components, ca-            Figure 5: An optimum matching network enhances antenna performance.                 apply.
   sing and proximity to the                                                                                                 Crystals vary, and each has
   ground planes also play a                   When designing the                     from the central frequency           an optimal bias level that
   role in the ultimate perfor-            Bluetooth module, a match-                 of 2.45GHz, so a matching            minimizes the phase noise
   mance of an antenna.                    ing network formed by L1                   component was required.              on the oscillator, so, when
     If selecting a module with-           and C1 is used to transform                Results showed that 44 per-          using a crystal, its bias level
   out an antenna, the designer            between the impedances of                  cent total antenna efficiency        must be individually config-
   must understand the envi-               the Tx differential port and               (at the peak of 2.45GHz) was         ured. In the case of certified
   ronment where the product               that of the balun (Figure 3).              achieved when using the op-          modules with an on-board
   will be used. Signal strength           The balun converts the dif-                timum matching network               crystal, the individual bias
   losses can occur if the feed            ferential signal into one                  (Table 1). Return loss in            levels are pre-stored on each
   between the radio and an-               single-ended signal that is                case 1 ranged from -2.9dB to         module to achieve minimum
   tenna is not well-matched               fed to a bandpass filter, then             -5dB and improved to -6.5dB          phase noise.
   and the signal is reflected             to the antenna port. Filte-                to -12.4dB with matching
   back into the circuit.                  ring formed with the L2/C2                 circuitry (Figure 6).                Standard Bluetooth devices
     If a designer selects a mo-           network prevents RF energy                   As this analysis shows, al-     are minimally equipped with a
   dule with an on-board an-               from contaminating the cir-                though the antenna is only        host controller interface (HCI)
   tenna, then the significant             cuit. The bandpass filter in               one component, designing it       stack, which supports basic
   antenna-matching work has               the signal path provides ad-               in a circuit requires the opti-   Bluetooth host protocols for se-
   already been done. If a mo-             ditional filtering for the Tx              mized performance of the          rial communications, such as
   dule without an antenna is              signal and suppresses inter-               other circuits, with special      synchronizing the hopping fre-
                                                                   18 Dec 2003        15: 49: 15
       CH1 S11       log MAG            5 dB/       REF    0 dB                  3: -5 11:47 dB                                                          Analyze spectral
                                                                    2    500   000     000 MHz                                                             properties        Noise generator

       PRm                                                                                                                                                   Spectrum             Bluetooth
                                                                                 1: -2.8822 dB
       Cor                                                                             2.4 GHz                                                               analyzer               signal
                                                                                 1: –2.8822 dB                                        Bluetooth                                   generator
       Del                                                                            2.45 GHz                                      tester E1852A                RF                   RF
                                                                                                                                               RF(I/O)          input              output




                                                                                                                                       Parallel              RF splitter
                                                    3                                                                                   port
                                                                                                                                                             Combiner
                                          1     2                                                                                        PC
                                                                                                                                        COM
                                                                                                                                       1 and 2




                                                                                                                                       Adapter              DUT RF port
                                                                                                                     DC supply          board
             START   2   000   000   000 MHz                STOP    3 000      000    000   MHz                                                                 DUT
                                                                                                                                 Interface between
                                                                                                                                 BT module and PC         Bluetooth module

      (a) Return loss plot (case 1) for a 0Ω matching network

                                                                  18 Dec 2003     17: 57: 44                  Figure 7: General RF test setup can examine a Bluetooth module for most
       CH1 S11       log MAG            5 dB/       REF    0 dB              3: -6 4821 dB
                                                                    2 500 000 000 MHz
                                                                                                              RF parameters such as Tx/Rx signal output and co-channel interference.
       PRm
                                                                               1: =10 328 dB
       Cor                                                                           2.4 GHz                     Additional test criteria will             most part, all the designer
       Del
                                                                               2: –12 359 dB
                                                                                    2.45 GHz                  var y by application. For in-                needs to do is ensure that ap-
                                                                                                              stance, Table 2 shows the                    propriate signal levels are pro-
                                                                                                              pass/fail parameters used to                 vided to the module and that
                                                                                                              evaluate a Bluetooth USB                     the correct application or
                                                                                                              printer adapter.                             stack is loaded onto the final
                                                    3
                                                                                                                 Some additional tests that                product.
                                                                                                              can be performed using the test                 For instance, using the USB
                                                                                                              setup in Figure 7 include:                   adapter example in Table 2, the
                                           1                                                                  • “Frequency vs. time” and                   designer simply needs to ensure
                                                2
                                                                                                                “power vs. time” perfor-                   that the proper USB signals are
                                                                                                                mance for the module;                      connected to the USB lines of
                                                                                                              • “Power vs. frequency” chan-                the module. The power, ground
             START   2   000   000   000 MHz                STOP    3 000      000    000   MHz                 nel number;                                and appropriate signal levels as
   (b) Return loss plot (case 2) plot for an optimum matching network.                                        • Co-channel interference;                   defined by the module specifi-
                                                                                                              • Adjacent channel                           cations should be applied when
Figure 6: Return loss in case 1 ranged from -2.9dB to -5dB and improved                                         interference;                              integrating the module.
to -6.5dB to -12.4dB with matching circuitry.                                                                 • Spectral contents of the signal;
                                                                                                              • Harmonics contents.                        Bluetooth qualification
quencies used by communica-                         as the Agilent E1852A/B or                                                                             Bluetooth qualification allows
ting Bluetooth products. A mo-                      Anritsu MT8850A. Addition-                                   When using a module with-                 OEMs to have a product listing
dule manufacturer can load a                        ally, a spectrum analyzer can be                          out an antenna, additional work              on the Bluetooth Website and
profile on top of the stack, such                   used to examine the spectral                              is needed to determine the                   gives them the ability to use the
as the serial port profile (SPP),                   contents of the signal on the RF                          matching circuitry. Also, more               Bluetooth brand on the product.
which allows for cable replace-                     port of the device for measure-                           extensive measurements will be               Qualification helps different
ment. Also, end-users can de-                       ments of adjacent channel in-                             required when the antenna is                 manufacturers ensure that their
velop custom stacks or pur-                         terference, signal spectrum,                              on-board, which may even de-                 products will operate with other
chase third-party stacks.                           harmonics, co-channel inter-                              mand the help of the antenna                 Bluetooth products and comply
                                                    ference and noise.                                        manufacturer if the proper                   with the Bluetooth specification.
What do I need to test for?                             The Bluetooth signal ge-                              equipment is not available at                The qualification process is di-
Figure 7 shows a setup that can                     nerator in Figure 7 is used to                            the design site.                             vided into four parts: radio link,
be used to test a Bluetooth mo-                     generate noise in the particular                             Using a pre-certified fully               protocol, profile and informa-
dule for most RF parameters                         bandwidth and frequency band                              integrated module eliminates                 tion requirements.
such as Tx/Rx signal output, co-                    of interest. The RF combiner/                             the need to test for RF confor-                 The entire qualif ication
channel interference, bit-error                     splitter is used to combine the                           mance testing or data trans-                 program is overseen and ad-
rate (BER) performance relative                     noise with the RF signal and                              mission rates, since the prod-               ministered by the BQRB.
to received signal strength indi-                   split the RF signal where it can                          uct is already certified by the              Qualification is based on con-
cator (RSSI) and adjacent chan-                     be routed to the spectrum ana-                            Bluetooth Qualification Body                 formance testing (defined by
nel interference.                                   lyzer and the Bluetooth tester.                           (BQB), CE and FCC. For the                   the Bluetooth Qualification
    The device under test                                                                                                                                  Program) against a reference
shown in Figure 7 is the actual                                         Frequency (MHz)            Eff. (%)   Peak gain (dBi)    Return loss (dB)          test system and functional
Bluetooth module. It is con-                                                    2.4                  16            -3.4                 -2.9               interoperability tests with an-
nected to a PC using an in-                               Case 1                2.45                 24            -1.8                 -3.7               other operational Bluetooth
terface board, which in this                                                    2.5                  36            -0.1                   -5               product. Testing is performed
case, requires DC supply. The                                                   2.4                  33            -0.6                -10.3               by a Bluetooth Qualification
                                                          Case 2                2.45                 44            0.5
PC is equipped with test setup                                                                                                         -12.4               Test Facility (BQTF) that has
                                                                                2.5                  31             -1                  -6.5
software.                                                                                                                                                  been accredited by the SIG’s
    A major component of this                       Table 1: Results show that 44 percent total antenna efficiency (at the peak                            BQRB.
setup is a Bluetooth tester, such                   of 2.45GHz) was achieved when using the optimum matching network.                                         In addition to this testing,
manufacturers seeking qualifi-      add several weeks to the design        vals. Although BQTFs have re-       designs must be clear on what
cation must submit compliance       cycle. The cost of certification       cently implemented price re-        their application requires and
declarations, which will be re-     for a new design varies and is de-     ductions, the use of pre-certi-     then carefully select the mo-
viewed by a BQB. In addition,       pendent upon which countries           fied modules still offers consi-    dule or chipset for the design.
Bluetooth products also need to     will be receiving the product—for      derable cost savings.               Fortunately, the technology
obtain approvals beyond those       instance, costs can exceed                Engineers implementing           has evolved so that designers
issued by the BQB, such as FCC      $100,000 for worldwide appro-          Bluetooth into new or existing      can implement Bluetooth
and CE.                                                                                                        functionality with a limited
                                     Average power                          0dBm min, +4dBm max
   If designers select a pre-        Peak power                             0dBm min, +4.00 max                amount of optimization and
certified module complete with       Sensitivity                            -80dBm max @ 0.1% bit error rate   RF circuitry design. Some of
antenna, no re-certification is      Freq offset                            -25kHz to +25kHz                   the latest modules also elimi-
                                     Freq drift                             -15kHz to +15kHz
required. If they select a module    ∆f1max “maximum modulation”            +140kHz to +175kHz                 nate the need for certification
that requires additional compo-      ∆f2min “minimum modulation”            >+115kHz                           and extensive design work, so
nents, including connectors and      ∆f2min/∆f1max                          >0.8                               designers can provide a reli-
antennas, then the design must      Table 2: Pass/fail parameters for a Bluetooth USB printer adapter.         able and fully certified design
be re-certified. This process can   Additional test criteria will vary by application.                         with a faster time-to-market.

				
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Description: Bluetooth module, an integrated Bluetooth chip for wireless network communications, the main sub-Bluetooth gps module, Bluetooth module BRF6100. Bluetooth Bluetooth chip production is the largest manufacturer CSR.