After A Slow Start, Bluetooth Shows Its Colors

After being widely booed and criticized last year, Bluetooth is finally here—big time. In fact, last year's embarrassment is today's cool trend and "must have" technology. Now, everyone wants to get on the Bluetooth bandwagon.

All the hype and vaporware of the past few years really confused prospective users and delayed the adoption of Bluetooth. Yes, it took time for Bluetooth to come to market. But Bluetooth has grown, matured, and been fine-tuned. In its current form, version 1.1, the standard is stable, and earlier bugs have been corrected. The IEEE just recently adopted and approved the Bluetooth protocol under its WPAN standards (IEEE 802.15.1).

To confuse matters more, some said Bluetooth directly competed with the IEEE 802.11b WLAN standard. This early misinformation caused some designers to pause and worry about making the wrong choice. The fact is that the two technologies are fully complementary and compatible because they were designed for different applications.

The big concern was interference because they share the same frequency band. Other wireless services occupying the 2.4-GHz ISM band include cordless telephones, microwave ovens, HomeRF LANs, and the forthcoming Bluetooth competitor, ZigBee (see "Wireless PAN Alternatives To Bluetooth," p. 70). You would think that with millions of Bluetooth-enabled products piled on, nothing would work, except for microwave ovens. Yet due to Bluetooth's very low power and short range, that interference probably won't prevent Bluetooth or any of those other services from being successful.

It also was argued that Bluetooth wouldn't be viable unless the BOM price dropped below $5. A few chip-set vendors are nearing that price point in very high volume. Today, the total cost of a Bluetooth interface is more like $20 to $35, although that hasn't stopped companies from incorporating Bluetooth into products. The cost of wireless can be justified in high-end products or where wireless is an essential feature.

As for the future, the Bluetooth Special Interest Group is working on a compatible next-generation version, called Radio2, that will operate at 3 Mbits/s instead of the current 1-Mbit/s raw rate. A 12-Mbit/s version has also been mentioned. Meanwhile, engineers are designing Bluetooth into products daily to deliver millions of chip sets annually. Figure 1 shows the positive forecasts made by research firm Frost & Sullivan for Bluetooth.

Waves Of Applications: Bluetooth products seem to be coming in waves. Real Bluetooth-enabled products first showed up in 2001. But a flood of new Bluetooth products is appearing this year, and more are on the way.

Currently, the biggest application is wireless cell-phone headsets. All major cell-phone manufacturers now have Bluetooth-enabled headset models. Another cell-phone application is a link to a laptop for e-mail and Internet access. This is a better option than trying to use e-mail and the Internet via a tiny 2.5G or 3G cell-phone screen, or even a PDA.

Leading the second wave of products are wireless printer connections. Several companies make a Bluetooth-enabled printer interface, such as 3Com's PC card and PC interfaces (Fig. 2). Also, Hewlett-Packard has a Bluetooth printer (Deskjet 995c). Other PC applications are wireless mouse and keyboard connections, thanks to Microsoft, which now provides Windows support for these devices. Apple's OS-X supports Bluetooth too. Of course, Bluetooth-enabled laptops and PDAs can now link wirelessly to others by using the piconet capability to form an ad hoc network in a meeting. A piconet is an informal, automatically established network of up to eight users whose Bluetooth devices are within range of one another.

The third big wave of Bluetooth products will hit consumer applications. A few examples include wireless MP3 players, wireless stereo headphones for audio and multimedia entertainment centers, and wireless links for digital cameras and game controllers. You will soon see Bluetooth in automotive telematics applications.

While Bluetooth hasn't really shown up in any industrial applications, it certainly has potential. Wireless data acquisition and remote control could benefit. The cost of wiring in an industrial setting is astronomical (hundreds of dollars per foot) given the standards, safety requirements, and hostile environment, not to mention the high cost of labor to lay conduit and cable. It may seem like a silly move to replace a cable with a complicated wireless data system, but you can frequently save big bucks. Although Bluetooth might be a bit of overkill for some industrial applications, the high volume of usage should lower the price to a very attractive level, overkill or not.

Oh, yes, one other thing: When addressing your application, you constantly have to ask yourself, why would anyone want to buy your product over the competition? What are you doing to make your product better and unique to differentiate it from the pack?

Numerous Choices: Once you have considered your options and selected Bluetooth for your wireless application, you can start what's typically a two-part design process: RF and baseband. Despite what you may have heard, it doesn't take an RF guru to design with Bluetooth. In fact, many say the real challenge is the baseband part of the design. You can solve both RF and baseband problems in one shot by picking the right chip-set vendor. Most major semiconductor companies offer Bluetooth chip sets, with both RF and baseband in one or two chips.

Two of the largest-volume Bluetooth chip vendors are Cambridge Silicon Radio (CSR) and Silicon Wave. Both ship millions of chip sets every year. CSR is the oldest Bluetooth chip supplier. Its newest product is the BlueCore-2 one-chip system (Fig. 3). All RF and baseband are on-chip. This 0.18->µm device operates from 1.8 V and comes in an 8- by 8-mm or 6- by 6-mm FBGA package. It contains a 4-dBm Class 2 power amplifier (PA) on-chip. The built-in 16-bit proprietary microcontroller has more than sufficient MIPS to run most Bluetooth application profiles. The chip has interfaces for USB, SPI, UART, and generic audio PCM. It supports up to 8 Mbits of external flash.

Like most big Bluetooth chip suppliers, CSR has lots of design experience that it's willing to share with customers. CSR also does custom designs and offers reference designs, complete modules, development hardware, software, and a broad range of design experience.

Silicon Wave is another Bluetooth pioneer. Its chips were the first to be certified under the version 1.1 standard. Silicon Wave's approach is a two-chip solution, the radio modem and the baseband IC. This technique is good for designers who want to do their own baseband as an ASIC, or use another vendor's baseband chip. In some applications, the processor may have the extra memory and MIPS to perform the baseband without a separate chip.

The SiW1701 radio handles both Class 2 and Class 3 power levels and has a single-ended I/O that eliminates the external balun most other chips require. It also is available in versions to support GSM (Global System for Mobile Communications) and CDMA cell-phone applications. The company's baseband chip, the SiW1750, contains an embedded ARM7 processor and interfaces for USB, UART, an audio codec, and a continuous-variable-slope delta (CVSD) transcoder, as well as general-purpose I/O. The SiW1770 version incorporates 256 kbytes of flash, eliminating the need for external flash in many applications. Silicon Wave also offers lots of development hardware, software, and general handholding that's usually necessary in Bluetooth development projects.

But while most of your problems will be solved with the right chip set, you still need to do some RF and baseband work yourself. In the RF section, you must add a crystal, impedance-matching circuit to the antenna, a balun, a receive filter, and possibly a transmit-receive switch. Some of these items are increasingly being built into the chip set or modules, except for the antenna where you're on your own.

Antennas are available commercially, like those from Ethertronics, gigAnt, and Sky Cross, or you can create pc-board designs yourself. The patch, meander line, and planar inverted F antenna (PIFA) designs are popular.

If you opt for the Class 1 power output (20 dBm, 100 mW) to get the maximum range and the most robust communications reliability, you will need to add an external PA. Typical of the devices available is SiGe Semicoductor's PA2423MB (Fig. 4). This silicon-germanium biCMOS device operates from 3.3 V and produces a 22.7-dBm output in its 45%-efficient Class AB amplifier. The extra gain is provided to overcome the inherent losses associated with matching networks and switches to the antenna. This product is compatible with and supported by most major chip-set vendors.

SiGe additionally offers the SE2520L linear PA with a gain of 22 dBm to work with applications that include both Bluetooth and 802.11b WLAN radios. This eradicates PA duplication, space, power consumption, and cost.

A challenge that most designers must face is incorporating Bluetooth into another RF device. Cell phones are the best example. Luckily, the frequency difference between Bluetooth and cell-phone radios minimizes the co-existence problems.

However, the problem is acute in laptops that must access an 802.11b Wi-Fi WLAN and Bluetooth-enabled devices because both wireless services implement the same frequency band. 802.11b uses direct-sequence spread spectrum (DSSS) and fewer frequencies in the 2.4-GHz band, as opposed to Bluetooth's frequency-hopping spread-spectrum scheme, which utilizes the entire 2.4-GHz ISM band. The two interfere with one another when operating simultaneously within about three feet of each other. Using separate antennas and keeping the circuitry spaced as far apart as possible helps, but clearly this is still a problem.

Mobilian is addressing this issue. It has developed TrueRadio, a two-chip set that implements both Bluetooth and 802.11b radios to operate simultaneously with minimum interference to one another. Mobilian's MN12100 digital chip and MN22100 analog chips aren't ready yet, although they will sample in the third quarter. They're targeting PC cards for laptops, PDAs, and PCs with Bluetooth mouse, keyboard, and 802.11b LAN capability.

An alternative approach is offered jointly by Intersil, the leading 802.11b silicon supplier, and Silicon Wave, a leading Bluetooth supplier. They recently announced their Blue802 technology, which integrates both protocols into a dual-mode chip set aimed at the laptop market.

Bluetooth and 802.11b co-existence is so important that the IEEE has a separate working group (802.15.2) devoted to seeking a solution. Among potential answers is an adaptive frequency-hopping (AFH) algorithm for Bluetooth that would take fewer hops while attempting to stay away from frequencies used by the 802.11b radio. This solution is forthcoming after a rule change by the FCC and a blessing by the Bluetooth SIG.

If you're working on a Bluetooth PDA project, you may want to consider TDK's Go Blue Wireless Development Tool Kit. It prepares developers to demonstrate and validate designs quickly to reduce time-to-market. TDK also supplies "clip-ons" that give both Palm and Compaq iPAQ PDAs Bluetooth capability.