Electronic Design

With Devices Ready To Go, Bluetooth Is Poised To Make Its Move

As semiconductor manufacturers gear up to mass-produce Bluetooth silicon, they're concentrating on solving technical and price hurdles.

One of the hottest topics in Europe is Bluetooth. The new standard was created by the Swedish telecommunications equipment manufacturer Ericsson. Named after the Danish King Harald II, who received the nickname "Bluetooth" when he unified Denmark and Norway in the 10th Century, the Bluetooth communications standard is now about to conquer the world. Over 1800 companies are already members of the Bluetooth Special Interest Group (SIG) and intend to use this RF short-range networking technology within their products. Members of the Bluetooth SIG can use the standard without paying royalties.

Perhaps this licensing factor was the reason why it took less than two years for Bluetooth to develop from scratch into a world standard. Currently, several companies are starting to develop commercial products. So far, Bluetooth is one of the fastest-growing technologies. Considering Europe alone, market researcher Frost & Sullivan predicts European revenues with Bluetooth devices of $36.7 million this year and almost $700 million for 2006.

Bluetooth is intended to provide an energy-saving, safe, and low-cost RF technology in order to eliminate cable connections over short distances. Bluetooth may be integrated in almost all kinds of electronic data-communications devices. Compared with equipment using infrared (IR) links, Bluetooth-based devices can communicate amongst each other without having a line-of-sight connection.

In principle, a Bluetooth unit consists of a baseband controller and an RF part. The controller needs an interface to the host system, such as a mobile cellular phone, cordless phone, laptop computer, PC, printer, headset, and PC peripheral. Bluetooth works in the industrial, scientific, and medical (ISM) band with frequencies between 2.402 and 2.480 GHz by using a frequency hopping mechanism, where 1600 frequency changes occur every second. A single Bluetooth connection uses 79 different frequencies with a channel separation of 1 MHz.

There are two main reasons for using frequency hopping. First, it provides a higher level of security against both eavesdropping and fraudulent access (in addition to existing encryption protection). The other reason is that RF disturbances may be eliminated. This is important in view of the fact that the operating frequencies of microwave ovens and several radio services are close to those of the ISM band used by Bluetooth. The use of forward error correction (FEC) by Bluetooth limits the impact of random noise on long-distance links. Whenever interferences occur on a specific frequency, this frequency isn't assigned during frequency hopping, resulting in a high level of robustness against external distortions. In most cases for such situations, the antenna will be implemented by assigning a short segment of conducting track on a pc board.

Communicating Over Distances
Currently, maximum transmission power for Bluetooth is 1 mW. This is enough to communicate through walls and briefcases over a distance of up to 10 m (or 33 feet). To enable communication over longer distances, power amplifiers capable of providing an output power of 100 mW will be used. This will allow communication up to 100 m (330 ft). On the receiver side, the Bluetooth specification describes an input sensitivity of −70 dBm working with an IF of 1 MHz.

Between two and eight devices may communicate within a so-called Piconet. Within two seconds, individual Bluetooth controllers inside of a Piconet identify themselves by using a unique 48-bit serial number. The first device identified takes over the master function, which includes determining the 1600 frequency hops per second. All users participating on the same Piconet are synchronized to this hopping sequence.

Several Piconets operating with individual frequency-hopping algorithms can communicate within a larger multiple-Piconet environment known as a Scatternet. In this case, communication takes place via the individual Piconet masters. Compared to other RF LAN technologies, Bluetooth works with significantly shorter data packets. The full-duplex data rate within a Scatternet that has 10 fully loaded independent Piconets is more than 6 Mbits/s. This is due to a data throughput reduction rate of less than 10% according to system simulations based on 0-dBm transmitting power at the antenna.

By combining circuit and packet switching techniques, the baseband controller not only prepares the data for transmission, but also controls the entire procedure. When voice audio data is transmitted, Bluetooth works with a transmission rate of 64 kbits/s in a synchronous mode. Every single data packet is transmitted at another hopping frequency. In most cases, a data packet is assigned to a single time slot. But, data packets may be extended to assign up to five slots.

Nonvoice data may be transmitted either asynchronously at net data rates of 721 kbits/s upstream and 57.6 kbits/s downstream, or synchronously at 432.6 kbits/s in both send and receive directions. If one adds the control and protocol bits, this adds up to a total data rate of 1 Mbits/s that needs to be transmitted physically. The next-generation Bluetooth protocol might offer a 2-Mbit/s option. The current Bluetooth specification is version 1.0, but version 2.0 is expected before the year's end.

Bluetooth supports the simultaneous transmission of a synchronous data channel together with three synchronous voice audio channels. In addition, it allows the simultaneous transmission of asynchronous data and synchronous voice audio data within a single channel.

Voice channels use the continuous variable-slope delta-modulation (CVSD) voice-coding scheme and never retransmit voice packets. The CVSD method was chosen for its robustness in handling dropped and damaged voice samples. Rising interference levels are experienced as increased background noise. Even up to a 4% bit-error rate, CVSD-coded voice is quite audible.

How Bluetooth Works
The entire connection is controlled by the Bluetooth link controller, which is an integral part of the baseband IC. It takes care of all the protocol- and link-access routines. At the beginning, all devices within a Piconet are in the standby mode. Every 1.28 seconds, however, they "listen" for any kind of signal. If a signal is detected, the Bluetooth module will try to look for the potential communications partner on 32 individually assigned frequencies.

The next step is assigning the master module by using a page message—if the address of the communications partner is known. On the other hand, if the page address of the communications partner isn't known, an address inquiry followed by a page message will be sent out.

At the beginning of the "paging" mode, the master sends out 16 identical page telegrams on 16 different hopping frequencies. If no answer is received, then the master resends its page telegrams. But, the telegrams will be sent on 16 different hopping frequencies. The maximum time delay a master needs in order to finally contact its slave is twice the wake-up period (2.56 s). In most cases, though, only one half of the wake-up time (or 0.64 s) is needed.

Typically, the inquiry telegram is used in order to identify Bluetooth devices nearby (like printers or fax machines) with a currently unknown address. The inquiry message is similar to a paging message. Still, it can demand an additional routine whenever answers from several devices need to be collected.

Whenever no data is transmitted, a Piconet master can assign its slaves to operate in the "hold" mode to conserve energy. In this mode, only an internal timer circuit keeps on working. The master sometimes assigns all slaves to operate in the hold mode (like when a Piconet needs to be quiet) when it wants to set up a Scatternet with an adjacent Piconet. On the other hand, slaves can request the master to allow them to change to the hold mode. When any kind of data communication is needed, the master wakes up the relevant slave.

Power-Saving Modes
In addition to the hold mode, Bluetooth offers two other power-saving modes, the "sniff" and "park" modes. In the sniff mode, a slave listens within its Piconet at a reduced scan rate that may be programmed according to the application. In the park mode, the slave module is still synchronized within the network, but it doesn't participate in data transmission anymore. Devices "parked" this way have already given up their 3-bit media access control (MAC).

Parked devices only occasionally listen to the Piconet in order to maintain synchronization and determine a wake-up call for themselves. Consequently, this is the most power-saving mode, followed by the hold mode that requires slightly more energy. The sniff mode consumes a little more power than the hold mode. In total, Bluetooth modules only need about 2 mW in the power-saving modes, making them well suited for battery operation.

Though few Bluetooth ICs are now commercially available on the market, mass production might start very soon. Several semiconductor manufacturers have already begun designing and even producing samples of Bluetooth chips and chip sets. Starting in 2001, several single-chip solutions for Bluetooth are scheduled to become available.

Almost every Bluetooth chip set consists of two chips. The first, an RF part, is realized mostly on a bipolar process. The other, a baseband part, is made on a CMOS process. Cambridge Silicon Radio (CSR), though, offers a single-chip solution for Bluetooth: The BlueCore01 IC (see the opening illustration).

Integrated on a 0.35-µm CMOS process, together with an external flash ROM containing the CSR Bluetooth software stack, it provides a fully compliant Bluetooth system for data and voice communications. By using a low receiver IF channel, filtering can be performed on-chip. A novel synthesizer technique removes the requirement for external varactor diodes and resonator capacitors.

An on-chip 16-bit microcontroller can support full-rate Bluetooth data communications at 723.2/57.6 kbits/s. The device works from a regulated supply of 2.7 to 3.3 V and consumes 40 mA. It offers power management including digital shut-down and wake-up commands as well as a low-power relaxation oscillator to reduce power consumption in park, sniff, and hold modes.

BlueCore01 provides dedicated logic for FEC, header-error control, cyclic redundancy checking (CRC), encryption bit-stream generation, whitening, transmit-pulse shaping, demodulation and access-code correlation. The IC also features transcoders for A-law, µ-law, and linear voice signals from the host, and A-law, µ-law, and CVSD voice over air. Its synchronous serial interface carries data rates of up to 4 Mbits/s. A UART interface offers a programmable baud rate of up to 1.5 Mbaud. Furthermore, it provides a full-speed USB interface supporting OHCI and UHCI protocols, plus a 13-bit PCM 8kss-1 synchronous bidirectional serial audio interface.

CSR also intends to offer the BlueCore02 chip. This will be implemented in 0.25-µm CMOS, allowing the additional integration of embedded program memory and full USB support. At first, this program memory will be flash, but later on it will be ROM.

CSR provides design-in support by offering its BlueCore Evaluation System. The evaluation system gives the Bluetooth designer access to PC-based command and watch windows, thereby allowing the sending and monitoring of individual commands/events and the exchange of simple data sequences (ACL and SCO packets) between Bluetooth systems. This enables the user to learn about Bluetooth, evaluate the BlueStack (provided by Cambridge Consultants), and evaluate the radio performance of BlueCore systems.

The system hardware consists of two units, each containing a Bluetooth module, including the BlueCore01 IC, flash memory, a crystal reference, and an antenna (Fig. 1). The hardware also consists of the motherboard, containing host I/O and man-machine interface elements. These include RS-232 drivers and an external connector, audio codec and external audio plugs for a headset, plus connectors for audio PCM stream and synchronous serial interfaces. These elements are integrated in a molded case, approximately 12 by 12 by 3 cm, with a removable lid. Full C-source files of the Bluetooth layers as well as other software and drivers are available from CSR too.

Ericsson Microelectronics offers the PBA 313 01/2. This is a short-range microwave frequency radio transceiver, operating in the 2.4- to 2.5-GHz ISM band. It requires the addition of an antenna, a 13-MHz reference-frequency crystal, and digital control and data circuitry to form a complete radio. The PBA 313 01/2 is provided in a 34-lead ceramic ball-grid-array package, measuring 10.2 by 14.0 by 1.6 mm.

No external shield is required because the transceiver is self-shielded. In accordance with the Bluetooth standard, the RF output power is 1 mW. A digital interface for control and data makes it straightforward to integrate the transceiver with the Ericsson Bluetooth baseband. A voltage-controlled oscillator and an antenna filter that bandpass filters the radio signal to and from the external antenna also are included on the chip.

Transmit and receive baluns are available to handle biasing of the output-amplifier stage and the transformation between balanced and unbalanced transmission. The antenna filter and the baluns are integrated into the transceiver's ceramic substrate. Operating from a 2.8-V supply, the device typically requires a supply current of 30 mA in the receive mode and 45 mA in transmit mode. A standby mode provides further power savings. Ericsson's baseband solution for Bluetooth, dubbed the Ericsson Bluetooth Core Product (EBCP), is an ASIC based on an ARM core.

Ericsson primarily promotes its entire prequalified Bluetooth 1.0B module, called ROK 101 007, rather than individual components (Fig. 2). The module consists of three major parts: a baseband controller, a flash memory, and a radio operating in the ISM band. Both data and voice transmission are supported by the module. Communication between the module and the host controller is carried out using a USB 1.1 interface or a UART/PCM interface. Using the USB interface, the module appears as a USB slave device and, therefore, requires no PC resources.

The easiest way to begin is to use the Ericsson Bluetooth Developers Kit (EBDK). It provides all the necessary parts for developing applications for Ericsson's Bluetooth module. It's a PC plug-and-play solution that includes all the necessary drivers and software, C++ version 5.0 source code for applications, pins for electrical measurements, and antennas. Developments can take place on the EBDK platform. Thereafter, the implementation of the full Bluetooth capability can be set up by the developed software/hardware and the Bluetooth module. The software includes the HCI driver that implements the HCI command driver used by the host; the L2CAP handling protocol multiplexing, segmentation, and reassembly of packets; the RCOMM providing serial-port emulation over the L2CAP protocol; and SDP, the service discovery protocol providing information about the services available on a Bluetooth device.

Lucent Technologies' Microelectronics Group offers a Bluetooth solution consisting of the V7020 radio subsystem and the W7400 baseband controller. At the heart of the W7020 is an integrated RF transceiver optimized for Bluetooth applications. The IC is flip-chip mounted onto a ceramic substrate, resulting in a footprint of 10 by 14 mm for the entire radio subsystem that interfaces directly to the antenna and the W7400. The W7020 requires no external RF components.

The W7400 performs all Bluetooth link-management and control functions, and includes both USB and serial interfaces to host applications. A link controller ASIC and an ARM7TDMI RISC core are at the heart of the low-power design. The ASIC supports all Bluetooth 1.0 packet types, full-speed asynchronous data rates of up to 721 kbits/s, several voice formats, point-to-multipoint communication links, Scatternet networks, and data encryption. It's available with a Lucent-supplied software protocol stack. To reduce development risk and costs, Lucent will precertify both components.

Philips Semiconductor claims to have been the first manufacturer to produce a commercially available Bluetooth chip set and to have sold more Bluetooth chip sets than any other manufacturer. The Philips solution consists of the UAA3558 RF transceiver and the VWS2602 baseband chip.

On the RF side, Philips contributes its "Low IF" transceiver technology, originally developed for DECT. The company has already incorporated its new UAA3558 Bluetooth transceiver into a thin-film hybrid RF module measuring 10 by 12 mm. The module doesn't require any alignment and consumes 30 mA in the receive mode and 45 mA in the transmit mode. The RF IC with an integrated VCO and a Bluetooth PLL synthesizer provides a target sensitivity of −85 dBm and a 4-dBm output preamplifier.

On the baseband side, Philips uses a baseband controller, which was developed by VLSI Technology and later acquired by the Dutch semiconductor company. This baseband controller, the VWS26002, is ARM7-based and has an embedded Ericsson Bluetooth Engine (EBC) while the Ericsson Protocol Stack is executed on-chip.

Philips' Velocity' Rapid Silicon Prototyping system has been upgraded with all the elements needed for hardware/software co-design of Bluetooth systems or embedded Bluetooth ASICs using libraries of fully tested and re-usable IP blocks. Hardware IP blocks will allow high-performance ARM or MIPS processor cores, memory systems, and peripheral interfaces (such as USB ports or UARTs) to be integrated alongside the company's new LightBlue Bluetooth link controller. Velocity's software design tools will enable designers to bring together only those software blocks needed for the desired Bluetooth profile, so they can meet the ROM-size requirements of their systems.

The Bluetooth Developer's Kit version 2.0 (BTDK) is Philips' platform for the development of Bluetooth applications. It contains two Bluetooth daughter cards (BTDCs), each working as a standalone platform, allowing a Bluetooth wireless link controlled only by a host computer to be established. Each BTDC comprises a single-chip baseband device, embedded software (protocol stack), radio module and FPGA, as well as other discrete components.

This June, Philips announced its so-called TrueBlue module at the Bluetooth Congress in Monaco. The TrueBlue (BGB100) 0-dBm radio module is a plug-and-play, fully integrated radio module for use in cellular and multimedia Bluetooth applications. The module comprises a fully integrated, near-zero IF transceiver chip, antenna filter, Tx/Rx switch, Tx and Rx baluns, VCO resonator, and supply decoupling. It's fully compliant with the Bluetooth radio specification version 1.0. The module doesn't require any external RF components—just connections to a suitable baseband controller and an antenna. Control of the module's operating mode is carried out using a simple serial 3-wire bus. A high-dynamic-range RSSI output allows near-instantaneous assessment of radio link quality.

This new radio module has a typical sensitivity of −85 dBm, in line with official Bluetooth specifications. Power consumption is reduced using open-loop demodulation, which reduces current consumption and the effects of reference-frequency breakthrough on reception quality. Due to the use of the near-zero IF architecture in the RF transceiver, there's no need for expensive SAW filters. The entire radio module is contained in a single plug-and-play module occupying 120 mm2.

National Semiconductor offers a two-chip Bluetooth solution consisting of the LMX3162 RF transceiver and the LMX5001 link/baseband controller. The LMX3162 contains all the transmit and receive functions necessary for a complete radio front end, including 1.3-GHz PLLs, a 2.4-GHz frequency doubler, a low-noise amplifier, a high-frequency buffer, and a 2-GHz low-noise mixer. The transceiver works with a single-conversion receiver architecture and direct VCO modulation. Operating together with the LMX3162, the LMX5001 functions as a Bluetooth link controller between the LMX3162 and a DSP. The LMX5001 complies with Bluetooth specification 1.0B and is capable of both Piconet and Scatternet communication.

Mitel and Philsar have jointly designed a Bluetooth solution consisting of the Philsar PH2401 RF IC and the Mitel MT1020A baseband IC. Philsar's PH2401 fully integrates VCO, synthesizer, power-amplification, and IF filters on the chip. It's manufactured on a 0.5-µm SiGe biCMOS process and operates with a supply of 1.8 V. Typically, the chip consumes less than 20 mA.

The PH2401 offers an RF sensitivity of up to −84 dBm and provides selectable output power between 0 and −10 dBm. In addition, Mitel's MT1020A also works with a minimum supply of 1.8 V and includes a Firefly-type embedded microcontroller core, the BBP block, a Bluetooth baseband peripheral. Also, it includes the audio codec, program memory, a general-purpose ADC, and USB and UART host interfaces. Its low-power feature allows the reduction of the clock speed to as low as 5 MHz.

All radio, modem, and synthesizer functions for a Bluetooth solution are included on a chip developed by Silicon Wave. The SiW015 radio modem IC chip works with the SiW016 link controller IC, and a customer-defined microcontroller or the host system's microprocessor, for complete Bluetooth functionality. The SiW016 link controller IC provides power control, data packet processing, error-detection/correction, and other data-processing functions.

Beyond the commercial availability of Bluetooth chips lies the problem of just how many performance features such chips should have. Bluetooth was intended to be employed in point-to-point connections in order to replace cable connections. An example is between a headset and a mobile phone. But, the more members the Bluetooth SIG gained, the more functions were requested. As a result, the Bluetooth specification was extended with networking features, like Piconet or Scatternet. These are useful functions, but also make for more complex ICs, leading to significant delays in market delivery. Currently, it's very difficult to determine which semiconductor manufacturer is really ready for mass production and which manufacturer is only able to show some samples.

Furthermore, price is a hot issue, because Bluetooth is intended for mass-market products like mobile phones. On the one hand, chips need to be very low in cost. At the same time, they must provide almost the full networking features found in a complex LAN IC.

More Software Needed
While the specifications of the RF part remain almost the same, every additional potential application of Bluetooth ICs requires more complex software stacks and faster, more powerful processor cores. This delays the development and increases design and manufacturing costs.

When it comes to the cost aspect, system integrators mostly talk about $5 as the cost for adding Bluetooth functionality to their existing designs. No one, however, explicitly specifies whether the $5 is part of a semiconductor IC's price, or part of what it costs for an entire Bluetooth board that's ready to be integrated into the host system.

"We won't reach the magic $5 mark within the next three years," says Randy Guisto, vice president of Worldwide Mobile Research at International Data Corp. (IDC). As Guisto points out, the additional hardware costs for implementing Bluetooth into a final product to be shipped in the year 2000 are in the range of $25 to $35. Plus, it's quite likely that the entire costs for adding Bluetooth, including manufacturing of the board, external components, etc., won't come down to the $5 dollar mark before 2004 or 2005.

Beyond single- and two-chip solutions lies the fact that there's still a lot more to do in order to implement Bluetooth devices in a system. You can't just take a single- or two-chip solution, connect it to the host system, and add a short strip-line antenna. In most cases, even single-chip solutions still need about 20 to 30 additional external and discrete components, making the solution more susceptible to manufacturing errors and, of course, increasing the price of the entire design.

Despite all of these challenges, the design and development of Bluetooth chips is nevertheless proceeding full-steam ahead. Look for some novel solutions this year and beyond.

Companies Mentioned In This Report
Cambridge Silicon Radio
+44 1223 424167

Ericsson AB
+46 8 757 4776

Lucent Technologies Inc.
Microelectronics Group
(800) 372-2447

Mitel Semiconductor
(613) 592-2122

National Semiconductor
(408) 721-5000

Philips Semiconductors
+31 40 27 82785
(800) 234-7381 (in U.S.)

Philsar Semiconductor
(613) 274-0922

Silicon Wave Inc.
(858) 453-9100
Fax (613) 592-6909

For More Information
To learn about the Bluetooth standard, the best way to begin is by pointing the browser to www.bluetooth.com, the official Bluetooth site. Check out the following sites for additional information:

www.palopt.com.au/bluetooth/index.htm (general information links);
www.rohde-schwarz.com/bluetooth (testers for Bluetooth);
www.zucotto.com/prod/prod_wire.html (Bluetooth and Java/Jini).

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