Hardware, Manufacturing And Host Integration
At the lowest level, a Bluetooth device has two key components: a radio and a baseband controller. Simple enough, right? But the small footprint, interoperability constraints and low-cost objectives of Bluetooth technology make manufacturing modules and devices a difficult engineering task when it comes to RF chip design. The challenge is appreciable enough that companies are fanatic about safeguarding their IP, and will often not provide detailed designs for the base Bluetooth IC/SoC even to the vendor that is manufacturing/integrating the final consumer device.
At the highest level of engineering design, the first decision to make about Bluetooth is its integration with the host product. There are almost as many ways to implement Bluetooth integration in a consumer end-product as there are classes of products. Broadly, they can be classified as:
- Integrated single-chip, where the baseband circuits and Bluetooth radio are completely integrated into the host SoC module. This type of approach is most commonly used in headsets, and the design complexity of a single chip like this is overshadowed by the lower cost of manufacturing and integration.
- Standalone single-chip, where a single Bluetooth SoC containing the baseband circuitry and radio is integrated into a larger system assembly. This is commonly seen on computer peripherals like Bluetooth keyboards and mice, or certain types of smartphones and tablets. Pre-certified Bluetooth modules can be used to save on costs.
- Dual-chip, where the baseband circuits and radio are housed in two separate IC packages. This approach has lost ground to the single-chip approach, and is most often seen when the radio sticks to analog operation and the baseband IC is digital.
The hardware integration is closely (but not always) tied to the partitioning of the Bluetooth protocol stack. Where the Bluetooth implementation is completely integrated with the host, it is the host’s software/firmware and host’s computing resources that are used to manage the upper and lower stacks and the API. In all other cases, the radio and baseband circuits always handle the lower stack (LM, LC and down), so the difference is in where and how the upper stack is managed. For a standalone single or radio-baseband-dual chip, a microcontroller implements the upper stack and there is often no need for the API. When Bluetooth shows up as a host add-on, for example in a Bluetooth adapter for a PC, the Bluetooth plug-in module handles the lower stack, the module communicates with its host through HCI and the host software/drivers handle the upper stack and API. Finally, in the host ASIC case, everything sits on the single Bluetooth chip, and the API on the host machine/device communicates with the module.
The actual Bluetooth radio and baseband chips (whether single SoC or dual-chip solutions) are manufactured using different technologies based on the application. There are variations on CMOS (complementary metal–oxide–semiconductor) chips, gallium-arsenide (GaAs) chips and the most common—silicon-germanium (SiGe) semiconductors in varying packages turned into modules using LTCC (low-temperature co-fired ceramic) films or PCBs (printed circuit boards).
CMOS variants can include the standard bulk CMOS approach, RF (radio frequency) CMOS and SOI (silicon-on-insulator). Traditional bulk CMOS is used to build the digital-only baseband chip, and then chained to an analog circuit for the Bluetooth radio. RF-CMOS adds the radio directly onto the CMOS chip, and SOI adds an insulator layer between the RF and BB circuits for isolation.
GaAs chips are used in “ruggedized” or military applications, since gallium arsenide devices are more resistant to high levels of electromagnetic pulsed radiation—they can be knocked offline by an EMP, but the component isn't reduced to slag. Since the manufacturing process for GaAs is completely different than CMOS (and far more expensive), most manufactures serving the consumer market no longer develop GaAs chips.
An RF chip made from SiGe has higher efficiency and greater throughput than a pure silicon semiconductor-based radio. The choice of silicon CMOS or SiGe BiCMOS depends on the application—where cost is a factor, a standard CMOS die is used, whereas for applications that require better RX or TX sensitivity/power or low power consumption, BiCMOS is used. The final packaging also depends on manufacturer requirements and final device/application: leaded SOIC (small outline integrated circuit), QFP (quad flat package) or PLCC (plastic leaded chip carrier).
Pictured above are the SOIC package and the BGA package.
Leadless designs (BGA—Ball Grid Array, CSP—Chip Scale Package, WLCSP—Wafer Level Chip Scale Package) are used for devices like smartphones, where small footprints are important and generally present good cost savings over QFP packages.
Qualification, Testing And Certification
Imagine a large room—a conference hall, perhaps—where engineers and representatives from dozens of manufacturers, either collaborators or competitors or sometimes both, bombard each other with Bluetooth signals. This is UnPlugFest, an event organized by the SIG, where manufacturers come to test the interoperability of their devices. Interoperability is a key aspect of the Bluetooth standard, and one of the many tests a device must undergo before it is qualified by the SIG.
The SIG imposes qualification requirements in the form of the Bluetooth Qualification Program (BQP), including product performance and compliance with the Bluetooth specifications. Once it passes the BQP, the product must be certified, by the FCC in the USA, CE in the EU, TELEC in Japan, etc. The entire certification cycle can take more than a year, and may cost up to tens of thousands of dollars in testing and administrative fees.
Given the complexity, length and high cost of designing and certifying Bluetooth modules, many manufacturers choose to use a pre-certified module in their final consumer product—laptops are a good example of this. Essentially, if a product uses a pre-certified module, the certificate comes with a very strict set of guidelines as to its maintenance, but otherwise can be used without further testing or qualification.