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Bluetooth® Low Energy Design 101: From Chipsets to Protocol Stacks to Modules

Contributed By Digi-Key's North American Editors

Bluetooth low energy or BLE—also known as Bluetooth Smart—has become a key enabler for connected wearables, smart appliances and proximity tags. The short-range wireless standard is designed to reduce power consumption through faster connections that transfer smaller amounts of data with lower latency.

The fact that Bluetooth Smart aims to spend approximately one-tenth of the power compared to Bluetooth Classic connections just shows the scale of engineering efforts being carried out to adapt this wireless connectivity mechanism for small form factor applications (Figure 1.)

Bluetooth Smart employs a link bit rate of 1Mbit/s and an application throughput of 800 Kbit/s. Here, the drop-in bit rate is offset by a reduction in latency to 6 ms as compared to 100 ms in the Bluetooth Classic specification. These innovations are taking Bluetooth Smart from being a connectivity vehicle in the usual wearable designs like smartwatches and wristbands to a wider array of wearable and Internet of Things (IoT) applications.

Image of Bluetooth Smart or BLE has evolved

Figure 1: Bluetooth Smart or BLE has evolved from the existing protocols to serve wearable and IoT devices (courtesy of Aislelabs).

For instance, wearable sensors in a virtual reality (VR) motion gaming platform are now using Bluetooth Smart connections to transfer data to the wireless headset with minimum latency. Then, there are hearing aids that employ BLE links to make sound adjustments, deliver alerts, check battery status, and make program changes over a smartphone.

Beacons, remote sensors and wearable biometric passports are other hotbeds of activity for Bluetooth Smart technology where it's facilitating a myriad of mobile advertising and commerce, ticketing, door-lock and other safety applications. Here, a Bluetooth Smart-capable device—smartphone, notebook, etc.—can monitor location, acceleration and proximity of any tagged device within a 5-meter to 30-meter radius.

The latest version—Bluetooth v4.2 specification—is now laying the groundwork for the next-generation wearable and IoT applications by enabling more devices or "things" to hook up in the hyper-connected world. For a start, it extends maximum data rates to 800 Kbit/s, which is 2.6 times faster than the previous versions, and allows faster data logs from sensors as well as quicker firmware updates.

Simplifying BLE design

A new crop of end-to-end BLE solutions—spanning silicon to software stacks to modules—is now adding key improvements in the BLE design from connectivity, security and power consumption standpoints. Let’s start with security, however, as it’s already been clearly identified as a major challenge for the IoT.

Bluetooth v4.2 brings a number of security upgrades, while making it more difficult to track devices through Bluetooth connections. First and foremost, it brings authentication mechanisms to the level of Bluetooth Classic, and allows the pairing of devices only when connections are fully secure.

Second, it offers automatic pairing as well as dual-mode communication, which makes pairing easier when in an open mode and requires a greater security for data transfers when in a closed mode. Another critical feature, at the intersection of security and power efficiency, mandates that beacons or proximity tags require permission from devices they are going to communicate with.

Such privacy and filtering features allow Bluetooth Smart chipsets to wake up only when an object designated as trustworthy comes within a user's proximity. Furthermore, the new BLE subsystems sip incremental power while they conserve energy by shutting themselves down when they are not in use.

Diagram of highly integrated Bluetooth SoCs and modules

Figure 2: Highly integrated Bluetooth SoCs and modules allow you to quickly incorporate BLE links in your wearable and IoT designs. (Image source: Cypress Semiconductor)

Bluetooth Smart chipsets can now shuttle among various power modes—active, sleep, deep sleep, hibernate, and stop—to keep power usage in check. For instance, the Bluetooth chip can figure out when to put the device in "deep sleep" mode where the CPU is turned off, but the BLE link is still active.

A Bluetooth Smart chip, when put in the deep-sleep mode, can consume less than 500 nA while it maintains data in the retention memory. On the other hand, hibernate and stop modes break the connection while allowing the chip to consume current in the nanoamps range.

As mentioned, development cost and board space are the two other major challenges confronting BLE designs. Here, single-chip Bluetooth solutions and highly integrated modules compatible with the latest version of Bluetooth specifications are helping designers to optimize the board space and save cost both in terms of lower BOM and smaller development time.

Single-chip BLE solutions

The use of multiple chips is antithetical to BLE design, both from real-estate and power-efficiency perspectives so you need to look instead at ultra-low-power systems-on-chip (SoCs) that combine an innovative processor architecture with multi-protocol radio circuitry that reduce cost, footprint, and power consumption.

In these SOCs, the on-board processor handles control functions like executing power modes that cater to particular needs at particular times. Then, with sufficient memory capacity, it runs qualified Bluetooth Smart protocol stacks that include security and multiple profiles. The single IC also provides memory for data storage and customer application software. Doing all this on board eliminates the need for the second microcontroller, with its associated cost, power consumption and data-interface power losses.

Next up, the multi-protocol Bluetooth radio allows designers to optimize BLE links for mission-critical data transfer while supporting low-latency applications like audio streaming with a 2.4 GHz proprietary protocol. A boost in the signal strength and multi-faceted data transfer approach help you lower the drain on battery life while holding the transmission range steady.

Of course, if you have limited experience in Bluetooth or RF design in general, the highly integrated SoCs help you address common design challenges and conveniently add BLE connectivity to your design. Moreover, Bluetooth SoCs offer improved radio sensitivity, greater range, and most importantly, a fully automatic power-management system.

Diagram of Cypress' low-power Bluetooth SoC

Figure 3: Cypress' low-power Bluetooth SoC is targeted at sensor-based wearable and IoT applications.

A good example is the PSoC 4 BLE chipset from Cypress Semiconductor. This integrates analog front-ends, digital logic, a Bluetooth Smart radio, and a capacitive sensor called CapSense. The chipset, based on an ARM® Cortex®-M0 processor, also includes a royalty-free BLE protocol stack that is compatible with the Bluetooth 4.2 specification.

Cypress is working to make it easy for you by building a complete design ecosystem around the PSoC 4, starting with a module. The EZ-BLE PSoC module includes the PSoC 4 BLE chip, an antenna, crystals, and all the passive components necessary to create a plug-and-play Bluetooth subsystem.

Image of EZ-BLE modules from Cypress Semiconductor

Figure 4: The EZ-BLE modules from Cypress Semiconductor comprise a full range of fully integrated and certified programmable modules that simplify and speed design, with on-board crystals, trace antenna, shield, and passives. For perspective, the 10 x 10 x 1.80 mm modules are smaller than a US penny.

Furthermore, Cypress provides an evaluation board that allows engineers to develop and evaluate applications on the EZ-BLE PSoC module. The evaluation board facilitates easy prototyping by routing GPIOs to components such as CapSense, LED, and switches. Around that it wraps its PSoC Creator quick-design graphical user interface (Figure 5.)

Image of Cypress PSoC Creator tool

Figure 5: The Cypress PSoC Creator tool facilitates quick design, in this case a BLE heart-rate monitor with a custom analog front end (AFE). (Image source: Cypress Semiconductor)

The tool provides prebuilt components in a graphical drag-and-drop interface and once the design is complete it then generates a set of applications programming interfaces (APIs) for each component in the schematic. The BLE Component simplifies stack and profile configuration.

Module: A complete BLE subsystem

It’s good for designers that the suppliers of Bluetooth Smart SoCs like Atmel, Cypress, and Silicon Labs are also offering modules. It’s also good for them, as they get to innovate around their ICs and provide more value to you, in terms of cost, footprint and low energy. So much so, that BLE modules are really the next design frontier in delivering a complete hardware subsystem for wearables and IoT products.

The modules incorporate all the hardware and firmware needed for the development of BLE-centric applications. They combine a Bluetooth Smart SoC with antenna and interfaces for connecting peripherals and sensors. These modules are pre-qualified and allow designers to bypass the complex antenna design and approval processes.

That said, handling RF communication over the Bluetooth antenna can still be tricky. Antenna design is crucial in Bluetooth because it has to be implemented in a specific position with a specific output profile. Otherwise, if the antenna gets buried in a wrong place on the board, it can severely impact performance (output radiated power and receive sensitivity) and subsequently battery life.

A number of BLE modules now come integrated with the front-end that combines ceramic chip antenna, low-pass filter and matched balun. A balun performs antenna matching by converting signals between balanced and unbalanced modes. That significantly lowers spurious emissions and harmonics, which in turn, allows wearable designs to lower the overall design footprint.

For instance, Skyworks Solutions’ SKY66111-11 front-end module (FEM) comprises a TX/RX and antenna switch, filtering and amplifier (Figure 6.) You’re most likely to find it alongside Bluetooth radios from Nordic Semiconductor, Dialog Semiconductor, Texas Instruments and others. The front-end module eliminates poor connections with the host Bluetooth ICs and brings down power consumption to as low as 10 mA at +10 dBm.

Diagram of Skyworks Solutions SKY66111-11

Figure 6: The Skyworks Solutions SKY66111-11 is a good example of an RF front-end module (FEM) that you’d add to a SoC to extend range. It looks simple but it’s highly integrated and performs a critical function in the RF domain when it comes to performance.

While the Cypress EZ-BLE module measures 10 x 10 mm, the Skyworks FEM adds only 3.3 x 3.0 mm, even with 20 pins. It operates off 1.8 to 5 V and has a sleep current of under 1 µA. In use, you should be careful to not overdrive the switch by applying too much RF on the input. Instead, start with an input power -20 dBm and work up from there.

Next up, take Silicon Labs’ Blue Gecko BGM113 Bluetooth low-energy module that combines a 2.4 GHz Blue Gecko wireless chipset with a high-efficiency chip antenna, again, to minimize development time and effort. The module comes with a Bluetooth 4.1-compliant software stack, but is software-upgradable to Bluetooth 4.2. On top of that, Silicon Labs offers development tools like Energy Profiler and Packet Trace.

Image of Blue Gecko BGM113 module from Silicon Labs

Figure 7: Blue Gecko BGM113 module from Silicon Labs is a pre-assembled and pre-tested platform that comes with an onboard stack, antenna, and certifications.

The BGM113 comes with its own DC-DC converter and also emphasizes security, with an autonomous hardware crypto accelerator and a true random number generator (TRNG).

Conclusion

It’s clear that when it comes to getting to market quickly and reliably, Bluetooth Smart modules and accompanying front-end modules are an excellent path to success. Designers know it, and suppliers and vendors also know it and are providing the requisite support system and software ecosystems to let innovation happen even faster.  Combined attention to detail on layout, matching components, and software development, you’re in the driving seat when it comes to creative wearable, connected home, and myriad other IoT applications.

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

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Digi-Key's North American Editors