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The role of BLE in wearable IoT designs

Posted: 27 Nov 2014 ?? ?Print Version ?Bookmark and Share

Keywords:MEMS sensors? wearable device? Activity Monitor? Bluetooth Low Energy? BLE?

In such systems, the use of multiple discrete components makes system design more complex in terms of the different parts being electrically compliant with each other and increasing testing complexity. In addition, there is a significant impact on power consumption (due to lack of control over the AFE when it is not in use), BOM cost, and the size of the PCB.

Using PSoc4 and PRoC to build a Bluetooth IoT device
To address these issues, multiple vendors have released devices based on a System-on-Chip (SoC) architecture. These devices not only have a controller but also integrate analogue and digital sub-systems which can be used to implement the basic analogue front end and other digital functionality. One such controller is the PSoC 4 BLE based on Cypress's Programmable System on Chip (PSoC) architecture. This SoC has been designed for the wearables market and includes a 48MHz Cortex M0 CPU, configurable analogue and digital resources, and a built-in BLE PRoC (programmable radio-on-chip) sub-system. Figure 4 shows the architecture of the PSoC 4 BLE controller.

 Activity Monitor

Figure 4: PSoC 4 BLE architecture.

In the analogue front, this device has four unconfigured opamps, two Low Power Comparators, one high speed SAR ADC, and a dedicated capacitive sensing block for enabling advanced touch-based user interfaces. On the digital side, it has two Serial Communication Blocks (SCBs) which can be used to implement I2C/UART/SPI protocols, four 16bit hardware Timer Counter PWMs (TCPWM), and four Universal Digital Block (UDB) for use in implementing digital logic in hardware just like an FPGA.

Figure 5 shows the implementation of the wristband discussed above using an PSoC 4 BLE device.

 Optical heart rate monitor

Figure 5: Optical heart rate monitorwrist bandPSoC 4 BLE.

In this implementation, the PSoC 4 BLE device implements all functionality required using its internal resources. The only components required outside the controller are a few passive components and a transistor for driving the LED, and those required as part of the RF matching network. With this integrated approach, developers have control over the power consumption of the AFE and can disable it when it is not in use, thus reducing the system BOM and PCB size. In addition, using an integrated SoC architecture helps reduce time to market:
???Ready-to-use firmware available for system development
???All the blocks within the same silicon can inter-operate, eliminating the need for developers to have to integrate these components themselves
???Configurable development environment provides flexibility to incorporate last minute changes easily and without major redesign

For some wearables designs, a Cortex-M0 core may not provide sufficient processing power to meet application requirements. For these applications, an M3 core can be used to handle system-related functions while a separate BLE-based SoC like the PSoC 4 BLE controls the Bluetooth interface along with the AFE and digital logic.

Increasing adoption of Bluetooth Smart Ready in devices like smart phones, tablets, and other portable devices has led to Bluetooth Low Energy as a popular choice for the communication protocol in wearable products. To support the power requirements of these applications, various silicon vendors have developed BLE controllers and SoCs supporting BLE. SoCs with BLE helps to reduce system power consumption, BOM, and size of products to make the wearables market even more attractive and promising.

About the authors
Pushek Madaan is currently working with Cypress Semiconductor India Pvt. Ltd. as a Senior Application Engineer. His interests lie in designing embedded system applications in C and assembly languages, working with analogue and digital circuits, developing GUIs in C# and, above all, enjoying adventure sports.

Richa Dham is a Product Apps Manager for the PSD division at Cypress Semiconductor. She has a working experience of 13 years in leading semiconductor companies and holds a Masters degree in Electronics and Communication.

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