As a continuation of our previous discussion about selection criteria of BLE SoC for building BLE based IoT devices, we will discuss in detail about the most important considerations for BLE RF layout design and antenna selection from various types available. The communication range of a wireless device with a current limited power source depends mainly on the RF layout, antenna design, and enclosure. Increased operating distance can be achieved with the type of antenna chosen together with carefully designed RF layout with few matching components to ensure most of the power from the BLE SoC reaches the antenna. The more power an antenna can transmit from the SoC, the larger the distance it can cover.

RF layout

RF layout involves routing the transmission lines from BLE SoC to antenna with few matching components in between. RF transmission lines acts as a medium that carry RF power from a BLE SoC to antenna, hence they need to be routed with many constraints to get maximum RF power delivery to antenna. There are several types of transmission lines, the two most popular types are:

  1. Microstrip Line
  2. Coplanar wave guide (CPWG)

Both of these are PCB traces differing in how they are constructed for maintaining the 50-ohm characteristic impedance. There are online calculators available which help us to calculate the impedance of the transmission based on our parameter input.

Microstrip Line – This type of transmission line has a signal trace on top of a substrate with a ground plane beneath the substrate. A microstrip line is simple to construct, simulate, and fabricate. The characteristic impedance of a Microstrip line depends on the following factors,

  1. Substrate height (H)
  2. Dielectric constant of the substrate (εr)
  3. Width of the trace (W)
  4. Thickness of the RF trace (T)
Transmission Line type

MicroStrip Line

CPWG – This is similar to the microstrip, but it has a copper pouring on either side of the RF trace with a gap between them. It provides better isolation for RF traces and a better EMI performance and makes it easier to support the grounding of matching components on an RF trace. The characteristic impedance of a CPWG depends on the following factors:

  1. Substrate height (H)
  2. Dielectric constant of the substrate (εr)
  3. Width of the trace (W)
  4. The gap between the trace and the adjacent ground fill (G)
  5. Thickness of the RF trace (T)
Transmission Line type

Coplanar Wave Guide

Nowadays the SoC manufacturers provide reference designs from which we get the guidelines for routing the RF transmission lines and the values (typically capacitance and inductance values) of the matching components. The designer in addition to the routing guidelines must also note the recommended PCB stackups for desired performances, since the impedance of the RF lines will change depending on the PCB layers stackups. In most of the cases, the PCB fabricator may not match the exact stackup as recommended and at these conditions there will be a need for slight changes in the RF trace width, gaps or thickness to ensure the correct impedance value.

Antenna Types

Antenna is a critical part of any wireless devices that transmits and receives electromagnetic radiation in free space. Antenna is nothing but a conductor exposed in space. When the length of a conductor is a certain multiple or ratio of the wavelength of the signal (λ) it behaves like an antenna and radiates the electrical energy into free space in the form of electromagnetic radiation of that frequency to free space. BLE device range requirement, costs and form factor are the main factors to be considered for choosing the antenna. For BLE applications (2.4GHz), most common types of PCB antennas are as follows,

  1. Wire antenna
  2. PCB Trace Antenna
  3. Chip antenna
  • Wire antenna: It is a piece of wire rise from PCB plane and protrudes to free space over a ground plane. Wire antenna produces best performance and RF range due to its dimension and better exposure. They can be in different forms such as straight wire, helix, loop, etc. A through-hole pad is sufficient to solder the wire antenna, thus saving the board dimension and hence low PCB cost.
Type of Wire antenna

Wire Antenna – Straight and Helix Type

  • PCB antenna: This is a copper trace drawn on the PCB. These antennas are inexpensive and easy to design, because they are a part of the PCB and provide good performance. Meandered trace, inverted F-trace is the most popular PCB antenna’s used in many designs. Meandered trace antenna is recommended for applications that require a minimum PCB area and Inverted F antenna is better compared to meandered antenna for radiation, but it requires space higher than meandered antenna. Main drawback of PCB antenna is that, it may require two or more revision to get expected range performance. This can be avoided by using the antenna design application notes and stack up recommended by the chip vendors carefully.
Types of PCB Antennas

PCB Antenna Types

  • Chip antenna: For applications where the PCB size is to be extremely small, chip antenna is a good choice. They are commercially off the shelf antennas that occupy very small PCB area and offers reasonable performance. But the disadvantage of chip antenna is the increased BoM and assembly cost since they are external components that need to be purchased and assembled. Also the chip antennas are very sensitive to RF ground clearance and the manufacturers RF ground clearance recommendations must be followed strictly.
Types of BLE Antenna

Chip Antenna

There are some applications which need antenna’s to be placed on or outside the enclosure for better reach. In such conditions, there are options for providing antenna connectors on board and extending the connection to the external antenna or other mating connector through shielded wire.

Types of external antenna connection

Antenna Connectors

  • U.FL connector: There are miniaturized RF connectors for high frequency signals. The male connectors are generally surface mounted and soldered directly to the PCB. The female connectors are crimped at one end of the shielded wire and the other end may be a PCB antenna or a mating connector such as SMA, MMCX, etc.
Type of antenna connector

U.FL Connectors

  • MMCX connector: These are Micro-Miniature Coaxial connector. They have a lock-snap mechanism which allows 360 degree rotation. It is comparatively better than U.FL in terms of insertion and removal lifetime and has over 10 times that of U.FL connectors. They are also available in surface mount package.
Type of MMCX connectors and cables

MMCX Connector

About Embien

Embien Technologies is a leading provider of embedded design services for the Semi-conductor, Industrial, Consumer and Health Care segments. Embien has successfully executed many projects like based on IoT such as healthcare Wearables, Gateways, and Data Analytics etc. Embien also offers a set of wearable design collections complete with electronics, firmware and Cloud that can be used to shorten product development costs and time significantly.

This blog is the sequel of blog “Bluetooth technology”. In the previous blog “Bluetooth Technology” we discussed in detail about the basics of Bluetooth, how communication takes place and how are they classified. In this blog, we will describe in detail about various parameters and options that are available in each while designing a Bluetooth Low Energy (BLE) based IoT device.

Today we find numerous BLE enabled IoT devices emerging in market with typical applications such as wrist wearable in healthcare, Beacons & tags in retail and many more in home automation, industrial, automotives etc. In all these domain applications, most important criteria’s while designing the device are as follows

  1. Cost
  2. Form factor
  3. Range
  4. Sensor integration
  5. User interface
  6. Power supply

In the following sections we will discuss in detail what are all important for selecting a BLE SoC in building a BLE based IoT devices and multiple options that are available to choose from.


BLE SoC is an integrated chip that includes both the Microcontroller and BLE transceiver. They are also named as wireless microcontrollers. The microcontroller part includes the core, flash memory, RAM and peripherals such as GPIO, I2C, SPI, UART, timers, ADC, etc. BLE part includes RF transceiver compatible with BLE specifications (usually v4.0, v4.1 or v4.2). In addition to BLE, some of the SoC also supports IEEE 802.15.4 standard compliance which is a standard that defines the operation of low-rate wireless personal area networks (LR-WPAN). It is the basis for the ZigBee, MiWi, Thread etc.

Following are the selection criteria for BLE SoC,

  1. Core: Most of the BLE SoC in the market is powered by ARM Cortex core such as Cortex-M0+, Cortex-M3 etc. There are few SoC with 8051 core also. The choice of the core depends on the nature of the application, where M3 will be a better choice for high computational performance, real time applications and M0+ for low cost yet better performance applications.
  2. Memory: All the SoC will have on-chip SRAM and Flash memory, where the size of the flash memory is of more concern which will be loaded with the application, OTA code and BLE stack.  Hence selecting SoC with sufficient flash memory will be advisable. In some cases the application code and BLE stack itself will accommodate the full flash memory and there will be no more memory to support OTA. In such case, there is no other option than going for external EEPROM which adds some cents to dollars in the BoM.
  3. TX/RX Power: For any BLE based wireless application, range will be an important factor. The power of the transceiver is the main factor deciding the range. The transceiver power will be specified in dBm. More the dBm, better is the range. The range factor will also depend on the type of antenna used in the design and the same will be discussed in the upcoming section.
  4. Power: Mostimportantof all criteria is the power consumption. Both MCU and RF transceiver power consumption should be taken into account while selecting the SoC. BLE TX/RX and core/peripheral power are the major power consuming sections. During selection of SoC, the most important points to be taken in to account with respect to power consumption is as follows
    1. Option for controlling the TX/RX power: Power consumption due to TX/RX can be controlled by varying the TX/RX power. Less the TX/RX power, lower is the power consumption but it has considerable impacts on range as well.
    2. Option for multiple low power operating modes: Low power modes are the operating modes where some of the peripherals, clocks, etc in the MCU are disabled for low power operation. By selecting appropriate low power mode based to the application, the power consumption can be reduced.
  5. Peripherals: The core section of the BLE SoC includes multiple peripherals such as I2C, SPI, I2S, GPIOs, Timers, UART, ADCs, etc. BLE SoC under consideration should have multiple options to support external interfaces such as sensors, actuators, displays, audio visual indications, etc. For example, a fitness tracker is a BLE based wearable device that requires multiple digital sensors to acquire the real time data from the body such as MEMS sensors like accelerometer, gyroscope, magnetometer etc and such sensors provide digital data that can be acquired by interfacing with the BLE SoC through I2C and SPI. For analog sensor based applications the analog signals from the analog front end circuits can be acquired using the high resolution ADC available in the SoC. Some devices may require audio notifications such as buzzers which can be driven by the PWM signals available in the timers.
  1. Package: BLE SoC’s are available in SMD packages such as QFN and BGA. Among them QFN package is most common. The soldering process recommended for both packages by the chip vendors will be machine soldering which adds extra assembly costs.
  2. Operating conditions: The operating grade is a very important during the selection of SoC. The designed must careful in selecting the domain where the device is going to be used such as industrial, automotive, commercial or medical. For example, a commercial grade SoC is not suitable for automotive grade applications.
  3. Availability of the evaluation platforms, source code and stack ups should be verified which can support rapid product development.

Following are the popular BLE SoC part numbers available in the market from various semiconductor manufacturers,

      • Texas Instruments: CC2540, CC2541, CC2640, CC2650
      • NXP Semiconductors: KW30Z/31Z, KW40Z/41Z
      • Renesas: RL78/G1D
      • Nordic: nRF52840, nRF52832, nRF51822, nRF51824, nRF51422
      • STMicroelectronics: BlueNRG-1

In addition to the SoC, for a device design that require only BLE connectivity, there are various modules available. These modules will include the SoC with inbuilt chip or PCB antenna. All the necessary peripherals will be brought to the expansion connectors and the power can be fed through the same. The communication with the BLE module will be an I2C/SPI/UART interface. The main advantage of those BLE modules is that, they are fully tested and compliance certified.

About Embien

Embien Technologies is a leading provider of embedded design services for the Semi-conductor, Industrial, Consumer and Health Care segments. Embien has successfully executed many projects like based on IoT such as healthcare Wearables, Gateways, and Data Analytics etc. Embien also offers a set of wearable design collections complete with electronics, firmware and Cloud that can be used to shorten product development costs and time significantly.

IoT – Internet of Things generally described as a system of interrelated devices with unique identifiers armed with the ability to transfer data over a network without requiring human or computer interactions. IoT has good market potential in Home automation, healthcare, automotive and industrial sectors. There are many use cases in these market segments and in design engineer point of view it is easy to define a use case, but very hard to build and realize the system. To realize a thing in IoT we need five components such as sensors, connectivity, processor, power supply and cloud. At present there are many semiconductor manufacturers provide best in class solutions for these components. Among them, connectivity is the most critical component to select.
There are plenty of connectivity options available and selecting the best connectivity for an IoT device requires a concern on the following factors,
1. The range of the communication
2. Data throughput
3. Power consumption
4. Location and Physical size of the embedded devices

Further in this blog we will discuss about the various wireless connectivity options available for developing an IoT device.

Wireless Connectivity options
At present there are many choices of wireless connectivity options available for electronics engineers to design an IoT system. Most commonly used wireless connectivity’s are as follows,

ZigBee is a wireless technology traditionally found in home automation. ZigBee profile is based on IEEE 802.15.4 standard operating at 2.4GHz mainly focusing on applications that require infrequent data transfers at low data rates around 250Kbps within a physical range of 10m to 20m. ZigBee also operates at unlicensed bands such as 915 MHz in USA and Australia, 784 MHz in China and 868 MHz in Europe.
The main advantage of ZigBee protocol is the ability to support mesh networking of up to 65,000 nodes. In mesh network, nodes are interconnected with other nodes such that multiple pathways connect each node. Connections between the nodes are updated dynamically and optimized through a sophisticated built-in mesh routing table.
ZigBee PRO is the advanced version of ZigBee offering significant advantages in many areas of operations such as scalability of large networks, ease of commissioning, network resilience and security. ZigBee/ZigBee PRO can be a good choice for many IoT devices connectivity in medical and naturally home automation segments.
ZigBee modules are cheaply available in markets for few cents and can be easily integrated to any device via UART, SPI interfaces. The module can run in simple battery power supply for a year sending periodic sensor data’s. Many semiconductors manufacturers such as NXP, Texas Instruments, STMicroelectronics, Microchip, Atmel, etc provide ZigBee IC’s most commonly in QFN packages with reference design very much useful for prototyping before mass production. Based on the available real estate either modules or IC’s can be chosen for design.

Bluetooth is a short range technology that is already available in most of the consumer electronics devices. Bluetooth has classic and low energy versions different from each other in many factors such as range, data rate and power consumption. The nominal frequency of Bluetooth is 2.4 GHz for both classic and low energy versions.
Bluetooth Low Energy (BLE) is considered to be the most common connectivity option particularly for wearable products connecting to smart phones. It offers almost similar range to Bluetooth at reduced power consumption. Reduced power consumption is achieved by sacrificing the data rates. Traditional Bluetooth classic supports high data rate of 1-3 Mbps whereas BLE supports maximum of 1Mbps. There are plenty of semiconductor manufacturers such as NXP, Renesas, TI, STM, Nordic, etc provide BLE transceiver IC’s supporting multiple RF standards such as ZigBee, ZigBee RF4CE, 6LoWPAN, etc selectable with the software stack running on top of it. Also the wireless IC includes MCU inbuilt by which it can act as a standalone IC with rich peripheral support such as UART, SPI, I2C, ADC, etc controlling the external sensors and monitoring modules.

Z-Wave, supported by Z-Wave Alliance, is another low power RF communication technology similar to ZigBee operating in sub GHz band primarily designed for home automation. It is optimized for low latency communication of small data packets with data rates up to 100Kbits per second with communication range up to 30m. It is immune to interferences from WiFi and other wireless technologies in 2.4 GHz range such as Bluetooth and ZigBee.
Z-Wave communication technology enables control of up to 232 devices. Its simple protocol enables faster and simpler development. The only drawback is that there is only one manufacturer named Sigma Designs providing Z-Wave chips when compared to multiple sources for other wireless technologies such as ZigBee, BLE, etc.

Wi-Fi is renowned long range communication technology which strikes when the bandwidth requirements of a particular application is big. Wi-Fi, with its array of 802.11 variants, offers fast data rates and ability to handle high quantities of data. At present the most common Wi-Fi standard used in home and other domain is 802.11n operating on both 2.4GHz and 5 GHZ band. It offers higher throughput ranging from 11-600Mbps sufficient for file transfers but may be too power-consuming for many IoT applications. The distance may range up to 100m.
New emerging 802.11ac uses the 2.5 – 5 GHz band with a combined bandwidth of 5.3 Gbps. A key challenge for the IoT developers is the power requirements. Wi-Fi communication requires far more power than other technologies. Hence Wi-Fi option is limited to the devices where it may be possible to deliver wired power. For more power limited budgets it may be possible by adding techniques such as sending data at pre-determined intervals and then go to sleep in order to preserve the battery lives.

Cellular communication technologies such as GPRS, EDGE, 3G, 4G are most popular on movable IoT devices such as cars, ambulance, trains etc. They have advantage of coverage and availability in large areas. They operate in frequencies ranging from 900 MHz in GSM standard to 2100 MHz in 4G mode. Most cellular based IoT devices aim to use 3G and Long Term Evolution (LTE) 4G networks. 3G and LTE both provide excellent bandwidth throughputs. LTE provides almost 300Mbits/second but the major problem is the recurring costs of the cellular connectivity since cellular operation requires plans from the service providers.
Apart from the 3G/4G communication there are low cost options such as GPRS/EDGE (2G) with low data rates up to 170 Kbps for GPRS and 384 Kbps for EGDE. The power consumption of cellular communication will be too high for many applications and this can be reduced by switching the modem off when not in use and ON while short burst of data is needed. The range for cellular communication may vary between 35 Km for GSM and 200 Km for 3G.

Sigfox is a long range communication technology which in terms of range lies between Wi-Fi and cellular. It operates in 900MHz frequency band, which does not require licenses to transmit the data to and from the connected devices. Sigfox will be a better connectivity option when an IoT application when running on small batteries where Wi-Fi range will be too short and cellular becomes too expensive. Sigfox is designed to handle only low data transfer rate of 10 to 1000 bits per second. Its power consumption is only 50 microwatts which is very low compared to 5000 microwatts for cellular communication.
Sigfox offers robust and power efficient communication that can be well suited for battery operated devices for various IoT/M2M applications such as smart meters, patient monitors, street lighting, security devices, etc. The range of the communication is about 30-50 km in rural environments and 3-10 km for urban environments. There are many silicon vendors such as Silicon labs, TI, Atmel, ON semiconductors provide hardware solutions in transceiver IC, SoC and in module form.

Another alternate option similar to Sigfox is Nuel which operates in sub 1GHz band capable of leveraging very small slices of TV white space spectrum to deliver high coverage, scalability, low power and low cost wireless networks for IoT. Nuel is based on a communication technology called Weightless, a new wide area networking technology designed specifically for the IoT, achieving coverage, battery life, low module cost and efficiency better than today’s GPRS, 3G and LTE WAN solutions.
Nuel transfers data at rate of few bits per second up to 100 kbps with low power consumption as little as 20 to 30 mA with range extends up to 10 Km.
At present Iceni chip by Neul is the only chip available for small footprint M2M applications and cost effective broadband Customer-Premises Equipment (CPE) to communicate on NuelNET networks. It can operate over the entire TV white space frequency range from 470 MHz to 790 MHz.

LoRA is a Low Power Wide Area Network (LPWAN) intended for wireless battery operated IoT applications. LoRA is targeted for the IoT applications which require secure bi-directional communication, mobility and localization services. It provides seamless interoperability between IoT devices without the need of local installations thus giving full freedom to the developer enabling the IoT.
Communication between end-devices and gateways is spread out on different frequency channels and data rates. Data rates ranges from 0.3 kbps to 50 kbps. It minimizes the power consumption by managing the data rate and RF output of each end-device individually by using a special scheme called Adaptive Data Rate (ADR). The physical range of LoRA network is 2-5 km for urban environment and 15 km for suburban environment. Lairdtech, Microchip, LinkLabs are some of the providers of LoRA modules.

Apart from the above IoT connectivity technologies there are other low power wireless options that compete for the same space such as 6LowPAN, MiWi, ANT operating in 2.4 MHz frequency band. Amongst them ANT is the popular wireless system architecture. ANT is well suited for wireless sensor networks and requires minimal memory for the stack and can run in a coin cell battery for years typically for low data rate applications. In addition to ANT providing the basic functionality, ANT+ protocol supports interoperability between ANT system nodes. ANT/ANT+ is widely used for Personal Area Network applications in fitness, wellness, sports and home health. The maximum data rate of ANT is 20kbps to 60kbps with average current consumption for low data rates less than 60 micro amps and can range up to 30 meter distance. ANT wireless, Dynastream innovations Inc, Nordic semiconductor offers modules with embedded ANT protocol designed to speed development of ANT/ANT+ applications.

Choice of Communication technology
With so many connectivity technologies, it may seem the designer is spoilt for choices. But in reality most of these are suitable for specific use cases. Baring a few technologies, each of them has unique feature that will suit particular application – long vs. short distance, low vs. high data rate, power hungry vs. low power operation, uni-directional vs. bi-directional, small form factor vs larger foot print etc. It is important to take in to account all these considerations when selecting the communication technology.
In the fore coming series of blogs, we will discuss in detail about these IoT Connectivity technologies in detail beginning with Bluetooth, their classifications and design considerations.

About Embien
Embien Technologies is a leading provider of embedded design services for the Semi-conductor, Industrial, Consumer and Health Care segments. Embien has successfully executed many projects based on IoT such as healthcare Wearables, Gateways, and Data Analytics etc. Embien also offers a set of wearable design collections complete with electronics, firmware and Cloud that can be used to shorten product development costs and time significantly.