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 

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.

In the previous blog “IoT Connectivity Technologies” we described in brief various wireless connectivity options available for developing an IoT device. In this blog, we will discuss in detail about the Bluetooth Technology – Physical and higher network layer and its classifications.

Bluetooth technology Introduction

Bluetooth is wireless technology standard using short wavelength Ultra High frequency radio waves in the license free Industrial, Scientific and Medical (ISM) frequency band. Bluetooth is managed by Bluetooth SIG (Special Interest Group) originally formed by five companies Ericsson, Nokia, IBM, Toshiba and Intel. The Bluetooth SIG will publish and update the Bluetooth specifications. The IEEE standardized Bluetooth as IEEE 802.15.1, but no longer maintains the standard. The Bluetooth radio interface enables reliable communications over short distances. It supports multiple channels with different power level and reliable forms of modulation.

Bluetooth Technology Basics

Bluetooth frequencies are located within the 2.4GHz ISM band. The frequency in ISM bands ranges from 2400MHz to 2483.5MHz. There is 1MHz space between each Bluetooth channel starting from 2402MHz and ending at 2480MHz. This can be calculated as 2401 + n, where n ranges from 1 to 79. This type of channel arrangement gives a guard band of 2MHz at the bottom end and 3.5MHz at the top, thus preventing interference. Bluetooth employs a technology called Frequency Hopping Spread Spectrum by which the radio signals are transmitted by rapidly switching the carrier signal among various frequency channels.  In this method the transmitted data is divided into packets and sent on one of 79 designated channels switched randomly at a rate of 1600 times per second. The main drawback of this technique is the occurrence of collision with another wireless device such as Wi-Fi when introduced into the same environment. To avoid this, the Adaptive Frequency hopping technique is introduced. The Adaptive Frequency Hopping technique allows the Bluetooth to adapt the environment by excluding the fixed sources of interference (i.e. bad channels) from the available list of channels. This technique of re-mapping reduces the number of channels to be used by the Bluetooth. The following figure illustrate the collision resulting from the random frequency hopping adapting to the environment

Collision in Random Frequency hopping

Random Frequency Hopping

The following figure illustrate the collision avoided using Adaptive Frequency Hopping

Advantage of Adaptive Frequency hopping

Adaptive Frequency Hopping

The digital data is conveyed using a modulation scheme called Gaussian Frequency Shift Keying. In this technique the bits of the transferred data corresponds to discrete frequency changes in the carrier signal. The binary one is represented by a positive frequency deviation and a binary zero is represented by a negative frequency deviation. With this technique, the basic data rate (BR) of 1 Mbps is achieved. To achieve higher data rates, Bluetooth uses another major class of modulation technique called Phase Shift Keying. Phase Shift Keying is a type of digital modulation scheme by which the digital data is conveyed by modulating the phase of the carrier wave. π/4 Differential Quadrature Phase Shift keying (π/4-DQPSK) and 8-ary Phase Shift Keying (8DPSK) are the different forms of PSK used for enhanced data rate (EDR) capability. By these techniques the Bluetooth can achieve data rate of 2Mbps with π/4-DQPSK and 3Mbps with 8DPSK. The combination of these BR and EDR mode is classified as a “BR/EDR radio”. Further improvement in the Bluetooth data rate up to 24 Mbps is achieved without changing the format of the Bluetooth modulation but by operating cooperatively with an IEEE 802.11g physical layer. Bluetooth Low Energy, a version of Bluetooth technology focused on low energy consumption than higher data rate also operates in the same frequency range of 2.4GHz to 2.4835GHz. Instead of the 79 1MHz channels, BLE has 40 2MHz channels and the data is transmitted using Gaussian Frequency Shift Keying. The bit rate of the BLE is 1Mbps similar to the Basic Rate (BR). With understanding of the physical layer, we will now explore the higher communication layers.

Bluetooth Communication

Bluetooth communication takes place a short range ad hoc network known as Piconet. A Piconet starts with two connected devices and can grow up to eight connected devices. In general, the Bluetooth communication sets one of the Bluetooth devices as a controlling unit (master unit) and other device as a slave unit to follow the master. Each device added to the Piconet will be assigned with a specific time period to transmit the data without colliding or overlapping with the other units. Bluetooth core specification supports connection of two or more Piconets to form a scatternet by which a device of one Piconet either operating as a master or slave can simultaneously play a slave role in the other. Hence communication between more than 8 devices is made possible. The following figure depicts the concept of scatternet,

Bluetooth Communicaton

Concept of Scatternet

Bluetooth Classification

Number of Bluetooth versions is developed to meet the specific requirements of the time with the update of fixing the previous version errors. All the updated versions of Bluetooth support backward compatibility. The following table describes the different versions of Bluetooth available 

Bluetooth Versions

Bluetooth Classifications

Why there is so much hype on BLE?

Bluetooth Classic has faced critical challenges such as fast battery draining and frequent loss of connection which requires frequent pairing. BLE has ability to overcome these challenges and this is the reason why it has become popular in this decade. BLE is more intelligent in managing connections while preserving the battery power. BLE rather maintaining constant bit streams of information sends small chunks of data when required and goes to sleep during the idle periods. Bluetooth/BLE Low Energy comes under the Personal Area Network (PAN) type of connectivity. An IoT device that supports Bluetooth/BLE connectivity can use smart phones as a gateway to the internet. At present, most of the smart phones being launched are Bluetooth Smart Ready, i.e. devices that can communicate with both Bluetooth classic and Bluetooth Low Energy devices. Since smart phones have become the norm, most of the IoT device developments especially in healthcare, home automation segments take place centered around BLE connectivity. IoT devices that supports BLE connectivity tends to be a Bluetooth Smart device that can connect only with the Smart ready devices. Bluetooth smart devices such as smart watches, car key fobs, heart rate monitor are stand-alone, small batter operated that mainly focus on the power consumption as low as possible. With the understanding of the Bluetooth technology and its classifications, we will discuss in detail about the design considerations for developing IoT devices with Bluetooth Low Energy connectivity.

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.