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Small Bluetooth module fits portable designs

The Internet of Things (IoT) market is growing at a rapid pace.  Analysts estimate over 20B devices will be connected to the Internet by 2020.  Many IoT devices connect to the Internet through a gateway that provides Internet Protocol message routing over the Internet for communication with remote IP devices or the Internet Cloud. These IoT devices can also connect to smart phones and tablets which provide Internet communication via LTE wireless phone networks.  Bluetooth BLE 4.x connectivity in our phones and tablets is creating the demand to drop-in BLE connectivity into wearables, portables and upgradeable appliances to enable IoT functionality.  Designers are challenged by smaller size designs that also must meet consumers’ wireless performance and range expectations.

 In this article we will discuss design considerations for designing our adding BLE wireless communications to small form-factor, portable devices to enable IoT connectivity.

This article will discuss these topics:

  • Size constraints and limits on range
  • Technology Innovations
  • Antenna issues
  • External Antennas
  • Modules
  • Silabs SiP Modules









Size Challenges

Size expectation is one of the most frequently asked questions when considering IoT devices.  Two major issues are packaging an IoT MCU and radio transmitter in a shrinking PCB space and co-packaging of the embedded MCU and Radio Transmitter in a system-on-chip (SoC) encapsulated device. Striking the balance between embedded design size and maintaining radio connectivity performance. Density of the transistor is increasing though innovation in antenna design is lagging.

Size constraints for wireless connected devices creates design complexity, such as the following:

  • Limited wireless design skills, resources, and experience
  • High development and certification costs
  • Short product development window

Wireless Technology Innovations

In 2000, the industry was called Machine-to-Machine (M2M) with wireless connectivity GPRS modems and Sub Gigahertz radios providing state-of-the-art communication in footprints equivalent to our current mobile phones. Advancement in semiconductor gate count has enabled the development of a single monolithic chip containing the MCU and RF Transmitter in an integrated system-on-chip (SoC).  The small size SoC enables the smaller IoT design, however, the complexity of the RF transmitter and antenna matching design requires RF design engineering expertise to deliver the meet the end user’s wireless performance and range demands.

In 2016, IoT component design architectures are shifting to wireless SoCs to save space and reduce component count.  The integration and small footprint SoCs haven’t solved the physics and design complexities of the antenna design, RF transmission, and RF regulatory certification costs. 

SoC integration enables the development of small footprint wireless modules with integrated antennas and regulatory certification.  A module design architecture that fits the size constraint can offer reduced design risk and faster time-to-market.  Figure 1 shows dimension scale modules with integrated antennas.  Designers should consider module venders that offer a software compatible SoC chip solution to meet future size challenged IoT designs.

Figure 1.  Wireless Modules dimension scale

Antenna issues

Antenna design innovation and size is evolving but not at the exponential integration rate of the semiconductor transistor count and mixed-signal RF integration.  Analog RF antenna matching becomes more difficult in constrained space designs. The antenna designer must take size and RF efficiency into account.  Antenna detuning issues exists across designs that have different enclosures but the same antenna architecture.  IoT Designers must resolve the antenna questions, such as:

  • How much space should it take?
  • What kind of antenna should be used?
  • Can a module with an integrated antenna fit?

PCB Trace Antennas.  
Most IoT designs use PCB trace antenna.  The most common PCB antenna is the inverted-F, shown in Figure 2, due to the low bill of material (BoM) costs. The low cost trade-offs are space and tuning. These printed PCB antennas take up significant PCB footprint space, typically 25mm to 50mm.  PCB antennas are also sensitive to detuning related to housing effects, which will require RF tuning design expertise.

Figure 2.  PCB Antenna

Chip Antennas. The antenna manufactures offer “chip antennas” which offer the benefits of small footprint size and reduced design complexity.   There are two types of “chip” antennas: and Coupled to GND. 

Not Coupled to GND . Antennas not coupled to the GND plane and will require a relatively large clearance area (or that is free from the ground, traces, and components). Examples of such antennas are monopole and inverted –F type antennas. 

Coupled to GND.  Antennas that are coupled to the GND plane and require either a relatively small clearance area beneath the antenna or don’t require clearance area at all. 

Both of these antenna types have space requirements on either clearance area, ground plane, and PCB size. The required space for the RF part of an IoT design should also include the needed clearance area because no components or traces can be placed here. The RF designers calculating design size and estimating the IoT device dimensions consider the PCB dimensions for the antenna, the required clearance areas, as well as the separation distances from the antenna with the edge of the housing.  

Small IoT designs the size of a coin-cell battery will have antenna efficiency trade-offs the compromise RF performance and range. Devices smaller than 10mm x 10mm operating in the 2.4GHz band, provide Bluetooth users connectivity of approximately 10 meters line-of-sight range with a mobile phone.  With larger the dimensions are 20mm x 10mm, the RF efficiency increases practical range 2X/4X to 20–40 meters with a mobile phone depending on the conditions.  An IoT design at 40mm x 40mm will allow maximum Bluetooth 4.2 range around 60 up to 400 meters in line of sight distance.

External Antennas

Wireless modules provide on-board antennas.  Some may offer U.Fl connectors for external antenna use.  Module vendors see a high majority that deploy with the on-board antenna.  The external antenna others benefit in IoT devices with metal case enclosure.  These external antenna designs are burdened by the antenna cost and the additional components in the antenna matching circuit.

SiP module in portable designs

Silicon Labs has combined its low-energy IoT SoC with Bluegiga antenna design layout skills to create a SiP module with the benefits of a SoC module combined with an ultra-small footprint. Figure 3 shows the total design footprint size including the antenna clearance area, approximately 50mm x 50mm.

Figure 3.  Bluetooth SiP Module antenna clearance

The BGM121 Bluetooth SiP modules are ideal for wearables and home automation devices that require a slim, small form-factor. The BGM12x SiP modules deliver a small footprint Bluetooth low energy solution (6.5 x 6.5 mm). The BGM12x has an ARM® Cortex™- M4F core MCU, plenty of flash and RAM, an integrated antenna, and an ultra-small clearance area of 5.0 mm x 3.0 mm to enable high-performance applications. The SiP module also integrates all required passive components, leaving the designer free from all RF-related design issues, assuming the designer follows Silicon Labs design recommendations for layout clearance area, module positioning, and distance from PCB edges.  The BGM module offers the fastest path to low-power wireless connectivity for the Internet of Things.

Silicon Labs Wireless Modules


Silicon Labs BGM121 / BGM123 Bluetooth SiP Module

  • Ultra-small BLE module
  • 5 x 6.5 x 1.4mm footprint
  • Includes antenna, matching network, and crystal
  • 51mm2 PCB area requirement including antenna clearance

Superior RF Performance

  • +3/+8 dBM TX options
  • -90 dBm RX sensitivity

Preprogrammed with latest BLE stack software (V2.0)

  • 0 mA RX current
  • 2 mA 0dBm TX current
  • 5 uA EM2 sleep current


For more information:

EFR32BG Blue Gecko SoC

Silicon Labs BGM Bluetooth modules

BGM12x module

Development kit link:  SLWSTK6101C 

BGM121 videos on YouTube:


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