Adding Wireless Functionality In Product Design
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by: Guest
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Everyone has come to expect wireless functionality that is simple to use and reliable, on all manner of widgets. There are a number of international standards such as Bluetooth, WiFi and Zigbee that are aimed at providing specific wireless features – some compete and others complement. Whether it is wireless headphones using Bluetooth, or Wireless meter reading using Zigbee the design criteria are usually very similar. Many companies have bought the marketing line that modern wireless solutions are simple and low risk to implement – leaving product developments in a mess when the development team get out of their depth, and are unable to deliver what was promised.
Products have been designed where the antenna was within the RFI shielding, or no thought has been put into antenna placement requiring complete and expensive redesigns. Wireless is not easy and requires attention to a number of details to be successful. The key considerations are laid out with a view to providing an overview of the process.
Firstly – all Wireless transmitters sold in Europe are required to be “Type Approved” whether licensed or unlicensed. Licensed radios use specific frequencies that are allocated to a company for their use/resale an example would be GSM phones where operators buy the right to use spectrum, whereas unlicensed bands (also known as Industrial, Scientific and Medical ISM bands) are allocated on the basis that due to their low power, and lack of interference potential no formal allocation is given, an example of an unlicensed radio is Bluetooth. Type approval involves a formal test against the standard by a “notified body”, along with the normal CE testing for product safety and EMC. Consortiums like Bluetooth may also require testing against their standard before allowing a company to place their logo on a product.
Adding a radio impacts the whole product – this needs to be understood from the outset, antenna placement is fundamental to performance, the industrial design team need to understand what is required in order to provide a workable solution. The normal EMC emissions limits required are well in excess of the noise levels that will stop a radio receiver working correctly, so the electronics including the power supply will need to be designed with the radio in mind. A frequently overlooked effect of adding wireless functionality is the impact on battery life, radios are power hungry and can account for most of the power budget.
RF PCB design is a specialist skill where track widths and gaps are required to conform to a strict set of rules in order to maintain a controlled impedance. Getting the impedance of the board wrong, can affect the design with a range of effects from reduced performance through to the design not working at all. The component layout and ground and power planes need to consider the high frequency effects, in order to achieve optimal performance. The layout is fundamental to RF design – so much so that special CAD tools exist to enable RF designers to simulate and assess the impact of the layout.
Finally radios need testing both during development and in production, equipment can be expensive and the testing needs to be carefully considered prior to committing adding the wireless functionality to the product.
The days where RF was considered a form of “black magic” are no longer relevant where single chip RF solutions are available. Ensuring that you are equipped with suitable tools (test equipment and RF CAD tools), it is possible to ensure that the risks involved in RF development are reduced. And as always in engineering – practice makes perfect, but if timescales or risks are high then consider using an RF professional.
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