This article focuses on the implementation of ZigBee products, and whether to make or buy the hardware platform. It discusses the pros and cons of designing from scratch using RFIC versus designing with ready-made modules. It shows some typical module implementations and summarises some performance data for such module solutions available today.
ZigBee emerged as a technology several years ago, and both the specification and the available hardware and software have matured greatly over the past years. The number of companies offering hardware or software stacks for ZigBee has also increased rapidly in the same period, making it a complex task for an engineer to select a hardware platform and software stack.
ZigBee hardware cost
When choosing a ZigBee platform, one of the first concerns will be to select a cost optimum solution. Many believe in the myth that a single-chip solution will always be the lowest cost solution, but for most applications this is not true. When starting to calculate the life cycle cost of a ZigBee hardware platform one will see that the 'single-chip' is only a fraction of the total cost.
Even so-called single-chip solutions require several handfuls of carefully chosen passive components, critically specified crystals, antenna including its matching, shielding can etc, in addition to a very careful layout on a high-frequency board or substrate to give the promised performance. Coming to development of the ZigBee-application firmware, the benefits of developing and debugging code on a proven and reliable hardware platform identical to the final hardware solution is obvious.
The development cost of making a ZigBee platform is often underestimated. This includes RF design, schematics, layout, test development, documentation, test, approval testing and possible re-runs. For mid and low volumes, this cost amortised over the end product quantity will often become a large percentage of the total cost. The RF test instrumentation required to verify and qualify an RF design at 2,45 GHz, only a few general electronics development labs have on their test bench or in their investment budget. Signal generators, spectrum analysers and network analysers can add up to hundreds of thousands of rands. And transferring such a design to manufacturing sites and developing automatic test systems that can handle radio frequency is another challenge solved by a modular approach.
For OEMs the modular approach not only provides benefits in terms of lower development cost and testing cost, but also on component sourcing and logistics. The complexity of sourcing numerous critical components from different vendors with unpredictable lead-times is reduced to sourcing a single component from a source that can make the best deals with the IC and component suppliers.
Module advantages
When buying an off-the-shelf module, developers can not only reduce the design cost, but also reduce the risk of introducing ZigBee into a product. By using a module, the entry fee into the ZigBee sphere will be reduced to a small percentage. Also, a large development investment might be wasted if new and better RF chips are available some months later. There will always be modules available with the latest ZigBee chips and the cost of replacing a module will be small compared to making a new RF design. Another part of the risk is the size of the solution and the radio performance. Modules available today, like the RC2300AT from Radiocrafts, are very small in size with proven performance over temperature and different antenna loading.
A short time to market for new products is always a success criterion. The time it takes to get a ZigBee solution specified, designed, qualified and geared up for mass production should not be underestimated. RF is tricky and simply 'getting the design to work' is not the same as having a good design with regards to yield and mass production. Using a module will eliminate the RF design effort from the timeline and the time to market will be significantly reduced.
When designing their own chip-based solution, how can the designer make it easy to re-use it in other products? RF design is challenging and every time a design is moved to a new PC board, with different properties, the RF design has to be done all over again, with tuning and impedance matching. The answer is of course to make their own module where the RF design can stay fixed when moving the design to new products. In this way, developers can end up spending lots of money and time on making something that is available off-the-shelf today.
Regulations
To get a clear picture of regulation issues such as maximum allowed spurious emission levels, maximum output power etc, adds even more headache to the design work. A pre-certified modular solution saves the integrator from extensive compliance testing with respect to the RF spectrum, provided that the module manufacturers' advice is followed.
Comparing with the more mature Bluetooth technology, the vast majority of Bluetooth solutions sold in products today are module based. After a slow start where several companies, mostly in the computer field, wanted to integrate chipset solutions, most of them have now ended up with more cost efficient module solutions.
As a module manufacturer, Radiocrafts has been working closely with Texas Instruments, a leading provider of RFICs for IEEE 802.15.4 (the physical layer) and ZigBee stack implementations. Radiocrafts was one of the first companies to launch a very compact ZigBee-based module (RC2200) in 2004, and later released the RC2300 platform. The RC2300AT measures only 12,7 x 25,4 x 2,5 mm, the outdoor range has been measured to more than 150 metres with the integrated chip-antenna and the current consumption at power down is as low as 0,9 μA.
For more information contact Kevin Jurrius, Components & System Design, +27 (0)11 979 4274, [email protected], www.csdcomponents.co.za
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