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03-16-2016 07:16 AM
When trying to save money by using a wireless system-on-a-chip (SoC), two options present themselves:
First, using a wireless SoC on the product printed circuit board (PCB). This is small and cheaper than a wireless module, but designing with it may be costly.
The second option involves using a wireless module with option 1's SoC inside. A majority of the design is already done including a fully-characterized PCB with RF optimization and antenna layout, shielding, timing components (crystals), external bill of materials (BOM), regulatory approvals, and standards certifications. But they are generally more expensive and larger than the SoC.
So, which one is the easier and more cost effective option? The answer changes depending on the product, the designer, time to market, and so on. Further, the best option changes with volume.
The modules cost more than their SoC equivalent, but companies use them widely Why? And what’s the breakeven volume for when to change from one option to the other?
Fig: High-level Cost Comparison of Wireless Module versus Wireless SoC
With certain assumptions, the annual breakeven volume falls bewtween 200K and 300K. While this may seem high, a breakeven on this is quite complicated. This is because modules remove unknown risks of designing with a wireless SoC, and unknown risks are, by definition, hard to quantify in dollars or weeks.
Hidden Cost #1: RF Engineers and Design
An RF engineer is required for an SoC design or, at a minimum, access to RF engineering expertise from the SoC supplier. RF engineers can be expensive and RF application notes are not always as easy as 1,2,3 since recommendations provided by SoC suppliers are hard to implement.
Hidden Cost #2: Lab Equipment and Facilities
RF engineering requires special equipment, software, and facilities to debug RF designs.
Hidden Cost #3: PCB Layout and Antenna Selection
Antenna application notes are often complex. An example of the nuances involved can be found in AN930, the Silicon Labs Blue Gecko Bluetooth Smart (BLE) 2.4GHz antenna application layout guidelines.
Fig: Image from AN930 on Blue Gecko Bluetooth Smart antenna matching
While it is designed to provide detailed RF help so customers can get close to a “perfect” layout on their early tries, there is still a good chance that the PCB will need tweaks to optimize antenna performance.
Hidden Cost #4: Regulatory Approvals and Wireless Standard Certifications
Products operating in the unlicensed frequency bands require regulatory “type approvals", and many also require a wireless standard certification like Bluetooth. Some wireless modules come pre-certified for type approval and wireless standards and adding them to a product brings these approvals and certifications along. Wireless SoCs do not come with such ceritifcations or approvals and the regulatory testing costs and type approvals vary by country.
Hidden Cost #5: Reduced Product Revenue from TTM Delays
One of the biggest hidden “costs” in using a wireless SoC versus a module is the risk of missing the market window due to incremental time to design it in, test it, debug it, type-approve it, and certify it. This delay can range from a few weeks to a few months. Removal of the risk of time to market is a key reason why some very large volume companies still use modules even though they cost more.
Hidden Cost #6: Supply Management and Assurance
For companies with low-volume production runs, modules can mitigate supply risk. A module supplier bargains for SoC supply in their modules on behalf of its entire customer base. Therefore, they consolidate demand and insulate small companies from potential line-down if there is a shortage of SoCs. Sourcing a single module is also simpler than sourcing all the components to put an SoC on the board.