Phones don't use FPGAs. They use SoCs or ASICs. An FPGA is basically a way to make something with silicon which requires no low-level chip design work and no special chip fabrication on the part of the client. An FPGA will be used in the server side or the backend. For example in telecoms switches.
FPGAs simply use too much power and are too large to use in something like a phone. At best you put them on a workstation. Quite often you initially prototype hardware on an FPGA and later design an ASIC with the same functionality if you have the resources for it. It is basically a programmable logic device which can be reconfigured to do the task you want. But like any programmable device it will be slower and use more power than doing a custom design specifically tailored for the application. It also needs to be programmed before being shipped to the final client while an ASIC can simply be socketed in and require no programming post board manufacture.
In some cases devices will ship with FPGAs instead of ASICs because the specific application is too niche to justify the cost of designing an ASIC. i.e. you are going to manufacture only a limited amount of units (from like dozens to thousands of units rather than millions).
If you are going to manufacture hundreds of thousands or more devices, like a smartphone, you are better off designing an ASIC. The fabrication cost of the ASIC might be like $5 USD per chip and the FPGA might cost like $50 USD per chip or more and be larger, slower, and use more power. The problem with an ASIC is that you will have higher design costs and need to manufacture the mask sets to be able to do photo-lithography for the ASIC. So there is a huge initial cost in an ASIC which in a small production run won't ever be recouped.
FPGAs simply use too much power and are too large to use in something like a phone. At best you put them on a workstation. Quite often you initially prototype hardware on an FPGA and later design an ASIC with the same functionality if you have the resources for it. It is basically a programmable logic device which can be reconfigured to do the task you want. But like any programmable device it will be slower and use more power than doing a custom design specifically tailored for the application. It also needs to be programmed before being shipped to the final client while an ASIC can simply be socketed in and require no programming post board manufacture.
In some cases devices will ship with FPGAs instead of ASICs because the specific application is too niche to justify the cost of designing an ASIC. i.e. you are going to manufacture only a limited amount of units (from like dozens to thousands of units rather than millions).
If you are going to manufacture hundreds of thousands or more devices, like a smartphone, you are better off designing an ASIC. The fabrication cost of the ASIC might be like $5 USD per chip and the FPGA might cost like $50 USD per chip or more and be larger, slower, and use more power. The problem with an ASIC is that you will have higher design costs and need to manufacture the mask sets to be able to do photo-lithography for the ASIC. So there is a huge initial cost in an ASIC which in a small production run won't ever be recouped.
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