rray) A chip that is programmed in the field rather than in a semiconductor facility (see fab
). Containing millions of logic gates, there are a variety of FPGA architectures on the market. Compared to ASIC chips custom-designed from scratch, FPGAs have a lower gate density. See gate array
and Boolean logic
Why Use FPGAs?
When hundreds of thousands of the same type of chip are required, it is generally custom designed (see ASIC
). However, when a limited number are needed, FPGAs are more viable. While an ASIC is being prepared for manufacturing, interim FPGAs can be used to deliver finished products sooner. In addition, FPGAs can be used to test the market before going into full-blown ASIC production.
SRAM, Flash and Antifuse Varieties
The vast majority of FPGAs use static RAM (SRAM) cells, which are volatile. Each time it is powered up, the SRAM-based FPGA must be loaded with its configuration, typically from a flash memory chip. SRAM FPGAs can also be dynamically reconfigured (see adaptive computing
). See static RAM
Flash memory-based FPGAs hold their content without power, but they can be reprogrammed in place. Permanently programmed antifuse-based FPGAs are popular for aerospace design because they are more radiation hardened (rad hard). See PLD
and adaptive computing
An Excellent Resource
Everything you wanted to know about FPGAs and more is in Clive "Max" Maxfield's book. Written in Maxfield's inimitable style, which makes it thoroughly enjoyable, this book is the definitive guide to the subject. (Newnes, 2004)