CHAPTER 1 ■ WHAT IS AN FPGA AND WHAT CAN IT DO?
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FPGAs allow designers to modify their designs very late in the design cycle —even after the end product
has been manufactured and deployed in the field. Sound familiar? It should sound a lot like Windows updates
or Android/Apple phone software updates. That's one of the most powerful and compelling features of
an FPGA but please don’t treat FPGA design as a software programming exercise for a microcontroller or
processor. An FPGA is not a processor with software. It is an amazing device that allows the average person to
create his or her very own digital circuit. You are designing a hardware digital circuit when you are creating an
FPGA design. You are going to use a hardware description language (which, incidentally, is used by Intel CPU
chip designers too) to design your FPGA. This is a very important concept. We will provide more details when
we are putting together some example designs in the later chapters. In the following sections we’ll provide a
little bit more detail about field-programmable, gates, and arrays and what they can do.
1.1 Field-Programmable
The most valuable FPGA feature is that the end user can program or configure it within seconds. This means
that the end user can change the hardware design in the FPGA chip quickly and at will. For example, the
FPGA can change from temperature sensor to LED (light-emitting diode) driver within a few seconds. This
means that FPGAs are useful for rapid product development and prototyping. This field-programmable
magic is done by a configuration file, often called a bit file which is created by a designer (you). Once loaded,
the FPGA will behave like the digital circuit you designed!
1.1.1 Configuration Technology
Table1-1 lists the three types of configuration technologies: static random access memory (SRAM), flash
memory, and antifuse.
Table 1-1. Different Types of Configuration Technology
SRAM Flash Antifuse
Achronix YES -- --
Altera YES -- --
Lattice YES -- --
Microsemi -- YES YES
Xilinx YES -- --
Most of the FPGA vendors are using SRAM technology. It is fast and small, and it offers unlimited
reprogrammability. One of the drawbacks though is that the FPGA needs time to reload the entire design
into SRAM every time you power up the FPGA. This approach also takes more power.
Flash and antifuse technologies are non-volatile (meaning that they can retain data even if the power is
turned off) so that they provide the benefit of “instant on” without needing to reload the FPGA bit file every
time we power up the FPGA or the system. They also draw less power than the SRAM approach.
Antifuse technology can only be programmed once and can’t match the performance of SRAM
technology. The only reasons to use an antifuse technology FPGA today is due to its super high reliability
and security.
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