Why Use an FPGA?
Benefits of Using an FPGA in Your Design
There are many reasons why Field Programmable Gate Arrays (FPGAs) are popular:
- Density and flexibilty
- Supports a wide range of applications
- Offers higher density than Complex Programmable Logic Devices (CPLDs)
- More flexible architecture
- More embedded features such as memory, Programmable Logic Devices (PLDs), and even processors
- Reprogrammability
- Minimizes the risk in the product development cycle. An FPGA design could be implemented in a matter of days or a few weeks, and it can be modified quickly to correct bugs found in the debug cycle. Reprogrammability also allows you to update fielded products to add features or correct bugs that were found after the product was released.
You have different options available for implementing a digital design. Some options offer more flexibility, while others offer higher performance.
Microprocessor Advantages
Using a microprocessor or microcontroller to implement a design provides you with a great deal of flexibility. A microprocessor contains all the functions of the central processing unit in a single chip. A microcontroller can be considered a simple computer with all the necessary peripherals, such as memory and timers, in a single chip. Microprocessors and microcontrollers execute programs based on the processor's instruction set. A general-purpose processor is flexible because you can write new code to add functionality or correct bugs. However, the microprocessor architecture might not be tuned to your specific application. For example, it might take many clock cycles to perform a multiplication operation on two numbers. Compared to an FPGA, a general-purpose processor has faster floating-point computations, a lower per-unit cost than an FPGA, and may be more power-efficient than an FPGA.
ASIC Advantages
An Application-Specific Integrated Circuit (ASIC) is a microchip designed for a specific application. ASICs are generally implemented as gate arrays, standard cells, or full custom designs. In gate arrays, the transistors and other active devices are predefined. The final metallization layer connects the transistors to implement the specific design. In standard cell designs, the mask is a custom design, but the silicon is made up of library components. This gives you a high degree of design flexibility, provided that the standard library functions meet the design requirements. A full-custom ASIC design is more complex than the gate array or standard cell design. Implementing a full custom design can decrease the size of an ASIC dramatically. ASICs generally incur some type of Non-recurring Engineering (NRE) charges. Compared to an FPGA, ASICs can be completely customized to implement the exact design you have in mind. ASICs have higher densities than FPGAs, allowing the integration of several different functionalities in a single device that might require multiple FPGAs, and ASICs have lower per-unit costs than FPGAs, provided that the volumes are high enough to offset the NRE charges.
FPGA Advantages
Refer to Figure 1 for a comparison of microprocessors, FPGAs, and ASICs. An FPGA offers a compromise between the application-specific performance of an ASIC and the flexibility of a general microprocessor. Compared to a general-purpose processor, FPGAs have lower latency. Latency is the time between the input and the response. One of the main reasons for this low latency is that FPGAs don't depend on an operating system to implement tasks. FPGAs have flexible I/O assignments. The logic elements in an FPGA can be connected to almost any pin, unlike microprocessors with fixed pin assignments. The flexible pin assignment of FPGAs can simplify your PC board layout. FPGAs perform parallel processing, whereas microprocessors execute instructions sequentially. Parallel processing allows FPGAs to respond to inputs more quickly.
FPGA reprogrammability supports field updates. These updates could be more extensive than just modifying the application code. Compared to an ASIC, FPGAs offer you faster time to market because the devices can be configured in the lab and modified as needed. Implementation times can be as short as a few days. FPGAs don't require any upfront non-recurring expenses like those associated with ASIC development. FPGAs have a simpler design cycle than ASICs; there's no complex floor planning or clock tree planning. Additionally, FPGAs have reduced development cycle risk. FPGAs are reprogrammable, so a bug found in the development phase can be quickly corrected. Fielded systems can be updated remotely by deploying a new bitstream.
Figure 1: FPGA and ASIC comparison
Summary
Market parallel processing, flexible pin assignments that simplify board layout, reprogrammability to support bug fixes and field updates, and no NRE charges are some of the attributes that make FPGAs a good alternative to ASICs or general-purpose processors in many of your digital designs.
Video Course
You can also find this training in video format from Microchip University as "Hello FPGA".