Introduction to FPGAs

Modern technology allows the construction of chips that contain configurable circuitry which can be changed in order to implement a wide range of different logic circuits. Two different types of chips fall under this approach – PLDs and ASICs.

The Application-Specific Integrated Circuit (ASIC) is a chip intended for very specific uses within a design. These chips lack the dynamic nature of PLDs and are usually custom-ordered from the vendor. On the other hand, ASICs offer improved performance which the PLC cannot provide due to its limited speed as a result of the consumption of valuable chip area by programmable switches. When ordered in bulk, ASICs may also offer lower costs and for this reason are often used in finalized and ready-to-sell devices.

The Programmable Logic Device (PLD) is a chip which includes an array of programmable switches which allow the user to reprogram the chip’s internal circuitry. The ability to reprogram the PLD numerous times has great advantages during the design iteration process (making corrections to a previous design) as well as the addition of further functions and features. PLDs are widely used in device and board development due to their incredibly small size and dynamic nature. Three common types of PLD technology are Programmable Array Logic (PAL), Complex PLD (CPLD), and the FPGA.

Field Programmable Gate Arrays (FPGAs) are sophisticated PLD integrated circuits which are specifically designed to be configured (programmed) by the customer after the chip has been manufactured. FPGAs now contain as much FPGAs fall into a niche of their own and are beginning to see a wide variety of applications in telecommunication, digital signal processing, aerospace, vision systems, speech recognition, cryptography, etc. The FPGA’s reconfigurable interconnects allow the chip’s internal “logic blocks” (programmable logic components which can act as complex functions or simple logic gates – AND, OR, etc.) to be wired as the user requests, making the FPGA act somewhat like a small, but highly powerful and reprogrammable breadboard.