Introduction to FPGA

Update Time: Mar 11, 2024    Readership: 470

What is an FPGA

In the realm of digital design, an FPGA, or Field-Programmable Gate Array, stands as a cornerstone of innovation. Initially introduced as an evolution of programmable devices like PAL, GAL, and CPLD, an FPGA transcends conventional circuitry limitations. Positioned as a semi-customized solution within the domain of Application-Specific Integrated Circuits (ASIC), it not only addresses the drawbacks of bespoke circuits but also surmounts them.


In essence, an FPGA is a chip imbued with the transformative power of programming. It represents a paradigm where the chip's internal architecture is not static but mutable. To unleash its potential, designers craft hardware description languages, which, upon programming, undergo a series of transformations—compilation, synthesis, layout, and routing—via Electronic Design Automation (EDA) tools. The resultant file is then loaded into the FPGA device, initiating a metamorphosis of internal wiring, culminating in the realization of specific functionalities. At this juncture, the FPGA stands as a malleable instrument primed for bespoke applications.


Comparatively, the FPGA diverges from its counterpart, the microcontroller, in structural essence. While microcontrollers mimic the role of a computer's CPU, operating within the realms of Harvard or von Neumann architectures, an FPGA's structure embodies the versatility of lookup tables. This intricate design renders it apt for sophisticated applications such as communication interface design and digital signal processing. Furthermore, FPGAs serve as instrumental tools for ASIC prototype validation.


Yet, despite its myriad virtues, an FPGA is not devoid of limitations. Though it boasts superior efficiency and diminished power consumption compared to microcontrollers and CPUs, its development complexity eclipses theirs. While FPGAs exhibit shorter lead times in digital chip design compared to ASICs, they grapple with issues such as cost, performance, and resource utilization, rendering them incapable of replacing ASICs entirely.


Basic Structure of FPGA

The foundational essence of FPGA lies in its programmability, a trait precluding the fixed logic gate circuits ubiquitous in dedicated ASICs. Instead, FPGAs embrace a flexible architecture conducive to iterative configuration. Central to this structure is the Lookup Table (LUT), an elemental component adept at embodying diverse digital logic functions. Predominantly, contemporary FPGA chips remain anchored in SRAM technology, harnessing its potency to facilitate seamless reconfiguration and adaptability.

Data Storage and Configuration Methods

Within the FPGA, there exists an on-chip RAM block dedicated to storing data, which is crucial for setting the device's operational status. For the FPGA to function properly, the on-chip RAM must be programmed accordingly. In scenarios involving extensive external data interaction, additional peripherals such as SDRAM or DDR3 memory modules are incorporated to temporarily store data. However, ultimately, data temporarily held in these peripherals must be channeled through and processed by the on-chip RAM within the FPGA.


Upon completion of program design within the Electronic Design Automation (EDA) tool, the software program is burned into the FPGA, employing various configuration modes. Here are some commonly utilized configuration modes:


Parallel Mode: This mode involves configuring the FPGA via parallel PROM and Flash memory modules.

Master-Slave Mode: Utilizes a single PROM to configure multiple FPGAs simultaneously.

Serial Mode: In this mode, a serial PROM is employed to configure the FPGA.

Peripheral Mode: Here, the FPGA functions as a peripheral device to a microprocessor, which programs it accordingly.

Presently, mainstream FPGAs predominantly rely on SRAM technology, with most FPGA development boards adopting the serial configuration mode. Since SRAM loses its internal data upon power loss, an external off-chip memory capable of retaining data during power interruptions is commonly interfaced to preserve programming. Consequently, upon power-up, the FPGA retrieves data from the external memory into its on-chip RAM for configuration. Once programmed, the FPGA transitions into its operational state; however, upon power-down, the data stored in the FPGA's internal SRAM is lost, resetting the logic.


This configuration method not only facilitates reusability but also obviates the need for manual reconfiguration. Following an initial configuration, the FPGA automatically executes its internal programming each time it is powered on, ensuring seamless functionality.


FPGA Design Process

The FPGA design process involves the development of FPGA chips using Electronic Design Automation (EDA) development software and programming tools. Two primary methods used for describing digital hardware circuits are schematic diagrams and HDL (Hardware Description Language). While both methods are common, the use of HDL offers superior portability, versatility, and facilitates modular design, making it widely adopted in both professional and academic settings. The typical FPGA development process is illustrated below, encompassing key steps such as function definition/device selection, design input, functional simulation, comprehensive optimization, post-synthesis simulation, implementation, post-routing simulation, board-level simulation, and chip programming and debugging

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