Field Programmable Gate Arrays (FPGAs) are integrated circuits that can be programmed and reconfigured to implement custom hardware functionality after manufacturing. Once seen as niche tools for hardware engineers, FPGAs are now mainstream processors powering innovations in every industry from aerospace to medical devices.
In this comprehensive guide, we‘ll demystify FPGAs and explore how they work starting from the ground up. You‘ll learn:
- What makes FPGAs unique compared to other integrated circuits
- The basic architecture and components inside an FPGA
- How FPGAs are programmed using hardware description languages
- Real-world applications where FPGAs shine
- Cutting-edge innovations to power the FPGAs of tomorrow
Whether you‘re an aspiring hardware developer or just FPGA-curious, you‘ll gain a solid understanding of these versatile chips and how they enable today‘s top technologies. Let‘s get started!
A Brief History of FPGAs
FPGAs were first introduced commercially in the mid-1980s by pioneers like Xilinx and Altera (now part of Intel). Early FPGAs were relatively small in capacity, but offered hardware designers flexibility compared to rigid application-specific integrated circuits (ASICs).
As Dr. Vaughn Betz, CEO of FPGA startup Flex Logix explains:
"Before FPGAs were invented in the mid 80s, chip designers had a choice. They could design their chips with gate arrays which were fast and low power, but inflexible, or they could design full custom chips which were flexible but slow and expensive. The genius of the FPGA was that it gave customers a chip which was both flexible and fast/low power for the first time.”
Through rapid innovation, FPGAs gained orders of magnitude more capacity along with hardened blocks for advanced functionality like DSP processing and high-speed transceivers. Today‘s FPGAs can implement entire systems on a chip (SoC) containing processors, peripherals and accelerators all on one package.
Now 30+ years since their debut, FPGAs are a $5 billion+ per year industry. With their flexibility and performance, FPGAs are the perfect platforms for deploying artificial intelligence, 5G telecommunications, data center acceleration and more in the 21st century.
FPGA Basics: Key Components and Capabilities
At the most fundamental level, FPGAs consist of a lattice of logic blocks linked by programmable routing resources. By custom configuring these basic building blocks, engineers can implement just about any hardware function they can dream up. That flexibility and configurability is what makes FPGAs unique.
Logic Block Architecture
The logic blocks inside an FPGA contain basic logical functions like NAND gates, flip flops and multiplexers. Combining these low-level Boolean logic gates allows implementing more complex functions just like combining LEGO blocks to build sophisticated structures.
Modern FPGAs contain a hierarchy of logic blocks with smaller blocks combined to enable larger functions:
Logic Cells → Logic Clusters → Logic Blocks
The exact architecture varies between FPGA vendors and families but generally follows this nested arrangement.
Xilinx 7-Series FPGAs for example have 6-input Look-Up Table (LUT) logic cells which can be combined into 2x slices, and then clustered in groups of 2, 4 or 8 to form Configurable Logic Blocks (CLBs):
By cascading multiple levels of logic blocks in flexible ways, very complex Boolean functions can be implemented across millions of gates.
Routing Resources
Getting data signals successfully from inputs to logic blocks then back out as outputs is just as important as the logic itself. The programmable routing in FPGAs connects everything together.
Routing resources include horizontal and vertical tracks plus more specialized connections like direct links supporting fast carry chains. Multiplexers and switches at each intersection allow the routing to be reconfigured.
Global buffer resources drive signals across longer distances to connect distant parts of large FPGA designs. Careful routing design ensures all logic blocks can access needed inputs and drive outputs reliably at blazing fast speeds.
Input/Output Blocks
A key part of any integrated circuit is getting data in and out. Input/output blocks provide the bridges between internal FPGA logic and other devices through external chip pins.
Common interfaces found in modern FPGA I/O include standards like PCI Express, Ethernet, USB, DDR memory as well as analog/mixed signal for sensor integration and other special functions.
High-speed serial transceivers now reach data rates measured in the gigabits/sec range. Dedicated anti-jitter circuitry ensures timing reliability even at blazing speeds.
Configuration Memory
Crucially, all FPGA routing and logic is configurable thanks to static RAM cells distributed across the device. These provide millions or even billions of bits to define user designs.
At power on, configuration bits stream in to program the desired functionality. SRAM storage means the design can be re-configured dynamically as often as needed. The configurable memory sets FPGAs apart from fixed-function chips like GPUs or ASICs.
Programming FPGAs Using Hardware Description Languages
To actually make use of all that blank configurable canvas inside FPGAs, engineers need ways to describe the desired hardware behavior. Just like software developers use high-level languages to create programs, FPGA designers write code using hardware description languages (HDLs).
Popular choices include:
- VHDL – VHSIC (Very High Speed Integrated Circuit) Hardware Description Language
- Verilog – Originally developed by Cadence as a proprietary language, before becoming an IEEE standard
- SystemVerilog – Superset of Verilog for more complex designs, adds features like classes and interfaces
Conceptually HDLs describe desired functionality in terms of regs/signals, modules/interfaces and concurrency/timing semantics. Code gets compiled to produce appropriate low-level bitstreams the FPGA can understand natively.
Unlike procedural software languages, HDLs define hardware circuits spatially using parallel module definitions rather than step-by-step imperative sequences. That makes them easier to optimize across FPGA resources supporting massive parallelism.
Here‘s a flavor of some simple Verilog code defining a 4-bit binary comparator module:
module compare4 (
input [3:0] a,b,
output equal,
output less,
output greater
);
assign equal = (a == b);
assign less = (a < b);
assign greater = (a > b);
endmoduleEven without prior HDL exposure, you can observe inputs/outputs, concurrent assignments defining parallel logic, bit-vector widths and other hardware constructs.
Increasingly higher levels of abstraction are also available through high-level synthesis (HLS) languages and tools to boost FPGA developer productivity beyond hand-coded HDL.
Why FPGA Flexibility and Performance Rule
We’ve covered FPGA capabilities and programmability features under the hood. Now why are FPGAs becoming one of the most pivotal silicon platforms across so many applications?
Flexibility to Accelerate Evolving Workloads
Application requirements constantly change and accelerate at the pace of Moore‘s Law. Network bandwidth doubles every 18 months. Video resolutions advance from 4K to 8K and beyond. AI inference demands skyrocket with neural net innovations.
In this environment, fixed-function ASIC chips start looking obsolete even before tapeout. FPGAs however offer the flexibility to adapt on the fly. Developers can update accelerators and algorithms as needs change without expensive and lengthy chip respins.
New cloud FPGA instances from Amazon and Microsoft make this agility easily accessible for data center workloads. FPGAs virtualize hardware acceleration, allocating patented bitstream IP to users while abstracting away implementation details developers don’t need to see.
Deterministic Real-Time Performance
Advanced applications like autonomous driving demand predictable high-performance —without any jitter or timing variation. FPGAs deliver on this stringent requirement thanks to their parallel hardware execution model.
All logic and routing happens in hardware leading to deterministic “speed of light” execution unlike software stack variables. Critical algorithms like sensor fusion, computer vision and decision making run more reliably on FPGAs as part of a safety-certified solution.
John Koeter, VP of Marketing for IP and Prototyping at Synopsys explains the advantage:
“The value of FPGA processing starts with hardware execution and timing determinism, both absolute necessities for these systems. No matter how many times the same algorithm runs through an FPGA, it will produce an identical output every single time.”
Cutting-Edge Applications Powered by FPGAs
FPGAs uniquely combine versatility, performance and power efficiency—capabilities fueling major advances across a spectrum of industries:
5G Network Infrastructure – New 5G base stations need to process ultra-wide bandwidth mobile signals across large frequency spectrums using techniques like massive MIMO. FPGAs provide the only economically feasible implementation combining high throughput, flexibility and scalability in a power efficient platform.
AI Acceleration – Highly parallel FPGAs speed up deep learning training and inference byorders of magnitude versus GPU-based servers. Microsoft has already ported major portions of its Bing search algorithm along with data center services to its homegrown Catapult FPGA accelerator delivering overwhelming ROI. Startups like Cerebras Systems are pushing AI chip boundaries even further with their Wafer Scale Engine packing 1.2 trillion transistors!
Aerospace and Defense – Today‘s radar and electronic warfare systems process signals across huge swaths of spectrum with extreme resolution unmatchable by digital processors. Custom FPGA-based systems offer superior performance tackling this analog/RF processing challenge with software-defined longevity.
The unmatched versatility of FPGAs will continue opening new possibilities across still more applications like high-frequency trading, genome sequencing and quantum computing in the years ahead.
The Future of FPGAs
Even after 35+ years, FPGAs remain one of computing’s most vibrant innovation spaces thanks to their versatility and increasing capacities following Moore’s Law. Here is just a sampling of exciting new frontiers ahead:
Security and Protection
With growing adoption, FPGAs face escalating threats from malicious attackers and hackers. Like all computing platforms, security is now an absolute requirement particularly in risk-sensitive settings like automotive or infrastructure. FPGA vendors have responded with new techniques to authenticate bitstreams, encrypt configuration data, isolate defects and actively detect threats.
3D Integration
Moore’s Law advancements continue yielding FPGAs containing over 10 million logic cells integrated monolithically. Just as abundant cores enabled CPU innovations like deep out-of-order speculative execution, gargantuan FPGA sizes open totally new architectural possibilities. 3D integration using Through-Silicon Vias (TSVs) promises still higher transistor budgets along with technology breakthroughs like photonic I/O links operating at light speed!
Democratization for All Developers
While hardware description languages provide unmatched control, their complexity limits accessibility for software developers. High-Level Synthesis (HLS) languages like C/C++ and OpenCL seek to bridge this gap by abstracting away low-level timing concerns while still harnessing FPGA hardware resources efficiently. Mainstream programming languages and interfaces will unlock innovation from millions more developers in the decade ahead.
Conclusion: FPGAs Deliver Flexible Acceleration for the Future
By giving hardware designers “accelerators without boundaries”, FPGAs unlock customized platforms optimized for the most demanding applications like 5G and AI. Unique FPGA attributes include:
Flexibility – Reconfigurable logic circuits enable evolving algorithms and standards without expensive redesign
Determinism – Hardwired signal routing provides cycle-exact precision impossible in software
Agility – Fast compile flows measurable in minutes rather than months accelerate verification and deployment
Security – Increasing protection against malware threats ensures safer FPGA-based system
Whether displacing GPUs training neural networks, enabling 100Gbps network data flows or running safety-critical automotive workloads, FPGAs outshine alternatives on flexibility, performance per watt, and accelerating ROI.
Now over 30 years since their game-changing debut, FPGAs only grow more pivotal across a booming range of data-intensive applications thanks to their versatility and increasing logic capacity. Both industry pioneers and savvy startups alike continue pushing FPGA capabilities to once unimaginable new heights. Expect still more innovative applications leveraging FPGA acceleration for decades more to come!
