FPGA vs ASIC: A Guide to Choosing Between Them

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Introduction to FPGA and ASIC Technology

Decades ago, when computation was getting complex and operations were difficult to perform, the tech world was more inclined to make a processor that could integrate numerous transistors on a microchip. Consequently, VLSI (very-large-scale integration) technology was introduced to embed billions of transistors on a single microchip easily. This technology improved efficiency, increased the computation power, decreased the cost, and made all these features possible on a single silicon chip!

FPGA And ASIC are the two VLSI technologies. FPGA (field programmable gate arrays) And ASIC (application-specific integrated circuits) are the two VLSI technologies. They have made the processing easier and optimized the computation. Multiple domains widely use both technologies nowadays, including:

  • Aerospace and defense
  • Medical electronics
  • Image processing
  • Consumer electronics
  • Industrial motor control
  • Scientific instruments
  • Cyber security system
  • Wireless communication
  • Artificial intelligence
  • data center hardware accelerators
  • Advanced driver assist system. 

This blog will cover the key features of FPGAs and ASICs and their key differences.

What is FPGA?

FPGA stands for Field Programmable Gate Array. It was first introduced in 1985 by Xilinx. Unlike the ASICs that are used for specific applications, FPGAs are flexible to use and can be reprogrammed even after they have been manufactured. They can be used for multiple applications. Hence, the FPGAs allow the system designers to blend and reprogram the FPGAs according to their system requirements, providing rapid prototyping, feasibility, ease of access, and adaptation to the changing design environment. 

The FPGA is an array of logic gates. It has multiple CLBs (configurable logic blocks) and programmable interconnects. CLBs are just like digital sub-circuits, which efficiently implement common functions and are highly flexible. The CLBs include look-up tables, storage elements such as flip flops or registers, and multiplexers that enable CLBS to perform the functions. The interconnects are also programmable. These are used to connect the CLBs to one another and also enable the CLBs to connect with the external circuitry within the FPGA. 

field programmable gate array

FPGA Architecture and Design

The FPGAs have a pipeline design that enables parallelism. FPGAs have high-speed serial transceivers which enable high-speed data transmission, reception, and communication with other devices. They also have phased locked loop PLL which are used for clock generation, distribution of stable and synchronized clock signals across different regions within FPGA and clock jitter reduction. FPGAs have external memory controllers and a column of dual port on-chip RAM that has 18k to 36k memory which helps store large data. There is a column of DSP 48 blocks that share the load of FPGA, enable arithmetic operations, and offer high computation.

FPGA Programming and Verification

The FPGA is programmed using hardware description languages such as VHDL and Verilog. 

FPGA verification is very crucial while finalizing the prototype. There are multiple ways for FPGA verification. The HDL tools can be used to detect syntax errors, design rule violations and undefined signals. The HDL simulators can be used to model the behavior of some design under various internal conditions and this way one can compare the output to the expected results and identify the functional errors, hence allowing FPGA verification. The FPGA verification can also be done by verifying the timing constraints and ensuring that the design operates at desired clock frequency. The FPGA verification can also be performed by validating the design in an actual environment through multiple test input signals by which we can easily identify the errors in functionality, timing, and interaction with other system components. We can also use the debugging tools provided by the OEM to verify FPGA.

What is ASIC?

ASIC stands for Application-Specific Integrated Circuits. Unlike FPGAs, the ASICs are used for highly specific tasks. For example, an ASIC responsible for sensor data detection in a car engine would only detect the data. It will not process it or activate the actuators. The ASICs are programmed for their specific applications at the time of manufacturing, they can neither be reprogrammed nor altered by anyone else once it is manufactured. The logic function of an ASIC cannot be changed as the circuitry, i.e., the number of gates and flip flops and their interconnections, is fixed. The design and manufacturing process for ASICs is complex and time, and it has a high initial cost as compared to the FPGA, but the cost of mass production is cheap as compared to the FPGA.

application specific integrated circuit

ASIC Design Process

As stated earlier, the manufacturing of ASICs is complex. During the design phase, multiple things are to be done:

  • The specifications and functionality of the ASIC.
  • The architecture and high-level design of the ASIC.
  • Selection of blocks/components such as logic gates, communication protocols, clock distribution network, and memory blocks utilized to achieve that specific architecture.
  • Design of the RTL (register transfer logic) code that defines the logic behavior of the ASIC. 
  • The next step is the verification and optimization of RTL code. The RTL code is fed into a logic synthesis tool, which converts it into a netlist at the gate level. This netlist shows flip-flops, transistors, logic gates, and interconnections. The design can be optimized by reducing the area by decreasing the number of gates, restructuring logic, adjusting the timings, and minimizing the power consumption.
  • The ASIC is then fabricated on a silicon wafer using photolithography, and a prototype is made.

Silicon wafer photolithography

ASICs have standard logic cells, which are the same as the CLBs in FPGAs. The ASICs have memory blocks, and the designer can choose any memory type such as SRAM (Static Random Access Memory), DRAM (Dynamic Random Access Memory), ROM (Only Memory), eNVM (Embedded Non-Volatile Memory), and Flash memory. Unlike the FPGAs, ASICs have analog circuitry. They have PLLs (phase locked loops), which are used for clock generation, distribution of stable and synchronized clock signals across different regions within ASIC, and clock jitter reduction. They also have specialized functional blocks that are used for specific functions such as machine learning accelerators, image/video processing units, communication interfaces (USBs, ethernet, peripheral component interconnect express PCIE, etc.), sensor interfaces, processor codes, and cryptographic accelerators.

Comparing ASIC vs FPGA

Although both are marvels of VLSI technology and do wonders, some differences exist between FPGAs and ASICs. The key differences are discussed below:

  • Their name distinguishes the key difference between both. The field programmable gate array (FPGA) allows for reprogramming multiple times to suit any custom design or application. In contrast, application-specific integrated circuits (ASICs) are designed for a specific task or application.
  • The FPGA circuitry design can be altered and reconfigurable, whereas the circuitry of ASIC cannot be altered or changed.
  • The design of both is specified using hardware description languages such as VHDL or Verilog.
  • The initial cost of FPGA is low compared to that of ASIC. However, the cost of mass production is high for FPGA as compared to the ASIC.
  • Suppose the FPGA is used for a  task that is similar to the one being performed by ASIC. In that case, ASIC will be more efficient than the FPGA, and its power consumption will be lower than that of FPGA because ASIC is specially designed for that specific application or task.
  • The ASIC is purely analog circuitry, whereas the FPGA cannot be configured with analog designs.
  • FPGAs are utilized in environments that undergo changes or require data upgrades, such as radars and cell phone base stations. On the other hand, manufacturers cannot use ASICs in dynamic environments. For instance, manufacturers cannot use ASICs designed for washing machines in smartphones.
  • The FPGAs can be used to validate or prototype a design because it can be changed over and over. However, the ASICS are not that flexible, and it is not recommended to prototype a design before it is validated.

Balancing Act: The FPGA vs ASIC Dilemma in VLSI Evolution

In the dynamic landscape of VLSI, the FPGA vs ASIC debate underscores the transformative journey from complex computation to integrated microchip solutions. FPGAs, with programmability and adaptability, redefine system design, while ASICs, tailored for specific tasks, excel in efficiency and cost-effectiveness. This exploration into FPGA vs ASIC architectures, design processes, and applications unveils the intricate tapestry of VLSI advancements. Whether embracing flexibility with FPGAs or precision with ASICs, both technologies in the FPGA vs ASIC saga continue to shape the future of computational possibilities with ongoing innovations in the ever-expanding realm of technology.

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