Overview: The article discusses ASICs in embedded systems, focusing on their advantages, types, and design processes and how they enhance performance for specialized applications in various electronics.

Moore's Law, which states that the number of transistors on a microchip doubles approximately every two years, has driven the miniaturization of electronic devices, resulting in smaller, faster, and more efficient chips.

This trend has enabled the creation of microprocessors and microcontrollers, which are utilized in a wide range of applications. They are utilized in various applications, from personal computers and smartphones to embedded systems in vehicles and appliances.

However, specific applications often require processors with unique requirements, leading to the development of specialized types like Application-Specific Integrated Circuits (ASICs) and Field-Programmable Gate Arrays (FPGAs). ASICs and FPGA are designed differently from general-purpose processors like x86 and ARM/RISC. 

While general processors can perform various calculations based on program instructions, ASICs are designed to execute specific calculations or algorithms for a particular task. VLSI technology allows for the integration of a large number of transistors on a single chip, enabling the creation of complex, efficient, and customized ICs like ASICs and FPGA for specific applications.

What is an FPGA?

An FPGA is a type of integrated circuit that can be programmed and reprogrammed after manufacturing. FPGAs consist of a matrix of configurable logic blocks and programmable interconnects, as shown in Fig. 1, allowing designers to customize the chip's functionality for specific applications.

Fig. 1 An FPGA architecture showing logic block and programmable interconnects. Source: IEEE Access

What is an Application-Specific Integrated Circuit?

An ASIC, as the name suggests, is a custom-designed IC for a specific task that, once manufactured, cannot be reprogrammed. They are extremely popular nowadays as they offer high performance, low power consumption, and excellent efficiency for their intended applications. In this article, an overview of ASIC is provided.

An ASIC is a custom-made chip designed for a specific application, regardless of whether it is analog, digital, or a combination of both. ASICs are created and utilized by a single company for a particular system, offering high performance and efficiency. 

ASICs are small, highly integrated devices that are expensive and resource-intensive to develop and are often used in large production volumes. While the initial development costs of ASICs can be high, the cost per unit decreases significantly as the production volume increases. This makes ASICs particularly cost-effective for applications where large quantities are shipped.

Types

These chips are non-programmable and integrate multiple components like processors, input/output interfaces, and memory onto a single chip. However, they can be customized using Electronic Design Automation tools and Hardware Description Languages like Verilog or VHD. This can be achieved through different design approaches, which classify ASICs into three main categories:

  • Full-custom ASIC
  • Semi-custom ASIC
  • Programmable ASIC

Full-Custom ASICs

Full-Custom ASICs are designed from scratch, offering complete control over every aspect of the chip, including logic cells, circuits, and layouts. This level of customization allows for optimal performance, size, and power consumption, making them suitable for high-end applications. They are extremely expensive, complex in design, and time-consuming. They are not reconfigurable after manufacturing, meaning that their interconnections cannot be changed once the chip is fabricated.

Semi-Custom ASICs

Semi-custom ASICs use pre-designed logic cells and some customized mask layers. They reduce design time and manufacturing costs compared to full-custom ASICs. They are divided into two main types: 

  • Standard-cell-based ASICs
  • Gate array-based ASICs

Standard-cell-based ASICs: They use pre-designed logic cells arranged in rows to form flexible blocks. The position of these cells can be changed during the design process, but the interconnections between them are fixed.

Gate array-based ASICs: These have predefined transistors on a silicon wafer. Customization occurs by defining interconnections between these transistors during the metallization stage. They are less customizable than standard cell ASICs but offer faster manufacturing times.

Programmable ASICs

These ASICs can be configured after manufacturing, allowing for reprogramming and adaptability. Their subtypes include:

  • Programmable logic devices
  • Field-programmable gate arrays

Programmable Logic Devices (PLDs): These are simpler programmable devices offering flexibility.

Field-Programmable Gate Arrays (FPGAs): They are more complex devices that can implement a wide range of logic functions. 

ASIC Design Flow

While ASICs and FPGAs share some similarities in their design flows, such as system specification and synthesis, there are significant differences due to their inherent characteristics and manufacturing processes. Fig. 2 displays the flow chart that illustrates the ASIC design flow.

Fig. 2 Various steps in ASIC design flow Source: MDPI

ASICS require more intense verification and testing due to their non-reprogrammable nature. This includes simulation, formal verification, and post-layout verification to ensure that the chip meets specifications and functions correctly. Various steps involved in the design flow of ASICs are listed below.

Step 1: System Specification
Step 2: Architectural Design
Step 3: RTL Design
Step 4: Functional Verification
Step 5: Synthesis (Gate Levell Netlist)
Step 6: Formal Verification
Step 7: Floor Planninig
Step 8: Placement and Routing
Step 9: Clock Tree Synthesis and Timing Analysis
Step 10: Layout Verification and Signoff
Step 11: ECO & Chip Fabrication
Step 12: Packaging and Testing
Step 13: Post Silicon Validation
Step 14: Final Chip 

ASICs have a longer time-to-market due to the complex design flow and manufacturing process. They also have higher non-recurring engineering costs but offer lower unit costs in high-volume production.

To conclude, ASICs are widely used across various industries, from the chips inside electronic toys to USB chargers to network switches, and even those in satellite cores are all ASICs. ASICs' compact size, reduced power consumption, and increased capability for specialized tasks make them appropriate for standalone image processing applications.

Summarizing the Key Points

  • ASICs are custom-made chips designed for specific applications, offering exceptional performance and efficiency that general-purpose processors cannot achieve for specialized tasks.
  • ASIC development is resource-intensive and expensive initially, but unit costs decrease significantly with higher production volumes, making them cost-effective for large-scale applications.
  • Three primary types of ASIC designs are available: Full-custom, semi-custom, and programable, each offering varying flexibility, complexity, and manufacturing costs.

Reference

Shantharama, P., Thyagaturu, A. S., & Reisslein, M. (2020). Hardware-Accelerated Platforms and Infrastructures for Network Functions: A survey of enabling technologies and research studies. IEEE Access, 8, 132021–132085.
https://doi.org/10.1109/access.2020.3008250

Franck, L. D., Ginja, G. A., Carmo, J. P., Afonso, J. A., & Luppe, M. (2023). Custom ASIC design for SHA-256 using Open-Source tools. Computers, 13(1), 9.
https://doi.org/10.3390/computers13010009

Mendez, T., Parupudi, T., K, V. K., & Nayak, S. G. (2024). Development of Power-Delay Product optimized ASIC-Based computational unit for medical image compression. Technologies, 12(8), 121. https://doi.org/10.3390/technologies12080121

The Octet Institute. (2021, June 22). ASIC Design Flow | How a chip is designed?? https://www.youtube.com/watch?v=1CFhcBH52Rc

Techquickie. (2022, February 25). These chips are better than CPUs (ASICs and FPGAs) [Video]. YouTube. https://www.youtube.com/watch?v=7Elgs5HzIbE