If an FPGA can be compared to a breadboard, then an ASIC is like a PCB.
The photo above is a PCB. To be precise, it has components mounted on top of it. It is commonly used in various home appliances such as smartphones and TVs.
To create a PCB, you need to draw a Schematic (circuit diagram). Then, create a PCB layout design. Finally, have it manufactured by a PCB manufacturer. If there is an error after manufacturing is complete, you must fix it. Do you need to change a PCB line (trace) or component? What steps should you take? To have a normal product, you need to modify the Schematic and PCB layout and manufacture it again. Of course, you can cut the line in the middle and connect it with an external wire. However, this will greatly reduce the stability of the product sold.
The reason for using Breadboard and PCB as examples is that FPGAs and ASICs [2] have similar differences. FPGAs and Breadboards can be modified directly on the spot if a problem occurs. On a Breadboard, if the wire connection is wrong, you can move it to another location. Connect it again to fix it immediately. For FPGAs, you can change the HDL code. Then proceed with the Place and Route process again. This is the biggest advantage and characteristic of FPGAs.
The reason for making ASICs or PCBs like this is their excellent performance. They can also be produced in large quantities. It is natural that ASICs have good performance. They are made by including only the necessary functions. Additionally, the path of each function is optimized. Also, depending on the number of chips (more than 100,000), there is a point where ASICs become cheaper in terms of cost (e.g., chips in smartphones, various electronic products, etc.). That’s why chips in smartphones, PCs, etc. are produced through ASICs.
FPGA vs. ASIC Comparison
| Item | FPGA | ASIC |
|---|---|---|
| Development Cost | Low initial cost | Millions to tens of millions of dollars |
| Design Flexibility | Possible (Can be changed via software) | Non possible (Cannot be modified after tape-out) |
| Development Time | A few weeks to several months | Several months to years |
| Performance | Relatively lower | Optimized (faster) |
| Power Consumption | Relatively higher | Lower (Can be optimized) |
| Mass Production Cost | Expensive per unit (Similar cost even in mass production) | Reduced cost in mess production |
ASICs have hardware circuits directly designed to perform specific functions. In contrast, FPGAs construct logic by combining general-purpose blocks such as LUTs (Look-up tables) and Configurable Logic Blocks (CLBs). This combination results in many unnecessary circuits. Therefore, FPGAs are disadvantageous in terms of speed and power efficiency.
FPGAs typically operate at speeds of around 200-500MHz. However, ASICs can easily achieve clock speeds of 1GHz or higher. Therefore, ASICs are much more beneficial when high-speed operations are required.
FPGAs consume more power than ASICs. This is because they use programmable logic. ASICs consume less power compared to FPGAs. They do not have unnecessary circuits and can be optimized. This makes ASICs more suitable for battery-based embedded systems and mobile devices.
ASICs can integrate multiple functions into a single chip. FPGAs have many programmable blocks, resulting in larger chip sizes for implementing the same task. Therefore, the same task can be implemented in a smaller size with an ASIC.