A custom IC is an application-specific integrated circuit. Some applications require that their ICs are specially built to meet their specifications. Therefore, some customers require IC companies to develop a custom IC for them. Custom ICs offer a lot of benefits. We will be exploring more on custom IC in this article.
What is a Custom IC?
A custom IC is sometimes referred to as a full-custom IC. This is type of integrated circuit enables the packaging of a subset of document into a reusable component. In a custom IC, all the mask layers are fully customized. Also, all circuits and logic cells are specifically designed. The custom IC design doesn’t integrate pre-characterized or pre-tested cells.
Furthermore, a custom IC integrates distinct building blocks are specially created for the required function. A custom IC is a complex system level part having several analog functions. Also, Custom IC design involves the use of standard cells and bigger macro functions like processor cores. The building blocks of a custom IC are specially built to offer certain capabilities.
The methods and procedures integrated to assemble custom devices are different. This is because these procedures must accommodate the special requirements of the custom IC.
Benefits of a Custom IC
Custom IC design approach can offer the required capability in cases where power, accuracy, size, or performance of a circuit is very crucial. For instance, power or analog ICs demand for these requirements. A good example is a frequency receiver for a 5G mobile phone that needs custom design because it requires accuracy and signal integrity.
Furthermore, ICs available in smart electric meters need some special design considerations that help them withstand the electric fields and extreme heat of these applications. Also, custom IC design plays significant roles in the creation of the building blocks utilized in ASIC or semi-custom design. This methodology uses standard cells that are specially designed with full custom procedures to ensure great performance and density.
Also, these cells are severally used. Therefore, it is crucial to create an optimal design. Furthermore, the custom IC design process is crucial for building low-level storage elements in memories. Another use case of custom IC is the datapath used in an embedded processor core. In order to back up the processor core’s operating clock frequency, the elements must function at a very high speed.
The elements of the datapath are therefore custom designed to allow routing by abutment. This means that all connections will be on the right and left sides of the datapath blocks. Also, this helps to minimize routing delays. However, this requires custom IC design to enhance this approach.
How to Design Custom ICs
There are several steps involved in custom IC design flow. Each of these steps is crucial in achieving a successful IC design.
Architectural design
This step involves specifying the IC’s functionality or the particular block. Also, it specifies the function, power consumption, and required speed of the IC. Furthermore, the architectural design step talks about the target cost of the custom IC design. Specifying all these factors will determine the specific technology used to integrate the device. This step only discusses what and not how to implement.
Circuit/logic design
In this stage, the macro-level building blocks are specially interconnected to integrate the functionality of the custom IC. Also, the device collection is specially simulated to confirm the design’s functionality. An analog simulator or a digital logic simulator will be integrated based on the required level of simulation detail.
Physical design
This step involves creation of the layout of interconnect shaped that integrate all the circuit elements. Also, this process starts with a floorplan that define where to locate all the chip’s primary functions and the primary input. However, you may skip this step if you are designing a smaller building block. Furthermore, a custom layout editor helps to integrate the physical payout of the shapes needed to build the circuit. Also, there are enhanced layout editors that offer real-time feedback on how the layout affects the performance and power of the design.
Physical verification
Physical verification is the last step in the custom IC design process. You will need to verify the custom IC design before sending it for manufacturing. In this step, you can now model all the physical effects of the design. Manufacturing variability and additional resistance from wiring are factors to consider.
Factors Impacting the Cost of Custom IC
When it comes to designing a custom integrated circuit for low quantities, most analog companies won’t do this. This is because of the NRE costs. Also, the companies will consider the lost opportunities while focusing on scarce resources on a part for one customer. A company can lose or gain everything on a customer when designing a custom IC.
We all need to understand that a custom IC is a complex system that features complex digital and several analog functions. When an IC company is in charge of an IC development, they consider several factors. Some of the factors include materials, teams, and equipment resources.
The team usually comprises various people. The team might divide its task between a subcontracted out or a small group. However, the cost is still important. Also, the team will comprise an analog design engineer, a layout engineer, a digital engineer, a product definition engineer, and more.
While labor is expensive, materials and tools aren’t also cheap. Each member of the team utilizes various software tools. one of the most expensive tools is the design software which charges the user for a project on a time basis. Design tools can amount to $1 million annually.
Also, the hardware for inspection, testing, and verification are expensive. This includes load boards, burn-in boards, and application boards. Furthermore, Burn-in boards are the costliest because they demand more HTOL sockets which is about $100 per piece.
The equipment resources are one of the factors that contribute to the cost of a custom IC. Also, these resources include mixed mode IC testers. Tester time is usually billed against a program. Furthermore, the development of a custom IC is usually a costly task with lots of risk.
Conclusion
The development of a custom IC requires much more complexity and design time. This is because the parts of a custom IC are specifically designed to suit the requirements proposed by the customer.
