What is Logic Design?

Requirement Analysis:

The design process begins by defining the desired functionality of the target silicon chip or sub-block of a larger chip. This could be as simple as a binary adder or as complex as a high-performance CPU, GPU, or AI neural network chip. Requirements are specified in terms of inputs, outputs, performance, power consumption, and other constraints.

The requirements for a digital logic design involve architectural analysis and exploration to arrive at an optimal architecture for the design. This is a critical step as the chosen architecture is the core of the design. A suboptimal architecture will lead to a suboptimal logic design.

Logic Synthesis:

The automated process of converting a high-level, human-readable hardware description (written in HDLs) into a gate-level representation suitable for implementation on silicon (such as FPGAs or ASICs). This process considers design constraints, such as area, speed, and power consumption, to generate an optimized netlist – a file containing the logic gates and all their interconnections and connections to the “outside world”. Logic synthesis is the cornerstone tool of logic design, making it possible to automate the creation of large designs by specifying a high-level language to describe the desired functionality. Key steps in logic synthesis are:

• Design Entry: The designer specifies the desired functionality using an HDL, usually at the RTL level.
• Elaboration: The tool reads the HDL and interprets and expands the design hierarchy.
• Optimization: The synthesized logic design is optimized for performance, area, or power, based on the constraints specified by the logic design engineer.
• Technology Mapping: The design is mapped to available gate types or cells in the target library, based on the silicon foundry that will be fabricating the silicon chip.
• Netlist Generation: The final output is a logic gate-level netlist—a detailed list of components and connections. 

Simulation & Verification:

Before physical implementation, logic designs are simulated using specialized software tools that read in and process the netlist. Simulation allows engineers to verify correct operation (the desired functionality), test various input scenarios, and identify potential issues without building the design in silicon or even going through physical design. Different types of simulation include functional simulation and timing verification.

Key benefits include:

• Reliability and Precision: Logic synthesis software ensures the output logic design – no matter how large – will always implement the RTL specification exactly, eliminating human error. Verification software can confirm the logical correctness of the output design by comparing the RTL specification with the output gate-level netlist.
• Scalability and Modularity: Complex systems can be constructed by combining simple logic blocks. This modularity simplifies design, testing, and maintenance, enabling rapid development and integration of new features. Proven, verified RTL blocks (for example adders, comparators, ALUs, etc.) can be reused as part of other new designs.
• Speed and Efficiency: Logic synthesis software can create many thousands – or millions – of connected logic gates forming digital chip designs fast and efficiently, without manual work. The design engineer can specify constraints to the synthesis tool, such as timing, power, or area constraints to guide the software to create and optimal output netlist.
• Programmability and Flexibility: Since HDLs allow specifying a logic design through a high-level language, it is very straightforward for logic designers to make changes, add or remove logic, etc. and quickly re-synthesize. HDLs make logic design highly programmable and flexible.

Simulation & Verification:

Before physical implementation, logic designs are simulated using specialized software tools that read in and process the netlist. Simulation allows engineers to verify correct operation (the desired functionality), test various input scenarios, and identify potential issues without building the design in silicon or even going through physical design. Different types of simulation include functional simulation and timing verification.