Getting started with Open Designs
When we look at IC design from a perspective angle, it's all about carefully arranging different parts of a circuit so they can work together to do specific jobs. Imagine putting together a puzzle where each piece has a special role to play. First, we need to decide what we want the puzzle to look like, or in IC design terms, what we want our chip to do. Then, we pick the right puzzle pieces, or circuit elements, to make it happen. These pieces need to fit together just right, like gears in a machine, to perform their tasks smoothly. Throughout this process, we need to keep in mind the limitations and requirements of what the chip will be used for. Ultimately, our goal is to create a chip that not only does its job well but also doesn't cost too much to make and can be produced efficiently.
While the specifics of IC design workflows can vary widely depending on factors like foundry, process, company, and individual preferences, they generally fall into four main domains:
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Digital: This domain focuses on designing ICs using transistors as switches and logic circuits. Digital IC design deals with processing binary data and implementing algorithms, often for tasks like computation, storage, and communication.
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Analog: Analog IC design involves working with real-world signals that haven't been digitized. It includes designing components such as amplifiers, filters, and voltage regulators, which are crucial for processing continuous signals like audio, video, and sensor data.
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RF (Radio Frequency): RF IC design is a specialized subset of analog design that deals specifically with signals at radio frequencies. It encompasses the design of components for wireless communication systems, such as antennas, amplifiers, and frequency synthesizers.
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Mixed-signal: Mixed-signal design combines elements of both digital and analog design to create integrated circuits that process both digital and analog signals. These ICs are common in applications such as data converters, sensor interfaces, and communication interfaces.
Each domain has its own set of design challenges, techniques, and methodologies. While digital design focuses on high-speed logic and optimization for power and area, analog design emphasizes precision, noise, and linearity. RF design requires specialized knowledge of electromagnetic theory and transmission line effects. Mixed-signal design integrates digital and analog circuits while managing their interactions and ensuring compatibility.
Overall, the IC design flow process may involve a combination of these domains, depending on the requirements of the project and the expertise of the design team.
Digital IC Design Flow
In semicustom digital ASIC design, a circuit is constructed by using a set of predefined logic components, known as standard cells. These cells are predesigned and their layouts are validated and tested by the foundry (or an specialized company). Standard-cell ASIC technology allows us to work at the gate level rather than at the transistor level and thus greatly simplifies the design process. The device manufactures usually provides a library of standard cells as the basic building blocks. The library normally consists of basic logic gates, simple combinational components (and-or inverters, multiplexers, full adders, etc.) and basic memory elements (D-type latch and flip-flop). Some libraries may also contain more sophisticated function blocks, such as an adder, barrel shifter, random access memory (RAM), etc.
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Design Specification: A concise functional and performance requirements of an integrated circuit (IC).
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High-level system design: Hardware Description Language (HDL) is a specialized programming language used to model and describe digital logic circuits and systems.It Involves Design Partition , Entry-Verilog Behavior Modeling, Simulation/Functional Verification, Integration and Verification.
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Logic Synthesis : Involves RTL(Register Transfer Level) description of the design into a netlist consisting of logic gates and flip-flops.
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Placement & Routing : Placement in IC design involves strategically positioning components and functional blocks on the chip's layout to optimize factors like signal integrity and area utilization. Routing involves establishing connections between these components through metal layers, ensuring efficient signal propagation while avoiding congestion and minimizing delay.
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Layout : IC level layout involves integrating all functional blocks onto the chip's layout, including cell placement, scan chain/clock tree insertion, and cell routing. It undergoes physical and electrical design rules checks, layout versus schematic verification, and parasitic extraction. Post-layout timing verification ensures timing requirements are met before GDSII creation and tape-out for fabrication.
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GDSII : A GDS file contains information about the geometric shapes, layers, and other physical properties of the components that make up an IC design. It's commonly used for transferring layout data between different electronic design automation (EDA) tools and for manufacturing masks used in the fabrication process.
Open-source Digital IC design tools
Behavioural Simulation Tools
Verification Tool
Synthesis Tool
RTL2GDS
Binary software distribution
Analog IC design Flow
Analog IC design and digital IC design follow distinct methodologies due to their inherent differences. While digital design operates largely at an abstract level, relying on automated processes for gate-level placement and routing, analog design demands a more personalized approach to each circuit, including detailed considerations of transistor sizing and configuration.
Analog design is predominantly a manual endeavor. It typically commences with the creation of a schematic diagram using a schematic editor. This schematic is then subjected to simulation using a SPICE-level simulator, with the resulting outputs scrutinized to ensure they meet performance criteria. If satisfactory, the next step involves the labor-intensive task of manually crafting the IC layout using a graphical layout editor. This layout is meticulously inspected to verify its accuracy and adherence to design specifications.
Open-source Analog IC design tools
Schematic Flow
Simulation
Physical Design
Netgen