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Analog design in the context of integrated circuit (IC) design is a discipline that focuses on the creation of circuits that operate in and are optimized for continuous time-domain behavior.
Typical objectives of analog design include:
When the term “integrated circuit design” is mentioned, most people think of the design of complex microprocessors. These circuits are designed using digital design techniques, which focus on the propagation of discrete values, i.e., “ones and zeros.” It’s important to understand that this model of propagating “ones and zeros” is used to simplify the analysis of huge networks. The actual devices in any circuit are responding to continuously varying stimulus, so analog circuit design is really the foundation of the design of digital circuits.
Since all the basic devices in an IC respond to continuous time stimulus, analog design forms the foundation for all IC design. Modern IC technology presents many design challenges. There is significant variability in the manufacturing process for advanced technology nodes. The actual operation of the high number of devices on advanced ICs also causes variability. This variability manifests as changes in operating voltage, operating temperature, and in performance. Densely packed devices can also interact with each other and with the silicon substrate, package, and board to cause signal distortions. All of these effects can occur between devices and within a single IC as well.
Analog design must compensate for all of these effects to ensure three basic qualities: fidelity/precision, consistency, and performance. Reliability analysis and signal integrity analysis are some of the activities that are used to model and mitigate these effects. Examples of the importance of these three items with regard to IC applications are as follows:
The primary difference between analog design and digital design is the type of underlying analysis that is used.
In analog design, circuit stimulus is treated as a continuously varying signal over time. The behavior of the circuit is modeled in the time and frequency domains with attention focused on the fidelity/precision, consistency, and performance of the resultant waveforms. Circuit variability, both manufacturing and design induced, must be modeled and compensated for as well.
Digital design treats circuit stimulus as a series of discrete logic “ones” and logic “zeros” over time. A logic “one” is typically represented by the presence of the supply voltage for the IC and a logic “zero” is represented by the absence of this voltage (i.e., zero volts). The devices in digital circuits must spend most of their time at either logic “one” or logic “zero”. As long as the circuits processing these signals are consistent in their response to these logic levels, digital design works well. Analog design is responsible to deliver these qualities.
This allows the behavior of the circuit to be analyzed using combinatorial and sequential models, only considering two voltages (“one” and “zero”), which substantially simplifies the design and verification process.
Analog IC design typically involves a top-down design and implementation process followed by a bottom-up verification process. There are many variations on this overall approach. Here are the basic steps:
The 草榴社区 Custom Design Platform is a unified suite of design and verification tools that accelerates the development of robust custom analog designs. Built on the Custom Compiler? custom design environment, the platform features industry-leading circuit simulation performance, a fast and easy-to-use layout editor, and best-in-class technologies for parasitic extraction, reliability analysis, and physical verification.
Platform tools include:
Custom Compiler facilitates design/layout collaboration that makes it easy to communicate design intent and achieve analog design closure, as shown below.