Parasitic extraction

Parasitic extraction is a key process in electronic design. It involves identifying and quantifying unintended, non-ideal electrical components that naturally occur in circuit designs due to their physical configuration and interaction with their environment. These unwanted components, known as parasitics, typically include parasitic capacitance, resistance, and inductance. The process involves detailed analysis often done by sophisticated software tools capable of modeling and simulating a circuit’s electromagnetic behaviors. These tools predict how parasitics can impact circuit performance, including their effects on signal integrity, timing, power consumption, and overall functionality.

Related products: Calibre xRC, Calibre xACT Parasitic Extraction, Calibre xL Extraction, Calibre xACT 3D Parasitic Extraction

Circuit Elements

This section presents the basic circuit elements along with an example of their functionality and applications. The basic circuit elements include:

Capacitance:

Capacitance is the ability of a system to store an electric charge when a potential difference exists between two conductors in the system. In practical circuits, this property is exhibited by a component called a capacitor. Capacitors consist of two or more conductive plates separated by an insulating material or dielectric.

• Functionality: Capacitors store electrical energy directly as an electrostatic field between the plates. They release energy by discharging the stored charge when the circuit requires it.
• Applications: Commonly used as energy storage units, they also function in filtering applications where they smooth out voltage fluctuations, in tuning resonant circuits, and in managing power flow in electronic devices.

Inductance:

Inductance is a property of an electrical conductor by which a change in current flowing through it induces an electromotive force (voltage) in both the conductor itself (self-inductance) and in any nearby conductors (mutual inductance). Inductors are the circuit components that exhibit inductance, typically consisting of a coil of conducting wire.

• Functionality: Inductors resist changes in the current passing through them. They store energy in the form of a magnetic field when current flows through them.
• Applications: These inductors are used in filters, transformers and power supply regulation to manage fluctuating voltages.

Resistance:

Resistance is a property of a material that impedes the flow of electric current. An inherent attribute of materials that causes them to oppose the flow of electrons. Resistors are the components used in circuits to provide a specific resistance.

• Functionality: Resistors convert electrical energy to heat as current passes through. They regulate the flow of electrical charges or adjust signal levels among other uses.
• Applications: "Resistors are widely used to limit current, divide voltages, and pullup/pull-down nodes in circuits.

The general connection in circuits can be summarized into two categories, namely:

Series Connection: A series connection is one in which the components are connected end-to-end, so they carry the same current but the voltage across each can differ. Total resistance in a series equals the sum of the individual resistances.

Parallel Connection: A parallel connection is a connection in which the components are connected across the same two points, carrying potentially different currents but subject to the same voltage. In parallel, resistances and inductances decrease while capacitances increase as more components are added.

Understanding and manipulating these elementary properties allows engineers to craft circuits with desired behaviors, achieve specific responses, and ensure stability and efficiency in electronic applications. They form the foundational basis from which complex electronic systems are developed.

Parasitic elements

Parasitic elements manifest as unintentional components that emerge due to the inherent physical attributes of constructing circuits. These include:

Parasitic capacitance: This occurs when adjacent conductors inadvertently create a capacitive effect, storing electrical energy unintentionally.

Parasitic inductance: This phenomenon arises when circuits loops inadvertently function as electromagnets, influencing the circuit’s current flow.

Parasitic resistance: This is present when parts of the circuit introduce unwanted resistance to electrical flow, analogous to friction impeding movement.

From left to right: Representations of parasitic capacitance, parasitic inductance and parasitic resistance.

Rule-based parasitic extraction tools

Rule-based parasitic extraction tools use predefined rules and algorithms based on geometric and electrical properties to estimate parasitic effects. These tools function by applying simple geometric parameters (e.g., width, spacing) and connectivity information to estimate parasitics quickly. The rules are derived from empirical data and basic electrical principles. The primary advantage is speed. These tools require less computational power and can quickly process large circuits, making them ideal for preliminary checks and less complex designs. Rule-based tools typically lack the accuracy for high-frequency or very advanced semiconductor designs, where non-ideal behaviors are more critical. Better suited for early design stages or less critical applications where high speed and lower computational cost are priorities, but with lower accuracy.

Example tools: Siemens’ Calibre xRC and Calibre xACT.

Field solver parasitic extraction tools

Field solver tools are based on solving Maxwell's equations to simulate electromagnetic fields and derive accurate parasitic values. These solvers consider the 3D structure of the layout and its material properties. They generally employ numerical methods such as Finite Element Method (FEM), Boundary Element Method (BEM), or Finite Difference Method (FDM) to achieve highly accurate parasitic estimations. Such tools offer high accuracy, especially significant in high-frequency designs and complex geometries where parasitic effects are non-trivial. This is, however, at the expense of high computational cost, and longer run times are key limitations, which can be a bottleneck in some design processes. Essential for advanced applications (like RF, analog, and mixed-signal designs), where accuracy and detailed parasitic effects are crucial, albeit at a higher computational cost.

Example tools: Siemens’ Calibre xL and Calibre xACT 3D.