元件模型在IC設計產業的角色

DaShiaSun@FB

A top-down design approach in IC industry comprises of three levels which includes:
( j8 Q# a% @$ B( [$ SIC design (circuit-level), model / device(device-level), IC process technology(fabrication-level).
On the circuit-level,
7 ]! {, J4 }# p- s) g6 sa compact model provides the external terminal electrical characteristics
resulted from the mathematic expressions of an electronic device.
% g+ u6 o4 \# N6 U: L/ v& QThe external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
are featured as the input and output ports values.
; @2 k6 }9 G/ q/ `  ?; w' i' f' eThe unknown ports values of a device are solved by a simulator when performing circuit analysis.
After the structure and behavior of the individual compact model is specified, the description(structure and behavior) are
, K, @. v% Y- g0 D& v; Hsubmit to the simulator. The simulator employees KCL and KVL to create a set of nonlinear equations.
The nonlinear differential equations are not solved directly, but with approximation and iterative methods. Under certain
  `7 q0 |6 \9 a8 sapproximation, the equations are solved with the Newton-Raphson method. The solutions are equilibrium points of nodal analysis.
9 W  _. x; L  _& O$ w) r: \+ ]" nIC design engineers work on a higher abstraction level than the device(transistor) level.
In other words, transistors are the primitive components in the eye of IC designer.
A virtual symbol is the representive of a real device(component).
* b0 Z  I  |  E% ^: y4 V/ ~5 _For instance, transistor's compact model is seen as a 4 pins symbol.
' ^, h+ P& N* K- L, P  t" H3 Z( oIn Advanced Design System(ADS),  three design types are allowed: schematic, symbol, and layout.
Those designs can all be stored in a small containner names "cell" and a big containner names "library".
IC designer works with the connection of some symbols in a schematic.
Each symbol represents an electronic device (component).
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Little knowledge of a device's internal structures and behaviours are required for IC designers. Because a device works as a funtional block. In stead, a device's external structures (connection) and behaviours are of concerns.
On the fabrication-level,
8 W# F2 ^/ u/ R7 V8 Na compact model has the internal description of the device characteristics by means of a set of physics-based expressions with
technology dependent model parameters. The physic-based model parameters values accounts for the actual behavior and properties
* K% f! {. [& ~' Zof a device are defined by its process variables such as: geometrical dimensions and doping profiles.
The true parameters values need to be carefully measured by the experimental setup of device characterization.
Accordingly,
$ f+ L6 k; a! xthe verified compact models are expected to be implemented in simulators.
Thus the modelling accuracy and computational efficiency that a simulator can provide to integrate circuits' analysis
is the same as its implemented compact model. Meanwhile, a compact model is the most crucial process design kit, which plays as the interface between circuit designers and device developers.
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