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:
) K* O5 M: V* E0 t# hIC design (circuit-level), model / device(device-level), IC process technology(fabrication-level).
3 d! y8 Z, y  v' b% g5 `2 XOn the circuit-level,
( v2 h9 \# X) F5 Za compact model provides the external terminal electrical characteristics
( W) M6 ]' J  I; ~. n3 S$ [% Kresulted from the mathematic expressions of an electronic device.
The external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
$ w6 |! r1 @8 O, Y! \" N5 t, Fare featured as the input and output ports values.
0 S  F6 C9 [& C8 H5 h- U" P; N) QThe 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* {6 {7 [submit to the simulator. The simulator employees KCL and KVL to create a set of nonlinear equations.
# r4 K6 @; I3 P2 S! S( nThe nonlinear differential equations are not solved directly, but with approximation and iterative methods. Under certain
) w9 i2 M- L5 l3 h' japproximation, the equations are solved with the Newton-Raphson method. The solutions are equilibrium points of nodal analysis.
IC design engineers work on a higher abstraction level than the device(transistor) level.
" G' R6 b2 s& W5 w) X$ {In other words, transistors are the primitive components in the eye of IC designer.
; Y. s8 L4 `0 N- wA virtual symbol is the representive of a real device(component).
' z  `7 C# {* x; G0 H! V8 NFor instance, transistor's compact model is seen as a 4 pins symbol.
In 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".
4 T' G& Q8 W9 i# y+ }2 B9 tIC designer works with the connection of some symbols in a schematic.
0 F; U+ F; k2 e; xEach 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,
a 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
of 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.
6 }) B% T5 L& W5 \' JAccordingly,
( H& m2 i0 X) Pthe 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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