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:
IC design (circuit-level), model / device(device-level), IC process technology(fabrication-level).
; C) _  F, f# m/ kOn the circuit-level,
& C  @" m8 s1 Z0 S$ D" X: Ga compact model provides the external terminal electrical characteristics
resulted from the mathematic expressions of an electronic device.
The external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
2 t0 \0 N9 Q8 {6 t" o  b* Uare featured as the input and output ports values.
The unknown ports values of a device are solved by a simulator when performing circuit analysis.
/ G( f, U/ }: B* y6 jAfter the structure and behavior of the individual compact model is specified, the description(structure and behavior) are
submit to the simulator. The simulator employees KCL and KVL to create a set of nonlinear equations.
( |- x3 ]0 T! ?! l9 uThe nonlinear differential equations are not solved directly, but with approximation and iterative methods. Under certain
7 R% S" X2 H- m9 z. sapproximation, the equations are solved with the Newton-Raphson method. The solutions are equilibrium points of nodal analysis.
8 P5 r# j: J9 a8 M8 Q2 \8 aIC design engineers work on a higher abstraction level than the device(transistor) level.
; G# q: M5 {* L4 F: CIn other words, transistors are the primitive components in the eye of IC designer.
3 i9 j+ R1 f, k0 R% j$ S6 x6 TA virtual symbol is the representive of a real device(component).
( y1 N; Z/ `- {0 YFor instance, transistor's compact model is seen as a 4 pins symbol.
5 s! s, ~  g3 ], }( f- n1 F- \* GIn Advanced Design System(ADS),  three design types are allowed: schematic, symbol, and layout.
% U, l9 {" R7 S  gThose designs can all be stored in a small containner names "cell" and a big containner names "library".
0 J. ^1 ]6 g+ C0 Y" ]IC designer works with the connection of some symbols in a schematic.
Each symbol represents an electronic device (component).



$ x. v, G* j/ _, eLittle 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.
% A, p& E- d" [& V- C( r, H! AOn the fabrication-level,
: f2 A2 z# L9 m( f/ }& K( p* ra 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' P' Z/ D" C- \of a device are defined by its process variables such as: geometrical dimensions and doping profiles.
" j- _; K1 Q, J. JThe true parameters values need to be carefully measured by the experimental setup of device characterization.
" X: n' [2 b: PAccordingly,
; Y9 I9 r  D, n( Xthe verified compact models are expected to be implemented in simulators.
, M  \" x  J; |0 H6 Z3 {8 N2 E  rThus the modelling accuracy and computational efficiency that a simulator can provide to integrate circuits' analysis
2 M' a# V* Q0 kis 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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