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).
0 D3 {* X* t0 a$ D1 f/ BOn the circuit-level,
a compact model provides the external terminal electrical characteristics
1 Y8 T1 p* ]: d7 c8 o7 t; S$ G, B- p1 Xresulted from the mathematic expressions of an electronic device.
$ J: x/ j+ ]3 n: E' ~The external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
; I6 \* b3 E/ Yare featured as the input and output ports values.
7 @' {$ W2 F# A; ^4 c; j  G+ J4 {The unknown ports values of a device are solved by a simulator when performing circuit analysis.
6 Q+ C" x. c# cAfter the structure and behavior of the individual compact model is specified, the description(structure and behavior) are
" h: U! s) Y- L+ Msubmit to the simulator. The simulator employees KCL and KVL to create a set of nonlinear equations.
' F5 h! Q7 B/ o: E: FThe nonlinear differential equations are not solved directly, but with approximation and iterative methods. Under certain
5 {8 P+ ~; \, R5 ?! a+ zapproximation, 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.
2 g) ?1 j3 N: M+ Y% WIn other words, transistors are the primitive components in the eye of IC designer.
A virtual symbol is the representive of a real device(component).
8 E0 X; D% \' o! y/ ~9 k* b  {7 oFor instance, transistor's compact model is seen as a 4 pins symbol.
" Y: \3 q+ H* |0 EIn 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.
0 I2 a# V/ C3 P4 q5 dEach symbol represents an electronic device (component).
/ N# E4 j- ~$ x8 ~
  m" V. X/ }, S9 b; p
( @, o3 G8 C+ I0 d( X! f
7 [/ j& U6 `! x/ Z9 R- b6 lLittle 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.
3 C7 ?" H! K  BOn the fabrication-level,
  w  X" Y  u* p3 z9 n* 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
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.
5 I' L" F' Y6 k' N8 w5 _0 @Accordingly,
8 a7 c- v+ W6 S! i8 n" E# E4 h$ Nthe verified compact models are expected to be implemented in simulators.
' V+ _& h% @1 y7 S: v% A" hThus 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.
( U" i: ^3 r. H
6 Q/ d4 w& N. h

) p# [+ E; @, D
: q; E. X7 n* N1 S

. D& J+ _& G& }/ j. e4 l
; W% L! v3 G0 h, y3 w' K: l
/ A; N6 n6 ^& c& \( _
0 k7 H9 v9 O3 U. H- l) I