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:
, L" y# M8 C3 O$ W, k  {IC design (circuit-level), model / device(device-level), IC process technology(fabrication-level).
; R3 Z  h, f% `$ C+ Y# |" HOn the circuit-level,
" P$ `" _. u6 r: L0 e- |- `: aa compact model provides the external terminal electrical characteristics
resulted from the mathematic expressions of an electronic device.
3 t( o7 a" O- f+ k. l2 QThe external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
8 K0 T# C9 Y( n- W6 ]are featured as the input and output ports values.
The unknown ports values of a device are solved by a simulator when performing circuit analysis.
) ^6 _/ e) ?- A0 nAfter the structure and behavior of the individual compact model is specified, the description(structure and behavior) are
+ p! e' H. V! |submit 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
: ?, e  Z4 S9 ]9 E/ d$ q7 Z) Y( Vapproximation, 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.
, k6 k1 G! e0 a+ u9 MIn other words, transistors are the primitive components in the eye of IC designer.
A virtual symbol is the representive of a real device(component).
For instance, transistor's compact model is seen as a 4 pins symbol.
/ O! D3 X6 V9 f( NIn 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".
. i" }  A* ~0 |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,
a compact model has the internal description of the device characteristics by means of a set of physics-based expressions with
+ r9 @" T4 Z& g7 o# z5 ztechnology dependent model parameters. The physic-based model parameters values accounts for the actual behavior and properties
- q7 \5 i* _: ]% I1 x. d8 @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.
+ R  f$ F3 U$ y/ M8 hAccordingly,
the verified compact models are expected to be implemented in simulators.
0 K. l5 W4 o' @2 f/ U' ^$ j* bThus 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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