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:
8 ?  K: h& f' V8 ~5 ]IC design (circuit-level), model / device(device-level), IC process technology(fabrication-level).
% h7 f2 r* n( M8 z/ yOn the circuit-level,
* c6 \* R$ _& X: i9 X. a3 A" k( fa compact model provides the external terminal electrical characteristics
resulted from the mathematic expressions of an electronic device.
* K3 C7 w: S; s8 S+ M+ j( V/ O, OThe external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
are featured as the input and output ports values.
3 r; R! \3 M2 S, t# bThe 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
! o9 W+ `, J- ]& D. Nsubmit 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
approximation, 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.
+ r0 p6 d6 y' @6 f0 J) @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).
For instance, transistor's compact model is seen as a 4 pins symbol.
0 D( W6 L( [9 RIn Advanced Design System(ADS),  three design types are allowed: schematic, symbol, and layout.
& s% T. b' X- FThose 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).



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,
3 h8 M2 O( B# v. k) {8 M( {a compact model has the internal description of the device characteristics by means of a set of physics-based expressions with
  v) }: e; c5 G! B+ rtechnology 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.
% m* K- n4 e8 e: ]The true parameters values need to be carefully measured by the experimental setup of device characterization.
Accordingly,
" c3 v  B: {& @* A# wthe verified compact models are expected to be implemented in simulators.
  p- z" }% }" ~Thus the modelling accuracy and computational efficiency that a simulator can provide to integrate circuits' analysis
/ P  E; }. o) Pis 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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