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).
( Y& m+ p( D" _" Y1 d% HOn the circuit-level,
) y6 X+ [5 K& h, sa compact model provides the external terminal electrical characteristics
6 L6 F- h) j! O" h1 u" iresulted from the mathematic expressions of an electronic device.
  g# ~  R/ u% HThe external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
are featured as the input and output ports values.
+ J: @0 b* ], E4 F  MThe unknown ports values of a device are solved by a simulator when performing circuit analysis.
( B* K7 V2 L3 S) b' ?4 Q# e# pAfter the structure and behavior of the individual compact model is specified, the description(structure and behavior) are
6 \7 k! ^( d) I  U4 ?; P* _' f% _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
approximation, the equations are solved with the Newton-Raphson method. The solutions are equilibrium points of nodal analysis.
5 I7 t0 a# t% `( }: wIC design engineers work on a higher abstraction level than the device(transistor) level.
2 j% w" ^. ~* e" w* e! d( v# @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.
In Advanced Design System(ADS),  three design types are allowed: schematic, symbol, and layout.
6 Y* `4 w" h& J; qThose 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).
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) U5 t. a! _" [- f$ iLittle 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.
Accordingly,
8 `" N# |3 ~- S- F( h# C+ q& Vthe verified compact models are expected to be implemented in simulators.
5 a# n4 f+ S  fThus 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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