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:
( ?9 z' \* {* K1 m: [IC design (circuit-level), model / device(device-level), IC process technology(fabrication-level).
On the circuit-level,
$ G* ?4 E6 X( q4 ^8 v1 Qa compact model provides the external terminal electrical characteristics
# M4 p$ R% O, d, N! W4 f9 vresulted from the mathematic expressions of an electronic device.
# P/ J! B% Q+ B% jThe external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
0 ~, Q. v4 g( }: X0 H$ j, ware featured as the input and output ports values.
The unknown ports values of a device are solved by a simulator when performing circuit analysis.
, J% m) ^' f* p: H( b" \  AAfter the structure and behavior of the individual compact model is specified, the description(structure and behavior) are
6 I8 o8 X5 Q9 e% w; ~1 Y+ osubmit 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
" h5 i: @, [- Y0 E) p6 sapproximation, the equations are solved with the Newton-Raphson method. The solutions are equilibrium points of nodal analysis.
5 L/ B. v2 H4 w+ u+ O1 Q8 LIC design engineers work on a higher abstraction level than the device(transistor) level.
/ z3 L3 z9 }3 n) N# `; ^, k/ q6 `In other words, transistors are the primitive components in the eye of IC designer.
/ e8 N- L0 Z, U' {; Q6 G1 nA 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.
: g8 t/ U2 i+ A3 R5 F% LThose 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.
- c' Y0 C+ G6 W3 O& B6 K# LEach symbol represents an electronic device (component).

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4 v0 |' M4 ?' l6 g6 l2 |1 V$ Q' cLittle 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.
" q: K3 p5 [9 }, i/ \% k) XOn the fabrication-level,
a compact model has the internal description of the device characteristics by means of a set of physics-based expressions with
' Q3 c' f6 J# U7 C+ \4 c9 atechnology dependent model parameters. The physic-based model parameters values accounts for the actual behavior and properties
2 f1 e0 `6 A: y$ w, G6 X/ h6 Q' `; Qof 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.
+ Z, k# }2 U& O6 Q$ e1 o7 q4 O5 q; _Accordingly,
the verified compact models are expected to be implemented in simulators.
Thus the modelling accuracy and computational efficiency that a simulator can provide to integrate circuits' analysis
6 P2 }& m( `, J3 O( T3 ^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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