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).
2 W. ]8 e; G7 E6 ?% K" {. ^0 y7 ]On the circuit-level,
a compact model provides the external terminal electrical characteristics
4 V: \" N! O1 t# xresulted from the mathematic expressions of an electronic device.
; E1 w; z3 c& {" {, A* AThe external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
are featured as the input and output ports values.
# I* c$ B: L* rThe unknown ports values of a device are solved by a simulator when performing circuit analysis.
. |% {0 X# U5 O0 w; i. HAfter the structure and behavior of the individual compact model is specified, the description(structure and behavior) are
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
+ C4 |" @: q9 B! P. V  I2 eapproximation, 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.
) C/ w9 N. g. A! \- G' CIn other words, transistors are the primitive components in the eye of IC designer.
A virtual symbol is the representive of a real device(component).
; i- {  O8 ]8 M6 QFor 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.
* F9 b; ~  |2 v5 i! \0 cThose designs can all be stored in a small containner names "cell" and a big containner names "library".
5 F% D9 j6 W1 Z; IIC designer works with the connection of some symbols in a schematic.
Each symbol represents an electronic device (component).
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! _6 r" r9 y9 @. E9 A  MLittle 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
6 k' |) ~/ ]  h; ^, p4 p$ m. Dtechnology dependent model parameters. The physic-based model parameters values accounts for the actual behavior and properties
2 A6 p$ y1 s8 Q! k, n( eof a device are defined by its process variables such as: geometrical dimensions and doping profiles.
; N* E8 A7 V3 RThe true parameters values need to be carefully measured by the experimental setup of device characterization.
Accordingly,
' U% |$ \7 F+ |+ Z! X* wthe verified compact models are expected to be implemented in simulators.
+ d/ H5 v0 q% s$ u  D0 T7 _! g, _Thus 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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