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:
4 y( D7 n9 o: }* p9 HIC design (circuit-level), model / device(device-level), IC process technology(fabrication-level).
7 v8 x# z+ M+ ]/ lOn the circuit-level,
a compact model provides the external terminal electrical characteristics
resulted from the mathematic expressions of an electronic device.
- D( o  x- q  b! ^8 bThe external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
9 S5 b# N: V1 \# @" u/ p* H2 vare featured as the input and output ports values.
- d& C& J( Z% u# t' |4 YThe unknown ports values of a device are solved by a simulator when performing circuit analysis.
* _5 U8 r+ \! F+ fAfter the structure and behavior of the individual compact model is specified, the description(structure and behavior) are
$ M& Q: z: O/ I" x8 [submit to the simulator. The simulator employees KCL and KVL to create a set of nonlinear equations.
) h8 ~$ C& ^/ M( w+ H8 kThe 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.
1 v* L/ m* S7 C! L/ q& u6 VIn 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.
2 ^- \( m! g) s+ |  ~9 bIn Advanced Design System(ADS),  three design types are allowed: schematic, symbol, and layout.
; E" t6 ]# {9 m0 {- WThose 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.
6 E, v* d! U" f* ]Each symbol represents an electronic device (component).
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8 x4 z% G0 P. f8 \* Q* HLittle 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.
5 `* z8 M+ [2 ^' u& rOn the fabrication-level,
. C$ f4 C; c# ea 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
: g5 ?; ~- P6 u1 W/ |of a device are defined by its process variables such as: geometrical dimensions and doping profiles.
6 u/ A/ {6 e) K, M. pThe true parameters values need to be carefully measured by the experimental setup of device characterization.
7 }; k( A8 P+ N7 z6 \- G" O8 \Accordingly,
2 E9 \! N2 d# z, C) _6 qthe 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
+ G5 y! z  \7 V( r5 @4 K' 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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