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:
1 W! H4 V. q6 j6 o; y1 {IC design (circuit-level), model / device(device-level), IC process technology(fabrication-level).
& N, _* i% Q1 B9 P2 x0 jOn the circuit-level,
9 h' L. q. J8 u' Za compact model provides the external terminal electrical characteristics
resulted from the mathematic expressions of an electronic device.
The external terminal characteristics (Pin Characteristics) includes terminal voltages, currents or charges,
are featured as the input and output ports values.
The 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
$ m  q4 j8 S! T: V' D" `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
. Q8 F: V$ Q( |* o' b' |0 @& Kapproximation, 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.
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).
. H4 I, Z7 A+ f: C* L$ t7 Q+ sFor 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.
! R7 S1 E+ t1 m# n& lThose designs can all be stored in a small containner names "cell" and a big containner names "library".
4 X# m7 j4 ~2 s- b  u: o/ ]IC designer works with the connection of some symbols in a schematic.
/ _' ?5 F! H  J. t6 z9 bEach symbol represents an electronic device (component).

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' \* L  Y, T* V! \4 f9 D5 W) `. ULittle 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.
/ `) a4 X! }' R  RAccordingly,
) j& ^+ Q7 i% w7 T0 R* U5 D* @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
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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