Page 272 - The Mechatronics Handbook

(a) Levels Views
Behavioral Structural Physical
4 Performance CPUs, Memory, Physical
Specifications Switches, Controllers, Partitions
Buses
3 Algorithms Modules, Clusters
Data Structures
2 ALUs, MUXs,
Register Transfers Floorplans
Registers
1 Boolean Equations, Gates, Cells,
FSMs Flip-flops Modules
0 Transfer Functions, Transistors, Wires, Layout
Timing Contacts, Vias Geometry

(b) Levels Views
Behavioral Structural Physical
4 Sensors, Physical
Performance Actuators,
Specifications Partitions
Systems
3 Multiple Energy
Domain Clusters
Components
2 Domain-Domain Floorplans
Components
1 Single Energy Cells,
Domain
Components Modules
0 Beams,
Transfer Functions, Membranes, Holes, Layout
Timing Geometry
Grooves, Joints
FIGURE 13.2 A taxonomy for component development (“levels and views”): (a) standard VLSI classifications,
(b) a partial classification for MEMS components.

A schematic diagram is an example of a structural description. Of course, not all circuit charac-
teristics can be completely encapsulated in a single one of these views. For example, if we change
the physical size of a wire, we will probably affect the timing, which is a behavioral property. The
principle of encapsulation leads naturally to the development of extensive IP (intellectual prop-
erty), i.e., libraries of increasingly sophisticated components that can be used as “black boxes” by
the system developer.
• Well-developed models for basic elements that clearly delineate effects due to changes in design,
fabrication process, or environment. For example, in [10], the factors in the basic first-order equa-
tions for I ds , the drain-to-source current in an NMOS transistor, can clearly be divided into those
under the control of the designer (W/L, the width-to-length ratio for the transistor channel), those
dependent on the fabrication process (ε, the permittivity of the gate insulator, and t ox , the thickness
of the gate insulator), those dependent on environmental factors (V ds and V gs , the drain-to-source
and gate-to-source voltages, respectively), and those that are a function of both the fabrication
process and the environment (µ, the effective surface mobility of the carriers in the channel, and V t ,
the threshold voltage). More detailed information on modeling MOSFETs can be found in [11].
Identification of fundamental parameters in one stage of the development process can be of great
value in other stages. For example, the minimum feature size λ for a given technology can be used
to develop a set of “design rules” that express mandatory overlaps and spacings for the different
physical materials. A design tool can then be developed to “enforce” these rules, and the conse-
quences can be used to simplify, to some extent, the modeling and simulation stages. The parameter
λ can also be used to express effects due to scaling when scaling is valid.

©2002 CRC Press LLC