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Appendix A
CMOS Device Modeling for Circuit
Design
Before a circuit is designed, to be integrated by CMOS VLSI technology, a
model must be adopted which will describe behavior of all components successfully.
A model means a set of mathematical formulas, circuit representations, tables,
reference standards etc.
A.1. Simple MOS large signal model
Lower case variables represent instantaneous values and upper case variables
represent averaged or rms values. Lower case subscripts are used for small signal values and upper case subscripts for large – signal values. This model was developed
by Sah and is also called the SPICE Level 1 Model. This model is given by
58
59
60
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A.2. Simple MOS Small – Signal Model
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Appendix B
The Cadence IC 445 set of tools
The IC 4.4.5 set of tools is a complete front-end to back-end design suite for
integrated circuit design. This chapter gives a summary of the different design tools
available to an analog circuit designer.
B.1 Design Entry
For analog design, the Composer Schematic Editor tool is used. This allows
easy entry of the schematic. The editor employs several useful options to make design
entry efficient. Some of these include gravity, object sensitive dialogs and pop-up
menus. It also includes a method for checking the validity of the design. The
schematic entry environment extracts a netlist called the CDL.
B.2 Simulation Environment
The analog artist simulation environment is used to simulate the design. This
is a front-end to the actual simulator. It allows one to choose the simulator and set the
54 options appropriate for the simulator through easy to use menus. Analog artist also
includes extensive post-processing facilities for analyzing the results of the circuit
63
simulation. Analog artist contains support for cdsSPICE, spectreS, HSPICE and other
simulators. cdsSPICE and spectreS are Cadence's simulators based on SPICE but
with some extensions. It supports all standard SPICE models. Specifically, BSIM3v3
models were used for the simulation of the circuits.
B.3 Design Synthesis and Layout
The device level editor (DLE) is used to generate the layout from the
schematic. This places all the devices in a layout window approximately in
accordance with their placement in the schematic. This also has facility for showing
the devices and nets that need to be connected. This allows one to do a layout that
corresponds exactly to the schematic. The Virtuoso layout editor is used for defining
the interconnects and other structures in the layout.
B.4 Design Verification
Once the layout is made, it has to be verified to be correct. For this, one does a
design rule check (DRC) using the Diva verification tool. After the design rule check
has been passed, a netlist has to be extracted from the layout. This netlist is then
compared with the schematic netlist using the “Layout vs. Schematic” option in Diva.
Diva also contains options for extraction of parasitic resistance and capacitance. This
information can be back annotated into the circuit and the simulation repeated to
verify that the circuit does indeed work with the parasitics.
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Appendix C
Acronyms
ADC
Analog to Digital Converter
BiCMOS
Bipolar Complementary Metal Oxide Semiconductor
BJT
Bipolar Junction Transistor
CAD
Computer Aided Design
CMOS
Complementary Metal Oxide Semiconductor
DAC
Digital to Analog Converter
IC
Integrated Circuit
MOS
Metal Oxide Semiconductor
MOSFET Metal Oxide Semiconductor Field Effect Transistor
VLSI
Very Large Scale Integration
65
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