silicon-vlsi / 15vlsi7t

VLSI Design Course for 7th Sem AEI, 2020

Table of Contents

• Overview
  • Cloning the Repo
  • Suggested Directory Structure
• NGSpice
  • QuickStart Guide
• CppSimLite
  • Sue2
• Technology

Overview

This is the repository for the VLSI Design Course for 7th Sem AEI, 2020. This repo contains the eda tools, Labs, assignments, docs, etc. related to the course.

Cloning the Repository

git clone https://www.github.com/silicon-vlsi/15VLSI7T

Suggested Directory Structure

<HOME_DIR>          [eg. /home/vlsi]
    ├── 15VLSI7T      [Git Repo, DO NOT WORK IN THIS DIR]
    ├── Desktop
          ├── myLab    [Your Wok Directory]

NGSpice

NGSpice is a open source spice simulator for electric and electronic circuits.

• NGSpice Reference Manual: Comple reference manual in HTML format.

After cloning this repo, a precompiled version (compiled in 64-bit LXLE/Ubuntu) will be available in <PATH-TO-REPO>/15VLSI7T/eda/ngspice-32. Add the following environment variables in your ~/.bashrc

export  SPICE_LIB_DIR=$HOME/projects/15VLSI7T/eda/ngspice-32/glnxa64/share/ngspice
export  SPICE_EXEC_DIR=$HOME/projects/15VLSI7T/eda/ngspice-32/glnxa64/bin
export  PATH=$PATH:$SPICE_EXEC_DIR

There is a initialization script in $SPICE_LIB_DIR/scripts/spinit. You can overwrite any of the initilization by adding commands to a local ~/.spiceinit . The directory stucture:

15VLSI7T/eda/ngspice-32
├── doc
│   └── ngspice-32-manual.pdf  (Complete Reference)
├── examples                   (Lots of Spice examples)
├── glnxa64
│   ├── bin
│   ├── include
│   └── share
│       ├── man
│       └── ngspice
│           └── scripts        (Scripts, including startup spinit)
└── models                     (Spice models)

Quick Start Guide

You can open a text editor create a netlist of the intended circuit for example of a voltage divider as shown below (say filename divider.sp):

First line in ngspice is always the title line
* This is a comment line
Vbat    vin     0       DC 5
R1      vin     vout    1k
R2      vout    0       1k

.control
tran 0.1u 1u
.endc

.end

Then start ngspice and source the netlist at the ngspice command prompt:

ngspice 1 -> source divider.sp

It should output the node voltages at the initial transient voltages. you can plot any of the nodes eg.:

ngspice 3 -> edit

NOTE : BUG -(once you source your (.sp file) after entering ngspice simulator, the file seems to disappear the next time u search it in your directory. That's because there is an error while editing the file in ngspice simulator..

SOLUTION: source and run in batch mode

• Sourcing:

ngspice circuit.sp

• Running:

ngspice -b -r sim.raw -o sim.log sim.sp

(Then it will run ngspice, store the output in sim.raw and log file in sim.log and not enter ngspice in interactive mode..)

And to quit simply type quit.

CppSimLite

CppSimLite is stripped down version of CppSim, (http://cppsim.com) developed by Mike Perrott for mixed-signal system and circuit modeling. Although CppSim is a suite of tools for doing mixed-signal simulation, CppSimLite is only for using the schematic editor Sue2 and it's accompanying toolboxes for Python and HSPC.

• Directory Structure

CppSimLite
├── CHANGES.md				;Changes made to CppSim
├── cppsim_bashrc_file_example		;example .bashrc 
├── CppSimShared
│   ├── bin
│   ├── Doc				;All documents kept here
│   ├── HspiceToolbox
│   ├── MatlabCode
│   ├── Python				;Python lib
│   ├── Sue2				;Sue2 scripts
│   └── SueLib				;All Sue2 Private Libs
├── Import_Export
├── Netlist				;Sue2 netlists resides here
├── SimRuns				;Sue2 NGSpice runs resides
├── SpiceModels				;**NOTE**NGspice models in ngspice
├── Sue2
├── SueLib				;Public Libraries
│   └── myLib
└── Todo-Bugs.md			;Keeping tracks of Bugs and Todos

• Setting the Environment Variables in ~/.bashrc

export CPPSIMHOME=$HOME/15VLSI7T/eda/CppSimLite
export CPPSIMSHAREDHOME=$CPPSIMHOME/CppSimShared
export EDITOR=/usr/bin/vim
export PATH=$PATH:$CPPSIMSHAREDHOME/bin

Sue2

• Once the environment variables are set, Sue2 can be started by typing

sue2

• The schematic editor will launch with an empty canvas and 3 library panels on the right.
• The first panel on the top is for schematic only and the bottom two for symbols or icons to use in the schematic.
• You can choose what library to appear in each panel by clicking the the menu bar in the panel. The menu will show a list of the available Libraries stored in $CPPSIMSHAREDHOME/SueLib(Private Libs) and $CPPSIMHOME/SueLib(Piblic Libs) and the list and the order is loaded from $CPPSIMHOME/Sue2/sue.lib
• To select a schematic, use the cursor to select the schematic (eg. invX1) and then click Shift-LeftMouseButton. NOTE There is bug in sue2 in Linux-LXLE distro where LeftMouseButton doesn't work. If you are working in any other Linux (eg. ubuntu) just LeftMouseButton works.
• You can create a netlist by clicking Tools -> Create a netlist (with top sub) and give a directory to save (default: $CPPSIMHOME/Netlist) NOTE While saving for the option File Type choose All () Another bug which creates two .sp extensions otherwise.
• Now you can can write a Spice testbench and include and instatiate the above created netlist. There is alrady a example testbench in $CPPSIMHOME/SimRuns/myLib/invX1/TB_invX1.sp

Technology

MOSIS Scalable CMOS (SCMOS)

SCMOS is a lambda-based scalable design rules that can be interfaced to many CMOS fabrication process available at MOSIS. NOTE The scalable design rules does not interface with Fabs now because of lot unique process nuances.

• The Spice model files are located at <PATH-TO-REPO>/project2020/eda/ngspice-32/models/scn4m_subm
• Typical MOS parameters:
  • NMOS: tox=7.6nm, nch=1.7e17/cm^3, Vt0=0.49V, un(mobility)=445 cm^2/Vs
  • PMOS: tox=7.6nm, nch=1.7e17/cm^3, Vt0=-0.66V, up(mobility)=151 cm^2/Vs

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