4-bit Carry Lookahead Adder

[ Course project for VLSI Design ]

This project is a 4-bit carry lookahead adder. The RTL implementation in Verilog, SPICE netlist and MAGIC layouts are present in this repository.

For more information about the design and implementation check out the project report

NOTE: In order to run the spice netlists and view the layouts in their original form, you will need tech files in the spice and layout directories. I have used the TSMC 180nm tech files. If you are using tech files of other technology nodes or from other vendors you will have to make some modifications to the design.

Run instructions

Spice

The spice netlists can be run using ngspice.

ngspice spice/full\ circuit/top.sp

Magic

The magic layouts are sorted into directories with self-explanatory names.

Verilog

The RTL model is written in Verilog and can be run using Icarus Verilog.

You can run each testbench as follows

iverilog -o tb tb.v
vvp tb

A vcd dumb will also be generated which can be viewed in GTKwave.

FuseSoC core

The RTL model can also be simulated on Icarus through FuseSoC. FuseSoC provides a convenient way of testing different parts of the circuit without having to manually select the files and top modules. The instructions are as follows:

• You must first have fusesoc installed on your system. You can do this using pip as follows

  pip3 install --upgrade fusesoc
  

  Visit [fusesoc documentation](https://fusesoc.readthedocs.io/en/stable/user/installation. html) for more information.

• Create/Move to a directory where you want to run the simulations.

• Add the core library using the following command

  fusesoc library add cla https://github.com/adithyasunil26/Carry-Lookahead-Adder
  

  Now you can run the simulations here using fuseSoC.

• To run the flipflop testbench

  fusesoc run --target ff_tb cla
  

  To run the lookahead adder testbench

  fusesoc run --target cla_tb cla
  

  To run the complete circuit (carry lookahead adder and the flipslops) testbench

  fusesoc run --target tb cla
  

• You should be able to see the results being printed out in the terminal by FuseSoC.

What next ?

• Port netlists and layouts to an open source PDK like skywater-pdk.
• Create a complete ASIC flow using OpenLane.