Okay before anybody say something I would like to mention that
1. No I could not have used a single voltage source because I have to give 4 bits of two numbers.
2. The circuit could not have been much easier as it is an abstraction of world's most fastest adder used in almost all electronics device today.
3. Due to stint of this software of having only 4 colors to display on graph, I couldn't plot all the input and output signals. Only SUM bits of each 4 bits are plotted and output carry is left open which shows overflow bit. But the circuit have been tested on modelsim and even on FPGA and it works well..
