3Transistor NAND gate using sky130pdk
This circuit simulation was completed using 
eSim :for schematic and  spice netlist generation
skywater 130  pdk : process node 
ngspice : for  circuit simulation

Below steps summarises tasks carried out during simulation

1. Steps to create schematic in eSim and obtain spice netlist
2.ngspice simulation
3.Debugging and Changes.

1.Steps  to create schematic in esim
 Firstly, all the requried installation is made as per the instruction given in eSim website.
Then after installation process is over open eSim  then following steps to create schematic for 3T nand cell:
   1.Click on Subcircuit option in left vertical bar then select New Subcircuit Schematic and enter the name in this project it is "nand2i3t"
   2.Schematic Sheet will be opened then click on "Opamp" like symbol on right vertical tool bar.
   3.click on sheet and a window will open to choose component in that  type "esim" all the esim components like mosfet,power  will be displayed
      In thst select the requried components and make proper connections using requried options present on right tool bar like pulse input,wire,portlabel,label,gnd etc
   4.Then connect circuit accordingly and add plot to the output and input add labels accordingly.I have made connections according to circuit given in reference circuit with proper connections.
   5.Last step is ERC(electrical rule check)in this  process the tool checks if the electrical connection are proper and if  components are properly annotated .
     To perform this there is option to annotate the circuit and do ERC on top toolbar on 10th section annotate circuit components (opamp like symbol) and right to annotate ERC check can be done by clicking that option
        If ERC errors are 0. Then circuit is properly connected.
                   After ERC step is performed  go to NET symbol on same tool bar to generate spice net list .
	 Click on spice tab  in popup window select on Default format and click on Generate option.
   Spice netlist will be generate save it in "ngspice"folder in Spice\bin.

2. ngspice simulation  
    copy sky130_fd_pr folder to ngspice
   After  extracting netlist from eSim made changes  like added sky130 mosfet models instead of mosfet models 
   After changing models  added the transient analysis part using .tran command and made analysis  and rectified the errors accordingly

3.Debugging and Changes
 eSim:

  In my circuit de bugging started from schematic part where Connections were improper like ports were not connected to right pin (this occoured due to improper placment of labels and plot pulse port are not aligned accorting lines ) .
  This error got rectifed as the eSim shows that label is connected properly label gets on the line without showing the small box icon. 
  At some voltage levels the power flags are added to remove error

 ngspice:

 In ngspice firstly I got "fatal error" .later got to know it willl occour due to improper decleration of sky130_fd_pr path in .cir file. Accordingly i changed path and got rectifed the error
 Next error was I  was unable to get  output plot but i was getting input plot correctly so after many attempts i cam to know some error was there in installation so I reinstalled and checked .
 I was able to get the results of output. 

Finally i got the NAND gate output for 2 input with three transistor only instead of 4 transistor.

Acknowledgements
SUMANTO KAR
Kunal Ghosh 