CE338 Digital VLSI Laboratory
The Inverter

Objectives:
Be able to layout and simulate an inverter in Electric.


Lab Tasks:

** Task 1: Create the schematic of the inverter.

Note that the bigger size of the number denotes the 'drain' side. Please a PMOS and an NMOS in the schematic view, rotate/mirror the PMOS to let the drain oriented to the NMOS. The PMOS is 20/2, the NMOS is 10/2.



Use the vdd and gnd symbols (they are global exports by default so don't export them again). Export the 'in' and 'out' ports for the inverter. Build create an icon view of it.



Run the DRC check to ensure it is error free.



Next, run a simulation to ensure that it inverts the input. Do not forget to set Spice models by selecting the PMOS or the NMOS one at a time and follow Tools - Simulation (Spice) - Set Spice Model. Name them as PMOS and NMOS respectively.



Next, run a transient simulation use a PULSE() input. The spice code is not provided here. Design it one your own.
The results looks like this:






** Task 2: Create the layout of the inverter. 

Build the layout of the inverter by following the tutorial here. Run DRC and LVS check before you move forward. Also, do not forget to set the Spice models for the PMOS and the NMOS.





** Task 3: Use the multiplier to build a larger inverter. 

The inverter you just built is 20/5 and 10/5. In this section, let's built a 100/2 and 50/2 inverter using the multiplier function in Electric.

First, duplicate the inverter cell and rename it as 'Inverter_100_50'. Click the new cell and select the PMOS. Then press tools --> Simulation (spice) --> add Multiplier to set the M=5 adding 5 parallel PMOS. Do the same to NMOS. Others are kept the same as before. We can get the following circuit.



In the layout view, copy/paste the existing PMOS, delete the metal contacts on the left side of the duplicate, then make the connection to the left. Make sure that the connection is built by the green wire (the active field) not the metal (blue).



After you done with the first duplicate, run a DRC check instantly before you moving forward. The gap size indicated in the following figure must be evenly spaced.



Get 5 of the PMOS and the NMOS in parallel and make them 5 times wider. Run DRC/LVS after this is done.






** Task 4: Run simulations to verify the driving capability of these two different inverters. 

First, create a simulation schematic view for the 20/10 inverter:



Run 3 simulations to let it drive 100 fF, 1 pF, and 10 pF caps respectively.

Cload = 100 fF



Cload = 1 pF (start having some difficulties to drive the cap).



Cload = 10 pF (can't drive it to the full voltage).



Next, let's grab the wider inverter and see how it goes. (you can directly replace the 20/10 one with the 100/50 one).

Cload = 100 fF



Cload = 1 pF



Cload = 10 pF
Now, you can tell the difference. The 100/50 inverter can drive bigger caps compare to the smaller one.





Lab reports grading rubric:

Task 1: 25 points.
Task 2: 25 points.
Task 3: 25 points.
Task 4: 25 points.
 





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The end of the lab.