ENGR338 SPRING 2021
Lab 3: Layout the R-2R DAC
Name: Caroline Kleven
Email:
cekleven@fortlewis.edu
1. Lab 3: Layout the R-2R DAC
For Lab 3 we had two objectives:
1. Create a layout of the R-2R DAC in Electric VLSI using N-Well resistors
2. Become familiar with Electric VLSI and LTSpice for integrated circuit
design
2. Introduction
During this lab, we completed two tasks:
1. Created a schematic of the subcells for the R-2R ladder
2. Created a layout of the subcells for the R-2R ladder
3. Materials and Methods
For Lab 3 we used:
1. Electric VLSI, to create layouts and schematics
2. LTspice, to run simulations
4. Results
For our first task, we created a schematic and icon in Electric VLSI for the subcell of an R-2R ladder, making sure to check for errors.
Fig. 1: R-2R ladder subcell schematic and icon
Next, we created a new schematic view of an R-2R ladder, using the icon from the subcell.
Fig. 2: R-2R ladder schematic
From our new schematic, we create an R-2R icon.
Fig. 3: New R-2R ladder icon
We check for errors, ensuring that it is DRC clean.
Fig. 4: Checking the new schematic and icon for errors
For our second task, we first created a layout view for the R-2R subcell.
We began by formatting our N-Well resistors
Fig. 5: Changing the N-Well resistor length, width, and resistance
We then created a layout of the R-2R subcell, using the N-Well resistors, ensuring that it is DRC clean, and passes NCC
Fig. 6: The R-2R subcell layout, checking for errors
We used the layout icon from the subcell to create a layout view of the R-2R ladder.
Fig. 7: The new R-2R layout, built using the subcell layout icon
Before proceeding, we verified that the new R-2R layout passed both DRC and NCC.
Fig. 8: Checking to make sure the new R-2R layout passes DRC and NCC
We then replaced the DAC we created in Lab 1 with the new R-2R Ladder.
Fig. 9: Replacing the DAC from Lab 1 with our new R-2R ladder icon
When we run the schematic in LTspice, we can see that our layout is correct.
Fig. 10: Running the new simulation through LTspice
5. Discussion
I had to perform this lab multiple times because I was copying the icon
from the wrong place for both the subcell and the completed R-2R
ladder. I couldn't figure out why my layouts weren't passing NCC until
I discovered my mistake. Now I know to copy it from the same layer,
rather than the icon layer, which is helpful for future labs.