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.
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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.
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Fig. 2: R-2R ladder schematic

From our new schematic, we create an R-2R icon.
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Fig. 3:
New R-2R ladder icon


We check for errors, ensuring that it is DRC clean.
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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

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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
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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.
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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.
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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.
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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.
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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.