ENGR338 2020 Spring
Lab 2 - Design a R-2R DAC
John Hitti
jdhitti@fortlewis.edu

Lab 2:
The purpose of this lab was to gain a better understanding of the function of ADC and DACs. This was done by analyzing both the input and output of ideal components and designing a R-2R DAC in Electric VLSI.

Task 1:
In task 1 we used Electric VLSI and Spice to graph the output of a sine wave signal processed an ideal ADC and DAC.

Figure 1. Both the ADC and DAC are connected in Electric VLSI


Figure 2. Using the LT Spice script, we are able to graph the output voltage compared to the input voltage





Task 2:
In task 2 we created a R-2R DAC to replace out ideal DAC. This R-2R dac uses n-well resistors to create a ladder of inputs that function as a DAC.

Figure 3. The R-2R DAC is built in Electric VLSI with both the schematic and layout view shown.

Figure 4. The R-2R DAC is connected to out ideal ADC.


Figure 5. The output of the R-2R DAC is graphed alongside the input of the ADC.



Task 3:
In task 3 we tested the time delay of the circuit when the 2-R2 DAC is driven only by the B9 pin and all others are shorted. The load tested is a 10pF capacitor.

Figure 6. An Electric VLSI schematic was made using the ideal ADC and R-2R DAC to measure the time delay across the 10pF capacitor.


Figure 7. The output of the circuit was graphed and the time delay measured using LT Spice.


Figure 8. The time delay calculated in LT Spice is in line with the time delay calculated by hand.



Discussion:
This lab was an excellent introduction to the operations of both ADC and DAC components and how they process digital and analog signals. Designing the 2-R2 DAC helped to display the inner workings of this type of DAC and how it converts digital signals to analog signals.