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March 2022 StudentZone Quiz Solution

Question:

Using Ohm's law and the formula for resistors in parallel, what is the output voltage of the R-2R DAC when inputs D7 and D6 are connected to each combination of ground and 3.3 volts? Please present the results as a table.

Answer:

The general formula for the R-2R ladder DAC circuit presented in the activity can be expressed as:

 

Where Vref = 3.3V and D7 – D0 can be either 0V or 3.3V.

In our particular situation, we only consider D7 and D6, therefore the equation becomes:

The output voltages for each combination of 0V and 3.3V for D7 and D6 becomes:

D7

D6

Vout

0V

0V

-3.3V

0

3.3V

-1.65V

3.3V

0V

0V

3.3V

3.3V

1.65V