DAC/ADC Problems

Discussion in 'Homework Help' started by McGuire406, May 4, 2014.

  1. McGuire406

    Thread Starter New Member

    Apr 28, 2014
    Hello, everyone! I'm having a few problems with some homework that I'm trying to do. It has to do with voltage, current, and resistance on ADC and DAC converters.

    Here are both types of questions that I'm stuck on:

    (1) What is the output voltage of a 4-bit binary-weighted DAC if the binary input is 1010 when the input voltage is 5V, the LSB resistor is 80kΩ, and Rf is 20kΩ? (Choices are 10V, 12.50V, 6.25V, or 8V)
    What I tried to do:
    I used the formula Vout=Vin(Rf/Rin)
    I plugged in the appropriate numbers to have 5v(20k/80k) and I got 1.25V, which isn't one of the solutions.

    (2) What is the current across the LSB "rung" of a 4-bit R/2R ladder DAC if the reference voltage is 6v and the R is 10kΩ? (Choices are 300mA, 600mA, 360mA, or 400mA)
    What I tried to do: Not knowing if I did this correctly, I went to old reliable, V=IR. When you break down a R/2R ladder, the lone resistance eft should be the value of R, or 10kΩ in this case. I divided 6V by 10kΩ, and I got 600μA, which isn't a solution.

    Sorry for sounding idiotic, I'm a novice to electronics. It's a bit overwhelming with how much information there is to take in, and I want to make sure that I understand it well. Thanks!
  2. w2aew

    Active Member

    Jan 3, 2012