A 4-bit R-2R digital to analog converter (DAC) has a reference of 5 Volts. What is the analog output for input code 1010?

Question

Question

This question was previously asked in

UPPSC AE Electrical 2019 Official Paper II (Held on 13 Dec 2020)

Answer 1

Concept:

R – 2R ladder DAC:

3 bit R – 2R DAC by using Inverting op-amp is shown below:

Output voltage is defined as:

V0 = - I1(RF) ⋯ (i)

Current is calculated as:

⋯ (ii)

Current drawn from the source is

I = V / R ⋯ (iii)

Current is calculated as:

The final output voltage is

For n bit DAC output voltage is

Calculation:

Given digital input is 1010 and the reference voltage is 5 V

a3 = 1, a2 = 0, a1 = 1, a0 = 0

considering the value of the feedback resistor for Op amp is R Ω

Output voltage is

V0 = -3.125 V