Electronics - Analog and Digital Converters - Discussion

2. 

A 4-bit R/2R digital-to-analog (DAC) converter has a reference of 5 volts. What is the analog output for the input code 0101.

[A]. 0.3125 V
[B]. 3.125 V
[C]. 0.78125 V
[D]. –3.125 V

Answer: Option B

Explanation:

No answer description available for this question.

Vimal said: (Oct 15, 2010)  
Here most significant bit '0' then it's value can be 5 (0/2+1/4+0/8+1/16).

Askani said: (Nov 17, 2010)  
Formula= Vref/2^n(msb bit*2^0+nextbit*2^1+nextbit*2^2+lsb bit*2^3)

Nirja said: (Mar 11, 2011)  
Vo = 5(Vi/16)

= 5(5/16)

= 1.5625

Sundar said: (Mar 12, 2011)  
A 4-bit R/2R digital-to-analog....

Here what about R/2R...?

I think 1.5625 x 2 = 3.125V

Anuradha Awasthi said: (Mar 23, 2011)  
Formula= Vref/2^n(msb bit*2^0+nextbit*2^1+nextbit*2^2+lsb bit*2^3)
where, n= no. of bits

output= (5/2^4)(0*1+1*2+0*4+1*8)
= (5/16)(10)
= 3.125 V

Nilima Sinha said: (Sep 10, 2011)  
Vo=Vref(0*2^0+1*2^-1+0*2^-2+1*2^-3)
=5(0.5+.25)
=3.125V

Thanihai said: (Oct 8, 2011)  
Formula= Vref/2^n(msb bit*2^3+nextbit*2^2+nextbit*2^1+lsb bit*2^0)
where, n= no. of bits

output= (5/2^4)(0*8+1*4+0*2+1*1)
= (5/16)(5)
= 1.5625 V

This should be the correct answer for any type of DACs.

Kiran said: (Oct 28, 2011)  
It can b solved as =ref. voltage * binary equivalent/ total no of steps.

Ankur said: (Dec 6, 2011)  
Formula= Vref/{(2^n)-1}(msb bit*2^0+nextbit*2^1+nextbit*2^2+lsb bit*2^3)
where, n= no. of bits

output= (5/2^4)(0*1+1*2+0*4+1*8)
= (5/15)(10)
= 3.125 V

Pushpinder Kansal said: (Dec 30, 2011)  
v=5(5/16)
=1.5625
now 1.5625*2=3.125ans

Manjeet said: (Mar 25, 2012)  
Vo = 5(Vi/16)

= 5(5/16)

= 1.5625
4-bit R/2R digital-to-analog....

Here what about R/2R...?

I think 1.5625 x 2 = 3.125V

Sumit Shah said: (Jun 6, 2012)  
Main equation is,
Vo= Vref * (b0*2^(-1)+b1*2^(-2)+....)
Vo= 5 * (1*2^(-1)+0*2^(-2)+1*2^(-3)+0*2^(-4))
Vo=3.125V

Ashu said: (Jul 31, 2012)  
Vo = 5(0/16+1/8+0/4+1/2).
Vo = 3.125.

Vidya said: (Dec 5, 2012)  
Vout = Resolution * Decimal equivalent of given No.
Where Resolution = Vref/(2^n)-1
Resolution = 5/(2^4)-1 = 5/7
And dec No = 5

So answer = 25/7 = 3.125.

Vaishnavi Murugan said: (Jul 5, 2013)  
Formula = [Vref/(2^n)] {msb bit * 2^0 + next bit * 2^1 + next bit * 2^2 + lsb bit * 2^3}.

Where n = no of bit,

Solution:

Vref = 5v;
n = 4;

=> (5/(2^4)) {0*0 + 1*2 + 0*4 + 1*8}

=> (5/16) {0 + 2 + 0 + 8}

=> (0.3125) {10}

=> 3.125.

Answer => 3.125.

Gopal said: (Jul 10, 2013)  
@Nirja.

Formula = (Vref/2^N)(dec equivalent of i/p).

N- is number of significant bits (here 3 as msb is 0).

Here 0101 = 101 hence consider 3 bit.

Therefore,
Vo = 5(Vi/8) = 3.12.

Shah said: (Oct 10, 2013)  
MOST EASY METHOD:

V(0ut) = (Vi/8)*digital input.

Nitu said: (Dec 20, 2014)  
Vo = (Rf/R)(Vref)(Do/16+D1/8+D2/4+D3/2).

Nisha said: (Feb 25, 2015)  
In case of inverting, Vo = -1.5625 V.

In case of non-inverting, Vo = 3.125V.

So the given answer is correct.

Sarika Rajesh Banda said: (Sep 3, 2015)  
Yes,

Actual answer is 1.5625 volts.

Given in the sum is reference voltage = 5v, and resolution = 4.

So voltage per lsb = vref/2^n = 5/2^4 = 0.3125 v/lsb.

Therefore = 0101 in decimal is 5 = 5*0.3125 = 1.5625.

Iuuu said: (Jul 20, 2016)  
Formula = Vref/2^n(msb bit * 2^0 + nextbit * 2^1 + nextbit * 2^2 + lsb bit * 2^3).

Mahesh R said: (Jul 22, 2016)  
Here Vref=+5 and the input is 0101(means 4 bit DAC).
In a 4-bit binary system, values should be 0000 to 1111 means 0 to 15 (or F).
As the R-2R ladder is connecting to inverting terminal of the Op-amp the output analog value will be ranging from 0V to -5V.

If the input is 0000 the output = 5 (0)/15 = 0 V.
If the input is 1111 the output = 5 (15)/15 = -5 V.

Here we have 0101 means 5.

So, output = -5 * 5/15 = -1.66 V.

The correct equation for 4 bit DAC should be,

Vo = -R(b3 * 2^3 + b2 * 2^2 + b1 * 2^1 + b0 * 2^0).
= -R (b3 * 8+b2 * 4+b1 * 2+b0 * 1)
Here R = Resolution = Vref/(2^n) - 1.
Correct me if I am wrong.

Akshay said: (Dec 25, 2016)  
@Vidya.

R2r ladder has resolution =Vr/2^n (only).

Kiran said: (Apr 3, 2017)  
Analog output for the input code 0101.

Formula: Va = Vref / 2^n * input code bit (Start from MSB).
Given : Vref = 5V; Input code bit = 0101.

Va = (Vref / 2^0 * 0) + (Vref / 2^1) * 1) + (Vref / 2^2 * 0) + (Vref / 2^3 * 1).
Va = (5 / 1 * 0) + (5 / 2 * 1) + (5 / 2^2 * 0) + (5 / 2^3 * 1).
Va = (5 / 1 * 0) + (5 / 2 * 1) + (5 / 4 * 0) + (5 / 8 * 1).
Va = (0) + (2.5) + (0) + (0.625).
Va = 3.125 V.

Subodhunu said: (Aug 5, 2017)  
Va= Vref(1/2 + 0/4 + 1/8 + 0/16) (because 0101).
= 3.125 v.

Mohith said: (Dec 31, 2017)  
Vref/8=5/8=0.625,
Va/0.625=5=0101,
Va=3.125.

Ravi said: (Mar 23, 2018)  
Thanks @Vidya.

Ajit Patil said: (Nov 12, 2018)  
Thanks @Vidya.

Chandrashekhar Pantina said: (Jun 19, 2019)  
5/16*5 = 1.5625.

As R/2R so 1.5635*2 = 5.125V.

Chandrashekhar Pantina said: (Jun 19, 2019)  
5/16*(5) = 1.5625V.

As R/2R network so,
1.5625*2 = 3.125V.

Pradeep Sharma said: (Aug 10, 2019)  
It should be 1.5 because it is resolution * decimal equivalent
And it is 4 bit dac so 2^n =16.

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