Electronics - Analog and Digital Converters - Discussion

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.

If the input code is 0101 then the answer should be 1.5625 volts. If we chose from the answer side then the input code should be 1010.

It should be 1.5 because it is resolution * decimal equivalent
And it is 4 bit dac so 2^n =16.

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.

Thanks @Vidya.

Vref/8=5/8=0.625,
Va/0.625=5=0101,
Va=3.125.

In case of inverting, Vo = -1.5625 V.

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

So the given answer is correct.

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.

Formula = Vref/2^n(msb bit * 2^0 + nextbit * 2^1 + nextbit * 2^2 + lsb bit * 2^3).

@Vidya.

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