# Digital to analog converters

1. Jul 9, 2015

### ranju

1. The problem statement, all variables and given/known data
The input bits 0 and 1 are represented by 0 volts and 5 volts respectively. The OP-AMP is ideal, but all the resistances and the 5 volts inputs have a tolerance o f ± 10%. The specification (rounded to the nearest multiple of 5%) for the tolerance of the DAC is??
In this question all I want to know is what is the physical significance of the term tolerance as given for the resistor , what's the purpose?? And we have to find tolerance of dac , what does this mean??

2. Relevant equations
In the solution , they found out the output voltage of op-amp and put the values of the individual tolerances..how they got to know that we have to find output voltage's tolerance from the given problem??
Voutput = -Vr [Rf/R] where Vr is the reference voltage

3. The attempt at a solution

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2. Jul 9, 2015

### Hesch

No resistors are exact. Say ( in this example ) that you have bought a resistor marked with the colors:
brown - black - orange - silver :
It means that this resistor is specified: 10 * 103Ω ± 10%

The shown DAC doesn't care about the voltages connected to the inputs, but about the currents flowing in the resistors: I = V / R. So if a connected voltage to some input is 10% too high, and that the resistor for the same input is 10% too small, what will the resulting output from the DAC be, as compared to the ideal output, due to this input?

3. Jul 9, 2015

### rude man

Confusing post.

Only thing I can figure out is you want to know the error band in the op amp's output given 10% tolerance on the 5V inputs and the resistors?

In which case, how do errors propagate when the output is a product of three parameters (2 resistors & 1 input voltage), all assumed independent of each other and normally distributed?