|
This example circuit shows the effect of using slightly mismatched resistors when building a R-2R DAC with discrete component (in this case, R=4.7K , 2R=10K).
In blue/red the DACs output values, in orange the difference between the two (basically, the error), green is the GND reference.
Notice how, for small input (digital) value of each counter the output is very similar between the two DACs, but gets more and more pronounced as the input value increases. You can set the R value to its proper value of 5K to check that the error goes basically to 0.
This can be compensated by using matched R-2R resistors with tight tolerances, but it usually gets expensive or not feasable.
For less than 6 bits you can usually get away with a ratio of (2R/R) = +/–5%.
Any thoughs?
|
