8-bit Digital to Analog converter (DAC)

Posted on Feb 5, 2014

This article aims to introduce to beginners and intermediate readers a simple solution to build a digital to analog converter, based on the famous r/2r resistors network. This article also discuss a problem encountered by many beginners while trying to build their own DAC, and proposes some very simple solutions to that problem. Through this artic

8-bit Digital to Analog converter (DAC)
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le, I am going to explain how to build an 8-bit digital to analog converter with parallel input. If you don`t know what this means, well its simply a circuit that will take as input a digital 8-bit number from 0 (00000000) to 255 (11111111), and output the relative value on a scale from 0 to 5v. Then the output voltage for the converter should be equal to the binary input multiplied by the step value, e. g. for an input of 129 (1000 0001 in binary) the output voltage should be: The digital data entering thought the 8 lines (D0 to D7) are going to be converted to an equivalent analog voltage (Vout) by the mean of the R/2R resistor network. Actually a lot of commercial Digital to Analog converter ICs are based on this same principle. The R/2R network is build by a set of resistors of two values, with one of them double the other (example 10K and 20K), in on of my circuits I used 1M ohm and 470K ohm resistors, which is quite near to the R/2R ratio, and this small difference didn`t cause any detectableerrors in most applications. However, if you want to build a very precise DAC, be precise when choosing the values of the resistors that will exactly match the R/2R ratio. Note that you can build a DAC with any number of bits you want, simply by enlarging the resistor network, by adding more R/2R branches (like the one shaded in green), BUT you must keep the 2R resistance connected to ground (shaded in light red) Now, in order to...

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