Integration of digital potentiometers in analog circuits

The implementation of digital potentiometers allows a more flexible and powerful management of the analog traditional circuit, being these devices driven by microcontrollers. Having at one's disposal the analog original circuit, the challenge is to substitute the digital potentiometer in place of the traditional one, modifying as less as possible the chosen circuit itself. This procedure can not be carried on directly, since the digital devices intrinsically address some new problems to the designer. For instance, issues can be related to the digital potentiometers’ supply and the relation between the latter and the analog signals involved. Furthermore, the injection of zipper noise into the signal path is also a major issue. This fact requires the design of specific circuital solution, which are the goal of this work. A preliminary analysis of the original analog circuit is mandatory in order to evaluate what are the condition in which the traditional potentiometers work. In conjunction to this, an overview of the functioning (and related commercial parameters) of the digital devices allows the designer to identify the critical issues of a direct substitution of the analog potentiometer. An exploration of some possible solutions is then performed, pointing out what are the advantages and disadvantages of different design, exploiting the measurement done on an experimental board specially design for this purpose. The results obtained are then reported and commented noticing how much a digital, in place of analog, implementation can bring both great advantages, from the user’s perspective, as well as some difficulties for the designer.