Design of mechatronic systems with aliased plant modes

When digital components are combined with analog systems, frequency components in the analog system which are above one-half the sampling frequency are excited by the output of digital-to-analog (D/A) converters and aliased to lower frequencies in analog-to-digital (A/D) conversion. Since low-frequency components in a digital signal excite only higher frequencies during D/A conversion which are aliased to the same lower frequencies during A/D conversion, the D/A converter, analog plant, and A/D converter can be modeled by an aliased frequency response function (AFRF) which includes these aliased frequency effects. System identification using digital excitation and acquisition can identify the AFRF directly, or it can be developed from the frequency response function of the analog plant. Using this AFRF, controller design can proceed using conventional methods, and issues of stability, controllability of aliased modes, etc., are automatically taken into account in the design process.