An ion mobility spectrometer instrument has a drift tube that is partitioned into a plurality of cascaded drift tube segments. A number of electric field activation sources may each be coupled to one or more of the plurality of drift tube segments. A control circuit is configured to control operation of the number of electric field activation sources in a manner that sequentially applies electric fields to the drift tube segments with a activation duration of at least one of the electric field activation sources different than that of the others to allow only ions having a predefined ion mobility or range of ion mobilities to travel through the drift tube. The drift tube segments may define a linear drift tube or a closed drift tube with a continuous ion travel path.