We report on the design and calibration of a high speed electro-optical variable circular retarder (EOVCR). This retarder consists of an electro-optical variable linear retarder and two quarter-wave plates aligned at specific angles. This EOVCR provides a pure polarization rotation that is independent of the initial incoming polarization. Application of this device in a rotationally symmetric microellipsometer design is also discussed. The use of such an EOVCR eliminates the vibrational noise reported in the previously reported microellipsometer design and allows a high speed nulling detection scheme to be used, substantially improving the accuracy of microellipsometer.