The characteristics of different generators of bi-frequency laser radiation used in differential LFM-lidars are comparatively analyzed, and the analysis results are presented. The development of amplitude-phase electrooptical devices of this class is shown to have considerable promise. Different schemes are considered. Results of experimental study of output spectral purity as a function of transformation parameters are presented. This function is considered as a main function determining the metrological characteristics of the LFM-lidar as a whole.