Direct period synthesis is a technique of using a base time unit and the time-average-frequency concept to synthesize clock frequency. Its distinguished capabilities include generating frequencies in very fine step and switching frequency in very fast speed. In this paper, the principle of fine frequency generation is presented. Using data collected from two 55-nm CMOS chips, experimental evidence of sub-ppm (0.04 ppm at finest) frequency resolution at 27 MHz, 1.5 GHz, and 2.4 GHz is provided. This feature of fine frequency resolution is very important in digital communication, especially for plesiochronous and heterochronous systems. It is a circuit level enabler for system level innovation. In the last part of this paper, several important applications of using these capabilities are explored.