A signal generating system for generating an output signal with a 50% duty cycle, comprising: a frequency dividing module, comprising an odd number of level triggering devices, for generating a plurality of frequency divided signals utilizing a frequency dividing ratio equaling to M, wherein the M is an positive integer; and a signal combining module, for combining at least two of the frequency divided signals to generate at least one output combined signal. The signal generating system generates the output signal based on the output combined signal. The frequency dividing module cooperates the signal combining module to provide a frequency dividing ratio equaling to N.5, wherein the N is a positive integer.