A fractional-N frequency synthesizer with phase synchronization and programmable phase control capability

Abstract

A fractional-N frequency synthesizer (FS) with phase synchronization and programmable phase control capacity is proposed. The issue of phase inconsistency among multiple FSs caused by the shift of delta-sigma modulator (DSM) output sequence is solved by means of the dual DSM switching technique. Following the FS core, a resettable divider (R-DIV) is presented, which can not only expand the final output frequency range, but also eliminate the phase uncertainty incurred by uncontrollable initial states inherent in the ordinary dividers. By adding initial values to the first order accumulator in the third-order DSM, the output clock phase of the FS can be controlled accordingly. The simulation results show that from a supply voltage of 1.2 V, the frequency range of the FS is 0.4∼12 GHz, and the phase synchronization time is < 10 μs. The minimum phase shift step size of the programmable phase control is 5.625°, the RMS phase error is < 0.9°, and the power consumption is 113.7 mW.