A new technique for the stabilization of local oscillators by the way of frequency synthesis is presented. A combination of both a PLL and a DLL in a novel frequency synthesizer architecture overcomes the drawback of PLL stability, while avoiding the classical DLL out-of-band spurious. Therefore, the Mixed P/DLL synthesizer can exhibit very wideband and, consequently, can dramatically reduce the local oscillator phase noise and the synthesizer settling time. Dynamic performances of an unstable PLL are then observed, while the system stability is guaranteed by the DLL first order loop behavior. A 130nm CMOS experimental demonstrator is presented, able to synthetize local oscillator form 1 to 3.5GHz, with settling time as low as 1.2μs.