Dead-zone-less PLL frequency synthesizer by hybrid phase detectors

In this paper, in order to achieve the low phase noise in a PLL frequency synthesizer, we propose a new dead-zone-less PLL frequency synthesizer by hybrid phase detectors. We have developed the combination divider with (N+½) programmable divider and (½) fixed divider and the 90 degrees shift circuit and developed hybrid phase detectors method with both the exclusive-OR type phase detector and the normal frequency-phase detector. The former detector requires the two input signals with 50% duty factor and π/2 phase difference under the locked state. A (N+½) programmable divider with a (½) fixed divider and the 90° phase shifter are effectively employed to meet the above conditions. Both the simulation and experimental results show that the proposed synthesizer works successfully