In modern RF communication systems, signal integrity is of prime importance. To meet the system requirements, amplifiers, mixers and modulators must have a low noise figure and low distortion products. Additionally, as system designers work to squeeze increasingly more data into the available bandwidth, low phase noise signal sources assume an equal importance. To address this need for low phase noise signal sources, we developed the LTC6945 and LTC6946 Phase Locked Loop (PLL) frequency synthesizers. Both parts deliver a low phase noise PLL core that not only has a low in-band noise floor, but also has a very low 1/f corner with exceptionally low spurious levels. The LTC6945 contains this low noise PLL core and provides inputs for an external VCO. The LTC6946 is a fully integrated frequency synthesizer combining the PLL core with an industry leading, low phase noise VCO. Additionally, the PLLWizard design tool facilitates the synthesizer design, accurately simulates its performance and gets the system up and running quickly. The LTC6945 and LTC6946 frequency synthesizers together with the PLLWizard design tool enables system designers to meet their signal generation requirements quickly with no surprises.