Improved concepts for the generation and the measurement of highly linear frequency ramps

A fractional ramp generator with an improved linearity and phase noise performance is presented. The fractional ramp synthesizer concept shown here is able to generate frequency ramps with a very low phase noise level and a very good frequency linearity and reproducibility. Related to the bandwidth of the generated frequency ramps of 4.5 GHz a relative linearity error below 3 · 10^-9 is demonstrated in a prototype system. This linearity error is close to the limit set by the phase noise floor of the ramp generators and marks a significant improvement over existing approaches by Musch, T. and Schiek, B., (2000). As the phase noise is important for the linearity of the frequency ramp the set-up has to be optimized for a good phase noise behavior, too. In order to achieve this good phase noise a special phase-frequency detector is introduced that is especially designed for the use in a fractional phase locked loop.