A Robust Programable Frequency Divider for Fractional Synthesizers

The phase selection technique is a good solution to design programable dividers widely used in fractional synthesizers. However, as the process parameters vary, the delays in the phase selection logic change, and they erroneously trigger the phase selection. This paper presents an improvement that consists on making the phase selection logic in a semi sequential fashion. In this way if there is any error due to process, temperature or voltage variations; the phase selection logic will correct and pass correctly the pulses in the next clock cycle. The proposed technique is verified with the fabrication of a programable frequency divider in a 0.35μm CMOS process.