Optimized MASH-SR Divider Controller for Fractional-N Frequency Synthesizers

The divider controller in a conventional phase-locked loop fractional- $N$ frequency synthesizer modulates the instantaneous division ratio of the feedback divider. The divider controller is typically a digital circuit that performs quantization of its input signal. Multi-stage noise shaping digital delta-sigma modulators (MASH DDSMs) and successive requantizer (SRs) are two representative divider controller architectures offering lower complexity and better spur performance, respectively. The MASH-SR, as a hybrid of these two classes of divider controllers, can achieve both lower hardware cost than the SR and better performance against spurs than a MASH DDSM. In this work, we present an optimized MASH-SR hybrid and compare the design with its conventional MASH DDSM and SR counterparts.