The Multi-stAge noiSe sHaping digital delta-sigma modulator (MASH DDSM) is the most used divider controller architecture for fractional-N frequency synthesis. It is well-known that a MASH DDSM divider controller can cause input-dependent spurious tones in the output spectrum of a synthesizer. This paper discusses MASH 1-1-1 DDSM-induced spurious tone patterns that are dependent on the initial conditions.

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.

The divider controller can contribute significantly to the phase noise and spur pattern in the output of a nonlinear fractional-N frequency synthesizer. A type of time-varying spurs caused by a MASH DDSM divider controller, termed wandering spurs, has been observed in simulations and measurements of real synthesizers. In this work, we propose and analyze several MASH-based divider controller architectures that mitigate wandering spurs in a fractional-N frequency synthesizer.

Frequency synthesizers based on finite state machines are notorious for producing spurious tones (spurs). These spurs can be inherent in the architecture or may result from interactions between quantization noise and nonlinearities. This paper presents recent results, including descriptions of the problems and emerging solutions thereto.