A Fourth-order MASH DDSM for Accurate Fractional Frequency Synthesizers

The output of a Digital Delta-Sigma Modulator (DDSM) is always a periodic signal and the input is constant. A hybrid DDSM is a premiere to its conventional counterpart for having a potential speed, by the choice of its smaller bus. This paper offers an implementation for multi-stage noise shaping (MASH) DDSMs that includes four modulators named hybrid DDSM-۱, DDSM-۲, DDSM-۳, and DDSM-۴. Also, it introduces a new solution, where the desired ratio in fractional frequency synthesizers is formed by combining four different modulos. The first stage modulator is a programmable modulus EFM۱ and has a modulus M۱ that is not a power of ۲. The second, third, and fourth stage modulators are modified MASH ۱-۱, multi-modulus MASH ۱-۱-۱, and the efficiently dithered MASH ۱-۱-۱-۱ modulator that has conventional modulus  M۲, M۳, and M۴, respectively. The M۱ modulus is optimally selected to synthesize the new structure of the desired frequencies. Design results confirm the suppositional predictions. In addition, the results of the circuit implementation proposed method offer a ۱۷% reduction in hardware complexity.

کلیدواژه ها:

Fractional frequency synthesizers ، Digital delta-sigma modulator ، dither ، low complexity ، hybrid modulators