Abstract
Digital Delta Sigma Modulator (DDSM) is responsible for generation of spurious tones at the output of fractional n frequency synthesizer due their inherent periodicity. This results in an impure output spectrum of frequency synthesizer when they are used to generate the fractional numbers in the divider of Phase Locked Loop (PLL) based frequency synthesizer. This paper presents the design of Error – Output feedback modulator based third order Multi – stage noise Shaping (MASH) structure with lesser hardware and effective error compensation network to break the underlying periodicity of DDSM. The DDSM is also analyzed by using non-shaped, shaped and self – dithering mechanism to achieve a pure output spectrum and reduced quantization noise.
Highlights
Phase Locked Loop based fractional N- frequency synthesizer is pillar of modern wireless communication system due to its wide range of application
Hybrid Key Error Feedback Modulator (HK – EFM) based Multi – stage noise Shaping (MASH) is proved to have long cycles which are vital to reduce the number of unwanted tones at its output
Digital delta sigma modulators are notorious for their spurious output due to periodic quantization noise generated due to its periodicity
Summary
Phase Locked Loop based fractional N- frequency synthesizer is pillar of modern wireless communication system due to its wide range of application. The position of spur in the output spectrum depends on the length of cycles produced by the DDSM. The extended cycle length reduces the quantization noise power in spurious [4], [5]. The dithering techniques are focus of the recent researches to eliminate the spurious tones and achieve the spectral purity at the output of DDSM. Authors have presented the Hybrid Key (HK) EFM structure in [11] with long cycle lengths to reduce the power of quantization noise tones. The DDSM and MASH structure is modified and efficient dithering schemes are implemented to reduce quantization noise and achieve the spectral purity.
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