Tone free Sigma-delta modulator with feedback dithering for RF fractional-N frequency synthesizer

作者：Liu Junhua^*; Liao Huailin; Zhang Guoyan; Huang Ru; Zhang Xing

来源：Chinese Journal of Electronics, 2007, 16(1): 59-62.

• Sigma-delta modulator (SDM)
• frequency synthesizer
• dither
• feedback

A new Sigma-delta modulator (SDM) for Radio frequency (RF) fractional-N frequency synthesizer is proposed with a new dither generating method and a dither feedback loop. In this structure, the output of the conventional Multi-stage noise shaping (MASH) structure is reshaped by low order filter to generate dither signal, and the dither signal is fed back into the MASH structure to smooth the output Power density spectrum (PDS). The new dither generating structure is simplified by reusing the self-generating signal of the eight-bit conventional MASH structure and the low order filter is easily realized with the three-bit first order accumulator. The validity of the elimination of idle tones for the proposed SDM is verified with full stable input range by both simulation and ASIC implementation. As the proposed 8-bit structure can generate tone free signal even better than the 14-bit MASH structure without feedback dither, it exhibits high potential for high frequency, low-power monolithic fractional-N frequency synthesizer.

• 出版日期2007-1
• 单位北京大学