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This paper presents a nested-PLL architecture for a low-noise wide-bandwidth fractional-N frequency synthesizer. In order to reduce the quantization noise, operating frequency of ΔΣ modulator (DSM) is increased by using an intermediate output of feedback divider. A PLL which serves as an anti-alias filter is added to suppress noise aliasing caused by the divider. Prototype implemented in a 0.13 μm CMOS using ring VCOs achieves 26.3 dB of quantization noise suppression while consuming 15.2 mW and occupying 0.17 mm2.
Date of Publication: Oct. 2012