An Alternative Analysis of Noise Folding in Fractional-N Synthesizers

A new method of analyzing the effect of charge pump mismatches upon the phase noise of ΣΔ fractional-N synthesizers is proposed. This approach produces a simple, universal relationship between the mismatch and the ratio of the noise floor to the peak of the quantization noise spectrum. Simulations confirm that the ratio is relatively independent of other synthesizer parameters such as the ΣΔ modulator order, the shape of the spectrum, and the maximum phase excursion at the feedback divider output.