Bandwidth extension of low noise fractional-N synthesizers

This paper examines issues with extending the bandwidth of fractional-N synthesizers. Quantization noise is shown to be the limiting factor in state-of-the-art fractional-N synthesis. A re-framing of the noise model used to analyze synthesizer phase noise leads directly to a methodology to enable high bandwidth synthesis. We present measured results from a synthesizer based on the proposed methodology that demonstrates >25 dB broadband phase noise reduction compared to a state-of-the-art ΣΔ synthesizer. Finally, we draw conclusions about the future direction of fractional-N synthesis.