Abstract
Wideband low-noise ΣΔ fractional-N synthesizers pose several design challenges due to the nonlinear time-varying nature of synthesizer building blocks such as phase frequency detectors (PFDs), charge pump, and frequency dividers. Loop nonlinearities can increase close-in phase noise and enhance spurious tones due to intermodulation of high-frequency quantization noise and tonal content; therefore, an accurate simulation model is critical for successful implementation of loop parameters and bandwidth widening techniques. In this paper a closed-loop non-linear simulation model for fractional-N synthesizers is presented. Inherent nonuniform sampling of the PFD is modeled through an event-driven dual-iteration-based technique. The proposed technique generates a vector of piecewise linear time-voltage pairs, denning the voltage-controlled oscillator (VCO) control voltage. This method also lends itself to modeling of cyclostationary thermal and nicker noise generated by time-varying charge-pump current pulses. A flexible third-order ΣΔ modulated RF synthesizer core with integrated loop filter and LC-tank VCO is designed and fabricated in 0.13-μm CMOS process in order to validate the technique experimentally. The proposed modeling technique was able to predict in-band spur power levels with 1.8-dB accuracy, and spur frequency offsets with lower than 400-Hz accuracy with several programmable nonidealities enabled.
Original language | English (US) |
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Article number | 1705684 |
Pages (from-to) | 3654-3663 |
Number of pages | 10 |
Journal | IEEE Transactions on Microwave Theory and Techniques |
Volume | 54 |
Issue number | 10 |
DOIs | |
State | Published - Oct 2006 |
Keywords
- Fractional-N frequency synthesizers
- Phase noise
- Phase-locked loops (PLLs)
- Quantization noise
- Sigma-delta modulation
- Spurs
ASJC Scopus subject areas
- Radiation
- Condensed Matter Physics
- Electrical and Electronic Engineering