This book presents a wideband GFSK-modulated
fractional-N frequency synthesizer which using the
two-point delta-sigma modulation (TPDSM). Two
bottlenecks in this design have been rigorously
investigated. One is the nonlinear performance of
fractional-N frequency synthesizers. The other one
is the inherent gain and delay mismatch between the
two modulation points. Both nonlinear and mismatch
factors dominate the modulation accuracy in the
closed phase-locked loop (PLL). The proposed
formulation can successfully predict the
dependencies of the modulation accuracy on both
factors. The comparison of the averaged frequency
deviation and frequency-shift-keying (FSK) error
between theory and measurement shows excellent
agreement. The modulated frequency synthesizer
implemented in this study can achieve a 2.5 Mbps
data rate as well as a 15 µs PLL stable time with
only 2.2 % FSK error under good design and operating
conditions.