Comparison of the Simulated Performance of Two Divider Controllers in a Fractional-N Frequency Synthesizer with a Piecewise-Linear Charge-Pump Nonlinearity

Reducing and ultimately eliminating nonlinearity-induced spurious tones (spurs) is a key motivation for the design of novel divider controllers for fractional-N frequency synthesizers. Two types of nonlinearities have... [ view full abstract ]

Reducing and ultimately eliminating nonlinearity-induced
spurious tones (spurs) is a key motivation for the
design of novel divider controllers for fractional-N frequency
synthesizers. Two types of nonlinearities have historically been
considered in this context: polynomial and piecewise-linear
(PWL). Successive requantizers (SQs) have been designed for
spur immunity in the presence of polynomial nonlinearities but
it has been shown that SQs produce spurious tones in the phase
noise spectrum in the presence of a PWL nonlinearity. Recently
a new type of modified second order SQ has been introduced
which tries also to minimize spurious tone production in the PWL
case. In this paper, the simulated performance of a fractional-N
frequency synthesizer incorporating the new divider controller is
compared with that of one which uses a novel dithered MASH 1-1
structure. Our novel divider controller matches the performance
of the modified higher-order SQ, but with less hardware.