Apparatus for mitigating nonlinearity-induced spurs and noise in a fractional-n frequency synthesizer

Abstract

An apparatus for mitigating nonlinearity-induced spurs and noise in a fractional-N frequency synthesizer A digital delta-sigma modulator (DDSM) is disclosed with an input signal x[n], an output signal y[n], a quantization error signal e[n] and a dither signal d[n], having an equation described in the z-domain by Y(z)=STF(z)X(z)+DTF(z)D(z)−NTF(z)E(z) wherein Y(z), X(z), D(z) andE(z) are z-transforms of the output signal, the input signal, the dither signal, and the quantization error signal, and wherein STF (z), DTF(z) and NTF(z) correspond to a transfer function of the input signal, a transfer function of the dither signal, and a transfer function of the quantization error signal, and wherein the transfer function of the quantization error signal is of the form: NTF ⁡ ( z ) = Az - Q ( 1 - z - 1 ) ⁢ ( 1 + ∑ i = 1 K c i ⁢ z - i ) where A , Q and K are constants, coefficients ci are real valued and cK≠0 and wherein at least one of the zeroes zj of ( 1 + ∑ i = 1 K c i ⁢ z - i ) satisfies zj≠+1 for j=1, 2, . . . , K

Dependencies are inferred from the claim text.