A 1 GHz /spl Sigma//spl Delta/ noise shaper for all digital PLLs with multiband UMTS modulation capability

Fully digital phase locked loops (PLLs) for wideband phase modulation set tough requirements on the digitally controlled oscillator (DCO). The frequency step size should be small while the linear tuning range should be very large. To find a solution for both requirements, oversampling at the DCO can be applied. This relaxes the requirements for the oscillator, but needs additional high speed circuitry for realization. This paper describes the detailed requirements of an oversampling circuit for UMTS modulation. A noise shaping method is proposed, which enables the realization of a UMTS compliant DCO design. Furthermore, the implementation of an 8 bit 2nd order SigmaDelta-modulator in 0.13 mum CMOS is shown