COMPARING PHASE NOISE OF INTEGER- N PHASE-LOCKED LOOP OF VOLTAGE-CONTROLLED AND DIGITALLY CONTROLLED OSCILLATORS

摘要

This article compares the phase noise of an integer-N phase-locked loop (PLL) obtained using a voltage-controlled oscillator (VCO) with those obtained using a digitally controlled oscillator (DCO). The cores of both VCO and DCO are single-ended Clapp oscillators. To select the frequency of oscillation, a conventional analogue control is used in the VCO while a five-bit digitally controlled circuit is adopted in the DCO. The VCO and DCO are designed and implemented using Agilent's GaAs HEMT ATF55143. Both are used in a PE3335 integer-N PLL from Peregrine Semiconductor, and the performance of each is investigated in terms of phase noise. Careful comparison reveals that the integer-N PLL with the DCO has a 7 dBc/Hz lower phase noise inside the loop bandwidth than the integer-N PLL with the VCO.