A low-phase-noise reference oscillator with integrated pMOS varactors for digital satellite receivers

A low-phase-noise LC reference oscillator (RO) for use in digital satellite receivers is described. This RO is an essential building block of a double-loop wide-band tuning system that reduces the phase noise of integrated quadrature voltage-controlled oscillators (VCOs) required for zero-IF receivers. In order to achieve a high degree of integration the RO is implemented using integrated varactors. Three varactor options which are available in a standard 11-GHz f/sub t/ bipolar technology are investigated: the p-n junction of an NPN, an active varactor circuit, and a pMOS varactor. Experimental results show that the integrated pMOS varactor combined with external inductors is the preferred choice to implement the resonator of the low-phase-noise RO. The achieved tuning range is 225-310 MHz. Carrier-to-noise levels of more than 87 dBc/Hz at 10-kHz offset are measured. The performance is realized with a RO dissipation of 14 mW at a supply voltage of 3.5 V.