An Ultra-Low Phase-Noise 20-GHz PLL Utilizing an Optoelectronic Voltage-Controlled Oscillator

This paper describes a novel phase-locked loop (PLL) architecture utilizing an optoelectronic oscillator (OEO) as a voltage-controlled oscillator (VCO). The OEO demonstrates excellent far-out phase-noise performance while the PLL reduces the close-in phase noise. The nonmonotonic VCO characteristics of the OEO placed stringent demands on the loop filter electronics and startup conditions. The crystal reference, prescalar, frequency synthesizer, and loop filter were all implemented with discrete high-performance components. The resulting frequency synthesizer yields a -10-dBm output at 20 GHz with phase noise of -80 dBc/Hz at 100-Hz offset, and -134 dBc/Hz at 10-kHz offset. These results are far superior to PLL synthesizers utilizing only an electronic VCO and illustrate the power of optoelectronic integration.