A low-power, low phase noise local oscillator for chip-scale atomic clocks

This paper presents a voltage controlled oscillator (VCO) for application in chip-scale atomic frequency references. At 3.4GHz (half of the Rubidium atom ground-state hyperfine transition frequency), the VCO demonstrates low phase noise (-33dBc@100Hz and -92dBc@10kHz) at 4.5mW power consumption with a circuit footprint <0.5cm/sup 2/. The temperature stability is 0ppm//spl deg/C at room temperature, and does not exceed -40ppm//spl deg/C over the range of -5/spl deg/C to +65/spl deg/C. Locking to the coherent population trapping (CPT) resonance of a NIST Rb clock is enabled by a weakly-coupled varactor diode which provides /spl sim/3MHz of tuning range. The oscillator is implemented using low-cost off-the-shelf surface-mount components, including a micro-coaxial resonator. To the authors' knowledge, this VCO has the lowest simultaneous size, phase noise, DC power consumption and thermal drift published in the literature.